Volume 49, Number 3

July 2014

Letter From the Guest Editors

H

ybrid imaging has gained significant importance for diagnosis and treatment monitoring by offering coregistered molecular or anatomical information. The latest clinical advance is a combination of positron emission tomography (PET) and magnetic resonance imaging (MRI), which followed previous developments of PET/computed tomography (CT) and single-photon emission CT/CT. PET-MR offers unique diagnostic opportunities combining the strengths of these 2 imaging modalities, which are believed to be synergistic and complementary. Thus, PET-MR combines high anatomical detail as well as biochemical and functional information from MRI with metabolic and molecular information from PET. Seminars in Roentgenology always attentive to new trends and innovations in diagnostic medical imaging has offered us the opportunity to share with the radiologic community at large our experience in PET-MR, as we were fortunate to have one of the first clinical units of this novel hybrid imaging technology in the United States. Our PET-MR has a sequential design and is composed of a 3 T MR unit and a time of flight–capable PET. The PET-MR is housed within radiology and nuclear medicine on the second floor of the Seidman Cancer Center in the University Hospitals Case Medical Center campus, which also includes the Rainbow Babies and Children's hospital. As such, the bulk of our experience and therefore of the articles included in the Seminars of Roentgenology volumes focus primarily on oncologic applications. Clinical PET-MR requires a different approach compared with previous hybrid imaging modalities and relies on a close collaboration between nuclear medicine and other subspecialties within radiology. The whole-body imaging information from PET raises diagnostic challenges within different parts of the body, all served by different organbased subspecialized radiologists in each area. We have been successful in creating a core team of nuclear medicine physicians and radiologists, who jointly review the request, determine the protocol, optimize PET imaging and particularly the MRI procedures during scanning, and then report the cases together. As early adopters of technology, we had to learn “as we went” not only how to interpret the imaging studies for our referring physicians but also regarding basic tasks. MR-based 236

http://dx.doi.org/10.1053/j.ro.2014.09.002 0037-198X/& 2014 Elsevier Inc. All rights reserved.

attenuation correction in both adult and pediatric patients, patient workflow, technique optimization combining both modalities, billing, and most importantly fusing both the MR and the nuclear medicine cultures for both physicians and technologists had to be explored and conquered. An important advantage of PET-MR is the improved soft tissue visualization compared with CT, which is particularly helpful in imaging the brain and the abdomen. In pediatric patients, the lack of radiation from MR is an important factor, particularly for follow-up imaging, although the longer acquisition time of MR vs CT has to be taken into consideration. An unresolved issue is the higher cost of PET-MRI, as the installation and maintenance is more expensive compared with PET/CT. Although PET-MR billing codes are not yet established, fluorodeoxyglucose (FDG)-PET can be billed with either CT or MR attenuation correction. A diagnostic MR of a particular body region is necessary for billing of the MR component of PET-MR. The lessons learned with the adoption of PET/CT are not directly translatable to PET-MR. In PET-MR, both the techniques are more equal partners, unlike in PET/CT, where CT is a key assistant for attenuation correction and anatomical localization, but the main information sought is the metabolic and molecular information provided by PET. In PET-MR, particularly when the multiparametric potential of MR is used, both parts of the hybrid unit are key contributors and therefore a true partnership of the 2 cultures becomes paramount. The articles in the Seminars of Roentgenology collect our experience since 2012 and are based on hundreds of cases both enrolled in prospective research protocols and routine clinically indicated cases. However, although our experience is still limited particularly when compared with the wealth of information in MRI and PET/CT, there are certain areas where PET-MRI is changing our established clinical practice, particularly in neuro- and pelvic-oncology. Muzic and DiFilippo describe the basic principles of PETMR, including different approaches from industry vendors to develop this technology. The challenge of deriving attenuation maps from MR are discussed as well as new technologies currently in development. A comprehensive overview on the management and organization of PET-MR is provided by Ros et al including necessary space requirements, the

Letter from the guest editors implementation of MR safety zone restrictions and controls, radiation safety, and staffing of PET-MR. Herrmann et al illustrate artifacts and diagnostic pitfalls in PET-MR as well as the potential role of PET-MR in gastrointestinal and abdominal malignancies and in the use in pelvic tumors. FDG-PET-MR was found to be equivalent to FDG-PET/CT in most of the clinical indications in the abdomen or the pelvis with the advantage of providing better soft tissue information. Robbin et al illustrate the PET-MR oncologic applications in bone and soft tissue sarcoma, and Wolansky et al discuss the role of PETMR in the evaluation of brain tumors and provide an overview on the current status and future prospects. The role of PET-MR in lung cancer is reviewed by Prabhakar et al. FDG-PET-MR is hampered by the inferior visualization of small subcentimeter lung lesions. Nevertheless, for larger lesions, the combination of PET and MR is powerful owing to the high soft tissue contrast, improved tissue characterization, multiplanar imaging, and functional imaging (ventilation, perfusion, and diffusion) without ionizing radiation. The lack of ionizing radiation is an important advantage in pediatric imaging in

237 addition to the improved soft tissue contrast as discussed by Bangert et al. Breast imaging is an important potential indication for FDG-PET-MR, and 2 articles by Plecha and Avril et al cover the use for imaging primary tumors and wholebody staging of patients with breast cancer. Although PET-MR provides unique diagnostic information, it has not yet found its place within clinical imaging, as a separate PET/CT and a dedicated MRI are often sufficient particularly when using (F-18)FDG. Nevertheless, new, more specific PET biomarkers will help to establish an increasing number of clinical indications, which is highlighted in a case report showing the advantage of obtaining changes in cell proliferation and perfusion parameters for as of assessment of treatment response early in the course of therapy. We hope the readership enjoys the series of articles based on our experience in clinical and research use of PET-MR. Norbert Avril, MD Pablo R. Ros, MD, MPH, MD Guest Editor

Letter from the guest editors.

Letter from the guest editors. - PDF Download Free
144KB Sizes 0 Downloads 6 Views