As blood clots it goes through predictable stages that reflect the oxygenation state of hemoglobin within the red cells. One of these stages results in the formation of methemoglobin. This substance acts an endogenous contrast agent when imaged using a T1-weighted magnetic resonance sequence (Magnetic Resonance Direct Thrombus Imaging, MRDTI) – appearing as high signal. MRDTI can therefore be used to detect subacute thrombosis. This technique has been applied in a number of clinical settings arising as a result of thrombosis. Deep vein thrombosis and pulmonary embolism are both readily detected using MRDTI, providing a single imaging modality for the detection of venous thromboembolic disease. The technique is also effective in the peripheral arterial tree. Furthermore, thrombosis within vessel wall atherosclerosis is a marker of vulnerable plaque likely to produce symptoms. The MRDTI technique has thus proved useful in identifying complicated plaque in the carotid arteries in the setting of transient and permanent cerebral ischemia. MRDTI therefore holds promise as a technique that is capable of detecting high risk vessel wall disease prior to significant or permanent end organ damage. Because of the non-invasive nature of magnetic resonance imaging (MRI), application of MRDTI in the research setting for the monitoring of therapeutic interventions in a wide number of settings within vascular disease is very appealing.
