EXHIBIT 5.1
 
                                          September 28, 1998
 
MEDIQ/PRN Life Support Services, Inc.
 
One Mediq Plaza
 
Pennsauken, New Jersey 08110
 
            Re: MEDIQ/PRN Life Support Services, Inc.
              11% Senior Subordinated Notes due 2008
 
Dear Sirs:
 
    We have acted as counsel for MEDIQ/PRN Life Support Services, Inc., a
Delaware corporation (the "Issuer"), and the subsidiaries of the Issuer listed
on Schedule A hereto (the "Guarantors") in connection with the filing by the
Issuer and the Guarantors of a Registration Statement on Form S-4, Registration
No. 333-58935 (the "Registration Statement"), with the Securities and Exchange
Commission for the purpose of registering up to $190 million aggregate principal
amount of the Issuer's 11% Senior Subordinated Notes due 2008 (the "New Notes")
under the Securities Act of 1933, as amended (the "Act"). The New Notes are to
be issued in exchange for an equal aggregate principal amount of the Issuer's
outstanding 11% Senior Subordinated Notes due 2008 (the "Existing Notes")
pursuant to the Registration Rights Agreement dated May 21, 1998 among the
Issuer, the Guarantors, MEDIQ Incorporated and Credit Suisse First Boston
Corporation, NationsBanc Montgomery Securities LLC and Banque Nationale de
Paris, filed as Exhibit 4.12 to the Registration Statement. The New Notes are to
be guaranteed on a senior subordinated basis (the "Guarantees") by each of the
Guarantors and are to be issued pursuant to the terms of the indenture (the
"Indenture") among the Issuer, the Guarantors and United States Trust Company of
New York, as trustee (the "Trustee"), filed as Exhibit 4.4 to the Registration
Statement. The Indenture is to be qualified under the Trust Indenture Act of
1939, as amended (the "TIA").
 
    In connection with the foregoing, we have reviewed such records, documents,
agreements and certificates, and examined such questions of law, as we have
considered necessary or appropriate for the purpose of this opinion. In making
our examination of records, documents, agreements and certificates, we have
assumed the authenticity of the same, the correctness of the information
contained therein, the genuineness of all signatures, the authority of all
persons entering and maintaining records or executing documents, agreements and
certificates (other than persons executing documents, agreements and
certificates on behalf of the Issuer and the Guarantors), and the conformity to
authentic originals of all items submitted to us as copies (whether certified,
conformed, photostatic or by other electronic means) of records, documents,
agreements or certificates. In rendering our opinion we have relied as to
factual matters upon certificates of public officials and certificates and
representations of officers of the Issuer and the Guarantors.
 
    We have assumed that the Indenture has been duly authorized, executed and
delivered by the Trustee and constitutes a legal, valid and binding agreement of
the Trustee. In addition, we have assumed that there will be no changes in
applicable law between the date of this opinion and the date of issuance and
delivery of the New Notes.
 
    Based upon the foregoing and having regard for such legal considerations as
we deem relevant, we are of the opinion that:
 
1.  The New Notes have been duly authorized by the Issuer and, when the
    Registration Statement has been declared effective, when the Indenture has
    been duly qualified under the TIA, when the New Notes have been duly
    executed by the Issuer and when the New Notes have been authenticated by the
    Trustee in accordance with the terms of the Indenture and issued and
    delivered against exchange of the Existing Notes in accordance with the
    terms set forth in the prospectus which is included in the Registration
    Statement, the New Notes will be valid and binding obligations of the
    Issuer.

2.  The Guarantees have been duly authorized by each of the Guarantors and, when
    the Registration Statement has been declared effective, when the Indenture
    has been duly qualified under the TIA, when the New Notes have been executed
    by the Issuer and when the New Notes have been duly authenticated by the
    Trustee in accordance with the terms of the Indenture and issued and
    delivered against exchange of the Existing Notes in accordance with the
    terms set forth in the prospectus which is included in the Registration
    Statement, the Guarantees will be valid and binding obligations of the
    Guarantors.
 
    Our opinion is subject to (i) the effect of applicable bankruptcy,
reorganization, insolvency, moratorium, arrangement and other laws affecting
creditors' rights, including, without limitation, the effect of statutory or
other laws regarding fraudulent conveyances, fraudulent transfers and
preferential transfers and (ii) limitations imposed by general principles of
equity (regardless of whether considered in a proceeding at law or in equity).
 
    This opinion is rendered to the Issuer in connection with the filing of the
Registration Statement and for no other purpose. We are members of the Bar of
the State of New York and express no opinion as to the laws of any jurisdiction
other than the laws of the United States of America, the State of New York and,
to the extent necessary to render the opinions set forth herein, the General
Corporation Law of the State of Delaware and the Business Corporation Law of the
Commonwealth of Pennsylvania.
 
    We hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement and to the use of our name under the caption "Legal
Matters" in the prospectus which is included in the Registration Statement. In
giving the foregoing consent, we do not admit that we come within the category
of persons whose consent is required by the Act or the rules and regulations
promulgated thereunder.
 
                                          Very truly yours,
                                          /s/ Dechert Price & Rhoads

                                                                      Schedule A
 


                THE GUARANTORS                          JURISDICTION OF INCORPORATION
- ----------------------------------------------  ----------------------------------------------
                                             
MEDIQ Diagnostic Centers, Inc.                  Delaware
MEDIQ Diagnostic Centers - I, Inc.              Delaware
MEDIQ Imaging Services, Inc.                    Delaware
MEDIQ Investment Services, Inc.                 Delaware
MEDIQ Management Services, Inc.                 Delaware
MEDIQ Mobile X-Ray Services, Inc.               Delaware
MDTC Haddon, Inc.                               Delaware
Value-Med Products, Inc.                        Delaware
American Cardiovascular Imaging Labs, Inc.      Pennsylvania