First Clinical Experience with Integrated Whole-Body PET/MR: Comparison to PET/CT in Patients with Oncologic Diagnoses

Abstract

The recently introduced first integrated whole-body PET/MR scanner allows simultaneous acquisition of PET and MRI data in humans and, thus, may offer new opportunities, particularly regarding diagnostics in oncology. This scanner features major technologic differences from conventional PET/CT devices, including the replacement of photomultipliers with avalanche photodiodes and the need for MRI-based attenuation correction. The aim of this study was to evaluate the comparability of clinical performance between conventional PET/CT and PET/MR in patients with oncologic diseases. Methods: Thirty-two patients with different oncologic diagnoses underwent a single-injection, dual-imaging protocol consisting of a PET/CT and subsequent PET/MR scan. PET/CT scans were performed according to standard clinical protocols (86 6 8 min after injection of 401 6 42 MBq of 18 F-FDG, 2 min/ bed position). Subsequently (140 6 24 min after injection), PET/ MR was performed (4 min/bed position). PET images of both modalities were reconstructed iteratively. Attenuation and scatter correction as well as regional allocation of PET findings were performed using low-dose CT data for PET/CT and Dixon MRI sequences for PET/MR. PET/MR and PET/CT were compared visually by 2 teams of observers by rating the number and location of lesions suspicious for malignancy, as well as image quality and alignment. For quantitative comparison, standardized uptake values (SUVs) of the detected lesions and of different tissue types were assessed. Results: Simultaneous PET/MR acquisition was feasible with high quality in short acquisition time (#20 min). No significant difference was found between the numbers of suspicious lesions (n 5 80) or lesion-positive patients (n 5 20) detected with PET/MR or PET/CT. Anatomic allocation of PET/ MR findings by means of the Dixon MRI sequence was comparable to allocation of PET/CT findings by means of low-dose CT. Quantitative evaluation revealed a high correlation between mean SUVs measured with PET/MR and PET/CT in lesions (r = 0.93) and background tissue (r = 0.92). Conclusion: This study demonstrates, for what is to our knowledge the first time, that integrated whole-body PET/MR is feasible in a clinical setting with high quality and in a short examination time. The reliability of PET/ MR was comparable to that of PET/CT in allowing the detection of hypermetabolic lesions suspicious for malignancy in patients with oncologic diagnoses. Despite different attenuation correction approaches, tracer uptake in lesions and background correlated well between PET/MR and PET/CT. The Dixon MRI sequences acquired for attenuation correction were found useful for anatomic allocation of PET findings obtained by PET/MR in the entire body. These encouraging results may form the foundation for future studies aiming to define the added value of PET/MR over PET/CT.

Correlation of the Apparent Diffusion Coefficient (ADC) with the Standardized Uptake Value (SUV) in Hybrid 18F-FDG PET/MRI in Non-Small Cell Lung Cancer (NSCLC) Lesions: Initial Results

“…One potential explanation is a difference regarding the type of PET attenuation correction. However, our findings are concordant with recently published PET/MRI studies by Drzezga et al and Wiesmüller et al [15,22]. The potential of FDG-PET/CT for staging in patients with diagnosed NSCLC has been demonstrated [2,23].…”

“…In oncologic patients examined with PET/CT and PET/MRI, the SUV max and SUV mean values generally correlate well in normal organ tissues [21]. Furthermore, SUV measurements revealed a high correlation between mean SUVs measured with PET/MRI and PET/ CT in lesions [15]. Concordantly, there was a significant correlation in this study between the SUV max and SUV mean of the NSCLCs when assessed by a simultaneous PET/MRI and PET/CT for NSCLC patients.…”

Conspicuity of FDG-Avid Osseous Lesions on PET/MRI Versus PET/CT: a Quantitative and Visual Analysis

“…Notably, the SUV-max for FFBLs was on average 6.2 % lower on PET/ MRI, a trend that approached significance (p = 0.068); thus, a larger FFBL sample size may have provided sufficient power to detect a statistical difference. For BB SUV-max and SUVmean, our relative PET/MRI values of −14.2 % and −20.5 % Abbreviations: FFBL -FDG-avid focal bone lesion; BB -background bone; NL -normal liver; SUV -standardized uptake value; iso -isocontour; TG -total glycolysis; SD -standard deviation a A and B column -FFBLs for which both readers gave the same conspicuity rating b A and/or B column -FFBLs for which either reader or both readers gave a particular conspicuity rating c Note: numbers in the A and B add to <50 FFBLs, as only lesions for which both readers reached the same assessment are included d Note: numbers in the A and/or B add to >50 FFBLs, as lesions for which readers had 'partial disagreements' are double-counted are comparable to what has been reported by other authors employing similar segmentation strategies (−17 % to −21 % for SUV-max; −14 % to −33 % for SUV-mean) [10,13,14]. Likewise, for FFBL SUV-max and SUV-mean, our relative PET/MRI values of −6.2 % and −6.5 % resemble those previously reported by studies with similar segmentation strategies (−11 % for SUV-max; −10 % to −12 % for SUVmean) [10,15].…”

The foundation layer of quantitative cardiac PET/MRI: Attenuation correction. Again

“…This implementation was initially evaluated in oncological patients and yielded a very good agreement. 5 However, all validation studies following, suffered from the fact that the reference PET/CT scans were acquired prior to the PET/MR examination using FDG, and significant temporal delays were found for logistical reasons. Thus, for physiological reasons, the uptake of FDG is not necessarily constant and this might be especially true if FGD uptake in oncological patients is considered.…”