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Purpose: Evaluate the feasibility of fluorine-18 ( 18 F) fluorodeoxyglucose (FDG) positron emission tomography (PET) and magnetic resonance (MR) imaging in patients with gastric cancer by optimizing the scan protocol and to compare the image quality to 18 F FDG PET and computed tomography (CT)., Methods: The PET/CT and PET/MR imaging were sequentially performed in 30 patients with gastric cancer diagnosed by gastroscope using a single-injection-with-dual-imaging protocol. After intravenous injection of 18 F-FDG (mean, 249 MBq), PET/CT imaging including low-dose CT was performed (mean uptake time, 47 ± 6 min), and PET/MR imaging including a T1-weighted Dixon sequence for attenuation correction and two different T2-weighted sequences was subsequently acquired (88 ± 15 min after 18 F-FDG injection). Four series of images (CT from PET/CT, T1W, T2W Half-Fourier acquisition single-shot turbo spin-echo [T2W-HASTE] and T2W-BLADE from PET/MR) were visually evaluated using a 3-4 points scale for: (1) image artifacts, (2) lesion conspicuity and (3) image fusion quality. The characteristics of the primary lesions were assessed and compared between the PET/CT and PET/MR acquisitions., Results: The image quality and lesion conspicuity of the T2W-HASTE images were significantly improved compared to that of the T2W-BLADE images. A significantly higher number of artifacts were seen in the T2W-HASTE images compared with the T1W and CT images (p < 0. 05). No differences in the accuracy of image fusion between PET/MR and PET/CT (p > 0. 05); however, significant difference was seen in the lesion conspicuity measurements (p < 0.05) with T2W-HASTE being superior. For information about the primary lesion characteristics, the T2W-HASTE images provided the most successful identifications compared with those of the T1W and PET/CT (13vs7vs5) images., Conclusions: PET/MR with the T2W-HASTE was better at revealing the details of local stomach lesions compared with PET/CT imaging. Combining the PET/MR with the T2W-HASTE technique is a promising imaging method for diagnosing and staging gastric cancer.

The aim of our study was to evaluate the effect of stepwise-reduced doses on objective and subjective image parameters and on oncologic readings in whole-body 18 F-FDG PET/MRI. Methods: We retrospectively simulated the stepwise reduction of 18 F-FDG doses of 19 patients (mean age ± SD, 50.9 ± 11.7 y; mean body mass index ± SD, 22.8 ± 3.2 kg/m 2 ) who received a whole-body PET/MRI examination from 3 to 0.5 MBq/kg of body weight (kgBW) in intervals of 0.25. Objective imaging parameters were assessed by measuring the SUV and coefficient of variation in different regions (aorta, liver, spleen, kidney, small bowel, lumbar vertebra, psoas muscle, urinary bladder) as well as the noise-equivalent counting rates in each bed position. Subjective image quality was evaluated with a masked reading of each simulated PET compared with the dose of 2 MBq/kgBW. Oncologic reading was performed first according to PERCIST in each dose and second by defining malignant lesions in doses of 2 MBq/kgBW and the maximum dose image (gold standard). The diagnostic confidence of each lesion was measured using a Likert scale. Results: With decreasing doses, regions in the mid abdomen showed a stronger decrease of SUV mean and noise-equivalent counting rates than regions in the upper abdomen (SUV mean , -45% and -15% on average in the small bowel and the liver, respectively). The coefficient of variation showed a nonlinear increase, pronounced below 1.5 MBq/kgBW. Subjective image quality was stable over a range between 1.25 and 2.75 MBq/kgBW compared with 2 MBq/kgBW. However, large photopenic areas in the mid abdomen were observed in 2 patients. In the PERCIST reading, target lesions were above the liver threshold with a stable SUV peak in all cases down to 2 MBq/kgBW. Eighty-six of 90 lesions were identified correctly with a dose of 2 MBq/kgBW; Likert scores did not differ significantly. Conclusion: A reduction of doses in 18 F-FDG PET/MRI might be possible down to 2 MBq/kgBW in oncologic whole-body examinations. The image quality in the mid abdomen seems to be more affected by lower doses than in the upper abdomen, and in single cases large photopenic areas can occur. Therefore, we do not recommend reducing doses below 3 MBq/kgBW in adults at this time., (© 2017 by the Society of Nuclear Medicine and Molecular Imaging.)

Purpose: The aim of the study was to investigate the influence of lung density changes as well as bone proximity on the attenuation correction of lung standardized uptake values (SUVs)., Methods and Materials: 15 patients with mostly oncologic diseases were examined in 18F-FDG-PET/CT and subsequently in a fully integrated PET/MR scanner. From each PET dataset acquired in PET/MR, four different PET reconstructions were computed using different attenuation maps (μ-maps): i) CT-based μ-map (gold standard); ii) CT-based μ-map in which the linear attenuation coefficients (LAC) of the lung tissue was replaced by the lung LAC from the MR-based segmentation method; iii) based on reconstruction ii), the LAC of bone structures was additionally replaced with the LAC from the MR-based segmentation method; iv) the vendor-provided MR-based μ-map (segmentation-based method). Those steps were performed using MATLAB. CT Hounsfield units (HU) and SUVmean was acquired in different levels and regions of the lung. Relative differences between the differently corrected PETs were computed., Results: Compared to the gold standard, reconstruction ii), iii) and iv) led to a relative underestimation of SUV in the posterior regions of -9.0%, -13.4% and -14.0%, respectively. Anterior and middle regions were less affected with an overestimation of about 6-8% in reconstructions ii)-iv)., Conclusion: It could be shown that both, differences in lung density and the vicinity of bone tissue in the μ-map may have an influence on SUV, mostly affecting the posterior lung regions.

Respiratory motion may reduce accuracy in the fusion of functional and anatomic images from combined PET/MRI systems. Methodologies for the correction of respiratory motion in PET acquisitions with such systems are mostly based on the use of respiration-synchronized MRI acquisitions to derive motion fields. Existing approaches based on tagging acquisitions may introduce artifacts in MR images, whereas motion model approaches require the acquisition of training datasets. The objective of this work was to investigate the possibility of generating 4-dimensional (4D) MR images and associated attenuation maps (AMs) from the combination of a single static MR image and motion fields obtained from simultaneously acquired 4D non-attenuation-corrected (NAC) PET images. Methods: Four-dimensional PET/MRI datasets were acquired for 11 patients on a simultaneous PET/MRI system. The 4D PET datasets were retrospectively binned into 4 motion amplitude frames corresponding to the simultaneously acquired T1-weighted 4D MR images. A T1-weighted 3-dimensional MRI sequence with Dixon-based fat and water separation was also acquired at the end of expiration for PET attenuation correction purposes. All reconstructed 4D NAC PET images were then elastically registered to the single end-of-expiration NAC PET image. The derived motion fields were subsequently applied to the end-of-expiration frame of the acquired 4D MRI volume and the AM derived from the Dixon MR image to generate respiration-synchronized MR images and corresponding AMs. Results: The accuracy of the proposed method was assessed by comparing the generated and acquired images according to metrics such as overall correlation coefficients and differences in distances of anatomic landmarks on the generated and acquired MRI datasets. High correlation coefficients (mean ± SD: 0.93 ± 0.03) and small differences (2.69 ± 0.5 mm) were obtained. Moreover, small tissue classification differences (2.23% ± 0.68%) between generated and 4D MRI-extracted AMs were observed. Conclusion: Our results confirm the feasibility of using 4D NAC PET images for accurate PET attenuation correction and respiratory motion correction in PET/MRI, without the need for patient-specific 4D MRI acquisitions., (© 2017 by the Society of Nuclear Medicine and Molecular Imaging.)

Objective: First, to investigate the diagnostic performance of fast T1-weighted sequences for lung nodule evaluation in oncologic magnetic resonance (MR)/positron emission tomography (PET). Second, to evaluate the influence of image acquisition in inspiration and expiration breath-hold on diagnostic performance., Materials and Methods: The study was approved by the local Institutional Review Board. PET/CT and MR/PET of 44 cancer patients were evaluated by 2 readers. PET/CT included lung computed tomography (CT) scans in inspiration and expiration (CTin, CTex). MR/PET included Dixon sequence for attenuation correction and fast T1-weighted volumetric interpolated breath-hold examination (VIBE) sequences (volume interpolated breath-hold examination acquired in inspiration [VIBEin], volume interpolated breath-hold examination acquired in expiration [VIBEex]). Diagnostic performance was analyzed for lesion-, lobe-, and size-dependence. Diagnostic confidence was evaluated (4-point Likert-scale; 1 = high). Jackknife alternative free-response receiver-operating characteristic (JAFROC) analysis was performed., Results: Seventy-six pulmonary lesions were evaluated. Lesion-based detection rates were: CTex, 77.6%; VIBEin, 53.3%; VIBEex, 51.3%; and Dixon, 22.4%. Lobe-based detection rates were: CTex, 89.6%; VIBEin, 58.3%; VIBEex, 60.4%; and Dixon, 31.3%. In contrast to CT, inspiration versus expiration did not alter diagnostic performance in VIBE sequences. Diagnostic confidence was best for VIBEin and CTex and decreased in VIBEex and Dixon (1.2 ± 0.6; 1.2 ± 0.7; 1.5 ± 0.9; 1.7 ± 1.1, respectively). The JAFROC figure-of-merit of Dixon was significantly lower. All patients with malignant lesions were identified by CTex, VIBEin, and VIBEex, while 3 patients were false-negative in Dixon., Conclusion: Fast T1-weighted VIBE sequences allow for identification of patients with malignant pulmonary lesions. The Dixon sequence is not recommended for lung nodule evaluation in oncologic MR/PET patients. In contrast to CT, inspiration versus expiratory breath-hold in VIBE sequences was less crucial for lung nodule evaluation but was important for diagnostic confidence.

Objective: Attenuation correction (AC) in fully integrated positron emission tomography (PET)/magnetic resonance (MR) systems plays a key role for the quantification of tracer uptake. The aim of this prospective study was to assess the accuracy of standardized uptake value (SUV) quantification using MR-based AC in direct comparison with computed tomography (CT)-based AC of the same PET data set on a large patient population., Materials and Methods: Sixty-six patients (22 female; mean [SD], 61 [11] years) were examined by means of combined PET/CT and PET/MR (11C-choline, 18F-FDG, or 68Ga-DOTATATE) subsequently. Positron emission tomography images from PET/MR examinations were corrected with MR-derived AC based on tissue segmentation (PET(MR)). The same PET data were corrected using CT-based attenuation maps (μ-maps) derived from PET/CT after nonrigid registration of the CT to the MR-based μ-map (PET(MRCT)). Positron emission tomography SUVs were quantified placing regions of interest or volumes of interest in 6 different body regions as well as PET-avid lesions, respectively., Results: The relative differences of quantitative PET values when using MR-based AC versus CT-based AC were varying depending on the organs and body regions assessed. In detail, the mean (SD) relative differences of PET SUVs were as follows: -7.8% (11.5%), blood pool; -3.6% (5.8%), spleen; -4.4% (5.6%)/-4.1% (6.2%), liver; -0.6% (5.0%), muscle; -1.3% (6.3%), fat; -40.0% (18.7%), bone; 1.6% (4.4%), liver lesions; -6.2% (6.8%), bone lesions; and -1.9% (6.2%), soft tissue lesions. In 10 liver lesions, distinct overestimations greater than 5% were found (up to 10%). In addition, overestimations were found in 2 bone lesions and 1 soft tissue lesion adjacent to the lung (up to 28.0%)., Conclusions: Results obtained using different PET tracers show that MR-based AC is accurate in most tissue types, with SUV deviations generally of less than 10%. In bone, however, underestimations can be pronounced, potentially leading to inaccurate SUV quantifications. In addition, SUV overestimations were found for some lesions close to lung borders. This has to be taken into account when comparing PET/CT- and PET/MR-derived SUVs.

Objective: The aim of this study was to evaluate the clinical applicability and technical feasibility of fluorodeoxyglucose (FDG) positron emission tomography (PET)/magnetic resonance imaging (MRI) compared with FDG PET/computed tomography (CT) in young children focusing on lesion detection, PET quantification, and potential savings in radiation exposure., Methods: Twenty examinations (10 PET/CT and 10 PET/MRI examinations) were performed prospectively in 9 patients with solid tumors (3 female, 6 male; mean age, 4.8 [1-6] years). Fluorodeoxyglucose PET/CT and FDG PET/MRI were performed sequentially after a single tracer injection. Lesion detection and analysis were performed independently in PET/CT and PET/MRI. Potential changes in diagnostic or therapeutic patient management were recorded. Positron emission tomography quantification in PET/MRI was evaluated by comparing standardized uptake values resulting from MRI-based and CT-based attenuation correction. Effective radiation doses of PET and CT were estimated., Results: Twenty-one PET-positive lesions were found congruently in PET/CT and PET/MRI. Magnetic resonance imaging enabled significantly better detection of morphologic PET correlates compared with CT. Eight suspicious PET-negative lesions were identified by MRI, of which one was missed in CT. Sensitivity, specificity, and accuracy for correct lesion classification were not significantly different (90%, 47%, and 62% in PET/CT; 100%, 68%, and 79% in PET/MRI, respectively). In 4 patients, the use of PET/MRI resulted in a potential change in diagnostic management compared with PET/CT, as local and whole-body staging could be performed within 1 single examination. In 1 patient, PET/MRI initiated a change in therapeutic management. Positron emission tomography quantification using MRI-based attenuation correction was accurate compared with CT-based attenuation correction. Higher standardized uptake value deviations of about 18% were observed in the lungs due to misclassification in MRI-based attenuation maps. Potential reduction in radiation dose was 48% in PET/MRI compared with PET/CT (P < 0.05)., Conclusions: FDG PET/MRI is at least equivalent to FDG PET/CT for oncologic imaging in young children. Specifically, superior soft tissue contrast of MRI results in higher confidence in lesion interpretation. Substantial savings in radiation exposure can be achieved, and the number of necessary imaging examinations can be reduced using PET/MRI compared with PET/CT.

Background: To analyze the regional composition of bone marrow (BM) in correlation with metabolic activity and diffusivity using simultaneous positron emission tomography (PET)/MRI., Methods: Retrospective analysis of 18F-FDG-PET/MR scans of 110 patients was performed. A three-dimensional gradient-echo sequence with Dixon-based fat-water separation was used for fat quantification. Dixon images, diffusion-weighted images (DWI) and 18F-FDG-PET were co-registered. Mean values of fat fraction (FF), standardized uptake value (SUV), and apparent diffusion coefficient (ADC) of BM were measured in different anatomical regions. Correlation of FF, SUV, and ADC and association of BM fat content and metabolic activity with anthropometric data was analyzed (Pearson). BM fat content and metabolic activity was compared in patients with and without chemotherapy (t-test)., Results: Regional differences in BM were found with highest fat content (93 ± 8%) and lowest ADC (0.22 ± 0.18 × 10(-3) mm(2) /s) in the peripheral skeleton and highest SUV in the spine (1.77 ± 0.6). There was a significant inverse correlation between FF and SUV (r = -0.73; P < 0.0001) and a significant inverse correlation between FF and ADC (r = -0.62; P < 0.0001). In patients with chemotherapy, a tendency to higher fat content and lower metabolic activity was observed in the proximal skeleton, although no statistical significance was reached., Conclusion: BM shows distinct regional variations in FF, SUV, and ADC. The inverse correlation of FF and SUV in BM suggests that BM adipose tissue does not have a comparable high metabolic activity as brown adipose tissue., (© 2015 Wiley Periodicals, Inc.)

Unlabelled: Pediatric imaging is regarded as a key application for combined PET/MR imaging systems. Because existing MR-based attenuation-correction methods were not designed specifically for pediatric patients, we assessed the impact of 2 potentially influential factors: inter- and intrapatient variability of attenuation coefficients and anatomic variability. Furthermore, we evaluated the quantification accuracy of 3 methods for MR-based attenuation correction without (SEGbase) and with bone prediction using an adult and a pediatric atlas (SEGwBONEad and SEGwBONEpe, respectively) on PET data of pediatric patients., Methods: The variability of attenuation coefficients between and within pediatric (5-17 y, n = 17) and adult (27-66 y, n = 16) patient collectives was assessed on volumes of interest (VOIs) in CT datasets for different tissue types. Anatomic variability was assessed on SEGwBONEad/pe attenuation maps by computing mean differences to CT-based attenuation maps for regions of bone tissue, lungs, and soft tissue. PET quantification was evaluated on VOIs with physiologic uptake and on 80% isocontour VOIs with elevated uptake in the thorax and abdomen/pelvis. Inter- and intrapatient variability of the bias was assessed for each VOI group and method., Results: Statistically significant differences in mean VOI Hounsfield unit values and linear attenuation coefficients between adult and pediatric collectives were found in the lungs and femur. The prediction of attenuation maps using the pediatric atlas showed a reduced error in bone tissue and better delineation of bone structure. Evaluation of PET quantification accuracy showed statistically significant mean errors in mean standardized uptake values of -14% ± 5% and -23% ± 6% in bone marrow and femur-adjacent VOIs with physiologic uptake for SEGbase, which could be reduced to 0% ± 4% and -1% ± 5% using SEGwBONEpe attenuation maps. Bias in soft-tissue VOIs was less than 5% for all methods. Lung VOIs showed high SDs in the range of 15% for all methods. For VOIs with elevated uptake, mean and SD were less than 5% except in the thorax., Conclusion: The use of a dedicated atlas for the pediatric patient collective resulted in improved attenuation map prediction in osseous regions and reduced interpatient bias variation in femur-adjacent VOIs. For the lungs, in which intrapatient variation was higher for the pediatric collective, a patient- or group-specific attenuation coefficient might improve attenuation map accuracy. Mean errors of -14% and -23% in bone marrow and femur-adjacent VOIs can affect PET quantification in these regions when bone tissue is ignored., (© 2015 by the Society of Nuclear Medicine and Molecular Imaging, Inc.)

Objectives: The objective of this study was to evaluate the frequency and characteristics of artifacts in segmentation-based attenuation correction maps (μ-maps) of positron emission tomography/magnetic resonance (PET/MR) and their impact on PET interpretation and the standardized uptake value (SUV) quantification in normal tissue and lesions., Materials and Methods: The study was approved by the local institutional review board. Attenuation maps of 100 patients with PET/MR and preceding PET/computed tomography examination were retrospectively inspected for artifacts (tracers: 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG), ¹¹C-Choline, ⁶⁸Ga-DOTATOC, ⁶⁸Ga-DOTATATE, ¹¹C-Methionine). The artifacts were subdivided into 9 different groups on the basis of their localization and appearance. The impact of μ-map artifacts in normal tissue and lesions on PET interpretation was evaluated qualitatively via visual analysis in synopsis with the non-attenuation-corrected (NAC) PET as well as quantitatively by comparing the SUV in artifact regions to reference regions., Results: Attenuation map artifacts were found in 72% of the head/neck data sets, 61% of the thoracic data sets, 25% of the upper abdominal data sets, and 26% of the pelvic data sets. The most frequent localizations of the overall 276 artifacts were around metal implants (16%), in the lungs (19%), and outer body contours (31%). Twenty-one percent of all PET-avid lesions (38 of 184 lesions) were affected by artifacts in the majority without further consequences for visual PET interpretation. However, 9 PET-avid lung lesions were masked owing to μ-map artifacts and, thus, were only detectable on the NAC PET or additional MR imaging sequences. Quantitatively, μ-map artifacts led to significant SUV changes in areas with erroneous assignment of air instead of soft tissue (ie, metal artifacts) and of soft tissue instead of lung. Nevertheless, no change in diagnosis would have been caused by μ-map artifacts., Conclusions: Attenuation map artifacts that occur in a considerable percentage of PET/MR data sets have the potential to falsify PET quantification and visual PET interpretation. Nevertheless, on the basis of the present data, in the clinical interpretation setup, no changes in diagnosis due to μ-map artifacts may occur, especially when the μ-maps are checked for artifacts and PET/MR is read in synopsis with the NAC PET, if artifacts are present.

Purpose: To characterize peritoneal carcinomatosis (PC) of different histologically proven primary tumors based on diffusion-weighted imaging (DWI) and (18) F-FDG positron emission tomography (PET)., Materials and Methods: Forty-one patients underwent simultaneous MR/PET after clinically indicated (18) F-FDG-PET/CT. For all patients, histology of the primary tumor was obtained. MR protocol comprised anatomical imaging and axial DWI. Apparent diffusion coefficient (ADC) maps and FDG-PET were co-registered for evaluation of ADC and standard uptake value (SUV) of peritoneal lesions. Both lesion- and patient-based analysis was performed. Up to four peritoneal lesions were evaluated per patient. Mean and maximum standard uptake value (SUVmean , SUVmax ), mean and minimum ADC (ADCmean , ADCmin ) of each lesion were assessed. Spearman rank correlation (rs ) of ADC and SUV were calculated. SUV and ADC of ovarian and colorectal cancer lesions were compared using Wilcoxon test., Results: Measurable lesions (n = 52) were found in 20 of 41 PC patients. Moderate, but significant correlation existed between ADC and SUV in the lesion-based as well as the patient-based analysis (lesion-based: SUVmean versus ADCmean rs = -0.58; SUVmax versus ADCmin rs = -0.56, all P < 0.0001; patient-based: SUVmean versus ADCmean rs = -0.64, P = 0.002; SUVmax versus ADCmin rs = -0.60, P = 0.005). ADC and SUV differed significantly between ovarian and colorectal cancer lesions (ADCmin : P < 0.0001; ADCmean : P < 0.0001; SUVmax : P = 0.002; SUVmean : P = 0.005). Overall, mucinous tumor entities showed a tendency to higher ADC and lower SUV., Conclusion: PC lesions showed significant differences in glucose uptake and diffusion characteristics depending on primary tumor histology. These differences should be considered when interpreting FDG-PET and DWI in PC patients., (© 2013 Wiley Periodicals, Inc.)

Purpose: To compare positron emission tomography (PET)/magnetic resonance (MR) imaging and PET/computed tomography (CT) for lesion detection and interpretation, quantification of fluorine 18 ((18)F) fluorodeoxyglucose (FDG) uptake, and accuracy of MR-based PET attenuation correction in pediatric patients with solid tumors. Materials and Methods This prospective study had local ethics committee and German Federal Institute for Drugs and Medical Devices approval. Written informed consent was obtained from all patients and legal guardians. Twenty whole-body (18)F-FDG PET/CT and (18)F-FDG PET/MR examinations were performed in 18 pediatric patients (median age, 14 years; range, 11-17 years). (18)F-FDG PET/CT and (18)F-FDG PET/MR data were acquired sequentially on the same day for all patients. PET standardized uptake values (SUVs) were quantified with volume of interest measurements in lesions and healthy tissues. MR-based PET attenuation correction was compared with CT-derived attenuation maps (µ-maps). Lesion detection was assessed with separate reading of PET/CT and PET/MR data. Estimates of radiation dose were derived from the applied doses of (18)F-FDG and CT protocol parameters. Descriptive statistical analyses were performed to report correlation coefficients and relative deviations for comparison of SUVs, rates of lesion detection, and percentage reductions in radiation dose., Results: PET SUVs showed strong correlations between PET of PET/CT (PETCT) and PET of PET/MR (PETMR) (r > 0.85 for most tissues). Apart from drawbacks of MR-based PET attenuation correction in osseous structures and lungs, similar SUVs were found on PET images corrected with CT-based µ-maps (13.1% deviation of SUVs for bone marrow and <5% deviation for other tissues). Lesion detection rate with PET/MR imaging was equivalent to that with PET/CT (61 areas of focal uptake on PETMR images vs 62 areas on PETCT images). Advantages of PET/MR were observed especially in soft-tissue regions. Furthermore, PET/MR offered significant dose reduction (73%) compared with PET/CT., Conclusion: Pediatric oncologic PET/MR is technically feasible, showing satisfactory performance for PET quantification with SUVs similar to those of PET/CT. Compared with PET/CT, PET/MR demonstrates equivalent lesion detection rates while offering markedly reduced radiation exposure. Thus, PET/MR is a promising modality for the clinical work-up of pediatric malignancies. Online supplemental material is available for this article., (© RSNA, 2014.)

Purpose: Multimodality imaging has become an important adjunct of state-of-the-art radiation therapy (RT) treatment planning. Recently, simultaneous PET/MR hybrid imaging has become clinically available and may also contribute to target volume delineation and biological individualization in RT planning. For integration of PET/MR hybrid imaging into RT treatment planning, compatible dedicated RT devices are required for accurate patient positioning. In this study, prototype RT positioning devices intended for PET/MR hybrid imaging are introduced and tested toward PET/MR compatibility and image quality., Methods: A prototype flat RT table overlay and two radiofrequency (RF) coil holders that each fix one flexible body matrix RF coil for RT head/neck imaging have been evaluated within this study. MR image quality with the RT head setup was compared to the actual PET/MR setup with a dedicated head RF coil. PET photon attenuation and CT-based attenuation correction (AC) of the hardware components has been quantitatively evaluated by phantom scans. Clinical application of the new RT setup in PET/MR imaging was evaluated in anin vivo study., Results: The RT table overlay and RF coil holders are fully PET/MR compatible. MR phantom and volunteer imaging with the RT head setup revealed high image quality, comparable to images acquired with the dedicated PET/MR head RF coil, albeit with 25% reduced SNR. Repositioning accuracy of the RF coil holders was below 1 mm. PET photon attenuation of the RT table overlay was calculated to be 3.8% and 13.8% for the RF coil holders. With CT-based AC of the devices, the underestimation error was reduced to 0.6% and 0.8%, respectively. Comparable results were found within the patient study., Conclusions: The newly designed RT devices for hybrid PET/MR imaging are PET and MR compatible. The mechanically rigid design and the reproducible positioning allow for straightforward CT-based AC. The systematic evaluation within this study provides the technical basis for the clinical integration of PET/MR hybrid imaging into RT treatment planning.

Objective: A potential major application of simultaneous avalanche photodiode-based positron emission tomography (PET)/magnetic resonance imaging (MRI) systems are quantitative brain studies for cerebral blood flow measurements in combination with blood-oxygen-level-dependent or perfusion MRI, requiring a high performance for both modalities. Thus, we evaluated PET quantification accuracy and homogeneity for 2 different simultaneous PET/MRI systems (whole-body and brain scanner) compared with those of a state-of-the-art PET detector (PET/computed tomography) using phantom studies. In addition, we investigated the long-term stability of PET and quality of functional MRI measurements of a clinical whole-body PET/MRI scanner., Materials and Methods: Phantom measurements were conducted using spheres filled with [F]-fluoride distributed in a homogeneous cylinder phantom at different positions inside the PET field of view. Recovery values and standard deviations were extracted from resulting PET images. The influence of magnetic resonance-based attenuation correction and that of activity outside the PET field of view on the recovery values of these spheres was evaluated. Furthermore, long-term PET stability of the whole-body PET/MRI system was assessed by evaluating position profiles, energy spectra, count rates, and recovery values from [Ge]-phantom scans. Functional MRI applicability was tested in accordance with the functional Biomedical Information Research Network procedure., Results: The BrainPET system showed high recovery values (up to 99%) but also increased variability (up to 7.4%). Significant underestimations in PET quantification near activity outside the PET field of view were found (up to 80%). Using magnetic resonance-based attenuation correction led to an underestimation in PET activity of approximately 7%. In distinction, the whole-body PET/MRI system revealed performance similar to the PET/computed tomographic scanner (recovery values up to approximately 60% with a variability of approximately 4%). Long-term stability and fMRI performance of the whole-body PET/MRI scanner showed no degradation compared with stand-alone systems., Conclusions: Homogeneity and accuracy of avalanche photodiode-based PET detectors is comparable with those of the state-of-the-art detectors based on photomultiplier tubes. However, attenuation correction on PET/MRI systems has to be adapted carefully for quantitative PET measurements. The BrainPET system needs improved scatter correction to perform quantitative brain studies. The whole-body PET/MRI scanner, however, is applicable for quantitative brain studies.

Background: Combined positron emission tomography (PET)/magnetic resonance imaging (MRI) is highly promising for biologically individualized radiotherapy (RT). Hence, the purpose of this work was to develop an accurate and robust registration strategy to integrate combined PET/MR data into RT treatment planning. Material and methods. Eight patient datasets consisting of an FDG PET/computed tomography (CT) and a subsequently acquired PET/MR of the head and neck (HN) region were available. Registration strategies were developed based on CT and MR data only, whereas the PET components were fused with the resulting deformation field. Following a rigid registration, deformable registration was performed with a transform parametrized by B-splines. Three different optimization metrics were investigated: global mutual information (GMI), GMI combined with a bending energy penalty (BEP) for regularization (GMI+ BEP) and localized mutual information with BEP (LMI+ BEP). Different quantitative registration quality measures were developed, including volumetric overlap and mean distance measures for structures segmented on CT and MR as well as anatomical landmark distances. Moreover, the local registration quality in the tumor region was assessed by the normalized cross correlation (NCC) of the two PET datasets., Results: LMI+ BEP yielded the most robust and accurate registration results. For GMI, GMI+ BEP and LMI+ BEP, mean landmark distances (standard deviations) were 23.9 mm (15.5 mm), 4.8 mm (4.0 mm) and 3.0 mm (1.0 mm), and mean NCC values (standard deviations) were 0.29 (0.29), 0.84 (0.14) and 0.88 (0.06), respectively., Conclusion: Accurate and robust multimodal deformable image registration of CT and MR in the HN region can be performed using a B-spline parametrized transform and LMI+ BEP as optimization metric. With this strategy, biologically individualized RT based on combined PET/MRI in terms of dose painting is possible.

Purpose: Our objective was a multifunctional imaging approach of chronic sclerodermatous graft-versus-host disease (ScGVHD) and its course during therapy using PET/MRI., Methods: We performed partial-body PET/CT and PET/MRI of the calf in 6 consecutively recruited patients presenting with severe ScGVHD. The patients were treated with different immunosuppressive regimens and supportive therapies. PET/CT scanning started 60.5 ± 3.3 minutes, PET/MRI imaging 139.5 ± 16.7 minutes after (18)F-FDG application. MRI acquisition included T1- (precontrast and postcontrast) and T2-weighted sequences. SUV(mean), T1 contrast enhancement, and T2 signal intensity from region-of-interest analysis were calculated for different fascial and muscular compartments. In addition, musculoskeletal MRI findings and the modified Rodnan skin score were assessed. All patients underwent imaging follow-up., Results: At baseline PET/MRI, ScGVHD-related musculoskeletal abnormalities consisted of increased signal and/or thickening of involved anatomical structures on T2-weighted and T1 postcontrast images as well as an increased FDG uptake. At follow-up, ScGVHD-related imaging findings decreased (SUV(mean) n = 4, mean T1 contrast enhancement n = 5, mean T2 signal intensity n = 3) or progressed (SUV(mean) n = 3, mean T1 contrast enhancement n = 2, mean T2 signal intensity n = 4). Clinically modified Rodnan skin score improved for 5 follow-ups and progressed for 2. SUV(mean) values correlated between PET/CT and PET/MRI acquisition (r = 0.660, P = 0.014), T1 contrast enhancement, and T2 signal (r = 0.668, P = 0.012), but not between the SUV(mean) values and the MRI parameters., Conclusions: PET/MRI as a combined morphological and functional technique seems to assess the inflammatory processes from different points of view and provides therefore in part complementary information.

Purpose: To compare anatomic alignment between morphologic and positron emission tomography (PET) images acquired in the abdomen and pelvis by using simultaneous magnetic resonance (MR)/PET, PET/computed tomography (CT), and retrospective MR/PET fusion and to compare alignment between MR and PET in simultaneous and sequential thoracic MR/PET by using different breathing, registration, and gating protocols., Materials and Methods: Informed consent and institutional review board approval were obtained. The misalignment in 28 abdominal patient datasets was analyzed in simultaneous MR/PET, PET/CT, and retrospective MR/PET fusion. In seven thoracic MR/PET datasets, the effect of different breathing protocols, simultaneous, sequential, and MR-gated data acquisition was evaluated, and the effect of rigid registration versus nonregistered images was evaluated. Analysis of variance and subsequent Tukey test were used for statistical analysis., Results: The misalignment in all abdominal organs was reduced in simultaneous MR/PET compared with retrospectively fused MR and PET images (means, 5.8 mm vs 11.9 mm; P < .001), and in the urinary bladder compared with PET/CT (means, 5.9 mm vs 11.0 mm; P < .007). Thoracic MR/PET with inspiratory breath-hold MR showed the largest misalignment (mean, 24.5 mm; P < .001). None of the other thoracic protocols that were composed of different acquisition, registration, or gating procedures differed significantly from one another., Conclusion: The alignment of hybrid datasets acquired in simultaneous whole-body MR/PET was more accurate than retrospective fusion in all investigated abdominal organs, and more accurate than PET/CT in the urinary bladder; the alignment of thoracic MR/PET with expiratory breath hold or free-breathing MR was more exact than with inspiratory MR. However in this preliminary work the clinical importance of these degrees of misalignment was not assessed.

Purpose: To compare the performance of magnetic resonance (MR)/positron emission tomography (PET) imaging in the staging of lung cancer with that of PET/computed tomography (CT) as the reference standard and to compare the quantification accuracy of a new whole-body MR/PET system with corresponding PET/CT data sets., Materials and Methods: Institutional review board approval and informed consent were obtained. Ten patients in whom bronchial carcinoma was proven or clinically suspected underwent clinically indicated fluorine 18 fluorodeoxyglucose (FDG) PET/CT and, immediately thereafter, whole-body MR/PET imaging with a new hybrid whole-body system (3.0-T MR imager with integrated PET system). Attenuation correction of MR/PET images was segmentation based with fat-water separation. Tumor-to-liver ratios were calculated and compared between PET/CT and MR/PET imaging. Tumor staging on the basis of the PET/CT and MR/PET studies was performed by two readers. Spearman rank correlation was used for comparison of data., Results: MR/PET imaging provided diagnostic image quality in all patients, with good tumor delineation. Most lesions (nine of 10) showed pronounced FDG uptake. One lesion was morphologically suspicious for malignancy at CT and MR imaging but showed no FDG uptake. MR/PET imaging had higher mean tumor-to-liver ratios than did PET/CT (4.4 ± 2.0 [standard deviation] for PET/CT vs 8.0 ± 3.9 for MR/PET imaging). Significant correlation regarding the tumor-to-liver ratio was found between both imaging units (ρ = 0.93; P < .001). Identical TNM scores based on MR/PET and PET/CT data were found in seven of 10 patients. Differences in T and/or N staging occurred mainly owing to modality-inherent differences in lesion size measurement., Conclusion: MR/PET imaging of the lung is feasible and provides diagnostic image quality in the assessment of pulmonary masses. Similar lesion characterization and tumor stage were found in comparing PET/CT and MR/PET images in most patients.

Purpose: The purpose of this study was to demonstrate the feasibility of voxel-wise multiparametric characterization of head and neck squamous cell carcinomas (HNSCC) using hybrid multiparametric magnetic resonance imaging and positron emission tomography with [18F]-fluorodesoxyglucose (FDG-PET/MRI) in a radiation treatment planning setup.Methods: Ten patients with locally advanced HNSCC were examined with a combined FDG-PET/MRI in an irradiation planning setup. The multiparametric imaging protocol consisted of FDG-PET, T2-weighted transverse short tau inversion recovery sequence (STIR) and diffusion-weighted MRI (DWI). Primary tumours were manually segmented and quantitative imaging parameters were extracted. PET standardized uptake values (SUV) and DWI apparent diffusion coefficients (ADC) were correlated on a voxel-wise level.Results: Images acquired in this specialised radiotherapy planning setup achieved good diagnostic quality. Median tumour volume was 4.9 [1.1-42.1] ml. Mean PET SUV and ADC of the primary tumours were 5 ± 2.5 and 1.2 ± 0.3 10-3 mm2/s, respectively. In voxel-wise correlation between ADC values and corresponding FDG SUV of the tumours, a significant negative correlation was observed (r = -0.31 ± 0.27, p < 0.05).Conclusion: Multiparametric voxel-wise characterization of HNSCC is feasible using combined PET/MRI in a radiation planning setup. This technique may provide novel insights into tumour biology with regard to radiation therapy in the future. [ABSTRACT FROM AUTHOR]