Semester of Graduation
Master of Science (MS)
Physics & Astronomy (Medical Physics)
Single Photon Emission Computed Tomography (SPECT) is a non-invasive imaging modality, frequently used in myocardial perfusion imaging. The biggest challenges facing the majority of clinical SPECT systems are low sensitivity, poor resolution, and the relatively high radiation dose to the patient. New generation systems (GE Discovery, DSPECT) dedicated to cardiac imaging improve sensitivity by a factor of 5-8. The purpose of this work is to investigate a new gamma camera design with 21 hemi-ellipsoid detectors each with a pinhole collimator for Cardiac SPECT for further improvement in sensitivity, resolution, imaging time, and radiation dose.
To evaluate the resolution of our hemi-ellipsoid system, GATE Monte-Carlo simulations were performed on point-sources, rod-sources, and NCAT phantoms. The purpose of point-source simulation is to obtain operating pinhole diameter by comparing the average FWHM (Full-width-half-maximum) of flat-detector system with curved hemi-ellipsoid detector system. The operating pinhole diameter for the curved hemi-ellipsoid detector was found to be 8.68mm. System resolution is evaluated using reconstructed rod-sources equally spaced within the region of interest. The results were compared with results of GE discovery system available in the literature. The system performance was also evaluated using the mathematical anthropomorphic NCAT (NURBS-based Cardiac Torso) phantom with a full (clinical) dose acquisition (25mCi) for 2 mins and an ultra-low-dose acquisition of 3mCi for 5.44mins.
On rod-sources, the average resolution after reconstruction with resolution recovery in the entire region of interest (ROI) for cardiac imaging was 4.44mm, with standard deviation 2.84mm, compared to 6.9mm reported for GE Discovery (Kennedy et al, JNC, 2014). For NCAT studies improved sensitivity allowed a full-dose (25mCi) 2 min acquisition (ELL8.68mmFD) which yielded 3.79M LV counts. This is ~3.35 times higher compared to 1.13M LV counts acquired in 2 mins for clinical full-dose for state-of-the-art DSPECT. The increased sensitivity also allowed an ultra-low dose acquisition protocol (ELL8.68mmULD). This ultra-low-dose protocol yielded ~1.23M LV-counts which was comparable to the full-dose 2min acquisition for DSPECT. The estimated NCAT average FWHM at the LV wall after 12 iterations of the OSEM reconstruction was 4.95mm and 5.66mm around the mid-short-axis slices for ELL8.68mmFD and ELL8.68mmULD respectively.
Bhusal, Narayan, "Third Generation Gamma Camera SPECT System" (2018). LSU Master's Theses. 4788.