CT Pulmonary Angiography > Pulmonary Embolus > Diagnostic Alternatives > MRDTI

MR Direct Thrombus Imaging

MR direct thrombus imaging (MRDTI) makes use of direct detection of methemoglobin in a thrombus, which appears bright on T1-weighted sequences owing to its T1 shortening effect. Utilization of this endogenous contrast permits visualization of a thrombus without the use of any contrast agent (hence the term “direct thrombus imaging”), and it is non-invasive. MRDTI can be used to detect subacute thrombosis. Deep vein thrombosis and pulmonary embolism can be both confirmed by MRDTI. Also, it does allow the detection of venous thromboembolic disease with a single imaging modality. The most significant advantage of MRDTI is the direct visualization of the thrombus, while other sequences rely on the detection of thrombus through a filling defect. Another advantage is that MRDTI allows to differentiate between old and new clots (high signal intensity indicates subacute thrombosis).

Several studies have been performed to determine the efficacy of MRDTI in detection of thrombus. In a study comparing MRDTI with contrast venography the sensitivity of MRDTI was 96% in 338 patients. In a smaller PE study involving 13 patients the sensitivity and specificity of MRDTI was 100% for both. MRDTI allowed the detection of three additional emboli not seen on conventional pulmonary angiography. A randomized trial of MRDTI for diagnosis of pulmonary embolism in 157 patients demonstrated similar patient outcomes compared with more extensive diagnostic strategies, including CT, VQ and D-dimer testing. These results make it possible that MRDTI may have a significant role in the future for the diagnosis and management of venous thromboembolism.

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