Development of a High Performance Clinical Cardiac SPECT/TCT System

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This proposal’s objective is to complete a Single Photon Emission Computed Tomography (SPECT) system dedicated to human cardiac imaging. It is stationary, in the sense that all views needed for a given configuration are simultaneously acquired over the Field of View (FOV), yet adaptive in that it can change its resolution-sensitivity-FOV tradeoff in about 10 seconds without needing to move the patient. To do this, it takes advantage of the separability of slit-slat collimation, which uses a slit to collimate the transverse direction and a set of slats to collimate the axial direction, similar to parallel-beam. The slits can be adapted into one of five view configurations using a high-precision, continuous-loop conveyor that moves different slit plates into position. The slats are adaptive into two positions using pneumatic actuators that compress adjacent slats into a single slat, doubling the sensitivity at the cost of resolution. The system also has a transmission source that allows for attenuation correction so that quantitative dynamic imaging is very realistic, in addition to accurate patient positioning before dynamic scanning. The prototype system is nearing completion. Adaptation to a clinical prototype (Aim 1) requires (i) adding a smart chair for positioning and re-positioning the patient so that different data can be acquired in different configurations (e.g., scout + hi-resolution + transmission); (ii) adding a cover with touch pads for patient safety; and (iii) completing software integration so that multiple modes (e.g., transmission and scout imaging) can be run with proper re-positioning of the patient (e.g., transmission followed by centering the heart for focal imaging based on online reconstruction). After system testing and optimization for static imaging (Aim 2) and dynamic imaging (Aim 3), we will then test dynamic cardiac imaging to quantify myocardial blood flow (MBF) in an animal model, with confirmation through microspheres (Aim 4). Successfully measuring MBF in patients, something that is commonplace in PET but extraordinary challenging in SPECT because (i) systems often need to rotate; (ii) quantification is sometime not available (e.g., D- SPECT); and (iii) the ability to apply appropriate corrections is compromised. For instance, dynamic imaging in SPECT really requires a high-sensitivity mode to capture the input function and fast dynamics, yet also requires high-resolution to correct for spill-over – due to limited spatial resolution and cardiac motion. Without these corrections, one cannot account for the non-linear extraction of the tracer (i.e., the extraction fraction decreases with increasing blood flow). We hypothesize that the combination of high-sensitivity for dynamic imaging, combined with high-resolution for quantitative corrects, coupled with both scatter and attenuation correction, will yield MBF in human patients comparable to that achieved with PET, as tested in Aim 5. We believe that if this project is successful, it could bring the quantification of PET for cardiac imaging to a much larger population, with tremendous possible implications on impacting health.