<PAGE>

                                                                    EXHIBIT 4.01



                               INVIVO CORPORATION
                             1994 STOCK OPTION PLAN
                                   AS AMENDED

1.    PURPOSE

            The Purpose of the Invivo Corporation 1994 Stock Option Plan (the
"Plan) is to enable Invivo Corporation (the "Company") and its subsidiaries to
attract and retain officers and other key employees, directors, and consultants
and to provide them with additional incentive to advance the interests of the
Company. Options qualifying as incentive stock options under Section 422 of the
Internal Revenue Code of 1986, as amended ("Code"), and non-qualified options
may be granted under the Plan.

2.    ADMINISTRATION

            (a) The Plan shall be administered by the Board of Directors of the
Company, or by a committee (the "Committee") of two or more directors selected
by the Board of Directors.

            (b) The Board of Directors or the Committee shall have the power,
subject to the express provisions of the Plan:

                  (1) To determine the recipients of options under the Plan, the
            time of grant of the options, and the number of shares covered by
            the grant.

                  (2) To prescribe the terms and provisions of each option
            granted (which need not be identical).

                  (3) To construe and interpret the Plan and options, to
            establish, amend, and revoke rules and regulations for the Plan's
            administration, and to make all other determinations necessary or
            advisable for the administration of the Plan.

3.    SHARES SUBJECT TO THE PLAN

            Subject to the provisions of Paragraph 7 (relating to the adjustment
upon changes in stock), the number of shares which may be sold pursuant to
options granted under the Plan shall not exceed in the aggregate 1,680,000
shares of Common Stock of the Company. Shares sold pursuant to options granted
under the Plan may be unissued shares or reacquired shares. If any options
granted under the Plan shall for any reason terminate or expire without having
been exercised in full, the shares not purchased under such options shall be
available again for the purposes of the Plan.

                                      -1-
<PAGE>
4.    ELIGIBILITY

            (a) Options under this Plan may be granted to officers and other key
employees and consultants of the Company or of its subsidiaries, provided that
incentive stock options may be granted hereunder only to officers and other key
employees (including directors who are also officers or employees).

            (b) Each person who is a director and not an employee of the Company
or a subsidiary of the Company on the date of adoption of this Plan by the Board
of Directors shall receive a non-qualified stock option under the Plan on the
date of such adoption. Thereafter, each director of the Company who is not an
employee of the Company or a subsidiary of the Company shall receive a
non-qualified stock option under the Plan immediately following each annual
meeting of shareholders of the Company (provided that a person whose term
expires on such day and who is not reelected to the Board of Directors shall not
receive such an option). The first option received by a director under this
paragraph 4(b) shall cover 8,000 shares of Common Stock of the Company and each
option received by a director under this Plan thereafter shall cover 4,000
shares of Common Stock of the Company. Each such option shall have an exercise
price equal to the fair market value of the Common Stock of the Company on the
date of adoption by the Board of Directors or of the annual meeting of
shareholders to which it relates, as the case may be determined in accordance
with the provisions of paragraph 5(a)(2) of this Plan. The number of options
that directors may receive pursuant to this paragraph 4(b) shall be
appropriately adjusted in accordance with the provisions of paragraph 7 of this
Plan. This paragraph 4(b) shall not be amended more than once every six months,
other than to comply with changes in the Internal Revenue Code, the Employee
Retirement Income Security Act or the rules or regulations thereunder.

            (c) Persons to whom options to purchase shares are granted are
hereinafter referred to as "optionee(s)." Subject to the provisions of
paragraphs 3 and 4(b) of the Plan, there is no limitation on the number of
options that may be granted to an optionee.

5.    TERMS OF OPTION AGREEMENTS

            (a) All Option Agreements. Options granted pursuant to the Plan
shall be evidenced by agreements specifying the number of shares covered
thereby, in such form as the Board of Directors or Committee shall from time to
time establish, which agreements may incorporate all or any of the terms hereof
by reference and shall comply with and be subject to the following terms and
conditions:

                  (1) The Board of Directors or Committee shall have the power
            to set the time or times within which each option shall be
            exercisable and to at any time accelerate the time or times


                                      -2-
<PAGE>
            of exercise (notwithstanding the terms of the option). Unless the
            stock option agreement executed by the optionee expressly otherwise
            provides, (i) an option granted to an officer or other key employee
            or consultant shall become exercisable on a cumulative basis as to
            one-quarter of the total number of shares covered thereby on each of
            the first, second, third, and fourth anniversary dates of the date
            of grant of the option, (ii) an option granted to a director who is
            not an employee of the Company shall become exercisable on a
            cumulative basis as to one-half of the total number of shares
            covered thereby on each of the first and second anniversary dates of
            the date of grant of the option, and (iii) an option shall not be
            exercisable after the expiration of ten years from the date of
            grant. Any option granted to an executive officer or director of the
            Company shall in no event be exercisable until the elapse of six
            months from the date of its grant.

                  (2) Except as provided in (b) below, the exercise price of any
            incentive stock option shall not be less than 100% of the fair
            market value of the shares of Common Stock of the Company on the
            date of the granting of the option and the exercise price of any
            non-qualified stock option shall not be less than 85% of the fair
            market value of the shares of Common Stock of the Company on the
            date of the granting of the option. The fair market value per share
            shall be as determined in good faith by the administrator of the
            Plan, provided that if the Company's Common Stock is publicly traded
            the fair market value shall be the closing bid price on the day the
            option is granted as reported on the Nasdaq National Market or the
            closing sale price on such stock exchange on which the shares may be
            listed if such exchange is then the principle market for the shares,
            or, if such shares are not then reported on the Nasdaq National
            Market or an exchange but quotations are reported on the National
            Association of Securities Dealers Automated Quotations System, the
            closing bid price on the day the option is granted, in either event
            as such price or quotes are listed in The Wall Street Journal,
            Western Edition (or if not so reported in The Wall Street Journal,
            any other listing service or publication known to the administrator
            of the Plan).

                  (3) To the extent that the right to purchase shares has
            accrued hereunder, options may be exercised from time to time by
            written notice to the Company, stating the number of shares being
            purchased and accompanied by the payment in full of the option price
            for such shares. Such payment shall be made in cash or in shares of
            the outstanding Common Stock of the Company which have been held by
            the optionee for at least six months (or such other period as is
            specified by the Board of Directors or the Committee) or in a
            combination of cash and such stock, except that the Board of
            Directors or the Committee in its sole discretion may authorize
            payment by any


                                      -3-
<PAGE>
            optionee (for all or part of his or her purchase price) by a
            promissory note or such other form of legal consideration that may
            be acceptable to the Board of Directors or Committee. Payment may
            also be made by delivering a copy of irrevocable instructions to a
            broker to deliver promptly to the Company the amount of sale or loan
            proceeds sufficient to pay the purchase price, and, if required, the
            amount of any federal, state, local or foreign withholding taxes.

                  If shares of Common Stock are used in part or full payment for
            the shares to be acquired upon exercise of the option, such shares
            shall be valued for the purpose of such exchange as of the date of
            exercise of the option in accordance with the provisions of (2)
            above and the notice of exercise shall be accompanied by such
            instruments and documentation as the Board of Directors or Committee
            require to effect the delivery of such shares. In the event the
            certificates tendered by the optionee in such payment cover more
            shares than are required for such payment, the certificates shall
            also be accompanied by instructions from the optionee to the
            Company's transfer agent with regard to disposition of the balance
            of the shares covered thereby.

                  If payment by promissory note is authorized, the interest
            rate, term, repayment schedule and other provisions of such note
            shall be as specified by the Board of Directors or the Committee;
            provided, however, that such note shall bear interest at a rate not
            less than the applicable test rate of interest prescribed by
            Regulation 1.483-1(d)(1) of the Income Tax Regulations, as in effect
            at the time the stock is purchased. The Board of Directors or
            Committee may require that the optionee pledge Common Stock of the
            Company for the purpose of securing the payment of such note, and
            the Company may hold the certificate(s) representing such stock in
            order to perfect its security interest.

                  An option may be exercised by a securities broker acting on
            behalf of an optionee pursuant to authorization instructions
            approved by the Company.

                  (4) The Company at all times shall keep available the number
            of shares of Common Stock required to satisfy options granted under
            the Plan.

                  (5) The Company may require any person to whom an option is
            granted, including his or her legal representative, heir, legatee,
            or distributee, as a condition of exercising any option granted
            hereunder, to give written assurance satisfactory to the Company to
            the effect that such person is acquiring the shares subject to the
            option for his or her own account for investment and not with any
            present intention of selling or otherwise distributing the same. The
            Company reserves the right to place a legend on any share
            certificate


                                      -4-
<PAGE>
            issued pursuant to this Plan to assure compliance with this
            paragraph. No shares of Common Stock of the Company shall be
            required to be distributed until the Company shall have taken such
            action, if any, as is then required to comply with the provisions of
            the Securities Act of 1933 or any other then applicable securities
            law.

                  (6) Neither a person to whom an option is granted, nor such
            person's legal representative, heir, legatee, or distributee, shall
            be deemed to be the holder of, or to have any of the rights of a
            holder with respect to, any shares of Common Stock subject to such
            option unless and until such person has exercised his or her option
            pursuant to the terms thereof.

                  (7) Options shall be transferable only by will or by the laws
            of descent and distribution, and during the lifetime of the person
            to whom they are granted such person alone may exercise them, except
            that a non-qualified stock option may be transferred pursuant to a
            qualified domestic relations order as defined by the Code or Title I
            of the Employee Retirement Income Security Act, or the rules
            thereunder and to the extent provided in the stock option agreement
            entered into in connection with such option (including any amendment
            of such agreement).

                  (8) An option granted to an employee or director shall
            terminate and may not be exercised if the person to whom it is
            granted ceases to be employed by the Company or by a subsidiary of
            the Company, or ceases to be a director (unless such person
            continues as an employee), with the following exceptions:

                        (i) If the employment or directorship is terminated for
                  any reason other than the person's death or disability, he or
                  she may at any time within not more than three months after
                  such termination exercise the option, but only to the extent
                  that it was exercisable by such person on the date of such
                  termination and otherwise remains exercisable in accordance
                  with its terms, or

                        (ii) If such person becomes disabled while in the employ
                  of the Company or of a subsidiary, or while a director, or
                  dies while in the employ of the Company or a subsidiary, or
                  while a director, or within 30 days after termination of such
                  person's employment with the Company or a subsidiary, or
                  status as a director, his or her option may be exercised by
                  his or her personal representatives, heirs or legatees at any
                  time within not more than 12 months following the date of
                  death or disability, but only to the extent such option was
                  exercisable by such person on the date of death or


                                      -5-
<PAGE>
                  disability and otherwise remains exercisable in accordance
                  with its terms.

                  An option granted to a consultant shall terminate in
            accordance with the terms specified in the stock option agreement.

                  (9) In no event may an option be exercised by anyone after the
            expiration of the term of the option established pursuant to (1)
            above.

                  (10) Each option granted pursuant to this Plan shall specify
            whether it is a non-qualified or an incentive stock option, provided
            that the Board of Directors or Committee may give the optionee the
            right to elect to receive either an incentive or a non-qualified
            stock option.

                  (11) An option granted pursuant to this Plan may have such
            other terms as the Board of Directors or Committee in its discretion
            may deem necessary or appropriate and shares issued upon exercise of
            any option hereunder may be subject to such restrictions as the
            Board of Directors or Committee deems appropriate.

            (b) Incentive Stock Options. In addition to the terms and conditions
specified above, incentive stock options granted under this Plan shall be
subject to the following terms and conditions:

                  (1) The aggregate fair market value (determined as of the time
            the option is granted) of the stock with respect to which incentive
            stock options are exercisable for the first time by any optionee
            during any calendar year (under all option plans of the Company or
            any parent and subsidiary corporations) shall not exceed $100,000,
            provided that to the extent that the aggregate fair market value of
            stock with respect to which options designated as Incentive Stock
            Options first become exercisable in any calendar year exceeds
            $100,000, such options shall be treated as non-qualified options.

                  (2) As to individuals otherwise eligible under this Plan who
            own more than 10 percent of the total combined voting power of all
            classes of stock of the Company and any parent and subsidiary
            corporations, an incentive option can be granted under this Plan to
            any such individual only if at the time such option is granted the
            option price is at least 110 percent of the fair market value of the
            stock subject to the option and such option by its terms is not
            exercisable after the expiration of five years from the date such
            option is granted.

                                      -6-
<PAGE>
6.    USE OF PROCEEDS FROM SHARES

            Proceeds from the sale of shares pursuant to options granted under
the Plan shall be used for general corporate purposes.

7.    ADJUSTMENT UPON CHANGES IN SHARES

            (a) If any change is made in the shares subject to the Plan,
including shares subject to any option granted under the Plan (through merger,
consolidation, reorganization, recapitalization, stock dividend, dividend in
property other than cash, stock split, liquidating dividend, combination of
shares, exchange of shares, change in corporate structure or otherwise),
appropriate adjustments shall be made by the Board of Directors or Committee in
the maximum number of shares subject to the Plan and the number of shares and
price per share of stock subject to outstanding options.

            (b) Other than in the case of a reincorporation of the Company in
another state, in the event of (i) approval by the shareholders of the Company
of the dissolution or liquidation of the Company, (ii) consummation of the sale
of all or substantially all of the assets of the Company, (iii) consummation of
a transaction in which more than 50 percent of the shares of the Company that
are entitled to vote are tendered or exchanged for cash or any other assets, or
(iv) any merger or consolidation or other reorganization in which the Company is
not the surviving corporation, or in which the Company becomes a subsidiary of
another corporation, outstanding options under this Plan shall become fully
exercisable immediately prior to any such event.

            (c) In lieu of permitting any exercise of an outstanding option
pursuant to (b) above, the Board of Directors or the Committee may, subject to
the approval of the corporation purchasing or acquiring the stock or assets of
the Company (the "Surviving Corporation"), arrange for the optionee to receive
upon surrender of optionee's option a new option covering shares of the
Surviving Corporation in the same proportion, at an equivalent option price and
subject to the same terms and conditions as the surrendered option.

8.    RIGHTS AS AN EMPLOYEE

            Nothing in this Plan or in any options awarded hereunder shall
confer upon any employee any right to continue in the employ, or as a director,
of the Company or of any of its subsidiaries or interfere in any way with the
right of the Company or any such subsidiary to terminate such employee's
employment or directorship at any time.

                                      -7-
<PAGE>
9.    WITHHOLDING TAX

            There shall be deducted from the compensation of any employee
holding options under this Plan the amount of any tax required by any
governmental authority to be withheld and paid over by the Company to such
governmental authority for the account of the person with respect to such
options.

10.   TERMINATION AND AMENDMENT OF PLAN

            The Board of Directors may at any time terminate this Plan or make
such modifications of the Plan as it shall deem advisable. Any modification
which increases the number of shares which may be issued under the Plan (other
than pursuant to Paragraph 7 hereof), or relaxes the requirements as to
eligibility for participation in the Plan, shall become effective only upon
approval of the holders of a majority of the securities of the Company present,
or represented, and entitled to vote at a meeting duly held in accordance with
the laws of the State of Delaware. Any options granted under the Plan prior to
shareholder approval of the Plan, and any options granted which are dependent
upon an amendment of the Plan requiring shareholder approval for their
effectiveness, shall be subject to shareholder approval of the Plan or such
amendment. If such approval is not obtained within 12 months of the date of
grant of any such option, such option shall expire without further action.

11.   EFFECTIVE DATE AND DURATION OF THE PLAN

            The Plan shall become effective on October 6, 1994. Any rights
granted under this Plan must be granted within ten (10) years of such effective
date.


                                      -8-