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Method for transforming CT images for attenuation correction in PET/CT imaging
Author(s) -
Carney Jonathan P. J.,
Townsend David W.,
Rappoport Vitaliy,
Bendriem Bernard
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2174132
Subject(s) - hounsfield scale , imaging phantom , nuclear medicine , correction for attenuation , attenuation , tomography , scanner , positron emission tomography , medical imaging , iterative reconstruction , materials science , physics , computed tomography , medicine , radiology , optics
A tube‐voltage‐dependent scheme is presented for transforming Hounsfield units (HU) measured by different computed tomography (CT) scanners at different x‐ray tube voltages (kVp) to 511 keV linear attenuation values for attenuation correction in positron emission tomography (PET) data reconstruction. A Gammex 467 electron density CT phantom was imaged using a Siemens Sensation 16‐slice CT, a Siemens Emotion 6‐slice CT, a GE Lightspeed 16‐slice CT, a Hitachi CXR 4‐slice CT, and a Toshiba Aquilion 16‐slice CT at kVp ranging from 80 to 140 kVp . All of these CT scanners are also available in combination with a PET scanner as a PET/CT tomograph. HU obtained for various reference tissue substitutes in the phantom were compared with the known linear attenuation values at 511 keV . The transformation, appropriate for lung, soft tissue, and bone, yields the function 9.6 × 10 − 5 · ( HU + 1000 ) below a threshold of ∼ 50 HU and a · ( HU + 1000 ) + b above the threshold, where a and b are fixed parameters that depend on the kVp setting. The use of the kVp‐dependent scaling procedure leads to a significant improvement in reconstructed PET activity levels in phantom measurements, resolving errors of almost 40% otherwise seen for the case of dense bone phantoms at 80 kVp . Results are also presented for patient studies involving multiple CT scans at different kVp settings, which should all lead to the same 511 keV linear attenuation values. A linear fit to values obtained from 140 kVp CT images using the kVp‐dependent scaling plotted as a function of the corresponding values obtained from 80 kVp CT images yielded y = 1.003 × − 0.001 with anR 2value of 0.999, indicating that the same values are obtained to a high degree of accuracy.