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                                                                   Exhibit 10.18

                                                               Customer No. 1385
                             MASTER LEASE AGREEMENT


Lessor:           TRANSAMERICA BUSINESS CREDIT CORPORATION
                  RIVERWAY II
                  WEST OFFICE TOWER
                  WEST HIGGINS
                  ROSEMONT, ILLINOIS  60018


Co-Lessees:
Collectively and  ACUSPHERE, INC.
individually      UNIVERSITY PARK @ MIT
referred to       38 SIDNEY STREET
herein as         CAMBRIDGE, MASSACHUSETTS 02139
"Lessee"

                  ACUSPHERE SECURITIES CORPORATION
                  UNIVERSITY PARK @ MIT
                  38 SIDNEY STREET
                  CAMBRIDGE, MASSACHUSETTS 02139


The lessor pursuant to this Master Lease Agreement ("Agreement") dated as of
February 21, 2001, is Transamerica Business Credit Corporation ("Lessor"). All
equipment, together with all present and future additions, parts, accessories,
attachments, substitutions, repairs, improvements, and replacements thereof or
thereto, which are the subject of a Lease (as defined in the next sentence)
shall be referred to as "Equipment." Simultaneous with the execution and
delivery of this Agreement, the parties are entering into one or more Lease
Schedules (each, a "Schedule") substantially in the form attached hereto as
Exhibit A which refer to and incorporate by reference this Agreement, each of
which constitutes a lease (each, a "Lease") for the Equipment specified therein.
Additional details pertaining to each Lease are specified in the applicable
Schedule. Each Schedule that the parties hereafter enter into shall constitute a
Lease. Lessor has no obligation to enter into any additional leases with, or
extend any future financing to, Lessee.


          1.   LEASE. Subject to and upon all of the terms and conditions of
this Agreement and each Schedule, Lessor hereby agrees to lease to Lessee and
Lessee hereby agrees to lease from Lessor the Equipment for the Term (as defined
in Paragraph 2 below) thereof. The timing and financial scope of Lessor's
obligation to enter into Leases hereunder are limited as set forth in the
Commitment Letter executed by Lessor and Lessee, dated as of December 5, 2000
and attached hereto as EXHIBIT A (the "Commitment Letter").

          2.   TERM. Each Lease shall be effective and the term of each Lease
("Term") shall commence on the commencement date specified in the applicable
Schedule and, unless sooner terminated (as hereinafter provided), shall expire
at the end of the term specified in such Schedule; PROVIDED, HOWEVER, that
obligations due to be performed by Lessee during the Term shall continue until
they have been performed in full. Schedules will only be executed after the
delivery of the Equipment to Lessee or upon completion of deliveries of items of
such Equipment with aggregate cost of not less than $50,000.

          3.   RENT. Lessee shall pay as rent to Lessor, for use of the
Equipment during the Term or Renewal Term (as defined in Paragraph 8), rental
payments equal to the sum of all rental payments including, without limitation,
security deposits, advance rents, and interim rents payable in the amounts and
on the dates specified in the applicable Schedule ("Rent"). If any Rent or other
amount payable by Lessee is not paid within five business days after the day on
which it becomes payable, Lessee will pay on demand, as a late charge, an amount
equal to 5% of such unpaid Rent or other amount but only to the extent permitted
by applicable law. All payments provided for herein shall be payable to Lessor
at its address specified above, or at any other place designated by Lessor.

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          4.   LEASE NOT CANCELABLE; LESSEE'S OBLIGATIONS ABSOLUTE. No Lease may
be canceled or terminated except as expressly provided herein. Lessee's
obligation to pay all Rent when due hereunder shall be absolute and
unconditional and shall not be subject to any delay, reduction, set-off,
defense, counterclaim, or recoupment for any reason whatsoever, including any
failure of the Equipment or any representations by the manufacturer or the
vendor thereof. If the Equipment is unsatisfactory for any reason, Lessee shall
make any claim solely against the manufacturer or the vendor thereof and shall,
nevertheless, pay Lessor all Rent payable hereunder.

          5.   SELECTION AND USE OF EQUIPMENT. Lessee agrees that it shall be
responsible for the selection and use of, and results obtained from, the
Equipment and any other associated equipment or services.

          6.   WARRANTIES. LESSOR WARRANTS TO LESSEE, SO LONG AS NO EVENT OF
DEFAULT OR EVENT WHICH, WITH THE GIVING OF NOTICE, THE PASSAGE OF TIME, OR BOTH,
WOULD CONSTITUTE AN EVENT OF DEFAULT, HAS OCCURRED, LESSOR WILL NOT DISTURB
LESSEE'S QUIET AND PEACEFUL POSSESSION AND UNRESTRICTED USE OF THE EQUIPMENT.
LESSOR MAKES NO OTHER WARRANTY, EXPRESS OR IMPLIED, AS TO ANY MATTER WHATSOEVER,
INCLUDING, WITHOUT LIMITATION, THE DESIGN OR CONDITION OF THE EQUIPMENT OR ITS
MERCHANTABILITY, SUITABILITY, QUALITY, OR FITNESS FOR A PARTICULAR PURPOSE, AND
HEREBY DISCLAIMS ANY SUCH WARRANTY. OTHER THAN THE ABOVE WARRANTY WITH RESPECT
TO QUIET AND PEACEFUL POSSESSION AND UNRESTRICTED USE OF THE EQUIPMENT, LESSEE
SPECIFICALLY WAIVES ALL RIGHTS TO MAKE A CLAIM AGAINST LESSOR FOR BREACH OF ANY
OTHER WARRANTY. LESSEE LEASES THE EQUIPMENT "AS IS." IN NO EVENT SHALL LESSOR
HAVE ANY LIABILITY, NOR SHALL LESSEE HAVE ANY REMEDY AGAINST LESSOR, FOR ANY
LIABILITY, CLAIM, LOSS, DAMAGE, OR EXPENSE CAUSED DIRECTLY OR INDIRECTLY BY THE
EQUIPMENT OR ANY DEFICIENCY OR DEFECT THEREOF OR THE OPERATION, MAINTENANCE, OR
REPAIR THEREOF OR ANY CONSEQUENTIAL DAMAGES AS THAT TERM IS USED IN SECTION
2-719(3) OF THE MODEL UNIFORM COMMERCIAL CODE, AS AMENDED FROM TIME TO TIME
("UCC"). Lessor grants to Lessee, for the sole purpose of prosecuting a claim,
the benefits of any and all warranties made available by the manufacturer or the
vendor of the Equipment to the extent assignable.

          7.   DELIVERY. Lessor hereby appoints Lessee as Lessor's agent for the
sole and limited purpose of accepting delivery of the Equipment from each vendor
thereof. Lessee shall pay any and all delivery and installation charges. Lessor
shall not be liable to Lessee for any delay in, or failure of, delivery of the
Equipment.

          8.   RENEWAL. So long as no Event of Default or event which, with the
giving of notice, the passage of time, or both, would constitute an Event of
Default, shall have occurred and be continuing, or Lessee shall not have
exercised its purchase option under Paragraph 9 hereof, each Lease will
automatically renew for a term of twelve months (the "Renewal Term") on the
terms and conditions of this Agreement or as set forth in the applicable
Schedule; PROVIDED, HOWEVER, that Obligations due to be performed by the Lessee
during the Renewal Term shall continue until they have been performed in full.

          9.   PURCHASE OPTION. So long as no Event of Default or event which,
with the giving of notice, the passage of time, or both, would constitute an
Event of Default, shall have occurred and be continuing, Lessee may, upon
written notice to Lessor received at least sixty days before the expiration of a
Term, purchase all, but not less than all, the Equipment covered by the
applicable Lease on the date specified therefor in the applicable Schedule
("Purchase Date"). The purchase price for such Equipment shall be its Fair
Market Value to be determined as set forth in the applicable Schedule
substantially in the form attached hereto as Exhibit A. So long as no Event of
Default or event which, with the giving of notice, the passage of time, or both,
would constitute an Event of Default shall have occurred and be continuing,
Lessee may, upon written notice to Lessor received at least sixty days prior to
the expiration of the Renewal Term, purchase all, but not less than all, the
Equipment covered by the applicable Schedule by the last date of the Renewal
Term (the "Alternative Purchase Date") at a purchase price equal to its then
Fair Market Value to be determined as set forth in the applicable Schedule. On
the Purchase Date or the Alternative Purchase Date, as the case may be, for any
Equipment, Lessee shall pay to Lessor the purchase price, together with all
sales and other taxes applicable to the transfer of the Equipment and any other
amount payable and arising hereunder, in immediately available funds, whereupon
Lessor

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shall transfer to Lessee, without recourse or warranty of any kind, express or
implied, all of Lessor's right, title, and interest in and to such Equipment on
an "As Is, Where Is" basis.

          10.  OWNERSHIP; INSPECTION; MARKING; FINANCING STATEMENTS. Lessee
shall affix to the Equipment any labels supplied by Lessor indicating ownership
of such Equipment. The Equipment is and shall be the sole property of Lessor.
Lessee shall have no right, title, or interest therein, except as lessee under a
Lease. The Equipment, other than leasehold improvements financed herein, is and
shall at all times be and remain personal property and shall not become a
fixture without Lessor's prior written consent. Other than leasehold
improvements financed herein, Lessee shall use commercially reasonable efforts
obtain and record such instruments and take such steps as may be necessary to
prevent any person from acquiring any rights in the Equipment by reason of the
Equipment being claimed or deemed to be real property. Lessee shall make the
Equipment and its maintenance records available for inspection by Lessor at
reasonable times and upon reasonable notice. Lessee shall execute and deliver to
Lessor for filing any UCC financing statements or similar documents Lessor may
reasonably request.

          11.  EQUIPMENT USE. Lessee agrees that the Equipment will be operated
by competent, qualified personnel in connection with Lessee's business for the
purpose for which the Equipment was designed and in accordance with applicable
operating instructions, laws, and government regulations, and that Lessee shall
use all reasonable precautions to prevent loss or damage to the Equipment from
fire and other hazards. Lessee shall procure and maintain in effect all orders,
licenses, certificates, permits, approvals, and consents required by federal,
state, or local laws or by any governmental body, agency, or authority in
connection with the delivery, installation, use, and operation of the Equipment,
except where the failure to so procure or maintain in effect has not or could
not reasonably be expected to adversely affect Lessor's rights in such
Equipment.

          12.  MAINTENANCE. Lessee, at its sole cost and expense, shall keep the
Equipment in a suitable environment as specified by the manufacturer's
guidelines or the equivalent, shall meet all recertification requirements, and
shall maintain the Equipment in its original condition and working order,
ordinary wear and tear excepted. At the reasonable request of Lessor, Lessee
shall furnish all documentary proof of maintenance.

          13.  ALTERATION; MODIFICATIONS; PARTS. Lessee may alter or modify the
Equipment only with the prior written consent of Lessor. Any alteration shall be
removed and the Equipment restored to its normal, unaltered condition at
Lessee's expense (without damaging the Equipment's originally intended function
or its value) prior to its return to Lessor. Any part installed in connection
with warranty or maintenance service or which cannot be removed in accordance
with the preceding sentence shall be the property of Lessor.

          14.  RETURN OF EQUIPMENT. Except for Equipment that has suffered a
Casualty Loss (as defined in Paragraph 15 below) and is not required to be
repaired pursuant to Paragraph 15 below or Equipment purchased by Lessee
pursuant to Paragraph 9 above, upon the expiration of the Renewal Term of a
Lease, or upon demand by Lessor pursuant to Paragraph 22 below, Lessee shall
contact Lessor for shipping instructions and, at Lessee's own risk, promptly
return the Equipment, freight prepaid, to a location in the continental United
States specified by Lessor. At the time of such return to Lessor, the Equipment
shall (i) be in the operating order, repair, and condition as required by or
specified in the original specifications and warranties of each manufacturer and
vendor thereof, ordinary wear and tear excepted, and (ii) be capable of being
promptly assembled and operated by a third party purchaser or third party lessee
without further repair, replacement, alterations, or improvements Lessee shall
return Equipment in a condition to allow Lessor to sell or market the Equipment
in a commercial manner. Except as otherwise provided under Paragraph 9 hereof,
at least sixty days before the expiration of the Renewal Term, Lessee shall give
Lessor notice of its intent to return the Equipment at the end of such Renewal
Term. During the sixty-day period prior to the end of a Term or the Renewal
Term, Lessor and its prospective purchasers or lessees shall have, upon not less
than two business days' prior notice to Lessee and during normal business hours,
or at any time and without prior notice upon the occurrence and continuance of
an Event of Default, the right of access to the premises on which the Equipment
is located to inspect the Equipment, and Lessee shall cooperate in all other
respects with Lessor's remarketing of the Equipment. The provisions of this
Paragraph 14 are of the essence of the Lease, and upon application to any court
of equity having jurisdiction in the premises, Lessor shall be entitled to a
decree against Lessee requiring specific performance of the covenants of Lessee
set forth in this Paragraph 14. If Lessee fails to return the Equipment when
required, the terms and conditions of the Lease shall

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continue to be applicable and Lessee shall continue to pay Rent until the
Equipment is received by Lessor.

          15.  CASUALTY INSURANCE; LOSS OR DAMAGE. Lessee will maintain, at its
own expense, liability and property damage insurance relating to the Equipment,
other than leasehold improvements financed herein, insuring against such risks
as are customarily insured against on the type of equipment leased hereunder by
businesses in which Lessee is engaged in such amounts, in such form, and with
insurers satisfactory to Lessor; PROVIDED, HOWEVER, that the amount of insurance
against damage or loss shall not be less than the greater of (a) the replacement
value of the Equipment and (b) the stipulated loss value of the Equipment
specified in the applicable Schedule ("Stipulated Loss Value"). Each liability
insurance policy shall provide coverage (including, without limitation, personal
injury coverage) of not less than $1,000,000 for each occurrence, and shall name
Lessor as an additional insured with respect to such Equipment; and each
property damage policy shall name Lessor as sole loss payee with respect to such
Equipment and all policies shall contain a clause requiring the insurer to give
Lessor at least thirty days' prior written notice of any alteration in the terms
or cancellation of the policy. Lessee shall furnish to Lessor a certificate of
insurance, and upon request, a copy of each insurance policy (with endorsements)
or other evidence satisfactory to Lessor that the required insurance coverage is
in effect; PROVIDED, HOWEVER, Lessor shall have no duty to ascertain the
existence of or to examine the insurance policies to advise Lessee if the
insurance coverage does not comply with the requirements of this Paragraph. If
Lessee fails to insure the Equipment as required, other than leasehold
improvements financed herein ,Lessor shall have the right but not the obligation
to obtain such insurance, and the cost of the insurance shall be for the account
of Lessee due as part of the next due Rent. Lessee consents to Lessor's release,
upon its failure to obtain appropriate insurance coverage, of any and all
information necessary to obtain insurance with respect to the Equipment or
Lessor's interest therein.

          After the Equipment is delivered to Lessee and until the Equipment is
returned to and received by Lessor as provided in Paragraph 14 above, Lessee
shall bear the entire risk of theft or destruction of, or damage to, the
Equipment including, without limitation, any condemnation, seizure, or
requisition of title or use ("Casualty Loss"). No Casualty Loss shall relieve
Lessee from its obligations to pay Rent except as provided in clause (b) below.
When any Casualty Loss occurs, Lessee shall immediately notify Lessor and, at
the option of Lessee, as long as no Event of Default has occurred or is
continuing, shall promptly (a) place such Equipment in good repair and working
order; or (b) pay Lessor an amount equal to the Stipulated Loss Value of such
Equipment and all other amounts (excluding Rent) due hereunder, whereupon Lessor
shall transfer to Lessee, without recourse or warranty (express or implied), all
of Lessor's interest, if any, in and to such Equipment on an "AS IS, WHERE IS"
basis. The proceeds of any insurance payable with respect to the Equipment shall
be applied, at the option of Lessor, either towards (i) repair of the Equipment
or (ii) payment of any of Lessee's obligations hereunder. Lessee hereby appoints
Lessor as Lessee's attorney-in-fact to make claim for, receive payment of, and
execute and endorse all documents, checks or drafts issued with respect to any
Casualty Loss under any insurance policy relating to the Equipment, as long as
no Event of Default has occurred or is continuing.

          16.  TAXES. Lessee shall pay when due, and indemnify and hold Lessor
harmless from, all sales, use, excise, and other taxes, charges, and fees
(including, without limitation, income, franchise, business and occupation,
gross receipts, licensing, registration, titling, personal property, stamp and
interest equalization taxes, levies, imposts, duties, charges, or withholdings
of any nature), and any fines, penalties, or interest thereon, imposed or levied
by any governmental body, agency, or tax authority upon or in connection with
the Equipment, its purchase, ownership, delivery, leasing, possession, use, or
relocation of the Equipment or otherwise in connection with the transactions
contemplated by each Lease or the Rent thereunder, excluding taxes on or
measured by the net income of Lessor. Upon request, Lessee will provide proof of
payment. Unless Lessor elects otherwise, Lessee will pay all property taxes on
the Equipment. Lessee shall timely prepare and file all reports and returns
which are required to be made with respect to any obligation of Lessee under
this Paragraph 16. Lessee shall, to the extent permitted by law, cause all
billings of such fees, taxes, levies, imposts, duties, withholdings, and
governmental charges to be made to Lessor in care of Lessee. Upon request,
Lessee will provide Lessor with copies of all such billings.

          17.  LESSOR'S PAYMENT. If Lessee fails to perform its obligations
under Paragraph 15 or 16 above, or Paragraph 23 below, Lessor shall have the
right to substitute performance, in which case Lessee shall immediately
reimburse Lessor therefor.

          18.  GENERAL INDEMNITY. Each Lease is a net lease. Therefore, Lessee
shall indemnify Lessor and its successors and assigns against, and hold Lessor
and its successors and assigns harmless

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from, any and all claims, actions, damages, obligations, liabilities, and all
costs and expenses, including, without limitation, reasonable legal fees
incurred by Lessor or its successors and assigns arising out of each Lease
including, without limitation, the purchase, lease, possession, maintenance,
condition, use, or return of the Equipment, or arising by operation of law,
except that Lessee shall not be liable for any claims, actions, damages,
obligations, and costs and expenses determined by a non-appealable, final order
of a court of competent jurisdiction to have occurred as a result of the gross
negligence or willful misconduct of Lessor or its successors and assigns. Lessee
agrees that upon written notice by Lessor of the assertion of any claim, action,
damage, obligation, liability, or lien, Lessee shall assume full responsibility
for the defense thereof, provided that Lessor's failure to give such notice
shall not limit or otherwise affect its rights hereunder. The provisions of this
Paragraph with regard to matters arising during a Lease shall survive the
expiration or termination of such Lease.

          19.  ASSIGNMENT BY LESSEE. Lessee shall not, without the prior written
consent of Lessor, which consent will not be unreasonably withheld (a) assign,
transfer, pledge, or otherwise dispose of any Lease or Equipment, or any
interest therein; (b) sublease or lend any Equipment or permit it to be used by
anyone other than Lessee and its employees, consultants and contractors; or (c)
move any Equipment from the location specified for it in the applicable
Schedule, except that Lessee may move Equipment to another location within the
United States provided that Lessee has delivered to Lessor (A) prior written
notice thereof and (B) duly executed financing statements and other agreements
and instruments (all in form and substance satisfactory to Lessor) necessary or,
in the opinion of the Lessor, desirable to protect Lessor's interest in such
Equipment. In the event Lessee takes any such action without the prior written
consent of Lessor, which consent shall not be unreasonably withheld, the parties
agree that Lessor may terminate any Lease and all applicable Schedules thereto,
and Lessee shall promptly pay Lessor all amounts then due thereunder, including
prepayment, if any, without further obligation to Lessor thereto.
Notwithstanding anything to the contrary in the immediately preceding sentence,
Lessee may keep any Equipment consisting of motor vehicles or rolling stock at
any location in the United States.

          20.  ASSIGNMENT BY LESSOR. Lessor may assign its interest or grant a
security interest in any Lease and the Equipment individually or together, in
whole or in part. If Lessee is given written notice of any such assignment, it
shall after thirty days of its receipt of such notice make all payments of Rent
and other amounts hereunder directly to such assignee. Each such assignee shall
have all of the rights of Lessor under each Lease assigned to it. Lessee shall
not assert against any such assignee any set-off, defense, or counterclaim that
Lessee may have against Lessor or any other person.

          21.  DEFAULT; NO WAIVER. Lessee or any guarantor of any or all of the
obligations of Lessee hereunder (together with Lessee, the "Lease Parties")
shall be in default under each Lease upon the occurrence of any of the following
events (each, an "Event of Default"): (a) Lessee fails to pay within five
business days of when due any amount required to be paid by Lessee under or in
connection with any Lease; (b) any of the Lease Parties fails to perform any
other material provision under or in connection with a Lease or violates any of
the material covenants or agreements of such Lease Party under or in connection
with a Lease; (c) any representation made or financial information delivered or
furnished by any of the Lease Parties under or in connection with a Lease shall
prove to have been inaccurate in any material respect when made; (d) any of the
Lease Parties makes an assignment for the benefit of creditors, whether
voluntary or involuntary, or consents to the appointment of a trustee or
receiver, or if either shall be appointed for any of the Lease Parties or for a
substantial part of its property without its consent and, in the case of any
such involuntary proceeding, such proceeding remains undismissed or unstayed for
forty-five days following the commencement thereof; (e) any petition or
proceeding is filed by or against any of the Lease Parties under any Federal or
State bankruptcy or insolvency code or similar law and, in the case of any such
involuntary petition or proceeding, such petition or proceeding remains
undismissed or unstayed for forty-five days following the filing or commencement
thereof, or any of the Lease Parties takes any action authorizing any such
petition or proceeding; (f) any of the Lease Parties fails to pay when due any
indebtedness for borrowed money or under conditional sales or installment sales
contracts or similar agreements, leases, or obligations evidenced by bonds,
debentures, notes, or other similar agreements or instruments to any creditor
(including Lessor under any other agreement) after any and all applicable cure
periods therefor shall have elapsed; (g) any judgment shall be rendered against
any of the Lease Parties which shall remain unpaid or unstayed for a period of
sixty days; (h) any of the Lease Parties shall dissolve, liquidate, wind up or
cease its business, sell or otherwise dispose of all or substantially all of its
assets, or make any material change in its lines of business; (i) any of the
Lease Parties shall amend or modify its name, unless such Lease Party delivers
to Lessor, thirty days prior to any such proposed amendment or modification,
written notice of such amendment or modification and within ten days before such

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amendment or modification delivers executed financing statements (in form and
substance satisfactory to the Lessor); (j) any of the Lease Parties shall merge
or consolidate with any other entity or make any material change in its capital
structure, in each case without Lessor's prior written consent, which shall not
be unreasonably withheld; (k) any of the Lease Parties shall suffer any loss or
suspension of any material license, permit, or other right or asset necessary to
the profitable conduct of its business, fail generally to pay its debts as they
mature, or call a meeting for purposes of compromising its debts; (l) any of the
Lease Parties shall deny or disaffirm its obligations hereunder or under any of
the documents delivered in connection herewith; (m) there is a change, which
change results from a single transaction or series of related transactions, but
not from the sale of newly issued securities to investors, in more than 35% of
the ownership of any equity interests of any of the Lease Parties on the date
hereof or more than 35% of such interests become subject to any contractual,
judicial or statutory lien, charge, security interest, or encumbrance; or (n)
any of the Lease Parties suffers a material adverse change in the business,
operations, results of operations, assets, liabilities, or condition (financial
or otherwise).

          22.  REMEDIES. Upon the occurrence and continuation of an Event of
Default, Lessor shall have the right, in its sole discretion, to exercise any
one or more of the following remedies: (a) terminate each Lease; (b) declare any
and all Rent and other amounts then due and any and all Rent and other amounts
to become due under each Lease (collectively, the "Lease Obligations")
immediately due and payable; (c) take possession of any or all items of
Equipment, wherever located, without demand, notice, court order, or other
process of law, and without liability for entry to Lessee's premises, for damage
to Lessee's property, or otherwise; (d) demand that Lessee immediately return
any or all Equipment to Lessor in accordance with Paragraph 14 above, and, for
each day that Lessee shall fail to return any item of Equipment, Lessor may
demand an amount equal to the Rent payable for such Equipment in accordance with
Paragraph 14 above; (e) lease, sell, or otherwise dispose of the Equipment in a
commercially reasonable manner, with or without notice and on public or private
bid; and (f) recover the following amounts from the Lessee (as damages,
including reimbursement of costs and expenses, liquidated for all purposes and
not as a penalty): (i) all costs and expenses of Lessor reimbursable to it
hereunder, including, without limitation, expenses of disposition of the
Equipment, reasonable legal fees, and all other amounts specified in Paragraph
23 below; (ii) an amount equal to the sum of (A) any accrued and unpaid Rent
through the later of (1) the date of the applicable default, (2) the date that
Lessor has obtained possession of the Equipment, or (3) such other date as
Lessee has made an effective tender of possession of the Equipment to Lessor
(the "Default Date") and (B) if Lessor resells or re-lets the Equipment, Rent at
the periodic rate provided for in each Lease for the additional period that it
takes Lessor to resell or re-let all of the Equipment; (iii) the present value
of all future Rent reserved in the Leases and contracted to be paid over the
unexpired Term of the Leases discounted at the rate of interest implicit in the
applicable Schedule interest; (iv) the reversionary value of the Equipment as of
the expiration of the Term of the applicable Lease as set forth on the
applicable Schedule; and (v) any indebtedness for Lessee's indemnity under
Paragraph 18 above, plus a late charge at the rate specified in Paragraph 3
above, less the amount received by Lessor, if any, upon sale or re-let of the
Equipment; and (g) exercise any other right or remedy to recover damages or
enforce the terms of the Leases. Upon the occurrence and continuance of an Event
of Default or an event which with the giving of notice or the passage of time,
or both, would result in an Event of Default, Lessor shall have the right,
whether or not Lessor has made any demand or the obligations of Lessee hereunder
have matured, to appropriate and apply to the payment of the obligations of
Lessee hereunder all security deposits and other deposits (general or special,
time or demand, provisional or final) now or hereafter held by and other
indebtedness or property now or hereafter owing by Lessor to Lessee. Lessor may
pursue any other rights or remedies available at law or in equity, including,
without limitation, rights or remedies seeking damages, specific performance,
and injunctive relief. Any failure of Lessor to require strict performance by
Lessee, or any waiver by Lessor of any provision hereunder or under any
Schedule, shall not be construed as a consent or waiver of any other breach of
the same or of any other provision. Any amendment or waiver of any provision
hereof or under any Schedule or consent to any departure by Lessee herefrom or
therefrom shall be in writing and signed by Lessor.

          No right or remedy is exclusive of any other provided herein or
permitted by law or equity. All such rights and remedies shall be cumulative and
may be enforced concurrently or individually from time to time.

          Upon the occurrence of an Event of Default, Lessor shall use
commercially reasonable efforts to mitigate its damages described above.

          23.  LESSOR'S EXPENSE. Lessee shall pay Lessor on demand all costs and
expenses (including legal fees and expenses) incurred in connection with the
preparation, execution and delivery of this Agreement and other agreement and
transaction contemplated hereby and all costs and expenses in protecting and

<PAGE>

enforcing Lessor's rights and interests in each Lease and the Equipment,
including, without limitation, reasonable legal and collection, reasonable
remarketing fees and expenses incurred by Lessor in enforcing the terms,
conditions, or provisions of each Lease or upon the occurrence and continuation
of an Event of Default. Legal expenses shall not exceed $10,000 without the
prior written consent of Lessee.

          24.  LESSEE'S WAIVERS. To the extent permitted by applicable law,
Lessee hereby waives any and all rights and remedies conferred upon a lessee by
Sections 2A-508 through 2A-522 of the UCC. To the extent permitted by applicable
law, Lessee also hereby waives any rights now or hereafter conferred by statute
or otherwise which may limit or modify any of Lessor's rights or remedies under
Paragraph 22. Any action by Lessee against Lessor for any default by Lessor
under any Lease shall be commenced within one year after Lessee's notice of any
such cause of action.

          25.  NOTICES; ADMINISTRATION. Except as otherwise provided herein, all
notices, approvals, consents, correspondence, or other communications required
or desired to be given hereunder shall be given in writing and shall be
delivered by overnight courier, hand delivery, or certified or registered mail,
postage prepaid, if to Lessor, then to Transamerica Technology Finance Division,
76 Batterson Park Road, Farmington, Connecticut 06032, Attention: Legal
Department, with a copy to Lessor at Riverway II, West Office Tower, 9399 West
Higgins Road, Rosemont, Illinois 60018, Attention: Legal Department, if to
Lessee, then to Acusphere, Inc., University Park @ MIT, 38 Sidney Street,
Cambridge, Massachusetts 02139, Attention: Vice President of Finance and
Administration or such other address as shall be designated by Lessee or Lessor
to the other party. All such notices and correspondence shall be effective when
received.

          26.  REPRESENTATIONS. Lessee represents and warrants to Lessor that
(a) Lessee is duly organized, validly existing, and in good standing under the
laws of the State of its incorporation; (b) the execution, delivery, and
performance by Lessee of this Agreement are within Lessee's powers, have been
duly authorized by all necessary action, and do not and will not contravene (i)
Lessee's organizational documents or (ii) any law, regulation, rule, or
contractual restriction binding on or affecting Lessee; (c) no authorization or
approval or other action by, and no notice to or filing with, any governmental
authority or regulatory body is required for the due execution, delivery, and
performance by Lessee of this Agreement; (d) each Lease constitutes the legal,
valid, and binding obligations of Lessee enforceable against Lessee in
accordance with its terms; (e) the cost of each item of Equipment reflects all
discounts, rebates, and allowances for the Equipment (including, without
limitation, discounts for advertising, prompt payment, testing, or other
services) given to the Lessee by the manufacturer, supplier, or any other
person; and (f) all information supplied by Lessee to Lessor in connection
herewith is, to its knowledge, correct and does not omit any material statement
necessary to insure that the information supplied is not misleading.

          27.  FURTHER ASSURANCES. Lessee, upon the request of Lessor, will
execute, acknowledge, record, or file, as the case may be, such further
documents and do such further acts as may be reasonably necessary, desirable, or
proper to carry out more effectively the purposes of this Agreement. Lessee
hereby appoints Lessor as its attorney-in-fact to execute on behalf of Lessee
and authorizes Lessor to file without Lessee's signature any UCC financing
statements and amendments Lessor deems advisable.

          28.  FINANCIAL STATEMENTS. Lessee shall deliver to Lessor: (a) as soon
as available, but not later than 120 days after the end of each fiscal year of
Lessee and its consolidated subsidiaries, the consolidated balance sheet, income
statement, and statements of cash flows and shareholders equity for Lessee and
its consolidated subsidiaries (the "Financial Statements") for such year,
reported on by independent certified public accountants without an adverse
qualification; and (b) as soon as available, but not later than 60 days after
the end of each of the first three fiscal quarters in any fiscal year of Lessee
and its consolidated subsidiaries, the Financial Statements for such fiscal
quarter, together with a certification duly executed by a responsible officer of
Lessee that such Financial Statements have been prepared in accordance with
generally accepted accounting principles and are fairly stated in all material
respects (subject to normal year-end audit adjustments).

          29.  CONSENT TO JURISDICTION. Lessee irrevocably submits to the
jurisdiction of any Illinois state or federal court sitting in Illinois for any
action or proceeding arising out of or relating to this Agreement or the
transactions contemplated hereby, and Lessee irrevocably agrees that all claims
in respect of any such action or proceeding may be heard and determined in such
Illinois state or federal court.

<PAGE>

          30.  WAIVER OF JURY TRIAL. LESSEE AND LESSOR IRREVOCABLY WAIVE ALL
RIGHT TO TRIAL BY JURY IN ANY ACTION, PROCEEDING, OR COUNTERCLAIM ARISING OUT OF
OR RELATING TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY.

          31.  FINANCE LEASE. Lessee and Lessor agree that each Lease is a
"Finance Lease" as defined by Section 2A-103(g) of the UCC. Lessee acknowledges
that Lessee has reviewed and approved each written Supply Contract (as defined
by UCC 2A-103(y)) covering Equipment purchased from each "Supplier" (as defined
by UCC 2A-103(x)) thereof.

          32.  NO AGENCY. Lessee acknowledges and agrees that neither the
manufacturer or supplier, nor any salesman, representative, or other agent of
the manufacturer or supplier, is an agent of Lessor. No salesman,
representative, or agent of the manufacturer or supplier is authorized to waive
or alter any term or condition of this Agreement or any Schedule and no
representation as to the Equipment or any other matter by the manufacturer or
supplier shall in any way affect Lessee's duty to pay Rent and perform its other
obligations as set forth in this Agreement or any Schedule.

          33.  SPECIAL TAX INDEMNIFICATION. Lessee acknowledges that Lessor, in
determining the Rent due hereunder, has assumed that certain tax benefits as are
provided to an owner of property under the Internal Revenue Code of 1986, as
amended (the "Code"), and under applicable state tax law, including, without
limitation, depreciation deductions under Section 168(b) of the Code, and
deductions under Section 163 of the Code in an amount at least equal to the
amount of interest paid or accrued by Lessor with respect to any indebtedness
incurred by Lessor in financing its purchase of the Equipment, are available to
Lessor as a result of the lease of the Equipment. In the event Lessor is unable
to obtain such tax benefits as a result of an act or omission of Lessee, is
required to include in income any amount other than the Rent, or is required to
recognize income in respect of the Rent earlier than anticipated pursuant to
this Agreement, Lessee shall pay Lessor additional rent ("Additional Rent") in a
lump sum in an amount needed to provide Lessor with the same after-tax yield and
after-tax cash flow as would have been realized by Lessor had Lessor (i) been
able to obtain such tax benefits, (ii) not been required to include any amount
in income other than the Rent, and (iii) not been required to recognize income
in respect of the Rent earlier than anticipated pursuant to this Agreement. The
Additional Rent shall be computed by Lessor, which computation shall be binding
on Lessee. The Additional Rent shall be due immediately upon written notice by
Lessor to Lessee of Lessor's inability to obtain tax benefits, the inclusion of
any amount in income other than the Rent or the recognition of income in respect
of the Rent earlier than anticipated pursuant to this Agreement. The provisions
of this Paragraph 33 shall survive the termination of this Agreement.

          34.  GOVERNING LAW; SEVERABILITY. EACH LEASE SHALL BE GOVERNED BY THE
LAWS OF THE STATE OF ILLINOIS WITHOUT GIVING EFFECT TO THE CONFLICT OF LAW
PRINCIPLES THEREOF. IF ANY PROVISION SHALL BE HELD TO BE INVALID OR
UNENFORCEABLE, THE VALIDITY AND ENFORCEABILITY OF THE REMAINING PROVISIONS SHALL
NOT IN ANY WAY BE AFFECTED OR IMPAIRED.

LESSEE ACKNOWLEDGES THAT LESSEE HAS READ THIS AGREEMENT AND THE SCHEDULE HERETO,
UNDERSTANDS THEM, AND AGREES TO BE BOUND BY THEIR TERMS AND CONDITIONS. FURTHER,
LESSEE AND LESSOR AGREE THAT THIS AGREEMENT, THE SCHEDULES DELIVERED IN
CONNECTION HEREWITH FROM TIME TO TIME, AND THE COMMITMENT LETTER ARE THE
COMPLETE AND EXCLUSIVE STATEMENT OF THE AGREEMENT BETWEEN THE PARTIES,
SUPERSEDING ALL PROPOSALS OR PRIOR AGREEMENTS, ORAL OR WRITTEN, AND ALL OTHER
COMMUNICATIONS BETWEEN THE PARTIES RELATING TO THE SUBJECT MATTER HEREOF. SHOULD
THERE EXIST ANY INCONSISTENCY BETWEEN THE TERMS OF THE COMMITMENT LETTER AND
THIS AGREEMENT, THE TERMS OF THIS AGREEMENT SHALL PREVAIL.

<PAGE>

          IN WITNESS WHEREOF, the parties hereto have executed or caused this
Agreement to be duly executed by their duly authorized officers as of the date
first written above.



                                   ACUSPHERE, INC.



                                   By: /s/ Sherri C. Oberg
                                      ------------------------------------------
                                      Name: Sherri C. Oberg
                                      Title: President and CEO
                                   Federal Tax ID No.:

                                   ACUSPHERE SECURITIES CORPORATION.


                                   By: /s/ Sherri C. Oberg
                                      ------------------------------------------
                                      Name: Sherri C. Oberg
                                      Title: President and CEO
                                   Federal Tax ID No.:

                                   TRANSAMERICA BUSINESS CREDIT CORPORATION


                                   By: /s/ Matthew N. McAlpre
                                      ------------------------------------------
                                      Name: Matthew N. McAlpre
                                      Title: SVP