3D Imaging and Activity Quantification Using a Portable Gamma Camera for Radiopharmaceutical Therapy.
Abstract
Purpose
The purpose of this study was to test the ability of a portable gamma camera capable of imaging gammas from 30 – 600 keV gammas to produce 3D imaging and activity quantification of radiopharmaceutical distributions for RPT verification and dosimetry.
Methods
A portable gamma imager capable of acquiring 3D gamma images was used to image a 2.54 cm diameter sphere filled with 99mTc (9.5 mCi) inside of a water filled Jaszczak phantom. First SPECT and CT images of the phantom were acquired using a clinical SPECT/CT imager. Next, with the portable camera, individual 3D gamma images were acquired at 0o (anterior), 45o, 60o and 90o (right lateral) around the phantom. Single 3D projection gamma images (at fixed angular position), as well as a combined 3D image of all projection images were compared to the SPECT/CT images. Finally, based on a sensitivity calibration (CPS/mCi) of the portable gamma camera, activity in the sphere was calculated and compared to the known activity in the filled phantom sphere.
Results
The single position 3D projection images were able to image and localize the radiopharmaceutical distribution in the 2D lateral dimensions. However, due to poor parallax of the portable imager the individual images showed poor depth resolution. By correctly co-registering the 3D gamma images to the CT images and combining multiple projection images the 99mTc distribution in the sphere could be localized in all 3-dimensions. Using the sensitivity of the camera, camera-to-phantom distance, and path length in the phantom, activity in the sphere was estimated from the images to be 9.1 ± 0.08 mCi.
Conclusion
The portable gamma imager was able to produce 3D images of radiopharmaceutical distribution and predict the activity in the phantom to within ~5%, showing feasibility of imaging and predicting activity for a wide range of current/future radiopharmaceuticals.