INNOVATION FUND Innovation, Integration, & Implementation Cardiovascular and Stroke Care SHOWCASE 2016 INNOVATION FUND Innovation, Integration, & Implementation Cardiovascular and Stroke Care SHOWCASE 2016

Low dose CT perfusion in acute ischemic stroke

Cardiovascular and Stroke Care


Richard Aviv

416 480 6100 ext. 7989

Sunnybrook AFP Association, Sunnybrook Health Sciences Centre, U of Toronto



Amanda Murphy

Neuroradiology fellow
Department of Medical Imaging
University of Toronto


Transformation – Based on the results of this investigation, current CT perfusion protocols can be modified to reduce radiation dose to an individual patient by 50% while maintaining accurate clinical information.  This has particular importance when considering the cumulative radiation dose to patients that require multiple CT perfusion scans.

Adoptability – At least one major teaching hospital in Toronto has altered their CT perfusion protocols, supported by the results of this investigation.  This significant dose reduction does not require additional expensive software, and can be implemented immediately.

Outcomes  –  We propose that this change be instituted in current CTP protocols, allowing optimal image quality with 50% lower effective dose.  Since concluding this investigation, several institutions have shown interest in these results as a way of supporting future dose reduction initiatives.



The purpose of this investigation is to determine if CT perfusion (CTP) measurements at low doses (LD = 20 mAs or 50 mAs) are similar to those obtained at regular doses (RD = 100 mAs), with and without the addition of adaptive statistical iterative reconstruction (ASIR).


A single-center, prospective study was performed in patients with acute ischemic stroke (n=37; 54% male; age =74 ± 15 years).  Two CTP scans were performed on each subject: one at 100 mAs (RD) and one at either 50 mAs or 20 mAs (LD).  CTP parameters were compared between the RD and LD scans in regions of ischemia, infarction, and normal tissue. Differences were determined using a within-subjects ANOVA (p<0.05) followed by a paired t-test post-hoc analysis (p<0.01).


At 50 mAs, there was no significant difference between cerebral blood flow (CBF), cerebral blood volume (CBV) or time to maximum enhancement (Tmax) values for the RD and LD scans in the ischemic, infarcted or normal contralateral regions (p<0.05).  At 20 mAs, there were significant differences between the RD and LD scans for all parameters in the ischemic and normal tissue regions (p>0.05).


CTP-derived CBF and CBV are not different at 50 mAs compared to 100 mAs, even without the addition of ASIR. Current CTP protocols can be modified to reduce the effective dose by 50% without altering CTP measurements.

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