A Prospective Method for Selecting the Optimal SPECT Pinhole Trajectory

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2021

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Abstract

AbstractPinhole imaging is a widely used method for high spatial resolution single gamma imaging with a small required field of view (FOV). Many factors affect pinhole imaging: (I) the geometric parameters of the pinhole imaging system, such as the pinhole diameter, focal length and opening angle; (II) the position, range, sampling interval, and sampling time of the pinhole trajectory; and (III) the image reconstruction algorithm. These differences result in different trade-offs between resolution, sensitivity, noise level, imaging FOV, and data-sampling integrity levels. In pinhole imaging, many different pinhole trajectories might be considered. The conventional approach to assessing different trajectories is to reconstruct images from the various trajectories and then assess which image is best. Such an approach is however time consuming, since (I) image reconstruction is time-consuming and (II) image analysis often requires ensembles of images, where the ensemble is time consuming to calculate, consumes considerable computer storage, and requires investigator time to organize and analyze. The object of this project is to develop a method to rapidly select the optimal SPECT pinhole trajectory from among several candidate trajectories. Equivalent Resolution Geometric Efficiency (ERGE) is proposed to represent the spatial resolution and geometric efficiency; a higher ERGE means a better trajectory. To verify this metric, two-dimensional and three-dimensional visualizations of the pinhole trajectory are implemented in software as a way to assess trajectories visually and qualitatively. Several different trajectories are employed, projection data are computer-simulated, including spatial resolution blurring and pseudo-random Poisson noise, and image reconstruction is performed using the OSEM algorithm. The reconstructed images are analyzed to characterize the performance of the different trajectories to assess whether the best trajectory can be determined by the sensitivity and resolution characteristics of the individual pinhole locations that make up the trajectory. Ultimately, the method proved to be effective. In this study, a relatively simple low-cost prospective method for selecting the optimal SPECT pinhole trajectory has been shown to be effective. Only very fast and simple calculations, utilizing Microsoft Excel for example, are required. The method does not require simulating or acquiring projection data and does not require image reconstruction. The ranking of ERGE matches well with the ranking of reconstructed images based on Root Mean Square Error (RMSE). In clinical and scientific research, many different pinhole trajectories might be considered for pinhole 3D SPECT imaging, but it is too time-consuming to assess each trajectory via reconstructed images. By demonstrating the validity of this method for assessing trajectories, it may facilitate the improved use of 3D pinhole SPECT imaging in clinical and scientific research. Keywords: Pinhole Trajectory, SPECT, Forward Projection, OSEM, Equivalent Resolution Geometric Efficiency (ERGE), Root Mean Square Error (RMSE).

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Tao, Xiangzhi (2021). A Prospective Method for Selecting the Optimal SPECT Pinhole Trajectory. Master's thesis, Duke University. Retrieved from https://hdl.handle.net/10161/24439.

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