Volume 33, Issue 4 p. 976-983
Nuclear medicine physics

Method for transforming CT images for attenuation correction in PET/CT imaging

Jonathan P. J. Carney

Jonathan P. J. Carney

Department of Medicine, University of Tennessee Medical Center, Knoxville, TN 37920

Current address: PET Facility B-938 PUH, Department of Radiology, University of Pittsburgh, 200 Lothrop St., Pittsburgh PA 15213; electronic mail: [email protected]

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David W. Townsend

David W. Townsend

Department of Medicine, University of Tennessee Medical Center, Knoxville, TN 37920

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Vitaliy Rappoport

Vitaliy Rappoport

Siemens Medical Solutions Molecular Imaging, Knoxville, TN 37932

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Bernard Bendriem

Bernard Bendriem

Siemens Medical Solutions Molecular Imaging, Knoxville, TN 37932

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First published: 21 March 2006
Citations: 212

Abstract

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 urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0001 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 urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0002. 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 urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0003. The transformation, appropriate for lung, soft tissue, and bone, yields the function urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0004 below a threshold of urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0005 and urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0006 above the threshold, where urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0007 and urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0008 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 urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0009. Results are also presented for patient studies involving multiple CT scans at different kVp settings, which should all lead to the same urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0010 linear attenuation values. A linear fit to values obtained from urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0011 CT images using the kVp-dependent scaling plotted as a function of the corresponding values obtained from urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0012 CT images yielded urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0013 with an urn:x-wiley:0094-2405:media:mp4132:mp4132-math-0014 value of 0.999, indicating that the same values are obtained to a high degree of accuracy.