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AJNR - American Journal of Neuroradiology

Published ahead of print on March 19, 2009
doi: 10.3174/ajnr.A1492

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Theoretic Basis and Technical Implementations of CT Perfusion in Acute Ischemic Stroke, Part 2: Technical Implementations

A.A. Konstas^a, G.V. Goldmakher^a, T.-Y. Lee^b and M.H. Lev^a

^a Department of Radiology, Massachusetts General Hospital, Boston, Mass
^b Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada

View larger version (19K): [in this window] [in a new window]   Fig 1. The maximum slope method. CBF can be calculated from the ratio of the maximum slope (Max Slope) of Q(t) to the maximum arterial concentration. The higher maximum slope in the contralateral region of interest (ROI) (ie, the region of interest without stroke) will give a higher CBF than that for the ipsilateral region of interest, for which the CBF will be reduced.

View larger version (85K): [in this window] [in a new window]   Fig 2. A–H, CTP maps calculated by using a delay-sensitive deconvolution algorithm that is affected by the delay (To) between arterial input and tissue curves. To simulate a range of To, we processed the dynamic images of a single section from a CTP study on a patient with brain tumor such that time-versus-enhancement curves from the entire left hemisphere were shifted forward in time by 2 seconds relative to the right hemisphere. The original and time-shifted CTP studies were then processed by Perfusion 3 (GE Healthcare) by using the same arterial input curve and venous curve from the right hemisphere. A and B, CBF maps for the original and the To = 2 second study. C and D, The corresponding CBV maps. E and F, The corresponding MTT maps. G and H, The corresponding To maps. As To increases, CBF decreases and MTT increases while CBV remains unchanged. The deconvolution algorithm is not able to estimate To. I–P, CTP maps calculated by using a delay-insensitive deconvolution algorithm that is unaffected by the To between arterial input and tissue curves. The original and time-shifted CTP studies of I–P are processed in the same way as A–H except that a delay-insensitive deconvolution algorithm (Perfusion 4, GE Healthcare) is used instead. I and J, The CBF maps for the original and To = 2 second study. K and L, The corresponding CBV maps. M and N, The corresponding MTT maps. O and P, The corresponding To maps. As To increases, CBF and CBV remain relatively unchanged and MTT increases slightly. The deconvolution algorithm is able to detect an increase in To, but the estimate of To is not accurate.