<PAGE>

                                                                 EXHIBIT 10.31


THE WARRANT REPRESENTED BY THIS CERTIFICATE AND THE SHARES ISSUABLE UPON
EXERCISE HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"), OR ANY STATE SECURITIES LAWS AND NEITHER SUCH SECURITIES
NOR ANY INTEREST THEREIN MAY BE OFFERED, SOLD, PLEDGED, ASSIGNED OR OTHERWISE
TRANSFERRED UNLESS (1) A REGISTRATION STATEMENT WITH RESPECT THERETO IS
EFFECTIVE UNDER THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS, OR (2) THE
COMPANY RECEIVES AN OPINION OF COUNSEL TO THE HOLDER OF SUCH SECURITIES, WHICH
COUNSEL AND OPINION ARE REASONABLY SATISFACTORY TO THE COMPANY, THAT SUCH
SECURITIES MAY BE OFFERED, SOLD, PLEDGED, ASSIGNED OR TRANSFERRED IN THE MANNER
CONTEMPLATED WITHOUT AN EFFECTIVE REGISTRATION STATEMENT UNDER THE ACT OR
APPLICABLE STATE SECURITIES LAWS.


                                 ECHOCATH, INC.

          Warrants for the Purchase of Shares of Class A Common Stock,
                             no par value per share

                      These Warrants Expire on June 1, 2004


                                                              575,000 Warrants

         THIS CERTIFIES that, for value received, Joseph J. Prischak, with an
address at 2425 West 23rd Street, Erie, Pennsylvania 16506 (including any
permitted transferee, the "Holder"), is the registered holder of the number of
warrants set forth above, each of which represents the right to purchase one
fully paid and nonassessable share of the Class A common stock, no par value
("Common Stock"), of EchoCath, Inc., a New Jersey corporation (the "Company"),
at an initial exercise price equal to $0.14 (fourteen cents) per share (subject
to adjustment as provided herein) (the "Exercise Price") upon the terms and
conditions set forth herein, at any time or from time to time before 5:00 P.M.
on June 1, 2004, New York time (the "Exercise Period").

         As used herein, the term "this Warrant" shall mean and include this
Warrant and any Warrant or Warrants hereafter issued as a consequence of the
exercise or transfer of this Warrant in whole or in part.

         The number of shares of Common Stock issuable upon exercise of the
Warrants (the "Warrant Shares") and the Exercise Price may be adjusted from time
to time as hereinafter set forth.

                  The Holder is also entitled to all rights described in the
subscription agreement between the Company and the original holder of this
Warrant, including, without limitation, certain registration rights.

         1. This Warrant may be exercised during the Exercise Period, as to the
whole or any lesser number of whole Warrant Shares, by the surrender of this
Warrant (with the election at the end hereof duly executed) to the Company, 4326

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<PAGE>

US Route 1, Monmouth Junction, New Jersey 08822, Attention: Dr. David
Vilkomerson, or at such other place as is designated in writing by the Company.
Such executed election must be accompanied by payment in an amount equal to the
Exercise Price multiplied by the number of Warrant Shares for which this Warrant
is being exercised. Such payment may be made by certified or bank cashier's
check payable to the order of the Company.

         2. Upon each exercise of the Holder's rights to purchase Warrant
Shares, the Holder shall be deemed to be the holder of record of the Warrant
Shares issuable upon such exercise, notwithstanding that the transfer books of
the Company shall then be closed or certificates representing such Warrant
Shares shall not then have been actually delivered to the Holder. As soon as
practicable after each such exercise of this Warrant, the Company shall issue
and deliver to the Holder a certificate or certificates for the Warrant Shares
issuable upon such exercise, registered in the name of the Holder or its
designee. If this Warrant should be exercised in part only, the Company shall,
upon surrender of this Warrant for cancellation, execute and deliver a new
Warrant evidencing the right of the Holder to purchase the balance of the
Warrant Shares (or portions thereof) subject to purchase hereunder.

         3. (a) Any Warrants issued upon the transfer or exercise in part of
this Warrant shall be numbered and shall be registered in a Warrant Register as
they are issued. The Company shall be entitled to treat the registered holder of
any Warrant on the Warrant Register as the owner in fact thereof for all
purposes and shall not be bound to recognize any equitable or other claim to or
interest in such Warrant on the part of any other person, and shall not be
liable for any registration or transfer of Warrants which are registered or to
be registered in the name of a fiduciary or the nominee of a fiduciary unless
made with the actual knowledge that a fiduciary or nominee is committing a
breach of trust in requesting such registration or transfer, or with the
knowledge of such facts that its participation therein amounts to bad faith.
This Warrant shall be transferable only on the books of the Company upon
delivery thereof duly endorsed by the Holder or by his duly authorized attorney
or representative, or accompanied by proper evidence of succession, assignment,
or authority to transfer. In all cases of transfer by an attorney, executor,
administrator, guardian, or other legal representative, duly authenticated
evidence of his or its authority shall be produced. Upon any registration of
transfer, the Company shall deliver a new Warrant or Warrants to the person
entitled thereto. This Warrant may be exchanged, at the option of the Holder
thereof, for another Warrant, or other Warrants of different denominations, of
like tenor and representing in the aggregate the right to purchase a like number
of Warrant Shares (or portions thereof), upon surrender to the Company or its
duly authorized agent. Notwithstanding the foregoing, the Company shall have no
obligation to cause Warrants to be transferred on its books to any person if, in
the opinion of counsel to the Company, such transfer does not comply with the
provisions of the Act and the rules and regulations thereunder.

         (b) The Holder acknowledges that the Holder has been advised by the
Company that neither this Warrant nor the Warrant Shares have been registered
under the Act, that this Warrant is being or has been issued and the Warrant
Shares may be issued on the basis of the statutory exemption provided by Section
4(2) of the Act or Regulation D promulgated thereunder, or both, relating to
transactions by an issuer not involving any public offering, and that the

                                       31
<PAGE>

Company's reliance thereon is based in part upon the representations made by the
original Holder in the original Holder's subscription agreement, dated the date
hereof between the Company and the original Holder hereof (the "Subscription
Agreement"), executed and delivered in accordance with the terms of the
Offering. The Holder acknowledges that he has been informed by the Company of,
or is otherwise familiar with, the nature of the limitations imposed by the Act
and the rules and regulations thereunder on the transfer of securities. In
particular, the Holder agrees that no sale, assignment or transfer of this
Warrant or the Warrant Shares issuable upon exercise hereof shall be valid or
effective, and the Company shall not be required to give any effect to any such
sale, assignment or transfer, unless (i) the sale, assignment or transfer of
this Warrant or such Warrant Shares is registered under the Act, it being
understood that neither this Warrant nor such Warrant Shares are currently
registered for sale and that the Company has no obligation or intention to so
register this Warrant or such Warrant Shares except as specifically provided
herein, or (ii) this Warrant or such Warrant Shares are sold, assigned or
transferred in accordance with all the requirements and limitations of Rule 144
promulgated under the Act, it being understood that Rule 144 is not available at
the time of the original issuance of this Warrant for the sale of this Warrant
or such Warrant Shares and that there can be no assurance that Rule 144 sales
will be available at any subsequent time, or (iii) such sale, assignment, or
transfer is otherwise exempt from registration under the Act.

         4. The Company shall at all times reserve and keep available out of its
authorized and unissued Common Stock, solely for the purpose of providing for
the exercise of the rights to purchase all Warrant Shares granted pursuant to
the Warrants, such number of shares of Common Stock as shall, from time to time,
be sufficient therefor. The Company covenants that all shares of Common Stock
issuable upon exercise of this Warrant, upon receipt by the Company of the full
purchase price therefor, shall be validly issued, fully paid, nonassessable, and
free of preemptive rights.

         5. (a) In case the Company shall at any time after the date the
Warrants were first issued (i) declare a dividend on the outstanding Common
Stock payable in shares of its capital stock, (ii) subdivide the outstanding
Common Stock, (iii) combine the outstanding Common Stock into a smaller number
of shares, or (iv) issue any shares of its capital stock by reclassification of
the Common Stock (including any such reclassification in connection with a
consolidation or merger in which the Company is the continuing corporation),
then, in each case, the Exercise Price, and the number of Warrant Shares
issuable upon exercise of this Warrant, in effect at the time of the record date
for such dividend or of the effective date of such subdivision, combination, or
reclassification, shall be proportionately adjusted so that the Holder after
such time shall be entitled to receive the aggregate number and kind of shares
which, if such Warrant had been exercised immediately prior to such time, he
would have owned upon such exercise and been entitled to receive by virtue of
such dividend, subdivision, combination, or reclassification. Such adjustment
shall be made successively whenever any event listed above shall occur.

         No adjustment in the Exercise Price shall be required if such
adjustment is less than $.05 (which amount will be proportionately adjusted in
the event of stock splits or the like); provided, however, that any adjustments
which by reason of this Section 5 are not required to be made shall be carried
forward and taken into account in any subsequent adjustment. All calculations

                                       32
<PAGE>

under this Section 5 shall be made to the nearest cent or to the nearest
one-thousandth of a share, as the case may be.

            (b) In any case in which this Section 5 shall require that an
adjustment in the Exercise Price be made effective as of a record date for a
specified event, the Company may elect to defer, until the occurrence of such
event, issuing to the Holder, if the Holder exercised this Warrant after such
record date, the shares of Common Stock, if any, issuable upon such exercise
over and above the shares of Common Stock, if any, issuable upon such exercise
on the basis of the Exercise Price in effect prior to such adjustment; provided,
however, that the Company shall deliver to the Holder a due bill or other
appropriate instrument evidencing the Holder's right to receive such additional
shares upon the occurrence of the event requiring such adjustment.

            (c) Whenever there shall be an adjustment as provided in this
Section 5, the Company shall promptly cause written notice thereof to be sent by
certified or registered mail, postage prepaid, to the Holder, at its address as
it shall appear in the Warrant Register, which notice shall be accompanied by an
officer's certificate setting forth the number of Warrant Shares purchasable
upon the exercise of this Warrant and the Exercise Price after such adjustment
and setting forth a brief statement of the facts requiring such adjustment and
the computation thereof, which officer's certificate shall be conclusive
evidence of the correctness of any such adjustment absent manifest error.

            (d) The Company shall not be required to issue fractions of shares
of Common Stock or other capital stock of the Company upon the exercise of this
Warrant. If any fraction of a share would be issuable on the exercise of this
Warrant (or specified portions thereof), the Company shall purchase such
fraction for an amount in cash equal to the same fraction of the market price of
such share of Common Stock on the date of exercise of this Warrant, as
determined in good faith by the Company's Board of Directors.

         6. (a) In case of any consolidation with or merger of the Company with
or into another corporation (other than a merger or consolidation in which the
Company is the surviving or continuing corporation), or in case of any sale,
lease, or conveyance to another corporation of the property and assets of any
nature of the Company as an entirety or substantially as an entirety, such
successor, leasing, or purchasing corporation, as the case may be, shall (i)
execute with the Holder an agreement providing that the Holder shall have the
right thereafter to receive upon exercise, of this Warrant solely the kind and
amount of shares of stock and other securities, property, cash, or any
combination thereof receivable upon such consolidation, merger, sale, lease, or
conveyance by a holder of the number of shares of Common Stock for which this
Warrant might have been exercised immediately prior to such consolidation,
merger, sale, lease, or conveyance, and (ii) make effective provision in its
certificate of incorporation or otherwise, if necessary, to effect such
agreement. Such agreement shall provide for adjustments which shall be as nearly
equivalent as practicable to the adjustments in Section 5 above.

                                       33
<PAGE>

            (b) In case of any reclassification or change of the shares of
Common Stock issuable upon exercise of this Warrant (other than a change in par
value or from a specified par value to no par, or as a result of a subdivision
or combination, but including any change in the shares into two or more classes
or series of shares), or in case of any consolidation or merger of another
corporation into the Company in which the Company is the continuing corporation
and in which there is a reclassification or change (including a change to the
right to receive cash or other property) of the shares of Common Stock (other
than a change in par value, or from no par value to a specified par value, or as
a result of a subdivision or combination, but including any change in the shares
into two or more classes or series of shares), the Holder shall have the right
thereafter to receive upon exercise of this Warrant solely the kind and amount
of shares of stock and other securities, property, cash, or any combination
thereof receivable upon such reclassification, change, consolidation, or merger
by a holder of the number of shares of Common Stock for which this Warrant might
have been exercised immediately prior to such reclassification, change,
consolidation, or merger. Thereafter, appropriate provision shall be made for
adjustments which shall be as nearly equivalent as practicable to the
adjustments in Section 5.

            (c) Notwithstanding anything to the contrary herein contained, in
the event of a transaction contemplated by Section 6(a) in which the surviving,
continuing, successor, or purchasing corporation demands that all outstanding
convertible notes and warrants be extinguished prior to the closing date of the
contemplated transaction, the Company shall give prior notice (the "Merger
Notice") thereof to the Holders advising them of such transaction. The Holders
shall have ten days after the date of the Merger Notice to elect to (i) exercise
the Warrants in the manner provided herein or (ii) receive from the surviving,
continuing, successor, or purchasing corporation the same consideration
receivable by a holder of the number of shares of Common Stock for which this
Warrant might have been exercised immediately prior to such consolidation,
merger, sale, or purchase reduced by such amount of the consideration as has a
market value equal to the Exercise Price, as determined by the board of
directors of the Company, whose determination shall be conclusive absent
manifest error. If any Holder fails to timely notify the Company of its
election, the Holder shall be deemed for all purposes to have elected the option
set forth in (ii) above. Any amounts receivable by a Holder who has elected the
option set forth in (ii) above shall be payable at the same time as amounts
payable to stockholders in connection with any such transaction.

            (d) The above provisions of this Section 6 shall similarly apply to
successive reclassifications and changes of shares of Common Stock and to
successive consolidations, mergers, sales, leases, or conveyances.

         7. In case at any time the Company shall propose to:

            (a) pay any dividend or make any distribution on shares of Common
Stock in shares of Common Stock or make any other distribution (other than
regularly scheduled cash dividends which are not in a greater amount per share
than the most recent such cash dividend) to all holders of Common Stock; or

                                       34
<PAGE>

            (b) issue any rights, warrants, or other securities to all holders
of Common Stock entitling them to purchase any additional shares of Common Stock
or any other rights, warrants, or other securities; or

            (c) effect any reclassification or change of outstanding shares of
Common Stock, or any consolidation, merger, sale, lease, or conveyance of
property, described in Section 6; or

            (d) effect any liquidation, dissolution, or winding-up of the
Company;


then, and in any one or more of such cases, the Company shall give written
notice thereof, by certified or registered mail, postage prepaid, to the Holder
at the Holder's address as it shall appear in the Warrant Register, mailed at
least 15 days prior to (i) the date as of which the holders of record of shares
of Common Stock to be entitled to receive any such dividend, distribution,
rights, warrants, or other securities are to be determined, (ii) the date on
which any such reclassification, change of outstanding shares of Common Stock,
consolidation, merger, sale, lease, conveyance of property, liquidation,
dissolution, or winding-up is expected to become effective, and the date as of
which it is expected that holders of record of shares of Common Stock shall be
entitled to exchange their shares for securities or other property, if any,
deliverable upon such reclassification, change of outstanding shares,
consolidation, merger, sale, lease, conveyance of property, liquidation,
dissolution, or winding-up, or (iii) the date of such action which would require
an adjustment to the Exercise Price.

         8. The issuance of any shares or other securities upon the exercise of
this Warrant, and the delivery of certificates or other instruments representing
such shares or other securities, shall be made without charge to the Holder for
any tax or other charge in respect of such issuance. The Company shall not,
however, be required to pay any tax which may be payable in respect of any
transfer involved in the issue and delivery of any certificate in a name other
than that of the Holder and the Company shall not be required to issue or
deliver any such certificate unless and until the person or persons requesting
the issue thereof shall have paid to the Company the amount of such tax or shall
have established to the satisfaction of the Company that such tax has been paid.

         9. The Warrant Shares issued upon exercise of the Warrants shall be
subject to a stop transfer order and the certificate or certificates evidencing
such Warrant Shares shall bear the following legend:

         "The securities represented by this certificate have not been
         registered under the Securities Act of 1933, as amended (the
         "Act"), or any state securities laws and neither such
         securities nor any interest therein may be offered, sold,
         pledged, assigned or otherwise transferred unless (1) a
         registration statement with respect thereto is effective under
         the Act and any applicable state securities laws, or (2) the
         Company receives an opinion of counsel to the holder of such
         securities, which counsel and opinion are reasonably

                                  35
<PAGE>

         satisfactory to the Company, that such securities may be
         offered, sold, pledged, assigned or transferred in the manner
         contemplated without an effective registration statement under
         the Act or applicable state securities laws."

         10. Upon receipt of evidence satisfactory to the Company of the loss,
theft, destruction, or mutilation of any Warrant (and upon surrender of any
Warrant if mutilated), and upon reimbursement of the Company's reasonable
incidental expenses and indemnity reasonably satisfactory to the Company, the
Company shall execute and deliver to the Holder thereof a new Warrant of like
date, tenor, and denomination.

         11. The Holder of any Warrant shall not have solely on account of such
status, any rights of a stockholder of the Company, either at law or in equity,
or to any notice of meetings of stockholders or of any other proceedings of the
Company, except as provided in this Warrant.

         12. This Warrant has been negotiated and consummated in the State of
New Jersey and shall be construed in accordance with the laws of the State of
New Jersey applicable to contracts made and performed within such State, without
regard to principles governing conflicts of law.

         13. Each of the Company and the Holder of this Warrant, irrevocably
consents to the jurisdiction of the courts of the State of New Jersey and of any
federal court located in such State in connection with any action or proceeding
arising out of or relating to this Warrant, any document or instrument delivered
pursuant to, in connection with or simultaneously with this Warrant, or a breach
of this Warrant or any such document or instrument. In any such action or
proceeding, the Company waives personal service of any summons, complaint or
other process and agrees that service thereof may be made in accordance with
Section 15 hereof.

         14. Any notice or other communication required or permitted to be given
hereunder shall be in writing and shall be mailed by certified mail, return
receipt requested, or by Federal Express, Express Mail or similar overnight
delivery or courier service or delivered (in person or by telecopy, telex or
similar telecommunications equipment) against receipt to the party to whom it is
to be given, (i) if to the Company, at 4326 US Route 1, Monmouth Junction, New
Jersey 08822, Attention: Dr. David Vilkomerson, (ii) if to the Holder, at its
address set forth on the first page hereof, or (iii) in either case, to such
other address as the party shall have furnished in writing in accordance with
the provisions of this Section 15. Notice to the estate of any party shall be
sufficient if addressed to the party as provided in this Section 15. Any notice
or other communication given by certified mail shall be deemed given at the time
of certification thereof, except for a notice changing a party's address which
shall be deemed given at the time of receipt thereof. Any notice given by other
means permitted by this Section 15 shall be deemed given at the time of receipt
thereof.

         15. No course of dealing and no delay or omission on the part of the
Holder in exercising any right or remedy shall operate as a waiver thereof or
otherwise prejudice the Holder's rights, powers or remedies. No right, power or

                                       36
<PAGE>

remedy conferred by this Warrant upon the Holder shall be exclusive of any other
right, power or remedy referred to herein or now or hereafter available at law,
in equity, by statute or otherwise, and all such remedies may be exercised
singly or concurrently.

         16. This Warrant may be amended or any of its provisions waived only by
a written consent or consents executed by the Company and Holders of Warrants
representing a majority of the shares underlying the Warrants issued and
outstanding to investors pursuant to the Memorandum. Any amendment or waiver
shall be binding upon all existing and future Holders.



Dated: May __, 2001


                                       ECHOCATH, INC.




                                       By:   ________________________________
                                             Name:  Frank DeBernardis
                                             Title: President





















                                       37
<PAGE>

                               FORM OF ASSIGNMENT

(To be executed by the registered holder if such holder desires to transfer the
attached Warrant.)

         FOR VALUE RECEIVED, ___________________ hereby sells, assigns, and
transfers unto _____________________________ ______________ Warrants, each
Warrant conveys the right to purchase one (1) share of Class A Common Stock, no
par value, of EchoCath, Inc. (the "Company"), together with all right, title,
and interest therein, and does hereby irrevocably constitute and appoint
_____________________________ attorney to transfer such Warrant on the books of
the Company, with full power of substitution.


Dated:
       ---------------


                                      Signature:
                                                 ------------------------------




                                     NOTICE

         The signature on the foregoing Assignment must correspond to the name
as written upon the face of this Warrant in every particular, without alteration
or enlargement or any change whatsoever.



















                                       38
<PAGE>

         To:  EchoCath, Inc.
         P.O. Box 7224
         Princeton, New Jersey  08543




                              ELECTION TO EXERCISE



         The undersigned hereby exercises his or its rights to purchase ______
Warrant Shares covered by the within Warrant certificate and tenders payment
herewith in the amount of $_____________ in accordance with the terms thereof,
and requests that certificates for such securities be issued in the name of, and
delivered to:

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________
     (Print Name, Address and Social Security or Tax Identification Number)


and, if such number of Warrant Shares shall not be all the Warrant Shares
covered by the within Warrant, that a new Warrant for the balance of the Warrant
Shares covered by the within Warrant be registered in the name of, and delivered
to, the undersigned at the address stated below.
Dated: ________________                   Name:________________________________
                                                           (Print)


Address:_______________________________________________________________________



                                              _________________________________
                                                          (Signature)












                                       39
<PAGE>

                                 PROMISSORY NOTE

                                                  MONMOUTH JUNCTION, NEW JERSEY

FOR VALUE RECEIVED, the undersigned, EchoCath, Inc. a New Jersey corporation
("ECHOCATH"), hereby promises to pay to the order of Joseph J. Prischak, an
individual with a place of business at 2425 West 23rd Street, Erie, Pennsylvania
16506 ("PAYEE")

                    The sum of Two Hundred Thousand Dollars
                                   ($200,000)

 with interest on the unpaid balance due thereon at 6.5% per annum (computed on
 the basis of a 360 day year) commencing on the date of execution of this Note,
             payable in full on the 181st day from the date hereof.

         Payments are to be made at the principal office of the PAYEE or at such
other place in the United States as PAYEE may specify, in any coin or currency
of the United States of America which at the time of payment is legal tender for
public and private debts.

Upon default occurring in the payment, as and when due of the principal balance
or accrued interest due under this Note, then the entire unpaid principal and
all accrued interest will be due and payable in full. In the event of a default,
ECHOCATH shall pay PAYEE all of PAYEE's reasonable attorneys fees incurred by
PAYEE in the collection of this Note.

         This Note and the Agreement shall be governed, construed and enforced
in accordance with the internal laws of the State of New Jersey notwithstanding
any conflicts of laws provisions to the contrary, and all disputes, claims and
litigation concerning this Note and said Agreement shall be exclusively brought
and resolved in the federal and state courts located in New Jersey.

                                   ECHOCATH, INC.


                                   By:
                                          -----------------------------------

                                   Name:  Frank DeBernardis

                                   Title: President

                                   Date:  May __, 2001











                                       40