Radiation dose reduction using a CdZnTe-based computed tomography system: comparison to flat-panel detectors.
OBJECTIVE
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.
Le Huy
Q
Q
Department of Radiological Sciences, University of California, Irvine, California 92697, USA.
Ducote
Justin L
JL
Molloi
Sabee
S
D001822:Body Burden; D019187:Cadmium Compounds; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D008327:Mammography / Q000295:instrumentation*; D011829:Radiation Dosage; D011835:Radiation Protection / Q000295:instrumentation*; D013691:Tellurium; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*; D014963:X-Ray Intensifying Screens
D019187:Cadmium Compounds; D013691:Tellurium; C028337:cadmium telluride
Med Phys. 2004 May;31(5):1061-71
15191293
Med Phys. 2005 Dec;32(12):3767-76
16475776
Annu Rev Biomed Eng. 2007;9:501-26
17506654
Radiology. 1993 Aug;188(2):297-301
8327668
Med Phys. 2005 Nov;32(11):3395-408
16372415
Radiology. 2008 Mar;246(3):725-33
18195383
Med Phys. 1981 May-Jun;8(3):353-7
7033756
Radiology. 2001 Dec;221(3):657-67
11719660
Med Phys. 1990 May-Jun;17(3):327-41
2385190
Phys Med Biol. 2008 Mar 7;53(5):1475-95
18296774
Med Phys. 2006 Jun;33(6):1612-22
16872069
Med Phys. 2009 Jul;36(7):3018-27
19673201
Acad Radiol. 2006 Jan;13(1):63-72
16399033
Phys Med Biol. 2008 Aug 7;53(15):4031-47
18612175
Phys Med. 2006;21 Suppl 1:72-5
17645999
Med Phys. 1997 Nov;24(11):1661-70
9394272
Phys Med Biol. 2008 Oct 21;53(20):5595-613
18799830
AJR Am J Roentgenol. 1987 Mar;148(3):525-6
3492880
Phys Med Biol. 2006 Sep 21;51(18):4497-515
16953039
Med Phys. 1999 Dec;26(12):2680-3
10619253
Phys Med Biol. 2004 Jul 21;49(14):N247-53
15357205
Med Phys. 1985 May-Jun;12(3):297-304
4010634
Med Phys. 1996 Dec;23(12):1997-2005
8994164
Phys Med Biol. 2006 Sep 7;51(17):4267-87
16912381
Med Phys. 2007 Jul;34(7):2995-3004
17822008
Med Phys. 1981 Sep-Oct;8(5):659-67
7290019
Phys Med Biol. 1976 Sep;21(5):733-44
967922
J Digit Imaging. 1995 Feb;8(1 Suppl 1):70-3
7734544