Document:

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                                                                   Exhibit 10.12

                    SUBORDINATED LOAN AND SECURITY AGREEMENT

         THIS AGREEMENT (the "Agreement"), dated as of October 16, 1998, is
entered into by and between Acusphere, Inc., a Delaware corporation, with its
chief executive office, and principal place of business located at 38 Sidney
Street, Cambridge, Massachusetts, 02139 (the "Borrower") and Comdisco, Inc., a
Delaware corporation, with its principal place of business located at 6111 North
River Road, Rosemont, Illinois 60018 (the "Lender" or sometimes, "Comdisco"). In
consideration of the mutual agreements contained herein, the parties hereto
agree as follows:

                                    RECITALS

         WHEREAS, Borrower has requested Lender to make available to Borrower a
loan in the aggregate principal amount of Five Million Dollars ($5,000,000.00)
in two installments, the first installment in the amount of Two Million Five
Hundred Thousand Dollars ($2,500,000.00) available immediately ("Loan I") and
the second installment in the amount Two Million Five Hundred Thousand Dollars
($2,500,000.00) available as set forth herein ("Loan II") (as the same may from
time to time be amended, modified, supplemented or revised, the "Loan"), which
would be evidenced by Subordinated Promissory Note(s) executed by Borrower
substantially in the form of Exhibit A hereto (as the same may from time to time
be amended, modified, supplemented or restated the "Note(s)").

         WHEREAS, Lender is willing to make the Loan on the terms and conditions
set forth in this Agreement, and

         WHEREAS, Lender and Borrower agree any Loan hereunder shall be
subordinate to Senior Debt (as defined herein) to the extent set forth in the
Subordination Agreement (as defined herein).

                                    AGREEMENT

         NOW, THEREFORE, in consideration of the premises and the mutual
agreements contained herein, Borrower and Lender hereby agree as follows:

SECTION 1.  DEFINITIONS

         Unless otherwise defined herein, the following capitalized terms shall
have the following meanings (such meanings being equally applicable to both the
singular and plural form of the terms defined);

         1.1 "ACCOUNT" means any "account," as such term is defined in Section
9106 of the UCC, now owned or hereafter acquired by Borrower or in which
Borrower now holds or hereafter acquires any interest and, in any event, shall
include, without limitation, all accounts receivable, book debts and other forms
of obligations (other than forms of obligations evidenced by Chattel Paper,
Documents or Instruments) now owned or hereafter received or acquired by or
belonging or owing to Borrower (including, without limitation, under any trade
name, style or division thereof) whether arising out of goods sold or services
rendered by Borrower or from any other, transaction, whether or not the same
involves the sale of goods or services by Borrower (including, without
limitation, any such obligation which may be characterized as an account or
contract right under the UCC) and all of Borrower's rights in, to and under all
purchase orders or receipts now owned or hereafter acquired by it for goods or
services, and all

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of Borrower's rights to any goods represented by any of the foregoing
(including, without limitation, unpaid seller's rights of rescission, replevin,
reclamation and stoppage in transit and rights to returned, reclaimed or
repossessed goods), and all monies due or to become due to Borrower under all
purchase orders and contracts for the sale of goods or the performance of
services or both by Borrower (whether or not yet earned by performance on the
part of Borrower or in connection with any other transaction), now in existence
or hereafter occurring, including, without limitation, the right to receive the
proceeds of said purchase orders and contracts, and all collateral security and
guarantees of any kind given by any Person with respect to any of the foregoing.

         1.2 "ACCOUNT DEBTOR" means any "account debtor," as such term is
defined in Section 9105(1)(a) of the UCC.

         1.3 "ADVANCE" means each installment made by the Lender to
Borrower pursuant to the Loan to be evidenced by the Note(s) secured by the
Collateral.

         1.4 "ADVANCE DATE" means the funding date of any Advance of the
Loan.

         1.5 "ADVANCE REQUEST" means the request by Borrower for an Advance
under the Loan, each to be substantially in the form of Exhibit C attached
hereto, as submitted by Borrower to Lender from time to time.

         1.6 "CHATTEL PAPER" means any "chattel paper," as such term is defined
in Section 9105(1)(b) of the UCC, now owned or hereafter acquired by Borrower or
in which Borrower now holds or hereafter acquires any interest.

         1.7 "CLOSING DATE" means the date hereof.

         1.8 "COLLATERAL" shall have the meaning assigned to such term in
Section 3 of this Agreement.

         1.9 "CONTRACTS" means all contracts, undertakings, franchise agreements
or other agreements (other than rights evidenced by Chattel Paper, Documents or
Instruments) in or under which Borrower may now or hereafter have any right,
title or interest, including, without limitation, with respect to an Account,
any agreement relating to the terms of payment or the terms of performance
thereof.

         1.10 "COPYRIGHTS" means all of the following now owned or hereafter
acquired by Borrower or in which Borrower now holds or hereafter acquires any
interest: (i) all copyrights, whether registered or unregistered, held pursuant
to the laws of the United States, any State thereof or of any other country;
(ii) registrations, applications and recordings in the United States Copyright
Office or in any similar office or agency of the United States, any state
thereof or any other country; (iii) any continuations; renewals or extensions
thereof; and (iv) any registrations to be issued in any pending applications.

         1.11 "COPYRIGHT LICENSE" means any written agreement granting any right
to use any Copyright or Copyright registration now owned or hereafter acquired
by Borrower or in which Borrower now holds or hereafter acquires any interest.

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         1.12 "DOCUMENTS" means any "documents," as such term is defined in
Section 9105(1)(f) of the UCC, now owned or hereafter acquired by Borrower or in
which Borrower now holds or hereafter acquires any interest.

         1.13 "EQUIPMENT" means any "equipment," as such term is defined in
Section 9109(2) of the UCC, now or hereafter owned or acquired by Borrower or in
which Borrower now holds or hereafter acquires any interest and any and all
additions, substitutions and replacements of any of the foregoing, wherever
located, together with all attachments, components, parts, equipment and
accessories installed thereon or affixed thereto.

         1.14 "EXCLUDED AGREEMENTS" means (i) any Warrant Agreement(s) executed
hereunder, and any other warrants (including without limitation, the warrant
agreements dated as of May 1, 1995, August 5, 1996, June 6, 1997 and February
26, 1998) to acquire, or agreements governing the rights of the holders of, any
equity security of Borrower, (ii) any stock of the Borrower issued or purchased
pursuant to the Warrant Agreement, and (iii) the Master Lease Agreement dated as
of between Borrower, as lessee, and Lender, as lessor, including, without
limitation, any Equipment Schedules and Summary Equipment Schedules to the
Master Lease Agreement executed or delivered by Borrower pursuant thereto and
any other modifications or amendments thereof, whereby Borrower (as lessee)
leases equipment, software, or goods from Lender (as lessor) to Borrower (as
lessee).

         1.15 "FACILITY FEE" means one percent (1.0%) of the principal amount of
Loan I due at the Closing Date and one percent (1.00%) of the principal amount
of Loan II due upon the Next Event as defined herein.

         1.16 "FIXTURES" means any "fixtures," as such term is defined in
Section 9313(1)(a) of the UCC, now or hereafter owned or acquired by Borrower or
in which Borrower now holds or hereafter acquires any interest and, now or
hereafter attached or affixed to or constituting a part of, or located in or
upon, real property wherever located, together with all right, title and
interest of Borrower in and to all extensions, improvements, betterments,
renewals, substitutes, and replacements of, and all additions and appurtenances
to any of the foregoing property, and all conversions of the security
constituted thereby, immediately upon any acquisition or release thereof or any
such conversion, as the case may be.

         1.17 "GENERAL INTANGIBLES" means any "general intangibles," as such
term is defined in Section 9106 of the UCC, now owned or hereafter acquired by
Borrower or in which Borrower now holds or hereafter acquires any interest and,
in any event, shall include, without limitation, all right, title and interest
which Borrower may now or hereafter have in or under any contract, all customer
lists, Copyrights, Trademarks, Patents, rights to Intellectual Property,
interests in partnerships, joint ventures and other business associations,
Licenses, permits, trade secrets, proprietary or confidential information,
inventions (whether or not patented or patentable), technical information,
procedures, designs, knowledge, know-how, software, data bases, data, skill,
expertise, recipes, experience, processes, models, drawings, materials and
records, goodwill (including, without limitation, the goodwill associated with
any Trademark, Trademark registration or Trademark licensed under any Trademark
License), claims in or under insurance policies, including unearned premiums,
uncertificated securities, cash and other forms of money or currency, deposit
accounts (including as defined in Section 9105(e) of the UCC), rights to sue for
past, present and future infringement of Copyrights, Trademarks and Patents,
rights to receive tax refunds and other payments and rights of indemnification.

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         1.18 "INSTRUMENTS" means any "instrument," as such term is defined in
Section 9105(1)(i) of the UCC, now owned or hereafter acquired by Borrower or in
which Borrower now holds or hereafter acquires any interest.

         1.19 "INTELLECTUAL PROPERTY" means all Copyrights, Trademarks, Patents,
trade secrets, source codes, customer lists, proprietary or confidential
information, inventions (whether or not patented or patentable), technical
information, procedures, designs, knowledge, know-how, software, data bases,
skill, expertise, experience, processes, models, drawings, materials and
records.

         1.20 "INVENTORY" means any "inventory," as such term is defined in
Section 9109(4) of the UCC, wherever located, now or hereafter owned or acquired
by Borrower or in which Borrower now holds or hereafter acquires any interest,
and, in any event, shall include, without limitation, all inventory, goods and
other personal property which are held by or on behalf of Borrower for sale or
lease or are furnished or are to be furnished under a contract of service or
which constitute raw materials, work in process or materials used or consumed or
to be used or consumed in Borrower's business, or the processing, packaging,
promotion, delivery or shipping of the same, and all furnished goods whether or
not such inventory is listed on any schedules, assignments or reports furnished
to Lender from time to time and whether or not the same is in transit or in the
constructive, actual or exclusive occupancy or possession of Borrower or is held
by Borrower or by others for Borrower's account, including, without limitation,
all goods covered by purchase orders and contracts with suppliers and all goods
billed and held by suppliers and all inventory which may be located on premises
of Borrower or of any carriers, forwarding agents, truckers, warehousemen,
vendors, selling agents or other persons.

         1.21 "LICENSE" means any Copyright License, Patent License, Trademark
License or other license of rights or interests now held or hereafter acquired
by Borrower or in which Borrower now holds or hereafter acquires any interest
and any renewals or extensions thereof.

         1.22 "LIEN" means any mortgage, deed of trust, pledge, hypothecation,
assignment for security, security interest, encumbrance, levy, lien or charge of
any kind, whether voluntarily incurred or arising by operation of law or
otherwise, against any property, any conditional sale or other title retention
agreement, any lease in the nature of a security interest, and the filing of any
financing statement (other than a precautionary financing statement with respect
to a lease that is not in the nature of a security interest) under the UCC or
comparable law of any jurisdiction.

         1.23 "LOAN DOCUMENTS" shall mean and include this Agreement, the
Note(s), and any other documents executed in connection with the Secured
Obligations or the transactions contemplated hereby, as the same may from time
to time be amended, modified, supplemented or restated, PROVIDED, that the Loan
Documents shall NOT include any of the Excluded Agreements.

         1.24 "MATERIAL ADVERSE EFFECT" means a material adverse effect upon:
(i) the business, operations, properties, assets or conditions (financial or
otherwise) of Borrower; or (ii) the ability of Borrower to perform, or of Lender
to enforce, the Secured Obligations.

         1.25 "MATURITY DATE" means the date thirty-six (36) months from the
Advance Date of each installment of the Loan.

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         1.26 "NEXT EVENT" means the first to occur of (a) the closing of an
equity round of financing in the minimum amount of Two Million Five Hundred
Thousand Dollars ($2,500,000.00); (b) an initial public offering or Merger or
(c) the execution and funding of a strategic pharmaceuticals partner agreement
for either Japan or Europe which includes a nonrefundable commitment to Borrower
in the amount of Two Million Five Hundred Thousand Dollars ($2,500,000.00).

         1.27 "PATENT LICENSE" means any written agreement granting any right
with respect to any invention on which a Patent is in existence now owned or
hereafter acquired by Borrower or in which Borrower now holds or hereafter
acquires any interest.

         1.28 "PATENTS" means all of the following now owned or hereafter
acquired by Borrower or in which Borrower now holds or hereafter acquires any
interest: (a) letters patent of, or rights corresponding thereto in, the United
States or any other county, all registrations and recordings thereof, and all
applications for letters patent of, or rights corresponding thereto in the
United States or any other country, including, without limitation,
registrations, recordings and applications in the United States Patent and
Trademark Office or in any similar office or agency of the United States, any
State thereof or any other country; (b) all reissues, continuations,
continuations-in-part or extensions thereof; (c) all petty patents, divisionals,
and patents of addition; and (d) all patents to issue in any such applications.

         1.29 "PERMITTED LIENS" means any and all of the following: (i) liens
in favor of Lender, (ii) liens related to, or arising in connection with,
Senior Debt.

         1.30 "PROCEEDS" means "proceeds," as such term is defined in Section
9306(1) of the UCC and, in any event, shall include, without limitation, (a) any
and all Accounts, Chattel Paper, Instruments, cash or other forms of money or
currency or other proceeds payable to Borrower from time to time in respect of
the Collateral, (b) any and all proceeds of any insurance, indemnity, warranty
or guaranty payable to Borrower from time to time with respect to any of the
Collateral, (c) any and all payments (in any form whatsoever) made or due and
payable to Borrower from time to time in connection with any requisition,
confiscation, condemnation, seizure or forfeiture of all or any part of the
Collateral by any governmental authority (or any Person acting under color of
governmental authority), (d) any claim of Borrower against third parties (i) for
past, present or future infringement of any Copyright, Patent or Patent License
or (ii) for past, present or future infringement or dilution of any Trademark or
Trademark License or for injury to the goodwill associated with any Trademark,
Trademark registration or Trademark licensed under any Trademark License and (e)
any and all other amounts from time to time paid or payable under or in
connection with any of the Collateral.

         1.31 "RECEIVABLES" shall mean and include all of the Borrowers
accounts, instruments, documents, chattel paper and general intangibles whether
secured or unsecured, whether now existing or hereafter created or arising, and
whether or not specifically sold or assigned to Lender hereunder.

         1.32 "SECURED OBLIGATIONS" shall mean and include all principal,
interest, fees, costs, or other liabilities or obligations for monetary amounts
owed by Borrower to Lender, whether due or to become due, matured or unmatured,
liquidated or unliquidated, contingent or non-contingent, and all covenants and
duties regarding such amounts, of any kind of nature, present or future, arising
under this Agreement, the Note(s), or any of the other Loan Documents, whether
or not evidenced by any Note(s), Agreement or other instrument, as the same may
from time to time be

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amended, modified, supplemented or restated, provided, that the Secured
Obligations shall not include any indebtedness or obligations of Borrower
arising under or in connection with the Excluded Agreements.

         1.33 "SENIOR CREDITOR" means a bank, insurance company, pension fund,
or other institutional lender to be determined, or a syndication of such
institutional lenders that provide Senior Debt financing to Borrower; PROVIDED,
that Senior Creditor shall not include any officer, director, shareholder,
venture capital investor, or insider of Borrower, or any affiliate of the
foregoing persons, except upon the express written consent of Lender, which
consent shall not be unreasonably withheld.

         1.34 "SENIOR DEBT" means any and all indebtedness and obligations for
borrowed money (including, without limitation, principal, premium (if any),
interest, fees charges, expenses, costs, professional fees and expenses, and
reimbursement obligations) at any time owing by Borrower to a Senior Creditor
under Senior Loan Documents, including, but not limited to such amounts as may
accrue or be incurred before or after default or workout or the commencement of
any liquidation, dissolution, bankruptcy, receivership or reorganization by or
against Borrower.

         1.35 "SENIOR LOAN DOCUMENTS" means the loan agreement between Borrower
and Senior Creditor and any other agreement, security agreement, document,
promissory note, UCC financing statement, or instrument executed by Borrower in
favor of Senior Creditor pursuant to or in connection with the Senior Debt or
the loan agreement, as the same may from time to time be amended, modified,
supplemented, extended, renewed, restated or replaced.

         1.36 "SUBORDINATION AGREEMENT" means the Subordination Agreement of
even date herewith, entered into between Borrower and Lender for the benefit of
Senior Creditor.

         1.37 "TRADEMARK LICENSE" means any written agreement granting any right
to use any Trademark or Trademark registration now owned or hereafter acquired
by Borrower or in which Borrower now holds or hereafter acquires any interest.

         1.38 "TRADEMARKS" means any of the following now owned or hereafter
acquired by Borrower or in which Borrower now holds or hereafter acquires any
interest: (a) any and all trademarks, tradenames, corporate names, business
names, trade styles, service marks, logos, other source or business identifiers,
prints and labels on which any of the foregoing have appeared or appear, designs
and general intangibles of like nature, now existing or hereafter adopted or
acquired, all registrations and recordings thereof, and any applications in
connection therewith, including, without limitation, registrations, recordings
and applications in the United States Patent; and Trademark Office or in any
similar office or agency of the United States, any State thereof or any other
country or any political subdivision thereof and (b) any reissues, extensions or
renewals thereof.

         1.39 "UCC" shall mean the Uniform Commercial Code as the same may, from
time to time, be in effect in the State of Illinois. Unless otherwise defined
herein, terms that are defined in the UCC and used herein shall have the
meanings given to them in the UCC.

         1.40 "WARRANT AGREEMENT(S)" shall mean those agreements entered into in
connection with the Loan, substantially in the form attached hereto as Exhibit
B-1 and B-2 pursuant to which Borrower granted Lender the right to purchase that
number of shares of Series D or E Preferred Stock of Borrower as more
particularly set forth therein.

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SECTION 2.  THE LOAN

         2.1  (a)  Loan I:

         The outstanding principal amount of the Loan I, together with interest
thereon precomputed at the rate of Prime Rate plus one (1.0%) percent per annum
fixed at the Advance Date, shall be due and payable in twelve (12) equal monthly
installments of interest only, payable on the first day of each month, followed
by twenty-four (24) equal monthly installments of principal and interest,
payable on the first day of each month, to and including the Maturity Date
(each, a "Payment Date"). If any payment under the Note(s) shall be payable on a
day other than a business day, then such payment shall be due and payable on the
next succeeding business day.

         In consideration for Loan I, Borrower shall issue Lender a Warrant
Agreement for the purchase of 75,758 shares of Borrower's Series D Preferred
Stock at a price per share of $3.30 (the "Exercise Price"), in the form of
Exhibit B-1 attached hereto.

         (b)      Loan II:

         Loan II shall be available upon the dosing of a Next Event as defined
in Section 1.26. Notwithstanding the foregoing, if the Next Event is such event
as described in Section 1.26(c), the availability of Loan II shall further be
conditioned upon Lender's subsequent review and approval. The outstanding
principal amount of the Loan II, together with interest thereon pre-computed at
the rate of Prime Rate plus one (1.0%) percent per annum fixed at the Advance
Date, shall be due and payable in twelve (12) equal monthly installments of
interest only, payable on the first day of each month, followed by twenty-four
(24) equal monthly installments of principal and interest, payable on the first
day of each month, to and including the Maturity Date (each, a "Payment Date").
If any payment under the Note(s) shall be payable on a day other than a business
day, then such payment shall be due and payable on the next succeeding business
day.

         In consideration for Loan II, Borrower shall issue Lender a Warrant
Agreement for the purchase of a number of shares of Borrower's Preferred Stock
equal to $250,000.00 divided by (i) the price per share paid by investors in the
Series E Preferred Stock financing or (ii) $4.50 per share if the Next Event is
pursuant to Section 1.26(c) (the "Exercise Price"), in the form of Exhibit B-2
attached hereto. In the event the Warrant Agreement is issued and priced in
accordance with (i) above, the Warrant Agreement shall be for the purchase of
Borrower's Series E Preferred Stock and if the Warrant Agreement is issued and
priced in accordance with (ii) above, the Warrant Agreement shall be for the
purchase of Borrower's Series D Preferred Stock.

         2.2 Borrower shall have the option to prepay the Loan, in whole or in
part, as of any Payment Date after the Advance Date by paying to Lender such
principal amount being prepaid together with all accrued and unpaid interest
with respect to such principal amount, as of the date of such prepayment.
Notwithstanding the foregoing, in the event the Loan is prepaid within the
twelve (12) months from the date hereof, Borrower shall pay Lender an additional
fee equal to one (1.00%) percent of the outstanding principal amount of the
Loan. Conversion of a portion of the loan in accordance with ss. 2.5 shall not
be treated as prepayment under this ss. 2.2.

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         2.3 (a) Notwithstanding any provision in this Agreement, the Note(s),
or any other Loan Document, it is not the parties' intent to contract for,
charge or receive interest at a rate that is greater than the maximum rate
permissible by law which a court of competent jurisdiction shall deem applicable
hereto (which under the laws of the State of Illinois shall be deemed to be the
laws relating to permissible rates of interest on commercial loans) (the
"Maximum Rate"). It the Borrower actually pays Lender an amount of interest,
chargeable on the total aggregate principal Secured Obligations of Borrower
under this Agreement and the Note(s) (as said rate is calculated over a period
of time from the date of this Agreement through the end of time that any
principal is outstanding on the Note(s)), which amount of interest exceeds
interest calculated at the Maximum Rate on said principal chargeable over said
period of time, then such excess interest actually paid by Borrower shall be
applied first, to the payment of principal outstanding on the Note(s); second,
after all principal is repaid, to the payment of Lender's out of pocket costs,
expenses, and professional fees which are owed by Borrower to Lender under this
Agreement or the Loan Documents; and third, after all principal, costs,
expenses, and professional fees owed by Borrower to Lender are repaid, the
excess (if any) shall be refunded to Borrower, and the effective rate of
interest will tie automatically reduced to the Maximum Rate.

                  (b) In the event any interest is not paid when due hereunder,
delinquent interest shall be added to principal and shall bear interest on
interest, compounded at the rate set forth in Section 2.1.

                  (c) Upon and during the continuation of an Event of Default
hereunder, all Secured Obligations, including principal, interest, compounded
interest, and professional fees, shall bear interest at a rate per annum equal
to the rate set forth in Section 2.1 plus five percent (5%) per annum ("Default
Rate").

         2.4 If the Borrower has not repaid the outstanding principal amount
under the Loan in its entirety by the Maturity Date (as defined in the
applicable Note(s)), then for each additional month, or portion thereof,
thereafter that the outstanding principal is not paid, Lender shall have the
right to purchase from the Borrower, at the Exercise Price (adjusted, as set
forth and defined in the Warrant Agreement), an additional number of shares of
Preferred Stock which number shall be determined by (i) multiplying the
outstanding principal amount which is due but unpaid by 1 % and (ii) dividing
the product thereof by the Exercise Price.

         2.5 Notwithstanding anything to the contrary contained in this
Agreement, Lender at its sole discretion, may convert up to thirty percent (30%)
of the outstanding principal balance of each of the Note(s) into shares of the
Borrower's equity securities at the closing of the Next Event as follows: (i) if
the Next Event shall be an event as described in Section 1.26(a), the
outstanding principal shall convert into the Security issued in such financing
at a price equal to thirty percent (30%) greater than the equity financing
price; (ii) if the Next Event shall be an event as described in Section 1.26(b),
the outstanding principal shall convert into Common Stock at a price per share
thirty percent (30%) less than the initial public offering or Merger price for
such Common Stock or (iii) if the Next Event shall be an event as described in
Section 1.26(c), the outstanding principal shall convert into shares of Series D
Preferred Stock at a price equal to $5.85 per share. In the event that a Merger
is structured as a "pooling of interests" and if Borrower's accountants advise
the Borrower that conversion of a portion of the Notes would prevent the Merger
from being treated as a pooling of interests, the Note(s) shall not be
convertible pursuant to this Section, and instead Borrower shall prepay the
Note(s) by prepaying the principal amount together with all accrued and unpaid
interest and a prepayment premium of 1.5% of the then outstanding principal
amount.

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SECTION 3.  SECURITY INTEREST

         As security for the prompt, complete and indefeasible payment when due
(whether at stated payment dates or otherwise) of all the Secured Obligations
and in order to induce Lender to make the Loan upon the terms and subject to the
conditions of the Note(s), Borrower hereby assigns, conveys, mortgages, pledges,
hypothecates and transfers to Lender for security purposes only, and hereby
grants to Lender a security interest in, all of Borrower's right, title and
interest in, to and under each of the following (all of which being hereinafter
collectively called the "Collateral"):

         (a)      All Receivables;

         (b)      All Equipment;

         (c)      All Fixtures;

         (d)      All Inventory;

         (e)      All other goods and personal property of Borrower now or
                  hereafter owned or existing, leased, consigned by or to, or
                  acquired by, Borrower and wherever located; and

         (g)      To the extent not otherwise included, all Proceeds of each of
                  the foregoing and all accessions to, substitutions and
                  replacements for, and rents, profits and products of each of
                  the foregoing.

SECTION 4.  REPRESENTATIONS AND WARRANTIES OF BORROWER

         The Borrower represents, warrants and agrees that;

         4.1 Borrower owns all right title and interest in and to the
Collateral, free of all liens, security interests, encumbrances and claims
whatsoever, except for Permitted Liens.

         4.2 Borrower has the full power and authority to, and does hereby grant
and convey to the Lender, a perfected security interest in the Collateral as
security for the Secured Obligations, free of all liens, security interests,
encumbrances and claims, other than Permitted Liens and shall execute such
Uniform Commercial Code financing statements in connection herewith as the
Lender may reasonably request. Except as set forth herein, no other lien,
security interest, adverse claim or encumbrance has been created by Borrower or
is known by Borrower to exist with respect to any Collateral.

         4.3 Borrower is a corporation duly organized, legally existing and in
good standing under the laws of the State of Delaware, and is duly qualified as
a foreign corporation in all jurisdictions in which the nature of its business
or location of its properties require such qualifications and where the failure
to be qualified would have a material adverse effect.

         4.4 Borrower's execution, delivery and performance of the Note(s), this
Agreement, all financing statements, all other Loan Documents required to be
delivered or executed in connection herewith, and the Warrant Agreement(s) have
been duly authorized by all necessary corporate action of Borrower, the
individual or individuals executing the Loan

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Documents and the Warrant Agreement(s) were duly authorized to do so; and the
Loan Documents and the Warrant Agreement(s) constitute legal, valid and binding
obligations of the Borrower, enforceable in accordance with their respective
terms, subject to applicable bankruptcy, insolvency, reorganization or other
similar laws generally affecting the enforcement of the rights of creditors.

         4.5 This Agreement, the other Loan Documents and the Warrant
Agreement(s) do not and will not violate any provisions of Borrower's
Certificate of Incorporation, bylaws or any contract, agreement, law,
regulation, order, injunction, judgment, decree or writ to which the Borrower is
subject, or result in the creation or imposition of any lien, security interest
or other encumbrance upon the Collateral, other than those created by this
Agreement.

         4.6 The execution, delivery and performance of this Agreement, the
other Loan Documents and the Warrant Agreement(s) do not require the consent or
approval of any other person or entity including, without limitation, any
regulatory authority or governmental body of the United States or any state
thereof or any political subdivision of the United States or any state thereof.

         4.7 To the Borrower's knowledge no event which has had or could
reasonably be expected to have a Material Adverse Effect has occurred and is
continuing.

         4.8 No fact or condition exists that would (or would, with the passage
of time, the giving of notice, or both) constitute a default under the Loan
Agreement between Borrower and Senior Creditor.

         4.9 Borrower has filed and will file all tax returns, federal, state
and local, which it is required to file and has duly paid or fully reserved for
all taxes or installments thereof (including any interest or penalties) as and
when due, which have or may become due pursuant to such returns or pursuant to
any assessment received by Borrower for the three (3) years preceding the
Closing Date, if any (including any taxes being contested in good faith and by
appropriate proceedings).

SECTION 5.  INSURANCE

         5.1 So long as there are any Secured Obligations outstanding, Borrower
shall cause to be carried and maintained comprehensive general liability
insurance against risks customarily insured against in Borrower's line of
business. Such risks shall include, without limitation, the risks of death,
bodily injury and property damage. So long as there are any Secured Obligations
outstanding, Borrower shall also cause to be carried and maintained insurance
upon the Collateral and Borrower's business, covering casualty, hazard and such
other property risks customarily insured against in Borrower's line of business.
Borrower shall deliver to Lender lender's loss payable endorsements (Form BFU
438 or equivalent) naming Lender as loss payee or additional insured, as
appropriate. Borrower shall use commercially reasonable efforts to cause all
policies evidencing such insurance to provide for at least thirty (30) days
prior written notice by the underwriter or insurance company to Lender in the
event of cancellation or expiration. Such policies shall be issued by such
insurers and in such amounts as are reasonably acceptable to Lender.

         5.2 Borrower shall and does hereby indemnify and hold Lender, its
agents and shareholders harmless from and against any and all claims, costs,
expenses, damages and liabilities (including, without limitation, such claims,
costs, expenses, damages and liabilities

                                       10
<PAGE>   11

based on liability in tort, including without limitation, strict liability in
tort), including reasonable attorneys' fees, arising out of the disposition or
utilization of the Collateral, other than claims arising at or caused by
Lender's gross negligence or willful misconduct.

SECTION 6.  COVENANTS OF BORROWER

         Borrower covenants and agrees as follows at all times while any of the
Secured Obligations remain outstanding:

         6.1 Borrower shall furnish to Lender the financial statements listed
hereinafter, each prepared in accordance with generally accepted accounting
principles consistently applied (the "Financial Statements"):

                  (a) as soon as practicable (and in any event within thirty
         (30) days) after the end of each month, unaudited interim financial
         statements as of the end of such month (prepared on a consolidated and
         consolidating, basis, if applicable), including balance sheet and
         related statements of income and cash flows accompanied by a report
         detailing any material contingencies (including the commencement of any
         material litigation by or against Borrower) or any other occurrence
         that could reasonably be expected to have a Material Adverse Effect,
         all certified by Borrower's Chief Executive Officer or Chief Financial
         Officer to be true and correct;

                  (b) as soon as practicable (and in any event within ninety
         (90) days) after the end of each fiscal year, unqualified audited
         financial statements as of the end of such year (prepared on a
         consolidated and consolidating basis, if applicable), including balance
         sheet and related statements of income and cash flows, and setting
         forth in comparative form the corresponding figures for the preceding
         fiscal year, certified by a firm of independent certified public
         accountants selected by Borrower and reasonably acceptable to Lender,
         accompanied by any management report from such accountants;

                  (c) promptly after the sending or filing thereof, as the case
         may be, copies of any proxy statements, financial statements or reports
         which Borrower has made available to its shareholders and copies of any
         regular, periodic and special reports or registration statements which
         Borrower files with the Securities and Exchange Commission or any
         governmental authority which may be substituted therefor, or any
         national securities exchange; and

                  (d) promptly, any additional information, financial or
         otherwise (including, but not limited, to tax returns and names of
         principal creditors) as Lender reasonably believes necessary to
         evaluate Borrower's continuing ability to meet its financial
         obligations.

         6.2 Borrower shall permit any authorized representative of Lender and
its attorneys and accountants on reasonable notice to inspect, examine and make
copies and abstracts of the books of account and records of Borrower at
reasonable times during normal business hours. In addition, such representative
of Lender and its attorneys and accountants shall have the right to meet with
management and officers of the Company to discuss such books of account and
records.

         6.3 Borrower will from time to time execute, deliver and file, alone or
with Lender, any financing statements, security agreements or other documents;
procure any instruments or

                                       11
<PAGE>   12

documents as may be requested by Lender; and take all further action that may be
necessary or desirable, or that Lender may request, to confirm, perfect,
preserve and protect the security interests intended to be granted hereby, and
in addition, and for such purposes only, Borrower hereby authorizes Lender to
execute and deliver on behalf of Borrower and to file such financing statements,
security agreement and other documents without the signature of Borrower either
in Lender's name or in the name of Borrower as agent and attorney-in-fact for
Borrower. The parties agree that a carbon, photographic or other reproduction of
this Agreement shall be sufficient as a financing statement and may be filed in
any appropriate office in lieu thereof.

         6.4 Borrower shall protect and defend Borrower's title as well as the
interest of the Lender against all persons claiming any interest adverse to
Borrower or Lender and shall at all times keep the Collateral free and clear
from any legal process, liens or encumbrances whatsoever (except any placed
thereon by Lender) and shall give Lender immediate written notice thereof.

         6.5 Without Lender's prior written consent, which consent shall not be
unreasonably withheld, Borrower shall not (a) grant any material extension of
the time of payment of any of the Receivables, (b) to any material extent,
compromise, compound or settle the same for less than the full amount thereof,
(c) release, wholly or partly, any Person liable for the payment thereof, or
allow any credit or discount whatsoever thereon other than trade discounts
granted in the ordinary course of business of Borrower.

         6.6 Borrower shall maintain and protect its properties, assets and
facilities, including without limitation, its Equipment and Fixtures, in good
order and working repair and condition (taking into consideration ordinary wear
and tear) and from time to time make or cause to be made all necessary and
proper repairs, renewals and replacements thereto and shall competently manage
and care for its property in accordance with prudent industry practices.

         6.7 Borrower shall not merge with and into any other entity except for
where Borrower is the surviving entity and Borrower's shareholders immediately
prior to the closing of such event shall hold at least fifty percent (50%) of
the voting power of the surviving or acquiring entity immediately after the
closing of such event; or sell or convey all or substantially all of its assets
or stock to any other person or entity without notifying Lender a minimum of
thirty (30) days prior to the closing date and requesting Lender's consent such
consent not to be unreasonably withheld to the assignment of all of Borrower's
Secured Obligations hereunder to the successor entity in form and substance
satisfactory to Lender. In the event Lender does not consent to such assignment
the parties agree Borrower shall prepay the Loan in accordance with Section 2.2
hereof and, so long as no Event of Default has occurred and is continuing, Such
prepayment shall be Lender's sole remedy.

         6.8 Borrower shall not, without the prior written consent of Lender,
such consent not to be unreasonably withheld, declare or pay any cash dividend
or make a distribution on , or redeem any class of stock, (other than pursuant
to employee repurchase plans, stock plans, stock restriction agreements and
similar arrangements with employees, consultants and others in connection with
their death or termination of employment or transfer), sell, lease, lend or in
any other manner convey any equitable, beneficial or legal interest in any
material portion of the assets of Borrower (except inventory sold in the normal
course of business).

         6.9 Upon the request of Lender, Borrower shall, during business hours,
make the Inventory and Equipment available to Lender for inspection at the place
where it is normally

                                       12
<PAGE>   13

located and shall make Borrower's log and maintenance records pertaining to the
Inventory and Equipment available to Lender for inspection. Borrower shall take
all action necessary to maintain such logs and maintenance records in a correct
and complete fashion.

         6.10 Borrower covenants and agrees to pay when due, all taxes, fees or
other charges of any nature whatsoever (together with any related interest or
penalties) now or hereafter imposed or assessed against Borrower, Lender or the
Collateral or upon Borrower's ownership, possession, use, operation or
disposition thereof or upon Borrower's rents, receipts or earnings arising
therefrom. Borrower shall file on or before the due date therefor all personal
property tax returns in respect of the Collateral. Notwithstanding the
foregoing, Borrower may contest, in good faith and by appropriate proceedings,
taxes for which Borrower maintains adequate reserves therefor.

         6.11 Borrower shall not relocate any item of the Collateral (other than
sale of inventory in the ordinary course of business) except: (i) with the prior
written consent of the Lender not to be unreasonably withheld; and (ii) if such
relocation shall be within the continental United States. If permitted to
relocate Collateral pursuant to the foregoing sentence, unless otherwise agreed
in writing by Lender, Borrower shall first (a) cause to be filed and/or
delivered to the Lender all Uniform Commercial Code financing statements,
certificates or other documents or instruments necessary to continue in effect
the perfected security interest of the Lender in the Collateral, and (b) have
given the Lender no less than thirty (30) days prior written notice of such
relocation.

         6.12     Borrower shall not sell, transfer, assign, hypothecate or
otherwise encumber its Intellectual Property without Lender's prior written
consent.

SECTION 7.  CONDITIONS PRECEDENT TO LOAN

         The obligation of Lender to fund the Loan on each Advance Date shall be
subject to Lender's discretion and satisfactory completion of its due diligence
and approval process, and satisfaction by Borrower or waiver by Lender, in
Lender's sole discretion, of the following conditions:

         7.1      (a) The Advance Date for any installment shall occur on or
before October 16, 1999.

         7.2      DOCUMENT DELIVERY.  Borrower, on or prior to the Closing Date,
shall have delivered to Lender the following:

                  (a) executed originals of the Agreement, the Warrant Agreement
         attached hereto as Exhibit B1 and any documents reasonably required by
         Lender to effectuate the liens of Lender, with respect to all
         Collateral;

                  (b) certified copy of resolutions of Borrower's board of
         directors evidencing approval of the borrowing and other transactions
         evidenced by the Loan Documents and the Warrant Agreement(s);

                  (c) certified copies of the Certificate of Incorporation and
         the Bylaws, as amended through the Closing Date, of Borrower;

                                       13
<PAGE>   14

                  (d) certificate of good standing for Borrower from its state
         of incorporation and similar certificates from all other jurisdictions
         in which it does business and where the failure to be qualified would
         have a Material Adverse Effect;

                  (e) payment of the Facility Fee for Loan I;

                  (f) such other documents as Lender may reasonably request.

         7.3      ADVANCE REQUEST.  Borrower shall:

WITH RESPECT TO LOAN I:

                  (a) deliver to Lender, at least forty-eight (48) hours prior
         to the Advance Date, written notice in the form of an Advance Request,
         or as otherwise specified by Lender from time to time, specifying the
         date and amount of such Advance.

                  (b) deliver executed original Note(s) as set forth in
         Section 2.1(a), as applicable.

                  (c) such other documents as Lender may reasonably request.

WITH RESPECT TO LOAN II:

                  (a) deliver to Lender, at least forty-eight (48) hours prior
         to the Advance Date, written notice in the form of an Advance Request,
         or as otherwise specified by Lender from time to time, specifying the
         date and amount of such Advance.

                  (b) deliver executed original Note(s) as set forth in
         SECTION 2.1(b), as applicable;

                  (c) payment of the Facility Fee as set forth in SECTION 1.15
         above;

                  (d) deliver executed Warrant Agreement as set forth in
         SECTION 2.1(b);

                  (e) either (i) deliver documentation satisfactory to Lender of
         completion of a Next Event as described in Section 1.26(a) or (ii)
         deliver documentation verifying completion of a Next Event as described
         in Section 1.26(c) and subject to Lender's further due diligence and
         approval.

         7.4 PERFECTION OF SECURITY INTERESTS. Borrower shall have taken or
caused to be taken such actions requested by Lender to grant Lender a first
priority perfected security interest in the Collateral, subject only to
Permitted Liens. Such actions shall include, without limitation, the delivery to
Lender of all appropriate financing statements, executed by Borrower, as to the
Collateral granted by Borrower for all jurisdictions as may be necessary or
desirable to perfect the security interest of Lender in such Collateral

         7.5 ABSENCE OF EVENTS OF DEFAULTS. As of the Closing Date or the
Advance Date, no fact or condition exists that would (or would, with the passage
of time, the giving of notice, or both) constitute an Event of Default under
this Agreement or any of the Loan Documents and no fact or condition exists that
would (or would, with the passage of time, the giving of notice, or

                                       14
<PAGE>   15

both) constitute a default under the Senior Loan Documents between Borrower and
Senior Creditor.

         7.6 MATERIAL ADVERSE EFFECT.  As of the Closing Date or the Advance
Date, no event which has had or could reasonably be expected to have a
Material Adverse Effect has occurred and is continuing.

SECTION 8.  DEFAULT

         The occurrence of any one or more of the following events (herein
called "Events of Default") shall constitute a default hereunder and under the
Note(s) and other Loan Documents:

         8.1 Borrower defaults in the payment of any principal, interest or
other Secured Obligation involving the payment of money under this Agreement,
the Note(s) or any of the other Loan Documents, and such default continues for
more than five (5) days after the due date thereof; or

         8.2 Borrower defaults in any material respect in the performance of any
other covenant or Secured Obligation of Borrower hereunder or under the Note(s)
or any of the other Loan Documents, and such default continues for more than
twenty (20) days after Lender has given notice of such default to Borrower.

         8.3 Any representation or warranty made herein by Borrower shall
prove to have been false or misleading in any material respect when made; or

         8.4 Borrower shall make an assignment for the benefit of creditors, or
shall admit in writing its inability to pay its debts as they become due, or
shall file a voluntary petition in bankruptcy, or shall file any petition or
answer seeking for itself any reorganization, arrangement, composition,
readjustment, liquidation, dissolution or similar relief under any present or
future statute, law or regulation pertinent to such circumstances, or shall seek
or consent to or acquiesce in the appointment of any trustee, receiver, or
liquidator of Borrower or of all or any substantial part (33-1/3% or more) of
the properties of Borrower; or Borrower or its directors or majority
shareholders shall take any action initiating the dissolution or liquidation of
Borrower; or

         8.5 Sixty (60) days shall have expired after the commencement of an
action by or against Borrower seeking reorganization, arrangement, composition,
readjustment, liquidation, dissolution or similar relief under any present or
future statute, law or regulation, without such action being dismissed or all
orders or proceedings thereunder affecting the operations or the business of
Borrower being stayed; or a stay of any such order or proceedings shall
thereafter be set aside and the action setting it aside shall not be timely
appealed; or Borrower shall file any answer admitting or not contesting the
material allegations of a petition filed against Borrower in any such
proceedings; or the court in which such proceedings are pending shall enter a
decree or order granting the relief sought in any such proceedings; or

         8.6 Sixty (60) days shall have expired after the appointment, without
the consent or acquiescence of Borrower, of any trustee, receiver or liquidator
of Borrower or of all or any substantial part of the properties of Borrower
without such appointment being vacated; or

                                       15

<PAGE>   16

         8.7 The material default, and the expiration of any applicable cure
period by Borrower under any Excluded Agreement(s), any other promissory note or
agreement for borrowed money, or any other agreement between Borrower and
Lender; or

         8.8 The occurrence of any default under any lease or other agreement or
obligation of Borrower involving an amount in excess of $100,000.00 or having a
Material Adverse Effect; or the entry of any judgment against Borrower involving
an award in excess of $100,000.00 that would have a Material Adverse Effect,
that has not been bonded or stayed on appeal within thirty (30) days; or

         8.9 The occurrence of any material default under the Senior Loan
Documents.

SECTION 9.  REMEDIES

         Upon the occurrence of any one or more Events of Default, Lender, at
its option, may declare the Note and all of the other Secured Obligations to be
accelerated and immediately due and payable (PROVIDED, that upon the occurrence
of an Event of Default of the type described in Sections 8.4 or 8.5, the Note(s)
and all of the other Secured Obligations shall automatically be accelerated and
made due and payable without any further act), whereupon the unpaid principal of
and accrued interest on such Note(s) and all other outstanding Secured
Obligations shall become immediately due and payable, and shall thereafter bear
interest at the Default Rate set forth in, and calculated according to, Section
2.3 (c) of this Agreement. Lender may exercise all rights and remedies with
respect to the Collateral under the Loan Documents or otherwise available to it
under applicable law, including the right to release, hold or otherwise dispose
of all or any part of the Collateral and the right to occupy, utilize, process
and commingle the Collateral.

         Upon the happening and during the continuance of any Event of Default,
Lender may then, or at any time thereafter and from time to time, apply,
collect, sell in one or more sales, lease or otherwise dispose of, any or all of
the Collateral, in its then condition or following any commercially reasonable
preparation or processing, in such order as Lender may elect, and any such sale
may be made either at public or private sale at its place of business or
elsewhere. Borrower agrees that any such public or private sale may occur upon
five (5) calendar days' prior written notice to Borrower. Lender may require
Borrower to assemble the Collateral and make it available to Lender at a place
designated by Lender which is reasonably convenient to Lender and Borrower. The
proceeds of any sale, disposition or other realization upon all or any part of
the Collateral shall be distributed by Lender in the following order of
priorities:

         First, to Lender in an amount sufficient to pay in full Lender's costs
         and professionals' and advisors' fees and expenses;

         Second, to Lender in an amount equal to the then unpaid amount of the
         Secured Obligations in such order and priority as Lender may choose in
         its sole discretion; and

         Finally, upon payment in full of all of the Secured Obligations, to
         Borrower or its representatives or as a court of competent jurisdiction
         may direct.

         Lender shall be deemed to have acted reasonably in the custody,
preservation and disposition of any of the Collateral if it complies with the
obligations of a secured party under Section 9207 of the UCC.

                                       16
<PAGE>   17
         Lender's rights and remedies hereunder are subject to the terms of the
Subordination Agreement.

SECTION 10.  MISCELLANEOUS

         10.1 CONTINUATION OF SECURITY INTEREST. This is a continuing Agreement
and the grant of a security interest hereunder shall remain in full force and
effect and all the rights, powers and remedies of Lender hereunder shall
continue to exist until the Secured Obligations are paid in full as the same
become due and payable and until Lender has executed a written termination
statement (which Lender shall execute within a reasonable time after full
payment of the Secured Obligations hereunder), reassigning to Borrower, without
recourse, the Collateral and all rights conveyed hereby and returning possession
of the Collateral to Borrower. The rights, powers and remedies of Lender
hereunder shall be in addition to all rights, powers and remedies given by
statute or rule of law and are cumulative. The exercise of any one or more of
the rights, powers and remedies provided herein shall not be construed as a
waiver of or election of remedies with respect to any other rights, powers and
remedies of Lender.

         10.2 SEVERABILITY. Whenever possible, each provision of this Agreement
shall be interpreted in such manner as to be effective and valid under
applicable law, but if any provision of this Agreement shall be prohibited by or
invalid under such law, such provision shall be ineffective only to the extent
and duration of such prohibition or invalidity, without invalidating the
remainder of such provision or the remaining provisions of this Agreement.

         10.3 NOTICE. Except as otherwise provided herein, all notices and
service of process required, contemplated, or permitted hereunder or with
respect to the subject matter hereof shall be in writing, and shall be deemed to
have been validly served, given or delivered upon the earlier of: (i) the first
business day after transmission by facsimile or hand delivery or deposit with an
overnight express service or overnight mail delivery service; or (ii) the third
calendar day after deposit in the United States mails, with proper first class
postage prepaid, and shall be addressed to the party to be notified as follows:

         (a)      IF TO LENDER:

                                 COMDISCO, INC.
                                Legal Department
                           Attention: General Counsel
                              6111 North River Road
                               Rosemont, IL 60018
                            Facsimile: (847) 518-5088

                  WITH A COPY TO:

                        COMDISCO, INC./COMDISCO VENTURES
                              6111 North River Road
                               Rosemont, IL 60018
                            Facsimile: (847) 518-5465

                                       17
<PAGE>   18

         (b)      IF TO BORROWER:

                                 ACUSPHERE, INC.
                              Attention: President
                                38 Sidney Street
                               Cambridge, MA 02139
                            Facsimile: (617) 5770233
                              Phone: (617) 577-8800

or to such other address as each party may designate for itself by like notice.

         10.4 ENTIRE AGREEMENT; AMENDMENTS. This Agreement, the Note(s), and the
other Loan Documents, and the Warrant Agreement(s) constitute the entire
agreement and understanding of the parties hereto in respect of the subject
matter hereof and thereof, and supersede and replace in their entirety any prior
proposals, term sheets, letters, negotiations or other documents or agreements,
whether written or oral, with respect to the subject matter hereof or thereof
(including, without limitation, Lender's proposal letter dated September 29,
1998, all of which are merged herein and therein. None of the terms of this
Agreement, the Note(s), any of the other Loan Documents or Warrant Agreement(s)
may be amended except by an instrument executed by each of the parties hereto.

         10.5 HEADINGS. The various headings in this Agreement are inserted for
convenience only and shall not affect the meaning or interpretation of this
Agreement or any provisions hereof.

         10.6 NO WAIVER. The powers conferred upon Lender by this Agreement are
solely to protect its interest in the Collateral and shall not impose any duty
upon Lender to exercise any such powers. No omission, or delay, by Lender at any
time to enforce any right or remedy reserved to it, or to require performance of
any of the terms, covenants or provisions hereof by Borrower at any time
designated, shall be a waiver of any such right or remedy to which Lender is
entitled, nor shall it in any way affect the right of Lender to enforce such
provisions thereafter.

         10.7 SURVIVAL. All agreements, representations and warranties contained
in this Agreement, the Note(s), the other Loan Documents and the Warrant
Agreement(s) or in any document delivered pursuant hereto or thereto shall be
for the benefit of Lender and shall survive the execution and delivery of this
Agreement and the expiration or other termination of this Agreement.

         10.8 SUCCESSOR AND ASSIGNS. The provisions of this Agreement, the other
Loan Documents and the Warrant Agreement(s) shall inure to the benefit of and be
binding on Borrower and its permitted assigns (if any). Borrower shall not
assign its obligations under this Agreement, the Note(s), any of the other Loan
Documents or the Warrant Agreement(s), without Lender's express written consent,
and any such attempted assignment shall be void and of no effect. Lender may
assign, transfer, or endorse its rights hereunder and under the other Loan
Documents or Warrant Agreement(s) without prior notice to Borrower, and all of
such rights shall inure to the benefit of Lender's successors and assigns.

         10.9 FURTHER INDEMNIFICATION. Borrower agrees to pay, and to save
Lender harmless from, any and all liabilities with respect to, or resulting from
any delay in paying, any and all excise, sales or other similar taxes which may
be payable or determined to be payable

                                       18
<PAGE>   19

with respect to any of the Collateral or in connection with any of the
transactions contemplated by this Agreement.

         10.10 GOVERNING LAW. This Agreement, the Note(s), the other Loan
Documents and the Warrant Agreement(s) have been negotiated and delivered to
Lender in the State of Illinois, and shall not become effective until accepted
by Lender, in the State of Illinois. Payment to Lender by Borrower of the
Secured Obligations is due in the State of Illinois. This Agreement, the
Note(s), the other Loan Documents and the Warrant Agreement(s) shall be governed
by, and construed and enforced in accordance with, the laws of the State of
Illinois, excluding conflict of laws principles that would cause the application
of laws of any other jurisdiction.

         10.11 CONSENT TO JURISDICTION AND VENUE. All judicial proceedings
arising in or under or related to this Agreement, the Note(s), any of the other
Loan Documents or Warrant Agreement(s) may be brought in any state or federal
court of competent jurisdiction located in the State of Illinois. By execution
and delivery of this Agreement, each party hereto generally and unconditionally:
(a) consents to personal jurisdiction in Cook County, State of Illinois; (b)
waives any objection as to jurisdiction or venue in Cook County, State of
Illinois; (c) agrees not to assert any defense based on lack of jurisdiction or
venue in the aforesaid courts; and (d) irrevocably agrees to be bound by any
judgment rendered thereby in connection with this Agreement, the Note(s), the
other Loan Documents or Warrant Agreement(s). Service of process on any party
hereto in any action arising out of or relating to this agreement shall be
effective if given in accordance with the requirements for notice set forth in
Section 10.3, above and shall be deemed effective and received as set forth in
Section 10.3, above. Nothing herein shall affect the right to serve process in
any other manner permitted by law or shall limit the right of either party to
bring proceedings in the courts of any other jurisdiction.

         10.12 MUTUAL WAIVER OF JURY TRIAL. Because disputes arising in
connection with complex financial transactions are most quickly and economically
resolved by an experienced and expert person and the parties wish applicable
state and federal laws to apply (rather than arbitration rules), the parties
desire that their disputes be resolved by a judge applying such applicable laws.
EACH OF BORROWER AND LENDER SPECIFICALLY WAIVES ANY RIGHT IT MAY HAVE TO TRIAL
BY JURY OF ANY CAUSE OF ACTION, CLAIM, CROSSCLAIM, COUNTERCLAIM, THIRD PARTY
CLAIM OR ANY OTHER CLAIM (COLLECTIVELY, "CLAIMS") ASSERTED BY BORROWER AGAINST
LENDER OR ITS ASSIGNEE AND/OR BY LENDER OR ITS ASSIGNEE AGAINST BORROWER. This
waiver extends to all such Claims, including, without limitation, Claims which
involve persons or entities other than Borrower and Lender; Claims which arise
out of or are in any way connected to the relationship between Borrower and
Lender; and any Claims for damages, breach of contract arising out of this
Agreement, any other Loan Document or any of the Excluded Agreements, specific
performance, or any equitable or legal relief of any kind.

         10.13 CONFIDENTIALITY. Lender acknowledges that certain items of
Collateral, including, but not limited to trade secrets, source codes, customer
lists and certain other items of Intellectual Property, and any Financial
Statements provided pursuant to Section 6 hereof, constitute proprietary and
confidential information of the Borrower (the "Confidential Information").
Accordingly, Lender agrees that any Confidential Information it may obtain in
the course of acquiring, perfecting or foreclosing on the Collateral or
otherwise provided under this Agreement, provided such Confidential Information
is marked as confidential by Borrower at the time of disclosure, shall be
received in the strictest confidence and will not be disclosed to any other
person or entity in any manner whatsoever, in whole or in part, without the
prior written consent of the Borrower, unless and until Lender has acquired
indefeasible title thereto.

                                       19
<PAGE>   20

         10.14 COUNTERPARTS. This Agreement and any amendments, waivers,
consents or supplements hereto may be executed in any number of counterparts,
and by different parties hereto in separate counterparts, each of which when so
delivered shall be deemed an original, but all of which counterparts shall
constitute but one and the same instrument.

IN WITNESS WHEREOF, the Borrower and the Lender have duly executed and delivered
this Agreement as of the day and year first above written.

         BORROWER:                      ACUSPHERE, INC.

                                        Signature: /s/ Sherri C. Oberg
                                                   -----------------------------

                                        Print Name: Sherri C. Oberg
                                                   -----------------------------

                                        Title:     President and C.E.O.
                                                   -----------------------------

ACCEPTED IN ROSEMONT, ILLINOIS:

         LENDER:                        COMDISCO, INC.

                                        Signature: /s/ James P. Labe
                                                   -----------------------------

                                        Print Name: James P. Labe
                                                   -----------------------------

                                        Title:     President
                                                   -----------------------------
                                                   Comdisco Ventures Division

                                       20
<PAGE>   21

        AMENDMENT NUMBER ONE TO SUBORDINATED LOAN AND SECURITY AGREEMENT
                      DATED AS OF OCTOBER 16, 1998 BETWEEN
            ACUSPHERE, INC., AS BORROWER AND COMDISCO, INC. AS LENDER

         This Amendment ("Amendment") is entered into this 9th day of August,
1999 by and between Acusphere, Inc., a Delaware corporation, with its chief
executive offices and principal place of business at 38 Sidney Street,
Cambridge, Massachusetts, 02139 ("Borrower") and Comdisco, Inc., a Delaware
corporation, with its chief executive offices and principal balance of business
at 6111 North River Road, Rosemont, IL 60018 ("Lender").

                                    RECITALS

         WHEREAS, Borrower and Lender have entered into that certain
Subordinated Loan and Security Agreement dated as of October 16, 1998, (the
"Agreement") whereby Borrower requested Lender make available to Borrower a loan
in the principal amount of up to FIVE MILLION and 00/100 DOLLARS
($5,000,000.00);

         WHEREAS, Borrower and Lender wish to amend certain terms and
conditions of the Agreement;

         WHEREAS, the Secured Obligations hereunder shall be expressly
subordinated, to the extent and in the manner set forth in the Subordination
Agreement;

                                    AGREEMENT

         NOW, THEREFORE, in consideration of the premises and mutual agreements
contained herein, Borrower and lender hereby agree as follows:

SECTION 1. DEFINITION

1.1.     Except as expressly set forth herein, all terms used herein shall have
the meanings set forth in the Agreement.

1.2.     The following definitions shall be added to Section 1 of the Agreement:

         "INITIAL PUBLIC OFFERING" means an initial public offering of
Borrower's securities.

         "MAXIMUM LOAN AMOUNT" means Five Million and No/100 Dollars
($5,000,000.00).

         "MERGER EVENT" means a capital reorganization of the shares of the
Borrower's stock (other than a combination, reclassification, exchange or
subdivision of shares otherwise provided for in Section 2.5 hereof), or a merger
or consideration of the Borrower with or into another corporation whether or not
the Borrower is the surviving corporation, or the sale of all or substantially
all of the Borrower's properties and assets to any other person.

         "PREFERRED STOCK" means, as used in this Amendment, the Borrower's
Series E Preferred Stock.

                                       1
<PAGE>   22

         "PURCHASE OPTION" shall have the meaning assigned to such term in
Section 2.5 of this Agreement.

SECTION 2.  THE LOAN

2.1.     LOAN I AND LOAN II

         Borrower and Lender agree that the Loans shall be due and payable in
eighteen (18) equal monthly installments of interest only, payable on the first
day of the month, followed by eighteen (18) equal monthly installments of
principal and interest, payable on the first day of each month, to and including
the Maturity Date (each, a "Payment Date").

2.2.     Section 2.5 of the Agreement shall be replaced with the following
language:

         2.5      PURCHASE OPTION

         2.5.1 Lender shall have the right to purchase shares of Borrower's
Preferred Stock with an aggregate value of up to thirty percent (30%) of the
Maximum Loan Amount (subject to increase as provided in Section 2.5.2) at any
time, at Lender's sole and absolute discretion (the "Purchase Option"). The
Purchase Option shall be exercisable by Lender at any time prior to either (i)
the Borrower's Initial Public offering, (ii) a Merger Event or (iii) August 9,
2004 at a purchase price equal to $4.29 per share (the "Purchase Price"). If
Borrower's accountants advise the Borrower that conversion of a portion of the
Notes would prevent the Merger from being treated as a pooling of interests, the
Note(s) shall not be convertible pursuant to this Section, and instead Borrower
shall prepay the Note(s) by prepaying the principal amount together with all
accrued and unpaid interest and a prepayment premium of 1.5% of the then
outstanding principal amount.

                  The number and purchase price of such shares are subject to
adjustment as provided in this Section 2.5.

                  2.5.2 If the Borrower has not repaid the outstanding principal
         amount under a Note in its entirety by the Maturity Date (as defined in
         the applicable Note(s)), then for each additional month, or portion
         thereof, thereafter that the outstanding principal is not paid, Lender
         shall have the right to purchase from the Borrower, at the Purchase
         Price (adjusted, as set forth and defined in Section 2.5.3 herein), an
         additional amount of Preferred Stock with a value equal to the product
         of (x) the outstanding principal amount which is due but unpaid and (y)
         one percent (1%).

                  2.5.3 The Purchase Price per share and the number of shares of
         Preferred Stock purchasable hereunder are subject to adjustment, as
         follows:

                           (a) If the Borrower at any time shall, by
         combination, reclassification, exchange or subdivision of the
         securities as to which purchase rights under this Purchase Option exist
         into the same or a different number as securities of any other class or
         classes, this Purchase Option shall thereafter represent the right to
         acquire such number and kind of securities as would have been issuable
         as the result of such change with respect to the securities which were
         subject to the purchase rights under this Purchase Option immediately
         prior to such classification, exchange, subdivision or other change.

                                       2
<PAGE>   23

                           (b) If the Borrower at any time shall combine or
         subdivide its Preferred Stock, the Purchase Price shall be
         proportionately decreased in the case of a subdivision, or
         proportionately increased in the case of a combination.

                           (c) If the Borrower at any time shall pay a dividend
         payable in, or Distribution of, the Borrower's stock for consideration
         on a per share value less than the Purchase Price (other than any
         distribution specifically provided for in the foregoing subsections (a)
         and (b), then upon conversion of the Preferred Stock purchasable
         hereunder into the Borrower's Common Stock, Lender shall be eligible
         for the conversion price adjustment as provided in the Borrower's
         Charter (as defined below). The provision shall apply regardless of
         whether Lender is a shareholder at the time of any dilutive issuance.

                           (d) Additional antidilution rights applicable to the
         Preferred Stock purchasable hereunder are as set forth in the
         Borrower's Certificate of Incorporation, as amended through the
         Effective Date, a true and complete copy of which is attached hereto as
         EXHIBIT D (the "Charter"). The Borrower shall promptly provide the
         Lender with any restatement, amendment, modification or waiver of the
         Charter. The Borrower shall provide Lender with prior written notice of
         any issuance of its stock or other equity security to occur after the
         Effective Date of this Purchase Option, which notice shall include (i)
         the price at which such stock or security is to be sold, (ii) the
         number of shares to be issued, and (iii) such other information as
         necessary for Lender to determine if a dilutive event has occurred.

                           (e) If: (i) the Borrower shall declare any dividend
         or distribution upon its stock, whether in cash, property, stock or
         other securities; (ii) the Borrower shall offer for subscription pro
         rata to the holders of any class of its preferred or other convertible
         stock any additional shares of stock of any class or other rights;
         (iii) there shall be any Merger Event; (iv) there shall be an Initial
         Public Offering; or (v) there shall be any voluntary dissolution,
         liquidation or winding up of the Borrower; then, in connection with
         each such event, the Borrower shall send to the Lender: (A) at least
         twenty (20) days' prior written notice of the date on which the books
         of the Borrower shall close or a record shall be taken for such
         dividend, distribution, subscription rights (specifying the date on
         which the holders of Preferred Stock shall be entitled thereto) or for
         determining rights to vote in respect of such Merger Event,
         dissolution, liquidation or winding up; (B) in the case of any such
         dissolution, liquidation or winding up, at least twenty (20) days'
         prior written notice of the date when the same shall take place (and
         specifying the date on which the holders of Preferred Stock shall be
         entitled to exchange their Preferred Stock for securities or other
         property deliverable upon dissolution, liquidation or winding up); and
         (C) in the case of a Initial Public Offering or Merger Event, the
         Borrower shall give the Lender at least twenty (20) days written notice
         prior to the effective date thereof.

                  Each such written notice shall set forth, in reasonable
         detail, (i) the event requiring the adjustment, (ii) the amount of the
         adjustment, (iii) the method by which such adjustment was calculated,
         (iv) the Purchase Price, and (v) the number of shares subject to
         purchase hereunder after giving effect to such adjustment, and shall be
         given by first class mail, postage prepaid, addressed to the Lender, at
         the address as shown on the books of the Lender.

                           (f) Failure to timely provide such notice required by
         subsection (e) above shall entitle Lender to retain the benefit of the
         applicable notice period

                                       3
<PAGE>   24

         notwithstanding anything to the contrary contained in any insufficient
         notice received by Lender. The notice period shall begin on the date
         Lender actually receives a written notice containing all the
         information specified above.

                  2.5.5 The Purchase Option is exercisable by the Lender, in
         whole or in part, at any time, or from time to time, prior to the
         earlier of or in conjunction with (i) Initial Public Offering, (ii)
         Merger Event or (iii) August 9, 2004. Lender may exercise its Purchase
         Option by tendering to the Borrower at its principal office a notice of
         exercise in the form attached hereto as EXHIBIT E (the "Notice of
         Purchase"), duly completed and executed. The Purchase Price for that
         portion of the Purchase Option so exercised may be payable, at Lender's
         option, in (a) cash, by bank cashier's or certified check or by wire
         transfer upon closing of the Merger Event, Initial Public Offering or
         August 9, 2004 or (b) Lender may satisfy all or a portion of the
         Purchase Price by tender of one or more Note(s), the outstanding
         principal and interest of which shall be credited against the Purchase
         Price, with the balance, if any, of the Purchase Price payable in cash
         or by check as provided above upon the closing of the Merger Event,
         Initial Public offering or August 9, 2004. In such event, the Note(s)
         so tendered will be deemed satisfied in full and will be cancelled by
         the Borrower and the Borrower will have no further obligation to the
         Lender under such Note(s).

                  Promptly upon receipt of the Notice of Purchase, Borrower
         shall execute the acknowledge of exercise in the form attached hereto
         as EXHIBIT F (the "Acknowledgement of Purchase") indicating the number
         of shares which remain subject to future purchases, if any. Upon
         receipt of the Purchase Price in accordance with the terms set forth
         above, the Borrower shall issue to the Lender a certificate for the
         number of shares of Preferred Stock purchased, no later than twenty-one
         (21) days thereafter.

                  2.5.6 During the term of this Purchase Option, the Borrower
         will at all times have authorized and reserved a sufficient number of
         shares of its Preferred Stock to provide for the exercise of the rights
         to purchase Preferred Stock as provided for herein.

                  2.5.7 No fractional shares or scrip representing fractional
         shares shall be issued upon the exercise of the Purchase Option, but in
         lieu of such fractional shares the Borrower shall make a cash payment
         therefor upon the basis of the Purchase Price then in effect.

                  2.5.8 This Purchase Option does not entitle the Lender to any
         voting rights or other rights as a shareholder of the Borrower prior to
         the exercise of the Purchase Option.

                  2.5.9 Borrower shall give Lender at least 45 days notice of
         its intent to consummate any Merger Event or any Initial Public
         Offering of its capital stock pursuant to a registration statement
         filed with the Securities and Exchange Commission. In either such
         event, Lender shall have the right to exercise its Purchase Option
         subject to and in conjunction with the successful completion of such
         Merger Event or Initial Public Offering. If such closing does not take
         place, the Borrower shall promptly notify the Lender that such proposed
         transaction has been terminated, and the Lender may rescind any
         exercise of its Purchase Option promptly after such notice of
         termination of the proposed transaction if the exercise of this
         Purchase Option has occurred after the Borrower notified the Lender
         that the Merger Event or Initial Public Offering was proposed.

                                       4
<PAGE>   25

SECTION 3    MISCELLANEOUS

3.1 Absence of Events of Defaults. As of the date hereof, no fact or condition
exists that would (or would, with the passage of time, the giving of notice, or
both) constitute an Event of Default under this Agreement or any of the Loan
Documents and no fact or condition exists that would (or would with the passage
of time, the giving of notice, or both) constitute a default under the Senior
Loan Documents between Borrower and Senior Creditor.

3.2 Material Adverse Effect. As of the date hereof, no event which has had or
could reasonably be expected to have a Material Adverse Effect has occurred and
is continuing.

3.3 Representations and Warranties of Borrower. As of the date hereof, the
representations and warranties made by Borrower in Section 2 of the Agreement
remain in full force and effect.

3.4 Section 10.8 of the Agreement shall be replaced by the following language:

         SUCCESSOR AND ASSIGNS. The provisions of this Agreement, the other Loan
Documents and the Warrant Agreement(s) shall inure to the benefit of and be
binding on Borrower and its permitted assigns (if any). Borrower shall not
assign its obligations under this Agreement, the Note(s), any of the other Loan
Documents or the Warrant Agreement(s), without Lender's express written consent,
and any such attempted assignment shall be void and of no effect. Lender may
assign, transfer, or endorse its rights hereunder and under the other Loan
Documents or Warrant Agreement(s) without prior notice to Borrower (i) to any
affiliate of Lender, in whole or in part or (ii) to any third party, in its
entirety, and all of such rights shall inure to the benefit of Lender's
successors and assigns.

3.5 Except as specifically amended hereby, the terms and conditions of the
Agreement are hereby reaffirmed and remain in full force and effect, and from
and after the date hereof the "Agreement" shall mean the "Agreement" as amended
by this Amendment.

3.6 This Amendment may be executed in any number of counterparts, and by
different parties hereto in separate counterparts, each of which when so
delivered shall be deemed an original, but all of which counterparts shall
constitute but one an the same instrument.

         IN WITNESS WHEREOF, Borrower and Lender have duly executed and
delivered this Amendment as of the day and year first above written.

BORROWER                                 ACUSPHERE, INC.

                                         Signature: /s/ Sherri C. Oberg
                                                    ----------------------------
                                         Print Name: Sherri C. Oberg
                                                     ---------------------------
                                         Title: President and CEO
                                                --------------------------------

                                       5
<PAGE>   26

ACCEPTED IN ROSEMONT, ILLINOIS

LENDER                              COMDISCO, INC.

                                    Signature: /s/ James Labe
                                               ---------------------------------
                                    Print Name: James Labe
                                                --------------------------------
                                    Title: President, Comdisco Ventures Division
                                           -------------------------------------

                                       6
<PAGE>   27

                                    EXHIBIT D

                                   THE CHARTER

                                       7
<PAGE>   28

                                    EXHIBIT E

                      NOTICE OF EXERCISE OF PURCHASE OPTION

TO:      _______________ ("Borrower")

(1)      The undersigned Lender hereby elects to exercise its Purchase Option
         with respect to ___________ shares of the Series ___ Preferred Stock of
         Borrower, pursuant to the terms of the Subordinated Loan and Security
         Agreement dated the 16th day of October, 1998 as amended (the "Loan
         Agreement") between Borrower and the Lender.

(2)      Lender shall tender payment of the Purchase Price for such shares in
         full, together with all applicable transfer taxes, if any by:

         (a)      Cash, bank cashier or certified check or wire transfer to an
                  account specified by Borrower in the amount of $___________

                  and/or

         (b)      Tender of one or more Note(s) in the principal
                  amount of $_________, plus accrued interest.

(3)      In exercising its rights with respect to the Purchase Option, the
         undersigned hereby represents and warrants to Borrower as follows:

         (a) The right to acquire Preferred Stock or the Preferred Stock
issuable upon exercise of the Lender's rights contained herein will be acquired
for investment and not with a view to the sale or distribution of any part
thereof, and the Lender has no present intention of selling or engaging in any
public distribution of the same except pursuant to a registration or exemption.

         (b) The Lender understands (i) that the Preferred Stock issuable upon
exercise of its Purchase Option is not registered under the 1933 Act nor
qualified under applicable state securities laws on the ground that the issuance
contemplated by its Purchase Option will be exempt from the registration and
qualifications requirements thereof, and (ii) that the Borrower's reliance on
such exemption is predicated on the representations set forth in this notice.

         (c) The Lender has such knowledge and experience in financial and
business matters as to be capable of evaluating the merits and risks of its
investment, and has the ability to bear the economic risks of its investment.

         (d) The Lender understands that if the Borrower does not register
with the Securities and Exchange Commission pursuant to Section 12 of the 1934
Act (the "1934 Act"), or file reports pursuant to Section 15(d), of the 1934
Act, or if a registration statement covering the securities under the 1933 Act
is not in effect when it desires to sell (i) the rights to purchase Preferred
Stock pursuant to this its Purchase Option, or (ii) the Preferred Stock issuable
upon exercise of the right to purchase, if may be required to hold such
securities for an indefinite period. The Lender also understands that any sale
of its

                                       8
<PAGE>   29

rights of the Lender to purchase Preferred Stock or Preferred Stock which
might be made by it in reliance upon Rule 144 under the 1933 Act may be made
only in accordance with the terms and conditions of that Rule.

         (e) Lender is an "accredited investor" within the meaning of the
Securities and Exchange Rule 501 or Regulation D, as presently in effect.

(4)      Subject to our review and acceptance of your Acknowledgment Certificate
         with respect to this Notice and payment of the Purchase Price in
         accordance with the terms hereof, please issue a certificate or
         certificates representing said shares of Series ___ Preferred Stock in
         the name of the undersigned or in such other name as is specified
         below.

                                           -------------------------------------
                                           (Name)

                                           -------------------------------------
                                           (Address)

                                           LENDER:  COMDISCO, INC.

                                           By:

                                           Title:_______________________________

                                           Date:________________________________

                                       9

<PAGE>   30

                                    EXHIBIT F

                       ACKNOWLEDGMENT OF RECEIPT OF NOTICE
                         OF EXERCISE OF PURCHASE OPTION

         The undersigned ________ ("Borrower") hereby acknowledges receipt of
the "Notice of Purchase" from Comdisco, Inc. ("Lender") to exercise its Purchase
Option with respect to ____ shares of the Series ___ Preferred Stock of
______________ pursuant to the terms of the Subordinate Loan and Security
Agreement dated October 16, 1998, as amended, (the "Agreement"). Borrower
further acknowledges that ____ shares remain subject to purchase under the terms
of the Agreement.

         In connection with such Purchase Option the undersigned hereby
represents, warrants and agrees as follows:

         (a) All representations and warranties of the Borrower made pursuant to
the Agreement are true and correct in all material respects on and as of the
date of this Acknowledgement with the same effect as though made on as of this
date (except as set forth in Schedule 1 to this Acknowledgment)

         (b) The Preferred Stock issuable upon exercise of the Lender's rights
has been duly and validly reserved and, when issued in accordance with the
provisions of the Purchase Option, will be validly issued, fully paid and
non-assessable, and will be free of any taxes, liens, charges or encumbrances of
any nature whatsoever; provided, however, that the Preferred Stock issuable
pursuant to the Purchase Option may be subject to restrictions on transfer under
state and/or Federal securities laws. The Borrower has made available to the
Lender true, correct and complete copies of its Charter and Bylaws, as amended.
The issuance of certificates for shares of Preferred Stock upon Purchase of the
Purchase Option shall be made without charge to the Lender for any issuance tax
in respect thereof, or other cost incurred by the Borrower in connection with
such Purchase and the related issuance of shares of Preferred Stock. The
Borrower shall not be required to pay any tax which may be payable in respect of
any transfer involved and the issuance and delivery of any certificate in a name
other than that of the lender.

         (c) The issuance to Lender of the right to acquire the shares of
Preferred Stock, has been duly authorized by all necessary corporate action on
the part of the Borrower, and the Purchase Option is not inconsistent with the
Borrower's Charter or Bylaws, does not contravene any law or governmental rule,
regulation or order applicable to it, does not and will not contravene any
provision of, or constitute a default under, any indenture, mortgage, contract
or other instrument to which it is a party or by which it is bound, and the
Purchase Option constitutes a legal, valid and binding agreement of the
Borrower, enforceable in accordance with its terms.

         (d) No consent or approval of, giving notice to, registration with, or
taking of any other action in respect of any state, Federal or other
governmental authority or agency is required with respect to the execution,
delivery and performance by the Borrower of its obligation sunder the Purchase
Option, except for the filing of notices pursuant to Regulation D under the 1933
Act and any filing required by applicable state securities law, which filings
will be effective by the time required thereby.

                                       10
<PAGE>   31

         (e) The Borrower is not, pursuant to the terms of any other agreement
currently in existence, under any obligation to register under the 1933 Act any
of its presently outstanding securities or any of its securities which may
hereafter be issued.

         (f) Subject to the accuracy of the Lender's representations in its
Notice, the issuance of the Preferred Stock upon exercise of the Purchase Option
will constitute a transaction exempt from (i) the registration requirements of
Section 5 of the 1933 Act, in reliance upon Section 4(2) thereof, and (ii) the
qualification requirements of the applicable state securities laws.

         (g) If Lender proposes to sell Preferred Stock issuable upon the
exercise of the Purchase Option in compliance with Rule 144 promulgated by the
Securities and Exchange Commission, the Borrower shall furnish to the Lender,
within ten days after receipt of a written request, a written statement
confirming the borrower's compliance with the filing requirements of the
Securities and Exchange Commission as set forth in such Rule, as such Rule may
be amended from time to time.

         Borrower acknowledges that Lender has the right to review Schedule 1 to
this Certificate and that Lender may in its sole discretion withdraw its notice
of exercise of Purchase Option within the [ten business] days after Lender's
receipt of this Acknowledgement.

                                BORROWER:     ACUSPHERE, INC.

                                              By:_______________________________

                                              Title:____________________________

                                              Date:_____________________________

                                       11<PAGE>   1
                                                                  Exhibit 10.13

         THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
         ACT OF 1933. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED,
          OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION
        STATEMENT RELATED THERETO OR AN OPINION OF COUNSEL (WHICH MAY BE
       COMPANY COUNSEL) REASONABLY SATISFACTORY TO THE COMPANY THAT SUCH
         REGISTRATION IS NOT REQUIRED UNDER THE SECURITIES ACT OF 1933.

                                WARRANT AGREEMENT

                  To Purchase Shares of the Preferred Stock of

                                 ACUSPHERE, INC.

                 Dated as of June 6, 1997 (the "Effective Date")

     WHEREAS, Acusphere, Inc., a Delaware corporation (the "Company") has
entered into a Master Lease Agreement dated as of May 1, 1995, Equipment
Schedule No. VL-5 dated June 7, 1997, and related Schedules (the "Leases") with
Comdisco, Inc., a Delaware corporation (the "Warrantholder"); and

     WHEREAS, the Company desires to grant to Warrantholder, in consideration
for such Leases, the right to purchase shares of its Preferred Stock;

     NOW, THEREFORE, in consideration of the Warrantholder executing and
delivering such Leases and in consideration of mutual covenants and agreements
contained herein, the Company and Warrantholder agree as follows:

     1.   GRANT OF THE RIGHT TO PURCHASE PREFERRED STOCK.

     The Company hereby grants to the Warrantholder, and the Warrantholder is
entitled, upon the terms and subject to the conditions hereinafter set forth, to
subscribe to and purchase, from the Company, 40,888 fully paid and
non-assessable shares of the Company's Series C Convertible Preferred Stock
("Preferred Stock") at a purchase price of $2.14 per share (the "Exercise
Price"). The number and purchase price of such shares are subject to adjustment
as provided in Section 8 hereof.

     2.   TERM OF THE WARRANT AGREEMENT.

     Except as otherwise provided for herein, the term of this Warrant Agreement
and the right to purchase Preferred Stock as granted herein shall commence on
the Effective Date and shall be exercisable for a period of ten (10) years.

     3.   EXERCISE OF THE PURCHASE RIGHTS.

     The purchase rights set forth in this Warrant Agreement are exercisable by
the Warrantholder, in whole or in part, at any time, or from time to time, prior
to the expiration of the term set forth in Section 2 above, by tendering to the
Company at its principal office a notice of exercise in the form attached hereto
as Exhibit I (the "Notice of Exercise"), duly completed and executed. Promptly
upon receipt of the Notice of Exercise and the payment of the purchase price in
accordance with the terms set forth below, and in no event later than twenty-one
(21) days thereafter, the Company shall issue to the Warrantholder a certificate
for the number of shares of Preferred Stock

<PAGE>   2

purchased and shall execute the Notice of Exercise indicating the number of
shares which remain subject to future purchases, if any.

     The Exercise Price may be paid at the Warrantholder's election either (i)
by cash or check, or (ii) by surrender of Warrants ("Net Issuance") as
determined below. If the Warrantholder elects the Net Issuance method, the
Company will issue Preferred Stock in accordance with the following formula:

          X = Y (A-B)
              -------
                 A

Where: X = the number of shares of Preferred Stock to be issued to the
           Warrantholder.

           Y = the number of shares of Preferred Stock requested to be exercised
               under this Warrant Agreement.

           A = the fair market value of one (1) share of Common Stock.

           B = the Exercise Price.

     As used herein, current fair market value of Common Stock shall mean with
respect to each share of Common Stock:

     (i) if the exercise is in connection with an initial public offering, and
     if the Company's Registration Statement relating to such public offering
     has been declared effective by the SEC, then the initial "Price to Public"
     specified in the final prospectus with respect to the offering;

     (ii) if this Warrant is exercised after, and not in connection with the
     Company's initial public offering, and:

          (a) if traded on a securities exchange, the fair market value shall be
          deemed to be the average of the closing prices over a twenty-one (21)
          day period ending three days before the day the current fair market
          value of the securities is being determined; or

          (b) if actively traded over-the-counter, the fair market value shall
          be deemed to be the average of the closing bid and asked prices quoted
          on the NASDAQ system (or similar system) over the twenty-one (21) day
          period ending three days before the day the current fair market value
          of the securities is being determined;

     (iii) if at any time the Common Stock is not listed on any securities
     exchange or quoted in the NASDAQ System or the over-the-counter market, the
     current fair market value of Common Stock shall be the highest price per
     share which the Company could obtain from a willing buyer (not a current
     employee or director) for shares of Common Stock sold by the Company, from
     authorized but unissued shares, as determined in good faith by its Board of
     Directors, unless the Company shall become subject to a merger, acquisition
     or other consolidation pursuant to which the Company is not the surviving
     party, in which case the fair market value of Common Stock shall be deemed
     to be the value received by the holders of the Company's Preferred Stock on
     a common equivalent basis pursuant to such merger or acquisition.

     Upon partial exercise by either cash or Net Issuance, the Company shall
promptly issue an amended Warrant Agreement representing the remaining number

                                       2
<PAGE>   3

of shares purchasable hereunder. All other terms and conditions of such amended
Warrant Agreement shall be identical to those contained herein, including, but
not limited to the Effective Date hereof.

     4.   RESERVATION OF SHARES.

     (a) AUTHORIZATION AND RESERVATION OF SHARES. During the term of this
Warrant Agreement, the Company will at all times have authorized and reserved a
sufficient number of shares of its Preferred Stock to provide for the exercise
of the rights to purchase Preferred Stock as provided for herein.

     (b) REGISTRATION OR LISTING. If any shares of Preferred Stock required to
be reserved hereunder require registration with or approval of any governmental
authority under any Federal or State law (other than any registration under the
1933 Act, as then in effect, or any similar Federal statute then enforced, or
any state securities law, required by reason of any transfer involved in such
conversion), or listing on any domestic securities exchange, before such shares
may be issued upon conversion, the Company will, at its expense and as
expeditiously as possible, use its best efforts to cause such shares to be duly
registered, listed or approved for listing on such domestic securities exchange,
as the case may be.

     5.   NO FRACTIONAL SHARES OR SCRIP.

     No fractional shares or scrip representing fractional shares shall be
issued upon the exercise of the Warrant, but in lieu of such fractional shares
the Company shall make a cash payment therefor upon the basis of the Exercise
Price, then in effect.

     6.   NO RIGHTS AS SHAREHOLDER.

     This Warrant Agreement does not entitle the Warrantholder to any voting
rights or other rights as a shareholder of the Company prior to the exercise of
the Warrant.

     7.   WARRANTHOLDER REGISTRY.

     The Company shall maintain a registry showing the name and address of the
registered holder of this Warrant Agreement.

     8.   ADJUSTMENT RIGHTS.

     The purchase price per share and the number of shares of Preferred Stock
purchasable hereunder are subject to adjustment, as follows:

     (a) MERGER AND SALE OF ASSETS. If at any time there shall be a capital
reorganization of the shares of the Company's stock (other than a combination,
reclassification, exchange or subdivision of shares otherwise provided for
herein), or a merger or consolidation of the Company with or into another
corporation when the Company is not the surviving corporation, or the sale of
all or substantially all of the Company's properties and assets to any other
person (hereinafter referred to as a "Merger Event"), then, as a part of such
Merger Event, lawful provision shall be made so that the Warrantholder shall
thereafter be entitled to receive, upon exercise of the Warrant, the number of
shares of preferred stock or other securities of the successor corporation
resulting from such Merger Event, equivalent in value to that which would have
been issuable if Warrantholder had exercised this Warrant immediately prior to
the Merger Event. In any such case, appropriate adjustment (as determined in

                                       3
<PAGE>   4

good faith by the Company's Board of Directors) shall be made in the application
of the provisions of this Warrant Agreement with respect to the rights and
interest of the Warrantholder after the Merger Event to the end that the
provisions of this Warrant Agreement (including adjustments of the Exercise
Price and number of shares of Preferred Stock purchasable) shall be applicable
to the greatest extent possible.

     (b) RECLASSIFICATION OF SHARES; PREFERRED STOCK CONVERSION. If the Company
at any time shall, by combination, reclassification, exchange or subdivision of
securities or otherwise, change any of the securities as to which purchase
rights under this Warrant Agreement exist into the same or a different number of
securities of any other class or classes, this Warrant Agreement shall
thereafter represent the right to acquire such number and kind of securities as
would have been issuable as the result of such change with respect to the
securities which were subject to the purchase rights under this Warrant
Agreement immediately prior to such combination, reclassification, exchange,
subdivision or other change. If at any time all of the outstanding shares of
Preferred Stock have been converted to shares of the Company's Common Stock,
then, from and after the date of such conversion, this Warrant Agreement shall
no longer be exercisable for Preferred Stock, but shall represent the right to
acquire that number of shares of Common Stock as shall be equal to the number of
shares issuable upon conversion of the Preferred Stock which would have been
issued on exercise of this Warrant Agreement had such exercise occurred
immediately prior to such conversion.

     (c) SUBDIVISION OR COMBINATION OF SHARES. If the Company at any time shall
combine or subdivide its Preferred Stock, the Exercise Price shall be
proportionately decreased in the case of a subdivision, or proportionately
increased in the case of a combination.

     (d) STOCK DIVIDENDS. If the Company at any time shall pay a dividend
payable in, or make any other distribution (except any distribution specifically
provided for in the foregoing subsections (a) or (b)) of the Company's stock,
then the Exercise Price shall be adjusted, from and after the record date of
such dividend or distribution, to that price determined by multiplying the
Exercise Price in effect immediately prior to such record date by a fraction (i)
the numerator of which shall be the total number of all shares of the Company's
stock outstanding immediately prior to such dividend or distribution, and (ii)
the denominator of which shall be the total number of all shares of the
Company's stock outstanding immediately after such dividend or distribution. The
Warrantholder shall thereafter be entitled to purchase, at the Exercise Price
resulting from such adjustment, the number of shares of Preferred Stock
(calculated to the nearest whole share) obtained by multiplying the Exercise
Price in effect immediately prior to such adjustment by the number of shares of
Preferred Stock issuable upon the exercise hereof immediately prior to such
adjustment and dividing the product thereof by the Exercise Price resulting from
such adjustment.

     (e) ANTIDILUTION RIGHTS. Additional antidilution rights applicable to the
Preferred Stock purchasable hereunder are as set forth in the Company's
Certificate of Incorporation, as amended through the Effective Date, a true and
complete copy of which is attached hereto as Exhibit __ (the "Charter"). The
Company shall promptly provide the Warrantholder with any restatement,
amendment, modification or waiver of the Charter. The Company shall provide
Warrantholder with prior written notice of any issuance of its stock or other
equity security to occur after the Effective Date of this Warrant, which notice
shall include (a) the price at which such stock or security is to be sold, (b)

                                       4
<PAGE>   5

the number of shares to be issued, and (c) such other information as necessary
for Warrantholder to determine if a dilutive event has occurred.

     (f) NOTICE OF ADJUSTMENTS. If: (i) the Company shall declare any dividend
or distribution upon its stock, whether in cash, property, stock or other
securities; (ii) the Company shall offer for subscription prorata to the holders
of any class of its Preferred or other convertible stock any additional shares
of stock of any class or other rights; (iii) there shall be any Merger Event; or
(iv) there shall be any voluntary or involuntary dissolution, liquidation or
winding up of the Company; then, in connection with each such event, the Company
shall send to the Warrantholder: (A) at least ten (10) days' prior written
notice of the date on which the books of the Company shall close or a record
shall be taken for such dividend, distribution, subscription rights (specifying
the date on which the holders of Preferred Stock shall be entitled thereto) or
for determining rights to vote in respect of such Merger Event, dissolution,
liquidation or winding up; and (B) in the case of any such Merger Event,
dissolution, liquidation or winding up, at least ten (10) days' prior written
notice of the date when the same shall take place (and specifying the date on
which the holders of Preferred stock shall be entitled to exchange their
Preferred Stock for securities or other property deliverable upon such Merger
Event, dissolution, liquidation or winding up). In the case of a public
offering, the Company shall give Warrantholder notice of filing of a
registration statement with the SEC promptly after such filing, but in no event
later than three (3) business days after such filing.

     Each such written notice shall set forth, in reasonable detail, (i) the
event requiring the adjustment, (ii) the amount of the adjustment, (iii) the
method by which such adjustment was calculated, (iv) the Exercise Price, and (v)
the number of shares subject to purchase hereunder after giving effect to such
adjustment, and shall be given by first class mail, postage prepaid, addressed
to the Warrantholder, at the address as shown on the books of the Company.

     (g) TIMELY NOTICE. Failure to timely provide such notice required by
subsection (f) above shall entitle Warrantholder to retain the benefit of the
applicable notice period notwithstanding anything to the contrary contained in
any insufficient notice received by Warrantholder. The notice period shall begin
on the date Warrantholder actually receives a written notice containing all the
information specified above.

9.   REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

     (a) RESERVATION OF PREFERRED STOCK. The Preferred Stock issuable upon
exercise of the Warrantholder's rights has been duly and validly reserved and,
when issued in accordance with the provisions of this Warrant Agreement, will be
validly issued, fully paid and non-assessable, and will be free of any taxes,
liens, charges or encumbrances of any nature whatsoever; provided, however, that
the Preferred Stock issuable pursuant to this Warrant Agreement may be subject
to restrictions on transfer under state and/or Federal securities laws. The
Company has made available to the Warrantholder true, correct and complete
copies of its Charter and Bylaws, as amended, and minutes of all Board of
Directors (including all committees of the Board of Directors, if any). The
issuance of certificates for shares of Preferred Stock upon exercise of the
Warrant Agreement shall be made without charge to the Warrantholder for any
issuance tax in respect thereof, or other cost incurred by the Company in
connection with such exercise and the related issuance of shares of Preferred
Stock. The Company shall not be required to pay any tax

                                       5
<PAGE>   6

which may be payable in respect of any transfer involved and the issuance and
delivery of any certificate in a name other than that of the Warrantholder.

     (b) DUE AUTHORITY. The execution and delivery by the Company of this
Warrant Agreement and the performance of all obligations of the Company
hereunder, including the issuance to Warrantholder of the right to acquire the
shares of Preferred Stock, have been duly authorized by all necessary corporate
action on the part of the Company, and the Leases and this Warrant Agreement are
not inconsistent with the Company's Charter or Bylaws, do not contravene any law
or governmental rule, regulation or order applicable to it, do not and will not
contravene any provision of, or constitute a default under, any indenture,
mortgage, contract or other instrument to which it is a party or by which it is
bound (except for any such provision or default as shall have been waived prior
to the execution hereof), and the Leases and this warrant Agreement constitute
legal, valid and binding agreements of the Company, enforceable in accordance
with their respective terms.

     (c) CONSENTS AND APPROVALS. No consent or approval of, giving of notice to,
registration with, or taking of any other action in respect of any state,
Federal or other governmental authority or agency is required with respect to
the execution, delivery and performance by the Company of its obligations under
this Warrant Agreement, except for the filing of notices pursuant to Regulation
D under the 1933 Act and applicable state securities law, which filings will be
effective by the time required thereby.

     (d) ISSUED SECURITIES. All issued and outstanding shares of Common Stock,
Preferred Stock or any other securities of the Company have been duly authorized
and validly issued and are fully paid and nonassessable. All outstanding shares
of Common Stock, Preferred Stock and any other securities were issued in full
compliance with all Federal and state securities laws. In addition:

     (i) The authorized capital of the Company consists of (A) 11,000,000 shares
of Common Stock, of which 3,862,163 shares are issued and outstanding, and (B)
7,071,046 shares of preferred stock, of which 816,169 shares are designated
Series A Convertible Preferred Stock, all of which are issued and outstanding
and are convertible into 816,169 shares of Common Stock; and 2,315,625 shares
are designated Series B Convertible Preferred Stock, of which 2,265,625 shares
are issued and outstanding and are convertible into 2,265,625 shares of Common
Stock; and 3,939,252 shares are designated Series C Convertible Preferred Stock,
3,913,551 of which are issued and outstanding and are convertible into 3,913,551
shares of Common Stock.

     (ii) The Company has reserved 1,426,346 shares of Common Stock for issuance
under its 1994 Stock Plan, under which 879,883 shares or options to shares have
been granted 978,228 shares at an average price of $0.15 per share. Except for
this Warrant Agreement and the Warrant Agreement dated as of May 1, 1995 and
August 5, 1996 between Comdisco, Inc. and the Company, and except as set forth
in this paragraph (d), there are no other options, warrants, conversion
privileges or other rights presently outstanding to purchase or otherwise
acquire any authorized but unissued shares of the Company's capital stock or
other securities of the Company.

     (e) INSURANCE. The Company has in full force and effect insurance policies,
with extended coverage, insuring the Company and its property and business
against such losses and risks, and in such amounts, as are customary for
corporations engaged in a similar business and similarly situated and as

                                       6
<PAGE>   7

otherwise may be required pursuant to the terms of any other contract or
agreement.

     (f) EXEMPT TRANSACTION. Subject to the accuracy of the Warrantholder's
representations in Section 10 hereof, the issuance of the Preferred Stock upon
exercise of this Warrant will constitute a transaction exempt from the
registration requirements of Section 5 of the 1933 Act, in reliance upon Section
4(2) thereof and applicable state securities law.

     (g) COMPLIANCE WITH RULE 144. At the written request of the Warrantholder,
who proposes to sell Preferred Stock issuable upon the exercise of the Warrant
in compliance with Rule 144 promulgated by the Securities and Exchange
Commission, the Company shall furnish to the Warrantholder, within ten days
after receipt of such request, a written statement confirming the Company's
compliance with the filing requirements of the Securities and Exchange
Commission as set forth in such Rule, as such Rule may be amended from time to
time.

10.  REPRESENTATIONS AND COVENANTS OF THE WARRANTHOLDER.

     This Warrant Agreement has been entered into by the Company in reliance
upon the following representations and covenants of the Warrantholder:

     (a) INVESTMENT PURPOSE. The right to acquire Preferred Stock or the
Preferred Stock issuable upon exercise of the Warrantholder's rights contained
herein will be acquired for investment and not with a view to the sale or
distribution of any part thereof, and the Warrantholder has no present intention
of selling or engaging in any public distribution of the same except pursuant to
a registration or exemption.

     (b) PRIVATE ISSUE. The Warrantholder understands (i) that the Preferred
Stock issuable upon exercise of this warrant is not registered under the 1933
Act or qualified under applicable state securities laws on the ground that the
issuance contemplated by this Warrant Agreement will be exempt from the
registration and qualifications requirements thereof, and (ii) that the
Company's reliance on such exemption is predicated on the representations set
forth in this Section 10.

     (c) COMPANY'S RIGHT OF FIRST REFUSAL. The Warrantholder hereby agrees with
the Company as follows:

     (i) Exercise of Right: If the Warrantholder or the Warrantholder's legal
representative (the "Transferor") desires to transfer all or any part of its
rights to acquire Preferred Stock hereunder, the Preferred Stock issued upon
exercise hereof or the Common Stock issuable upon conversion of the Preferred
Stock (collectively, the "Securities") to any person other than the Company (an
"Offeror"), the Transferor shall: (A) obtain in writing an irrevocable and
unconditional bona fide offer (the "Offer") for the purchase thereof from the
Offeror; and (B) give written notice (the "Notice") to the Company setting forth
the Warrantholder's desire to transfer such Securities, which Notice shall be
accompanied by a photocopy of the Offer and shall set forth at least the name
and address of the Offeror and the price and terms of the bona fide offer. Upon
receipt of the Notice, the Company shall have an assignable option to purchase
any or all of such Securities (the "Company Option Securities") specified in the
Notice, such option to be exercisable by giving, within thirty (30) days after
receipt of the Notice, a written counter-notice to the Transferor. If the
Company elects to purchase any or all of such Company Option Securities, it
shall be obligated to purchase, and the

                                       7
<PAGE>   8

Warrantholder shall be obligated to sell to the Company, such Company Option
Securities at the price and terms indicated in the Offer within thirty (30) days
from the date of delivery by the Company of such counter-notice.

     (ii) Sale of Securities to Offeror: The Transferor may, for sixty (60) days
after the expiration of the thirty (30) day period during which the Company may
give the counter-notice, sell, pursuant to the terms of the offer, any or all of
such Company Option Securities not purchased or agreed to be purchased by the
Company or its assignee; provided, however, that the Transferor shall not sell
such Company Option Securities to the Offeror if the Offeror is a competitor of
the Company and the Company gives written notice to the Transferor, within
thirty (30) days of its receipt of the Notice, stating that the Transferor shall
not sell such Company Option Securities to such Offeror; and provided, further,
that prior to the sale of such Company Option Securities to the Offeror, the
Offeror shall execute an agreement with the Company pursuant to which the
Offeror agrees to be subject to the restrictions set forth in this Agreement. If
any or all of such Company Option Securities are not sold pursuant to an offer
within the time permitted above, the unsold Company Option Securities shall
remain subject to the terms of this Agreement.

     (iii) Failure to Deliver Company Option Securities: If the Transferor fails
or refuses to deliver on a timely basis duly endorsed certificates representing
Company Option Securities to be sold to the Company or its assignee pursuant to
this Agreement, the Company shall have the right to deposit the purchase price
for such Company Option Securities in a special account with any bank or trust
company in the Commonwealth of Massachusetts or State of Delaware, giving notice
of such deposit to the Transferor, whereupon such Company Option Securities
shall be deemed to have been purchased by the Company. All such monies shall be
held by the bank or trust company for the benefit of the Transferor. All monies
deposited with the bank or trust company remaining unclaimed for two years after
the date of deposit shall be repaid by the bank or trust company to the Company
on demand, and the Transferor shall thereafter look only to the Company for
payment. The Company may place a legend on any stock certificate delivered to
the Transferor reflecting the restrictions on transfer provided in this
Agreement.

     (iv) Expiration of Company's Right of First Refusal: The first refusal
rights of the Company set forth above shall remain in effect until such time, if
ever, as a distribution to the public is made of shares of the Company's Common
Stock pursuant to a registration statement filed under the Securities Act of
1933, as amended, or a successor statute, at which time the first refusal rights
of the Company set forth herein will automatically expire.

     (d) DISPOSITION OF WARRANTHOLDER'S RIGHTS. In no event will the
Warrantholder make a disposition of any of its rights to acquire Preferred Stock
or Preferred Stock issuable upon exercise of such rights or Common Stock
issuable upon conversion of such Preferred Stock unless and until (i) it shall
have notified the Company of the proposed disposition, and (ii) if requested by
the Company, it shall have furnished the Company with an opinion of counsel
(which counsel may either be inside or outside counsel to the Warrantholder)
satisfactory to the Company and its counsel to the effect that (A) appropriate
action necessary for compliance with the 1933 Act has been taken, or (B) an
exemption from the registration requirements of the 1933 Act is available.
Notwithstanding the foregoing, the restrictions imposed upon the transferability
of any of its rights to acquire Preferred Stock or Preferred Stock issuable on
the exercise of such rights do not apply to transfers from the beneficial owner
of any of the aforementioned securities to its nominee or from such nominee to
its beneficial owner, and shall terminate as to any particular

                                       8
<PAGE>   9

share of Preferred Stock when (1) such security shall have been effectively
registered under the 1933 Act and sold by the holder thereof in accordance with
such registration or (2) such security shall have been sold without registration
in compliance with Rule 144 under the 1933 Act, or (3) a letter shall have been
issued to the Warrantholder at its request by the staff of the Securities and
Exchange Commission or a ruling shall have been issued to the Warrantholder at
its request by such Commission stating that no action shall be recommended by
such staff or taken by such Commission, as the case may be, if such security is
transferred without registration under the 1933 Act in accordance with the
conditions set forth in such letter or ruling and such letter or ruling
specifies that no subsequent restrictions on transfer are required. Whenever the
restrictions imposed hereunder shall terminate, as hereinabove provided, the
Warrantholder or holder of a share of Preferred Stock then outstanding as to
which such restrictions have terminated shall be entitled to receive from the
Company, without expense to such holder, one or more new certificates for the
Warrant or for such shares of Preferred Stock not bearing any restrictive
legend.

     (e) FINANCIAL RISK. The Warrantholder has such knowledge and experience in
financial and business matters as to be capable of evaluating the merits and
risks of its investment, and has the ability to bear the economic risks of its
investment.

     (f) RISK OF NO REGISTRATION. The Warrantholder understands that if the
Company does not register with the Securities and Exchange Commission pursuant
to Section 12 of the 1933 Act, or file reports pursuant to Section 15(d), of the
Securities Exchange Act of 1934 (the "1934 Act"), or if a registration statement
covering the securities under the 1933 Act is not in effect when it desires to
sell (i) the rights to purchase Preferred Stock pursuant to this Warrant
Agreement, or (ii) the Preferred Stock issuable upon exercise of the right to
purchase, it may be required to hold such securities for an indefinite period.
The Warrantholder also understands that any sale of its rights of the
Warrantholder to purchase Preferred Stock or Preferred Stock which might be made
by it in reliance upon Rule 144 under the 1933 Act may be made only in
accordance with the terms and conditions of that Rule.

11.  TRANSFERS. Subject to the terms and conditions contained in Section 10
hereof, this Warrant Agreement and all rights hereunder are transferable in
whole or in part by the Warrantholder and any successor transferee, provided,
however, in no event shall the number of transfers of the rights and interests
in all of the Warrants exceed three (3) transfers. The transfer shall be
recorded on the books of the Company upon receipt by the Company of a notice of
transfer in the form attached hereto as Exhibit II (the "Transfer Notice"), at
its principal offices and the payment to the Company of all transfer taxes and
other governmental charges imposed on such transfer.

12.  MISCELLANEOUS.

     (a) EFFECTIVE DATE. The provisions of this Warrant Agreement shall be
construed and shall be given effect in all respects as if it had been executed
and delivered by the Company on the date hereof. This Warrant Agreement shall be
binding upon any successors or assigns of the Company.

     (b) ATTORNEYS' FEES. In any litigation, arbitration or court proceeding
between the Company and the Warrantholder relating hereto, the prevailing party
shall be entitled to attorneys' fees and expenses and all costs of proceedings
incurred in enforcing this Warrant Agreement.

                                       9
<PAGE>   10

     (c) GOVERNING LAW. This Warrant Agreement shall be governed by and
construed for all purposes under and in accordance with the laws of the
Commonwealth of Massachusetts.

     (d) COUNTERPARTS. This Warrant Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

     (e) NOTICES. Any notice required or permitted hereunder shall be given in
writing and shall be deemed effectively given upon personal delivery, facsimile
transmission (provided that the original is sent by personal delivery or mail as
hereinafter set forth) or seven (7) days after deposit in the United States
mail, by registered or certified mail, addressed (i) to the Warrantholder at
6111 North River Road, Rosemont, Illinois 60018, attention: James Labe, Venture
Leasing Director, cc: Legal Department, (and/or, if by facsimile, (708) 518-5465
and (ii) to the company at 38 Sidney Street, Cambridge, Massachusetts 02139,
(and/or if by facsimile, (617) 577-0233 or at such other address as any such
party may subsequently designate by written notice to the other party.

     (f) REMEDIES. In the event of any default hereunder, the non-defaulting
party may proceed to protect and enforce its rights either by suit in equity
and/or by action at law, including but not limited to an action for damages as a
result of any such default, and/or an action for specific performance for any
default where Warrantholder will not have an adequate remedy at law and where
damages will not be readily ascertainable. The Company expressly agrees that it
shall not oppose an application by the Warrantholder or any other person
entitled to the benefit of this Agreement requiring specific performance of any
or all provisions hereof or enjoining the Company from continuing to commit any
such breach of this Agreement.

     (g) NO IMPAIRMENT OF RIGHTS. The Company will not, by amendment of its
Charter or through any other means, avoid or seek to avoid the observance or
performance of any of the terms of this Warrant, but will at all times in good
faith assist in the carrying out of all such terms and in the taking of all such
actions as may be necessary or appropriate in order to protect the rights of the
Warrantholder against impairment.

     (h) SURVIVAL. The representations, warranties, covenants and conditions of
the respective parties contained herein or made pursuant to this Warrant
Agreement shall survive the execution and delivery of this Warrant Agreement.

     (i) SEVERABILITY. In the event any one or more of the provisions of this
Warrant Agreement shall for any reason be held invalid, illegal or
unenforceable, the remaining provisions of this warrant Agreement shall be
unimpaired, and the invalid, illegal or unenforceable provision shall be
replaced by a mutually acceptable valid, legal and enforceable provision, which
comes closest to the intention of the parties underlying the invalid, illegal or
unenforceable provision.

     (j) AMENDMENTS. Any provision of this warrant Agreement may be amended by a
written instrument signed by the Company and by the Warrantholder.

     (k) ADDITIONAL DOCUMENTS. The Company, upon execution of this Warrant
Agreement, shall provide the Warrantholder with certified resolutions
authorizing the execution, delivery and performance of this Warrant Agreement
and the Leases referred to herein.

                                       10
<PAGE>   11

     IN WITNESS WHEREOF, the parties hereto have caused this Warrant Agreement
to be executed by its officers thereunto duly authorized as of the Effective
Date.

                                        Company: ACUSPHERE, INC.

                                        By: /s/ Sherri C. Oberg
                                            ------------------------------------

                                        Title: President and CEO
                                               ---------------------------------

                                        Warrantholder: COMDISCO, INC.

                                        By: /s/ James P. Labe
                                            ------------------------------------

                                                JAMES P. LABE, PRESIDENT
                                        Title: COMDISCO VENTURES DIVISION
                                               ---------------------------------

                                       11
<PAGE>   12

                                    EXHIBIT I

                               NOTICE OF EXERCISE

To:_________________________________________

(1)  The undersigned Warrantholder hereby elects to purchase ________ shares of
     the Preferred Stock of ____________________, pursuant to the terms of the
     Warrant Agreement dated the ______ day of _____________________, 19__ (the
     "Warrant Agreement") between __________________ and the Warrantholder, and
     tenders herewith payment of the purchase price for such shares in full,
     together with all applicable transfer taxes, if any.

(2)  In exercising its rights to purchase the Preferred Stock of
     _____________________, the undersigned hereby confirms and acknowledges the
     investment representations and warranties made in Section 10 of the Warrant
     Agreement.

(3)  Please issue a certificate or certificates representing said shares of
     Preferred Stock in the name of the undersigned or in such other name as is
     specified below.

--------------------------------------------
(Name)

--------------------------------------------
(Address)

Warrantholder:   COMDISCO, INC.

By:_________________________________________

Title:______________________________________

Date:_______________________________________

                                       12
<PAGE>   13

                          ACKNOWLEDGEMENT OF EXERCISE

     The undersigned ____________________________, hereby acknowledge receipt
of the "Notice of Exercise" from Comdisco, Inc., to purchase ________ shares of
the Preferred Stock of _______________________, pursuant to the terms of the
Warrant Agreement, and further acknowledges that ________ shares remain subject
to purchase under the terms of the Warrant Agreement.

                                        Company:

                                        By:_____________________________________

                                        Title:__________________________________

                                        Date:___________________________________

                                       13
<PAGE>   14

                                   EXHIBIT II

                                 TRANSFER NOTICE

     (To transfer or assign the foregoing Warrant Agreement execute this form
     and supply required information. Do not use this form to purchase shares.)

     FOR VALUE RECEIVED, the foregoing warrant Agreement and all rights
evidenced thereby are hereby transferred and assigned to

________________________________________________________________________________
     (Please Print)

whose address is________________________________________________________________

________________________________________________________________________________

                         Dated__________________________________________________

                         Holder's Signature_____________________________________

                         Holder's Address_______________________________________

________________________________________________________________________________

Signature Guaranteed:___________________________________________________________

     NOTE: The signature to this Transfer Notice must correspond with the name
               as it appears on the face of the Warrant Agreement, without
               alteration or enlargement or any change whatever. Officers of
               corporations and those acting in a fiduciary or other
               representative capacity should file proper evidence of authority
               to assign the foregoing Warrant Agreement.

                                       14

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