Small Animal Single Photon Emission Computed Tomography Research Articles

SemiSPECT: A small‐animal single‐photon emission computed tomography (SPECT) imager based on eight cadmium zinc telluride (CZT) detector arrays

The first full single-photon emission computed tomography (SPECT) imager to exploit eight compact high-intrinsic-resolution cadmium zinc telluride (CZT) detectors, called SemiSPECT, has been completed. Each detector consists of a CZT crystal and a customized application-specific integrated circuit (ASIC). The CZT crystal is a 2.7 cm x 2.7 cm x -0.2 cm slab with a continuous top electrode and a bottom electrode patterned into a 64 x 64 pixel array by photolithography. The ASIC is attached to the bottom of the CZT crystal by indium-bump bonding. A bias voltage of -180 V is applied to the continuous electrode. The eight detectors are arranged in an octagonal lead-shielded ring. Each pinhole in the eight-pinhole aperture placed at the center of the ring is matched to each individual detector array. An object is imaged onto each detector through a pinhole, and each detector is operated independently with list-mode acquisition. The imaging subject can be rotated about a vertical axis to obtain additional angular projections. The performance of SemiSPECT was characterized using 99mTc. When a 0.5 mm diameter pinhole is used, the spatial resolution on each axis is about 1.4 mm as estimated by the Fourier crosstalk matrix, which provides an algorithm-independent average resolution over the field of view. The energy resolution achieved by summing neighboring pixel signals in a 3 x 3 window is about 10% full-width-at-half-maximum of the photopeak. The overall system sensitivity is about 0.5 x 10(-4) with the energy window of +/-10% from the photopeak. Line-phantom images are presented to visualize the spatial resolution provided by SemiSPECT, and images of bone, myocardium, and human tumor xenografts in mice demonstrate the feasibility of preclinical small-animal studies with SemiSPECT.

Performance amelioration for small animal SPECT using optimized pinhole collimator and image correction technique

The aim of this study was to improve the performance of pinhole single photon emission computed tomography (SPECT) fabricated with a position sensitive photomultiplier tube using an optimized pinhole collimator and image correction technique. The center-of-rotation was aligned to prevent mechanical shift using a leveling-laser system. Based on the previous results of pinhole aperture simulation and optimization study, a pinhole collimator for the small animal SPECT was fabricated in the range of optimal pinhole diameter and channel height. Previously reported image correction technique of position mapping, energy calibration and flood correction procedures developed for array type scintillator was revised and applied to plate type crystal. Phantom and small animal studies were performed to investigate the system performance. Image corrections, center-of-rotation alignment, and collimator optimization were necessary to obtain high resolution and high quality SPECT images. The SPECT system ameliorated by this study could be utilized in small animal and molecular imaging studies required to provide high spatial resolution with moderate sensitivity.

A restraint-free small animal SPECT imaging system with motion tracking

We report on an approach toward the development of a high-resolution single photon emission computed tomography (SPECT) system to image the biodistribution of radiolabeled tracers such as Tc-99m and I-125 in unrestrained/unanesthetized mice. An infrared (IR)-based position tracking apparatus has been developed and integrated into a SPECT gantry. The tracking system is designed to measure the spatial position of a mouse's head at a rate of 10-15 frames per second with submillimeter accuracy. The high-resolution, gamma imaging detectors are based on pixellated NaI(Tl) crystal scintillator arrays, position-sensitive photomultiplier tubes, and novel readout circuitry requiring fewer analog-digital converter (ADC) channels while retaining high spatial resolution. Two SPECT gamma camera detector heads based upon position-sensitive photomultiplier tubes have been built and installed onto the gantry. The IR landmark-based pose measurement and tracking system is under development to provide animal position data during a SPECT scan. The animal position and orientation data acquired by the tracking system will be used for motion correction during the tomographic image reconstruction.

TU-D-J-6B-01: Small Animal PET and SPECT: Instrumentation, Performance, and Applications

In recent years both industrial and academic institutions have been intrigued with the possibility of using in vivo imaging assays in small animal models to study cellular and molecular processes associated with diseases such as cancer, heart disease, and neurological disorders. The ultimate goals of these in vivo imaging efforts are to facilitate the discovery of new drugs and treatments for disease and accelerate their translation into the clinic. Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) are highly sensitive in vivo imaging modalities that can detect extremely low concentrations of radionuclide-labeled probes that target the disease process of interest at the molecular level. This presentation will review PET and SPECT small animal imaging instrumentation requirements, challenges, performance characteristics, and applications in imaging subtle molecular signals associated with disease.