On the accuracy and reproducibility of a novel probabilistic atlas-based generation for calculation of head attenuation maps on integrated PET/MR scanners

• Published in: European journal of nuclear medicine and molecular imaging 2017-03, Vol.44 (3), p.398-407
• Main Authors: Chen, Kevin T., Izquierdo-Garcia, David, Poynton, Clare B., Chonde, Daniel B., Catana, Ciprian
• Format: Article
• Language: English
• Subjects: Accuracy; Algorithms; Brain; Cardiology; Data Accuracy; Head - anatomy & histology; Head - diagnostic imaging; Humans; Imaging; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Magnetic Resonance Imaging - standards; Medical imaging; Medicine; Medicine & Public Health; Methods; Multimodal Imaging - instrumentation; Multimodal Imaging - methods; Multimodal Imaging - standards; Nuclear Medicine; Oncology; Original Article; Orthopedics; Photons; Positron-Emission Tomography - instrumentation; Positron-Emission Tomography - methods; Positron-Emission Tomography - standards; Radiology
• ISSN: 1619-7070; 1619-7089
• DOI: 10.1007/s00259-016-3489-z

Purpose To propose an MR-based method for generating continuous-valued head attenuation maps and to assess its accuracy and reproducibility. Demonstrating that novel MR-based photon attenuation correction methods are both accurate and reproducible is essential prior to using them routinely in research and clinical studies on integrated PET/MR scanners. Methods Continuous-valued linear attenuation coefficient maps (“μ-maps”) were generated by combining atlases that provided the prior probability of voxel positions belonging to a certain tissue class (air, soft tissue, or bone) and an MR intensity-based likelihood classifier to produce posterior probability maps of tissue classes. These probabilities were used as weights to generate the μ-maps. The accuracy of this probabilistic atlas-based continuous-valued μ-map (“PAC-map”) generation method was assessed by calculating the voxel-wise absolute relative change (RC) between the MR-based and scaled CT-based attenuation-corrected PET images. To assess reproducibility, we performed pair-wise comparisons of the RC values obtained from the PET images reconstructed using the μ-maps generated from the data acquired at three time points. Results The proposed method produced continuous-valued μ-maps that qualitatively reflected the variable anatomy in patients with brain tumor and agreed well with the scaled CT-based μ-maps. The absolute RC comparing the resulting PET volumes was 1.76 ± 2.33 %, quantitatively demonstrating that the method is accurate. Additionally, we also showed that the method is highly reproducible, the mean RC value for the PET images reconstructed using the μ-maps obtained at the three visits being 0.65 ± 0.95 %. Conclusion Accurate and highly reproducible continuous-valued head μ-maps can be generated from MR data using a probabilistic atlas-based approach.