MRV is a diagnostic process using a combination of a huge magnet, computer, and radio frequencies for producing detailed images of structures and organs within the body. The MRV would make use of magnetic resonance technology along with intravenous contrast dye for visualizing the veins.
Contrast dye makes the blood vessels difficult to view on the x-ray image. It enables the physician to visualize and evaluate the blood vessels. MRV has been immensely useful in most cases, as it could help detect causes of leg pain other than vein problems.
Magnetic resonance venography or MRV has been the most sensitive and specific test designed. It has been used for assessing the deep and shallow venous disease in the pelvis and lower legs. These areas would not be accessible by means of other modalities.
Uses of MRV
MRV is popularly used for helping in the detection of previously unsuspected nonvascular causes of leg pain along with edema when the clinical presentation had erroneously suggested venous obstruction and venous insufficiency.
The present advancement in technology has enabled the inclusion of computed tomography and MRV for the evaluation of venous disease. However, the use of MRV needs intravenous contrast material along with appropriate timing for obtaining a venogram. It has been the best technique allowing proper visualization for assessing obstructive disease, perforating veins, varicose veins, and other kinds of venous abnormalities.
Two major groups
MRV could be bifurcated in two major groups –
- Non Contrast MRV
- Contrast-enhanced MRV
Both the groups have been based on the use of gadolinium-based contrast agents. Noncontrast MRV would be performed most commonly using phase contrast or time of flight techniques.
Time of flight MRV
This type of MRI would rely on bright blood or gradient echo imaging. When subjected to a lengthy series of RF pulses along with a short echo time, flowing blood would show signal enhancement, as motion enables these moving protons to experience only a limited number of RF excitations before moving out of the imaged volume. It would also be inclusive of the continuous refreshment or inflow of spins into the imaging volume. It ensures a maximal alignment of protons and the external magnetic field before the RF pulses.
On the other hand, stationary tissues would have partially relaxed signals leading to lower signal intensity. Despite not using the contrast, the TOF images would show hyper-intense signals in the vessels. Moreover, the technique has been relatively strong as long as the protons in the blood experience only a few RF pulses before it is refreshed.