Workflow and Scan Protocol Considerations for Integrated Whole-Body PET/MRI in Oncology

Abstract

Learning Objectives: On successful completion of this activity, participants should be able to describe (1) special requirements for planning whole-body PET/MRI examinations; (2) general aspects of whole-body PET/MRI protocols in oncology; and (3) possible artifacts in PET/MRI.Financial Disclosure: An author of this article is a meeting participant or lecturer for Siemens AG. No other relevant relationships that could be perceived as a real or apparent conflict of interest were reported. CME Credit: SNMMI is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to sponsor continuing education for physicians. SNMMI designates each JNM continuing education article for a maximum of 2.0 AMA PRA Category 1 Credit. Physicians should claim only credit commensurate with the extent of their participation in the activity. For CE credit, participants can access this activity through the SNMMI Web site (http:// www.snmmi.org/ce_online) through September 2013.Integrated PET/MRI systems open exciting possibilities for clinical and research applications. However, compared with PET/CT, PET/MRI is a complex technique resulting in new problems and challenges, especially regarding workflow, scan protocols, and data analysis. This complexity applies in particular to examinations in oncology with partial-or whole-body coverage extending over several bed positions. Unlike diagnostic PET/CT, for which the clinical CT protocols can largely be copied from stand-alone CT, the design of a diagnostic MRI protocol for partial-or whole-body coverage is more complex and has to be adapted to the special requirements of PET/MRI to be both time-efficient and comprehensive. Here, we describe basic considerations concerning workflow, imaging protocols, and image analysis for whole-body PET/MRI in oncology, based on our experience with the first integrated PET/MRI scanner. The aim is to fully and optimally make use of the combined PET/MRI measurements in oncology, including identifying and reducing image artifacts as well as optimizing workflow beyond the mere fusion of 2 image datasets. Thesuccessofcombi ned PET and CT has demonstrated the clinical value of multimodality imaging technology, providing both anatomic and molecular information within a single imaging session. However, whereas CT and especially modern multislice CT are a powerful imaging tool, they still have shortcomings, such as low soft-tissue contrast when compared with MRI. Thus, the combination of PET and MRI might be clinically advantageous over PET/ CT for some indications. Moreover, because MRI has more potential for functional and molecular imaging than does CT, the combination of PET with MRI offers completely new opportunities for research applications and for molecular imaging in general.As a consequence, a lot of effort has been put into the development of combined PET and MRI. The first preclinical combined PET/MRI systems were introduced in the 1990s (1-3). Clinically, a PET insert for a standard 3.0-T MRI scanner for simultaneous PET/MRI of t...

Diagnostic Accuracy of PET/MR for Evaluating Central Lymph Node Status in Patients with Papillary Thyroid Carcinoma

“…PET/MR is a new diagnostic method that combines morphological and functional imaging, and has been widely adopted in clinical fields such as oncology, Accuracy of PET/MR in PTC cardiology, and neurology (17,18). To date, studies regarding the efficacy of PET/MR in thyroid carcinoma have rarely been reported.…”

“…The PET/MR images were analyzed visually, and primary PTC lesions as well as regional LNs were evaluated. Suspicious LNs were diagnosed if LNs had higher 18 F-FDG uptake than the surrounding tissue and abnormal findings such as necrosis, cystic change, calcification, heterogeneous enhancement, or hyper-enhancement were present (9,10). Necrotic LNs with T2 MRI hyperintensity and irregular peripheral solid enhancement were considered to be a malignant feature, regardless of 18 F-FDG avidity.…”

“…Various alternative imaging modalities have been introduced to increase the sensitivity of the detection of metastatic LNs, such as magnetic resonance imaging (MRI) or 18 F-fluorodeoxyglucosepositron emission tomography (FDG-PET), despite problems associated with poor costeffectiveness.…”

Pediatric Oncologic Imaging: A Key Application of Combined PET/MRI

“…Numerous workflows have already been proposed for simultaneous PET/MRI [13,14]. Despite the high number of possible acquisition strategies, in practice most pediatric whole-body protocols show certain similarities.…”

“…However, this approach not only increases local radiation dose of the urinary bladder but also increases the potential risk of premature termination of the examination by the patient before PET data are acquired. The examination usually starts with a basic module consisting of a whole-body PET acquisition accompanied by simultaneous wholebody MR imaging, mostly using coronal fat-saturated T2-weighted or inversion recovery sequences [7,13,14], in a bed-per-bed manner. Depending on the simultaneous MR protocol, PET acquisition time is usually between 4 and 6 minutes per bed position.…”