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Analysis
We visually analyzed 3-D volume rendered images, together with traditional, transverse, sagittal and coronal images. A 3-D surface program is used to render and view surfaces in 3-D from any direction. Designated thresholds define surface deficits. This particular program only works in filtered transverse or oblique reformatted files. (Picker, Nuclear Med, manual). One set of the traditional "opaque" volume rendered 3-D images was created with only one cut-off or threshold of 60-65% of the maximum value, depending on the mean absolute cortical blood flow obtained using the Xe-133 inhalation technique prior to the Tc-99m injection. This display method provides an excellent means for anatomic localization of cortical perfusion deficits.
A second set of 3-D images had two thresholds set. The high one was set the same for all patients at 88%. It was used to identify areas that had a relative perfusion within 12% of the maximum cortical blood flow. These areas were presented in blue. Both cortical as well as sub-cortical areas of relatively high blood flow can be seen in this display form, since the cortex is displayed as a see-through lattice. The lattice points join regions with a second, lower cut-off value that was the same as used in the first 3-D image. These values fluctuate between 60-65% of the maximum value. The cortical areas corresponding to these values were connected by a red lattice-work like a Buckyball. The 3-D images, were presented in 5 standard views: anterior, left and right lateral, as well as the vertex views allowed ready appreciation of alteration of perfusion in the temporal lobes. In addition, analysis was made directly from the computer monitor that allowed rotation of any of the 3D volume rendered images about all three axes of the model.
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