Loss of TREM2 rescues hyperactivation of microglia, but not lysosomal deficits and neurotoxicity in models of progranulin deficiency.

Haploinsufficiency of the progranulin (PGRN)-encoding gene (GRN) causes frontotemporal lobar degeneration (GRN-FTLD) and results in microglial hyperactivation, TREM2 activation, lysosomal dysfunction, and TDP-43 deposition. To understand the contribution of microglial hyperactivation to pathology, we used genetic and pharmacological approaches to suppress TREM2-dependent transition of microglia from a homeostatic to a disease-associated state. Trem2 deficiency in Grn KO mice reduced microglia hyperactivation. To explore antibody-mediated pharmacological modulation of TREM2-dependent microglial states, we identified antagonistic TREM2 antibodies. Treatment of macrophages from GRN-FTLD patients with these antibodies led to reduced TREM2 signaling due to its enhanced shedding. Furthermore, TREM2 antibody-treated PGRN-deficient microglia derived from human-induced pluripotent stem cells showed reduced microglial hyperactivation, TREM2 signaling, and phagocytic activity, but lysosomal dysfunction was not rescued. Similarly, lysosomal dysfunction, lipid dysregulation, and glucose hypometabolism of Grn KO mice were not rescued by TREM2 ablation. Synaptic loss and neurofilament light-chain (NfL) levels, a biomarker for neurodegeneration, were further elevated in the Grn/Trem2 KO cerebrospinal fluid (CSF). These findings suggest that TREM2-dependent microglia hyperactivation in models of GRN deficiency does not promote neurotoxicity, but rather neuroprotection.

Subcortical tau is linked to hypoperfusion in connected cortical regions in 4-repeat tauopathies.

Four-repeat (4R) tauopathies are neurodegenerative diseases characterized by cerebral accumulation of 4R tau pathology. The most prominent 4R tauopathies are progressive supranuclear palsy (PSP) and corticobasal degeneration characterized by subcortical tau accumulation and cortical neuronal dysfunction, as shown by PET-assessed hypoperfusion and glucose hypometabolism. Yet, there is a spatial mismatch between subcortical tau deposition patterns and cortical neuronal dysfunction, and it is unclear how these two pathological brain changes are interrelated. Here, we hypothesized that subcortical tau pathology induces remote neuronal dysfunction in functionally connected cortical regions to test a pathophysiological model that mechanistically links subcortical tau accumulation to cortical neuronal dysfunction in 4R tauopathies. We included 51 Aß-negative patients with clinically diagnosed PSP variants (n = 26) or corticobasal syndrome (n = 25) who underwent structural MRI and 18F-PI-2620 tau-PET. 18F-PI-2620 tau-PET was recorded using a dynamic one-stop-shop acquisition protocol to determine an early 0.5-2.5 min post tracer-injection perfusion window for assessing cortical neuronal dysfunction, as well as a 20-40 min post tracer-injection window to determine 4R-tau load. Perfusion-PET (i.e. early window) was assessed in 200 cortical regions, and tau-PET was assessed in 32 subcortical regions of established functional brain atlases. We determined tau epicentres as subcortical regions with the highest 18F-PI-2620 tau-PET signal and assessed the connectivity of tau epicentres to cortical regions of interest using a resting-state functional MRI-based functional connectivity template derived from 69 healthy elderly controls from the ADNI cohort. Using linear regression, we assessed whether: (i) higher subcortical tau-PET was associated with reduced cortical perfusion; and (ii) cortical perfusion reductions were observed preferentially in regions closely connected to subcortical tau epicentres. As hypothesized, higher subcortical tau-PET was associated with overall lower cortical perfusion, which remained consistent when controlling for cortical tau-PET. Using group-average and subject-level PET data, we found that the seed-based connectivity pattern of subcortical tau epicentres aligned with cortical perfusion patterns, where cortical regions that were more closely connected to the tau epicentre showed lower perfusion. Together, subcortical tau-accumulation is associated with remote perfusion reductions indicative of neuronal dysfunction in functionally connected cortical regions in 4R-tauopathies. This suggests that subcortical tau pathology may induce cortical dysfunction, which may contribute to clinical disease manifestation and clinical heterogeneity.

Astroglial glucose uptake determines brain FDG-PET alterations and metabolic connectivity during healthy aging in mice.

PURPOSE: 2-Fluorodeoxyglucose-PET (FDG-PET) is a powerful tool to study glucose metabolism in mammalian brains, but cellular sources of glucose uptake and metabolic connectivity during aging are not yet understood. METHODS: Healthy wild-type mice of both sexes (2-21 months of age) received FDG-PET and cell sorting after in vivo tracer injection (scRadiotracing). FDG uptake per cell was quantified in isolated microglia, astrocytes and neurons. Cerebral FDG uptake and metabolic connectivity were determined by PET. A subset of mice received measurement of blood glucose levels to study associations with cellular FDG uptake during aging. RESULTS: Cerebral FDG-PET signals in healthy mice increased linearly with age. Cellular FDG uptake of neurons increased between 2 and 12 months of age, followed by a strong decrease towards late ages. Contrarily, FDG uptake in microglia and astrocytes exhibited a U-shaped function with respect to age, comprising the predominant cellular source of higher cerebral FDG uptake in the later stages. Metabolic connectivity was closely associated with the ratio of glucose uptake in astroglial cells relative to neurons. Cellular FDG uptake was not associated with blood glucose levels and increasing FDG brain uptake as a function of age was still observed after adjusting for blood glucose levels. CONCLUSION: Trajectories of astroglial glucose uptake drive brain FDG-PET alterations and metabolic connectivity during aging.

Validity and value of metabolic connectivity in mouse models of ß-amyloid and tauopathy.

Among functional imaging methods, metabolic connectivity (MC) is increasingly used for investigation of regional network changes to examine the pathophysiology of neurodegenerative diseases such as Alzheimer's disease (AD) or movement disorders. Hitherto, MC was mostly used in clinical studies, but only a few studies demonstrated the usefulness of MC in the rodent brain. The goal of the current work was to analyze and validate metabolic regional network alterations in three different mouse models of neurodegenerative diseases (ß-amyloid and tau) by use of 2-deoxy-2-[18F]fluoro-d-glucose positron emission tomography (FDG-PET) imaging. We compared the results of FDG-µPET MC with conventional VOI-based analysis and behavioral assessment in the Morris water maze (MWM). The impact of awake versus anesthesia conditions on MC read-outs was studied and the robustness of MC data deriving from different scanners was tested. MC proved to be an accurate and robust indicator of functional connectivity loss when sample sizes ≥12 were considered. MC readouts were robust across scanners and in awake/ anesthesia conditions. MC loss was observed throughout all brain regions in tauopathy mice, whereas ß-amyloid indicated MC loss mainly in spatial learning areas and subcortical networks. This study established a methodological basis for the utilization of MC in different ß-amyloid and tau mouse models. MC has the potential to serve as a read-out of pathological changes within neuronal networks in these models.

Towards multicenter ß-amyloid PET imaging in mouse models: A triple scanner head-to-head comparison.

AIM: ß-amyloid (Aß) small animal PET facilitates quantification of fibrillar amyloidosis in Alzheimer's disease (AD) mouse models. Thus, the methodology is receiving growing interest as a monitoring tool in preclinical drug trials. In this regard, harmonization of data from different scanners at multiple sites would allow the establishment large collaborative cohorts and may facilitate efficacy comparison of different treatments. Therefore, we objected to determine the level of agreement of Aß-PET quantification by a head-to-head comparison of three different state-of-the-art small animal PET scanners, which could help pave the way for future multicenter studies. METHODS: Within a timeframe of 5 ± 2 weeks, transgenic APPPS1 (n = 9) and wild-type (WT) (n = 8) mice (age range: 13-16 months) were examined three times by Aß-PET ([18F]florbetaben) using a Siemens Inveon DPET, a MedisonanoScan PET/MR, and a MedisonanoScan PET/CT with harmonized reconstruction protocols. Cortex-to-white-matter 30-60 min p.i. standardized uptake value ratios (SUVRCTX/WM) were calculated to compare binding differences, effect sizes (Cohen's d) and z-score values of APPPS1 relative to WT mice. Correlation coefficients (Pearson's r) were calculated for the agreement of individual SUVR between different scanners. Voxel-wise analysis was used to determine the agreement of spatial pathology patterns. For validation of PET imaging against the histological gold standard, individual SUVR values were subject to a correlation analysis with area occupancy of methoxy­X04 staining. RESULTS: All three small animal PET scanners yielded comparable group differences between APPPS1 and WT mice (∆PET=20.4 % ± 2.9 %, ∆PET/MR=18.4 % ± 4.5 %, ∆PET/CT=18.1 % ± 3.3 %). Voxel-wise analysis confirmed a high degree of congruency of the spatial pattern (Dice coefficient (DC)PETvs.PET/MR=83.0 %, DCPETvs.PET/CT=69.3 %, DCPET/MRvs.PET/CT=81.9 %). Differences in the group level variance of the three scanners resulted in divergent z-scores (zPET=11.5 ± 1.6; zPET/MR=5.3 ± 1.3; zPET/CT=3.4 ± 0.6) and effect sizes (dPET=8.5, dPET/MR=4.5, dPET/CT=4.1). However, correlations at the individual mouse level were still strong between scanners (rPETvs.PET/MR=0.96, rPETvs.PET/CT=0.91, rPET/MRvs.PET/CT=0.87; all p ≤ 0.0001). Methoxy-X04 staining exhibited a significant correlation across all three PET machines combined (r = 0.76, p < 0.0001) but also at individual level (PET: r = 0.81, p = 0.026; PET/MR: r = 0.89, p = 0.0074; PET/CT: r = 0.93, p = 0.0028). CONCLUSIONS: Our comparison of standardized small animal Aß-PET acquired by three different scanners substantiates the possibility of moving towards a multicentric approach in preclinical AD research. The alignment of image acquisition and analysis methods achieved good overall comparability between data sets. Nevertheless, differences in variance of sensitivity and specificity of different scanners may limit data interpretation at the individual mouse level and deserves methodological optimization.

Characterization of tau propagation pattern and cascading hypometabolism from functional connectivity in Alzheimer's disease.

Tau pathology and its spatial propagation in Alzheimer's disease (AD) play crucial roles in the neurodegenerative cascade leading to dementia. However, the underlying mechanisms linking tau spreading to glucose metabolism remain elusive. To address this, we aimed to examine the association between pathologic tau aggregation, functional connectivity, and cascading glucose metabolism and further explore the underlying interplay mechanisms. In this prospective cohort study, we enrolled 79 participants with 18F-Florzolotau positron emission tomography (PET), 18F-fluorodeoxyglucose PET, resting-state functional, and anatomical magnetic resonance imaging (MRI) images in the hospital-based Shanghai Memory Study. We employed generalized linear regression and correlation analyses to assess the associations between Florzolotau accumulation, functional connectivity, and glucose metabolism in whole-brain and network-specific manners. Causal mediation analysis was used to evaluate whether functional connectivity mediates the association between pathologic tau and cascading glucose metabolism. We examined 22 normal controls and 57 patients with AD. In the AD group, functional connectivity was associated with Florzolotau covariance (ß = .837, r = 0.472, p < .001) and glucose covariance (ß = 1.01, r = 0.499, p < .001). Brain regions with higher tau accumulation tend to be connected to other regions with high tau accumulation through functional connectivity or metabolic connectivity. Mediation analyses further suggest that functional connectivity partially modulates the influence of tau accumulation on downstream glucose metabolism (mediation proportion: 49.9%). Pathologic tau may affect functionally connected neurons directly, triggering downstream glucose metabolism changes. This study sheds light on the intricate relationship between tau pathology, functional connectivity, and downstream glucose metabolism, providing critical insights into AD pathophysiology and potential therapeutic targets.

Associations between sex, body mass index and the individual microglial response in Alzheimer's disease.

BACKGROUND AND OBJECTIVES: 18-kDa translocator protein position-emission-tomography (TSPO-PET) imaging emerged for in vivo assessment of neuroinflammation in Alzheimer's disease (AD) research. Sex and obesity effects on TSPO-PET binding have been reported for cognitively normal humans (CN), but such effects have not yet been systematically evaluated in patients with AD. Thus, we aimed to investigate the impact of sex and obesity on the relationship between ß-amyloid-accumulation and microglial activation in AD. METHODS: 49 patients with AD (29 females, all Aß-positive) and 15 Aß-negative CN (8 female) underwent TSPO-PET ([18F]GE-180) and ß-amyloid-PET ([18F]flutemetamol) imaging. In 24 patients with AD (14 females), tau-PET ([18F]PI-2620) was additionally available. The brain was parcellated into 218 cortical regions and standardized-uptake-value-ratios (SUVr, cerebellar reference) were calculated. Per region and tracer, the regional increase of PET SUVr (z-score) was calculated for AD against CN. The regression derived linear effect of regional Aß-PET on TSPO-PET was used to determine the Aß-plaque-dependent microglial response (slope) and the Aß-plaque-independent microglial response (intercept) at the individual patient level. All read-outs were compared between sexes and tested for a moderation effect of sex on associations with body mass index (BMI). RESULTS: In AD, females showed higher mean cortical TSPO-PET z-scores (0.91 ± 0.49; males 0.30 ± 0.75; p = 0.002), while Aß-PET z-scores were similar. The Aß-plaque-independent microglial response was stronger in females with AD (+ 0.37 ± 0.38; males with AD - 0.33 ± 0.87; p = 0.006), pronounced at the prodromal stage. On the contrary, the Aß-plaque-dependent microglial response was not different between sexes. The Aß-plaque-independent microglial response was significantly associated with tau-PET in females (Braak-II regions: r = 0.757, p = 0.003), but not in males. BMI and the Aß-plaque-independent microglial response were significantly associated in females (r = 0.44, p = 0.018) but not in males (BMI*sex interaction: F(3,52) = 3.077, p = 0.005). CONCLUSION: While microglia response to fibrillar Aß is similar between sexes, women with AD show a stronger Aß-plaque-independent microglia response. This sex difference in Aß-independent microglial activation may be associated with tau accumulation. BMI is positively associated with the Aß-plaque-independent microglia response in females with AD but not in males, indicating that sex and obesity need to be considered when studying neuroinflammation in AD.

Added value of FDG-PET for detection of progressive supranuclear palsy.

BACKGROUND: Diagnostic criteria for progressive supranuclear palsy (PSP) include midbrain atrophy in MRI and hypometabolism in [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) as supportive features. Due to limited data regarding their relative and sequential value, there is no recommendation for an algorithm to combine both modalities to increase diagnostic accuracy. This study evaluated the added value of sequential imaging using state-of-the-art methods to analyse the images regarding PSP features. METHODS: The retrospective study included 41 PSP patients, 21 with Richardson's syndrome (PSP-RS), 20 with variant PSP phenotypes (vPSP) and 46 sex- and age-matched healthy controls. A pretrained support vector machine (SVM) for the classification of atrophy profiles from automatic MRI volumetry was used to analyse T1w-MRI (output: MRI-SVM-PSP score). Covariance pattern analysis was applied to compute the expression of a predefined PSP-related pattern in FDG-PET (output: PET-PSPRP expression score). RESULTS: The area under the receiver operating characteristic curve for the detection of PSP did not differ between MRI-SVM-PSP and PET-PSPRP expression score (p≥0.63): about 0.90, 0.95 and 0.85 for detection of all PSP, PSP-RS and vPSP. The MRI-SVM-PSP score achieved about 13% higher specificity and about 15% lower sensitivity than the PET-PSPRP expression score. Decision tree models selected the MRI-SVM-PSP score for the first branching and the PET-PSPRP expression score for a second split of the subgroup with normal MRI-SVM-PSP score, both in the whole sample and when restricted to PSP-RS or vPSP. CONCLUSIONS: FDG-PET provides added value for PSP-suspected patients with normal/inconclusive T1w-MRI, regardless of PSP phenotype and the methods to analyse the images for PSP-typical features.

Image-based dosimetry for [225Ac]Ac-PSMA-I&T therapy and the effect of daughter-specific pharmacokinetics.

PURPOSE: Although 221Fr and 213Bi have sufficient gamma emission probabilities, quantitative SPECT after [225Ac]Ac-PSMA-I&T therapy remains challenging due to low therapeutic activities. Furthermore, 221Fr and 213Bi may underlie a different pharmacokinetics due to alpha recoil. We conducted a quantitative SPECT study and a urine analysis to investigate the pharmacokinetics of 221Fr and 213Bi and the impact on image-based lesion and kidney dosimetry. METHODS: Five patients (7.7 ± 0.2 MBq [225Ac]Ac-PSMA-I&T) underwent an abdominal SPECT/CT (1 h) at 24 and 48 h (Siemens Symbia T2, high-energy collimator, 440 keV/218 keV (width 20%), 78 keV (width 50%)). Quantitative SPECT was reconstructed using MAP-EM with attenuation and transmission-dependent scatter corrections and resolution modelling. Time-activity curves for kidneys (CT-based) and lesions (80% isocontour 24 h) were fitted mono-exponentially. Urine samples collected along with each SPECT/CT were measured in a gamma counter until secular equilibrium was reached. RESULTS: Mean kidney and lesion effective half-lives were as follows: 213Bi, 27 ± 6/38 ± 10 h; 221Fr, 24 ± 6/38 ± 11 h; 78 keV, 23 ± 7/39 ± 13 h. The 213Bi-to-221Fr kidney SUV ratio increased by an average of 9% from 24 to 48 h. Urine analysis revealed an increasing 213Bi-to-225Ac ratio (24 h, 0.98 ± 0.15; 48 h, 1.08 ± 0.09). Mean kidney and lesion absorbed doses were 0.17 ± 0.06 and 0.36 ± 0.1 Sv RBE = 5 /MBq using 221Fr and 213Bi SPECT images, compared to 0.16 ± 0.05/0.18 ± 0.06 and 0.36 ± 0.1/0.38 ± 0.1 Sv RBE = 5 /MBq considering either the 221Fr or 213Bi SPECT. CONCLUSION: SPECT/CT imaging and urine analysis showed minor differences of up to 10% in the daughter-specific pharmacokinetics. These variances had a minimal impact on the lesion and kidney dosimetry which remained within 8%.

PET/CT imaging of differentiated and medullary thyroid carcinoma using the novel SSTR-targeting peptide [18F]SiTATE - first clinical experiences.

PURPOSE: The novel 18F-labeled somatostatin receptor (SSTR)-directed radiotracer [18F]SiTATE demonstrated promising results for the imaging of various SSTR-expressing tumor types. Although thyroid carcinomas (TC) express SSTR, data on [18F]SiTATE PET/CT imaging in TC are lacking. This study explores the use of [18F]SiTATE PET/CT in a patient cohort with histologically proven TC. METHODS: As part of a prospective observational study at a single tertiary cancer center, 21 patients with TC (10 medullary (MTC) and 11 differentiated (DTC)) who underwent at least one [18F]SiTATE PET/CT were included (37 scans in total). Mean SUVmax and SUVmean of tumoral lesions, mean total-tumor-volume (TTV), and whole-body (WB)-SUVmax and WB-SUVmean on PET with their standard deviations (SDs) were determined. PET parameters were correlated to clinical parameters including tumor marker levels (thyroglobulin for DTC, calcitonin for MTC). RESULTS: 89 lesions were included in the analysis. Metastases were localized in the bone, lymph nodes, lung, soft tissue, and thyroid bed. Osseous (31 lesions; SUVmax 8.6 ± 8.0; SUVmean 5.8 ± 5.4) and nodal (37 lesions; SUVmax 8.7 ± 7.8; SUVmean 5.7 ± 5.4) metastases showed the highest uptake. The MTC disease burden on PET significantly correlated with the calcitonin tumor marker level (e.g., TTV: r = 0.771, r2 = 0.594, p = 0.002). For DTC, no such correlation was present. CONCLUSION: Our data demonstrate high feasibility of [18F]SiTATE PET/CT in a small cohort of patients with MTC and DTC. The use of [18F]SiTATE may overcome logistical disadvantages of 68Ga-based tracers and facilitate SSTR-targeted PET/CT imaging of thyroid carcinoma.

Assessment of [18F]PI-2620 Tau-PET Quantification via Non-Invasive Automatized Image Derived Input Function.

PURPOSE: [18F]PI-2620 positron emission tomography (PET) detects misfolded tau in progressive supranuclear palsy (PSP) and Alzheimer's disease (AD). We questioned the feasibility and value of absolute [18F]PI-2620 PET quantification for assessing tau by regional distribution volumes (VT). Here, arterial input functions (AIF) represent the gold standard, but cannot be applied in routine clinical practice, whereas image-derived input functions (IDIF) represent a non-invasive alternative. We aimed to validate IDIF against AIF and we evaluated the potential to discriminate patients with PSP and AD from healthy controls by non-invasive quantification of [18F] PET. METHODS: In the first part of the study, we validated AIF derived from radial artery whole blood against IDIF by investigating 20 subjects (ten controls and ten patients). IDIF were generated by manual extraction of the carotid artery using the average and the five highest (max5) voxel intensity values and by automated extraction of the carotid artery using the average and the maximum voxel intensity value. In the second part of the study, IDIF quantification using the IDIF with the closest match to the AIF was transferred to group comparison of a large independent cohort of 40 subjects (15 healthy controls, 15 PSP patients and 10 AD patients). We compared VT and VT ratios, both calculated by Logan plots, with distribution volume (DV) ratios using simplified reference tissue modelling and standardized uptake value (SUV) ratios. RESULTS: AIF and IDIF showed highly correlated input curves for all applied IDIF extraction methods (0.78 < r < 0.83, all p < 0.0001; area under the curves (AUC): 0.73 < r ≤ 0.82, all p ≤ 0.0003). Regarding the VT values, correlations were mainly found between those generated by the AIF and by the IDIF methods using the maximum voxel intensity values. Lowest relative differences (RD) were observed by applying the manual method using the five highest voxel intensity values (max5) (AIF vs. IDIF manual, avg: RD = -82%; AIF vs. IDIF automated, avg: RD = -86%; AIF vs. IDIF manual, max5: RD = -6%; AIF vs. IDIF automated, max: RD = -26%). Regional VT values revealed considerable variance at group level, which was strongly reduced upon scaling by the inferior cerebellum. The resulting VT ratio values were adequate to detect group differences between patients with PSP or AD and healthy controls (HC) (PSP target region (globus pallidus): HC vs. PSP vs. AD: 1.18 vs. 1.32 vs. 1.16; AD target region (Braak region I): HC vs. PSP vs. AD: 1.00 vs. 1.00 vs. 1.22). VT ratios and DV ratios outperformed SUV ratios and VT in detecting differences between PSP and healthy controls, whereas all quantification approaches performed similarly in comparing AD and healthy controls. CONCLUSION: Blood-free IDIF is a promising approach for quantification of [18F]PI-2620 PET, serving as correlating surrogate for invasive continuous arterial blood sampling. Regional [18F]PI-2620 VT show large variance, in contrast to regional [18F]PI-2620 VT ratios scaled with the inferior cerebellum, which are appropriate for discriminating PSP, AD and healthy controls. DV ratios obtained by simplified reference tissue modeling are similarly suitable for this purpose.

[68Ga]Ga-FAPI-46 PET/CT for penile cancer - a feasibility study.

PURPOSE: Penile cancer is a rare entity and has a good prognosis in localized stage. Delayed surgical treatment of lymphatic disease is associated with poor overall survival but conventional imaging cannot detect occult lymph node metastasis sufficiently. Imaging cancer related fibroblasts has shown promising results as non-invasive staging tool in various tumor entities but has not yet been evaluated in penile cancer. METHODS: In this single-center pilot study, patients planned for surgical treatment for penile cancer underwent preoperatively [68Ga]Ga-FAPI-46 PET/CT. Post-operative histopathology was compared to [68Ga]Ga-FAPI-46 PET/CT results. RESULTS: From January 2022 to June 2022, a total number 11 patients with histopathologically proven penile cancer underwent surgery and received [68Ga]Ga-FAPI-46 PET/CT prior therapy. 8 primary tumor sites and 4 lymph node regions were analyzed. FAPI uptake was increased on primary tumor site (SUVmax 16.2 (9.1 - 25.8)). Histopathological proven lymph node regions showed highly increased FAPI uptakes (SUVmax 17.9 (16.4 - 23.5) on [68Ga]Ga-FAPI-46 PET/CT. CONCLUSION: In this first pilot cohort, there were no false-positive FAPI uptake which might allow the detection of occult lymph node metastasis by [68Ga]Ga-FAPI-46 PET/CT and might consequently lead to omitting lymph node regions during surgery that had no increased FAPI uptake pre-operatively.

Visual reading for [18F]Florzolotau Tau PET scans in progressive supranuclear palsy.

PURPOSE: The identification of tau accumulation within living brains holds significant potential in facilitating accurate diagnosis of progressive supranuclear palsy (PSP). While visual assessment is frequently employed, standardized methods for tau positron emission tomography (PET) specifically in PSP are absent. We aimed to develop a visual reading algorithm dedicated to the evaluation of [18F]Florzolotau PET in PSP. METHODS: 148 PSP and 30 healthy volunteers were divided into a development set (for the establishment of the reading rules; n = 89) and a testing set (for the validation of the reading rules; n = 89). For differential diagnosis, 55 α-synucleinopathies were additionally included into the testing set. The visual reading method was established by an experienced assessor (Reader 0) and was then validated by Reader 0 and two additional readers on regional and overall binary manners. A positive binding in both midbrain and globus pallidus/putamen regions was characterized as a PSP-like pattern, whereas any other pattern was classified as non-PSP-like. RESULTS: Reader 1 (94.4%) and Reader 2 (93.8%) showed excellent agreement for the overall binary determination against Reader 0. The regional binary determinations of midbrain and globus pallidus/putamen showed excellent agreement among readers (kappa > 0.80). The overall binary evaluation demonstrated reproducibility of 86.1%, 94.4% and 77.8% for three readers. The visual reading algorithm showed high agreement with regional standardized uptake value ratios and clinical diagnoses. CONCLUSION: Through the application of the suggested visual reading algorithm, [18F]Florzorotau PET imaging demonstrated a robust performance for the imaging diagnosis of PSP.

EANM practice guidelines for an appropriate use of PET and SPECT for patients with epilepsy.

Epilepsy is one of the most frequent neurological conditions with an estimated prevalence of more than 50 million people worldwide and an annual incidence of two million. Although pharmacotherapy with anti-seizure medication (ASM) is the treatment of choice, ~30% of patients with epilepsy do not respond to ASM and become drug resistant. Focal epilepsy is the most frequent form of epilepsy. In patients with drug-resistant focal epilepsy, epilepsy surgery is a treatment option depending on the localisation of the seizure focus for seizure relief or seizure freedom with consecutive improvement in quality of life. Beside examinations such as scalp video/electroencephalography (EEG) telemetry, structural, and functional magnetic resonance imaging (MRI), which are primary standard tools for the diagnostic work-up and therapy management of epilepsy patients, molecular neuroimaging using different radiopharmaceuticals with single-photon emission computed tomography (SPECT) and positron emission tomography (PET) influences and impacts on therapy decisions. To date, there are no literature-based praxis recommendations for the use of Nuclear Medicine (NM) imaging procedures in epilepsy. The aims of these guidelines are to assist in understanding the role and challenges of radiotracer imaging for epilepsy; to provide practical information for performing different molecular imaging procedures for epilepsy; and to provide an algorithm for selecting the most appropriate imaging procedures in specific clinical situations based on current literature. These guidelines are written and authorized by the European Association of Nuclear Medicine (EANM) to promote optimal epilepsy imaging, especially in the presurgical setting in children, adolescents, and adults with focal epilepsy. They will assist NM healthcare professionals and also specialists such as Neurologists, Neurophysiologists, Neurosurgeons, Psychiatrists, Psychologists, and others involved in epilepsy management in the detection and interpretation of epileptic seizure onset zone (SOZ) for further treatment decision. The information provided should be applied according to local laws and regulations as well as the availability of various radiopharmaceuticals and imaging modalities.

Tau accumulation is associated with dopamine deficiency in vivo in four-repeat tauopathies.

PURPOSE: We hypothesized that severe tau burden in brain regions involved in direct or indirect pathways of the basal ganglia correlate with more severe striatal dopamine deficiency in four-repeat (4R) tauopathies. Therefore, we correlated [18F]PI-2620 tau-positron-emission-tomography (PET) imaging with [123I]-Ioflupane single-photon-emission-computed tomography (SPECT) for dopamine transporter (DaT) availability. METHODS: Thirty-eight patients with clinically diagnosed 4R-tauopathies (21 male; 69.0 ± 8.5 years) and 15 patients with clinically diagnosed α-synucleinopathies (8 male; 66.1 ± 10.3 years) who underwent [18F]PI-2620 tau-PET and DaT-SPECT imaging with a time gap of 3 ± 5 months were evaluated. Regional Tau-PET signals and DaT availability as well as their principal components were correlated in patients with 4R-tauopathies and α-synucleinopathies. Both biomarkers and the residuals of their association were correlated with clinical severity scores in 4R-tauopathies. RESULTS: In patients with 4R-tauopathies, [18F]PI-2620 binding in basal ganglia and midbrain regions was negatively associated with striatal DaT availability (i.e. globus pallidus internus and putamen (ß = - 0.464, p = 0.006, Durbin-Watson statistics = 1.824) in a multiple regression model. Contrarily, [18F]PI-2620 binding in the dentate nucleus showed no significant regression factor with DaT availability in the striatum (ß = 0.078, p = 0.662, Durbin-Watson statistics = 1.686). Patients with α-synucleinopathies did not indicate any regional associations between [18F]PI-2620-binding and DaT availability. Higher DaT-SPECT binding relative to tau burden was associated with better clinical performance (ß = - 0.522, p = 0.011, Durbin-Watson statistics = 2.663) in patients with 4R-tauopathies. CONCLUSION: Tau burden in brain regions involved in dopaminergic pathways is associated with aggravated dopaminergic dysfunction in patients with clinically diagnosed primary tauopathies. The ability to sustain dopamine transmission despite tau accumulation may preserve motor function.

Metabolic network alterations as a supportive biomarker in dementia with Lewy bodies with preserved dopamine transmission.

PURPOSE: Metabolic network analysis of FDG-PET utilizes an index of inter-regional correlation of resting state glucose metabolism and has been proven to provide complementary information regarding the disease process in parkinsonian syndromes. The goals of this study were (i) to evaluate pattern similarities of glucose metabolism and network connectivity in dementia with Lewy bodies (DLB) subjects with subthreshold dopaminergic loss compared to advanced disease stages and to (ii) investigate metabolic network alterations of FDG-PET for discrimination of patients with early DLB from other neurodegenerative disorders (Alzheimer's disease, Parkinson's disease, multiple system atrophy) at individual patient level via principal component analysis (PCA). METHODS: FDG-PETs of subjects with probable or possible DLB (n = 22) without significant dopamine deficiency (z-score < 2 in putamen binding loss on DaT-SPECT compared to healthy controls (HC)) were scaled by global-mean, prior to volume-of-interest-based analyses of relative glucose metabolism. Single region metabolic changes and network connectivity changes were compared against HC (n = 23) and against DLB subjects with significant dopamine deficiency (n = 86). PCA was applied to test discrimination of patients with DLB from disease controls (n = 101) at individual patient level. RESULTS: Similar patterns of hypo- (parietal- and occipital cortex) and hypermetabolism (basal ganglia, limbic system, motor cortices) were observed in DLB patients with and without significant dopamine deficiency when compared to HC. Metabolic connectivity alterations correlated between DLB patients with and without significant dopamine deficiency (R2 = 0.597, p < 0.01). A PCA trained by DLB patients with dopamine deficiency and HC discriminated DLB patients without significant dopaminergic loss from other neurodegenerative parkinsonian disorders at individual patient level (area-under-the-curve (AUC): 0.912). CONCLUSION: Disease-specific patterns of altered glucose metabolism and altered metabolic networks are present in DLB subjects without significant dopaminergic loss. Metabolic network alterations in FDG-PET can act as a supporting biomarker in the subgroup of DLB patients without significant dopaminergic loss at symptoms onset.

Neuroinflammation Parallels 18F-PI-2620 Positron Emission Tomography Patterns in Primary 4-Repeat Tauopathies.

BACKGROUND: Preclinical, postmortem, and positron emission tomography (PET) imaging studies have pointed to neuroinflammation as a key pathophysiological hallmark in primary 4-repeat (4R) tauopathies and its role in accelerating disease progression. OBJECTIVE: We tested whether microglial activation (1) progresses in similar spatial patterns as the primary pathology tau spreads across interconnected brain regions, and (2) whether the degree of microglial activation parallels tau pathology spreading. METHODS: We examined in vivo associations between tau aggregation and microglial activation in 31 patients with clinically diagnosed 4R tauopathies, using 18F-PI-2620 PET and 18F-GE180 (translocator protein [TSPO]) PET. We determined tau epicenters, defined as subcortical brain regions with highest tau PET signal, and assessed the connectivity of tau epicenters to cortical regions of interest using a 3-T resting-state functional magnetic resonance imaging template derived from age-matched healthy elderly controls. RESULTS: In 4R tauopathy patients, we found that higher regional tau PET covaries with elevated TSPO-PET across brain regions that are functionally connected to each other (ß = 0.414, P < 0.001). Microglial activation follows similar distribution patterns as tau and distributes primarily across brain regions strongly connected to patient-specific tau epicenters (ß = -0.594, P < 0.001). In these regions, microglial activation spatially parallels tau distribution detectable with 18F-PI-2620 PET. CONCLUSIONS: Our findings indicate that the spatial expansion of microglial activation parallels tau distribution across brain regions that are functionally connected to each other, suggesting that tau and inflammation are closely interrelated in patients with 4R tauopathies. The combination of in vivo tau and inflammatory biomarkers could therefore support the development of immunomodulatory strategies for disease-modifying treatments in these conditions. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Individual regional associations between Aß-, tau- and neurodegeneration (ATN) with microglial activation in patients with primary and secondary tauopathies.

ß-amyloid (Aß) and tau aggregation as well as neuronal injury and atrophy (ATN) are the major hallmarks of Alzheimer's disease (AD), and biomarkers for these hallmarks have been linked to neuroinflammation. However, the detailed regional associations of these biomarkers with microglial activation in individual patients remain to be elucidated. We investigated a cohort of 55 patients with AD and primary tauopathies and 10 healthy controls that underwent TSPO-, Aß-, tau-, and perfusion-surrogate-PET, as well as structural MRI. Z-score deviations for 246 brain regions were calculated and biomarker contributions of Aß (A), tau (T), perfusion (N1), and gray matter atrophy (N2) to microglial activation (TSPO, I) were calculated for each individual subject. Individual ATN-related microglial activation was correlated with clinical performance and CSF soluble TREM2 (sTREM2) concentrations. In typical and atypical AD, regional tau was stronger and more frequently associated with microglial activation when compared to regional Aß (AD: ßT = 0.412 ± 0.196 vs. ßA = 0.142 ± 0.123, p < 0.001; AD-CBS: ßT = 0.385 ± 0.176 vs. ßA = 0.131 ± 0.186, p = 0.031). The strong association between regional tau and microglia reproduced well in primary tauopathies (ßT = 0.418 ± 0.154). Stronger individual associations between tau and microglial activation were associated with poorer clinical performance. In patients with 4RT, sTREM2 levels showed a positive association with tau-related microglial activation. Tau pathology has strong regional associations with microglial activation in primary and secondary tauopathies. Tau and Aß related microglial response indices may serve as a two-dimensional in vivo assessment of neuroinflammation in neurodegenerative diseases.

ESR Essentials: role of PET/CT in neuroendocrine tumors-practice recommendations by the European Society for Hybrid, Molecular and Translational Imaging.

Neuroendocrine neoplasms (NEN) originate from the secretory cells of the neuroendocrine system, with the majority arising in the gastrointestinal tract and pancreas. Given the heterogeneity in the biological behavior and morphological differentiation of these tumors, advanced imaging techniques are crucial for supporting the suspected diagnosis, accurate staging, and monitoring therapy. As most well-differentiated NEN demonstrate overexpression of somatostatin receptors (SSR) on the cell surface, SSR-directed PET/CT is considered the reference standard for imaging of this particular entity. SSR-PET/CT should be the imaging method of choice in every NEN G1 or G2 and considered for re-staging after both potentially curative and non-curative surgeries. The extent of SSR expression is also crucial for determining a patient's eligibility for peptide receptor radionuclide therapy (PRRT). PRRT utilizes [177Lu]Lu-DOTA-TATE to target the SSR receptor and can significantly prolong progression-free survival in patients with advanced, progressive neuroendocrine tumor of the gastroenteropancreatic system (GEP-NET). PET/CT is a central component of the multidisciplinary management of NEN. Variable follow-up intervals are recommended, considering that tumors with higher proliferation rates or advanced metastatic disease require more frequent assessments. The combination with other imaging modalities, like MRI, complements SSR-PET/CT, further enhancing overall diagnostic accuracy. KEY POINTS: Somatostatin receptor-PET/CT (SSR-PET/CT) is the guideline-recommended reference standard for imaging well-differentiated neuroendocrine tumors (NET). SSR-PET/CT should be the diagnostic imaging of choice for staging and post-therapy re-staging of grade 1 or 2 NET (G1 or G2). Variable follow-up intervals are recommended for NET G1 and G2. Tumors with higher proliferation rates or advanced metastatic disease necessitate more frequent assessments.

ESR Essentials: staging and restaging with FDG-PET/CT in oncology-practice recommendations by the European Society for Hybrid, Molecular and Translational Imaging.

Positron emission tomography (PET) stands as the paramount clinical molecular imaging modality, especially in oncology. Unlike conventional anatomical-morphological imaging methods such as computed tomography (CT) and magnetic resonance imaging (MRI), PET provides detailed visualizations of internal activity at the molecular and cellular levels. 18-fluorine-fluorodeoxyglucose ([18F]FDG)-PET combined with contrast-enhanced CT (ceCT) significantly improves the detection of various cancers. Appropriate patient selection is crucial, and physicians should carefully assess the appropriateness of [18F]FDG-PET/CT based on specific clinical criteria and evidence. Due to its high diagnostic accuracy, [18F]FDG-PET/CT is indispensable for evaluating the extent of disease, staging, and restaging known malignancies, and assessing the response to therapy. PET/CT imaging offers significant advantages in patient management, particularly by identifying occult metastases that might otherwise go undetected. This can help prevent unnecessary surgeries, allowing many patients to be redirected to systemic chemotherapy instead. However, it is important to note that the gold standard for surgical planning remains CT and/or MRI, depending on the body region. These imaging modalities, with or without associated angiography, provide superior contrast and spatial resolution, essential for detailed surgical preparation and planning. [18F]FDG-PET/CT has a central role in the precise and early diagnosis of cancer, contributing significantly to personalized treatment plans. However, it has limitations, including non-tumor-specific uptake and the potential to inaccurately capture the metabolic activity of certain tumor types due to low uptake in some well-differentiated tumor cell lines. Therefore, it should be utilized in clinical scenarios where it offers crucial diagnostic insights not readily available with other imaging modalities. KEY POINTS: Use [18F]FDG-PET/CT selectively based on clinical appropriateness criteria and existing evidence to optimize resource utilization and minimize patient exposure. Employ [18F]FDG-PET/CT in treatment planning and monitoring, particularly for assessing chemotherapy or radiotherapy response in FDG-avid lymphoma and solid tumors. When available, [18F]FDG-PET/CT can be integrated with other diagnostic tools, such as MRI, to enhance overall diagnostic accuracy.