Richard Hausmann

Flow-Dependent Acquisition Techniques

In MR imaging (MRI), the signal intensity of blood is extremely variable due to the complexity of the hematic components and the physiological motion of the blood. Blood is composed of water (80%), cells, and plasma elements such as organic macromolecules and electrolytes. Several studies have suggested that in the physiological state unclotted whole blood has long Tl (780–1000 ms) and T2 (150 ms) relaxation times , which in theory results in a low signal intensity on Tl-weighted images and a high signal intensity on T2-weighted images (Wehrli et al. 1988). For clotted blood, the signal intensity varies, depending on the time between bleeding and imaging, as it is related to the relative amount of hemoglobin degradation products present within a hematoma.