Exhibit 10.57

                           WARRANT PURCHASE AGREEMENT

THIS WARRANT PURCHASE  AGREEMENT (the "Agreement") is made and entered into this
21st day of October,  1997 by and between IMATRON INC., a New Jersey corporation
(the "Company") and TeraRecon Inc., a Delaware corporation (the "Investor").

                                R E C I T A L S:

WHEREAS,  the Company  desires to issue to Investor and the Investor  desires to
purchase from the Company a warrant (the "Warrant") to purchase 2,000,000 shares
of the Company's  common stock (the  "Shares")  all on the terms and  conditions
hereinafter  provided.  The  Warrant and the Shares are  hereafter  collectively
referred to as the "Securities".

                    NOW, THEREFORE, IT IS AGREED AS FOLLOWS:

1. Issuance of Warrant.  For an aggregate  purchase price of One Million Dollars
($1,000,000),  the  receipt  and  sufficiency  of which is  acknowledged  by the
Company,  the Company agrees to issue to Investor the Warrant, the form of which
is attached hereto as Exhibit A.

2. Investor  Representations.  Investor  hereby  represents  and warrants to the
Company as follows:

(a) The Investor  understands  that: (a) The offer and sale of the Securities by
the Company to Investor has not been registered under the Securities Act of 1933
(the  "Securities  Act"),  in reliance on an  exemption  from such  registration
available  under  the  Securities  Act and  rules  adopted  thereunder;  (b) The
Investor  must  hold  the  Warrant   indefinitely   unless  the  Securities  are
subsequently  registered under the Securities Act and qualified under applicable
state  securities  laws,  or unless an  exemption  from  such  registration  and
qualification is available.

(b) The Investor is acquiring  the  Securities  for his or her own account,  for
investment,  and not with a view to any  sale or  distribution  of any  interest
therein.

(c) The Investor has such  knowledge  and  experience  in financial and business
matters as to be capable of evaluating  the merits and risks of an investment in
the  Securities,  and the Investor is able to bear the economic risks of such an
investment.

(d) All statements  made,  and  information  furnished,  by the Investor in this
certificate and all other information  furnished by the Investor to the Company,
are true and complete, to the best of the Investor's knowledge.

3. Restrictions on Transfer. The Investor agrees that:

(a) The Investor will not attempt to transfer the Securities in violation of the
restrictions set forth in this Agreement.

(b) The Company may note such restrictions on transfer in its records and refuse
to recognize any transfer which violates this agreement or for which the Company
has not received an  acceptable  opinion of counsel  stating that such  transfer
will not violate such restrictions.

(c) One or more legends  indicating a lack of registration  under the Securities
Act and a lack of qualification under state securities laws will be imprinted on
the Securities. One such legend shall read substantially as follows:

THE  SECURITIES  HAVE  NOT BEEN  REGISTERED  WITH THE  SECURITIES  AND  EXCHANGE
COMMISSION UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND ANY SALE, TRANSFER,
PLEDGE OR OTHER DISPOSITION THEREOF MAY BE MADE ONLY (i) IN A REGISTRATION UNDER
SAID ACT OR (ii) IF AN EXEMPTION FROM  REGISTRATION  UNDER SAID ACT IS AVAILABLE
AND THE  COMPANY HAS  RECEIVED  AN OPINION OF COUNSEL TO THAT EFFECT  REASONABLY
SATISFACTORY TO IT.

4. Binding on Successors;  Indemnification.  The Investor  agrees that the above
representations  and  warranties  are binding on the  Investor's  successors and
assigns and are made for the  benefit of the  Company and any other  persons who
may become liable for violations of federal or state securities laws as a result
of the  falsity of any of the  Investor's  representations  or  warranties.  The
Investor  agrees to indemnify,  defend,  and hold harmless such persons from any
liability arising from the falsity of any of the Investor's  representations  or
warranties or from the breach of any covenant of Investor contained herein.

5.  Registration  Rights.  The Company  hereby  grants to Investor the following
registration rights with respect to the Shares:

(a) Definitions.

"Commission"  shall mean the  Securities  and Exchange  Commission  or any other
federal  agency  at the  time  administering  the  Securities  Act of 1933  (the
"Securities Act").

"Register," "registered," and "registration" refer to a registration effected by
preparing and filing a registration  statement in compliance with the Securities
Act of 1933,  and the  declaration  or  ordering  of the  effectiveness  of such
registration statement.

"Registration  Expenses"  shall mean all  expenses  incurred  by the  Company in
compliance with the provisions of this Section 5, including, without limitation,
all registration and filing fees,  printing expenses,  fees and disbursements of
counsel for the  Company,  blue sky fees and  expenses,  and the expenses of any
special audits incident to or required by any such  registration  (but excluding
the compensation of regular employees of the Company, which shall be paid in any
event by the Company).

"Selling Expenses" shall mean all underwriting discounts and selling commissions
applicable  to the sale of Shares and all fees and  disbursements  of counsel to
Investor.

"Shares"  means the  shares  of the  Company's  common  stock  exercisable  upon
exercise of the Warrant and any common stock issued with respect  thereto  (e.g.
upon a stock split or stock dividend.

"Investor" means the person set forth above and any permitted assignee.

(b) Company Registration.

i) Notice of  Registration.  If, at any time after the date hereof,  the Company
shall determine to register any of its securities  either for its own account or
the account of a security holder or holders  exercising their respective  demand
registration  rights,  other than a  registration  relating  solely to  employee
benefit  plans,  or a  registration  relating  solely to a  Commission  Rule 145
transaction,  or a registration on any  registration  form which does not permit
secondary sales, the Company will:

a) promptly give to Investor  written notice thereof (which shall include a list
of the  jurisdictions  in which the Company  intends to attempt to qualify  such
securities under the applicable blue sky or other state
securities laws); and

b) include in such  registration (and any related  qualification  under blue sky
laws or other  compliance),  and in any underwriting  involved therein,  all the
Shares  specified  in a written  request or  requests,  made by Investor  within
fifteen (15) days after receipt of the written notice from the Company described
in this clause (i), except as set forth in
Section 5(b)(ii) below.

ii) Underwriting. If the registration of which the Company gives notice is for a
registered  public  offering  involving an  underwriting:  the Company  shall so
advise  Investor as part of the written  notice  given  pursuant to Section 5(b)
hereof.  In such event,  the right of Investor to registration  pursuant to this
Section  5  shall  be  conditioned   upon  Investor's   participation   in  such
underwriting  and the inclusion of Investor's  Shares in the underwriting to the
extent provided herein. Investor shall (together with the Company, its directors
and officers,  and any other shareholders  distributing their securities through
such underwriting)  enter into an underwriting  agreement in customary form with
the underwriter or underwriters selected for underwriting by the Company.

Notwithstanding  any  other  provision  of this  Section  5, if the  underwriter
determines  that marketing  factors require a limitation on the number of shares
to be  underwritten,  the  underwriter  may exclude from such  registration  and
underwriting  some or all of the Shares which would  otherwise  be  underwritten
pursuant hereto.  Any securities so excluded shall be apportioned pro rata among
Investor and any other  shareholders  distributing their securities through such
underwriting  according to the total amount of securities  otherwise entitled to
be included therein owned by such  shareholders or in such other  proportions as
shall mutually be agreed upon.

If Investor  disapproves of the terms of any such underwriting,  it may elect to
withdraw  therefrom by written  notice to the Company and the  underwriter.  Any
Shares excluded or withdrawn from such underwriting shall be withdrawn from such
registration.

The Company shall bear all Registration Expenses incurred in connection with any
registration,  qualification  and  compliance  by the  Company  pursuant to this
Section  5(b).  All  Selling  Expenses  shall  be borne  by the  holders  of the
securities so registered  pro rata on the basis of the number of their shares so
registered.

iii)  Registration  Procedures.  In the  case of  registration  effected  by the
Company  pursuant to this Agreement,  the Company will keep Investor  advised in
writing as to the initiation of registration  and as to the completion  thereof.
At its expense, the Company will:

a) keep such  registration  effective for a period of one year or until Investor
has completed the distribution  described in the registration statement relating
thereto, whichever first occurs;

b) furnish such number of prospectuses  and other documents  incident thereto as
Investor from time to time may reasonably request; and

c) use its best efforts to register or qualify the Shares  under the  securities
or blue  sky laws of such  jurisdictions  as  Investor  may  request;  provided,
however,  that the Company  shall not be  obligated  to register or qualify such
Shares in any particular  jurisdiction in which the Company would be required to
execute a  general  consent  to  service  of  process  in order to  effect  such
registration,  qualification,  or  compliance,  unless  the  Company  is already
subject to service in such  jurisdiction  and except as may be  required  by the
Securities Act or applicable rules or regulations thereunder.

d) Notify the holder of Shares  covered by such  registration  statement  at any
time when a prospectus  relating  thereto is required to be delivered  under the
Act of the happening of any event as a result of which the  prospectus  included
in such registration  statement, as then in effect, includes an untrue statement
of a  material  fact or omits to state a  material  fact  required  to be stated
therein or necessary to make the statements  therein not misleading in the light
of the circumstances then existing.

(c)  Request  for  Registration.  In case the  Company  shall  receive  from the
Investor  a  written   request  that  the  Company   effect  any   registration,
qualification,  or  compliance  with  respect to all or a part of the Shares the
Company  will:  (i) as soon as  practicable,  use its  diligent  best efforts to
effect  all  such  registrations,  qualifications  and  compliances  (including,
without  limitations,  the execution of an  undertaking  to file  post-effective
amendments,  appropriate  qualifications  under the applicable blue sky or other
state  securities  laws and appropriate  compliance  with exemptive  regulations
issued  under the  Securities  Act and any other  governmental  requirements  or
regulations)  as may be so requested and as would permit or facilitate  the sale
and  distribution  of all  or  such  portion  of the  Investor's  Shares  as are
specified in such  request,  together  with all or such portion of the Shares of
any Holder or  Holders  joining in such  request as are  specified  in a written
request given within  thirty days after receipt of such written  notice from the
Company;  provided that the Company shall not be obligated to take any action to
effect  such  registration,   qualification  or  compliance   pursuant  to  this
subparagraph  5(c):  (A) After the Company has effected  two such  registrations
pursuant to this subparagraph 5(c) and such  registrations have been declared or
ordered effective;  or (B) If the amount of securities being offered for sale is
less than 25 percent of the Shares.

Subject to the  foregoing  clauses (A)  through  (B),  the Company  shall file a
registration statement covering the Shares so requested to be registered as soon
as practical,  but in any event within ninety days, after receipt of the request
or requests  of the  Investor;  provided,  however,  that if the  Company  shall
furnish to such  Investor a  certificate  signed by the President of the Company
stating  that in the good faith  judgment of the Board of  Directors it would be
seriously  detrimental to the Company and it stockholders for such  registration
statement  to be filed at the date filing  would be required and it is therefore
essential to defer the filing of such registration statement,  the Company shall
have an additional period of not more than ninety days within which to file such
registration statement.

The Investor shall bear all  Registration  Expenses  incurred in connection with
any  registration,  qualification and compliance by the Company pursuant to this
Section  5(c).  All  Selling  Expenses  shall  be borne  by the  Holders  of the
securities so registered  pro rata on the basis of the number of their shares so
registered.

(d)      Indemnification.

i) The Company will indemnify the Investor, each of its officers,  directors and
partners,  and each  person  controlling  such  Investor  within the  meaning of
Section  15 of the  Securities  Act or the  1934  Act,  with  respect  to  which
registration,  qualification  or compliance  has been effected  pursuant to this
Agreement,  and each  underwriter,  if any,  and each  person who  controls  any
underwriter  within the meaning of Section 15 of the  Securities Act or the 1934
Act, against all expenses, claims, losses, damages or liabilities (or actions in
respect thereof),  including any of the foregoing  incurred in settlement of any
litigation,  commenced  or  threatened,  arising  out of or based on any  untrue
statement (or alleged  untrue  statement)  of a material  fact  contained in any
registration statement,  prospectus, offering circular or other document, or any
amendment   or   supplement   thereto,   incident  to  any  such   registration,
qualification or compliance,  or based on any omission (or alleged  omission) to
state therein a material fact required to be stated therein or necessary to make
the statements  therein,  in the light of the  circumstances  in which they were
made, not misleading,  or any violation by the Company of the Securities Act, or
the 1934 Act, or any rule or regulation promulgated under the Securities Act, or
the 1934 Act, or under any state securities law or under common law,  applicable
to the  Company  in  connection  with any such  registration,  qualification  or
compliance,  and the Company will reimburse the Investor,  each of its officers,
directors  and partners,  and each person  controlling  the Investor,  each such
underwriter and each person who controls any such underwriter, for any legal and
any other  expenses  reasonably  incurred,  as such  expenses are  incurred,  in
connection  with  investigating,  preparing or defending  any such claim,  loss,
damage,  liability or action;  provided,  however,  that the Company will not be
liable (i) for  amounts  paid in  settlement  of any such loss,  claim,  damage,
liability or action if such  settlement  is effected  without the consent of the
Company (which consent shall not be unreasonably  withheld) and (ii) in any such
case to the extent  that any such  claim,  loss,  damage,  liability  or expense
arises out of or is based on any untrue  statement or omission or alleged untrue
statement  or omission,  made in reliance  upon and in  conformity  with written
information  furnished  to the  Company by an  instrument  duly  executed by the
Investor,  controlling  person or underwriter and stated to be specifically  for
use therein.

ii) The  Investor  will,  if Shares  held by the  Investor  are  included in the
securities as to which such  registration,  qualification or compliance is being
effected,  indemnify  the Company,  each of its  directors  and  officers,  each
underwriter,  if any, of the Company's securities covered by such a registration
statement,  each person who controls the Company or such underwriter  within the
meaning of Section 15 of the Securities Act against all claims,  losses, damages
and liabilities (or actions in respect  thereof)  arising out of or based on any
untrue  statement (or alleged untrue  statement) of a material fact contained in
any  such  registration  statement,   prospectus,  offering  circular  or  other
document, or any omission (or alleged omission) to state therein a material fact
required to be stated  therein or necessary to make the  statements  therein not
misleading, and will reimburse the Company, such directors,  officers,  persons,
underwriters or control  persons for any legal or any other expenses  reasonably
incurred in connection  with  investigating  or defending any such claim,  loss,
damage, liability or action, in each case to the extent, but only to the extent,
that such untrue statement (or alleged untrue statement) or omission (or alleged
omission) is made in such registration statement,  prospectus, offering circular
or other  document in reliance upon and in conformity  with written  information
furnished  to the Company by an  instrument  duly  executed by the  Investor and
stated to be specifically for use therein.  Notwithstanding  the foregoing,  the
liability of the Investor under this subsection  shall not apply to amounts paid
in  settlement  of any such loss,  claim,  damage,  liability  or action if such
settlement is effected  without the consent of the Investor (which consent shall
not be unreasonably  withheld),  and (ii) shall be limited in an amount equal to
the  aggregate  net proceeds of the shares sold by the  Investor,  except to the
extent such  liability  arises out of or is based on willful  misconduct  by the
Investor.

iii) Each  party  entitled  to  indemnification  under  this  Section  5(d) (the
"Indemnified  Party")  shall  give  notice  to the  party  required  to  provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the  Indemnifying  Party to assume  the  defense of any such claim or any
litigation  resulting  therefrom,  provided  that  counsel for the  Indemnifying
Party,  who shall  conduct  the  defense of such claim or  litigation,  shall be
approved by the  Indemnified  Party (whose  approval shall not  unreasonably  be
withheld),  and the  Indemnified  Party may  participate in such defense at such
party's expense,  and provided further that the failure of any Indemnified Party
to give notice as provided  herein shall not relieve the  Indemnifying  Party of
its  obligations  under this Agreement  except to the extent that the failure to
give such notice is materially prejudicial to an Indemnifying Party's ability to
defend such action and provided further,  that the Indemnifying  Party shall not
assume the  defense  for  matters as to which there is a conflict of interest or
separate  and  different  defenses,  but shall pay the fees and  expenses of one
separate counsel retained by the Indemnified Party in the event of such conflict
of  interest.  No  Indemnifying  Party,  in the  defense  of any  such  claim or
litigation, shall, except with the consent of each Indemnified Party, consent to
entry of any judgment or enter into any settle-ment which does not include as an
unconditional  term  thereof  the giving by the  claimant or  plaintiff  to such
Indemnified  Party of a release  from all  liability in respect to such claim or
litigation.

iv) If the indemnification  provided for in this Section 5(d) is held by a court
of competent jurisdiction to be unavailable to an indemnified party with respect
to any loss, liability,  claim, damage, or expense referred to therein, then the
Indemnifying  Party, in lieu of indemnifying  such Indemnified  Party hereunder,
shall  contribute to the amount paid or payable by such  Indemnified  Party as a
result of such loss, liability,  claim, damage, or expense in such proportion as
is appropriate to reflect the relative  fault of the  Indemnifying  Party on the
one  hand and of the  Indemnified  Party on the  other  in  connection  with the
statements or omissions that resulted in such loss, liability, claim, damage, or
expense as well as any other  relevant  equitable  considerations.  The relative
fault of the Indemnifying Party and of the Indemnified Party shall be determined
by  reference  to,  among other  things,  whether  the untrue or alleged  untrue
statement of a material fact or the omission to state a material fact relates to
information  supplied by the indemnifying  party or by the indemnified party and
the parties' relative intent, knowledge, access to information,  and opportunity
to correct or prevent such statement or omission.

v) The obligations of the Company and the Investor under this Section 5(d) shall
survive the  completion  of any offering of Shares in a  registration  statement
under this Section 5 and otherwise.

vi) Information by Investor. The Investor of Shares included in any registration
shall furnish to the Company such  information  regarding  Investor,  the Shares
held by it and the  distribution  proposed  by such  Investor as the Company may
reasonably request in writing and as shall be reasonably  required in connection
with  any  registration,   qualification  or  compliance  referred  to  in  this
Agreement.

vii)  Transfer  of  Registration  Rights.  The  rights to cause the  Company  to
register  securities  granted  Holders  under  Section  5 may be  assigned  to a
transferee or assignee in  connection  with any transfer or assignment of Shares
by a Holder  provided  that:  (i) such  transfer  may  otherwise  be effected in
accordance with applicable  securities laws and (ii) such assignee or transferee
becomes a party to this  Agreement  and  assumes all of the  obligations  of the
transferring Holder under Section 5.

6. Rule 144 Reporting.  With a view to making  available the benefits of certain
rules and regulations of the Commission which may at any time permit the sale of
the Shares to the public without registration, Imatron agrees to use its best
efforts to:

(a) Make and keep public  information  available,  as those terms are understood
and  defined  in Rule 144  under the  Securities  Act,  at all  times  after the
effective date that Imatron becomes subject to the reporting requirements of the
Securities Act or the Securities
Exchange Act of 1934, as amended.

(b) File with the Commission in a timely manner all reports and other  documents
required of Imatron under the Securities Act and the Securities  Exchange Act of
1934,  as amended  (at any time after it has  become  subject to such  reporting
requirements); and

(c) So long as Investor owns any Shares,  to furnish to the Purchaser  forthwith
upon  request a written  statement  by  Imatron  as to its  compliance  with the
reporting  requirements  of said Rule 144 (at any time  after  ninety  (90) days
after the effective date of the first  registration  state-ment filed by Imatron
for an offering of its securities to the general public),  and of the Securities
Act and the  Securities  Exchange  Act of 1934 (at any time  after it has become
subject to such  reporting  requirements),  a copy of the most recent  annual or
quarterly report of the Company, and such other reports and documents of Imatron
and other  information in the possession of or reasonably  obtainable by Imatron
as a  Shareholder  may  reasonably  request  in  availing  itself of any rule or
regulation of the Commission  allowing a Shareholder to sell any such securities
without registration.

7.  Governing  Law.  This  Agreement  shall  be  governed  by and  construed  in
accordance with the laws of the State of California.

8.  Counterparts.  This Agreement may be executed in any number of counterparts,
each of which shall be an original,  but all of which together shall  constitute
one instrument.

IN WITNESS  WHEREOF,  the  undersigned  purchasers of securities and the Company
have executed this Agreement as of the day and year first above written.


                                    COMPANY:

                                  IMATRON INC.



                                       By:
                                    President


                                    INVESTOR:

                                 TERARECON INC.



                                       By:
                                       Its