This paper describes and compares procedures to obtain attenuation maps used for the absorption correction (AC) of PET brain scans if a transmission scan is not available as in the case of future MR-PET scanners. A previously reported approach called MBA (MRT-based attenuation correction) used Tl- weighted MR images which were segmented into four tissue types representing brain tissue, bone, other tissue and sinus to which appropriate attenuation coefficients were assigned. In this work a template-based attenuation correction (TBA) is presented which applies an attenuation template to single subjects. A common attenuation template was created from transmission scans of 10 normal volunteers and spatially normalized to the SPM2 standard brain shape. For each subject the Tl-MR template of SPM2 was warped onto the subject's individual MR image. The resulting warping matrix was applied to the common attenuation template so that an attenuation map matching the subject's brain shape was obtained. The attenuation maps of MBA and TBA were forward projected into attenuation factors which were alternatively used for AC. FDG scans of four subjects were reconstructed after AC with MBA and TBA and compared to images whose ACs were based on conventional attenuation maps (PBA=PET-based attenuation correction). Using PBA as reference in a region of interest analysis, MBA and TBA showed similar under- and overestimation of the reconstructed radioactivity up to -10% and 9%, respectively. The procedure to obtain the attenuation template needs still some improvements. Nevertheless, the TBA method of attenuation correction is a promising alternative to MBA with its still complex and not yet resolved accurate segmentation of MR images.
[1]
A. Buck,et al.
PET attenuation coefficients from CT images: experimental evaluation of the transformation of CT into PET 511-keV attenuation coefficients
,
2002,
European Journal of Nuclear Medicine and Molecular Imaging.
[2]
H. Zaidi,et al.
Magnetic resonance imaging-guided attenuation and scatter corrections in three-dimensional brain positron emission tomography.
,
2003,
Medical physics.
[3]
Habib Zaidi,et al.
Quantitative analysis of template-based attenuation compensation in 3D brain PET
,
2007,
Comput. Medical Imaging Graph..
[4]
J. Ashburner,et al.
Nonlinear spatial normalization using basis functions
,
1999,
Human brain mapping.
[5]
Richard M. Leahy,et al.
BrainSuite: An Automated Cortical Surface Identification Tool
,
2000,
MICCAI.
[6]
W. J. Lorenz,et al.
Measured attenuation correction methods
,
2004,
European Journal of Nuclear Medicine.
[7]
E. Hoffman,et al.
Quantitation in positron emission computed tomography: 2. Effects of inaccurate attenuation correction.
,
1979,
Journal of computer assisted tomography.
[8]
Habib Zaidi,et al.
Atlas-guided non-uniform attenuation correction in cerebral 3D PET imaging
,
2005,
NeuroImage.
[9]
Paul Kinahan,et al.
Attenuation correction for a combined 3D PET/CT scanner.
,
1998,
Medical physics.