Radiation dose reduction using a CdZnTe-based computed tomography system: Comparison to flat-panel detectors

• Published in: Medical physics (Lancaster) Vol. 37; no. 3; pp. 1225 - 1236
• Main Authors: Le, Huy Q., Ducote, Justin L., Molloi, Sabee
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01.03.2010
• Subjects: APATITES; BIOMEDICAL RADIOGRAPHY; Body Burden; Breast imaging; CADMIUM COMPOUNDS; Cancer; Charge transfer; Computed tomography; computerised tomography; COMPUTERIZED TOMOGRAPHY; DOSIMETRY; ENERGY RESOLUTION; Equipment Design; Equipment Failure Analysis; Humans; II‐VI semiconductors; Image detection systems; Image sensors; IODINE; MAMMARY GLANDS; Mammography; Mammography - instrumentation; Medical image noise; Medical imaging; Medical X‐ray imaging; NEOPLASMS; NOISE; PATIENTS; PHANTOMS; photon counting; photon counting detector; PHOTONS; PMMA; RADIATION DETECTORS; Radiation Dosage; radiation dose; RADIATION DOSES; Radiation Imaging Physics; Radiation Protection - instrumentation; RADIOLOGY AND NUCLEAR MEDICINE; SEMICONDUCTOR MATERIALS; SIMULATION; Tellurium; Tomography, X-Ray Computed - instrumentation; X RADIATION; X-Ray Intensifying Screens; X‐ray detectors; zinc compounds; CT; radiation dose; Breast imaging; photon counting detector
• ISSN: 0094-2405; 2473-4209; 0094-2405
• DOI: 10.1118/1.3312435

Purpose: Although x-ray projection mammography has been very effective in early detection of breast cancer, its utility is reduced in the detection of small lesions that are occult or in dense breasts. One drawback is that the inherent superposition of parenchymal structures makes visualization of small lesions difficult. Breast computed tomography using flat-panel detectors has been developed to address this limitation by producing three-dimensional data while at the same time providing more comfort to the patients by eliminating breast compression. Flat panels are charge integrating detectors and therefore lack energy resolution capability. Recent advances in solid state semiconductor x-ray detector materials and associated electronics allow the investigation of x-ray imaging systems that use a photon counting and energy discriminating detector, which is the subject of this article. Methods: A small field-of-view computed tomography (CT) system that uses CdZnTe (CZT) photon counting detector was compared to one that uses a flat-panel detector for different imaging tasks in breast imaging. The benefits afforded by the CZT detector in the energy weighting modes were investigated. Two types of energy weighting methods were studied: Projection based and image based. Simulation and phantom studies were performed with a 2.5 cm polymethyl methacrylate (PMMA) cylinder filled with iodine and calcium contrast objects. Simulation was also performed on a 10 cm breast specimen. Results: The contrast-to-noise ratio improvements as compared to flat-panel detectors were 1.30 and 1.28 (projection based) and 1.35 and 1.25 (image based) for iodine over PMMA and hydroxylapatite over PMMA, respectively. Corresponding simulation values were 1.81 and 1.48 (projection based) and 1.85 and 1.48 (image based). Dose reductions using the CZT detector were 52.05% and 49.45% for iodine and hydroxyapatite imaging, respectively. Image-based weighting was also found to have the least beam hardening effect. Conclusions: The results showed that a CT system using an energy resolving detector reduces the dose to the patient while maintaining image quality for various breast imaging tasks.