Abstract
3325
Introduction: Peripheral Vascular Disease (PVD) is an epidemic affecting approximately 8 million Americans [1] and an estimated 10% of the worldwide population. PVD is closely associated with coronary artery disease and remains a relatively under-diagnosed disease [2]. To address this need, a dedicated, state-of-the-art PVD clinical Dynamic Extremity SPECT (DE-SPECT) scanner is being developed for the simultaneous cardiac and peripheral assessment of molecular and physiological changes of the lower extremities in PVD patients.
The DE-SPECT detector ring is a heptagon where the lower side has an opening for leg access and all other 6 sides consist of panels of CZT detector modules (DM) in a 4×4 checkerboard pattern with 8 DM per panel. The system has the unique feature of switching between two different collimation modes: large field of view (FOV) and small FOV. These modes can be used either for (i) dual/single leg imaging or (ii) scout/high-resolution imaging, respectively. In both uses, fast switching between modes is important, either to allow capturing the input function followed by detailed imaging, or to allow the identification of a region of interest in a wide FOV, followed by focusing in the region for high-resolution detailed imaging, with the expectation that neither the system nor patient will be moved between modes (or that movement will be carefully controlled) so that joint reconstruction of all data may be possible.
The DE-SPECT system deploys six pinhole-modular adaptive panels (PMAP) that adjust simultaneously. We explore the performance of a PMAP mechanism for joint reconstruction with axial stepping.
Methods: We have developed a fast mode-switching mechanism compatible with the overall DE-SPECT system concept. Two collimator types are mounted on a monolith tungsten plate with one DM module offset between configurations to take advantage of the checkerboard detector array for the axial translation. A pneumatic actuator (PA) connected to the tungsten plate toggles between physical stops that allow for precise repositioning in the axial direction. The PA is controlled by an air flow regulator module with use of analog input voltage. There are two control methods developed; the first method uses toggle switches to generate discrete input voltages corresponding to desired positions and the second method uses a computer to control input voltage.
A PMAP is built and the reproducibility of the adaptive mechanism is evaluated using both voltage toggle circuit and a computer control. In both cases, a dial caliper was used to measure the positions during 25 re-positioning experiments. All six PMAPs are tested independently and the simultaneous collective effect of all 6 PMAPs will be evaluated.
Results: Reproducibility was measured in prototype experiments and preliminary results are presented. Initial experiments with a PMAP indicate better reproducibility with the circuit than by direct computer control. Our current understanding of this result is that the computer interface converts the digital signal to an analog voltage, which is used to control the position of the actuator. In comparison, the custom circuit directly sets that analog voltage. Both control systems give submillimeter reproducibility with 2 seconds to exchange pinhole types.
PA are equipped with a servo position sensor. Sole use of voltage toggle circuit disables the sensor. On the other hand, computer controls provide position feedback and lower reproducibility. We will fuse together the toggle circuit idea and computer control to develop a novel control system to reach higher reproducibility and position readings.
Conclusions: We have developed a fast-switching collimator mechanism for dynamic dual-FOV imaging without disturb patient in imaging state. A prototype PMAP for 2 FOV has been built to demonstrate proof of concept. We have explored two methods of controlling the PA. We will present mechanical design and simultaneous position reproducibility measures with all assembled PMAPs.