Diagnosis of femoropopliteal venous thrombosis with MR imaging: a comparison of four MR pulse sequences.

In a prospective study, MR images were evaluated in seven patients with femoropopliteal venous thrombosis with symptoms of less than 5 days duration. T1-weighted (600/25 [TR/TE]), intermediate (2000/30), and T2-weighted (2000/100) spin-echo series and a gradient-recalled acquisition in the steady state (GRASS) series were compared. Using venography as the standard for diagnosis, we found GRASS to be the most sensitive of the MR techniques, showing thrombi in all patients. It provided good contrast between the low-intensity thrombus and high-intensity flowing blood and also between thrombus and intermediate- or high-intensity perivascular tissues. The T1-weighted series was the least sensitive technique. All thrombi showed heterogeneity in the transaxial image with differences in signal between the peripheral and central regions. A higher intensity signal in the center than in the periphery at some level of the thrombus was found in six of seven T2-weighted or GRASS images. Heterogeneity in the signal intensity was more frequent in distal portions of thrombi, whereas the most proximal extent was homogeneous in appearance in six of seven cases. The heterogeneous appearance may be related to the greater age of the distal thrombus, because deep venous thrombi are known to begin in the calf and extend proximally over time. We conclude, on the basis of our experience with a small number of patients, that the GRASS MR technique is more sensitive for detecting acute deep venous thrombosis than T1-weighted, intermediate, and T2-weighted MR images.