Figure 3.

In this patient with two pulmonary emboli (arrows in panels a and b), the embolus in the right upper lobe (a) looks smaller than the one in the right lower lobe (b) on MR angiography (MRA). However, on time-resolved perfusion MRI, the embolus in the right upper lobe is causing a much larger perfusion defect (*) (c) than the one in the right lower lobe (d). This suggests that direct assessment of pulmonary function (perfusion in this case) can provide information that is not available on morphologic MRA alone.