MR venography plays an important clinical role in the evaluation of venous disease. It is uniquely suited for evaluation of the veins of the abdomen, thorax, and extremities. This article reviews MR venography techniques and clinical implications.
is an Associate Professor of Radiology, New York University
School of Medicine, New York, NY.
Magnetic resonance (MR) venography is uniquely suited for
evaluation of the veins of the abdomen, thorax, and extremities, as
no ionizing radiation is used and contrast agents are
MR imaging of the venous system is less hindered by technical
limitations and bolus timing that are commonly encountered with
imaging the arterial system. In addition, veins deep in the chest
and pelvis are readily evaluated with this robust technique.
Conventional contrast-enhanced veno-graphy is an invasive
procedure that requires cannulation of a small vein, iodinated
contrast, and ionizing radiation. The main role of this technique
today is less for diagnosis and more for therapeutic purposes
(prior to lytic or interventional therapy). Duplex sonography has
become the first-line examination for evaluation of the venous
system, especially in the extremities. Sonography, however, is
limited by acoustic access, especially in the evaluation of the
deep veins of the pelvis, thorax, and calf.
MR venography now plays an important clinical role in the
evaluation of venous disease, despite its higher cost and limited
availability. In some clinical instances, such as evaluation of the
pelvic veins, it has become the test of choice. Advances in local
coils, gradient systems, and other system hardware and software
have enabled faster scanning, reduced artifacts, increased
signal-to-noise, and reduced examination times. Comprehensive
examinations of the entire venous system can be performed in <30
MR venography techniques
Two-dimensional (2D) time-of-flight (TOF) MR angiography is a
widely used, noninvasive technique for evaluation of the venous
However, due to saturation and flow effects, which may result in
nondiagnostic studies, three-dimensional (3D) gadolinium-enhanced
gradient-recalled echo (GRE) imaging may be used for problem
solving. Alternatively, many centers now forego TOF and go directly
to a 3D contrast-enhanced approach.
Stationary protons within an imaging volume, such as a vessel
wall and adjacent connective tissue, quickly become saturated by
the application of rapidly repeated radiofrequency (RF) pulses.
Flowing blood that enters the imaging volume does not have the same
"excitation history" as stationary tissue. Because it has not been
exposed to prior RF pulses, this unsaturated flowing blood
generates greater signal intensity than saturated stationary
tissues. As a result, the flowing blood appears bright against a
When a saturation pulse is applied adjacent to the imaging
volume, on the side from which arterial blood is flowing, the
arterial signal is saturated before it reaches the imaging slice.
Venous blood will generate high signal intensity while both the
stationary tissue and arterial blood are suppressed and remain
dark. The presaturation pulse, known as a traveling saturation
band, moves as the 2D imaging slice changes position.
Slice orientation is critical with TOF imaging. Optimally, the
imaging plane is positioned orthogonally to the vessel. If
positioned parallel to the imaging plane, flowing blood will be
exposed to the RF pulses for a longer period of time and may become
saturated, a process known as in-plane saturation. This is
especially problematic when imaging the great veins of the chest,
as the subclavian and axillary veins are "in-plane" with an axial
acquisition performed for evaluation of the superior vena cava or
jugular veins. Careful attention to selection of slice thickness,
orientation, repetition time (TR), echo time (TE), and flip angle
will minimize saturation effects. In particular, thinner slices and
a longer TR may lessen saturation effects.
Time-of-flight imaging may also be degraded by patient motion,
magnetic field inhomogeneity, and susceptibility artifacts from
adjacent air or metal (Figure 1). Under these circumstances, the
short TE (<2 msec ) and small voxel size achievable with
gadolinium-enhanced 3D techniques can minimize these causes of
artifactual signal loss. The hyperintense signal from acute venous
thrombosis may also mimic flow-relat-ed enhancement with TOF
imaging, resulting in a false-negative diagnosis of deep venous
thrombosis (DVT) (Figure 2). Finally, imaging large blocks of
anatomy may result in lengthy examination times.
Contrast-enhanced MR venography
The use of the T1-shortening effect of gadolinium within
circulating blood has had dramatic effect on MR angiography of the
A similar technique can be used to image the venous system. Because
this approach does not rely on flow-related enhancement (only on
the decreased T1 of enhanced venous blood), large field-of-view,
time-efficient coronal "in-plane" imaging can be performed without
saturation effects. This volumetric approach (without imaging gaps)
provides high spatial resolution, high signal-to-noise studies
resulting in near isotropic 3D data sets that can be reconstructed
in any plane. This is an accurate method of evaluating the arterial
system, but this method has not been exploited as much in venous
imaging, probably because 2D TOF often results in robust image
quality and does not require intravenous (IV) access or the
additional cost of contrast agents.
Excellent opacification of the venous system is attainable if a
longer scan delay time is used (when compared with "first pass"
arterial imaging) following injection of gadolinium. Because this
is a recirculation technique (vein to artery to vein), a dose of up
to 0.2 mmol/kg of gadolinium may be required when imaging multiple
anatomic stations (chest/ abdomen/pelvis). For evaluation of a
single anatomic station (ie, iliofemoral veins), 0.1 mmol/kg is
usually sufficient, injected at 1 to 2 mL/sec. The body coil is
adequate for imaging the chest, abdomen, and pelvis and provides
faster data reconstruction times than phased-array coils. The TR
should be as short as possible, to minimize acquisition time and
provide reasonable breath-holds (<25 seconds). The TE should be
as short as possible, to minimize magnetic susceptibility effects
that can result in signal loss. The flip angle can vary between 15˚
and 60˚. Fat-suppression is helpful in the abdomen and pelvis but
may be deleterious in the chest. Magnetic susceptibility effects
from aerated lung may result in frequency shifts in adjacent fat-
and water-containing tissues.
Thus, when a spectrally selective fat-saturation technique is used,
regions of water, and not adjacent fat, may be inadvertedly
suppressed, resulting in intravascular signal loss.
When performing dynamic gadolinium- enhanced 3D GRE studies,
several acquisitions are acquired sequentially. The initial
acquisition is timed with the gadolinium's first pass through the
arterial system but prior to substantial venous enhancement.
Multiple acquisitions are performed following the arterial phase;
these images usually have both arterial and venous enhancement. A
selective venous study can be generated by subtracting the
arterial-phase study from a mixed venous-arterial phase study.
The arterial signal is nullified, while the subtracted data set
contains only venous signal.
Direct venography is a novel technique similar to conventional
catheter venography in which very dilute gadolinium (5 mL in 250 mL
of saline) is injected directly into the distal extremity of
expected pathology and imaged with a 3D GRE sequence.
This can be incorporated with a moving table technique to image
from the feet to the inferior vena cava (IVC).
However, this technique requires venous cannulation of the affected
extremity and cannot demonstrate alternative sites of intravenous
access if thrombus or obstruction is identified.
Postprocessing and image interpretation
Evaluation of the source data and reformatted images is
essential, as low signal intensity thrombus may not be seen with
the maximum intensity projection algorithm. The latter should be
reserved for providing images that demonstrate collateral vessels
in the setting of extensive thrombosis (Figure 3) or demonstrating
alternative sites for achieving central venous access.
Differentiating acute from chronic venous thrombosis with TOF
imaging may be problematic. However, with gadolinium-enhanced
venography, source images demonstrate intense periadventitial
enhancement with acute thrombosis (Figure 4).
When the clot becomes chronic, this enhancement may no longer be
seen, vessel size decreases, and intravascular webs may appear.
Deep venous thrombosis
The literature supports the claim that MR venography is the "new
gold standard" for the diagnosis of suspected DVT. Using 2D TOF,
Laissy et al
demonstrated that MR venography was as accurate as conventional
venography, and more accurate than color Doppler sonography for the
diagnosis of lower extremity deep venous thrombosis in 37 patients.
In a larger study with 101 patients, Fraser et al
confirmed the high accuracy of 2D TOF for iliofemoral and
femoropopliteal DVT with sensitivities of 100% and 97%,
respectively. However, TOF imaging may be indeterminate for DVT
when flow is stagnant, resulting in poor intravascular signal from
saturation effects (Figure 5).
Evaluation of the chest and upper extremity veins for venous
Spontaneous thrombosis of the deep chest veins can be seen in
patients with hypercoagulable states and thoracic outlet syndrome.
However, the widespread use of long-term indwelling central venous
catheters for alimentation, chemotherapy, and hemodialysis has
resulted in a marked increase in the number of patients with upper
extremity and thoracic DVT. The ideal imaging test would not only
detect and quantify clot burden, but also provide alternative sites
of access (Figure 6). These goals can be readily achieved with
gadolin-ium-enhanced venography. Multiple studies with small
numbers of patients have demonstrated the efficacy of this
technique for upper extremity DVT.
Differentiating bland from tumor thrombus
Differentiating bland from tumor thrombus may be critical when
staging neoplasms with a propensity for venous extension and for
preoperative surgical planning. Direct visualization of thrombus
enhancement is a reliable sign for malignancy as bland thrombus
will not enhance (Figure 7). Time-of-flight imaging cannot reliably
differentiate bland from tumor thrombus, especially when the vein
is not expanded.
Contrast-enhanced MR venography is a robust technique that can
evaluate the deep veins of the chest, abdomen, and pelvis without
the flow artifacts, saturation effects and lengthy examination
times inherent in 2D-TOF imaging. Because it does not expose the
patient to ionizing radiation or potentially nephrotoxic contrast
agents, it is an attractive alternative to computed tomography.
Further improvements in hardware and pulse sequences will render
this technique the "gold standard" for imaging the deep venous
system, especially in anatomic regions that cannot be evaluated