Arterial Spin Labeling (ASL) in Neuroradiological Diagnostics - Methodological Overview and Use Cases.

BACKGROUND: Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI)-based technique using labeled blood-water of the brain-feeding arteries as an endogenous tracer to derive information about brain perfusion. It enables the assessment of cerebral blood flow (CBF). METHOD: This review aims to provide a methodological and technical overview of ASL techniques, and to give examples of clinical use cases for various diseases affecting the central nervous system (CNS). There is a special focus on recent developments including super-selective ASL (ssASL) and time-resolved ASL-based magnetic resonance angiography (MRA) and on diseases commonly not leading to characteristic alterations on conventional structural MRI (e. g., concussion or migraine). RESULTS: ASL-derived CBF may represent a clinically relevant parameter in various pathologies such as cerebrovascular diseases, neoplasms, or neurodegenerative diseases. Furthermore, ASL has also been used to investigate CBF in mild traumatic brain injury or migraine, potentially leading to the establishment of imaging-based biomarkers. Recent advances made possible the acquisition of ssASL by selective labeling of single brain-feeding arteries, enabling spatial perfusion territory mapping dependent on blood flow of a specific preselected artery. Furthermore, ASL-based MRA has been introduced, providing time-resolved delineation of single intracranial vessels. CONCLUSION: Perfusion imaging by ASL has shown promise in various diseases of the CNS. Given that ASL does not require intravenous administration of a gadolinium-based contrast agent, it may be of particular interest for investigations in pediatric cohorts, patients with impaired kidney function, patients with relevant allergies, or patients that undergo serial MRI for clinical indications such as disease monitoring. KEY POINTS: · ASL is an MRI technique that uses labeled blood-water as an endogenous tracer for brain perfusion imaging.. · It allows the assessment of CBF without the need for administration of a gadolinium-based contrast agent.. · CBF quantification by ASL has been used in several pathologies including brain tumors or neurodegenerative diseases.. · Vessel-selective ASL methods can provide brain perfusion territory mapping in cerebrovascular diseases.. · ASL may be of particular interest in patient cohorts with caveats concerning gadolinium administration..

New Perspectives in Radiological and Radiopharmaceutical Hybrid Imaging in Progressive Supranuclear Palsy: A Systematic Review.

Progressive supranuclear palsy (PSP) is a neurodegenerative disease characterized by four-repeat tau deposition in various cell types and anatomical regions, and can manifest as several clinical phenotypes, including the most common phenotype, Richardson's syndrome. The limited availability of biomarkers for PSP relates to the overlap of clinical features with other neurodegenerative disorders, but identification of a growing number of biomarkers from imaging is underway. One way to increase the reliability of imaging biomarkers is to combine different modalities for multimodal imaging. This review aimed to provide an overview of the current state of PSP hybrid imaging by combinations of positron emission tomography (PET) and magnetic resonance imaging (MRI). Specifically, combined PET and MRI studies in PSP highlight the potential of [18F]AV-1451 to detect tau, but also the challenge in differentiating PSP from other neurodegenerative diseases. Studies over the last years showed a reduced synaptic density in [11C]UCB-J PET, linked [11C]PK11195 and [18F]AV-1451 markers to disease progression, and suggested the potential role of [18F]RO948 PET for identifying tau pathology in subcortical regions. The integration of quantitative global and regional gray matter analysis by MRI may further guide the assessment of reduced cortical thickness or volume alterations, and diffusion MRI could provide insight into microstructural changes and structural connectivity in PSP. Challenges in radiopharmaceutical biomarkers and hybrid imaging require further research targeting markers for comprehensive PSP diagnosis.

Dose development in sinonasal imaging over the last decade - a retrospective patient study.

BACKGROUND: Computed tomography (CT) has become the primary imaging modality for visualization of the paranasal sinuses. In this retrospective, single center patient study the radiation dose development in the past 12 years in CT imaging of the paranasal sinuses was assessed. METHODS: The computed tomography dose index (CTDIVol) and dose length product (DLP) of a total of 1246 patients (average age: 41 ± 18 years, 361 females, 885 males) were evaluated, who received imaging of the paranasal sinuses either for chronic sinusitis diagnostic, preoperatively or posttraumatically. Scans were performed on three different CT scanners (Somatom Definition AS, Somatom Definition AS+, Somatom Force, all from Siemens Healthineers) and on one CBCT (Morita) ranging from 2010 to 2022. Reconstruction techniques were filtered back projection and three generations of iterative reconstruction (IRIS, SAFIRE, ADMIRE, all from Siemens Healthineers). Group comparisons were performed using either parametrical (ANOVA) or non-parametrical tests (Kruskal-Wallis Test), where applicable. RESULTS: Over the past 12 years, there was a 73%, 54%, and 66% CTDIVol reduction and a significant (p < 0.001) 72%, 33%, and 67% DLP reduction in assessing the paranasal sinuses for chronic sinusitis, preoperatively and posttraumatically, respectively. CONCLUSION: Technological developments in CT imaging, both hardware and software based, have led to a significant reduction in dose exposure in recent years. Particularly in imaging of the paranasal sinuses, the reduction of radiation exposure is of great interest due to the often young patient age and radiation-sensitive organs in the area of radiation exposure.

Tin filter compared to low kV protocols - optimizing sinonasal imaging in computed tomography.

OBJECTIVES: Paranasal sinus imaging due to chronic inflammatory disease is one of the most common examinations in head and neck radiology with CT imaging considered the current gold standard. In this phantom study we analyzed different low dose CT protocols in terms of image quality, radiation exposure and subjective evaluation in order to establish an optimized scanning protocol. METHODS: In a phantom study, an Alderson phantom was scanned using 12 protocols between 70-120 kV and 25-200 mAs with and without tin filtration. For all datasets, iterative reconstruction was used. Data were objectively evaluated (image noise, (dose-weighted) contrast-to-noise ratio) and for subjective evaluation an online survey using a Likert scale was performed to reach a large group of clinically experienced reader (n = 62). The protocol was considered diagnostically insufficient if the median score was 4 and above and if more than 10% of raters scored 4 and above on the Likert scale. For an interreader agreement an ICC was calculated. To compare clinical value in relation to the applied dose and the objective image parameters, we calculated a figure of merit (FOM) and ranked the protocols accordingly. RESULTS: There was an overall moderate agreement between the 62 readers for the 12 examined CT protocols. In this phantom study, protocols with 100 kV with spectral shaping and 50-100 mAs obtained the best results for its combination of dose, image quality and clinical information value for diagnosing sinusitis (FOM 1st- 2nd place) with the 70 kV and 50 mAs as a good alternative as well (Sinusitis: FOM shared 2nd). For preoperative planning, where a higher dose is necessary, 100 kV with spectral shaping and 100 mAs achieved the overall best results (FOM 1st place) with 70 kV and 50 mAs ranking 4th. CONCLUSION: 100-kV protocols with spectral shaping or low kV protocols (70 kV) with a similarly low dose showed the best figure of merit for imaging sinonasal disease and preoperative planning. With modern scanner technology available, spectral shaping or low KV protocols should be used for sinusitis imaging.

Quantitative analysis of regional distribution of tau pathology with 11C-PBB3-PET in a clinical setting.

PURPOSE: The recent developments of tau-positron emission tomography (tau-PET) enable in vivo assessment of neuropathological tau aggregates. Among the tau-specific tracers, the application of 11C-pyridinyl-butadienyl-benzothiazole 3 (11C-PBB3) in PET shows high sensitivity to Alzheimer disease (AD)-related tau deposition. The current study investigates the regional tau load in patients within the AD continuum, biomarker-negative individuals (BN) and patients with suspected non-AD pathophysiology (SNAP) using 11C-PBB3-PET. MATERIALS AND METHODS: A total of 23 memory clinic outpatients with recent decline of episodic memory were examined using 11C-PBB3-PET. Pittsburg compound B (11C-PIB) PET was available for 17, 18F-flurodeoxyglucose (18F-FDG) PET for 16, and cerebrospinal fluid (CSF) protein levels for 11 patients. CSF biomarkers were considered abnormal based on Aß42 (< 600 ng/L) and t-tau (> 450 ng/L). The PET biomarkers were classified as positive or negative using statistical parametric mapping (SPM) analysis and visual assessment. Using the amyloid/tau/neurodegeneration (A/T/N) scheme, patients were grouped as within the AD continuum, SNAP, and BN based on amyloid and neurodegeneration status. The 11C-PBB3 load detected by PET was compared among the groups using both atlas-based and voxel-wise analyses. RESULTS: Seven patients were identified as within the AD continuum, 10 SNAP and 6 BN. In voxel-wise analysis, significantly higher 11C-PBB3 binding was observed in the AD continuum group compared to the BN patients in the cingulate gyrus, tempo-parieto-occipital junction and frontal lobe. Compared to the SNAP group, patients within the AD continuum had a considerably increased 11C-PBB3 uptake in the posterior cingulate cortex. There was no significant difference between SNAP and BN groups. The atlas-based analysis supported the outcome of the voxel-wise quantification analysis. CONCLUSION: Our results suggest that 11C-PBB3-PET can effectively analyze regional tau load and has the potential to differentiate patients in the AD continuum group from the BN and SNAP group.

Clinicoanatomical substrates of selfish behaviour in amyotrophic lateral sclerosis - An observational cohort study.

OBJECTIVE: ALS primarily affects motor functions, but cognitive functions, including social understanding, may also be impaired. Von Economo neurons (VENs) are part of the neuronal substrate of social understanding and these cells are histopathologically altered in ALS. We investigated whether activity in areas including VENs is associated with an impairment of cognitive tasks that mirror social functioning. METHODS: In this observational prospective study, ALS patients (N = 26) were tested for cognitive behavioural function, encompassing different aspects of empathetic understanding (interpersonal reactivity index, IRI), social behaviour (ultimatum game), recognition of faux-pas situations, and general cognitive functioning (Edinburgh Cognitive and Behavioural ALS Screen, ECAS). For in vivo pathological staging according to Braak, DTI-MRI was performed to determine those ALS patients with expected pathological involvement of VENs (B ALS stages 3 + 4) compared to those without (B ALS stages 1 + 2). Expected hypometabolism of cerebral areas was determined with 18F-FDG PET in N = 20 ALS patients and compared to N = 20 matched healthy controls. Volume of interest analysis was performed in the anterior cingulate cortex (ACC) and the anterior insular cortex (AIC), which contain high numbers of VENs. RESULTS: Compared to those without expected pathological involvement of VENs (B/B ALS stages 1 + 2), ALS patients with anticipated pathological involvement of VENs (B/B ALS stages 3 + 4) presented with significantly reduced fantasy to understand the mindset of others (IRI) and, social behaviour was more selfish (ultimatum game) despite the fact that cognitive understanding of socially inappropriate behaviour of others (faux-pas) was unimpaired. 18F-FDG-PET showed hypometabolism in ACC and AIC in ALS patients with anticipated pathological involvement of VENs compared to those without and this was significantly correlated to cognitive-behavioral functions in certain tasks. CONCLUSION: Here, we present evidence of altered social behaviour in ALS patients associated with regional 18FDG-PET hypometabolism in areas with a high density of VENs, thereby suggesting a possible causal association.

Transport of asymmetric dimethylarginine (ADMA) by cationic amino acid transporter 2 (CAT2), organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1).

Asymmetric dimethylarginine (ADMA), inhibiting the nitric oxide (NO) synthesis from L-arginine, is a known cardiovascular risk factor. Our aim was to investigate if ADMA and/or L-arginine are substrates of the human cationic amino acid transporters 2A (CAT2A, SLC7A2A) and 2B (CAT2B, SLC7A2B), the organic cation transporter 2 (OCT2, SLC22A2), and the multidrug and toxin extrusion protein 1 (MATE1, SLC47A1). We systematically investigated the kinetics of ADMA and L-arginine transport in human embryonic kidney (HEK293) cells stably overexpressing CAT2A, CAT2B, OCT2, or MATE1. Vector-only transfected HEK293 cells served as controls. Compared to vector control cells, uptake of ADMA and L-arginine was significantly higher (p < 0.05) in cells expressing CAT2B and OCT2 at almost all investigated concentrations, while cells expressing CAT2A only showed a significant uptake at concentrations above 300 µM. Uptake of MATE1 overexpressing cells was significantly (p < 0.05) higher at pH 7.8 and 8.2 than controls. Apparent V max values (nmol mg protein(-1) min(-1)) for cellular uptake of ADMA and L-arginine were ≈11.8 ± 1.2 and 19.5 ± 0.7 for CAT2A, ≈14.3 ± 1.0 and 15.3 ± 0.4 for CAT2B, and 6.3 ± 0.3 and >50 for OCT2, respectively. Apparent K m values (µmol/l) for cellular uptake of ADMA and L-arginine were ≈3,033 ± 675 and 3,510 ± 419 for CAT2A, ≈4,021 ± 532 and 952 ± 92 for CAT2B, and 967 ± 143 and >10,000 for OCT2, respectively. ADMA and L-arginine are substrates of human CAT2A, CAT2B, OCT2 and MATE1. Transport kinetics of CAT2A, CAT2B, and OCT2 indicate a low affinity, high capacity transport, which may be relevant for renal and hepatic elimination of ADMA or L-arginine.

Interaction of the cardiovascular risk marker asymmetric dimethylarginine (ADMA) with the human cationic amino acid transporter 1 (CAT1).

Elevated plasma concentrations of endogenously formed asymmetric (ADMA) and symmetric dimethyl-l-arginine (SDMA) are associated with adverse clinical outcomes. Our aim was to investigate the cellular uptake properties of ADMA by the human cationic amino acid transporter 1 (CAT1; SLC7A1). Human embryonic kidney cells (HEK293) stably overexpressing CAT1 (HEK-CAT1) and vector-transfected control cells (HEK-VC) were established to determine cellular uptake of labeled [(3)H]ADMA and [(3)H]l-arginine. Uptake of ADMA and l-arginine were significantly (p<0.001) higher in HEK-CAT1 than in HEK-VC at all investigated concentrations. Apparent V(max) values of cellular ADMA and l-arginine uptake by CAT1 were 26.9 ± 0.8 and 11.0 ± 0.2 nmol mg protein(-1) min(-1), respectively. K(m) values were 183 ± 21 µmoll(-1) (ADMA) and 519 ± 36 µmoll(-1) (l-arginine). Uptake of ADMA was inhibited by l-arginine and SDMA with IC(50) values (95% CI) of 227 (69-742) µmoll(-1) and 273 (191-390) µmoll(-1), respectively. ADMA and SDMA inhibited CAT1-mediated uptake of l-arginine with IC(50) values of 758 (460-1251) µmoll(-1) and 789 (481-1295) µmoll(-1), respectively. Efflux of ADMA was significantly increased in HEK-CAT1 cells as compared to HEK-VC (p<0.05). CAT1 mediates the cellular uptake of ADMA. In its physiological concentration range ADMA is unlikely to impair CAT1-mediated transport of l-arginine. Conversely, high (but still physiological) concentrations of l-arginine can inhibit CAT1-mediated cellular uptake of ADMA.

Dimethylarginine dimethylaminohydrolase overexpression ameliorates atherosclerosis in apolipoprotein E-deficient mice by lowering asymmetric dimethylarginine.

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is increasingly recognized as a novel biomarker in cardiovascular disease. To date, it remains unclear whether elevated ADMA levels are merely associated with cardiovascular risk or whether this molecule is of functional relevance in the pathogenesis of atherosclerotic vascular disease. To clarify this issue, we crossed dimethylarginine dimethylaminohydrolase (DDAH) transgenic mice that overexpress the human isoform 1 of the ADMA degrading enzyme DDAH into ApoE-deficient mice to generate ApoE(-/-)/hDDAH1(+/-) mice. In these mice, as well as ApoE(-/-) wild-type littermates, atherosclerosis within the aorta as well as vascular function of aortic ring preparations was assessed. We report here that overexpression of hDDAH1 reduces plaque formation in ApoE(-/-) mice by lowering ADMA. The extent of atherosclerosis closely correlated with plasma ADMA levels in male but not female mice fed either a standard rodent chow or an atherogenic diet. Functional analysis of aortic ring preparations revealed improved endothelial function in mice overexpressing hDDAH1. Our findings provide proof-of-principle that ADMA plays a causal role as a culprit molecule in atherosclerosis and support recent evidence indicating a functional relevance of DDAH enzymes in genetic mouse models. Together, these results demonstrate that pharmacological interventions targeting the ADMA/DDAH pathway may represent a novel approach in the prevention and management of cardiovascular diseases.

Rac2 regulation of phospholipase C-beta 2 activity and mode of membrane interactions in intact cells.

Phospholipase C-beta (PLCbeta) isozymes play important roles in transmembrane signaling. Their activity is regulated by heterotrimeric G proteins. The PLCbeta(2) isozyme is unique in being stimulated also by Rho GTPases (Rac and Cdc42). However, the mechanism(s) of this stimulation are still unclear. Here, we employed fluorescence recovery after photobleaching to investigate the interaction of green fluorescent protein (GFP)-PLCbeta(2) with the plasma membrane. For either GFP-PLCbeta(2) or GFP-PLCbeta(2)Delta, a C-terminal deletion mutant lacking the region required for stimulation by Galpha(q), these interactions were characterized by a mixture of exchange with a cytoplasmic pool and lateral diffusion. Constitutively active Rac2(12V) stimulated the activity of both GFP-PLCbeta(2) and GFP-PLCbeta(2)Delta in live cells, and enhanced their membrane association as evidenced by the marked reduction in their fluorescence recovery rates. Both effects required the putative N-terminal pleckstrin homology (PH) domain of PLCbeta(2). Importantly, Rac2(12V) dramatically increased the contribution of exchange to the fluorescence recovery of GFP-PLCbeta(2), but had the opposite effect on GFP-PLCbeta(2)Delta, where lateral diffusion became dominant. Our results demonstrate for the first time the regulation of membrane association of a PLCbeta isozyme by a GTP-binding protein and assign a novel function to the PLCbeta(2) C-terminal region, regulating its exchange between membrane-bound and cytosolic states.