Dynamic CT perfusion for acute cerebral ischemia: increasing anatomical coverage with the “toggling table” technique
Computed tomography (CT) has experienced a revival for perfusion assessment in acute stroke. However, so far it is limited by its small anatomical coverage. We studied a toggling table approach to (multislice) dynamic perfusion CT for extended coverage in patients with suspected acute MCA ischemia. In 20 patients with suspected acute MCA ischemia, a dynamic CT perfusion scan was performed on a multidetector scanner. To increase anatomical coverage, 2 distinct “toggling” table positions (each consisting of two 1cm slices) were chosen to represent the MCA territory and scanned in an alternating fashion during the bolus injection of 40mL contrast agent. Dynamic images were evaluated on a ROI and pixel-by-pixel basis, estimating peak density change, time to peak (TTP), integral (rCBV), mean transit time (MTT), and flow (rCBF). Acutely acquired CT perfusion data were compared with follow-up CT or MR (perfusion and diffusion) images. With the toggling table approach, temporal resolution is reduced to approximately 5 secs. Four imaging slices at two distinct locations can be obtained, covering the MCA territory. In 15 patients, perfusion CT revealed focal abnormalities in at least one slice, most commonly on MTT maps. In 14 of these 15 patients, the area of perfusion abnormality was a good predictor of the ultimate infarct. A single table location approach would have underestimated or missed the involved tissue in most cases. In 5 of the 20 patients, perfusion maps failed to delineate any abnormality: in 4 cases, MRI confirmed the absence of ischemia, in 1 case, CT failed to reveal a small ischemic injury visible on diffusion MRI. Addition of the dynamic CT perfusion scan adds less than 5 minutes to a CT stroke protocol and can be coupled with CTA studies to image the cervical and cerebral vasculature in acute stroke. The dynamic CT perfusion technique is a practical and useful tool for the emergency assessment of acute stroke patients. By employing the toggling table approach, perfusion information can be obtained over an extended anatomic area and thus reveal the presence and the extent of presumed tissue ischemia.