Scatter and attenuation correction in technetium-99m brain SPECT

We propose a practical method for scatter and attenuation compensation in ^99mTc-ECD brain SPECT using a simultaneous emission CT (ECT) and transmission CT (TCT) acquisition system that includes the following major components: (a) triple-headed SPECT gamma camera equipped with fan beam collimators; (b) external line sources containing ^99mTC placed at the focal lines of the collimators; and (c) scatter correction by the triple- energy-window (TEW) method. Methods: Projection images were obtained over a 360°rotation scan. After acquisition, scatter correction was performed using the TEW method, which corrected scattered photons pixel by pixel in the projection data. Scatter-corrected ECT images were compensated for attenuation using the TCT images with Chang'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 imaging using a combination of 925 MBq ^99mTc- ECD as a radio pharmaceutical and 222 MBq ^99mTc as an external source. ECT and TCT data were acquired separately or simultaneously. Results: SPECT quantification and image quality were improved by performing this correction. The activity concentration images obtained with the simultaneous acquisition were almost identical to those obtained with the separate acquisition. Conclusion: This method was clinically practical and cost-effective for reconstructing quantitative ^99mTc brain SPECT images.