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                                  Exhibit 10.20

                                SIGNATURE CENTER
                            FIRST AMENDMENT TO LEASE

THIS First Amendment to Lease dated October 19, 2000, by and between PRINCIPAL
LIFE INSURANCE COMPANY, AN IOWA CORPORATION, F/K/A Principal Mutual Life
Insurance Company, an Iowa corporation, ("Landlord") and INVIVO CORPORATION, a
Delaware corporation, F/K/A Safetytek Corporation, a Delaware Corporation, for
the premises located at 4900 Hopyard Road, Suite 210, Pleasanton, CA 94588.

                                    RECITALS

On February 26, 1996, Principal Life Insurance Company, and Iowa corporation,
("Landlord") and Invivo Corporation, a Delaware corporation, ("Tenant"), entered
into an Office Lease ("Lease").

Landlord and Tenant desire to modify the terms and conditions of the Lease so as
to further extend the Term thereof, to modify the monthly Base Rent, among other
changes, effective April 15, 2001.

NOW THEREFORE, for good and valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, Landlord and Tenant hereby agree that the
lease will be amended as follows:

Article 1      Term

               The term of the lease shall be extended to April 14, 2006.

Article 3      Basic Rent

               Effective April 15, 2001, Tenant's base monthly rent shall be as
follows.

<TABLE>
<CAPTION>
                                                      Monthly
                        Year                          Amount
                        ----                        ----------
                        <S>                         <C>
                         1                          $11,189.50
                         2                          $11,637.08
                         3                          $12,116.63
                         4                          $12,596.18
                         5                          $13,107.70
</TABLE>

Article 4(ii)  Rental Adjustment, Direct Expense Base

               The amount of annual Direct Expenses which Landlord has included
               in Annual Basic Rent, which amount is Tenant's Percentage of the
               actual Direct Expenses for 2001. If the Project is less than
               ninety-five percent (95%) occupied during any calendar year of
               the term, an adjustment shall be made in computing the Direct
               Expenses for such year so that Direct Expenses shall be computed
               as though the Project were ninety-five percent 995%) occupied.

Tenant hereby represents and warrants to Landlord that the Lease as amended
constitutes a valid and binding obligation of Tenant, enforceable against Tenant
in accordance with their terms, and Tenant has no defenses, offsets or
counterclaims with respect to its obligations thereunder. Except as modified
here, the Lease shall continue unmodified and in full force and effect.

LANDLORD:

PRINCIPAL LIFE INSURANCE COMPANY, an Iowa corporation

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By: PRINCIPAL CAPITAL MANAGEMENT, LLC, a Delaware limited liability company, its
authorized signatory

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TENANT:

By:     INVIVO CORPORATION, a Delaware corporation

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