Combined PET/MRI: Global Warming-Summary Report of the 6th International Workshop on PET/MRI, March 27-29, 2017, Tübingen, Germany

Abstract

The 6th annual meeting to address key issues in positron emission tomography (PET)/magnetic resonance imaging (MRI) was held again in Tübingen, Germany, from March 27 to 29, 2017. Over three days of invited plenary lectures, round table discussions and dialogue board deliberations, participants critically assessed the current state of PET/MRI, both clinically and as a research tool, and attempted to chart future directions. The meeting addressed the use of PET/MRI and workflows in oncology, neurosciences, infection, inflammation and chronic pain syndromes, as well as deeper discussions about how best to characterise the tumour microenvironment, optimise the complementary information available from PET and MRI, and how advanced data mining and bioinformatics, as well as information from liquid biomarkers (circulating tumour cells and nucleic acids) and pathology, can be integrated to give a more complete characterisation of disease phenotype. Some issues that have dominated previous meetings, such as the accuracy of MR-based attenuation correction (AC) of the PET scan, were finally put to rest as having been adequately addressed for the majority of clinical situations. Likewise, the ability to standardise PET systems for use in multicentre trials was confirmed, thus removing a perceived barrier to larger clinical imaging trials. The meeting openly questioned whether PET/MRI should, in all cases, be used as a whole-body imaging modality or whether in many circumstances it would best be employed to give an in-depth study of previously identified disease in a single organ or region. The meeting concluded that there is still much work to be done in the integration of data from different fields and in developing a common language for all stakeholders involved. In addition, the participants advocated joint training and education for individuals who engage in routine PET/MRI. It was agreed that PET/MRI can enhance our understanding of normal and disrupted biology, and we are in a position to describe the in vivo nature of disease processes, metabolism, evolution of cancer and the monitoring of response to pharmacological interventions and therapies. As such, PET/MRI is a key to advancing medicine and patient care.

Keywords: Hybrid imaging; Infection; Inflammation; MR-PET; MRI; Molecular imaging; Multi-parametric imaging; Neurology; Oncology; PET; PET/CT; PET/MRI; Quantification.

Fig. 1.

Patient with oropharyngeal carcinoma pre- and post-RT. a [¹⁸F]FDG-PET/CT prior to RT. Oral mucosa delineated in pink, clinical target volume (CTV) in red. b [¹⁸F]FDG-PET/CT during week 4 of RT. For the analysis, the CTV was subtracted from mucosa. ( Courtesy of S. Zschaeck, MD, Charité Berlin)

Fig. 2.

Joint PET and MR image reconstruction. Simulated PET and undersampled (5 of 8 coils) T1-w MR data. First independent reconstructions were performed, using least squares reconstruction with joint total variation (TV) prior to MR and ML reconstruction with a TV prior to PET. Then, a simultaneous MR and PET reconstruction with the joint TV prior was performed. The resolution of the PET image improves a little, whilst the changes to the MR image appear very minor at best (courtesy of J Nuyts, Leuven/BE).

Fig. 3.

Co-registration of imaging and histopathology data. a Work flow schematic. b Pre-operative T2w image with annotated resection margins. c 3D print mold. f Fixated axially processed specimen with g annotated tissue blocks. h Stitching of tissue slices. i Screenshot of in-house written software for co-registration and regional analysis of imaging and histopathology data (courtesy of Rickmer Braren, Katja Steiger, Franz Irlinger and Maximilian Baust).

Fig. 4.

Selection of target structures on effector T cells as well as probes and nuclides to develop safe and efficient imaging strategies to track T cells during immunotherapy (courtesy of Sabine Mall and Angela Krackhardt).

Fig. 5.

Tracking of intravenously injected T-cell receptor (TCR)-transduced central memory T cells within antigen-expressing tumours by Zr-89-labelled aTCRmu-F(ab′)₂ using PET/CT. a TCR-transgenic T cells were injected intravenously after tumour engraftment followed by i.v. injection of [⁸⁹Zr]-labelled aTCRmu-F(ab′)₂ 48 h after adoptive T-cell transfer. b Heterogeneity of T-cell infiltration, as seen in the zoom in, has been validated by semi-quantitative analysis using immunohistochemistry [55] (courtesy of Sabine Mall and Angela Krackhardt).