<Page>


                                                                    EXHIBIT 10.6


                             SECURED PROMISSORY NOTE

$1,000,000                                                Dated: August 15, 2000


         FOR VALUE RECEIVED, the undersigned, DIGIRAD CORPORATION, a Delaware
corporation ("BORROWER"), HEREBY PROMISES TO PAY to the order of MMC/GATX
PARTNERSHIP NO. I ("LENDER") the principal amount of One Million Dollars
($1,000,000) or such lesser amount as shall equal the outstanding principal
balance of the Loan made to Borrower by Lender pursuant to the Loan and Security
Agreement referred to below (the "LOAN AGREEMENT"), and to pay all other amounts
due with respect to the Loan on the dates and in the amounts set forth in the
Loan Agreement.

         Interest on the principal amount of this Note from the date of this
Note shall accrue at the Loan Rate or, if applicable, the Default Rate. The Loan
Rate for this Note is 13.70% per annum based on a year of twelve 30-day months.
Commencing on October 1, 2000, and continuing on the first day of each
subsequent month (each, a "PAYMENT DATE"), Borrower shall make to Lender
thirty-six (36) equal payments of principal plus accrued interest on the then
outstanding principal amount in the amount of $34,032.00.

         Principal, interest and all other amounts due with respect to the Loan,
are payable in lawful money of the United States of America to Lender by wire
transfer according to the wire transfer instructions set forth in the Loan
Agreement. The principal amount of this Note and the interest rate applicable
thereto, and all payments made with respect thereto, shall be recorded by Lender
and, prior to any transfer hereof, endorsed on the grid attached hereto which is
part of this Note.

         This Note is one of the Notes referred to in, and is entitled to the
benefits of, the Loan and Security Agreement, dated as of October 27, 1999 and
amended as of August 14, 2000, to which Borrower and Lender are parties. The
Loan Agreement, among other things, (a) provides for the making of a secured
Loan to Borrower, and (b) contains provisions for acceleration of the maturity
hereof upon the happening of certain stated events.

         This Note may be not be prepaid except as set forth in Section 2.01(d)
of the Loan Agreement.

         This Note and the obligation of Borrower to repay the unpaid principal
amount of the Loan, plus the Applicable Premium, interest on the Loan and all
other amounts due Lender under the Loan Agreement is secured under the Loan
Agreement.

         Presentment for payment, demand, notice of protest and all other
demands and notices of any kind in connection with the execution, delivery,
performance and enforcement of this Note are hereby waived.

         Borrower shall pay all reasonable fees and expenses, including, without
limitation, reasonable attorneys' fees and costs, incurred by Lender in the
enforcement or attempt to enforce


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any of Borrower's obligations hereunder not performed when due. This Note
shall be governed by, and construed and interpreted in accordance with, the
laws of the State of California.

         IN WITNESS WHEREOF, Borrower has caused this Note to be duly executed
by one of its officers thereunto duly authorized on the date hereof.


                                           DIGIRAD CORPORATION

                                           By:      /s/ Scott Huennekens
                                              ----------------------------------

                                           Name:    Scott Huennekens
                                                --------------------------------

                                           Title:   Pres. & CEO
                                                 -------------------------------


                                       2
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                   AMENDMENT TO SECURED PROMISSORY NOTE NO. 3


         This Amendment to Secured Promissory Note No. 3 (this "Amendment")
amends that certain Secured Promissory Note dated August 21, 2000 (the "Original
Note") made by Digirad Corporation ("Borrower") payable to the order of MMC/GATX
Partnership No. I, a California general partnership ("Lender") in the original
principal amount of One Million Dollars ($1,000,000). Unless otherwise defined
in this Amendment, capitalized terms have the meaning given such terms in the
Original Note.

         Borrower and Lender agree that commencing December 1, 2000 (in addition
to the payments previously made by Borrower through and including November 1,
2000), Borrower shall make twenty-four (24) equal monthly payments of principal
plus accrued interest on the outstanding principal plus accrued interest on the
outstanding principal amount of the Loan in the amount of $ 45,693.67.

         Except as specifically amended by this Amendment the Original Note
remains in full force and effect.

Dated:  November 27, 2000


DIGIRAD CORPORATION                           MMC/GATX PARTNERSHIP NO.  I
                                              By:   GATX Capital Corporation,
                                                    Its general partner

By:        /s/ Scott Huennekens               By:     /s/ Patricia W. Leicher
    ---------------------------------             ------------------------------

Name:      Scott Huennekens                   Name:   Patricia W. Leicher
      -------------------------------               ----------------------------

Title:     President & CEO                    Title:  VP
       ------------------------------                ---------------------------


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                               DIGIRAD CORPORATION
                       AMORTIZATION SCHEDULE #3 - REVISED


Loan Amount:                                                         $954,511.14
Loan Interest Rate:                                                       13.70%
Original Funding Date:                                                   8/15/00
Revised:                                                                 11/8/00

<Table>
<Caption>

--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
       PAYMENT              NEW              PRINCIPAL            INTEREST          TOTAL DEBT            PRINCIPAL
       NUMBER               DATE             REPAYMENT            PAYMENT            SERVICE               BALANCE
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
<S>                   <C>                <C>                 <C>                <C>                 <C>
        0**               11/08/00                0.00         $     0.00          $     0.00          $954,511.14
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         1                12/01/00           34,796.33         $10,897.34          $45,693.67          $919,714.81
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         2                01/01/01           35,193.59         $10,500.08          $45,693.67          $884,521.21
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         3                02/01/01           35,595.39         $10,098.28          $45,693.67          $848,925.83
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         4                03/01/01           36,001.77         $ 9,691.90          $45,693.67          $812,924.06
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         5                04/01/01           36,412.79         $ 9,280.88          $45,693.67          $776,511.27
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         6                05/01/01           36,828.50         $ 8,865.17          $45,693.67          $739,682.77
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         7                06/01/01           37,248.96         $ 8,444.71          $45,693.67          $702,433.81
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         8                07/01/01           37,674.22         $ 8,019.45          $45,693.67          $664,759.60
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         9                08/01/01           38,104.33         $ 7,589.34          $45,693.67          $626,655.27
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         10               09/01/01           38,539.36         $ 7,154.31          $45,693.67          $588,115.91
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         11               10/01/01           38,979.35         $ 6,714.32          $45,693.67          $549,136.56
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         12               11/01/01           39,424.36         $ 6,269.31          $45,693.67          $509,712.20
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         13               12/01/01           39,874.46         $ 5,819.21          $45,693.67          $469,837.75
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         14               01/01/02           40,329.69         $ 5,363.98          $45,693.67          $429,508.06
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         15               02/01/02           40,790.12         $ 4,903.55          $45,693.67          $388,717.94
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         16               03/01/02           41,255.81         $ 4,437.66          $45,693.67          $347,462.13
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         17               04/01/02           41,726.81         $ 3,966.86          $45,693.67          $305,735.32
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         18               05/01/02           42,203.19         $ 3,490.48          $45,693.67          $263,532.13
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         19               06/01/02           42,685.01         $ 3,008.66          $45,693.87          $220,847.12
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         20               07/01/02           43,172.33         $ 2,521.34          $45,693.67          $177,674.79
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         21               08/01/02           43,665.22         $ 2,028.45          $45,693.67          $134,009.57
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         22               09/01/02           44,163.73         $ 1,529.94          $45,693.67          $ 89,845.84
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         23               10/01/02           44,667.93         $ 1,025.74          $45,693.67          $ 45,177.91
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------
         24               11/01/02           45,177.91         $   515.78          $45,693.69          $       .00
--------------------- ------------------ ------------------- ------------------ ------------------- ------------------

</Table>

**ASSUMES NOVEMBER 1, 2000 PAYMENT HAS BEEN MADE