FOURTH AMENDMENT TO
                       AGREEMENT OF LIMITED PARTNERSHIP OF
                   SAN DIEGO LITHOTRIPTERS LIMITED PARTNERSHIP

                  THIS  AMENDMENT,  effective  as of the 15TH  day of  February,
1999,  is  entered  into by and  among  Lithotripters,  Inc.,  a North  Carolina
corporation  and  the  General  Partner  of  San  Diego  Lithotripters   Limited
Partnership,  a California  limited  partnership  (the  "Partnership"),  and the
Limited Partners of the Partnership.

                                                 R E C I T A L S:
                                                 ---------------

                  1. The General Partner and the Limited  Partners,  hereinafter
collectively  referred  to as  the  "Partners,"  are  parties  to  that  certain
Agreement of Limited Partnership of San Diego Lithotripters Limited Partnership,
as amended (the "Agreement").

                  2. Effective as of February 15, 1999, the General  Partner and
the  requisite  percentage of the Limited  Partners  consented in writing to the
following  amendments to the Agreement,  such amendments  intended to: (i) allow
the General  Partner the  authority to  periodically  offer and sell  additional
limited  partner  interests  (a  "Dilution  Offering")  to local  investors;(ii)
clarify and strengthen the  noncompetition  provisions of Articles 15.3 and 18.4
of the  Agreement;  (iii) add a new  provision  to the  Agreement to prevent the
disclosure  of  Confidential   Partnership   Information  that  might  harm  the
Partnership and its Partners;  and (iv) allow the General  Partner,  in its sole
discretion, to elect to assign to the Partnership its rights under Article 18 of
the Agreement to purchase the Partnership Interest of any deceased, insolvent or
competing Limited Partner:

                  NOW,  THEREFORE,  in accordance with Articles 29 and 30 of the
Partnership Agreement and pursuant to the written consent of the General Partner
and the requisite  percentage of the Limited Partners,  the parties hereto agree
as follows:

                           The  Agreement  is  hereby  amended  as set  forth in
                           Exhibits A, B and C attached hereto.



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                  IN WITNESS WHEREOF, the Partners have hereunto set their hands
and seals effective as of the date first above written.

                           GENERAL PARTNER:

                           LITHOTRIPTERS, INC., a North Carolina corporation and
                                   sole general partner of the Partnership

                                   By:_________________________________________
                                Title:________________________________________



                                                 ALL THE LIMITED PARTNERS OF
                                                 THE PARTNERSHIP WHOSE NAMES
                                                 APPEARED ON SCHEDULE A-3

                                                     By:/s/ Joseph Jenkins, M.D.
                                                     ---------------------------
                                                     Joseph Jenkins, M.D.
                                                     Attorney-in-Fact*
--------
     *Pursuant  to a Power of  Attorney  given by the  Limited  Partners  in the
Agreement.

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                                    EXHIBIT A

                           DILUTION OFFERING AMENDMENT

1.       Capitalized  terms used in this Exhibit and not otherwise defined shall
         have  the  same  meaning  as  provided  in  the  Agreement  of  Limited
         Partnership (the  "Partnership  Agreement") of San Diego  Lithotripters
         Limited Partnership (the "Partnership").

2.       The purpose of this Exhibit is to set forth a proposed amendment to the
         Partnership Agreement that would give the General Partner the authority
         periodically  to offer and sell additional  limited  partner  interests
         ("Dilution  Offerings") to local investors who are not Limited Partners
         in the Partnership ("Qualified Investors").  As required by Articles 28
         and 29 of the  Partnership  Agreement,  to be effective  this amendment
         must  be  approved  by  the  Partners  representing  two-thirds  of the
         aggregate interests in the Partnership.

3.   The purposes of a Dilution Offering are (i) to raise additional capital for
     any valid  Partnership  purpose,  and (ii) to assure the highest quality of
     patient care by admitting  Qualified  Investors to the Partnership who will
     be dedicated and motivated as owners to follow the Partnership's  treatment
     protocol,  and comply  with its  quality  assurance  and  outcome  analysis
     programs.  Any additional  capital raised by the  Partnership in a Dilution
     Offering  can be used for any  legitimate  Partnership  purpose,  including
     upgrading the  Partnership's  Lithostar(TM)Mobile  System,  and/or upon the
     vote of a Majority in Interest of the Limited Partners,  the acquisition of
     an additional lithotripter and transport vehicle.

4.   In the  event  the  Dilution  Offering  Amendment  receives  the  requisite
     approval of the Limited Partners,  the General Partner intends to conduct a
     Dilution  Offering for the purposes of raising  additional  capital for (i)
     upgrading and refurbishing the Partnership's  Lithostar(TM)  Mobile System,
     and (ii)  acquiring  and operating a new Storz  Modulith(R)SLX-T  ("SLX-T")
     model  lithotripter and a new mobile transport vehicle for transporting the
     SLX-T from site to site in the  Partnership's  current  service area. It is
     estimated  that  the cost  for the  SLX-T  and  transport  vehicle  will be
     approximately  $525,000. In the event the proceeds of the Dilution Offering
     alone are insufficient to fund the necessary  upgrades of the Lithostar(TM)
     Mobile  System and the purchases of the SLX-T and  transport  vehicle,  the
     necessary additional funds will be borrowed (the "Loan") by the Partnership
     from a commercial financial institution  acceptable to the General Partner.
     The General Partner  anticipates that the Partnership will be the principal
     guarantor of the Loan.  Therefore,  the Limited Partners will not be liable
     for such debt individually.  However, payments by the Partnership under the
     Loan  will  impact  the cash flow of the  Partnership,  and  therefore  the
     distributions  to be  received  by the Limited  Partners  from  Partnership
     operations during the term of the Loan.

         The General Partner believes that the acquisition of a new lithotripter
         and transport vehicle are in the best interests of the Partnership. Due
         to certain market forces existing in the

W#876952.1

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         Partnership's   current   service  area,  the  demand  for  alternative
         technology  to  the  Partnership's  Lithostar(TM)  has  increased.  The
         General Partner and the Partnership's Medical Director believe that the
         best means for the  Partnership  to address  such  demand,  and thereby
         remain competitive in the Partnership's  market area, is to provide the
         equipment  technology  available with the SLX-T.  The General  Partner,
         however,  reserves the right to pursue  technology other than the SLX-T
         if such  alternative  technology is more  beneficial to the Partnership
         and the Limited Partners.  As required by Article 28 of the Partnership
         Agreement, the acquisition of a new lithotripter, and the Partnership's
         incurrence of debt in excess of $100,000 per year (if necessary to fund
         the acquisition of the  lithotripter  and transport  vehicle),  must be
         approved  by the  General  Partner  and a Majority  in  Interest of the
         Limited Partners.

5.       Any sale of limited  partner  interests  to  Qualified  Investors  will
         result in the  proportionate  dilution  of the  Partnership  Percentage
         Interests of the existing Partners;  i.e., the interests of the General
         Partner  and the  Limited  Partners in  Partnership  allocations,  cash
         distributions  and voting rights will be  proportionately  reduced by a
         successful Dilution Offering.

6.       The  Percentage  Interests of the existing  Partners  cannot be diluted
         through  Dilution  Offerings by more than 20% in the aggregate  without
         the  prior  written  consent  of a  Majority  in  Interest  of all  the
         Partners.  Without  obtaining  this  additional  consent,  the existing
         Partners  cannot  be  diluted  to less  than  80% of  their  Percentage
         Interest ownership at the time of this Amendment.

7.       The  General  Partner has  determined  that the  purchase  price per 1%
         Partnership  Interest offered in the initial planned Dilution  Offering
         will be at its fair market value as determined by an independent  third
         party appraiser (Philpott, Ball & Company). The price for Units sold in
         future  Dilution  Offerings  also  must be at a price no less than fair
         market  value as  determined  by the General  Partner and a third party
         appraiser.

8.       Upon  the  successful  sale  of  Partnership  Interests  in a  Dilution
         Offering,  the General Partner will prepare and attach a new Schedule A
         to the  Partnership  Agreement  to reflect (i) the  Partners'  adjusted
         Percentage Interests in the Partnership,  and (ii) the admission of the
         new Limited Partners to the Partnership.



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                                    EXHIBIT B

                          NONCOMPETITION PROVISION AND
                          ----------------------------
                      CONFIDENTIALITY PROVISION AMENDMENTS
                       --------------- --------- ---------


                  Capitalized  terms  used in  this  Exhibit  and not  otherwise
defined  shall have the same  meaning as  provided in the  Agreement  of Limited
Partnership (the  "Partnership  Agreement") of San Diego  Lithotripters  Limited
Partnership (the "Partnership"), and any amendments thereto.

                                        Noncompetition Provision Amendment

                  Article 15.3 of the Partnership Agreement is hereby amended by
deleting the current  provision in its entirety and by substituting the language
set forth below:

                           15.3 Outside  Activities.  The Limited Partners agree
         that  they  owe  fiduciary   duties  to  the  Partnership   and,  as  a
         consequence,  each Limited  Partner (that is not the General Partner or
         an  Affiliate of the General  Partner)  agrees that he or she shall not
         engage in "Outside  Activities" (as defined below) in the "Market Area"
         (as  defined  below)  while  he or  she  is a  Limited  Partner  in the
         Partnership.   The  phrase  "Outside   Activities"  means  directly  or
         indirectly owning, leasing or subleasing a lithotripter (or any similar
         equipment or competing devices used for treating renal or biliary stone
         disease).  Prohibited  indirect  ownership  shall include the direct or
         indirect ownership of any interest in a business venture (through stock
         ownership,  partnership  interest ownership,  ownership by or through a
         close family  member,  or as otherwise  determined in good faith by the
         General Partner) involving the ownership,  purchase,  lease,  sublease,
         promotion,  management  or  operation  of a  lithotripter  (or  similar
         equipment or competing devices used for treating renal or biliary stone
         disease),  unless the General Partner  determines that such activity by
         the Limited  Partners is not  detrimental  to the best interests of the
         Partnership.

                           Upon  the   termination  or  transfer  of  a  Limited
         Partner's  interest  in the  Partnership  for any  reason,  including a
         transfer  pursuant to Article  18.4  hereof,  the  withdrawing  Limited
         Partner shall not, for a period of two (2) years  following the date of
         his or her withdrawal,  engage in any Outside Activities in any "Market
         Area" in which the  Partnership is  transacting  business or within the
         prior  twelve  months  has   transacted   business   (the   "Restricted
         Facilities").  For the purposes of this Article 15.3,  the term "Market
         Area"  shall  mean  (i)  the  area  within  a ten  mile  radius  of any
         Restricted  Facility,  but if such  area is  determined  by a court  of
         competent  jurisdiction  to be too  broad,  then it shall mean (ii) the
         area within a five mile radius of any Restricted Facility,  but if such
         area is determined by a court of competent jurisdiction to be too broad
         then it shall  mean  (iii)  the area  within a two mile  radius  of any
         Restricted Facility.



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                           In the event a Limited  Partner wishes and intends to
         engage in an Outside  Activity in a Market Area, he or she must provide
         written notice of such intent to the General  Partner prior to engaging
         in the Outside Activity. The written notice shall be deemed an election
         by the Limited Partner to withdraw from the Partnership (the "Notice of
         Withdrawal"),  and shall give the  General  Partner  and/or the Limited
         Partners the purchase rights as provided in Article 18.4 hereof.  After
         the Notice of Withdrawal,  the former Limited  Partner may engage in an
         Outside  Activity in the Market  Area only after  waiting the period of
         two years specified in this Article 15.3. In the event of breach of the
         waiting period,  the Partnership shall be entitled to any remedy at law
         or equity with respect to such breach,  including without limitation an
         injunction or suit for damages.

                           If a Limited Partner during his or her  participation
         in the  Partnership  engages in an Outside  Activity  in a Market  Area
         without  first  notifying  the  General  Partner in  violation  of this
         Article  15.3,  the  Limited  Partner  shall be deemed to have  given a
         Notice of  Withdrawal  on the date the General  Partner  first  becomes
         aware of the Limited  Partner's  Outside  Activity in the Market  Area.
         Upon receiving a Limited  Partner's  Notice of Withdrawal or equivalent
         thereof,  the General  Partner and/or  Limited  Partners may invoke the
         purchase  rights  provided in Article 18.4 and shall be entitled to any
         other  remedy  at  law  or  equity  including  without   limitation  an
         injunction or suit for damages.

                  Article 18.4 of the Partnership Agreement is hereby amended by
deleting the current  provision in its entirety and by substituting the language
set forth below.

                           18.4 Breach of Article 15.3. In the event the General
         Partner  either  receives a Notice of Withdrawal as provided in Article
         15.3 or  receives  notice  of a breach  of  Article  15.3 by a  Limited
         Partner (the  "Defaulting  Limited  Partner"),  the General Partner may
         elect, in its sole  discretion,  to treat such event as a default under
         this  Agreement and enforce the provisions of this Article 18.4. If the
         General  Partner elects to enforce the provisions of this Article 18.4,
         the General  Partner  shall give written  notice of such  election (the
         "Notice of Default") to the Defaulting  Limited Partner within 180 days
         of the date the General Partner first received notice of the defaulting
         event.  Upon giving the Notice of Default,  the General Partner,  shall
         have the option to  purchase  at the  Closing  (as  defined  below) the
         Partnership   Interest  of  the  Defaulting   Limited   Partner  (which
         Defaulting  Limited  Partner  shall then become  obligated to sell such
         Partnership Interest) at the price determined in the manner provided in
         Article 18.6 of this Agreement and on the terms and conditions provided
         in Article 18.7 of this  Agreement.  The General  Partner  shall have a
         period of thirty (30) days  following the date of the Notice of Default
         (the  "First  Option  Period")  within  which to notify in writing  the
         Defaulting  Limited  Partner,  whether  the General  Partner  wishes to
         purchase all or a portion of the Partnership Interest of the Defaulting
         Limited Partner. If the General Partner does not elect to purchase the



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         entire  Partnership  Interest of the Defaulting  Limited Partner before
         the  expiration of the First Option  Period and in the manner  provided
         herein,  the Limited  Partners shall have the option to purchase all or
         any part of the Partnership  Interest of the Defaulting Limited Partner
         not  purchased by the General  Partner at the price  determined  in the
         manner  provided in Article 18.6 of this Agreement and on the terms and
         conditions  provided  in Article  18.7 of this  Agreement.  Any Limited
         Partner  desiring  to  purchase  any  part  or  all  of  the  remaining
         Partnership Interest of the Defaulting Limited Partner shall deliver to
         the General  Partner a written  election to purchase all or a specified
         portion  of such  Partnership  Interest  within the ten (10) day period
         immediately following the close of the First Option Period (the "Second
         Option  Period").  If the Limited  Partners in the  aggregate  elect to
         purchase  more  than the  Partnership  Interest  then  available,  each
         electing  Limited  Partner  shall have a priority,  up to that  portion
         specified in his or her notice of election, to purchase such proportion
         of the  Partnership  Interest of the  Defaulting  Limited  Partner then
         available  as his or her  Percentage  Interest  bears to the  aggregate
         Percentage Interests of the Limited Partners electing to purchase. That
         portion of the Defaulting  Limited Partner's  Partnership  Interest not
         purchased  on such a priority  basis shall be  allocated in one or more
         successive  allocations to those remaining Limited Partners electing to
         purchase  more of the  Partnership  Interest  than they have a priority
         right, up to the portion  specified in their respective  elections,  in
         the proportion  that each of their  Percentage  Interests  bears to the
         aggregate  Percentage  Interests of all of them. The Valuation Date for
         determining  the  price  paid  for  the  Defaulting  Limited  Partner's
         interest  under  Article  18.6  shall  be the  last  day  of the  month
         immediately   preceding  the  month  in  which  occurs  the  Notice  of
         Withdrawal or breach of Article 15.3.

                           Within the ten (10) day period immediately  following
         the close of the Second Option Period (the "Confirmation  Period"), the
         General  Partner  shall  inform each  electing  Limited  Partner of the
         portion of the Partnership  Interest of the Defaulting  Limited Partner
         as to which his or her election is effective. The General Partner shall
         give notice to the Defaulting  Limited  Partner within the ten (10) day
         period   following   the  close  of  the   Confirmation   Period   (the
         "Notification  Period")  of the  election  by the  Limited  Partners to
         exercise  their option.  Such notice shall  indicate the portion of the
         Defaulting  Limited  Partner's   Partnership   Interest  that  will  be
         purchased by each of the  purchasing  Limited  Partners and the General
         Partner, if any.

                       Confidentiality Provision Amendment

                  Article 15 of the  Partnership  Agreement is hereby amended by
adding a new Article 15.5 as set forth below:

15.5 Disclosure of Confidential  Information.  Each Limited Partner acknowledges
     and agrees that his or her participation in the Partnership under this




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         Agreement  necessarily  involves his or her understanding of and access
         to certain trade secrets and other confidential  information pertaining
         to the business of the Partnership.  Accordingly,  each Limited Partner
         (other than the General  Partner and its Affiliates  that may also hold
         Limited Partner  interests)  agrees that at all times during his or her
         participation  in the  Partnership as a Limited Partner and thereafter,
         he or she will not, directly or indirectly, without the express written
         authority of the  Partnership,  unless required by law or directed by a
         applicable  legal  authority  having   jurisdiction  over  the  Limited
         Partner, disclose or use for the benefit of any person,  corporation or
         other entity (other than the Partnership),  or himself or herself,  (i)
         any trade,  technical,  operational,  management or other secrets,  any
         patient or customer lists or other  confidential or secret data, or any
         other   proprietary,   confidential   or  secret   information  of  the
         Partnership or (ii) any confidential  information concerning any of the
         financial  arrangements,  financial  positions,  hospital or  physician
         contracts,  third  party  payor  arrangements,  quality  assurance  and
         outcome analysis  programs,  competitive  status,  customer or supplier
         matters, internal organizational matters, technical abilities, or other
         business  affairs  of or  relating  to  the  Partnership.  The  Limited
         Partners  (other than the General  Partner and its Affiliates  that may
         also  hold  Limited  Partner  interests)  acknowledge  that  all of the
         foregoing constitutes proprietary  information,  which is the exclusive
         property  of the  Partnership.  In the event of breach of this  Article
         15.5 as determined by the General  Partner,  the  Partnership  shall be
         entitled  to any remedy at law or equity with  respect to such  breach,
         including without limitation, an injunction or suit for damages.



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                                    EXHIBIT C

                      PURCHASE OPTION ASSIGNMENT AMENDMENT
                       -----------------------------------


                  Capitalized  terms  used in  this  Exhibit  and not  otherwise
defined  shall have the same  meaning as  provided in the  Agreement  of Limited
Partnership (the  "Partnership  Agreement") of San Diego  Lithotripters  Limited
Partnership (the "Partnership").

                      Purchase Option Assignment Amendment

                  Articles 18.1.2,  18.2.2, 18.3.2 and 18.4.2 are hereby amended
to allow the General  Partner to either  exercise  its  purchase  option  rights
during the First Option Period as provided in such  Articles,  or to assign such
purchase  option rights in whole or in part to the  Partnership.  If the General
Partner's  purchase  option rights are assigned to the  Partnership  as provided
herein,  the  Partnership  shall have the right to use  Partnership  revenues to
exercise  such  rights.  Further,  Articles  18.6 and 18.7 are also  amended  by
substituting the Partnership as a buyer to the extent the General Partner elects
to assign to the Partnership  its purchase option rights under Articles  18.1.2,
18.2.2,  18.3.2 and 18.4.2. If the Partnership  acquires a Partnership  Interest
pursuant to the terms of this Amendment, then the General Partner shall have the
authority  to amend  Schedule A to the  Partnership  Agreement  to  reflect  the
deletion  of the  interests  held by the  selling  Limited  Partners  (or  their
successors in interest),  and to reflect the increased  Percentage  Interests of
the remaining Partners resulting from the redemption.




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