MRI-guided attenuation correction in whole-body PET/MR: assessment of the effect of bone attenuation
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ORIGINAL ARTICLE
MRI-guided attenuation correction in whole-body PET/MR: assessment of the effect of bone attenuation A. Akbarzadeh • M. R. Ay • A. Ahmadian N. Riahi Alam • H. Zaidi
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Received: 2 June 2012 / Accepted: 11 November 2012 / Published online: 21 December 2012 Ó The Japanese Society of Nuclear Medicine 2012
Abstract Objective Hybrid PET/MRI presents many advantages in comparison with its counterpart PET/CT in terms of improved soft-tissue contrast, decrease in radiation exposure, and truly simultaneous and multi-parametric imaging capabilities. However, the lack of well-established methodology for MR-based attenuation correction is hampering further development and wider acceptance of this technology. We assess the impact of ignoring bone attenuation and using different tissue classes for generation of the attenuation map on the accuracy of attenuation correction of PET data. A. Akbarzadeh M. R. Ay (&) A. Ahmadian N. Riahi Alam Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran e-mail: [email protected] A. Akbarzadeh M. R. Ay A. Ahmadian Medical Imaging Systems Group, Research Center for Molecular and Cellular Imaging, Tehran University of Medical Sciences, Tehran, Iran M. R. Ay Research Institute for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran
Methods This work was performed using simulation studies based on the XCAT phantom and clinical input data. For the latter, PET and CT images of patients were used as input for the analytic simulation model using realistic activity distributions where CT-based attenuation correction was utilized as reference for comparison. For both phantom and clinical studies, the reference attenuation map was classified into various numbers of tissue classes to produce three (air, soft tissue and lung), four (air, lungs, soft tissue and cortical bones) and five (air, lungs, soft tissue, cortical bones and spongeous bones) class attenuation maps. Results The phantom studies demonstrated that ignoring bone increases the relative error by up to 6.8 % in the body and up to 31.0 % for bony regions. Likewise, the simulated clinical studies showed that the mean relative error reached 15 % for lesions located in the body and 30.7 % for lesions located in bones, when neglecting bones. These results demonstrate an underestimation of about 30 % of tracer uptake when neglecting bone, which in turn imposes substantial loss of quantitative accuracy for PET images produced by hybrid PET/MRI systems. Conclusion Considering bones in the attenuation map will considerably improve the accuracy of MR-guided attenuation correction in hybrid PET/MR to enable quantitative PET imaging on hybrid PET/MR technologies.
H. Zaidi Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, 1211 Geneva, Switzerland e-mail: [email protected]
Keywords PET/MRI PET/CT Attenuation correction Tissue classification Quantification
H. Zaidi Geneva Neuroscience Center, Geneva Unive
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