Color Doppler Ultrasound Imaging of Lower-Extremity Venous Disease by smapdi62

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                                                           Color Doppler      Ultrasound    Imaging
                                                           of Lower-Extremity        Venous

                                                                                                                       #{149}:;                                ,.                     ,

                              w. Dennis Foley1                A color      Doppler      uftrasound       imaging       device     was     used    to evaluate          475 patients         with
                       William    D. Middleton2            suspected       lower-extremity         venous thrombosis.   OccIusiv                  and nonocciusive               femoral and
                         Thomas       L. Lawson1           popliteal thrombi were              detected   in 200 studies (42%).                    In phase 1 of the study (240
                                                           examinations),          peripheral     augmentation          with the use of periodic                calf compression            was
                                Scott   Erickson1
                                                           required to show color flow throughout the femoropopifteal                                  venous segment               In phase 2
                        Francisco      A. Quiroz1
                                                           (235 examinations),             with   a software        upgrade       to enhance             detectability        of slow flow,
                   Stephanus       Macrander1              spontaneous         flow could be appreciated                in the normal,         partly     thrombosed,           and recanal-
                                                           ized femoral        popliteal     veins wfthout augmentation.                 Augmentation             was often necessary
                                                           to view tibioperoneal             veins. Of the total study              group,       conventional           venography          was
                                                           performed        for correlation       in 47 patients.         In the other patients,              clinicians       relied    on the
                                                           color Doppler test for the definftive                  diagnosis      of the presence               or absence           of femoral
                                                           popliteal venous thrombosis               and treated        these patients on the basis of the color Doppler
                                                           test result. In the femoral veins, color Doppler studies and venography                                         agreed in all 12
                                                           positive      and 35 negative           cases.     In the popliteal         veins, there was agreement                        in five
                                                           isolated popliteal thromboses                and in 10 femoral popliteal thromboses;                            there were two
                                                           false-negative         color Doppler       studies      of isolated      popliteal        thromboses.          In four patients,
                                                           Doppler studies detected              nonocclusive         thrombus not evident on venography.
                                                               Color Doppler imaging is easy to perform                      and does         not require        augmentation           to view
                                                           color flow in the femoropopliteal                   venous       segment         Eccentric         thrombus          and partially
                                                           canalized       thrombus       can be shown.          Initial experience            suggests         color Doppler imaging
                                                           may be useful in the detection               of tibioperoneal         venous thrombosis.

                                                              Color Doppler ultrasound           is a new technical        development      that provides     a corn-
                                                           bination    gray-scale      or tissue image and a dynamic-color-flow                    vascular    image
                                                           [1 , 2]. Recant studies have documented                the high sensitivity     and specificity    of real-
                                                           time B-mode        sonography       with compression         technique      in the evaluation      of sus-
                                                           pected femoral popliteal venous thrombosis                [3, 4]. Color Doppler imaging combines
                                                           the advantages       of a compression         sonographic     technique     with the additional    advan-
                                                           tage that the flow lumen is defined in color in a manner analogous                      to that achieved
                                                           with iodinated     contrast    agents.
                                                              This report details our experience             in the use of color Doppler extremity            venog-
                                                           raphy, with particular       emphasis      on the diagnosis      of recanalized     thrombus     and early
   Received June 30, 1988; accepted     after revision
September    23, 1988.
                                                           evaluation    of the technique       in tibioperoneal     venous imaging.
   1 Department    of Radiology, Medical College of
Wisconsin,   8700 W. Wisconsin     Ave., Milwaukee,
WI 53226. Address reprint requests to W. D. Foley.         Materials        and    Methods
   2 Department  ofRadiology,  Mallinckrodt  Institute
                                                               In the first 22 months of operation, 475 venous color Doppler studies were performed at
ofRadiology,     Washington    University School of Med-
                                                           the Medical College of Wisconsin for suspected deep-vein thrombosis. Patients were referred
icirie, 510    S. Kingshighway     Blvd., St. Louis, MO
63110.                                                     from either medical inpatient services or outpatient      clinics.
                                                               The color Doppler studies were performed        by using a sequential linear-array system with
   3 Radiology   Associates  of Appleton,     S.C., 424
E. Wisconsin   Ave., Ste. 103, Appleton,     WI 54912.     7.5- and 5.0-MHz transducers (QAD I Quantum Medical Systems, Issaquah, WA). All studies
                                                           were performed with a fluid-filled,    plastic, wedge-shaped       standoff attached  directly to the
AJR 152:371-376,       February 1989
0361 -803x/89/1     522-0371                               transducer. This created an angie between          the sound beam and the longitudinal axis of
C American     Roentgen    Ray SOciety                     vessels running parallel to the skin surface. Returning echoes were analyzed for amplitude,
372                                                                                                                                           FOLEY          ET   AL.                                                             AJR:152,         February     1989

phase, and frequency                                 shift. Amplitude                data provided                      a gray scale or                       ologists      who were unaware             of the results         of the other diagnostic
tissue         image;          phase            nd         fsequency            shifts       were         produced                   by moving                technique.      The   examinations        were     interpreted      prospectively,          and    the
targets            (RBCs).             Color         assignment                (either       red       or blue)               depended                  on    prospective results were used in comparative    analysis. Of the 31
flow        direction          with       respect            to the      transducer                and      was         selected               by the         studies performed before the software upgrade, comparison         was
operator.               Color saturation                      or hue reflected                     the extent of frequency                                    made only in the femoropopliteal venous system.   Of the 1 6 studies
shift,        which          was         dependent                 on    flow       velocity          and the angle of the                                    performed after the software upgrade, comparison included the ti-
sound            beam          in relation              to     the      longitudinal               axis      of        the      flow          lumen.          bioperoneal       veins    in addition      to   the   proximal      deep      veins.      Patients
High-frequency                        shifts       resulted          in greater            color         saturation               toward               the    who had both color Doppler and venographic examinations were 35-
whiter shades of red and blue. The amplitude of the Doppler signal                                                                                            80 years old; 60% were men and 40% were women. There was a
was dependent on power output, reflectivity of the moving RBCs,                                                                                               similar age and gender distribution in the 428 other patients, who
and receiver gain. The amplitude of the color flow signal on the video-                                                                                       had color Doppler examinations but did not have venography.
display terminal was controlled by a display threshold setting. With
the 7.5-MHz   probe (3 cm in length), the image repetition rate was 18
frames/sec at a depth of 4 cm and 12 frames/sec at a depth of 6 cm.                                                                                           Results
With         the      5.0-MHz               transducer               (4 cm        in length),              the      image                 repetition          Normal        Examinations
rate was 12 frames/sec at a depth of 6 cm, nine frames/sec at a
                                                                                                                                                                   In lower-extremity           venous         imaging,        in which vessels              run
depth  of 9 cm, and seven frames/sec at a depth of 1 i .5 cm.
                                                                                                                                                              parallel to the skin surface                     without       tortuosity,        all venous
   Transverse and longitudinal images of the common femoral vein
and superficial femoral vein were obtained with the patient supine                                                                                            segments         were encoded            in blue and corresponding                      arteries
and the leg slightly externally rotated. The proximal medial saphenous                                                                                        in red. Normal phasic venous flow caused by respiration                                     could
and profunda femoral vein were also imaged routinely. The popliteal                                                                                           be appreciated            on the real-time               color image in a normal
vein        was        studied           with        the     patient         decubitus              and      the         knee             flexed        to    femoral popliteal venous system (Fig. 1). Venous flow in the
approximately                        segments were examined for the
                                   30#{176}. venous
                                         All                                                                                                                  lower extremity            was decreased                during       inspiration        and in-
characteristics    of venous flow and the effects of compression.                                                                                             creased during expiration.                 Flow reversal             caused by the Val-
    We recorded on videotape selected segments in the longitudinal                                                                                            salva maneuver            or by heart pressures                  elevated       on the right
and transverse planes of the common femoral vein; saphenofemoral                                                                                              or localized      to the upper surface of normal valve cusps was
junction;  superficial femoral and profunda femoral vein junction; prox-
                                                                                                                                                              documented           easily. Arterial          flow reversal            in early diastole,
imal,        middle,           and        distal        superficial             femoral          vein;       and             popliteal             vein.
                                                                                                                                                              which is a normal phenomenon                           in lower-extremity               arteries
These selected recordings were then available for subsequent replay
and analysis. Point spectral analysis was not performed;         this was                                                                                     with triphasic flow characteristics,                    was also seen easily.
unnecessary     because all relevant Doppler information was encoded                                                                                               In the first 1 2 months of operation,                   with the use of an initial
as a color-flow signalthroughout    the fulllength of the venous segment                                                                                      production-type           QAD I system,               color-flow         venous       signal in
being imaged at any one time.                                                                                                                                 the mid and distal superficial                    femoral       vein in most patients
   In the last 1 0 months of the study, upgraded software, in conjunc-                                                                                        was appreciated           only with augmentation                   created by distal calf
tion      with       a slow            pulse         repetition         frequency               for the          color-flow                 compo-            compression.          In the final 1 0 months                 of operation,           with up-
nent of the sonographic                                    image, enabled operators                                to portray                   color-        graded software,            color-flow      venous signal throughout                     the full
flow         signals          in the           tibioperoneal              veins          from       the      ankle             to the           knee.
                                                                                                                                                              length of the femoral                popliteal       venous         segments         could be
When imaging the tibioperoneal venae comitantes,          the transverse
                                                                                                                                                              appreciated        in all normal patients                without        augmentation.             In
plane was preferred to the longitudinal plane. In the transverse plane,
                                                                                                                                                              normal patients,          the color-flow           signal occupied           the full cross-
color-flow venous signal from both venae comitantes of a selected
tibioperoneal   vessel could be imaged simultaneously.       These veins                                                                                      sectional      area of the venous lumen during maximum                                  venous
were examined with the patient supine and the knee slightly flexed,                                                                                           flow. Normal veins were uniformly                         compressible,           with appo-
internally rotated for the anterior tibial venae comitantes and exter-                                                                                        sition of the anterior and posterior                   venous walls. Compression
naily rotated for the posterior tibial and peroneal venae comitantes.                                                                                         was shown best in the transverse                          plane, because             the corn-
In the             longitudinal                plane,         with       a sagittal,               parasagittal,                     or      coronal          pressing      transducer        often displaced             the underlying            vein me-
projection,                it often       was         not    possible           to include           both         venae           comitantes                  dially or laterally in the longitudinal                  plane.
within the ultrasonic beam profile. When using thelongitudinal  imaging                                                                                            Spontaneous          or augmented               color-flow         signals      from the
plane, the anterior tibial venae comitantes were imaged in a sagittal
                                                                                                                                                              venae comitantes             of the anterior and posterior                    tibial and the
or parasagittal projection and the peroneal and posterior tibial venae
                                                                                                                                                              peroneal      arteries were detectable,                   with the slow-flow-sensi-
comitantes in a coronal projection. In this phase of the study, 235
                                                                                                                                                              tivity software         upgrade,       in the proximal              and distal calf (Fig.
patients were evaluated.
       Of the total                   475        patients            studied,            correlative              venograms                        were
                                                                                                                                                              2). In only a minority             of patients         were spontaneous,                 phasic
obtained at the request of the referring medical service in 47 patients,                                                                                      flow signals elicited from deep veins of the calf. Most patients
31 before the installation ofthe slow-flow sensitivity software upgrade                                                                                       required     augmentation,            which in the latter part of the study
and i 6 subsequent to installation. In other patients, clinicians using                                                                                       was provided           by a mechanical               sleeve compressor                 at ankle
the      published             literature             relating          to compression                     B-mode               sonography                    level (Venodyne          model EPS 400, Division of Advanced                              Instru-
[3, 4] relied on the color Doppler                                           test for the definitive                           diagnosis                of    ments, Needham              Heights,       MA). This mechanical                 compressor
the      presence                or      absence              of     femoral         popliteal             venous               thrombosis.                   cycled once every 5 sec.
Patients with demonstrated                                     femoropopliteal                   venous thrombosis                                 were
treated            with      anticoagulation                       or caval        filters       as appropriate.                            Patients
without             evidence              of      femoropopliteal                   thrombosis                    on         color          Doppler           Venous        Thrombosis
imaging             were       not       treated.
       of    the      47 patients                who         had     color       Doppler           and       venographic                       exam-             Venous thrombosis      was diagnosed     in 42% of all femoral
inations,            the     studies            were         performed             independently                   by different                    radi-      and popliteal veins. Intraluminal  thrombus    was recognized   as
AJR:152,   February    1989                                COLOR   DOPPLER     OF    VENOUS        THROMBOSIS                                                        373

     Fig. 1.-Longitudinal        view of proximal   super-
ficial femoral vein shows normal phasic venous
flow. Femoral        artery (red) is anterior to femoral
vein (blue). Minimal flow signal is appreciated in
profunda      artery, which, owing to the use of the
mechanical       plastic sleeve oftset, is almost par-
allel to the face of the transducer.
     A, Flow is minimal         or absent    in superficial
femoral    vein during inspiration.
     B, Normal venous flow is seen during expira-

      Fig. 2.-A,  Transverse       view of patent posterior tibial venae comitantes       in proximal calf. Two normal venae comitantes     are seen adjacent  to posterior
 tibial artery.
     B, Accompanying       anatomic      cross-sectional  line drawing illustrates location and depth of field of color Doppler image obtained with 7.5-MHz probe. Top
 of image is anterior      boSom is posterior.
     C, Segmental     longitudinal     view of posterior   tibial vein in proximal calf. Although normal venous flow pattems      are appreciated in patent tibioperoneal
 veins, spatial resolution      of ultrasound      images does not appear sufficient    to exclude minor degrees   of recanalized thrombus.

     Fig. 3.-Segmental    longitudinal    view of mid
 thigh shows partly occluding     thrombus    with ec-
 centric flow channels (arrows)     in mid superficial
 femorai vein.

     Fig. 4.-Eccentric        mural thrombus      in popliteal
 vein. Thrombus          is predominantly      on posterior
 wall of popliteal vein. Color Doppler study does
 not distinguish       between     acute, partially occlud-
 ing thrombus      and old recanalized       thrombus.
374                                                                           FOLEY     ET AL.                                                              AJR:152,      February     1989

an intraluminal       echogenic       filling defect, which in most acute                the color Doppler         study showed          recanalized       thrombus,        al-
deep vein thromboses            expanded         the venous lumen. Thrombi               though the conventional            contrast    venogram        failed to fill the
were recognized           in both the transverse                 and longitudinal        femoral venous segment             (Fig. 5). In these patients,           the con-
planes when evaluating            the femoropopliteal             venous system.         trast material injected into a superficial             foot vein flowed pref-
Hypoechoic        clot could be distinguished                  from intraluminal         erentially via superficial       saphenous       collaterals    to the proximal
echoes due to rouleaux formation                 by the presence or absence              saphenofemoral         junction.     The color Doppler             studies     were
of the color-flow       signal. Extension          of superficial      femoral vein      performed       with     augmentation          produced         by distal         calf
or saphenous         vein thrombus            to the common           femoral    vein    compression.       The conventional         venograms        were obtained          in
could be documented             easily. In contradistinction            to an acute      the standard     manner with the patient in a semiupright                  position
hypoechoic      thrombus,       chronic thrombus           was relatively      echo-     and the use of ankle tourniquets.
genic and did not expand                 the venous      lumen. Patients         with        In the separate      subset of 1 6 patients           in whom imaging of
recanalized     thrombus        had torturous         eccentric     flow channels        the tibioperoneal      veins could be compared,              there was agree-
filled with color-flow       signal (Fig. 3). With the slow-flow-sensi-                  ment between         both techniques         in the 12 negative           and four
tivity software      upgrade,      more flow signal from the eccentric                   positive cases (Fig. 6). Isolated calf vein thrombosis                   occurred
channels could be appreciated                than when the norrnal-sensitiv-             in none of the positive cases.
ity mode was used. Nonocclusive                 mural thrombus          had a single
eccentric    flow lumen (Fig. 4). Periarterial                and intramuscular
collateral   veins could be recognized                 owing to spontaneous
color flow within their lumen. Collateral                 veins could be seen                Contrast       venography           is the accepted         gold standard           in the
entering    the femoral         vein above          a segmentally         occluding      diagnosis       of lower-extremity             deep vein thrombosis.               However,
thrombus.                                                                                the technique          is invasive, is painful for the patient, and carries
                                                                                         the possibility          of chemically          induced      phlebitis       and resultant
                                                                                         phlebothrombosis              in 1-2% of examinations                   [5, 6]. For these
Color   Doppler     Imaging     and Venography
                                                                                         reasons,       clinicians       have evaluated            various      indirect     noninva-
    Of the 47 patients who had color Doppler and conventional                            sive tests, including             continuous-wave              Doppler         sonography,
venography,       1 0 had femoral popliteal venous thrombosis,                 two       impedance          plethysrnography,             and 1251-fibrinogen            scanning     as
had isolated fernoral vein thrombosis,              and seven had isolated               alternative        noninvasive           means       of diagnosing            or excluding
popliteal vein thrombosis.          There was complete            agreement        in    deep vein thrombosis                 [7-i 0]. The reported               accuracies       with
the 1 2 positive and 35 negative             studies of the femoral vein.                continuous-wave              Doppler sonography                and plethysmography
There were two false-negative               color Doppler       studies     in pa-       for thigh and calf vein thrombosis                     vary widely among institu-
tients with isolated popliteal          vein thrombosis.       The two false-            tions and investigators               [7-1 2]. False-negative              plethysmogra-
negative color Doppler studies of the popliteal vein were due                            phy and continuous-wave                     Doppler       sonography          can occur in
to (1) failure to recognize         a recanalized       thrombus       in an ex-         the presence          of occlusive         and nonocclusive             femoral popliteal
tremely obese patient in whom the image quality of the study                             thrombi and well-established                   collateral     venous circulation           [1 1,
was relatively       poor and (2) failure to detect the free-floating                    1 2]. False-positive             plethysmography              and continuous-wave
head of thrombus          in the distal popliteal      vein associated         with      Doppler       sonography           can occur in patients                 with congestive
calf vein thrombosis.          Both false-negative          studies     occurred         heart failure,           venous        insufficiency,        and extrinsic            venous
relatively   early in our experience           and before the addition            of     compression           [1 1 , 1 2]. Some investigators,               citing a sensitivity
the slow-flow-sensitivity        software      upgrade.                                  and specificity           value for plethysmography                     and continuous-
    Of the 1 2 patients         with femoral       vein thrombosis           docu-       wave Doppler             sonography          of 95% for the femoral                 popliteal
mented by both methods,              there were four patients           in whom          venous       system,        would institute           or withhold          antithrombotic

                                                                                                                               Fig. 5.-Recanalized             thrombus     involving     su-
                                                                                                                          perficial   and profunda          femorai veins.
                                                                                                                              A, Longitudinal         view of proximal thigh shows
                                                                                                                          narrowed,       tortuous      channels      in both superficial
                                                                                                                          femoral     vein (more anterior)           and profunda       fern-
                                                                                                                          oral vein (more posterior).
                                                                                                                               B, Contrast      venogram        shows patent profunda
                                                                                                                          fernoral    vein with adherent             mural thrombi       and
                                                                                                                          normal common            fernoral    vein proximally.       Super-
                                                                                                                          tidal femoral        vein is not seen.
AJR:152,   February   1989                          COLOR        DOPPLER          OF    VENOUS         THROMBOSIS                                                          375

   Fig. 6.-Popliteal,        posterior    tibial, and peroneal venous thrombosis.
   A, Longitudinal       color Doppler image at level of adductor             region in left distal thigh shows patent superficial femoral   vein filled by venous collateraL
There is echo-free        thrombus     in distal femoral   vein.
   B, Longitudinal       color Doppler study shows expending            echo-free    thrombus   in the popliteal vein.
   C, Segmental       longitudinal     view of posterior tibiai artery in distal calf. Minimal venous color flow signal is seen adjacent     to posterior tibial artery (arrow).
Venous flow signal in posterior tibial vein was not appreciated                 in mid or proximal calf.
   D, Contrast      venogram       shows upper extent of popliteal vein thrombus in distal thigh. Note collateral        inflow (arrow) corresponding to venous collaterals
seen on color Doppler study (A).
   E, Contrast venogram           shows almost completely        occlusive    thrombi in posterior tibial and peroneai veins and patent anterior tibial vein (arrows).    Patent
anterior tibial vein was also seen on color Doppler study. Popllteal vein was completely                     occluded.
   F, Schematic       diagram      shows locations     of color Doppler images in distal thigh (A), knee (B), and distal calf (C) and venogram at distal thigh (D) and
proximal calf (E).

therapy on the basis of these noninvasive              test results [7, 8].                plethysmogram       who have a clinical condition       that could result
However,   other investigators,    whose results with plethysmog-                          in a false-positive     examination,     such as cardiac          failure or
raphy are less impressive       (sensitivity,      60-70%),     advise the                 pelvic mass, should have a contrast           venogram      [1 1 , 12].
use of a contrast    venogram    in patients       with a negative pleth-                     125l-fibrinogen   scanning    is of major value in detecting           calf
ysmogram     who are known to be at high risk for deep vein                                vein thrombi and is a useful complement           to plethysmography,
thrombosis    [1 1 , 1 2]. In addition,       patients    with a positive                  which has a low sensitivity          in detecting    calf vein thrombi.
376                                                                                         FOLEY       ET        AL.                                                                AJR:152,      February     1989

However,       the 72-hr delay in obtaining                    the test result and the                   comitantes         of the tibioperoneal           veins can be shown by the
low sensitivity        to thrombus            more than 7 days old make the                              slow-flow-sensitivity           mode of the color-flow            instrument.        How-
test an unsuitable              screening        examination           for most hospital                 ever, preliminary          results suggest         that augmentation,             prefera-
inpatients.                                                                                              bly by a mechanical             sleeve compressor           at ankle level, will be
    Initial results with compression                      B-mode          sonography            are      necessary        for most patients.           Further evaluation           of the accu-
very encouraging             [3, 4]. This technique               uses direct visualiza-                 racy and reproducibility                of color Doppler          imaging        and MR
tion of the femoral popliteal                 venous lumen with compression                              imaging      with the fast-scan             technique      (partial-flip-angle         gra-
to confirm venous patency. As such, it is a direct noninvasive                                           dient-recalled        echo) [1 3] in the detection            of both above-knee
study, as compared                with plethysmography                    and continuous-                and below-knee            venous thrombosis             would be of interest.             As
wave Doppler            sonography,            which are indirect                noninvasive             a practical        matter,     color Doppler         imaging       has a significant
studies. Plethysmography                    evaluates       venous capacitance                 and       advantage         over MR imaging in that it is a portable                     technique
emptying       rate; continuous-wave                   Doppler        sonography           evalu-        that can be performed               in the intensive care unit.
ates isolated         spectral wave forms from the popliteal,                             medial             The clinical value of a total-extremity                 (thigh and calf), non-
saphenous,         and common              femoral veins and the venous flow                             invasive but direct imaging test of the deep venous system is
response      to augmentation               and the Valsalva maneuver.                                   difficult to assess at this time. Some authorities                        suggest       that
    Color     Doppler          imaging         combines            the advantages                  of    pulmonary         embolism,       as a consequence            of undiagnosed            and
compression          sonography            with the ability to visualize                sponta-          untreated       deep venous            thrombosis       confined        to the calf, is
neous venous flow in color without                          the injection         of contrast            extremely       rare. These authorities              suggest      that serial nonin-
material. With the advent of the slow-flow-sensitivity                                software           vasive studies (plethysmography                     and continuous-wave               Dop-
upgrade,        spontaneous             color-flow         signal       outlining       the full         pIer sonography)           are effective means of detecting                progressior
cross-sectional          area of the femoral popliteal vein during max-                                  of previously         undiagnosed          calf vein thrombosis               to femoral
imum flow can be appreciated                        in normal patients.               Augmen-            popliteal     thrombosis         before there is a significant               risk of pul-
tation to enhance              the Doppler           signal is unnecessary;                  thus,       monary embolism              [8]. Whether        provision     of an accurate           and
the examination            is simplified        considerably.          In these patients,                repeatable        noninvasive        test for the diagnosis           of both femoral
compression          to document            the absence of intraluminal                   throm-         popliteal and calf deep vein thrombosis                    would alter this mode
bosis appears           unnecessary.             The permanent               record of this              of practice is uncertain.
anatomic      and physiologic             test is maintained            on videotape           and
can be replayed             for analysis.         The major advantage                   of color
Doppler      venous imaging would appear to be demonstration                                             REFERENCES
of recanalized          venous        segments          that cannot           be shown by                    1 . Middleton        WD, Foley WD, Lawson TL. Flow reversal in the normal carotid
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                                                                                                             2.    Mitchell DG, Needleman          L, Bessi M, et al. Femoral artery pseudoaneurysm:
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                                                                                                                   thrombosis     complicating      phlebography. AJR 1980134:1169-1172
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                                                                                                             7.    Hull R, Hirsh J, Sackett          DL, et al. Combined use of leg scanning                      and
 and contrast venography.                 Complete         reliance cannot be placed                               impedance      plethysmography          in suspected       venous thrombosis:           an after-
on a negative test in the presence                       of clinical findings sugges-                              native to venography.         N Eng! J Med 1977:296:1497-1500
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                                                                                                                   scanning:    a less invasive approach.          Ann Intern Med 1981:94:12-15
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 vasively.     Both continuous-wave                      Doppler         sonography            and                 plethysmography,            and    radiolabeled        flbnnogen.         JAMA        1977;237:
 plethysmography              have reported            sensitivities       of 20% or less                          2195-21      98
                                                                                                         10. Sumner             DS, Lambeth A. Reliability        of Doppler     US in the diagnosis of acute
 in the evaluation             of calf vein thrombosis                    [7, 8, 1 2]. 1251..
                                                                                                             venous             thrombosis  both above           and below        the knee. AJR 1979;138:
fibrinogen      scanning,         although        it has a reported             sensitivity        of              205-210
 60% in the diagnosis                of calf vein thrombosis                   [8], may not              1 1 . Ramchandani         P, Soulen      R, Fedullo          L, Gaines    V. Deep vein thrombosis:
 provide a definite answer for 72 hr after injection;                              is probably                 significant   limitations    of noninvasive          tests. Radiology      1985;156:47-49

 insensitive     to clot more than 7 days old; and may give false-                                       12. Holden RW, Klatte EC, Park HM, et                       al. Efficacy of noninvasive        modalities
                                                                                                               for the diagnosis       of thrombophlebitis.            Radiology    1981;141 :63-66
 positive results for femoropopliteal                     venous thrombosis                 in the
                                                                                                         13. Spritzer      CE, Sussman          5K, Bunder             RA, Saeed M, Hertkens             RJ. Deep
acute postoperative               period, particularly            in patients who have                         venous thrombosis           evaluation     with       limited flip-angle,    gradient     refocused
 had hip or leg surgery. Spontaneous                         phasic flow in the venae                          MR imaging: preliminary           experience.          Radiology    1988;166(2):371-375

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