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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3656_Библиотеки_им_академика_М_И_Перельмана
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190 Computed tomography and magnetic resonance imaging in venous disease
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(a)
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(c)
Figure 16.21 Renal cell carcinoma with renal vein and inferior vena cava (IVC) tumor thrombus. (a) Arterial phase 3D fat-
saturated spoiled gradient echo image demonstrates extensive renal vein and IVC thrombus (arrows). Note linear enhancing thrombus in the left renal vein. (b) Black blood single shot fast spin echo image reveals large filling defect in IVC and
right atrium (arrows) consistent with tumor thrombus.
(arrowhead) and renal vein tumor thrombus (arrow).
adjusting the strength of these velocity-encoding gradients, a range of velocities can be detected and measured.
e major advantage of phase-contrast venography is that
it generates images in which the velocity of each pixel can
be determined. By incorporating ECG triggering, venous
ow can be measured with high accuracy. is can be useful in the setting of chronic mesenteric ischemia and in
evaluating the signicance of a venous stenosis. e major
limitation of phase-contrast techniques is that the acquisition times are longer than for time-of-ight and SSFP
sequences.
CE MR venography is probably the most widely used
technique currently. is technique is essentially identical to 3D CE MR angiography, employing a 3D spoiled
gradient echo sequence, with or without fat saturation, in
conjunction with a bolus of gadolinium-based contrast
(c) Axial steady state free precession image reveals left renal mass
(Figures16.21 and 16.23 through 16.25). Vascular contrast
is the result of the T1-shortening eects of gadolinium on
adjacent water protons and has relatively little dependence
on inow eects. e T1-weighted 3D SPGR sequence provides a moderate amount of background suppression.
24–26
e simplest 3D CE MR venography techniques involve
one or more additional acquisitions aer performing MRA:
the contrast bolus is injected and MRA is performed when
the concentration of the gadolinium contrast agent is maximal in the arteries. Additional phases are then acquired
until venous contrast is maximal. Alternatively, a test bolus
or uoroscopic triggering can be used to optimize the
timing of the acquisition to maximize venous rather than
arterial concentration: this reduces the total number of
acquisitions, but does limit opportunities for subtraction of
arterial phase data.
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16.3 Imaging technologies: MRI of venous disease 191
Figure 16.22 Inferior vena cava (IVC) sarcoma imaged with non-contrast black and bright blood techniques. Axial fast spin
echo (FSE) black blood image
the absence of flow voids in the left (small arrow) and right hepatic veins due to the presence of slow in-plane flow. A flow
void is present in the middle hepatic vein (arrowhead). Diffusion-weighted image (b) at a similar location again shows the
IVC mass, with greater contrast in comparison to the FSE image. Diffusion-weighted images show a more robust black
blood effect, with dark flow voids in all hepatic veins. Bright blood axial 2D steady-state free precession (SSFP) image
(c) again demonstrates an IVC mass, with bright signal intensity in the hepatic veins. Coronal 3D SSFP image (d) reveals
a small amount of tumor thrombus in the orifice of the middle hepatic vein (arrowhead). Note also bland thrombus with
darker, more uniform signal intensity along the inferior margin of the IVC mass (arrow).
(a) reveals a large heterogeneous mass expanding the intrahepatic IVC (large arrow). Note
A signicant advantage of 3D CE MR venography relative to time-of-ight MR venography techniques is that the
acquisition times are generally short enough for acquisition
in a single breath-hold. Since there is no reliance on vascular inow eects, the plane of acquisition has no eect on
the vascular signal. e 3D acquisition volume can therefore
be optimized for maximum eciency: oblique coronal for
visualizing the IVC, pelvic veins, and extremity veins, for
example, achieving maximal volumetric coverage within a
breath-hold.
CE MR venography has some limitations compared with
the more common MRA technique: the contrast bolus is less
compact and more dilute by the time it reaches the venous
system, and therefore the maximal contrast enhancement
in veins is generally lower than that achieved in arteries. Nevertheless, it is usually more than adequate for
diagnostic purposes. e addition of fat saturation (usually
via chemical saturation pulses) is oen helpful in reducing
background signal and improving venous contrast, albeit
at the cost of slightly longer acquisition times. Finally, the
requirement for breath-hold imaging places fundamental constraints on achievable spatial resolution and SNR:
increments in both spatial resolution and SNR generally
require increased acquisition times, and increased spatial
resolution results in reduced SNR. Breath-hold imaging is
not a requirement in some anatomic regions, such as the
pelvis and extremities; in these cases, multiple acquisitions
can be performed with relatively high spatial resolution and
highSNR.
e recent introduction of an intravascular—or blood
pool—gadolinium-based contrast agent (gadofosveset
tridsodium) has increased the exibility of 3D CE MRV.
27
192 Computed tomography and magnetic resonance imaging in venous disease
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(a)
(b)
Figure 16.23 Chronic IVC occlusion with collateral
formation. Maximum intensity projection image from
contrast-enhanced 3D spoiled gradient echo acquisition
demonstrates occlusion of the IVC below the renal veins
(arrow) with massive dilatation of the left gonadal vein
(arrowheads).
Figure 16.24 IVC thrombosis. Partial volume maximum
intensity projection image from 3D spoiled gradient echo
acquisition reveals extensive bland thrombus in the IVC
and left renal vein (arrows).
Figure 16.25 Axillary and subclavian vein thrombosis.
Source images from 3D contrast-enhanced MR venography reveal occlusive thrombus (arrows).
Intravascular agents reversibly bind to albumin and have
an intravascular half-life of approximately 30 minutes,
which improves the intravascular SNR over a long temporal window and allows for multiple repeated acquisitions.
Intravascular agents are particularly helpful for visualizing
slow-lling structures such as complex venous malformations (Figure 16.26), and also allow extended eld-of-view
examinations, where previously excretion of contrast and
loss of intravascular signal would be problematic by the
end of the examination. e lengthened temporal window
for vascular imaging also means that higher-spatial resolution images can be acquired, particularly in regions without
underlying motion (extremities and pelvis).
3D MR venography data can be reconstructed using
standard techniques, such as reformatting, maximum
intensity projection, and volume rendering. Partial volume
minimum intensity projection images may be useful for
accentuating venous thrombosis. Subtraction techniques
are sometimes useful for removing background signal or
arterial signal. If pure arterial phase images are acquired,
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16.3 Imaging technologies: MRI of venous disease 193
for example, these can be subtracted from venous phase
images to generate a purely venous dataset (Figure16.27b).
Likewise, simply subtracting a pre-contrast mask acquisition from the optimal venous phase data will reduce the
amount of background signal and may improve the quality
of the 3D reconstructed images. Subtraction techniques rely
on the assumption that there is no shi in position between
the two acquisitions; this is not always the case, particularly in patients who are not consistent breath-holders.
Limitations of the CE MR venography techniques include
the need for intravenous contrast: there is an association
between gadolinium contrast administration and nephrogenic sclerosing brosis in patients with severe renal insufciency,28 and as a general rule, gadolinium-based contrast
agents are not recommended in patients with an estimated
glomerular ltration rate of <30 mL/minute/1.73 m2. In
addition, there is also a small risk of allergic reaction to
gadolinium-based contrast agents, although this is probably
somewhat lower than the risk associated with the iodinated
contrast agents used in CT. Occasionally, the amount of
contrast in the veins is not adequate for optimal visualization; this is probably most common in the lower extremities
and pelvis in patients with very slow venous return. In these
cases, an increased contrast dose or multi-excitation acquisitions may improve image quality. An important advantage of
MR venography with respect to CT is that the exact timing
of the venous phase acquisition is less important: there is no
penalty in MRI for acquiring multiple acquisitions until the
venous contrast is optimal, whereas the cumulative radiation
dose is a signicant consideration in CT.
Direct MR venography is a technique that is advocated by
several authors in which a dilute bolus of gadolinium contrast is injected directly into the venous territory of interest
Figure 16.26 Klippel–Trenaunay syndrome in the right
lower extremity demonstrated using an intravascular
contrast agent. Axial fat-suppressed 3D spoiled gradient
recalled echo (SPGR) image
10 minutes after contrast injection demonstrates massive
enlargement of the central right popliteal vein (arrow) in
comparison with the normal left side, with multiple additional enhancing intramuscular and subcutaneous varicosities. Coronal 3D SPGR image (b) again demonstrates
extensive right calf varicosities, as well as an expanded
thrombosed intramuscular vein (arrow). Volume-rendered
(c) again demonstrates extensive deep and super-
image
ficial varicosities in the right calf in comparison to the
normal left-sided arteries and veins.
(a) obtained approximately
Figure 16.27 (a) Arterial and (b) venous phase maximum
intensity projection images from contrast-enhanced
MR angiography/venography in patient with severe IVC
stenosis following radiation therapy to a lumbar vertebral
metastasis. Note thread-like IVC (arrow) in (b). Residual
arterial contrast was removed from the venous phase
image by subtracting the arterial phase source images
from the venous phase source images.
194 Computed tomography and magnetic resonance imaging in venous disease
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or occlusion (Figures 16.20, 16.25, and 16.28).
and non-contrast techniques
can be combined with anatomic imaging to characterize
obstructing lesions in the mediastinum.
16.3.3.2 PULMONARY VEINS
Assessment of pulmonary veins with MRV is useful both
before (to dene anatomy) and aer (to detect complications, such as pulmonary vein stenosis or occlusion)
RF ablation of arrhythmogenic foci in the le atrium
(Figure 16.29).33 Pulmonary MRV can be combined
with cardiac MRI; some authors have suggested that
the presence of atrial late gadolinium enhancement
may be helpful in planning therapeutic interventions.34
Congenital anomalies of the pulmonary veins, such as
anomalous pulmonary venous return, are also well seen
with MRV (Figure 16.30),35 and can be combined with
functional assessment of the heart and quantication of
shunt severity by measurement of the ratio of pulmonaryartery to aortic blood ow (Qp/Qs).
16.3.3.3 IVC AND RENAL VEINS
Figure 16.28 Direct venogram in patient with subclavian
vein thrombosis. Volume-rendered image from contrastenhanced 3D spoiled gradient echo sequence obtained
while injecting dilute gadolinium contrast into a peripheral right-sided vein reveals patent SVC (arrow), occluded
distal right subclavian vein (arrowhead), and extensive
collateral formation (asterisks).
e IVC can be accurately assessed with CE or non-contrast
MRV. Venous extension is an important consideration in
staging and treating renal cell carcinoma: the renal vein is
invaded in as many as 20% of cases and the IVC in approximately 10%. MRI is an ideal technique for the evaluation of
renal cell carcinoma. It is highly accurate at detecting and
characterizing renal masses. Regional adenopathy, direct
invasion of adjacent structures, and distant metastases are
while simultaneous scanning is performed (Figure 16.28).
is avoids the problem of contrast dilution that occurs
when the contrast bolus rst passes through the arterial
system. e two major limitations of this technique are that
venous access needs to be established in a peripheral vein
of interest (typically the hand or foot) and that unless both
arms or legs are injected simultaneously, there will be only
minimal visualization of contralateral veins.
28–30
easily visualized. Vascular staging including MR venography reveals the presence or absence of bland or tumor
thrombus in the renal veins and IVC, as well as the venous
anatomy, and this information plays a role in choosing the
most appropriate surgical approach and technique.
Tumor thrombus enhances aer contrast administration
and is generally heterogeneous in appearance, whereas
bland thrombus is uniformly dark on all pre- and postcontrast sequences (Figures 16.21 and 16.31). Several recent
16.3.3 Clinical applications
studies have compared MRI with multi-detector CT for the
vascular staging of renal cell carcinoma, and have generally
MR venography generally plays a secondary role in venous
imaging. Duplex Doppler sonography is generally the rst
test performed in assessing lower or upper extremity veins
for thrombosis. Sonography is accurate, portable, and considerably less expensive than MR venography, but is occasionally limited. Sonography is less eective at visualizing
the central veins of the thorax, the entire extent of the IVC,
found both techniques to be highly accurate.
and CT are commonly used to screen potential living renal
transplant donors: the number and location of renal arteries
and veins is important in surgical planning. MR venography in conjunction with MRA can answer these questions
eectively, without exposing patients to iodinated contrast
and ionizing radiation.
and the iliac veins.
16.3.3.4 PORTAL, HEPATIC, AND MESENTERIC VEINS
16.3.3.1 UPPER EXTREMITY AND CENTRAL
THORACIC VEINS
Deep and supercial veins of the upper extremity are generally well seen with sonography; however, visualization of
more central thoracic veins is limited, and MRV can generally provide diagnostic images in patients with suspected
SVC, brachiocephalic, subclavian, or jugular vein stenosis
e portal, hepatic, and mesenteric veins are well visualizedduring standard abdomina l MRI; thrombosis ca n easily be detected, and oen the underlying cause elucidated.
MRI is an excellent technique for the detection and characterization of hepatic masses, and invasion of hepatic or
portal veins is usually well seen (Figure 16.32). Varices in
the setting of portal hypertension can be demonstrated,
25,30
31,3 2
are eective, and MRV
39
Both CE
23,24,36–38
37, 38
Both MRI
16.3 Imaging technologies: MRI of venous disease 195
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and the direction of portal venous ow determined using
phase-contrast techniques.40 Sono graphy is the primary
technique used to assess for vascular complications following hepatic transplantation. MRI is a useful secondary examination technique when sonography is limited or
indeterminate. Portal vein and IVC anastomoses can be
directly visualized and stenosis or thrombosis detected.
Figure 16.29 Pulmonary vein stenosis following left atrial
radiofrequency ablation of the left atrium. Posterior
volume-rendered image from 3D gadolinium-enhanced
pulmonary venogram demonstrates severe stenosis of the
left superior pulmonary vein (arrow) at its junction with
the left atrium.
Computed tomographic angiography (CTA) is probably
slightly more sensitive for the detection of arterial complications; however, MRI excels at the assessment of the
biliary tree and hepatic parenchyma. Some authors have
also advocated the use of phase-contrast techniques in
patients with suspected chronic mesenteric ischemia,
demonstrating a lack of normal increased ow in the
superior mesenteric vein following a fatty meal.
16.3.3.5 ILIAC AND LOWER EXTREMITY VEINS
Deep vein thrombosis (DVT) is a fairly common problem,
with approximately 260,000 cases diagnosed in the United
States every year. e diagnosis is most oen made with
duplex sonography, which is usually highly accurate for
the detection of femoral and popliteal DVT, but is somewhat limited in the evaluation of pelvic and calf veins, obese
patients, and chronic asymptomatic thrombus.
Several studies have demonstrated the eectiveness of
MR venography for detecting pelvic and lower extremity
venous thrombosis.
19,20,27,41–43
Carpenter etal.19 reported a
sensitivity of 100% and specicity of 96% for the evaluation of DVT from the IVC to the popliteal vein compared
with 2D time-of-ight MR venography and conventional
venography. Evans et al.20 found MR venography to be
more sensitive than sonography, but of equivalent specicity for femoropopliteal DVT. More recently, Fraser
etal.41 employed a CE subtraction technique to evaluate
femoral and iliac veins for DVT, nding sensitivity and
specicity values of 100% in comparison to conventional
venography. Ruehm et al.42 achieved excellent image
Figure 16.30 Scimitar syndrome. Partial maximum intensity projection (MIP) image (a)and volume-rendered image (b)
from 3D gadolinium-enhanced pulmonary venogram reveal a large anomalous vein draining the right lung and entering
the inferior vena cava just above the diaphragm.
196 Computed tomography and magnetic resonance imaging in venous disease
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(a)
(b)
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Figure 16.31 Renal cell carcinoma (asterisk) with tumor thrombus and bland thrombus. (a) Coronal fat-saturated steady-
state free precession image reveals a right renal mass with expansion of the renal vein and IVC and absence of the normal
bright-blood signal within these vessels. Note the difference between the more heterogeneous and higher signal intensity
tumor thrombus extending superiorly (arrows) and the bland thrombus in the IVC below the level of the renal vein (arrow-
(b, c) Axial contrast-enhanced fat-saturated 3D spoiled gradient echo images show similar findings, with enhancing,
head).
heterogeneous tumor thrombus at the level of the left renal vein (arrow in
more inferiorly (arrowhead).
b), and uniform, non-enhancing bland thrombus
quality in a CE direct MR venography study of the lower
extremity veins.
Although non-contrast techniques have proved sensitive and specic in several studies, their acquisition times
can be quite long, potentially reducing patient cooperation
and image quality—the major advantage of the CE methods is probably their the much shorter acquisition and
reduced total examination times (Figures 16.26 and 16.33).
An additional advantage of MR and CT venography compared with conventional venography in the evaluation of
iliac and lower extremity veins is the excellent so tissue
detail inherent in these techniques, which can provide
insight into the cause of venous thrombosis (Figure 16.34).
Figure 16.32 Infiltrative hepatocellular carcinoma (HCC)
predominantly involving the portal vein. Axial venous phase
post-gadolinium 3D spoiled gradient recalled echo image
demonstrates expansion of the main and peripheral portal
veins with heterogeneously enhancing tumor (arrowheads).
16.3.3.6 SPECIFIC SYNDROMES AND
SPECIALSITUATIONS
May–urner syndrome represents symptomatic stenosis
or thrombosis of the le common iliac vein by the overlying
16.3 Imaging technologies: MRI of venous disease 197
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Figure 16.33 Superficial venous thrombosis in the calf.
(a,b) Coronal and (c) axial contrast-enhanced fat-saturated
3D spoiled gradient echo images reveal filling defects in
bilateral veins (arrowheads), surrounded by inflammatory
enhancement of the vessel walls and adjacent muscle.
right common iliac arter y. MRA/MRV can show the course of
both the iliac arteries and veins (Figure 16.35), and the use of
an intravascular contrast agent allows for additional maneuvers (prone imaging to demonstrate persistent iliac vein stenosis) without the need for additional contrast injection.
(c)
Figure 16.34 Ewing sarcoma with venous extension. (a,b)
Axial contrast-enhanced fat-saturated spoiled gradient
echo images reveal a mass in the right iliac bone with
extension into the adjacent muscle. Note enlarged right
internal iliac vein filled with tumor thrombus (arrowhead
ina), and bland thrombus in the external iliac vein at a
lower level (arrowhead in b). (c) Coronal 3D spoiled gradient echo image again demonstrates tumor thrombus in
the right common iliac vein (arrowhead).
Nutcracker syndrome describes compression of the le
renal vein between the abdominal aorta and superior mesenteric artery, with resultant development of venous varicosities adjacent to the le kidney and ureter and dilatation of
198 Computed tomography and magnetic resonance imaging in venous disease
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the le gonadal vein (Figure 16.36). Demonstration of these
ndings is most easily accomplished with coronal CE MRA/
MRV.
Pelvic congestion syndrome describes chronic pelvic
pain associated with pelvic venous congestion and incompetent, dilated ovarian veins. Standard CE or non-contrast
pulse sequences can demonstrate prominent parametrial
pelvic veins, which is a relatively non- specic nding. Timeresolved MRA has been proposed as an additional technique, with demonstration of contrast reux from therenal
veins into the dilated, incompetent ovarian veins.
Venous thoracic outlet syndrome occurs with chronic
thrombotic (Paget–Schroetter syndrome) or nonthrombotic (McCleery syndrome) compression of the
subclavian veins. Sonography is oen adequate for diagnosis; however, MRV is useful in equivocal cases.45 Images
can be acquired with provocative maneuvers, and the use
of an intravascular gadolinium contrast agent allows for
multiple acquisitions following a single dose of contrast
(Figure 16.37).
44
Figure 16.35 May–Thurner syndrome. Coronal volume-
rendered image from 3D contrast-enhanced MRA/MRV
demonstrates focal thrombosis of the left common iliac
vein (arrow) distal to the overlying right common iliac
artery.
)
16.3.3.7 VENOUS AND ARTERIOVENOUS
MALFORMATIONS
Arteriovenous malformations exhibit rapid lling from
feeding arteries with immediate visualization of draining
(c)
Figure 16.36 Nutcracker syndrome. Axial (a) and sagittal (b) reformatted images from 3D contrast-enhanced MRV dem-
onstrate marked compression and narrowing of the left renal vein by the overlying superior mesenteric artery (arrows).
Coronal oblique volume-rendered image (c) again shows focal compression of the left renal vein, as well as a dilated left
gonadal vein and small varicocele.
16.3 Imaging technologies: MRI of venous disease 199
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)
)
Figure 16.37 Venous thoracic outlet syndrome. Volume-
rendered image from a thoracic venogram with the arms in
a neutral position (a) obtained following a single injection
of intravascular gadolinium contrast agent, demonstrating
normal appearance of the thoracic veins. Volume-rendered
image with the arms elevated (b) reveals severe stenosis of
the subclavian veins bilaterally (arrows), as well as stenosis
of the left subclavian artery (arrowhead).
veins. Time-resolved CE MRV acquisitions are helpful in
order to fully depict the anatomy of these lesions. Venous
malformations may ll slowly, and delayed acquisitions can
be helpful for appreciating the extent of the lesions, particularly following injection of an intravascular contrast agent.
16.3.3.8 POST-OPERATIVE IMAGING
MRV can be very useful for assessing complications
following venous surgery (Figure 16.38), although visual-
ization of the vessel lumen may be limited following stent
placement.
16.3.4 MR versus CT venography
e major advantages of CT with respect to MR are its
speed and spatial resolution. Large volumes can be covered
in only a few seconds with state-of-the-art, 64-row multidetector CT, with an isotropic spatial resolution of less than
Figure 16.38 Stenosis of a femoral–femoral venous bypass
graft in a patient with chronic left iliac vein thrombosis.
Volume-rendered image from contrast-enhanced MRV
(a)demonstrates extensive venous collateral vessels near
the left-sided anastomosis. Filling defect in the inferior
vena cava (arrow) represents an occluded left common iliac
vein stent. Sub-volume volume-rendered image
the collateral veins removed reveals multiple stenoses near
the left-sided anastomosis and within the graft (arrowheads). A patent surgical arteriovenous fistula (arrow) has
been placed in order to improve flow within the graft.
(b)with
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