TY - JOUR
T1 - A new method to correct the attenuation map in simultaneous transmission/emission tomography using 153Gd/ 67Ga radioisotopes
AU - Kheruka, Subhash Chand
AU - Hutton, Brian F.
AU - Naithani, Umesh Chand
AU - Aggarwal, Lalit Mohan
AU - Painuly, Nirmal Kumar
AU - Maurya, Anil Kumar
AU - Gambhir, Sanjay
PY - 2012/1
Y1 - 2012/1
N2 - Reconstruction of the tomographic images without attenuation correction can cause erroneously high count densities and reduced image contrast in low attenuation regions. In order to solve the problem of photon attenuation, one needs to know the attenuation coefficient for the individual patient being studied. Therefore, we made an attempt to correct the attenuation map in simultaneous transmission/emission tomography with 153Gd/ 67Ga using maximum likelihood method using the expectation maximization (ML-EM) algorithm to correct the transmission window for both the spillover and downscatter. Spillover fraction, scatter fraction and parameters for the scatter function (A, b and c) were determined experimentally and optimized using the optimization program written in IDL based on simplex theory. All measurements were performed on a Vertex gamma camera using the anthropomorphic thorax phantom for validation of data obtained by the proposed method. It was observed that without spillover and downscatter correction, the mean counts were 19.29 in liver and 26.90 in lung, whereas after after applying the corrections, the mean counts were reduced to 3.80 and 15.10 in liver and lung, respectively, which were close to true mean counts (liver 2.15 and lung 14.89). In this proposed method, we introduced the set of F t (spillover) and K t (downscatter) to account for the variations in projection pixels (f t and k t) with the density and thickness. The F t and K t were determined using the transmission data by an iterative process. The quantitative error was reduced by 98.0% for lung and 90.0% for liver when the corrected transmission images were obtained after the subtraction of spillover and downscatter fraction.
AB - Reconstruction of the tomographic images without attenuation correction can cause erroneously high count densities and reduced image contrast in low attenuation regions. In order to solve the problem of photon attenuation, one needs to know the attenuation coefficient for the individual patient being studied. Therefore, we made an attempt to correct the attenuation map in simultaneous transmission/emission tomography with 153Gd/ 67Ga using maximum likelihood method using the expectation maximization (ML-EM) algorithm to correct the transmission window for both the spillover and downscatter. Spillover fraction, scatter fraction and parameters for the scatter function (A, b and c) were determined experimentally and optimized using the optimization program written in IDL based on simplex theory. All measurements were performed on a Vertex gamma camera using the anthropomorphic thorax phantom for validation of data obtained by the proposed method. It was observed that without spillover and downscatter correction, the mean counts were 19.29 in liver and 26.90 in lung, whereas after after applying the corrections, the mean counts were reduced to 3.80 and 15.10 in liver and lung, respectively, which were close to true mean counts (liver 2.15 and lung 14.89). In this proposed method, we introduced the set of F t (spillover) and K t (downscatter) to account for the variations in projection pixels (f t and k t) with the density and thickness. The F t and K t were determined using the transmission data by an iterative process. The quantitative error was reduced by 98.0% for lung and 90.0% for liver when the corrected transmission images were obtained after the subtraction of spillover and downscatter fraction.
KW - Optimization
KW - SPECT
KW - spillover and downscatter fraction
KW - transmission map
UR - http://www.scopus.com/inward/record.url?scp=84857306910&partnerID=8YFLogxK
U2 - 10.4103/0971-6203.92720
DO - 10.4103/0971-6203.92720
M3 - Article
C2 - 22363112
AN - SCOPUS:84857306910
SN - 0971-6203
VL - 37
SP - 46
EP - 53
JO - Journal of Medical Physics
JF - Journal of Medical Physics
IS - 1
ER -