Attenuation correction for small animal SPECT imaging using x-ray CT data
Phantom for calibration of CT images. The main cavity is filled with water, and the inner tubes are filled with materials of known composition. An x-ray CT image of the phantom is shown to the right. Three tubes containing varying concentrations of solutions are visible within the outer cylinder filled with water.
Correlation between CT image intensity (HU) and linear attenuation coefficients for (I-125) photons. The linear attenuation values include coherent scatter.
Plot of attenuation coefficient as a function of CT image values for a range of anode current values. An analysis of the data shows that there is no significant effect of tube current on the CT value.
CT image of a uniform, water filled cylinder . An axial slice is shown on the left; a coronal image is shown on the right. These images demonstrate that there is no systematic variation in CT image intensity across the field of view except for a slight decrease in image intensity in the center of the cylinder due to beam hardening.
Plot of the signal-to-noise ratio in CT images of a uniform phantom as a function of the -ray tube anode current.
This graph compares CT calibration results obtained with and without water in the outer cylinder of the phantom. The graph demonstrates that changing amounts of beam hardening will affect the calibration results.
The top image shows a reconstructed SPECT image of a uniform tank filled with iodine-125. A line profile drawn through the center of the image shows that the intensity in the center is decreased, a common effect of photon attenuation. The bottom image demonstrates that adding attenuation correction removes this artifact.
Myocardial perfusion SPECT images obtained using -iodorotenone injected in a rat. Attenuation correction increased the apparent uptake in the base of the inferior wall, as well as improved the uniformity of the image.
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