5569 Background: For patients with ovarian cancer undergoing neoadjuvant chemotherapy, the effectiveness of treatment is not evaluable by conventional methods until all or much of the treatment has been given. The purpose of this study is to investigate the performance of FDG PET, dynamic contrast-enhanced (DCE) and intra-voxel incoherent motion (IVIM) MR as early predictors of treatment response. Methods: Subjects with a new diagnosis of epithelial ovarian cancer underwent 3 cycles of standardized chemotherapy followed by cytoreduction. FDG PET/MR including DCE and IVIM was performed at baseline (T0), after cycle 1 (T1) and after cycle 3 (T2) of chemotherapy. Final responses were categorized at T2 by RECIST 1.1. Image volumes at T1 were analyzed as predictors of final response. Parametric images of molecular diffusion restriction (D), tissue perfusion (D*), vascular volume fraction (F), blood- > interstitium constant of transfer (Ktrans), interstitum- > plasma constant of transfer (Kep), extravascular/extracellular volume % (Ve) and plasma volume % (Ve) were investigated along with routine measures of SUV and ADC. Results: Nine subjects were enrolled, 8 were responders by RECIST at T2 and one had stable disease. At T0 the mean, min, and max SUVmax of dominant tumor deposits was 11.5, 6.3, 19.0, respectively. Mean, min, and max values were 1.0, 0.75 and 1.63 for ADCmean and 0.62, 0.30, 0.96 for ADCmin. At T1, ADCmean increased in 8 subjects by +0.22% (s.d. +/- 13%) and decreased by -3% in one subject. ADCmin increased in 8 subjects by +21% (s.d. +/-11%) and decreased by -23% in one subject. D increased for 8 subjects (average +29% s.d. +/- 13%) and decreased by -10% in one. D*, F, Kep, Ktrans, Ve and Vp had no recognizable pattern. At T2, SUVmax, SUVmin, and ADCmean maintained their change direction across all subjects with measurable lesions. The only subject with a complete response at T2 had the highest ADCmin and ADCmean change at +45% after one cycle of chemotherapy (T1). The subject with stable disease at T2 had no significant difference in changes amongst all metrics. Conclusions: FDG PET/MR SUVmax and ADCmean values obtained after one cycle of neoadjuvant chemotherapy were consistently associated with partial anatomical treatment responses after three cycles. Molecular diffusion restriction also was reliably associated with treatment response. Future studies evaluating FDG PET/MR in platinum-resistant patients may allow for early discontinuation of ineffective and toxic treatment.

Fluorodeoxyglucose (FDG) positron emission tomography-magnetic resonance (PET/MR) is useful for the evaluation of cognitively-impaired patients. This study aims to assess two different attenuation correction (AC) methods (Dixon-MR and atlas-based) versus index-standard computed tomography (CT) AC for the visual interpretation of regional hypometabolism in patients with cognitive impairment. Two board-certified nuclear medicine physicians blindly scored brain region FDG hypometabolism as normal versus hypometabolic using two-dimensional (2D) and 3D FDG PET/MR images generated by MIM software. Regions were quantitatively assessed as normal versus mildly, moderately, or severely hypometabolic. Hypometabolism scores obtained using the different methods of AC were compared, and interreader, as well as intra-reader agreement, was assessed. Regional hypometabolism versus normal metabolism was correctly classified in 16 patients on atlas-based and Dixon-based AC map PET reconstructions (vs. CT reference AC) for 94% (90%-96% confidence interval [CI]) and 93% (89%-96% CI) of scored regions, respectively. The averaged sensitivity/specificity for detection of any regional hypometabolism was 95%/94% (P = 0.669) and 90%/91% (P = 0.937) for atlas-based and Dixon-based AC maps. Interreader agreement for detection of regional hypometabolism was high, with similar outcome assessments when using atlas- and Dixon-corrected PET data in 93% (Κ =0.82) and 93% (Κ =0.84) of regions, respectively. Intrareader agreement for detection of regional hypometabolism was high, with concordant outcome assessments when using atlas- and Dixon-corrected data in 93%/92% (Κ =0.79) and 92/93% (Κ =0.78). Despite the quantitative advantages of atlas-based AC in brain PET/MR, routine clinical Dixon AC yields comparable visual ratings of regional hypometabolism in the evaluation of cognitively impaired patients undergoing brain PET/MR and is similar in performance to CT-based AC. Therefore, Dixon AC is acceptable for the routine clinical evaluation of dementia syndromes.

Yttrium-90 (90Y) radioembolization involves the intra-arterial delivery of radioactive microspheres to treat hepatic malignancies. Though this therapy involves careful pre-treatment planning and imaging, little is known about the precise location of the microspheres once they are administered. Recently, there has been growing interest post-radioembolization imaging using positron-emission tomography (PET) for quantitative dosimetry and identifying lesions that may benefit from additional salvage therapy. In this study, we aim to measure the inter-center variability of 90Y PET measurements as measured on PET/MRI in preparation for a multi-institutional prospective phase I/II clinical trial.

Purpose The aim of this study was to conduct a prospective pilot study comparing the diagnostic performance of MRI alone and 18F-FDG simultaneous PET/MRI using a diuresis protocol in bladder cancer patients. Methods Twenty-two bladder cancer patients underwent 18F-FDG PET/MRI, using intravenous furosemide and oral hydration for bladder clearance. A radiologist scored probability of tumor in 3 locations (urinary bladder, pelvic lymph nodes, nonnodal pelvis) using 1- to 3-point scale (1 = negative, 2 = equivocal, 3 = definite tumor). A nuclear medicine physician reviewed fused PET/MRI images, after which scores were reassigned based on combined findings. Follow-up pathologic and imaging data served as reference. Performances of MRI alone and PET/MRI were compared. Results Of these patients, 82%, 38%, and 18% were positive for bladder, pelvic nodal, and nonnodal pelvic tumor, respectively. At a score of 3, PET/MRI exhibited greater accuracy for detection of bladder tumor (86% vs 77%), metastatic pelvic lymph nodes (95% vs 76%), and nonnodal pelvic malignancy (100% vs 91%). In the bladder, PET changed the level of suspicion in 36% of patients (50% increased suspicion, 50% decreased suspicion), with 75% of these changes deemed correct based on reference standard. For pelvic lymph nodes, PET changed suspicion in 52% (36% increase, 64% decrease), with 95% of changes deemed correct. For nonnodal pelvis, PET changed suspicion in 9% (100% increase), with 100% deemed correct. Conclusions Additional PET information helped to appropriately determine level of suspicion in multiple anatomic sites for otherwise equivocal findings on MRI alone. Although requiring larger studies, findings suggest a possible role for simultaneous PET/MRI to assist bladder cancer management.

2672 Objectives 1. Review the existing literature on radio-guided surgery using conventional nuclear medicine and PET radiopharmaceuticals, gamma cameras and PET/CT scanners. 2. Learn about a new technique using PET/MR in the pre-operative localization of lesions prior to radio-guided surgery. Background: Radiopharmaceuticals have been used in conjunction with gamma cameras and PET scanners to localize tumor deposits prior to radio-guided surgery using intra-operative probes, often assisted by portable cameras. One disadvantage of PET/CT scanners is that pre-operative lesion localization may require multiple CT acquisitions, thus increasing radiation exposure to the patient. This exhibit will briefly review conventional techniques to localize non-palpable tumor deposits before surgery using nuclear medicine techniques, and will demonstrate in detail a new method of FDG PET/MR-guided pre-operative lesion localization prior to radio-guided surgery. A major focus of this review will be on case examples of patients with non-palpable subcutaneous FDG-avid tumor deposits for which surgical resection is the gold standard for management. After confirming uptake on whole-body PET/CT, patients are referred to the PET/MR Department on the day of surgery. FDG is injected and lesions are imaged on a Siemens Biograph mMR PET/MR scanner using conventional static PET and STIR MR sequences. A vitamin E marker is used in conjunction with an FDG point source to mark the tumor location on the skin, and the best orientation for surgical dissection and patient positioning is reviewed. A PET probe is used intra-operatively to assist in identification of tumor deposits. Methods - Results - Conclusions: -

1977 Objectives PET/MR may be used in the evaluation of cognitively impaired patients. There are known quantitative differences between PET images obtained on PET/MR scanners when reconstructed with Dixon-MR, CT-based or atlas-based attenuation correction (AC) maps. This study seeks to assess the impact, if any, of these three-different AC methods on the blinded visual interpretation of regional hypometabolism in patients with cognitive impairment. Methods Forty-five minutes following injection of 10 mCi of FDG, 15 patients with cognitive impairment underwent brain PET/CT. PET/MR scanning with a 10 minute PET acquisition and Dixon MR imaging was subsequently performed on a Siemens Biograph mMR scanner under an IRB-approved protocol, at approximately two hours post-injection. A manufacturer-provided non-product offline reconstruction tool was used to reconstruct PET data obtained from PET/MR with AC based on the patient’s own CT images, a Dixon-MR derived AC map and an atlas-based AC map that combined Dixon-MR with a segmentation of bony skull structures. Two nuclear medicine physicians blindly scored brain regions (frontal, temporal, parietal, occipital, precuneus) as normal versus hypometabolic using 2D and 3D images generated by MIM software. Abnormal regions were scored as mild, moderate, or severely hypometabolic (score of 0, 1, 2 or 3 respectively). The hypometabolism scores obtained using the different methods of AC were compared and reader agreement assessed. All statistical tests were conducted at the two-sided 5% significance level using SAS 9.3 (SAS Institute, Cary, NC). Results Regional hypometabolism versus normal metabolism was correctly classified (accuracy) for 150 regions in 15 patients by two readers on atlas- and Dixon-based AC map PET reconstructions (versus CT reference AC) for 94% (90 - 96% c.i.) and 93% (89 - 96% c.i.) of all regions. The averaged sensitivity/specificity for detection of any regional hypometabolism was 95%/94% and 90%/91% for atlas-based and Dixon-based AC maps, respectively, compared to the reference standard CT images. The mean absolute error of regional hypometabolism scores for atlas- and Dixon-based PET reconstructions (versus CT) was 0.25 +/- 0.44 and 0.21 +/- 0.42 . There were no statistically significant differences between the visual assessments. Intra-reader agreement for detection of regional hypometabolism was high, with similar outcome assessments when using atlas- and Dixon-corrected PET data in 93% and 93% of scored regions, respectively. The simple kappa coefficient to assess reader agreement in terms of hypometabolism versus normal regions was 0.82 for atlas- and 0.84 for Dixon-based AC. The weighted kappa coefficient to assess reader agreement in terms of the hypometabolism score was 0.75 for atlas- and 0.77 for Dixon-AC. Conclusions Despite the more accurate FDG SUV quantification with CT-based and atlas-based attenuation correction in brain PET/MR compared to Dixon AC, there were no measureable differences between the three AC methods with respect to visual identification of regional hypometabolism in the evaluation of cognitively impaired patients.

PurposeDiffusion‐weighted imaging (DWI) and 18F‐fluorodeoxyglucose–positron emission tomography (18F‐FDG–PET) independently correlate with malignancy in breast cancer, but the relationship between their structural and metabolic metrics is not completely understood. This study spatially correlates diffusion, perfusion, and glucose avidity in breast cancer with simultaneous PET/MR imaging and compares correlations with clinical prognostics.MethodsIn this Health Insurance Portability and Accountability Act‐compliant prospective study, with written informed consent and approval of the institutional review board and using simultaneously acquired FDG‐PET and DWI, tissue diffusion (Dt), and perfusion fraction (fp) from intravoxel incoherent motion (IVIM) analysis were registered to FDG‐PET within 14 locally advanced breast cancers. Lesions were analyzed using 2D histograms and correlation coefficients between Dt, fp, and standardized uptake value (SUV). Correlations were compared with prognostics from biopsy, metastatic burden from whole‐body PET, and treatment history.ResultsSUV||Dt correlation coefficient significantly distinguished treated (0.11 ± 0.24) from nontreated (−0.33 ± 0.26) patients (P = 0.005). SUV||fp correlations were on average negative for the whole cohort (−0.17 ± 0.13).ConclusionSimultaneously acquired and registered FDG‐PET/DWI allowed quantifiable descriptions of breast cancer microenvironments that may provide a framework for monitoring and predicting response to treatment. Magn Reson Med 78:1147–1156, 2017. © 2016 International Society for Magnetic Resonance in Medicine

1818 Objectives An area of PET research is repeatability. When evaluating small changes in PET uptake consistency in reconstruction is imperative. Part of this is consistency in the attenuation map (umap). In PET-MRI the reconstruction uses an MRI-based umap. The goal is to test the repeatability of the MR-based umap. Methods Seven separate 19 sec dixon brain umap acquisitions were obtained on the Siemens Biograph mMR. The first 3 acquisitions included no change in patient position or scanner bed movement. For scans 4 and 5 the scanner bed was moved to the home position and re-centered with no change in patient position. In scans 6 and 7, the patient comes off the scanner bed for a total change in patient position. Each of the number 2 - 6 images were compared to image 1. The total change in sinus volume was evaluated. Subtraction images were generated after the umaps were aligned. Results Supplemental images indicate there is greater difference in attenuation maps with increasing change in patient position. Scans 1 - 3 with no change in bed or patient position had no reported visual change in the umap. There is change in sinus volume seen after the bed is moved with no patient motion seen in scans 4 and 5. The results of each scan after the sinus volume threshold are reported by voxel size (mm3) and volume size (mm3), respectively. Scan 1 has a voxel size of 194 mm3 and volume size of 4104.8 mm3. Scan 2 has 141 mm3 and 2983.4 mm3 while Scan 3 has 191 mm3 and 4041 mm3 which is similar to the first scan. This may have been due to motion by the patient to be proven with further analysis. Scan 4 has no sinus cavity and scan 5 has a peculiar air cavity with 88 mm3 and 1861.97 mm3. Scan 6 and 7 have the same reading of 181 mm3 and 3829.75 mm3 but have different ROIs. Conclusions Conclusion: There is greater change in images 1 and 7 where there was total change in patient position. However, with no patient or bed movement, there was none or no significant change. There is proven repeatability in the acquisitions as shown in the above results.

Purpose The aim of this study was to compare coregistration of the bladder wall, bladder masses, and pelvic lymph nodes between sequential and simultaneous PET and MRI acquisitions obtained during hybrid 18F-FDG PET/MRI performed using a diuresis protocol in bladder cancer patients. Methods Six bladder cancer patients underwent 18F-FDG hybrid PET/MRI, including IV Lasix administration and oral hydration, before imaging to achieve bladder clearance. Axial T2-weighted imaging (T2WI) was obtained approximately 40 minutes before PET (“sequential”) and concurrently with PET (“simultaneous”). Three-dimensional spatial coordinates of the bladder wall, bladder masses, and pelvic lymph nodes were recorded for PET and T2WI. Distances between these locations on PET and T2WI sequences were computed and used to compare in-plane (x-y plane) and through-plane (z-axis) misregistration relative to PET between T2WI acquisitions. Results The bladder increased in volume between T2WI acquisitions (sequential, 176 [139] mL; simultaneous, 255 [146] mL). Four patients exhibited a bladder mass, all with increased activity (SUV, 9.5-38.4). Seven pelvic lymph nodes in 4 patients showed increased activity (SUV, 2.2-9.9). The bladder wall exhibited substantially less misregistration relative to PET for simultaneous, compared with sequential, acquisitions in in-plane (2.8 [3.1] mm vs 7.4 [9.1] mm) and through-plane (1.7 [2.2] mm vs 5.7 [9.6] mm) dimensions. Bladder masses exhibited slightly decreased misregistration for simultaneous, compared with sequential, acquisitions in in-plane (2.2 [1.4] mm vs 2.6 [1.9] mm) and through-plane (0.0 [0.0] mm vs 0.3 [0.8] mm) dimensions. FDG-avid lymph nodes exhibited slightly decreased in-plane misregistration (1.1 [0.8] mm vs 2.5 [0.6] mm), although identical through-plane misregistration (4.0 [1.9] mm vs 4.0 [2.8] mm). Conclusions Using hybrid PET/MRI, simultaneous imaging substantially improved bladder wall coregistration and slightly improved coregistration of bladder masses and pelvic lymph nodes.

Dixon-based MR is acquired for attenuation correction of brain PET during PET/MR. Early adopters of PET/MR have noted variability in the performance of Dixon-based tissue segmentation, and questions exist regarding potential impacts on quantitative accuracy in dual-time-point studies. Ten patients injected with 10 mCi FDG underwent dual-time-point clinical brain PET/MR on a Siemens mMR, with image reconstructions based on data acquired at 45 – 60 and 75 – 90 minutes. Dixon μmaps were obtained the time of FDG injection and at 75 minutes. 8 cc of Gadavist was injected for post-contrast MR at 30 minutes. Subjects were removed from the table and re-positioned prior to the 75 minute scan. The delayed μmap was registered to the original μmap using MIMneuro. The aligned image data was copied onto the original μmap DICOM file using Matlab. Early time-point PET data was reconstructed using both the early and delayed μmaps. Atlas-based segmentation was performed to compare regional SUV values. When comparing the delayed versus original μmap reconstructions, regional SUV values varied on average by +1.9% for both SUVmax and SUVmean. For large brain structures, SUVmax and SUVmean varied by -0.5% to +5.6% and -0.2 to +4.7%, respectively. For deep brain structures, SUVmax using the delayed reconstruction varied by -0.5% to +3.7% and SUVmean varied by -0.3% to +3.6%. Most differences in SUV were higher when using the delayed μmap. There is variability in regional SUV values for brain PET data reconstructed using two different aligned Dixon acquisitions performed on subjects undergoing repeat same-day PET/MR imaging, with SUV values ~2% higher using the delayed μmap. This variability may impact results in dual-time-point brain PET/MR.

Purpose: Radiomics involves the extraction of texture features from different imaging modalities with the purpose of developing models to predict patient treatment outcomes. The purpose of this study is to investigate texture feature reproducibility across [18F]FDG PET/CT and [18F]FDG PET/MR imaging in patients with primary malignancies. Methods: Twenty five prospective patients with solid tumors underwent clinical [18F]FDG PET/CT scan followed by [18F]FDG PET/MR scans. In all patients the lesions were identified using nuclear medicine reports. The images were co-registered and segmented using an in-house auto-segmentation method. Fifty features, based on the intensity histogram, second and high order matrices, were extracted from the segmented regions from both image data sets. One-way random-effects ANOVA model of the intra-class correlation coefficient (ICC) was used to establish texture feature correlations between both data sets. Results: Fifty features were classified based on their ICC values, which were found in the range from 0.1 to 0.86, in three categories: high, intermediate, and low. Ten features extracted from second and high-order matrices showed large ICC ≥ 0.70. Seventeen features presented intermediate 0.5 ≤ ICC ≤ 0.65 and the remaining twenty three presented low ICC ≤ 0.45. Conclusion: Features with large ICC values could be reliable candidates for quantification as they lead to similar results from both imaging modalities. Features with small ICC indicates a lack of correlation. Therefore, the use of these features as a quantitative measure will lead to different assessments of the same lesion depending on the imaging modality from where they are extracted. This study shows the importance of the need for further investigation and standardization of features across multiple imaging modalities.

OBJECTIVE:The purpose of this study was to assess the correlation between standardized uptake value (SUV) and apparent diffusion coefficient (ADC) of neoplastic lesions in the use of a simultaneous PET/MRI hybrid system. SUBJECTS AND METHODS:Twenty-four patients with known primary malignancies underwent FDG PET/CT. They then underwent whole-body PET/MRI. Diffusion-weighted imaging was performed with free breathing and a single-shot spin-echo echo-planar imaging sequence with b values of 0, 350, and 750 s/mm(2). Regions of interest were manually drawn along the contours of neoplastic lesions larger than 1 cm, which were clearly identified on PET and diffusion-weighted images. Maximum SUV (SUVmax) on PET/MRI and PET/CT images, mean SUV (SUVmean), minimum ADC (ADCmin), and mean ADC (ADCmean) were recorded on PET/MR images for each FDG-avid neoplastic soft-tissue lesion with a maximum of three lesions per patient. Pearson correlation coefficient was used to asses the following relations: SUVmax versus ADCmin on PET/MR and PET/CT images, SUVmean versus ADCmean, and ratio of SUVmax to mean liver SUV (SUV ratio) versus ADCmin. A subanalysis of patients with progressive disease versus partial treatment response was performed with the ratio of SUVmax to ADCmin for the most metabolically active lesion. RESULTS:Sixty-nine neoplastic lesions (52 nonosseous lesions, 17 bone metastatic lesions) were evaluated. The mean SUVmax from PET/MRI was 7.0 ± 6.0; SUVmean, 5.6 ± 4.6; mean ADCmin, 1.10 ± 0.58; and mean ADCmean, 1.48 ± 0.72. A significant inverse Pearson correlation coefficient was found between PET/MRI SUVmax and ADCmin (r = -0.21, p = 0.04), between SUVmean and ADCmean (r = -0.18, p = 0.07), and between SUV ratio and ADCmin (r = -0.27, p = 0.01). A similar inverse Pearson correlation coefficient was found between the PET/CT SUVmax and ADCmin. Twenty of 24 patients had previously undergone PET/CT; five patients had a partial treatment response, and six had progressive disease according to Response Evaluation Criteria in Solid Tumors 1.1. The ratio between SUVmax and ADCmin was higher among patients with progressive disease than those with a partial treatment response. CONCLUSION:Simultaneous PET/MRI is a promising technology for the detection of neoplastic disease. There are inverse correlations between SUVmax and ADCmin and between SUV ratio and ADCmin. Correlation coefficients between SUVmax and ADCmin from PET/MRI were similar to values obtained with SUVmax from the same-day PET/CT. Given that both SUV and ADC are related to malignancy and that the correlation between the two biomarkers is relatively weak, SUV and ADC values may offer complementary information to aid in determination of prognosis and treatment response. The combined tumoral biomarker, ratio between SUVmax and ADCmin, may be useful for assessing progressive disease versus partial treatment response.

and j (Figure 1A). Cross-validation was performed by using different subsets of the NC group to fit and test the GLM. Results: We demonstrate the approach using the Alzheimer’s Disease Assessment Scale (ADAScog). GLMNET predicted w40% of the variance using residuals from w150 ROI pairs (Figure 1B). As shown in Figure 1C, the strongest coefficients were found for ROI pairs including entorhinal cortex (EC), middle temporal gyrus (MTG), superior parietal gyrus (SPG), precuneus (PCUN), postcentral lobule (PCL), and superior frontal gyrus (SFG). Conclusions: The GLMNETapproach provides a novel and robust way to associate an entire network based upon cortical thickness correlations with cognitive scores. For the ADAS-cog example, a majority of coefficients were positive (red), indicating that an abnormal relationship predicts a higher level of dementia; while some coefficients were negative (blue), which may suggest compensatory changes. Model coefficients can also be used to identify which network edges make the strongest contribution to the model’s prediction. This method is applicable both as a means of linking anatomical MRI to cognitive and clinical status in individual subjects, and as a method for associating specific components of cortical networks with the performance of cognitive tasks.

Histogram analysis of intravoxel incoherent motion (IVIM)-MRI and FDG-PET parameters in breast cancer patients Eric Edward Sigmund, Linda Moy, Jin Ah Kim, Sungheon Kim, Akshat Pujara, Alana Amarosa, Komal Jhaveri, James Babb, Christian Geppert, Christopher Glielmi, Gene Young Cho, Thorsten Feiweier, Kimberly Jackson, and Amy Melsaether Radiology, NYU Langone Medical Center, New York, NY, United States, Oncology, NYU Langone Medical Center, New York, NY, United States, Siemens Medical Solutions, New York, NY, United States, Healthcare Sector, Siemens AG, Erlangen, Germany

A recently introduced integrated scanner combining simultaneous PET and MR (PET-MR/mMR) acquisition (Biograph mMR, Siemens, AG) presents a unique set of opportunities for neuroimaging research and dementia in particular. Among these, the intrinsic co-registration of the images has the potential to reduce errors in multi-modality image registration, which could lead to better quantification of longitudinal volumetric changes in neuroanatomical features that are important for assessing disease progression. In this study we demonstrate the improvements in neuroanatomical quantification that derive from the simultaneous nature of the image acquisition. Fourteen brain studies including 3 frontotemporal dementia (FTD), 10 possible AD, and 1 other type of dementia were performed on a FDA-approved 3T mMR whole body system. All scans started after injection of 15 mCi of FDG tracer followed by a PET/CT scan (45 minutes post-injection). After completion of the PET/CT scan, simultaneous MR/PET acquisition was performed with advanced MRI sequences for quantifying functional/structural connectivity and blood flow. Voxel-wise whole brain analysis showed highly consistent FDG uptake patterns of mMR (P<0.01) using two MRI-based attenuation correction (AC) methods (i.e. Dixon and UTE). The majority of brain voxels (>95%) showed significant correlations (r>0.54, P<0.05) between mMR (Dixon AC method) and PET/CT ratio of standard uptake (rSUV) values with cerebellum as the reference region (Figure 1A). Additionally, the regional rSUV values from mMR and PET/CT were tightly coupled, e.g. the middle temporal gyrus (MTG) (r=0.97, slope =1.02, P<0.001) shown in Figure1B. The dispersion of rSUV among subjects (coefficient of variation =0.15) was similar for both scans in the temporal region, and might reflect the heterogeneity of subject age and disease severity. Compared to FTD patients, AD patients showed significantly reduced left MTG volume (P=0.02) as well as severer global brain volume loss (P=0.03), and a trend towards decreased hippocampal neuronal activity (P=0.07).