SNM: Modified protocol cuts PET/CT dose in Alzheimer's
Article Thumbnail ImageJune 11, 2012 -- Researchers from South Korea were able to reduce the radiation dose in PET/CT studies with a slow-acting radiotracer by using just one CT acquisition for multiple PET scans, according to a presentation at the Society of Nuclear Medicine (SNM) meeting in Miami Beach, FL.
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In a study of five volunteers who were scanned after injection of a new radiotracer for detecting amyloid plaque, realigning the original CT data to correspond to a second PET acquisition reduced radiation dose significantly compared to two PET/CT acquisitions, lead author Joong Hyun Kim and colleagues from Seoul National University reported.

CT is useful for reducing PET scan times and boosting image quality, but there is room for reducing the radiation dose by avoiding the redundancy of repetitive scans, co-author Jae Sung Lee said in a statement accompanying the study's release. Their study sought to minimize dose by performing only a single CT scan per subject and utilizing image registration to line up the CT data to both PET scans.

The five volunteers were imaged in two sessions of dynamic brain PET/CT with a new biomarker for amyloid plaque (F-18 SNUBH-NM-333). After a 10-minute pause between imaging sessions, the subjects were repositioned and another PET scan (80 minutes) was performed.

The realigned first CT exam was formed by adding the patient bed image and realigned head part of the first CT using the transformation parameters from first to second PET images reconstructed without attenuation correction, the authors wrote. The second PET images with eight frames were then reconstructed after attenuation correction using three different CT images -- the original and realigned first CT scans, and the original second CT scan.

The authors calculated the area under the curve (AUC) of time activity curve and distribution volume ratio (DVR) in five brain regions -- cerebellum, frontal, parietal, posterior, and temporal cortex -- and compared them.

Compared to attenuation-corrected images using the second CT, images using the original and realigned first CT exams yielded differences in AUC of -9.3 ± 17.3% and -1.5 ± 2.6%, respectively, the group reported. The realigned first CT yielded insignificant differences in DVR relative to the second CT (-0.1 ± 0.2%).

Multiple-session brain PET/CT studies with only a single CT scan are feasible and will be useful for minimizing radiation exposure, they wrote.