Emission tomography through advanced 3-D position-sensitive CZT spectrometers

Jin, Yifei

Permalink

https://hdl.handle.net/2142/125806 Copy

Description

Title

Emission tomography through advanced 3-D position-sensitive CZT spectrometers

Author(s)

Jin, Yifei

Issue Date

2024-07-11

Director of Research (if dissertation) or Advisor (if thesis)

Meng, Ling-Jian

Doctoral Committee Chair(s)

Meng, Ling-Jian

Committee Member(s)

• Fulvio, Angela Di
• Stubbins, James F
• Metzler, Scott D

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Emission tomography
• CZT detectors

Abstract

To address clinical challenges such as peripheral vascular disease and breast cancer, we explored emission tomography, including single photon emission computed tomography (SPECT), positron emission tomography (PET), and Compton imaging, using an advanced 3-D position-sensitive Cadmium Zinc Telluride (CZT) imaging spectrometer. This spectrometer offers superior energy resolutions (3 keV at 200 keV, 4.5 keV at 450 keV, and 5.4 keV at 511 keV full width at half maximum (FWHM)) and spatial resolution (~0.5 mm in three dimensions), as well as the ability to detect multiple gamma-ray interactions simultaneously. These capabilities provide detailed insights into radiotracer distribution, enabling comprehensive assessments at the molecular and microvascular levels in theragnostics. Despite these capabilities, spatial distortion and other issues limit their immediate applicability. To address the limitations, we demonstrated the effectiveness of our proposed maximum-likelihood-based data preconditioning technique effectiveness in both projection and imaging domains. This technique only utilizes final spectral and spatial information for correction, suggesting broader applications beyond CZT detectors, for other position-sensitive solid state detectors. Based on the advanced CZT sensors and preconditioning technique, we developed and constructed the Dynamic Extremity SPECT (DE-SPECT) system, the first clinical SPECT system based on 1-cm-thick CZT detectors with depth-of-interaction (DOI) capabilities. The system is tailored for multi-functional imaging of Peripheral Vascular Disease (PVD) in lower extremities. Through phantom studies, the system demonstrated impressive capabilities in dual-leg and single-leg configurations, achieving spatial resolutions of approximately 12 mm and 6 mm FWHM, respectively. This system has proven its efficacy in multi-tracer imaging with multi-tracer phantom studies, showcasing its versatility and potential in clinical settings. The DE-SPECT system's ability to perform in vivo gamma-ray spectrometry on a voxel-by-voxel basis enhances the precision of diagnostic imaging and offers a more comprehensive understanding of various pathological conditions. In therapeutic radionuclide SPECT imaging, the low radioactive uptake within the tissues of interest, even with high administered activity, results in limited measured counts, which can undermine the efficacy of traditional scatter correction methods. To address this challenge, we introduced the Spectral-Temporal Double Coincidence (STDC) technique, designed specifically to eliminate down-scattered and crosstalk contamination in low-activity scenarios. We experimentally evaluated the STDC-SPECT system, demonstrating significant improvements in Spectral-SCR (signal-to-contamination ratio) and Projection-SCR, and substantial reductions in normalized contamination. These findings highlight STDC's superior capability to mitigate down-scattered contamination, especially at lower activity levels, dramatically enhancing image quality compared to conventional methods. We also evaluated a prototype PET system based on the advanced CZT sensors. Using various sources and phantoms, we demonstrated an imaging resolution of approximately 0.75 mm in PET images and investigated the impact of DOI resolution on image quality. Although the current CZT-PET prototype has a relatively poor timing resolution due to its specific timing signal readout approach, this could potentially be alleviated by employing a cathode-signal-based technique. Despite the limitations, the higher Compton fraction in CZT detectors enables the use of Compton kinematics to enhance SPECT and PET imaging, improving image quality and expanding the field of view. To effectively utilize Compton information, we developed a numerical integration technique to model the near-field Compton response of the CZT detectors, incorporating the influence of Doppler broadening, finite detector resolutions, and the distance between the first and second interactions. By optimizing Noise Equivalent Count Rate (NECR) and evaluating the rejection accuracy, we demonstrated that Compton kinematics significantly improve PET image quality by rejecting random and scattered coincidences. Further research through simulations and experimental validations is essential to fully realize the benefits of Compton techniques for PET imaging and to enhance imaging capabilities for breast cancer detection and staging.

Graduation Semester

2024-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/125806

Copyright and License Information

Copyright 2024 Yifei Jin

Owning Collections