Document:

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                    Hines-Sumisei U.S. Core Office Fund, L.P.
                       2800 Post Oak Boulevard, Suite 5000
                              Houston, Texas 77056

__________________, 2004

Hines U.S. Core Office Capital LLC
Hines U.S. Core Office Capital Associates II Limited Partnership
Hines REIT Properties, L.P.
2800 Post Oak Boulevard, Suite 5000
Houston, Texas 77056

         Re:      Rights of Hines REIT Properties, L.P.
                  to acquire an interest and invest in Hines-Sumisei
                  U.S. Core Office Fund L.P.

Ladies and Gentlemen:

                  The purpose of this letter agreement is to document the rights
of Hines REIT Properties, L.P. (together with any wholly-owned subsidiary
thereof, the "Public REIT OP"), a Delaware limited partnership, to acquire an
interest in and to participate in future offerings of Hines-Sumisei U.S. Core
Office Fund, L.P. (the "Partnership"), a Delaware limited partnership.
Capitalized terms used and not otherwise defined herein have the meanings given
to them in the Amended and Restated Agreement of Limited Partnership of the
Partnership as such agreement may be amended from time to time (the "Partnership
Agreement").

                  For good and valuable consideration, the receipt and
sufficiency which are hereby acknowledged, the parties hereto agree as follows:

Initial Purchase Right

                  The Public REIT OP shall have the right and obligation (the
"Initial Investment Right") to acquire a portion of the Capital Interest (as
defined below) in the Partnership held by Hines U.S. Core Office Capital
Associates II Limited Partnership (the "Hines Limited Partner") up to a maximum
amount of $35 million in interest (the "Interest"). To the extent the Public
REIT OP receives net proceeds from the public offering of common shares
contemplated by Hines Real Estate Investment Trust, Inc. (the "Public REIT") or
contributed to the Public REIT OP by Hines Real Estate Holdings Limited
Partnership ("Net Proceeds"), the Public REIT OP shall use all such Net Proceeds
to acquire all or a portion of the Interest. As used herein, the term "Capital
Interest" of the Hines Limited Partner in the Partnership means all right, title
and interest of the Hines Limited Partner in and to the Partnership Units held
by it. The Public REIT OP's right and obligation to acquire the Interest shall
terminate on December 31, 2004. The Hines Limited Partner shall not divest
itself of any portion of its Capital Interest in the Partnership prior to the
Termination Date without the prior consent of the Public REIT OP, except to the
extent such Capital Interest exceeds $35 million in interest plus an amount
necessary to satisfy the Hines Capital Requirement.

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                  The Public REIT OP will deliver all Net Proceeds it receives,
until the Public REIT OP has acquired the entire Interest. The sale of any
portion of the Interest shall be conditioned upon (i) the Public REIT OP
receiving Net Proceeds and (ii) the satisfaction of the conditions to the
transfer of a Partnership Interest set forth in Section 10.5 of the Partnership
Agreement and the execution and delivery of an Investor Questionnaire and
Subscription Agreement by the Public REIT OP to the Partnership in form and
substance reasonably satisfactory to the General Partner.

                  Upon the delivery of any Net Proceeds to the Hines Limited
Partner as contemplated above, the following shall take place:

                  1.  The Public REIT OP shall deliver the applicable Net
                      Proceeds to the Hines Limited Partner by wire transfer of
                      immediately available funds to an account designated by
                      the Hines Limited Partner;

                  2.  The Units associated with the portion of the Interest
                      being acquired by the Public REIT OP (determined by
                      dividing the applicable Net Proceeds delivered by the
                      original per Unit issue price paid for the Units) shall be
                      transferred on the books of the Partnership to the Public
                      REIT OP;

                  3.  The Public REIT OP shall be admitted to the Partnership as
                      a Non-Managing General Partner as contemplated by Section
                      5.11 of the Partnership Agreement and the applicable Units
                      shall automatically be deemed to be non-managing general
                      partner interests in the Partnership; and

                  4.  The General Partner shall amend the Partnership Agreement
                      to the extent necessary to give effect to the foregoing in
                      accordance with the terms of the Partnership Agreement, it
                      being understood that the Public REIT OP will only hold a
                      general partner interest in the Partnership, unless the
                      Public REIT OP agrees to acquire another interest in the
                      Partnership.

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Pre-Emptive Right

                  Following the Initial Offering Period, for so long as the
Public REIT OP is a partner in the Partnership, the Partnership shall give the
Public REIT OP written notice (an "Offer Notice") of any proposed offering of
Units for cash at least 90 days prior to the anticipated closing date of such
offering, which notice shall specify the total number of Units being offered and
the price per Unit at which the Partnership is offering Units in such offering.
The Public REIT OP shall have the right (a "Preemptive Right") to acquire up to
20% of the Units sold by the Partnership in any such offering provided that the
Public REIT OP's investment in the Partnership may be for non-managing general
partner interests, if the Public REIT OP so chooses, rather than the Units
offered by the Partnership. In order to exercise its Pre-Emptive Right, the
Public REIT OP must deliver a written notice (an "Exercise Notice") within 30
days after delivery of notice of such offering to the Partnership and the
General Partner, which Exercise Notice must specify the total number of Units
(or equivalent interest) the Public REIT OP wishes to acquire, up to 20% of the
total number of Units (or equivalent interest) issued in such offering. If the
Public REIT OP delivers an Exercise Notice within such 30 day period, then the
Public REIT OP will be obligated to buy, and the Partnership shall be obligated
to sell to the Public REIT OP, that number of Units (or equivalent interest)
specified in the Exercise Notice, up to 20% of the total number of Units (or
equivalent interest) issued in such offering; provided that the Holding
Partnership shall have no obligation to sell any Units to the Public REIT OP if
such offering is cancelled.

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Miscellaneous

                  This letter agreement shall be governed by the laws of the
State of New York. This letter agreement may be signed in multiple counterparts,
which, taken together, shall constitute one and the same agreement.

                  This letter agreement, and all rights and obligations arising
hereunder (including the Initial Investment Right and the Preemptive Right),
shall terminate immediately in the event that the Public REIT is no longer
advised by Hines Advisors Limited Partnership, or another affiliate of Hines
Interests Limited Partnership.

                  Please indicate your agreement with the foregoing by signing
below.

                           Very Truly Yours,

                           HINES-SUMISEI U.S. CORE OFFICE FUND, L.P.

                                    By:  Hines US Core Office Capital LLC

                                      By:  Hines Interests Limited Partnership

                                         By:  Hines Holdings, Inc.

                                         By:
                                             ---------------------------------
                                             Name:
                                             Title:

AGREED:

HINES US CORE OFFICE CAPITAL LLC

   By:  Hines US Core Office Capital LLC

     By:  Hines Interests Limited Partnership

       By:  Hines Holdings, Inc.

       By:
           -----------------------------------
           Name:
           Title:

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Hines US CORE OFFICE CAPITAL ASSOCIATES II LIMITED PARTNERSHIP

   By:  Hines US Core Office Capital LLC

     By:  Hines Interests Limited Partnership

       By:  Hines Holdings, Inc.

        By:
           ---------------------------------------------------
            Name:
            Title:

HINES REIT PROPERTIES, L.P.

   By:  Hines Real Estate Investment Trust, Inc.

        By:
           ---------------------------------------------------
            Name:
            Title:<PAGE>

                                                                    EXHIBIT 10.1

                            STOCK PURCHASE AGREEMENT

         This Stock Purchase Agreement, dated as of April 7, 2004, is made and
entered into by and between Aspect Medical Systems, Inc., a Delaware corporation
(the "Company"), and Boston Scientific Corporation, a Delaware corporation (the
"Purchaser"). The Company and the Purchaser are collectively referred to as the
"Parties."

         WHEREAS, the Company desires to issue and sell, and the Purchaser
desires to purchase, shares of the Company's common stock, $0.01 par value per
share (the "Common Stock"); and

         WHEREAS, in connection with the execution and delivery of this
Agreement, the Company and the Purchaser will amend the Registration Rights
Agreement, dated as of August 7, 2002, by and between the Company and the
Purchaser as provided for in Section 9.13 hereof, pursuant to which the Company
will grant certain rights pertaining to the shares of Common Stock to be
purchased by the Purchaser pursuant to this Agreement.

         NOW THEREFORE, in consideration of the representations, warranties and
covenants herein contained, and other good and valuable consideration, the
receipt and adequacy of which is hereby acknowledged, the Company and the
Purchaser agree as follows:

         1.       Sale of Shares. Subject to the terms and conditions of this
Agreement, at the Closing (as defined in Section 2 hereof) the Purchaser agrees
to purchase, and the Company agrees to sell and issue to the Purchaser, 500,000
shares of Common Stock (the "Shares") at a purchase price per share as
calculated in the manner set forth in Section 2.2 hereof.

         2.       The Closing.

                  2.1      Closing. The closing (the "Closing") of the sale and
purchase of the Shares under this Agreement will take place at the offices of
Hale and Dorr LLP, 60 State Street, Boston, Massachusetts at 10:00 a.m. on May
27, 2004, or at such other time, date and place as are mutually agreeable to the
Company and the Purchaser. The date of the Closing is hereinafter referred to as
the "Closing Date."

                  2.2      Delivery of Shares; Payment of Purchase Price. At the
Closing, the Company will deliver to the Purchaser a certificate registered in
the name of the Purchaser representing the Shares against payment therefor by
the Purchaser to the Company by wire transfer of an amount equal to the number
of Shares being purchased under this Agreement multiplied by the "Market Value"
of the Common Stock. The "Market Value" of the Common Stock means the average of
the last reported sales price (at the 4:00 p.m., eastern time, end of regular
trading hours) of the Common Stock on The Nasdaq National Market for the thirty
(30) consecutive trading days ending on the third trading day prior to the
Closing Date.

                  2.3      Use of Proceeds. The Company agrees to use the
proceeds from the sale of the Shares for working capital and other general
corporate purposes.

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         3.       Representations of the Company. The Company represents and
warrants to the Purchaser that the statements contained in this Section 3 are
true and correct, except as set forth in the disclosure schedule provided by the
Company to the Purchaser on the date hereof (the "Disclosure Schedule"). The
Disclosure Schedule shall be arranged in paragraphs corresponding to the
numbered and lettered sections contained in this Section 3, and the disclosures
in any section or subsection of the Disclosure Schedule shall qualify the
corresponding section or subsection of this Section 3 and other sections and
subsections in this Section 3 only to the extent it is clear (by cross-reference
or otherwise) from a reading of the disclosure that such disclosure is
applicable to such other sections and subsections. For purposes of this
Agreement, the phrase "to the knowledge of the Company" or any phrase of similar
import shall mean and be limited to the actual knowledge of the officers
identified below, such other information that such officers should have known of
in the exercise of reasonable diligence in the performance of their duties, as
well as such other information that has come to the attention of the officers
identified below sufficient to put such officers on notice of, or cause such
officers to make further inquiry into, the existence or absence of any material
information or fact bearing on the matter: J. Neal Armstrong, Nassib G. Chamoun
and J. Breckenridge Eagle and (i) in Section 3.8 (Intellectual Property) such
officers shall also include Philip Devlin and (ii) in Section 3.9 (FDA and
Regulatory Matters) such officers shall also include Paul Manberg.

                  3.1      Organization, Qualification and Corporate Power. The
Company is duly organized, validly existing and in good standing under the laws
of the State of Delaware. The Company is duly qualified to conduct the business
it is currently engaged in and is in corporate and tax good standing under the
laws of each jurisdiction in which the nature of its businesses or the ownership
or leasing of its properties requires such qualification, except where the
failure to be so qualified or in good standing is not reasonably likely to have
a Company Material Adverse Effect (as defined below). The Company has all
requisite corporate power and authority to (i) enter into and to perform its
obligations under this Agreement in accordance with its terms and (ii) carry on
its business as currently conducted and to own and use the properties owned and
used by it. As used in this Agreement, "Company Material Adverse Effect" means a
material adverse effect on or a material adverse change in, or group of such
effects on or changes in, the assets, liabilities, business, condition
(financial or otherwise), or results of operations of the Company and its
Subsidiaries, taken as a whole.

                  3.2      Capitalization. The authorized capital stock of the
Company consists of (a) 60,000,000 shares of Common Stock, of which 19,678,252
shares were issued and outstanding as of April 2, 2004, and (b) 5,000,000 shares
of Preferred Stock, $0.01 par value per share (the "Preferred Stock"), of which
no shares are issued or outstanding as of the date hereof. All of the issued and
outstanding shares of Common Stock are duly authorized, validly issued, fully
paid, nonassessable and free of all preemptive rights and were issued in
compliance with all applicable state and federal securities laws. Options to
purchase an aggregate of 5,103,781 shares of Common Stock were outstanding as of
April 2, 2004. Except as set forth in this Section 3.2, there are no outstanding
options, warrants, instruments (including convertible debt instruments), rights
(including conversion or preemptive rights and rights of first refusal), proxy
or stockholder agreements, or other agreements or instruments of any kind to
which the Company or any of its Subsidiaries is a party or by which the Company
or any of its Subsidiaries is bound for the purchase or acquisition from the
Company of any of its Securities. Except as contemplated by this Agreement, the
Company is not a party or subject to any agreement or

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understanding with any Person (as defined below) which affects or relates to the
voting or giving of written consents with respect to any Security. As used in
this Agreement, the term "Person" means any natural person, corporation, limited
liability company, general or limited partnership, limited liability
partnership, joint venture, joint stock company, trust, unincorporated
organization, association, sole proprietorship, governmental body, or agency or
political subdivision of any government.

                  3.3      Issuance of Shares.

                           (a)      Subject to the approval of the Company's
stockholders of the issuance and sale of the Shares by the Company to the
Purchaser in accordance with the Marketplace Rules of The Nasdaq Stock Market,
the offer, issuance, sale and delivery of the Shares in accordance with this
Agreement have been duly authorized by all necessary corporate action on the
part of the Company. The Shares, when issued, sold and delivered against payment
therefor in accordance with the provisions of this Agreement, will be duly and
validly issued, fully paid and nonassessable, and will be free of any lien or
encumbrance; provided, however, that the Shares may be subject to restrictions
on transfer under state or federal securities laws as set forth herein or as
otherwise required by such laws at the time a transfer is proposed. The sale of
the Shares is not, and the issuance of the Shares will not be, subject to any
preemptive right or right of first refusal that has not been properly waived or
complied with.

                           (b)      Assuming the correctness of the
representations and warranties made by the Purchaser in Section 4, no change in
applicable law and no unlawful distribution of the Shares by the Purchaser or
any other Person, the offer, issuance and sale of the Shares will comply with
applicable exemptions from (A) the registration and prospectus delivery
requirements of the Securities Act of 1933, as amended (the "Securities Act"),
and (B) the registration and qualification requirements of all applicable
securities laws of the states of the United States. Neither the Company nor any
authorized agent acting on its behalf will take any action hereafter that would
cause the loss of such exemptions.

                  3.4      Validity and Noncontravention. This Agreement has
been duly and validly executed and delivered by the Company and constitutes
valid and binding obligations of the Company, enforceable against the Company in
accordance with its terms, except as such enforceability may be limited by
bankruptcy, insolvency, moratorium or other similar laws affecting or relating
to creditors' rights generally, and general principles of equity. Subject to
compliance with the applicable filing and other requirements of the Securities
Act and any applicable state securities laws, and the Securities Exchange Act of
1934, as amended (the "Exchange Act"), neither the execution and delivery by the
Company of this Agreement, nor the consummation by the Company of the
transactions contemplated hereby, will (a) conflict with or violate any
provision of the Restated Certificate of Incorporation or the Amended and
Restated By-Laws of the Company, (b) require on the part of the Company or any
of its Subsidiaries any filing with, or permit, authorization, consent or
approval of, any court, arbitrational tribunal, administrative agency or
commission or other governmental or regulatory authority or agency (a
"Governmental Entity"), except for the applicable notification requirements
under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the
"Hart-Scott-Rodino Act"), (c) conflict with, result in breach of, constitute
(with or without due notice or lapse of time or both) a default under, result in
the forfeiture of any rights under, result in the acceleration of

                                      -3-
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obligations under, create in any party any right to terminate, modify or cancel,
or require any notice, consent or waiver under, any contract or instrument to
which the Company or any of its Subsidiaries is a party or by which it or any of
its Subsidiaries is bound or to which any of its or their assets are subject,
(d) violate any order, writ, injunction, decree, statute, rule or regulation
applicable to the Company or any of its Subsidiaries or any of its or their
properties or assets, or (e) result in the creation of any mortgage, pledge,
lien, charge or encumbrance upon any of the properties or assets of the Company
or any of its Subsidiaries, or the suspension, revocation, impairment,
forfeiture or non-renewal of any Permits (as defined in Section 3.10 below).

                  3.5      Reports and Financial Statements. The Company has
previously furnished or made available to the Purchaser complete and accurate
copies, as amended or supplemented, of all reports and other documents filed by
the Company with the Securities and Exchange Commission (the "SEC") pursuant to
the Exchange Act (collectively, the "Company SEC Filings"). The Company SEC
Filings constitute all of the documents required to be filed by the Company
under the Exchange Act with the SEC through the date of this Agreement. All
contracts and other documents required to be filed by the Company with the SEC
as exhibits to the Company SEC Filings have been filed. The Company SEC Filings
complied as to form in all material respects with the requirements of the
Exchange Act and the rules and regulations thereunder when filed. As of their
respective dates, the Company SEC Filings did not contain any untrue statement
of a material fact or omit to state a material fact required to be stated
therein or necessary to make the statements therein, in light of the
circumstances under which they were made, not misleading. The audited financial
statements and unaudited interim financial statements of the Company included in
the Company SEC Filings (a) complied as to form in all material respects with
applicable accounting requirements and the published rules and regulations of
the SEC with respect thereto when filed, (b) were prepared in accordance with
United States generally accepted accounting principles applied on a consistent
basis throughout the periods covered thereby (except as may be indicated therein
or in the notes thereto, and in the case of quarterly financial statements, as
permitted by Form 10-Q under the Exchange Act), (c) fairly present, in all
material respects, the consolidated financial condition, results of operations
and cash flows of the Company as of the respective dates thereof and for the
periods referred to therein, and (d) are consistent with the books and records
of the Company. Except as set forth on Section 3.5 of the Disclosure Schedule
and except for Indebtedness reflected in the financial statements in the Company
SEC Filings and Indebtedness contemplated to be incurred under the Revolving
Credit Facility, dated as of May 16, 2001, as amended, by and between the
Company and Fleet National Bank, the Company has no Indebtedness for borrowed
money outstanding at the date hereof. The Company is not in default with respect
to any outstanding Indebtedness or any instrument or agreement relating thereto,
nor is there any event which, with the passage of time or giving of notice, or
both, would result in a default, and no such Indebtedness or any instrument or
agreement relating thereto purports to limit the issuance of any Securities by
the Company or the operation of the business of the Company. Complete and
correct copies of all instruments (including all amendments, supplements and
consents) relating to the Indebtedness of the Company for borrowed money have
been furnished to the Purchaser.

                  3.6      Reporting Requirements. The Company has registered
its Common Stock pursuant to Section 12(g) of the Exchange Act and is in full
compliance with all reporting requirements of the Exchange Act. The Common Stock
is currently quoted for trading on The Nasdaq National Market, and there are no
proceedings to revoke or suspend such listing.

                                      -4-
<PAGE>

                  3.7      Litigation. Except as disclosed in the Company SEC
Filings, there is no Legal Proceeding (as defined below) which (a) is pending or
has been, to the knowledge of the Company, threatened against the Company or any
Subsidiary of the Company or (b) to the knowledge of the Company, is pending or
has been threatened against any of the officers or directors of the Company or
any Subsidiary of the Company and which, in the case of clauses (a) and (b), (i)
is reasonably likely to have a Company Material Adverse Effect or (ii) in any
manner challenges or seeks to prevent, enjoin, alter or delay the transactions
contemplated by this Agreement. The foregoing representation includes, without
limitation, Legal Proceedings pending or, to the knowledge of the Company,
threatened involving the prior employment of any of the Company's employees,
their use in connection with the Company's business of any information or
techniques allegedly proprietary to any of their former employers, or their
obligations under any agreements with prior employers. There is no Legal
Proceeding filed by the Company currently pending or that the Company intends as
of the date hereof to initiate. As used in this Agreement, the term "Legal
Proceeding" means any action, suit, proceeding, claim, arbitration or
investigation before any Governmental Entity or before any arbitrator.

                  3.8      Intellectual Property.

                           (a)      To the knowledge of the Company, the
operation of the business of the Company as currently conducted or as currently
proposed by the Company to be conducted does not interfere with, conflict with,
infringe upon, misappropriate or otherwise violate the Intellectual Property
rights of any third party, and no action or claim is pending or, to the
knowledge of the Company, threatened alleging that the operation of such
business interferes with, conflicts with, infringes upon, misappropriates or
otherwise violates the Intellectual Property rights of any third party. The
Company has no knowledge that the Company Owned Intellectual Property and any
Intellectual Property licensed to the Company under the Company Licensed
Intellectual Property, are invalid or unenforceable, and, to the Company's
knowledge, the same have not been adjudged invalid or unenforceable in whole or
in part.

                           (b)      To the knowledge of the Company, the Company
is the owner of the right, title and interest in and to, or has a valid license
or other legal right under, the Company Owned Intellectual Property and the
Company Licensed Intellectual Property used in or necessary to the operation of
its business as currently conducted or as currently proposed by the Company to
be conducted, subject to the terms of the license agreements governing the
Company Licensed Intellectual Property. No Legal Proceedings have been filed,
are pending or, to the knowledge of the Company, threatened against the Company
(i) based upon or challenging or seeking to deny or restrict the ownership by
the Company of any of the Company Owned Intellectual Property or, to the
knowledge of the Company, the license rights of the Company to any Company
Licensed Intellectual Property, (ii) alleging that any services provided by,
processes used by, or products manufactured or sold by the Company infringe or
misappropriate any Intellectual Property right of any third party, or (iii)
alleging that the Company Licensed Intellectual Property is being licensed or
sublicensed in conflict with the terms of any license or other agreement.

                                      -5-
<PAGE>

                  3.9      FDA and Regulatory Matters.

                           (a)      (i) With respect to the products of the
Company that are currently marketed or sold by the Company (collectively, the
"Company Products"), (A) the Company has obtained all necessary approvals,
clearances, authorizations, licenses and registrations required by the United
States Federal government or its agencies and all material approvals,
clearances, authorizations, licenses and registrations required by foreign
governments or government agencies, to permit the design, development,
pre-clinical and clinical testing, manufacture, labeling, sale, distribution and
promotion of the Company Products in jurisdictions where the Company currently
conducts such activities or contemplates conducting such activities (the
"Activities to Date") with respect to each Company Product (collectively, the
"Company Licenses"); (B) the Company is in material compliance with all terms
and conditions of each Company License and with all applicable laws pertaining
to the Activities to Date with respect to each Company Product which is not
required to be the subject of a Company License; (C) the Company is in material
compliance with all applicable laws regarding registration, license,
certification for each site at which a Company Product is manufactured, labeled,
sold or distributed; and (D) to the extent any Company Product has been exported
from the United States, the Company has exported such Company Product in
compliance in all material respects with applicable laws; (ii) all manufacturing
operations performed by the Company have been and are being conducted in all
material respects in compliance with the Quality Systems regulations of the U.S.
Food and Drug Administration (the "FDA") (21 CFR Part 820) and, to the extent
applicable to the Company, counterpart regulations in the European Union and all
other countries where compliance is required; (iii) all non-clinical laboratory
studies of Company Products under development, sponsored by the Company and
intended to be used to support regulatory clearance or approval, have been and
are being conducted in material compliance with the FDA's good Laboratory
Practice for Non-Clinical Studies regulations (21 CFR Part 58) in the United
States and, to the extent applicable to the Company, counterpart regulations in
the European Union and all other countries; and (iv) the Company is in material
compliance with all applicable reporting requirements for all Company Licenses
or plant registrations described in clause (i) above, including, but not limited
to, applicable adverse event reporting requirements in the United States and
outside of the United States under applicable laws. The Company has not received
any written notice or other written communication from the FDA or any other
Governmental Entity (x) contesting the pre-market clearance or approval of, the
uses of or the labeling and promotion of any of the Company Products or (y)
otherwise alleging any violation of any laws by the Company. There have been no
recalls, field notifications or seizures ordered or adverse regulatory actions
taken (or to the knowledge of the Company threatened) by the FDA or any other
Governmental Entity with respect to any of the Company Products.

                           (b)      All of the Company's filings with and
submissions to the FDA and any corollary entity in any other jurisdiction with
regard to the Company Products were true, accurate and complete, in all material
respects, as of the date made, and did not materially misstate any of the
statements or information included therein, or omit to state a material fact
necessary to make the statements therein not misleading. To the extent required
by applicable law, the Company has updated all filings and submissions to the
FDA and any corollary entity in any other jurisdiction with regard to the
Company Products.

                                      -6-
<PAGE>

                  3.10     Compliance with Laws; Permits. The Company is not in
violation of any applicable statute, rule, regulation, order, judgment, decree,
writ or restriction of any Governmental Entity in respect of the conduct of its
business or the ownership of its properties (including without limitation
environmental and occupational health and safety laws), which violation has had
or could reasonably be expected to have a Company Material Adverse Effect. The
Company has all material franchises, permits, licenses and any similar authority
necessary for the conduct of its business as now being conducted by it (the
"Permits"), the lack of which has had or could reasonably be expected to have a
Company Material Adverse Effect. As of the date hereof, no suspension or
cancellation of any of the Permits is pending or, to the knowledge of the
Company, threatened.

                  3.11     Registration or First Offer Rights. Except as
provided in or contemplated by this Agreement, the Registration Rights
Agreement, dated as of August 7, 2002, by and between the Company and the
Purchaser and the Fourth Amended and Restated Registration Rights Agreement
dated as of December 17, 1998 by and among the Company and the parties named on
the signature pages thereto, the Company has not granted or agreed to grant any
registration rights, including piggyback rights, or any right of first offer or
other pre-emptive rights to any Person.

                  3.12     Contracts. Except for this Agreement, since January
1, 2004, neither the Company nor any Subsidiary of the Company has entered into
any contract or other agreement which would be required to be filed by the
Company with the SEC pursuant to Item 601(b)(10) of Regulation S-K of the SEC.

                  3.13     Material Adverse Changes. Since March 12, 2004, there
has been no material adverse effect on or material adverse change in, or group
of such effects on or changes in, the assets, liabilities, business, condition
(financial or otherwise) or results of operations of the Company and its
Subsidiaries, taken as a whole.

                  3.14     Certain Relationships and Related Transactions. Since
April 17, 2003 (the date on which the Company filed with the SEC the proxy
statement for its 2003 Annual Meeting of Stockholders), neither the Company nor
any of its Subsidiaries has entered into any new relationship or transaction
with any director, director nominee or executive officer of the Company (or any
member of the immediate family of any of the foregoing) or, to the knowledge of
the Company, any security holder (other than the Purchaser) of the Company who
is known to the Company to own of record or beneficially more than 5% of the
Common Stock (or any member of the immediate family of such Person), which
relationship or transaction would be required to be disclosed by the Company
pursuant to Item 404 of Regulation S-K of the SEC.

                  3.15     Brokers. No broker, finder or investment banker is
entitled to any brokerage, finder's or other fee or commission in connection
with the transactions contemplated by this Agreement. The Company will indemnify
and hold the Purchaser harmless from and against any and all claims, liabilities
or obligations with respect to brokerage or finders' fees or commissions, or
consulting fees in connection with the transactions contemplated by this
Agreement asserted by any Person on the basis of any agreement, arrangement,
statement or representation alleged to have been made by the Company.

                                      -7-
<PAGE>

                  3.16     Taxes. Each of the Company and its Subsidiaries has
duly and timely filed all tax returns required to have been filed by it on or
prior to the date hereof and has duly paid or made provisions for the payment of
all taxes which have been incurred or are due or claimed to be due from it by
any taxing authority on or prior to the date of this Agreement other than (a)
taxes which are not yet delinquent or are being contested in good faith and have
not been finally determined, or (b) tax returns or taxes as to which the failure
to file, pay or make provision for will not, individually or in the aggregate,
have a Company Material Adverse Effect. There is no material liability
outstanding for or relating to any taxes, and there are no material liens for
taxes (other than current taxes not yet due and payable) on any of the Company
Owned Intellectual Property or Company Licensed Intellectual Property.

                  3.17     Environmental. To the knowledge of the Company, the
Company does not have any material liability relating to or arising out of any
judgment, decree or order relating to the environment or occupational health and
safety.

         4.       Representations of the Purchaser. The Purchaser represents and
warrants to the Company as follows:

                  4.1      Investment. The Purchaser is acquiring the Shares for
its own account for investment and not with a view to, or for sale in connection
with, any distribution thereof, nor with any present intention of distributing
or selling the same. The Purchaser is an "accredited investor" as defined in
Rule 501(a) under the Securities Act. The Purchaser has no present agreement,
undertaking, arrangement, obligation or commitment providing for the disposition
of the Shares, and has not been organized, reorganized or recapitalized
specifically for the purpose of investing in the Shares. The Purchaser
understands that the Shares may not be assigned, sold, pledged, transferred or
otherwise disposed of unless registered under the Securities Act and applicable
state securities laws, or an opinion is given by counsel reasonably satisfactory
to the Company that such registration is not required; provided that no such
opinion shall be required for any transfer of Shares that is exempt from such
registration under Rule 144(k) under the Securities Act. The Purchaser
understands that the Company may affix a legend to any certificates representing
the Shares to the foregoing effect. As of the date hereof, the Purchaser
"beneficially owns" (as defined under the Exchange Act) 3,855,708 shares of the
Common Stock.

                  4.2      Incorporation, Authority, Validity and
Noncontravention. The Purchaser is duly organized, validly existing and in good
standing under the laws of the State of Delaware. The Purchaser has all
requisite corporate power and authority to enter into and to perform its
obligations under this Agreement in accordance with its terms. This Agreement
has been duly and validly executed and delivered by the Purchaser and
constitutes valid and binding obligations of the Purchaser, enforceable against
the Purchaser in accordance with its terms, except as such enforceability may be
limited by bankruptcy, insolvency, moratorium or other similar laws affecting or
relating to creditors' rights generally, and general principles of equity.
Subject to compliance with the applicable filing and other requirements of the
Securities Act, the Exchange Act and any applicable state securities laws,
neither the execution and delivery by the Purchaser of this Agreement, nor the
consummation by the Purchaser of the transactions contemplated hereby, will (a)
conflict with or violate any provision of the Second Restated Certificate of
Incorporation, as amended, or the Restated By-laws of the Purchaser, (b) require

                                      -8-
<PAGE>

on the part of the Purchaser any filing with, or permit, authorization, consent
or approval of, any Governmental Entity (other than filings required under the
Exchange Act and the applicable notification requirements under the
Hart-Scott-Rodino Act), (c) conflict with, result in breach of, constitute (with
or without due notice or lapse of time or both) a default under, result in the
acceleration of obligations under, create in any party any right to terminate,
modify or cancel, or require any notice, consent or waiver under, any contract
or instrument to which the Purchaser is a party or by which it is bound or to
which any of its assets are subject, or (d) violate any order, writ, injunction,
decree, statute, rule or regulation applicable to the Purchaser or any of its
Subsidiaries or any of its or their properties or assets.

                  4.3      Experience. The Purchaser has carefully reviewed the
representations concerning the Company contained in this Agreement, and has made
detailed inquiry concerning the Company, its business and its personnel; the
officers of the Company have made available to the Purchaser any and all written
information which it has requested and have answered to such Purchaser's
satisfaction all inquiries made by the Purchaser; and the Purchaser has
sufficient knowledge and experience in finance and business that it is capable
of evaluating the risks and merits of its investment in the Company and the
Purchaser is able financially to bear the risks thereof. Nothing in this Section
4.3 shall be deemed to limit or modify the Purchaser's right to rely on the
representations and warranties made herein.

                  4.4      Shares Not Registered. The Purchaser understands that
the Shares have not been registered under the Securities Act, by reason of their
issuance by the Company in a transaction exempt from the registration
requirements of the Securities Act, and that the Shares must continue to be held
by the Purchaser unless a subsequent disposition thereof is registered under the
Securities Act or is exempt from such registration. The Purchaser understands
that the exemptions from registration afforded by Rule 144 (the provisions of
which are known to it) promulgated under the Securities Act depend on the
satisfaction of various conditions, and that, if applicable, Rule 144 may afford
the basis for sales only in limited amounts.

                  4.5      Brokers. The Purchaser (a) has not retained a finder
or broker in connection with the transactions contemplated by this Agreement,
and (b) will indemnify and hold the Company harmless from and against any and
all claims, liabilities or obligations with respect to brokerage or finders'
fees or commissions, or consulting fees in connection with the transactions
contemplated by this Agreement asserted by any Person on the basis of any
agreement, arrangement, statement or representation alleged to have been made by
the Purchaser.

         5.       Conditions to the Obligations of the Company and the
Purchaser. The respective obligations of the Company and the Purchaser to
consummate the transactions contemplated by this Agreement at the Closing are
subject to the satisfaction of the following conditions:

                  5.1      Stockholder Approval. The sale of the Shares by the
Company to the Purchaser as contemplated by this Agreement shall have received
the approval of a majority of the votes present in person or represented by
proxy at the Company's 2004 Annual Meeting of Stockholders.

                                      -9-
<PAGE>

                  5.2      Hart-Scott-Rodino Act. All applicable waiting periods
(and any extensions thereof) under the Hart-Scott-Rodino Act shall have expired
or otherwise been terminated.

                  5.3      No Governmental Proceedings. No proceeding
challenging this Agreement or the transactions contemplated hereby, or seeking
to prohibit, alter, prevent or materially delay the Closing, shall have been
instituted before any Governmental Entity and shall be pending.

         6.       Conditions to the Obligations of the Purchaser. The obligation
of the Purchaser to purchase the Shares at the Closing is subject to the
fulfillment, or the waiver by the Purchaser, of each of the following conditions
on or before the Closing:

                  6.1      Accuracy of Representations and Warranties. Each
representation and warranty contained in Section 3 shall be true and correct on
and as of the Closing Date with the same effect as though such representation
and warranty had been made on and as of that date.

                  6.2      Performance. The Company shall have performed and
complied in all material respects with all agreements and conditions contained
in this Agreement required to be performed or complied with by the Company prior
to or at the Closing.

                  6.3      Legal Opinions. The Purchaser shall have received
from Hale and Dorr LLP, counsel to the Company, opinions substantially in the
form attached hereto as Exhibit A.

                  6.4      Qualifications. All authorizations, approvals or
permits, if any, of any Governmental Entity that are required as of the Closing
Date in connection with the issuance and sale of the Shares to the Purchaser
pursuant to this Agreement shall be duly obtained and effective as of the
Closing Date.

                  6.5      Other Matters. All corporate and other proceedings in
connection with the transactions contemplated by this Agreement and all
documents and instruments incident to such transactions shall be reasonably
satisfactory in substance and form to the Purchaser, and the Purchaser shall
have received all such counterpart originals or certified or other copies of
such documents as it may reasonably request.

         7.       Condition to the Obligations of the Company. The obligations
of the Company under Section 1 of this Agreement are subject to fulfillment of
the following condition on or before the Closing:

                  7.1      Accuracy of Representations and Warranties. The
representations and warranties of the Purchaser contained in Section 4 shall be
true and correct on and as of the Closing Date with the same effect as though
such representations and warranties had been made on and as of that date.

                  7.2      Performance. The Purchaser shall have performed and
complied in all material respects with all agreements and conditions contained
in this Agreement required to be performed or complied with by the Purchaser
prior to or at the Closing.

                                      -10-
<PAGE>

         8.       Transfer of Shares.

                  8.1      Restricted Shares. "Restricted Shares" means (a) the
Shares and (b) any other shares of capital stock of the Company issued in
respect of such shares (as a result of stock splits, stock dividends,
reclassifications, recapitalizations or similar events); provided, however, that
shares of Common Stock which are Restricted Shares shall cease to be Restricted
Shares (x) upon any sale pursuant to an effective registration statement under
the Securities Act or Rule 144 under the Securities Act or (y) at such time as
they become eligible for sale under Rule 144(k) under the Securities Act.

                  8.2      Requirements for Transfer. The Purchaser acknowledges
and agrees that the Restricted Shares shall not be sold or transferred unless
either (a) they first shall have been registered under the Securities Act or (b)
the Company first shall have been furnished with an opinion of legal counsel,
reasonably satisfactory to the Company, to the effect that such sale or transfer
is exempt from the registration requirements of the Securities Act.

                  8.3      Legend. Each certificate representing Restricted
Shares shall bear a legend substantially in the following form:

                  "The shares represented by this certificate have not been
                  registered under the Securities Act of 1933, as amended, and
                  may not be offered, sold or otherwise transferred, pledged or
                  hypothecated unless and until such shares are registered under
                  such Securities Act or an opinion of counsel satisfactory to
                  the Company is obtained to the effect that such registration
                  is not required."

The Purchaser acknowledges and agrees that the Company, in its discretion, may
cause stop transfer orders to be placed with its transfer agent with respect to
the certificates representing any Restricted Shares in order to facilitate the
transfer restrictions referred to in Section 8.2. The Company shall remove the
legend from the certificates representing any Restricted Shares, at the request
of the holder thereof, at such time as they become eligible for resale pursuant
to Rule 144(k) under the Securities Act or sold pursuant to an effective
registration statement under the Securities Act.

         9.       Miscellaneous.

                  9.1      Definitions. The following terms shall have the
follow meanings when used herein:

                           (a)      "Company Licensed Intellectual Property"
means all (i) licenses of Intellectual Property to the Company or any of its
Subsidiaries by any third party, and (ii) licenses of Intellectual Property by
the Company or any of its Subsidiaries to any third party.

                           (b)      "Company Owned Intellectual Property" means
all Intellectual Property owned by the Company or any of its Subsidiaries.

                           (c)      "Indebtedness" means as applied to any
Person, (i) all indebtedness for borrowed money, whether current or funded, or
secured or unsecured, (ii) all indebtedness for

                                      -11-
<PAGE>

the deferred purchase price of property or services represented by a note or
other security, (iii) all indebtedness created or arising under any conditional
sale or other title retention agreement with respect to property acquired (even
though the rights and remedies of the seller or lender under such agreement in
the event of default are limited to repossession or sale of such property), (iv)
all indebtedness secured by a purchase money mortgage or other lien to secure
all or part of the purchase price of property subject to such mortgage or lien,
(v) all obligations under leases which shall have been or must be, in accordance
with United States generally accepted accounting principles, recorded as capital
leases in respect of which such Person is liable as lessee, (vi) any liability
in respect of banker's acceptances or letters of credit, and (vii) all
indebtedness referred to in clause (i), (ii), (iii), (iv), (v) or (vi) above
which is directly or indirectly guaranteed by or which such Person has agreed
(contingently or otherwise) to purchase or otherwise acquire or in respect of
which it has otherwise assured a creditor against loss.

                           (d)      "Intellectual Property" means intellectual
property or proprietary rights of any description, including (i) rights in any
patent, patent application (including any continuation, continuation-in-part and
divisional filings), copyright, industrial design, URL, domain name, trademark,
service mark, logo, trade dress or trade name, (ii) related registrations and
applications for registration, (iii) trade secrets, moral rights or publicity
rights, (iv) inventions, discoveries or improvements, modification, know-how,
technique, methodology, writing, work of authorship, design or data, whether or
not patented, patentable, copyrightable or reduced to practice, including any
inventions, discoveries, improvements, modification, know-how, technique,
methodology, writing, work of authorship, design or data embodied or disclosed
in any: (1) computer source codes (human readable format) and object codes
(machine readable format); (2) specifications; (3) manufacturing, assembly,
test, installation, service and inspection instructions and procedures; (4)
engineering, programming, service and maintenance notes and logs; (5) technical,
operating and service and maintenance manuals and data; (6) hardware reference
manuals; and (7) user documentation, help files or training materials, and (v)
good will related to any of the foregoing.

                           (e)      "Securities" means all shares of Common
Stock and Preferred Stock, all outstanding options, warrants, convertible notes,
rights of conversion and other rights to acquire capital stock of the Company,
and all shares issuable upon exercise or conversion of the Preferred Stock,
options, warrants, convertible notes, rights of conversion and other rights to
acquire capital stock of the Company, outstanding from time to time, whether or
not then currently vested, exercisable or convertible.

                           (f)      "Subsidiary" or "Subsidiaries" of any Person
means any corporation, partnership, limited liability company, joint venture or
other legal entity of which such Person (either above or through or together
with any other subsidiary) owns, directly or indirectly, more than 50% of the
stock or other equity interests the holders of which are generally entitled to
vote for the election of the board of directors or other governing body of such
corporation or other legal entity.

                  9.2      Successors and Assigns. This Agreement shall be
binding upon and inure to the benefit of the Company and the Purchaser and their
respective successors and permitted assigns.

                                      -12-
<PAGE>

                  9.3      Severability. The invalidity or unenforceability of
any provision of this Agreement shall not affect the validity or enforceability
of any other provision of this Agreement.

                  9.4      Specific Performance. In addition to any and all
other remedies that may be available at law in the event of any breach of this
Agreement, each Party shall be entitled to specific performance of the
agreements and obligations of the other Party hereunder and to such other
injunctive or other equitable relief as may be granted by a court of competent
jurisdiction.

                  9.5      Governing Law. This Agreement shall be governed by
and construed in accordance with the internal laws of the State of Delaware
(without reference to the conflicts of law provisions thereof).

                  9.6      Notices. All notices, requests, consents and other
communications under this Agreement shall be in writing and shall be deemed
delivered (a) two business days after being sent by registered or certified
mail, return receipt requested, postage prepaid or (b) one business day after
being sent via a reputable nationwide overnight courier service guaranteeing
next business day delivery, in each case to the intended recipient as set forth
below:

                  If to the Company, at 141 Needham Street, Newton,
Massachusetts 02464-1505, Attention: President, or at such other address or
addresses as may have been furnished in writing by the Company to the Purchaser,
with a copy to Susan W. Murley, Esq., Hale and Dorr LLP, 60 State Street,
Boston, Massachusetts 02109-1803; and

                  If to the Purchaser, at One Boston Scientific Place, Natick,
Massachusetts 01760-1537, Attention: Chief Financial Officer, or at such other
address or addresses as may have been furnished in writing by the Purchaser to
the Company, with a copy to Boston Scientific Corporation, One Boston Scientific
Place, Natick, Massachusetts 01760-1537, Attention: General Counsel.

                  Either Party may give any notice, request, consent or other
communication under this Agreement using any other means (including, without
limitation, personal delivery, messenger service, telecopy, first class mail or
electronic mail), but no such notice, request, consent or other communication
shall be deemed to have been duly given unless and until it is actually received
by the other Party. Either Party may change the address to which notices,
requests, consents or other communications hereunder are to be delivered by
giving the other Party notice in the manner set forth in this Section 9.6.

                  9.7      Complete Agreement. This Agreement constitutes the
entire agreement and understanding of the Parties with respect to the subject
matter hereof and supersedes all prior agreements and understandings relating to
such subject matter.

                  9.8      Amendments and Waivers. Except as otherwise expressly
set forth in this Agreement, any term of this Agreement may be amended or
terminated and the observance of any term of this Agreement may be waived
(either generally or in a particular instance and either retroactively or
prospectively), with the written consent of the Company and the Purchaser.

                                      -13-
<PAGE>

                  9.9      Counterparts; Facsimile Signatures. This Agreement
may be executed in any number of counterparts, each of which shall be deemed to
be an original, and all of which shall constitute one and the same document. The
delivery of a signature page of this Agreement by one Party to the other Party
via facsimile transmission shall constitute the execution and delivery of this
Agreement by the transmitting Party.

                  9.10     Section Headings. The section headings are for the
convenience of the Parties and in no way alter, modify, amend, limit or restrict
the contractual obligations of the Parties.

                  9.11     Legal Fees and Expenses. Each of the Parties to this
Agreement will bear its own legal fees and other expenses with respect to the
transaction contemplated by this Agreement. All filing fees related to filings
made pursuant to the Hart-Scott-Rodino Act shall be paid by the Purchaser.

                  9.12     Publicity. The Parties agree that no public release
or announcement concerning this Agreement shall be issued by either Party
without the prior consent of the other Party (which consent shall not be
unreasonably withheld), except as such release or announcement may be required
by law or the rules or regulations of any securities exchange or the National
Association of Securities Dealers, in which case the Party required to make the
release or announcement shall use its reasonable best efforts to allow the other
Party reasonable time to comment on such release or announcement, in advance of
such issuance.

                  9.13     Amendment to Registration Rights Agreement.

                           (a)      The Company and the Purchaser hereby agree
and acknowledge that the Registration Rights Agreement, dated as of August 7,
2002, by and between the Company and the Purchaser be amended as of the Closing
Date such that the definition of the term "Shares" in Section 1 thereof is
deleted and replaced in its entirety as follows:

                  "Shares" shall have the meaning specified in Section 1 of the
                  Stock Purchase Agreement, dated as of August 7, 2002, by and
                  between the Company and the Purchaser, and Section 1 of this
                  Agreement."

                           (b)      The Company and the Purchaser hereby agree
and acknowledge that the Registration Rights Agreement, dated as of August 7,
2002, by and between the Company and the Purchaser be amended as of the Closing
Date such that Section 2.1(c) thereof is deleted and replaced in its entirety as
follows:

                  "(c)     The Company shall not be required to effect more than
                  three (3) registrations pursuant to this Agreement. Any
                  Registration Statement to be filed by the Company hereunder
                  shall permit the Holders to offer and sell, on a delayed or
                  continuous basis pursuant to Rule 415 under the Securities Act
                  (or any similar rule then in effect), any or all of the
                  Combined Registrable Shares. The Company shall be required to
                  keep each Registration Statement effective until such date
                  that is the earlier of (i) the date when all of the Combined
                  Registrable Shares registered thereunder shall have been sold,
                  or (ii) the later of (A) the date that is two

                                      -14-
<PAGE>

                  years from the initial effective date of such Registration
                  Statement and (B) the date that is three months following the
                  date on which the Purchaser is no longer an Affiliate of the
                  Company (the "Termination Date"). Thereafter, the Company
                  shall be entitled to withdraw the Registration Statement and
                  the Holders shall have no further right to offer or sell any
                  of the Combined Registrable Shares pursuant to the
                  Registration Statement. For purposes of the first sentence of
                  this Section 2.1(c), a Registration Statement shall not be
                  counted until such time as such Registration Statement has
                  been declared effective by the Commission (unless the
                  Purchaser withdraws its request for such registration (other
                  than as a result of material information concerning the
                  business or financial condition of the Company which is first
                  made known to the Purchaser after the date on which such
                  registration was requested) and elects not to pay the
                  Registration Expenses therefore pursuant to Section 2.3)."

                  [Remainder of page intentionally left blank]

                                      -15-
<PAGE>

         Executed as of the date first written above.

                                  THE COMPANY:

                                  ASPECT MEDICAL SYSTEMS, INC.

                                  By: /s/ J. NEAL ARMSTRONG
                                      ------------------------------
                                      Name: J. NEAL ARMSTRONG
                                      Title: CFO

                                  THE PURCHASER:

                                  BOSTON SCIENTIFIC CORPORATION

                                  By: /s/ LAWRENCE C. BEST
                                      ------------------------------
                                      Name: LAWRENCE C. BEST
                                      Title: CHIEF FINANCIAL OFFICER

                                      -16-

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