TY - GEN
T1 - Improved contrast-to-noise ratio of photon counting clinical x-ray CT images using a model-selection based approach
AU - Srivastava, Somesh
AU - Taguchi, Katsuyuki
PY - 2010
Y1 - 2010
N2 - Energy sensitive photon counting x-ray detectors (PCXD) [1] have many advantages over energy-integrating x-ray detectors (EIXD) in x-ray computed tomography (CT), such as the ability to measure the spectrum of x-ray beams. When such PCXDs are operated under a high count rate in clinical scanners, coincident photons would distort the recorded energy spectrum due to the limited speed of the detector. To compensate for the spectrum distortions, we have developed analytical models for them [3] and integrated one such model into an image reconstruction process using a sinogram restoration framework [6]. In this method, the attenuation of the object was modeled as a sum of line integrals of N basis functions, where N was fixed at 3 for the entire sinogram when a contrast agent is involved. The method allowed us to reconstruct accurate images, compensating for the effect of spectrum distortion of PCXD; however, the contrast-to-noise (CNR) of the images were only comparable to that obtained by EIXDs. We believe the main reason is an increased statistical uncertainty in the estimated line integrals introduced by the 3rd basis function. In this paper, we propose a method to improve the CNR by employing the fewest number of basis functions Nm (≤N) as necessary for an individual sinogram ray. Our simulation studies indicate that the CNR achieved for a Gd-based contrast agent by PCXDs could be 12% better than the conventional method of [6], and 28% better than EIXDs for scans with similar number of x-ray photons, which points to a dose reduction of 20% and 39% respectively.
AB - Energy sensitive photon counting x-ray detectors (PCXD) [1] have many advantages over energy-integrating x-ray detectors (EIXD) in x-ray computed tomography (CT), such as the ability to measure the spectrum of x-ray beams. When such PCXDs are operated under a high count rate in clinical scanners, coincident photons would distort the recorded energy spectrum due to the limited speed of the detector. To compensate for the spectrum distortions, we have developed analytical models for them [3] and integrated one such model into an image reconstruction process using a sinogram restoration framework [6]. In this method, the attenuation of the object was modeled as a sum of line integrals of N basis functions, where N was fixed at 3 for the entire sinogram when a contrast agent is involved. The method allowed us to reconstruct accurate images, compensating for the effect of spectrum distortion of PCXD; however, the contrast-to-noise (CNR) of the images were only comparable to that obtained by EIXDs. We believe the main reason is an increased statistical uncertainty in the estimated line integrals introduced by the 3rd basis function. In this paper, we propose a method to improve the CNR by employing the fewest number of basis functions Nm (≤N) as necessary for an individual sinogram ray. Our simulation studies indicate that the CNR achieved for a Gd-based contrast agent by PCXDs could be 12% better than the conventional method of [6], and 28% better than EIXDs for scans with similar number of x-ray photons, which points to a dose reduction of 20% and 39% respectively.
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U2 - 10.1109/NSSMIC.2010.5874442
DO - 10.1109/NSSMIC.2010.5874442
M3 - Conference contribution
AN - SCOPUS:79960291865
SN - 9781424491063
T3 - IEEE Nuclear Science Symposium Conference Record
SP - 3425
EP - 3428
BT - IEEE Nuclear Science Symposuim and Medical Imaging Conference, NSS/MIC 2010
T2 - 2010 IEEE Nuclear Science Symposium, Medical Imaging Conference, NSS/MIC 2010 and 17th International Workshop on Room-Temperature Semiconductor X-ray and Gamma-ray Detectors, RTSD 2010
Y2 - 30 October 2010 through 6 November 2010
ER -