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CT Assessment of Cerebral Perfusion: Experimental Validation and Initial Clinical Experience¹

¹ From the Imaging Research Laboratories, John P Robarts Research Institute, PO Box 5015, 100 Perth Drive, London, Ontario, N6A 5K8 Canada (D.G.N., A.C., T.Y.L.); Dept of Radiology and Lawson Research Institute, St Joseph's Health Centre, London, Ontario (A.C., J.D.B., R.K., T.Y.L.); Dept of Anaesthesia (R.A.C., A.W.G.), London Health Sciences Centre, University Campus, Ontario; and Dept of Neurology, Westfälische Wilhelms-Universität, Munster, Germany (D.G.N.). Received Aug 26, 1998; revision requested Oct 22; final revision received Jan 14, 1999; accepted Feb 15. Supported in part by Medical Research Council of Canada, Heart and Stroke Foundation of Canada, and GE Medical Systems. D.G.N. supported by a research grant of the Deutsche Forschungsgemeinschaft. Address reprint requests to T.Y.L. (e-mail: tlee@irus.rri.on.ca).

View larger version (22K): [in a new window]   Figure 1a. (a) Graph shows illustrative examples of CT contrast enhancement curves obtained from the ICA (•), a noncarotid artery of the neck (), gray matter (), and white matter () brain tissue in a dog. For a better illustration, the tissue curves are displayed by using a separate scale of CT numbers (HU) (right y axis). Note the higher contrast enhancement of the gray matter as compared with white matter, which reflects differences in CBV. (b) Graph shows that after deconvolution of the arterial and tissue enhancement curves, the input-independent impulse residue functions for gray () and white () matter were obtained. According to Equation (3), deconvolution of Q(t) and Ca(t) gives the product of CBF and R(t). Because R(t) is dimensionless, the scaled R(t) has the same units as CBF.

View larger version (14K): [in a new window]   Figure 1b. (a) Graph shows illustrative examples of CT contrast enhancement curves obtained from the ICA (•), a noncarotid artery of the neck (), gray matter (), and white matter () brain tissue in a dog. For a better illustration, the tissue curves are displayed by using a separate scale of CT numbers (HU) (right y axis). Note the higher contrast enhancement of the gray matter as compared with white matter, which reflects differences in CBV. (b) Graph shows that after deconvolution of the arterial and tissue enhancement curves, the input-independent impulse residue functions for gray () and white () matter were obtained. According to Equation (3), deconvolution of Q(t) and Ca(t) gives the product of CBF and R(t). Because R(t) is dimensionless, the scaled R(t) has the same units as CBF.

View larger version (155K): [in a new window]   Figure 2. Axial CT image of the dog's head in the prone position. Arrows indicate small cortical gray matter ROIs, arrowheads indicate small white matter ROIs, and BS denotes brain stem ROI. At the bottom of the Figure, the circular ROIs over the two ICAs and four noncarotid arteries (NCA) are displayed.

View larger version (97K): [in a new window]   Figure 3. Axial dynamic CT scan obtained during patient studies. The patient's head was placed in the head holder, and one of the forearms was supported above the head with a platform we made. The space between the plastic support and the forearm is filled with foam (arrows). Note the enhancement of the radial (RA) and ulnar (UA) arteries. The arterial contrast enhancement curves were obtained from the radial artery by using a 4-pixel-diameter circular ROI. The set of standardized tissue ROIs were drawn by using the method described in Materials and Methods.

View larger version (11K): [in a new window]   Figure 4a. Scatterplot shows linear regression of ICA-derived values versus noncarotid-derived (NCA) values of (a) CBV and (b) CBF in beagles. For both parameters, a strong correlation was found with slopes close to unity.

View larger version (18K): [in a new window]   Figure 4b. Scatterplot shows linear regression of ICA-derived values versus noncarotid-derived (NCA) values of (a) CBV and (b) CBF in beagles. For both parameters, a strong correlation was found with slopes close to unity.

View larger version (16K): [in a new window]   Figure 5. Bar graph shows absolute differences between ICA-derived and noncarotid-derived CBF values. On the y axis, the frequency of ROI is shown as a percentage. Note that for approximately two-thirds of the ROIs, the CBF difference was less than 10 mL/100 g/min. Differences greater than 20 mL/100 g/min were relatively rare for all ROIs (black bars) and nearly absent for ROIs with flow values less than 80 mL/100 g/min (gray bars).

View larger version (13K): [in a new window]   Figure 6. Line graph shows the time course of mean CBF ± SD (error bars) in the two patients with subarachnoid hemorrhage (SAH). Much lower overall mean CBF values beyond day 9 were observed in the patient with vasospasm (•) compared with those in the patient free of vasospasm ().

View larger version (7K): [in a new window]   Figure a1. Schematic shows the impulse residue function in the case when extravasation of contrast material occurs. The gray area denotes the intravascular portion, and the black area denotes the extravascular portion of the contrast material.