An energy-optimized collimator design for a CZT-based SPECT camera

Fenghua Weng; Srijeeta Bagchi; Yunlong Zan; Qiu Huang; Youngho Seo

doi:10.1016/j.nima.2015.09.115

An energy-optimized collimator design for a CZT-based SPECT camera

Nucl Instrum Methods Phys Res A. 2016 Jan 11:806:330-339. doi: 10.1016/j.nima.2015.09.115.

Authors

Fenghua Weng¹, Srijeeta Bagchi², Yunlong Zan¹, Qiu Huang¹, Youngho Seo³

Affiliations

¹ School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China.
² Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA.
³ Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA ; Department of Radiation Oncology, University of California, San Francisco, CA, USA.

Abstract

In single photon emission computed tomography, it is a challenging task to maintain reasonable performance using only one specific collimator for radio-tracers over a broad spectrum of diagnostic photon energies, since photon scatter and penetration in a collimator differ with the photon energy. Frequent collimator exchanges are inevitable in daily clinical SPECT imaging, which hinders throughput while subjecting the camera to operational errors and damage. Our objective is to design a collimator, which independent of the photon energy performs reasonably well for commonly used radiotracers with low- to medium-energy levels of gamma emissions. Using the Geant4 simulation toolkit, we simulated and evaluated a parallel-hole collimator mounted to a CZT detector. With the pixel-geometry-matching collimation, the pitch of the collimator hole was fixed to match the pixel size of the CZT detector throughout this work. Four variables, hole shape, hole length, hole radius/width and the source-to-collimator distance were carefully studied. Scatter and penetration of the collimator, sensitivity and spatial resolution of the system were assessed for four radionuclides including ⁵⁷Co, ^99m Tc, ¹²³I and ¹¹¹In, with respect to the aforementioned four variables. An optimal collimator was then decided upon such that it maximized the total relative sensitivity (TRS) for the four considered radionuclides while other performance parameters, such as scatter, penetration and spatial resolution, were benchmarked to prevalent commercial scanners and collimators. Digital phantom studies were also performed to validate the system with the optimal square-hole collimator (23 mm hole length, 1.28 mm hole width, 0.32 mm septal thickness) in terms of contrast, contrast-to-noise ratio and recovery ratio. This study demonstrates promise of our proposed energy-optimized collimator to be used in a CZT-based gamma camera, with comparable or even better imaging performance versus commercial collimators such as low-energy high resolution (LEHR) and medium energy general purpose (MEGP) collimators.

Keywords: CZT detector; Monte Carlo simulation; SPECT; collimator design.

Grants and funding

R01 EB012965/EB/NIBIB NIH HHS/United States