K Nikolaou

Combined PET/MRI: Multi-modality Multi-parametric Imaging Is Here: Summary Report of the 4th International Workshop on PET/MR Imaging; February 23-27, 2015, Tübingen, Germany.

This paper summarises key themes and discussions from the 4th international workshop dedicated to the advancement of the technical, scientific and clinical applications of combined positron emission tomography (PET)/magnetic resonance imaging (MRI) systems that was held in Tübingen, Germany, from February 23 to 27, 2015. Specifically, we summarise the three days of invited presentations from active researchers in this and associated fields augmented by round table discussions and dialogue boards with specific topics. These include the use of PET/MRI in cardiovascular disease, paediatrics, oncology, neurology and multi-parametric imaging, the latter of which was suggested as a key promoting factor for the wider adoption of integrated PET/MRI. Discussions throughout the workshop and a poll taken on the final day demonstrated that attendees felt more strongly that PET/MRI has further advanced in both technical versatility and acceptance by clinical and research-driven users from the status quo of last year. Still, with only minimal evidence of progress made in exploiting the true complementary nature of the PET and MRI-based information, PET/MRI is still yet to achieve its potential. In that regard, the conclusion of last year’s meeting “the real work has just started” still holds true.

Combined PET/MRI: from Status Quo to Status Go. Summary Report of the Fifth International Workshop on PET/MR Imaging; February 15–19, 2016; Tübingen, Germany

This article provides a collaborative perspective of the discussions and conclusions from the fifth international workshop of combined positron emission tomorgraphy (PET)/magnetic resonance imaging (MRI) that was held in Tübingen, Germany, from February 15 to 19, 2016. Specifically, we summarise the second part of the workshop made up of invited presentations from active researchers in the field of PET/MRI and associated fields augmented by round table discussions and dialogue boards with specific topics. This year, this included practical advice as to possible approaches to moving PET/MRI into clinical routine, the use of PET/MRI in brain receptor imaging, in assessing cardiovascular diseases, cancer, infection, and inflammatory diseases. To address perceived challenges still remaining to innovatively integrate PET and MRI system technologies, a dedicated round table session brought together key representatives from industry and academia who were engaged with either the conceptualisation or early adoption of hybrid PET/MRI systems. Discussions during the workshop highlighted that emerging unique applications of PET/MRI such as the ability to provide multi-parametric quantitative and visual information which will enable not only overall disease detection but also disease characterisation would eventually be regarded as compelling arguments for the adoption of PET/MR. However, as indicated by previous workshops, evidence in favour of this observation is only growing slowly, mainly due to the ongoing inability to pool data cohorts from independent trials as well as different systems and sites. The participants emphasised that moving from status quo to status go entails the need to adopt standardised imaging procedures and the readiness to act together prospectively across multiple PET/MRI sites and vendors.

Decoding Intratumoral Heterogeneity of Breast Cancer by Multiparametric In Vivo Imaging: A Translational Study

Differential diagnosis and therapy of heterogeneous breast tumors poses a major clinical challenge. To address the need for a comprehensive, noninvasive strategy to define the molecular and functional profiles of tumors in vivo, we investigated a novel combination of metabolic PET and diffusion-weighted (DW)-MRI in the polyoma virus middle T antigen transgenic mouse model of breast cancer. The implementation of a voxelwise analysis for the clustering of intra- and intertumoral heterogeneity in this model resulted in a multiparametric profile based on [(18)F]Fluorodeoxyglucose ([(18)F]FDG)-PET and DW-MRI, which identified three distinct tumor phenotypes in vivo, including solid acinar, and solid nodular malignancies as well as cystic hyperplasia. To evaluate the feasibility of this approach for clinical use, we examined estrogen receptor-positive and progesterone receptor-positive breast tumors from five patient cases using DW-MRI and [(18)F]FDG-PET in a simultaneous PET/MRI system. The postsurgical in vivo PET/MRI data were correlated to whole-slide histology using the latter traditional diagnostic standard to define phenotype. By this approach, we showed how molecular, structural (microscopic, anatomic), and functional information could be simultaneously obtained noninvasively to identify precancerous and malignant subtypes within heterogeneous tumors. Combined with an automatized analysis, our results suggest that multiparametric molecular and functional imaging may be capable of providing comprehensive tumor profiling for noninvasive cancer diagnostics. Cancer Res; 76(18); 5512-22. ©2016 AACR.

Assessment of image quality of a radiotherapy-specific hardware solution for PET/MRI in head and neck cancer patients

Background and purpose Functional PET/MRI has great potential to improve radiotherapy planning (RTP). However, data integration requires imaging with radiotherapy-specific patient positioning. Here, we investigated the feasibility and image quality of radiotherapy-customized PET/MRI in head-and-neck cancer (HNC) patients using a dedicated hardware setup. Material and methods Ten HNC patients were examined with simultaneous PET/MRI before treatment, with radiotherapy and diagnostic scan setup, respectively. We tested feasibility of radiotherapy-specific patient positioning and compared the image quality between both setups by pairwise image analysis of 18F-FDG-PET, T1/T2-weighted and diffusion-weighted MRI. For image quality assessment, similarity measures including average symmetric surface distance (ASSD) of PET and MR-based tumor contours, MR signal-to-noise ratio (SNR) and mean apparent diffusion coefficient (ADC) value were used. Results PET/MRI in radiotherapy position was feasible – all patients were successfully examined. ASSD (median/range) of PET and MR contours was 0.6 (0.4–1.2) and 0.9 (0.5–1.3) mm, respectively. For T2-weighted MRI, a reduced SNR of −26.2% (−39.0–−11.7) was observed with radiotherapy setup. No significant difference in mean ADC was found. Conclusions Simultaneous PET/MRI in HNC patients using radiotherapy positioning aids is clinically feasible. Though SNR was reduced, the image quality obtained with a radiotherapy setup meets RTP requirements and the data can thus be used for personalized RTP.

Kombinierte Ganzkörper-18F-FDG-PET/MRT zur onkologischen Diagnostik bei Kleinkindern – technische Machbarkeit und diagnostische Güte im direkten Vergleich zur 18F-FDG-PET/CT

Zielsetzung: Ziel dieser prospektiven Studie war die Untersuchung der technischen Machbarkeit und diagnostischen Gute der kombinierten FDG-PET/MRT zur onkologischen Diagnostik bei Kleinkindern. Dies erfolgte im direkten Vergleich zur FDG-PET/CT. Material und Methodik: 10 Doppeluntersuchungen wurden an 9 Patienten (4 Madchen; 3,8 ± 1,8J.) durchgefuhrt. Zunachst erfolgte die PET/CT 60 min nach Injektion von 115 ± 13 MBq 18F-FDG. Im Anschluss wurde 120 min nach FDG-Injektion die PET/MRT durchgefuhrt. Neben einer T1-Gradientenecho-Sequenz zur PET-Schwachungskorrektur wurden folgende MR-Sequenzen akquiriert: GK-STIR cor, GK-DWI, axiale STIR des Halses/Thorax, axiale T2 TSE des Abdomens/Beckens, axiale GK-T1-Flash-3D. PET/CT und PET/MRT wurden unabhangig voneinander durch zwei Befunderpaare klinisch ausgewertet. Zudem erfolgte eine quantitative Auswertung der PET-Datensatze hinsichtlich Genauigkeit der PET-Quantifizierung. Eff. Dosen wurden anhand des Dosislangenproduktes und der applizierten FDG-Dosis errechnet. Ergebnisse: Insgesamt wurden mittels PET-CT bzw PET-MRT jeweils 21 PET-positive und 7 bzw 8 PET-negative Lasionen detektiert. Dabei konnte mittels CT bzw MRT in 13 bzw 20 von 21 Fallen ein sicheres morphologisches PET- Korrelat identifiziert werden. In 5 von 10 Untersuchungen fuhrte die PET/MRT im Vergleich zur PET/CT zu einer potentiellen Anderung des weiteren klinischen Vorgehens. Die quantitative Auswertung der PET-Komponente ergab einen hohen Grad der Ubereinstimmung der PET-SUVs zwischen PET/CT und PET/MRT. Lediglich intrapulmonal und intraossar ergaben sich relevante Abweichungen der SUV-Werte um 10 bis 15%, was auf Ungenauigkeiten der MR-basierten PET-Schwachungskarte zuruckzufuhren war. Die theoretische Reduktion der eff. Dosis betrug ca 48%, Schlussfolgerungen: Die FDG-PET/MRT ist in der onkologischen Diagnostik bei Kleinkindern zuverlassig durchfuhrbar und zeigt zur PET/CT diagnostisch gleichwertige Ergebnisse mit Vorteilen in der Detektion von Weichteillasionen. Dabei ist mindestens eine Halbierung der eff. Dosis moglich.

Therapy response assessment with quantitative PET: evaluation of a shortened acquisition protocol with dynamic PET/CT

Purpose The results of SUV quantification for prediction of histopathological response in patients with oesophageal carcinoma show high variations with different accuracy. However, the routine use of a full dynamic PET is limited because of long acquisition times. We tested a shortened acquisition protocol for quantitative PET to overcome that limitation. Material and methods 13 patients with histopathologically proven oesophageal adenocarcinoma underwent a combined dynamic and static 18 F-FDG PET/CT including CT tumour perfusion (Siemens, Biograph mCT). Dynamic PET (listmode) was acquired for 60 min resulting in 38 frames from 10 to 600 sec duration for the full dynamic dataset and 2 frames each with 600 sec duration (20-30 min and 50-60 min p.i.) for dual time point PET (DTP). We evaluated the metabolic rate Ki using different models: 2-compartment irreversible model (Fit), Patlak plot and DTP (van den Hoff et al). The CT tumour perfusion protocol included the parameters blood flow, blood volume and permeability. Results