Integrated 18F-FDG PET/MRI compared to MRI alone for identification of local recurrences of soft tissue sarcomas: a comparison trial.

PURPOSE: To assess and compare the diagnostic accuracy of PET/MRI and MRI alone for the detection of local recurrences of soft tissue sarcomas (STS) after initial surgical resection of the primary tumors. MATERIAL AND METHODS: A total of 41 patients with clinically suspected tumor relapse of STS underwent an 18F-FDG-PET/MRI examination for assessment of local recurrence. Two experienced physicians interpreted the MRI data and subsequently the PET/MRI datasets in two separate reading sessions and were instructed to identify potential local tumor recurrences. Additionally, the diagnostic confidence in each reading for the identification of malignant lesions was determined. A McNemar test was applied to test for differences of both ratings and a Wilcoxon signed-rank test was used to identify differences of the confidence levels. Histopathological verification and follow-up imaging were applied for standard of reference. RESULTS: Tumor relapse was present in 27/41 patients. Calculated sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy for the detection of local tumor recurrence was 82%, 86%, 92%, 71% and 83% for MRI, and 96%, 79%, 90%, 92% and 90% for PET/MRI (p > 0.05). Furthermore, PET/MRI showed significantly higher confidence levels (p < 0.05) for the determination of malignant lesions. CONCLUSION: Our results endorse 18F-FDG PET/MRI to be an excellent imaging method in the evaluation of recurrent STS after surgical excision, yielding superior tumor detection when compared to MRI alone.

Response assessment of bevacizumab therapy in GBM with integrated 11C-MET-PET/MRI: a feasibility study.

BACKGROUND: The objective of this study was to evaluate the potential of integrated 11C-MET PET/MR for response assessment of relapsed glioblastoma (GBM) receiving bevacizumab treatment. METHODS: Eleven consecutive patients with relapsed GBM were enrolled for an integrated 11C-MET PET/MRI at baseline and at follow-up. Treatment response for MRI was evaluated according to Response Assessment in Neuro-oncology (RANO) criteria and integrated 11C-MET PET was assessed by the T/N ratio. RESULTS: MRI showed no patient with complete response (CR), six of 11 patients with PR, four of 11 patients with SD, and one of 11 patients with progressive disease (PD). PET revealed metabolic response in five of the six patients with partial response (PR) and in two of the four patients with stable disease (SD), whereas metabolic non-response was detected in one of the six patients with PR, in two of the four patients with SD, and in the one patient with PD. Morphological imaging was predictive for PFS and OS when response was defined as CR, PR, SD, and non-response as PD. Metabolic imaging was predictive when using T/N ratio reduction of >25 as discriminator. Based on the morphologic and metabolic findings of this study a proposal for applying integrated PET/MRI for treatment response in relapsed GBM was developed, which was significantly predictive for PFS and OS (P = 0.010 respectively 0,029, log). CONCLUSIONS: This study demonstrates the potential of integrated 11C-MET-PET/MRI for response assessment of GBM and the utility of combined assessment of morphologic and metabolic information with the proposal for assessing relapsed GBM.

Diagnostic value of integrated PET/MRI for detection and localization of prostate cancer: Comparative study of multiparametric MRI and PET/CT.

PURPOSE: To evaluate the diagnostic value of integrated positron emission tomography/magnetic resonance imaging (PET/MRI) compared with conventional multiparametric MRI and PET/computed tomography (CT) for the detailed and accurate segmental detection/localization of prostate cancer. MATERIALS AND METHODS: Thirty-one patients who underwent integrated PET/MRI using 18 F-choline and 18 F-FDG with an integrated PET/MRI scanner followed by radical prostatectomy were included. The prostate was divided into six segments (sextants) according to anatomical landmarks. Three radiologists noted the presence and location of cancer in each sextant on four different image interpretation modalities in consensus (1, multiparametric MRI; 2, integrated 18 F-FDG PET/MRI; 3, integrated 18 F-choline PET/MRI; and 4, combined interpretation of 1 and 18 F-FDG PET/CT). Sensitivity, specificity, accuracy, positive and negative predictive values, likelihood ratios, and diagnostic performance based on the DOR (diagnostic odds ratio) and NNM (number needed to misdiagnose) were evaluated for each interpretation modality, using the pathologic result as the reference standard. Detection rates of seminal vesicle invasion and extracapsular invasion were also evaluated. RESULTS: Integrated 18 F-choline PET/MRI showed significantly higher sensitivity than did multiparametric MRI alone in high Gleason score patients (77.0% and 66.2%, P = 0.011), low Gleason score patients (66.7% and 47.4%, P = 0.007), and total patients (72.5% and 58.0%, P = 0.008) groups. Integrated 18 F-choline PET/MRI and 18 F-FDG PET/MRI showed similar sensitivity and specificity to combined interpretation of multiparametric MRI and 18 F-FDG PET/CT (for sensitivity, 58.0%, 63.4%, 72.5%, and 68.7%, respectively, and for specificity, 87.3%, 80.0%, 81.8%, 72.7%, respectively, in total patient group). However, integrated 18 F-choline PET/MRI showed the best diagnostic performance (as DOR, 11.875 in total patients, 27.941 in high Gleason score patients, 5.714 in low Gleason score groups) among the imaging modalities, regardless of Gleason score. Integrated 18 F-choline PET/MRI showed higher sensitivity and diagnostic performance than did integrated 18 F-FDG PET/MRI (as DOR, 6.917 in total patients, 15.143 in high Gleason score patients, 3.175 in low Gleason score groups) in all three patient groups. CONCLUSION: Integrated PET/MRI carried out using a dedicated integrated PET/MRI scanner provides better sensitivity, accuracy, and diagnostic value for detection/localization of prostate cancer compared to multiparametric MRI. Generally, integrated 18 F-choline PET/MRI shows better sensitivity, accuracy, and diagnostic performance than does integrated 18 F-FDG PET/MRI as well as combined interpretation of multiparametric MRI with 18 F-FDG PET/CT. LEVEL OF EVIDENCE: 2 J. Magn. Reson. Imaging 2017;45:597-609.

Diagnostic impact of integrated 18F-FDG PET/MRI in cerebral staging of patients with non-small cell lung cancer.

Background Integrated positron emission tomography/magnetic resonance imaging (PET/MRI) systems are increasingly being available and used for staging examinations. Brain metastases (BM) are frequent in patients with non-small cell lung cancer (NSCLC) and decisive for treatment strategy. Purpose To assess the diagnostic value of integrated 18F-2-fluoro-2-deoxy-D glucose (18F-FDG) PET/MRI in initial staging in patients with NSCLC for BM in comparison to MRI alone. Material and Methods Eighty-three patients were prospectively enrolled for an integrated 18F-FDG PET/MRI examination. The 3 T MRI protocol included a fluid-attenuated inversion-recovery sequence (FLAIR) and a contrast-enhanced three-dimensional magnetization prepared rapid acquisition GRE sequence (MPRAGE). Two neuroradiologists evaluated the datasets in consensus regarding: (i) present lesions; (ii) size of lesions; and (iii) number of lesions detected in MRI alone, compared to the PET component when reading the 18F-FDG PET/MRI. Results Based on MRI alone, BM were detected in 15 out of the 83 patients, comprising a total of 39 metastases. Based on PET alone, six patients out of the 83 patients were rated positive for metastatic disease, revealing a total of 15 metastases. PET detected no additional BM. The size of the BM correlated positively with sensitivity of detection in PET. Conclusion The sensitivity of PET in detection of BM depends on their size. 18F-FDG PET/MRI does not lead to an improvement in diagnostic accuracy in cerebral staging of NSCLC patients, as MRI alone remains the gold standard.

Value of Molecular Typing Combined with Integrated Positron Emission Tomography/Magnetic Resonance Imaging in Risk Stratification of Endometrial Cancer.

Objective: In this study, we investigated the value of molecular typing combined with integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) semi-quantitative indices in endometrial cancer risk stratification. Methods: A retrospective study was conducted on 86 patients who were pathologically diagnosed with endometrial cancer and underwent surgical treatment after curettage at the Department of Obstetrics and Gynecology, Xuanwu Hospital, Capital Medical University between January 2017 and March 2023. Prior to surgery, each patient underwent integrated PET/MRI examination. The postoperative samples were subjected to pathological diagnosis, immunohistochemistry, and POLE gene sequencing. The differences in clinicopathological features between the four molecular subtypes and the differences in integrated PET/MRI semi-quantitative indexes (SUV max, ADC min) between the four molecular subtypes were analyzed. The cutoff value of molecular typing combined with integrated PET/MRI semi-quantitative indices for endometrial cancer risk stratification was determined. Results: There were statistically significant differences in pathological types and tumor grades among the four molecular subtypes of endometrial cancer. The values of the four integrated PET/MRI semi-quantitative indices (SUV max and ADC min) of the molecular subtypes were statistically different. The SUV max was greater in the p53abn mutation group than in the POLE mutation group (P < 0.05). The ADC minimum of the POLE mutation group and the MMR-d group was lower than the NSMP group (P < 0.05). Molecular typing combined with the integrated PET/MRI semi-quantitative SUV max index can predict the low/medium risk group of endometrial cancer and the medium-high/high risk group, and the cut-off value of SUV max for predicting the risk of early endometrial cancer was 14.72 (sensitivity 66.7%, specificity 68.7%). Conclusion: Molecular typing combined with integrated PET/MRI semi-quantitative indicators is useful to achieve risk stratification in patients diagnosed with endometrial cancer and guide individualized treatment.

Integrated Positron Emission Tomography/Magnetic Resonance Imaging for Resting-State Functional and Metabolic Imaging in Human Brain: What Is Correlated and What Is Impacted.

Integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) could simultaneously obtain both functional MRI (fMRI) and 18F-fluorodeoxyglucose (FDG) PET and thus provide multiparametric information for the analysis of brain metabolism. In this study, we aimed to, for the first time, investigate the interplay of simultaneous fMRI and FDG PET scan using a randomized self-control protocol. In total, 24 healthy volunteers underwent PET/MRI scan for 30-40 min after the injection of FDG. A 22-min brain scan was separated into MRI-off mode (without fMRI pulsing) and MRI-on mode (with fMRI pulsing), with each one lasting for 11 min. We calculated the voxel-wise fMRI metrics (regional homogeneity, amplitude of low-frequency fluctuations, fractional amplitude of low-frequency fluctuations, and degree centrality), resting networks, relative standardized uptake value ratios (SUVr), SUVr slope, and regional cerebral metabolic rate of glucose (rCMRGlu) maps. Paired two-sample t-tests were applied to assess the statistical differences between SUVr, SUVr slope, correlation coefficients of fMRI metrics, and rCMRGlu between MRI-off and MRI-on modes, respectively. The voxel-wise whole-brain SUVr revealed no statistical difference (P > 0.05), while the SUVr slope was significantly elevated in sensorimotor, dorsal attention, ventral attention, control, default, and auditory networks (P < 0.05) during fMRI scan. The task-based group independent-component analysis revealed that the most active network components derived from the combined MRI-off and MRI-on static PET images were frontal pole, superior frontal gyrus, middle temporal gyrus, and occipital pole. High correlation coefficients were found among fMRI metrics with rCMRGlu in both MRI-off and MRI-on mode (P < 0.05). Our results systematically evaluated the impact of simultaneous fMRI scan on the quantification of human brain metabolism from an integrated PET/MRI system.

High-quality PET image synthesis from ultra-low-dose PET/MRI using bi-task deep learning.

Background: Lowering the dose for positron emission tomography (PET) imaging reduces patients' radiation burden but decreases the image quality by increasing noise and reducing imaging detail and quantifications. This paper introduces a method for acquiring high-quality PET images from an ultra-low-dose state to achieve both high-quality images and a low radiation burden. Methods: We developed a two-task-based end-to-end generative adversarial network, named bi-c-GAN, that incorporated the advantages of PET and magnetic resonance imaging (MRI) modalities to synthesize high-quality PET images from an ultra-low-dose input. Moreover, a combined loss, including the mean absolute error, structural loss, and bias loss, was created to improve the trained model's performance. Real integrated PET/MRI data from 67 patients' axial heads (each with 161 slices) were used for training and validation purposes. Synthesized images were quantified by the peak signal-to-noise ratio (PSNR), normalized mean square error (NMSE), structural similarity (SSIM), and contrast noise ratio (CNR). The improvement ratios of these four selected quantitative metrics were used to compare the images produced by bi-c-GAN with other methods. Results: In the four-fold cross-validation, the proposed bi-c-GAN outperformed the other three selected methods (U-net, c-GAN, and multiple input c-GAN). With the bi-c-GAN, in a 5% low-dose PET, the image quality was higher than that of the other three methods by at least 6.7% in the PSNR, 0.6% in the SSIM, 1.3% in the NMSE, and 8% in the CNR. In the hold-out validation, bi-c-GAN improved the image quality compared to U-net and c-GAN in both 2.5% and 10% low-dose PET. For example, the PSNR using bi-C-GAN was at least 4.46% in the 2.5% low-dose PET and at most 14.88% in the 10% low-dose PET. Visual examples also showed a higher quality of images generated from the proposed method, demonstrating the denoising and improving ability of bi-c-GAN. Conclusions: By taking advantage of integrated PET/MR images and multitask deep learning (MDL), the proposed bi-c-GAN can efficiently improve the image quality of ultra-low-dose PET and reduce radiation exposure.

Integrated Positron Emission Tomography/Magnetic Resonance Imaging in clinical diagnosis of Alzheimer's disease.

Alzheimer's disease (AD), a progressive neurodegenerative disease which seriously endangers the health of the aged, is the most common etiology of senile dementia. With the increasing progress of neuroimaging technology, more and more imaging methods have been applied to study Alzheimer's disease. The emergence of integrated PET/MRI (Positron Emission Tomography/Magnetic Resonance Imaging) is a major advance in multimodal molecular imaging with many advantages on the structure of resolution and contrast of image over computed tomography (CT), PET and MRI. PET/MRI is now used stepwise in neurodegenerative diseases, and also has broad prospect of application in the early diagnosis of AD. In this review, we emphatically introduce the imaging advances of AD including functional imaging and molecular imaging, the advantages of PET/MRI over other imaging methods and prospects of PET/MRI in AD clinical diagnosis, especially in early diagnosis, clinical assessment and prediction on AD.

RF shielding materials for highly-integrated PET/MRI systems.

Integration of magnetic resonance imaging (MRI) and positron emission tomography (PET) into a simultaneous device calls for adaptations of the radio frequency (RF) shielding concept. Conventional PET module housings fully encase the entire PET detector to reduce mutual interference. Excluding passive components, i.e. scintillators, from the housings, offers integration advantages, e.g. by reducing the overall housing volume or utilizing bigger scintillators. However, locating the scintillator outside of the RF shielding requires an optically transparent RF shielding interface between the scintillators and the photodetector to close the aperture. Therefore, a careful evaluation and selection of RF materials is essential to ensure an excellent PET/MRI system performance. To this end, we examined 10 materials (coated glasses, coated foils, meshes). The shielding effectiveness (SE) was evaluated at 100 and 300 MHz. PET performance was tested for single event registration and coincident events by integrating the material into the PET detector stack between the digital silicon photomultiplier photodetector array and one-to-one coupled scintillator. We determined photon attenuation (PA), energy resolution (dE/E), and coincidence resolving time (CRT) and compared to reference measurements for each material group. MRI compatibility was assessed by analyzing the material influence on the main magnetic field (B0) homogeneity. The coated glasses and foils exhibited SEs of up to 25 dB at 300 MHz. Both had a PA < 23% with dE/E and CRT comparable to the reference measurements, and no measurable impact on the B0field was registered. The meshes exhibited higher SEs up to 56 dB, but also a PA > 58% with a higher impact on dE/E and CRT. Only one mesh affected B0homogeneity. Overall, we recommend the coated foil HS 9400 for integration concepts as it exhibited a good performance with SE = 25 dB, PA = 22%, resulting in a PET performance of dE/E = 12% and CRT = 274 ps.

Fully Integrated PET/MR Imaging for the Assessment of the Relationship Between Functional Connectivity and Glucose Metabolic Rate.

In the past, determination of absolute values of cerebral metabolic rate of glucose (CMRGlc) in clinical routine was rarely carried out due to the invasive nature of arterial sampling. With the advent of combined PET/MR imaging technology, CMRGlc values can be obtained non-invasively, thereby providing the opportunity to take advantage of fully quantitative data in clinical routine. However, CMRGlc values display high physiological variability, presumably due to fluctuations in the intrinsic activity of the brain at rest. To reduce CMRGlc variability associated with these fluctuations, the objective of this study was to determine whether functional connectivity measures derived from resting-state fMRI (rs-fMRI) could be used to correct for these fluctuations in intrinsic brain activity. METHODS: We studied 10 healthy volunteers who underwent a test-retest dynamic [18F]FDG-PET study using a fully integrated PET/MR system (Siemens Biograph mMR). To validate the non-invasive derivation of an image-derived input function based on combined analysis of PET and MR data, arterial blood samples were obtained. Using the arterial input function (AIF), parametric images representing CMRGlc were determined using the Patlak graphical approach. Both directed functional connectivity (dFC) and undirected functional connectivity (uFC) were determined between nodes in six major networks (Default mode network, Salience, L/R Executive, Attention, and Sensory-motor network) using either a bivariate-correlation (R coefficient) or a Multi-Variate AutoRegressive (MVAR) model. In addition, the performance of a regional connectivity measure, the fractional amplitude of low frequency fluctuations (fALFF), was also investigated. RESULTS: The average intrasubject variability for CMRGlc values between test and retest was determined as (14 ±8%) with an average inter-subject variability of 25% at test and 15% at retest. The average CMRGlc value (umol/100 g/min) across all networks was 39 ±10 at test and increased slightly to 43 ±6 at retest. The R, MVAR and fALFF coefficients showed relatively large test-retest variability in comparison to the inter-subjects variability, resulting in poor reliability (intraclass correlation in the range of 0.11-0.65). More importantly, no significant relationship was found between the R coefficients (for uFC), MVAR coefficients (for dFC) or fALFF and corresponding CMRGlc values for any of the six major networks. DISCUSSION: Measurement of functional connectivity within established brain networks did not provide a means to decrease the inter- or intrasubject variability of CMRGlc values. As such, our results indicate that connectivity measured derived from rs-fMRI acquired contemporaneously with PET imaging are not suited for correction of CMRGlc variability associated with intrinsic fluctuations of resting-state brain activity. Thus, given the observed substantial inter- and intrasubject variability of CMRGlc values, the relevance of absolute quantification for clinical routine is presently uncertain.

Comparison of integrated PET/MRI with PET/CT in evaluation of endometrial cancer: a retrospective analysis of 81 cases.

BACKGROUND: The objective of this study was to compare the diagnostic value of integrated PET/MRI with PET/CT for assessment of regional lymph node metastasis and deep myometrial invasion detection of endometrial cancer. METHODS: Eighty-one patients with biopsy-proven endometrial cancer underwent preoperative PET/CT (n = 37) and integrated PET/MRI (n = 44) for initial staging. The diagnostic performance of PET/CT and integrated PET/MRI for assessing the extent of the primary tumor and metastasis to the regional lymph nodes was evaluated by two experienced readers. Histopathological and follow-up imaging results were used as the gold standard. McNemar's test was employed for statistical analysis. RESULTS: Integrated PET/MRI and PET/CT both detected 100% of the primary tumors. Integrated PET/MRI proved significantly more sensitivity and specificity than PET/CT in regional lymph node metastasis detection (P = 0.015 and P < 0.001, respectively). The overall accuracy of myometrial invasion detection for PET/CT and Integrated PET/MRI was 45.9% and 81.8%, respectively. Integrated PET/MRI proved significantly more accurate than PET/CT (P < 0.001). CONCLUSION: Integrated PET/MRI, which complements the individual advantages of MRI and PET, is a valuable technique for the assessment of the lymph node metastasis and myometrial invasion in patients with endometrial cancer.

Towards quantitative [18F]FDG-PET/MRI of the brain: Automated MR-driven calculation of an image-derived input function for the non-invasive determination of cerebral glucose metabolic rates.

Absolute quantification of PET brain imaging requires the measurement of an arterial input function (AIF), typically obtained invasively via an arterial cannulation. We present an approach to automatically calculate an image-derived input function (IDIF) and cerebral metabolic rates of glucose (CMRGlc) from the [18F]FDG PET data using an integrated PET/MRI system. Ten healthy controls underwent test-retest dynamic [18F]FDG-PET/MRI examinations. The imaging protocol consisted of a 60-min PET list-mode acquisition together with a time-of-flight MR angiography scan for segmenting the carotid arteries and intermittent MR navigators to monitor subject movement. AIFs were collected as the reference standard. Attenuation correction was performed using a separate low-dose CT scan. Assessment of the percentage difference between area-under-the-curve of IDIF and AIF yielded values within ±5%. Similar test-retest variability was seen between AIFs (9 ± 8) % and the IDIFs (9 ± 7) %. Absolute percentage difference between CMRGlc values obtained from AIF and IDIF across all examinations and selected brain regions was 3.2% (interquartile range: (2.4-4.3) %, maximum < 10%). High test-retest intravariability was observed between CMRGlc values obtained from AIF (14%) and IDIF (17%). The proposed approach provides an IDIF, which can be effectively used in lieu of AIF.

Prognostic value of simultaneous 18F-FDG PET/MRI using a combination of metabolo-volumetric parameters and apparent diffusion coefficient in treated head and neck cancer.

BACKGROUND: The aim of this study was to determine the usefulness of combined positron emission tomography (PET)/magnetic resonance imaging (MRI) parameters provided by simultaneous 18F-fluorodeoxyglucose (FDG) PET/MRI for the prediction of treatment failure in surgically resected head and neck cancer. We hypothesized that PET parameters corrected by tumor cellularity (combined PET/MRI parameters) could predict the prognosis. On regional PET, maximum standardized uptake value (SUVmax) was measured as metabolic parameters. In addition, metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were checked as metabolo-volumetric parameters. Mean apparent diffusion coefficient (ADCmean) of tumor was evaluated as the MRI parameter on the ADC map. Ratios between metabolic/metabolo-volumetric parameters and ADC were calculated as combined PET/MRI parameters. PET, MRI, and combined PET/MRI parameters were compared with clinicopathologic parameters in terms of treatment failure. RESULTS: Seventy-two patients (mean age = 55.9 ± 14.6 year, M: F = 45: 27) who underwent simultaneous 18F-FDG PET/MRI before head and neck cancer surgery were retrospectively enrolled. Twenty-two patients (30.6%) showed tumor treatment failure after head and neck cancer surgery (mean treatment failure = 13.0 ± 7.0 months). In the univariate analysis, MTV (P = 0.044) and ratios between metabolo-volumetric parameters and ADC (MTV/ADCmean, P = 0.022; TLG/ADCmean, P = 0.044) demonstrated significance among 18F-FDG PET/MRI parameters. Lymphatic invasion (P = 0.044) and perineural invasion (P = 0.046) revealed significance among clinicopathologic parameters. In the multivariate analysis, MTV (P = 0.026), MTV/ADCmean (P = 0.011), and TLG/ADCmean (P = 0.002) with lymphatic invasion (P = 0.026, 0.026, and 0.044, respectively) showed significance. CONCLUSIONS: Combined PET/MRI parameters (PET metabolo-volumetric parameters corrected by tumor cellularity) could be effective predictors of tumor treatment failure after head and neck cancer surgery in addition to MTV and clinicopathologic parameter.

Integrated (18)F-fluorodeoxyglucose positron emission tomography magnetic resonance imaging ((18)F-FDG PET/MRI), a multimodality approach for comprehensive evaluation of dementia patients: A pictorial essay.

Dementia, caused by irreversible neurodegenerative disorders such as Alzheimer's disease or reversible non-degenerative conditions, is rapidly becoming one of the most alarming health problems in our aging society. This cognitive disorder associated with a multitude of clinical differentials with overlapping clinical, pathological, and imaging features is difficult to diagnose and treat, as it often presents late after significant neuronal damage has already occurred. Novel disease-modifying treatments being developed will have to be corroborated with innovative imaging biomarkers so that earlier reliable diagnosis can be made and treatment initiated upon. Along with new specific PET radiotracers, integrated PET/MRI with combined methodological advantage and simultaneously acquired structural-cum-functional information may help achieve this goal. The present pictorial essay details our experiences with PET/MRI in dementing disorders, along with reviewing recent advances and future scope.

An SPM8-based approach for attenuation correction combining segmentation and nonrigid template formation: application to simultaneous PET/MR brain imaging.

UNLABELLED: We present an approach for head MR-based attenuation correction (AC) based on the Statistical Parametric Mapping 8 (SPM8) software, which combines segmentation- and atlas-based features to provide a robust technique to generate attenuation maps (µ maps) from MR data in integrated PET/MR scanners. METHODS: Coregistered anatomic MR and CT images of 15 glioblastoma subjects were used to generate the templates. The MR images from these subjects were first segmented into 6 tissue classes (gray matter, white matter, cerebrospinal fluid, bone, soft tissue, and air), which were then nonrigidly coregistered using a diffeomorphic approach. A similar procedure was used to coregister the anatomic MR data for a new subject to the template. Finally, the CT-like images obtained by applying the inverse transformations were converted to linear attenuation coefficients to be used for AC of PET data. The method was validated on 16 new subjects with brain tumors (n = 12) or mild cognitive impairment (n = 4) who underwent CT and PET/MR scans. The µ maps and corresponding reconstructed PET images were compared with those obtained using the gold standard CT-based approach and the Dixon-based method available on the Biograph mMR scanner. Relative change (RC) images were generated in each case, and voxel- and region-of-interest-based analyses were performed. RESULTS: The leave-one-out cross-validation analysis of the data from the 15 atlas-generation subjects showed small errors in brain linear attenuation coefficients (RC, 1.38% ± 4.52%) compared with the gold standard. Similar results (RC, 1.86% ± 4.06%) were obtained from the analysis of the atlas-validation datasets. The voxel- and region-of-interest-based analysis of the corresponding reconstructed PET images revealed quantification errors of 3.87% ± 5.0% and 2.74% ± 2.28%, respectively. The Dixon-based method performed substantially worse (the mean RC values were 13.0% ± 10.25% and 9.38% ± 4.97%, respectively). Areas closer to the skull showed the largest improvement. CONCLUSION: We have presented an SPM8-based approach for deriving the head µ map from MR data to be used for PET AC in integrated PET/MR scanners. Its implementation is straightforward and requires only the morphologic data acquired with a single MR sequence. The method is accurate and robust, combining the strengths of both segmentation- and atlas-based approaches while minimizing their drawbacks.

Usefulness of Integrated PET/MRI in Head and Neck Cancer: A Preliminary Study.

PURPOSE: The new modality of an integrated positron emission tomography/magnetic resonance imaging (PET/MRI) has recently been introduced but not validated. Our objective was to evaluate clinical performance of (18)F-fluoro-2-deoxyglucose ((18)F-FDG) PET/MRI in patients with head and neck cancer. METHODS: This retrospective study was conducted between January 2013 and February 2013. Ten patients (eight men, two women; mean age, 61.4 ± 13.4 years) with histologically proven head and neck tumors were enrolled. Whole-body PET/MRI and regional positron emission tomography (PET) with dedicated MRI were sequentially obtained. Maximum standardized uptake value (SUVmax), SUVmean, metabolic tumor volume, total lesion glycolysis and contrast enhancement were analyzed. A total of ten whole-body positron emission tomography (PET), ten regional positron emission tomography (PET), ten dedicated MRI and ten regional PET/gadolinium-enhanced T1-weighted (Gd)-MRI images were analyzed for initial staging. Two nuclear medicine physicians analyzed positron emission tomography (PET) and PET/MRI with a consensus. One radiologist analyzed dedicated MRI. The primary lesions and number of metastatic lymph nodes analyzed from each image were compared. RESULTS: Eight patients were diagnosed with head and neck cancer (one tongue cancer, four tonsillar cancers, one nasopharyngeal cancer and two hypopharyngeal cancers) by histological diagnosis. Two benign tumors (pleomorphic adenoma and Warthin tumor) were diagnosed with surgical operation. Whole-body positron emission tomography (PET) and regional positron emission tomography (PET) attenuated by MRI showed good image quality for the lesion detection. Whole-body positron emission tomography (PET) and regional positron emission tomography (PET) detected ten primary sites and compensated for a missed lesion on dedicated MRI. A discordant number of suspicious lymph node metastases was noted according to the different images; 22, 16, 39 and 40 in the whole-body positron emission tomography (PET) only, dedicated MR, regional positron emission tomography (PET) only and regional PET/Gd-MRI, respectively. There was no distant metastasis based on analysis of whole-body positron emission tomography (PET) and whole-body PET/Dixon-volume interpolated breathhold examination (VIBE) MRI. Regional PET/Gd-MRI combined with whole-body PET/MRI modified staging in three patients. Lesions of primary tumor and suspicious metastasis were well detected on both value of SUVmax and visual analysis. The regional PET/Gd-MRI combined with whole-body PET/MRI showed convenient clinical staging performance compared with positron emission tomography (PET) and MRI alone. CONCLUSION: In this preliminary study, PET attenuated by MRI showed good image quality to detect lesions. And whole-body PET/MRI as a single modality was feasible for staging in a clinical setting. Whole-body positron emission tomography (PET), regional positron emission tomography (PET), dedicated MRI and regional PET/Gd-MRI showed discordant results in lesion detection. These discordant results might be synergistic effect for accurate staging.