CT Perfusion

CT Perfusion allows existing CT scanners in hospitals to measure tissue blood flow via a software program developed in Dr. T.-Y. Lee's lab. GE Healthcare has licensed the software for use on their CT scanners to study stroke, cancer and heart attack patients.


Vessel damage assessment (C) in a stroke patient with ischemia in the right half of the brain (A). The patient progressed to bleeding as indicated by red arrows in (D) a few days later.
T.-Y. Lee
CT imaging, tracer kinetics modelling, deconvolution analysis, stroke imaging
A. So
Cardiac Imaging
E.E. Stewart
cancer (liver) imaging
G. Wisenberg
J.A. White



Future Directions

Although CT perfusion provides useful information in the management of stroke, it also delivers a substantial radiation dose to the patient. We are developing new imaging processing techniques to reduce the radiation dose so that CT Perfusion studies can be more widely used without concern for the associated risks.

We are expanding the applications of CT. Perfusion into measurement of tumour blood flow for the monitoring of anti-angiogenesis therapy and of myocardial blood flow for identifying patients who would benefit from revascularization in ischemic heart disease.

Key Accomplishments

Extending the stroke treatment window: The only approved drug for stroke is the clot dissolving drug (rtPA). For rtPA to be effective, it is important to determine before the drug is given whether there is surviving (viable) brain tissue to be salvaged since rtPA can cause bleeding in already dead brain tissue resulting in greater disabilities and even death. Currently there is no reliable diagnostic method for such a determination. Emergency physicians rely on an empirical rule, albeit well tested, based on time since onset of symptoms to decide if rtPA can be given: and this time window is only 3 to 4.5 hours. Because of this very narrow treatment window, only 5% of stroke patients benefit from this treatment. With support from the Canadian Stroke Network we have developed a CT scanning method that is able to accurately identify survivng brain tissue in stroke patients. Before this method can be widely adopted, a multi-centre trial is required to prove its validity.

Enhancing the safety of rtPA:  Although rtPA is effective in dissolving the blood clots that cause stroke, it also damages blood vessels already affected by stroke resulting in bleeding in some patients. To enhance the safety of rtPA, a method to assess stroke damage to blood vessels is urgently required. With support from the Ontario Research Fund, we have developed a CT scanning method to assess vessel damage in the brain and have identified the threshold beyond which the likelihood of bleeding is much greater, putting the patient at risk. We are now supported by the Heart and Stroke Foundation to validate this vessel damage assessment method in a larger sample of stroke patients to be recruited in London, Toronto and Ottawa.

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