Document:

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                                                                     EXHIBIT 4.6

                                LETTER AGREEMENT

                          201 Main Street, Suite 3100
                            Fort Worth, Texas 76102

                                October 19, 2000

Lone Star Technologies, Inc.
15660 N. Dallas Parkway, Suite 500
Dallas, TX 75248
Attention: Mr. Robert F. Spears
Vice President, General Counsel and Secretary

Gentlemen:

    Lone Star Technologies, Inc. has offered to include Alpine Capital, L.P. as
a selling stockholder in Lone Star's Registration Statement on Form S-3 to
enable Alpine Capital to sell up to 1,000,000 shares of Lone Star common stock
under such Registration Statement.

    In consideration of Lone Star's inclusion of Alpine Capital's common stock
in the Registration Statement, each of Alpine Capital, Keystone, Inc. and The
Anne T. and Robert M. Bass Foundation hereby agrees to execute a lock-up
agreement, if requested by Lone Star or the underwriters, in connection with any
offering of common stock (or securities convertible into common stock) by Lone
Star under the Registration Statement so long as such stockholders continue to
hold in the aggregate greater than 5% of the outstanding common stock of Lone
Star. Any such lock-up agreement will be on customary terms and will be for a
period of time ending no more than 90 days after the closing of each offering of
such securities under the Registration Statement.

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<S>                                                    <C>  <C>
                                                       Sincerely yours,

                                                       ALPINE CAPITAL, L.P.

                                                       By:       Algenpar, Inc., General Partner

                                                       By:            /s/ J. Taylor Crandall
                                                            -----------------------------------------
                                                                  J. Taylor Crandall, President

                                                       KEYSTONE, INC.

                                                       By:            /s/ J. Taylor Crandall
                                                            -----------------------------------------
                                                              J. Taylor Crandall, Vice President and
                                                                     Chief Operating Officer

                                                       THE ANNE T. AND ROBERT M. BASS FOUNDATION

                                                       By:            /s/ J. Taylor Crandall
                                                            -----------------------------------------
                                                                  J. Taylor Crandall, Treasurer
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                         FORM OF EMPLOYMENT AGREEMENT

This Employment Agreement ("Agreement") is entered into as of November __,
2000 between RADIOLOGIX, INC., a Delaware corporation (the "Company"), and
Mark L. Wagar ("Wagar").

In consideration of the mutual covenants and conditions set forth herein, the
parties hereby agree as follows:

1.      EMPLOYMENT. The Company hereby employs Wagar in the capacity of
Chairman of the Board and Chief Executive Officer. Wagar accepts such
employment and agrees to perform such services as are customary to such
office and as shall from time to time be assigned to him by the Board of
Directors.

2.      TERM. The employment hereunder shall be for a period of 3 years,
commencing on the date of the closing of the merger (the "Merger")
contemplated by the Amended and Restated Agreement and Plan of Merger dated
as of September 12, 2000 by and among the Company, SKM-RD LLC and SKM-RD
Acquisition Corp. (the "Commencement Date"), and shall be automatically
renewed for successive one-year periods unless earlier terminated as provided
in Section 4. Wagar's employment will be on a full-time basis requiring the
devotion of such amount of his productive time as is necessary for the
efficient operation of the business of the Company.

3.      COMPENSATION AND BENEFITS.

        3.1    SALARY. For the performance of Wagar's duties hereunder, the
Company shall pay Wagar an annual salary of $425,000, payable (less required
withholdings) no less frequently than twice monthly (the "Base Salary").

        3.2    BONUS. The Company shall also pay Wagar an annual cash bonus,
which bonus shall be payable in a single installment within 30 days following
the end of the employment year for which it is earned. The annual bonus for
the calendar year 2000 (the "First Employment Year") will be determined in
accordance with the bonus plan in effect for the Company prior to the Merger.
For each calendar year thereafter (the "Additional Employment Years"), the
annual bonus for Wagar will be determined in accordance with a performance
matrix to be adopted by the Board of Directors (the "Matrix"); provided that
the potential amount of such bonus will in no event be less than 60% of the
Base Salary in effect for such Additional Employment Year (such amount
determined by the Board of Directors in accordance with the Matrix, the
"Bonus").

        3.3    STOCK OPTIONS. Following the Commencement Date, the Company
will grant Wagar, pursuant to an option agreement in the form of EXHIBIT A
hereto, options under the Radiologix, Inc. 2000 Stock Option Plan (the "Stock
Option Plan") to purchase 475,000 shares of the Company's common stock at an
exercise price of $7.35 per share. Thereafter, Wagar will participate in the
Stock Option Plan and other plans granting options or stock awards to top

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executives. The options will vest in accordance with the plan and option
award agreement under which such options are granted.

        3.4    BENEFITS. Wagar shall be entitled to such medical, dental,
disability and life insurance coverage, paid time-off and holiday benefits,
if any, and any other benefits as are made available to the Company's top
executive personnel, all in accordance with the Company's benefits program in
effect from time to time.

        3.5    REIMBURSEMENT OF EXPENSES. Wagar shall be entitled to be
reimbursed for all reasonable expenses, including but not limited to expenses
for travel, meals and entertainment, incurred by Wagar in connection with and
reasonably related to the furtherance of the Company's business.

        3.6    ANNUAL REVIEW. In the first week of December of each
Additional Employment Year, the Board of Directors will review Wagar's
performance and compensation hereunder (including salary, bonus and stock
options and/or other equity incentives) and will consider whether to increase
such compensation, but will not have authority, as the result of such review,
to decrease the then applicable Base Salary or maximum amount of the
potential Bonus without the written consent of Wagar.

4.      TERMINATION.

        4.1    TERMINATION EVENTS. The employment hereunder will terminate
upon the occurrence of any of the following events:

               (a)    Wagar dies;

               (b)    the Company, by written notice to Wagar or his personal
representative, discharges Wagar due to the inability to perform the duties
assigned to him hereunder for a continuous period exceeding 120 days by
reason of injury, physical or mental illness or other disability, which
condition has been certified by a physician; provided, however, that prior to
discharging Wagar due to such disability, the Company shall give a written
statement of findings to Wagar or his personal representative setting forth
specifically the nature of the disability and the resulting performance
failures, and Wagar shall have a period of ten (10) days thereafter to
respond in writing to the Board of Directors' findings;

               (c)    Wagar is discharged by the Board of Directors of the
Company for Cause. As used in this Agreement, the term "Cause" shall mean:

                      (i)    Wagar's conviction of (or pleading guilty or
nolo contendere to) any misdemeanor involving dishonesty or moral turpitude
or a felony; provided, however, that prior to discharging Wagar for Cause,
the Company shall give a written statement of findings to Wagar setting forth
specifically the grounds on which Cause is based, and Wagar shall have a
period of ten (10) days thereafter to respond in writing to the Board of
Directors' findings;

                      (ii)   (A) the willful and continued failure of Wagar
to substantially perform his duties with the Company (other than any such
failure resulting from illness or disability) after a

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written demand for substantial performance is requested by the Company's
Board of Directors, which specifically identifies the manner in which it is
claimed Wagar has not substantially performed his duties, or (B) the personal
dishonesty, willful misconduct or breach of a fiduciary duty in respect of
any matter which has, or can reasonably be expected to have, a direct and
material adverse effect on the Company or its reputation. For purposes of
this Section, no act or failure to act on Wagar's part shall be considered
"willful" if done, or omitted to be done, by Wagar in good faith and with
reasonable belief that Wagar's action or omission was in the best interest of
the Company;

                      (iii)  the willful breach by Wagar of any written
covenant or agreement with the Company not to disclose confidential
information pertaining to the Company or not to compete or interfere with the
operation of the Company's business; or

                      (iv)   the abuse of alcohol or illegal drugs by Wagar
while performing his employment-related duties that affects the performance
by Wagar of his employment-related duties.

        No termination shall be effected for Cause unless Wagar has been
provided with specific information as to the acts or omissions which form the
basis of the allegation of Cause, and Wagar has had an opportunity to be
heard, with counsel if so desired, before the Board of Directors and such
Board determines, by majority vote, in good faith that Wagar was guilty of
conduct constituting "Cause" as herein defined, specifying the particulars
thereof in detail;

        (d)    Wagar is discharged by the Board of Directors of the Company
without Cause, which the Company may do at any time, with at least 30 days
advance written notice;

        (e)    Wagar voluntarily terminates his employment due to either (i)
a default by the Company in the performance of any of its obligations
hereunder, or (ii) an Adverse Change in Duties (as defined below), which
default or Adverse Change in Duties remains unremedied by the Company for a
period of ten days following its receipt of written notice thereof from
Wagar;

        As used herein, "Adverse Change in Duties" means an action or series
of actions taken by the Company, without Wagar's prior written consent, which
results in:

        (1) A material change in Wagar's reporting responsibilities, titles,
job responsibilities or offices which results in a material diminution of his
status, control or authority; or

        (2) The assignment to Wagar of any positions, duties or
responsibilities which are materially inconsistent with Wagar's positions,
duties and responsibilities or status with the Company; or

        (3) A requirement by the Company that Wagar be based or perform his
duties anywhere other than (i) at the Company's corporate office location on
the date of this Agreement, or (ii) if the Company's corporate office
location is moved after the date of this Agreement, at a new location that is
no more than 60 miles from such prior location; or

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        (4) A failure by the Company to provide for Wagar's participation in
any current or future benefits or plans at a level or to an extent
commensurate with that of other top executives of the Company;

        (f)    Wagar voluntarily terminates his employment for any reason
other than the Company's default or an Adverse Change in Duties, which Wagar
may do at any time with at least 30 days advance notice; or

        (g)    Wagar is discharged by the Board of the Directors as a result
of a material underperformance by the Company as measured against the
Company's business plan, with such underperformance to be reasonably
determined by the Board of Directors in good faith (a "Material
Underperformance").

        4.2    EFFECTS OF TERMINATION.

        (a)    Upon termination of Wagar's employment hereunder for any
reason, the Company will promptly pay Wagar all compensation owed to Wagar
and unpaid through the date of termination (including, without limitation,
salary, accrued paid time off, accrued but unpaid Bonus for the prior
employment year in the event Wagar is terminated following the end of such
prior employment year and employee expense reimbursements).

        (b)    In addition, if the employment is terminated under Section
4.1(d) at a time at which there is not a Material Underperformance or under
Sections 4.1(b) or (e), the Company shall also pay Wagar, immediately upon
such termination of employment, a lump sum severance amount equal to two and
one-half times the then applicable Base Salary, excluding Bonus. In addition,
if Wagar is terminated pursuant to the foregoing sentence, Wagar shall also
be entitled to receive an additional six months of his then applicable Base
Salary, excluding Bonus, if he is unable to secure a position with (i)
reasonably equivalent duties and (ii) a cash compensation package
substantially similar to his Base Salary at the time of termination (an
"Equivalent Position"); provided, however, that payments pursuant to this
sentence would be paid monthly and only until such time as Wagar secured an
Equivalent Position. If the employment is terminated under Section 4.1(d) at
a time at which there is a Material Underperformance or under Section 4.1(g),
the Company shall only pay Wagar, immediately upon such termination of
employment, a lump sum severance amount equal to one-half of the then
applicable Base Salary, excluding Bonus. If Wagar is terminated under
Sections 4.1(a), (c) or (f), Wagar will not be entitled to any severance
payment.

        (c)    Wagar agrees that, during the term of his employment and for
the one year period following the Termination Event (subject to any
limitations set forth below):

                      (i)    Wagar will not directly or indirectly, whether
as an individual, employee, director, consultant or advisor, or in any other
capacity whatsoever, provide services to any person, firm, corporation or
other business enterprise which is involved in the acquisition and management
of radiology physician practices or diagnostic imaging centers, unless he
obtains the prior written consent of the Board of Directors; provided,
however, that in the event that Wagar is terminated under Section 4.1(d) at a
time at which there is a Material Underperformance or under Section 4.1(g),
the limitations contemplated by this Section 4.2(c)(i)

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will be effective only during the term of his employment and for six months
following such Termination Event.

                      (ii)   Wagar will not directly or indirectly encourage
or solicit, or attempt to encourage or solicit, any individual to leave the
Company's employ for any reason or interfere in any other manner with the
employment relationships at the time existing between the Company and its
current or prospective employees.

                      (iii)  Wagar will not induce or attempt to induce any
provider, payor, customer, supplier, distributor, licensee or other business
relation of the Company to cease doing business with the Company or in any
way interfere with the existing business relationship between any such
customer, supplier, distributor, licensee or other business relation and the
Company.

                      (iv)   Wagar will not disclose or use for himself or
others, directly or indirectly (except for information disseminated by Wagar
in the good faith performance of his duties for the Company prior to a
Termination Event), any trade secrets or confidential information in written,
oral, electronic or other form regarding the Company and its affiliates and
their respective businesses, equipment, products or employees.

        Wagar acknowledges that monetary damages may not be sufficient to
compensate the Company for any economic loss which may be incurred by reason
of breach of the foregoing restrictive covenants. Accordingly, in the event
of any such breach, the Company shall, in addition to any remedies available
to the Company at law, be entitled to obtain equitable relief in the form of
an injunction precluding Wagar from continuing to engage in such breach.

        If any restriction set forth in this paragraph is held to be
unreasonable, then Wagar and the Company agree, and hereby submit, to the
reduction and limitation of such prohibition to such area or period as shall
be deemed reasonable.

5.      GENERAL PROVISIONS.

        5.1    ASSIGNMENT. Neither party may assign or delegate any of his or
its rights or obligations under this Agreement without the prior written
consent of the other party.

        5.2    ENTIRE AGREEMENT. This Agreement contains the entire agreement
between the parties with respect to the subject matter hereof and supersedes
any and all prior agreements between the parties (including the Company's
predecessors) relating to such subject matter, including the Employment
Agreement, dated as of May 29, 1998, between American Physician Partners,
Inc. and Wagar, and the amendments thereto.

        5.3    MODIFICATIONS. This Agreement may be changed or modified only
by an agreement in writing signed by both parties hereto.

        5.4    SUCCESSORS AND ASSIGNS. The provisions of this Agreement shall
inure to the benefit of, and be binding upon, the Company and its successors
and permitted assigns and Wagar and Wagar's legal representatives, heirs,
legatees, distributees, assigns and transferees by

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operation of law, whether or not any such person shall have become a party to
this Agreement and have agreed in writing to join and be bound by the terms
and conditions hereof.

        5.5    GOVERNING LAW. This Agreement shall be governed by, and
construed in accordance with, the laws of the State of Texas.

        5.6    SEVERABILITY. If any provision of this Agreement is held by a
court of competent jurisdiction to be invalid, void or unenforceable, the
remaining provisions shall nevertheless continue in full force and effect.

        5.7    FURTHER ASSURANCES. The parties will execute such further
instruments and take such further actions as may be reasonably necessary to
carry out the intent of this Agreement.

        5.8    NOTICES. Any notices or other communications required or
permitted hereunder shall be in writing and shall be deemed received by the
recipient when delivered personally or, if mailed, five (5) days after the
date of deposit in the United States mail, certified or registered, postage
prepaid and addressed, in the case of the Company, to Radiologix, Inc. c/o
SKM-RD LLC, 262 Harbor Drive, Stamford, CT  06902, Attn: William Gumina,
Facsimile No.: (203) 708-6677, and in the case of Wagar, to the address shown
for Wagar on the signature page hereof, or to such other address as either
party may later specify by at least ten (10) days advance written notice
delivered to the other party in accordance herewith.

        5.9    NO WAIVER. The failure of either party to enforce any
provision of this Agreement shall not be construed as a waiver of that
provision, nor prevent that party thereafter from enforcing that provision or
any other provision of this Agreement.

        5.10   LEGAL FEES AND EXPENSES. In the event of any disputes under
this Agreement, each party shall be responsible for their own legal fees and
expenses which it may incur in resolving such dispute, unless otherwise
prohibited by applicable law or a court of competent jurisdiction.

        5.11   COUNTERPARTS. This Agreement may be executed in counterparts,
each of which shall be deemed to be an original, but all of which together
shall constitute one and the same instrument.

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        IN WITNESS WHEREOF, the Company and Wagar have executed this
Agreement, effective as of the day and year first above written.

COMPANY                                    WAGAR

RADIOLOGIX, INC., a Delaware corporation

By:                                        By:
        -----------------------------              -----------------------------
        Name:                                      Mark L. Wagar
        Title:                                     Address:
                                                   17 Windsor Ridge
                                                   Frisco, TX 75034

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