Current commercial techniques for MRI‐guided attenuation correction are insufficient and will limit the wider acceptance of PET/MRI technology in the clinic

Abstract

OVERVIEWWhole-body hybrid PET/MR imaging has been used since its introduction in 2010 in clinical and research settings for diagnosis, staging and restaging, assessment of response to treatment, and radiation therapy planning. However, the quantitative potential of PET/MRI is challenged by the lack of reliable and accurate MRI-guided attenuation correction (MRAC) owing to the lack of direct relationship between MRI signal, reflecting proton density and relaxation time properties, and electron density, which is linked to photon attenuation properties of biological tissues. Despite the progress made during the last decade, MRAC is still in its infancy and remains problematic particularly in whole-body imaging. While some think that current techniques implemented on commercial systems for MRAC do not constitute a viable solution and are hampering the wider acceptance of PET/MRI technology in the clinic, others think that, despite their limitations, these techniques provide adequate correction fulfilling the requirements of the different clinical applications of this technology. This is the topic of this month's Point/Counterpoint debate.Arguing for the Proposition is Ciprian Catana, MD, PhD. Over the last decade, he has concentrated on further developing and validating this novel technology, identifying and implementing methods to best exploit the combined data, and developing quantitative PET/MRI for human use. Working closely with dozens of basic science researchers and physician-scientists, Dr. Catana is currently applying these advanced tools to the study of normal brain and neuropsychiatric diseases as well as exploring the clinical potential of this technology for wholebody oncological applications. Dr. Catana has authored more than 75 peer-reviewed manuscripts and book chapters and holds or has filed provisional patent applications for several technological and methodological innovations in the field of PET/MRI.

Deep learning-based attenuation correction in the absence of structural information for whole-body positron emission tomography imaging

“…Though PET/MRI has been increasingly implemented in daily clinical applications, serious technical challenges remain in deriving accurate quantitative measurements. One major concern is the bias caused by current vendor implementations of MR-based AC methods and the resultant limitation in quantitative longitudinal therapy monitoring studies (Catana et al, 2018). We evaluate the reliability of the proposed method on quantifying tracer update changes over sequential scans and found that tracer uptake changes calculated on DL-AC PET matches the references well within 3% ("difference" rows in Table 3).…”

Magnetic Resonance-Based Attenuation Correction and Scatter Correction in Neurological Positron Emission Tomography/Magnetic Resonance Imaging—Current Status With Emerging Applications

“…However, it seems that there is still an ongoing discussion whether reasonably accurate methods have become commercially available, especially in challenging clinical applications [134], while the accuracy of MRAC can be considered adequate for the majority of routine clinical situations [47]. Furthermore, future efforts for standardization and quality control are important for accurate and robust results in both research and clinics and are needed for PET/MR as well [135].…”

An international expert opinion statement on the utility of PET/MR for imaging of skeletal metastases

“…On the methodological side, the major obstacle slowing the widespread clinical adoption of PET/MR has been the challenge of generating accurate attenuation correction (AC) maps [2,3]. A correction must be applied to PET data to account for attenuation of the emitted photons prior to reaching the PET detectors [4,5].…”