Comparison of Methods of µ-Map Generation: MR-Based Method in PET/MR Imaging Versus Pseudo-CT Method in Radiotherapy Dose Planning

Introduction: Attenuation correction is essential for accurate PET imaging and radiotherapy (RT) dose planning. However, PET/MR systems face a significant challenge due to the lack of direct attenuation data from MR images, unlike PET/CT where CT provides inherent attenuation information. Similarly, the increasing use of MRI in RT planning necessitates pseudo-CT methods for accurate dose calculation. This study compares MR-based µ-map generation for PET/MR and pseudo-CT methods for RT planning, addressing their challenges and limitations to improve treatment accuracy and patient care. Material and Methods: The study involved patient selection, image processing, and generation of MR-based attenuation maps (µ-maps) for PET attenuation correction and pseudo-CTs for RT dose planning using advanced computational software. Results: MR-based µ-maps, potentially useful for PET attenuation correction, and pseudo CTs, potentially applicable in radiotherapy planning, were successfully generated. Head images showed MR-based µ-maps overestimating bone for two patients (deviations of 4.0% and 4.2%). Both MR-based and CT µ-maps exhibited dynamic and continuous µ-values for head bone. In the pelvis, pseudo-CT underestimated bone volume in five patients (deviations of 18.7%, 21.3%, 9.6%, 14%, and 10%). Pseudo-CT's bone µ-values lacked continuity compared to CT µ-maps. Pelvis studies revealed more dynamic and broader µ-value range for muscle in CT µ-maps than pseudo-CT and MRI µ-map. Conclusion: These findings suggest the need for careful consideration and validation of attenuation correction methods, especially in regions with complex anatomical structures, to ensure accurate treatment delivery and enhance patient care in the context of PET/MR and radiotherapy.