SCATTER AND ATTENUATION CORRECTION IN TC-99M BRAIN SPECT

We propose a practical method for scatter and attenuation compensation in Tc-99m-ECD brain SPECT using a simultaneous emission CT (ECT) and transmission CT (TCT) acquisition system that includes the following m ajor components: (a) triple-headed SPECT gamma camera equipped with fa nbeam collimators; (b) external line sources containing Tc-99m placed at the focal lines of the collimators; and (c) scatter correction by t he triple-energy-window (TEW) method. Methods: Projection images were obtained over a 360 degrees rotation scan. After acquisition, scatter correction was performed using the TEW method, which corrected scatter ed photons pixel by pixel in the projection data. Scatter-corrected EC T images were compensated for attenuation using the TCT images with Ch ang's iterative method, and were converted to activity concentration ( kBq/ml) images by obtaining a cross-calibration scan. After validating this method with phantom studies, it was applied to clinical brain im aging using a combination of 925 MBq Tc-99m-ECD as a radiopharmaceutic al and 222 MBq Tc-99m as an external source. ECT and TCT data were acq uired separately or simultaneously. Results: SPECT quantification and image quality were improved by performing this correction. The activit y concentration images obtained with the simultaneous acquisition were almost identical to those obtained with the separate acquisition. Con clusion: This method was clinically practical and cost-effective for r econstructing quantitative Tc-99m brain SPECT images.