Perfusion MRI plays an important role in brain tumor assessment, especially for tumor grading and differentiation of tumor progression from pseudoprogression. Arterial spin labeling (ASL) MRI is a non-invasive method for measuring cerebral blood flow (CBF) using blood water as an endogenous tracer, which has great clinical potential for brain tumor imaging and might help to lower the use of gadolinium-based contrast agents. In this review, we discuss recent advances of the ASL method with a special focus on brain tumors, including multi-time point ASL which not only allows more accurate CBF quantification, but also yields arterial transit time (ATT) maps. Another method to reduce dependency on ATT is velocity-selective ASL, for which labeling is directly performed in the imaging volume. By performing a physiological challenge, like a hypercapnia breathing challenge, the reactivity of the tumor’s neovasculature can be determined. More recent advances in ASL allow probing the blood–brain barrier (BBB) integrity by measuring the rate of water transport across the BBB (BBB-ASL). By labeling only a single artery, selective ASL sequences can help to identify what part of the tumor is fed by which artery. In conclusion, we see the future potential of ASL MRI not only in replacing contrast agents for perfusion assessment but also in providing additional information to the MRI exam, such as BBB integrity or the architecture of the vascular feeders.

Cerebrovascular reactivity (CVR) is a key indicator of vascular health. It is typically assessed using a vasoactive stimulus such as hypercapnia while recording perfusion changes using blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) data or measuring cerebral blood flow (CBF) directly, for example, with arterial spin labelling (ASL). Commonly used BOLD-CVR estimates, however, may be biased by differences in (baseline) cerebral blood volume (CBV). To investigate this, we acquired data from 50 participants at 3 T, obtaining BOLD-CVR, dynamic CBF-CVR, time-encoded CBF-CVR, relative CBV (rCBV) and relative oxygen extraction fraction. Additionally, dynamic simulations of BOLD signal changes were conducted. Our results showed a pronounced contrast between grey matter and white matter in BOLD-CVR, whereas CBF-CVR was similar across tissues. Both inter-subject and intra-subject analyses indicated that this grey matter/white matter contrast in BOLD-CVR primarily reflects differences in rCBV. Other potential factors, such as variations in arterial transit time or baseline CBF, did not show significant correlations. The simulations further supported these findings and, interestingly, pointed to a slow decrease of oxygen metabolism during hypercapnia. In conclusion, BOLD-CVR strongly depends on CBV, a relationship highly relevant for studies in pathologies with altered CBV, such as cerebrovascular diseases or brain tumors.

In the brain, vasomotor dynamics at infra-slow frequencies (∼0.1 Hz), driven by synchronized oscillations of smooth muscle cells in vessel walls, are thought to play a crucial role in regulating cerebral perfusion and underlie resting-state functional connectivity (FC), typically measured by correlated time courses of functional signals. In particular, rodent studies have demonstrated that vasomotor activity contributes to the coherence of blood oxygenation level dependent (BOLD) signal fluctuations. However, in humans, detecting this contribution non-invasively remains challenging due to the limited spatiotemporal sensitivity of functional magnetic resonance imaging (fMRI) to vasomotion. Given that prior studies have identified internal carotid artery stenosis (ICAS) as an informative conditional lesion model of vasomotor and hemodynamic impairments in humans, we investigated whether ICAS affects interhemispheric BOLD coherence at ∼0.1 Hz. Using a multi-modal fMRI framework integrating resting-state fMRI with quantitative mapping of cerebral blood volume, blood flow, oxygen metabolism, and BOLD time lag, we compared BOLD coherence between patients with asymptomatic unilateral ICAS and healthy controls. Frequency-specific analysis revealed significantly diminished inter-hemispheric BOLD coherence at ∼0.1 Hz across canonical resting-state networks in ICAS patients, while ultra-slow (<0.05 Hz) coherence remained largely preserved. This reduction was spatially widespread across brain networks and particularly pronounced in watershed areas, i.e., border zones between major vascular territories, associated with significantly increased lateralization of cerebral blood volume (p < 0.01). Notably, coherence-based FC patterns at ∼0.1 Hz were heterogeneous within watershed areas but homogeneous outside, suggesting an interplay between compensatory mechanisms and cerebrovascular impairment. Taken together, our findings demonstrate that ICAS induces subtle, frequency-and region-specific alterations in interhemispheric FC, consistent with a model in which impaired vasomotor activity and hemodynamic dysfunctions impact resting-state FC in the human brain.

Background:To evaluate whether blood-brain barrier (BBB) mapping via arterial spin-labeling (ASL)-derived exchange time (T ex) can differentiate high-grade gliomas from brain metastases and to compare regional BBB alterations with dynamic susceptibility contrast (DSC)-derived leakage parameters (K2). Methods:A total of 18 patients with therapy-naive cerebral masses (11 gliomas, 7 metastases) underwent multi-echo-ASL and DSC perfusion MRI. T ex maps were obtained using a validated extended two-compartment model. K2 maps were derived from single-echo DSC. T ex and absolute K2 (|K2|) were quantified in contrast-enhancing tumor (CET), peritumoral T2/FLAIR hyperintense region (PTR), gray matter (GM), and white matter (WM). Regional differences were assessed using Wilcoxon signed-rank and Mann-Whitney U tests. Receiver operating characteristic (ROC) analyses evaluated discrimination between gliomas and metastases. Results:T ex was significantly lower in PTR of gliomas versus metastases (P = 0.046). In receiver operating characteristic analysis, T ex slightly outperformed |K2| alone (area under the curve [AUC] = 0.792, 95% confidence interval [CI] [0.535, 0.986] vs. AUC = 0.760, 95% CI [0.508, 0.959]), with further improvement upon combination (AUC = 0.833, 95% CI [0.577, 1.000]). In gliomas, T ex was significantly lower in CET than in GM and WM (both P < 0.01) and PTR showed significantly lower T ex than WM (p < .01). |K2| was significantly higher in CET than all other regions (all p < .01) but did not differ between PTR and GM/WM. Conclusion:In this exploratory study, ASL-derived T ex suggests stronger BBB alterations in peritumoral tissue of high-grade gliomas compared with brain metastases. Adding |K2| further improved discrimination. This supports ASL-based BBB mapping as a complement to DSC leakage imaging. Validation in larger multicenter cohorts is warranted.

BACKGROUND AND PURPOSE:Individualized diagnostic approaches are crucial in cerebrovascular diseases, such as internal carotid artery stenosis (ICAS). To evaluate individual collateral blood supply, vessel-selective imaging has gained high relevance. However, clinically established digital subtraction angiography (DSA) exposes patients to intervention risks and radiation. Two noninvasive MRI-based alternatives are super-selective pseudo-continuous arterial spin labeling (ss-pCASL, a technique for selective labeling of arterial blood-water) for perfusion territory mapping and four-dimensional vessel-selective angiography (4D-sPACK). We hypothesized that asymptomatic atherosclerosis-induced ICAS and Moyamoya disease result in chronic malperfusion. Therefore, we aimed towards quantitative assessment of collateral blood flow by ss-pCASL. METHODS:In this prospective monocentric study, we acquired data in three subgroups (n = 23): patients with asymptomatic unilateral atherosclerosis-induced ICAS, Moyamoya disease, and age-matched healthy controls (HCs). On the basis of vascular territories from ss-pCASL, we introduced four parameters: volume, territorial shift, overlap with an atlas, and cerebral blood flow (CBF). For patients with atherosclerosis-induced ICAS, ipsi- and contralateral hemispheres were compared (paired t-test), and hemispheric lateralization Δ was calculated subjectwise and compared between patients and HCs (unpaired t-test) (p < 0.05). RESULTS:We included data from 20 subjects (8 ICAS, 3 Moyamoya, 9 HC). Group-level results showed ICAS-induced shifts with significant lateralization compared to HCs (ΔVolume,ICAS = 18% ± 10%, p < 0.001; ΔShift,ICAS = 4.9% ± 5.8%, p = 0.027; ΔOverlap,ICAS = 0.2 ± 0.3, p = 0.033, ΔCBF,ICAS = 3 ± 3 mL/100 g/min, p = 0.045). Furthermore, collateral blood supply in Moyamoya disease was assessed by 4D-sPACK and showed comparable diagnostic value as DSA. CONCLUSION:Perfusion territory mapping by ss-pCASL revealed chronic malperfusion in asymptomatic ICAS that can be objectively quantified, and 4D-sPACK added diagnostic value similar to DSA.

In the human brain, substance clearance is intimately connected to the cerebrospinal fluid (CSF) and its flow. CSF extends from the lateral ventricles (LVs) to the parenchyma’s perivascular spaces. Macroscopic undulating CSF flow is present during both wakefulness and sleep and can be experimentally induced. However, the mechanisms generating this flow and its contribution to brain clearance remain unclear. Using fMRI and PET across various conditions, we demonstrate that LV-volume oscillations drive undulating CSF flow in the ventricles and subarachnoid basal cisternae. LV oscillations are driven by cortical blood-volume changes induced by neuronal activity, heartbeat and respiration. LV oscillations’ amplitudes determine PET-tracer clearance from the LVs. Conclusively, induced by extra- and intracranial physiological drivers and mediated by cortical blood-volume changes, LV-volume oscillations drive macroscopic CSF flow and clearance. ### Competing Interest Statement The authors have declared no competing interest. German Research Foundation, 395030489, 491096247, DFG SFB/TRR167 B07 Federal Ministry of Education and Research (BMBF)

PURPOSE:In brain tumors, disruption of the blood-brain barrier (BBB) indicates malignancy. Clinical assessment is qualitative; quantitative evaluation is feasible using the K2 leakage parameter from dynamic susceptibility contrast MRI. However, contrast agent-based techniques are limited in patients with renal dysfunction and insensitive to subtle impairments. Assessing water transport times across the BBB (Tex) by multi-echo arterial spin labeling promises to detect BBB impairments noninvasively and potentially more sensitively. We hypothesized that reduced Tex indicates impaired BBB. Furthermore, we assumed higher sensitivity for Tex than dynamic susceptibility contrast-based K2, because arterial spin labeling uses water as a freely diffusible tracer. METHODS:We acquired 3T MRI data from 28 patients with intraparenchymal brain tumors (World Health Organization Grade 3 & 4 gliomas [n = 17] or metastases [n = 11]) and 17 age-matched healthy controls. The protocol included multi-echo and single-echo Hadamard-encoded arterial spin labeling, dynamic susceptibility contrast, and conventional clinical imaging. Tex was calculated using a T2-dependent multi-compartment model. Areas of contrast-enhancing tissue, edema, and normal-appearing tissue were automatically segmented, and parameter values were compared across volumes of interest and between patients and healthy controls. RESULTS:Tex was significantly reduced (-20.3%) in contrast-enhancing tissue compared with normal-appearing gray matter and correlated well with |K2| (r = -0.347). Compared with healthy controls, Tex was significantly lower in tumor patients' normal-appearing gray matter (Tex,tumor = 0.141 ± 0.032 s vs. Tex,HC = 0.172 ± 0.036 s) and normal-appearing white matter (Tex,tumor = 0.116 ± 0.015 vs. Tex,HC = 0.127 ± 0.017 s), whereas |K2| did not differ significantly. Receiver operating characteristic analysis showed a larger area under the curve for Tex (0.784) than K2 (0.604). CONCLUSION:Tex is sensitive to pathophysiologically impaired BBB. It agrees with contrast agent-based K2 in contrast-enhancing tissue and indicates sensitivity to subtle leakage.

In the mammalian brain, the directed motion of cerebrospinal fluid (CSF-flux) is instrumental in the distribution and removal of solutes. Changes in total cerebral blood volume (CBV) have been hypothesized to drive CSF-flux. We tested this hypothesis in two multimodal brain imaging experiments in healthy humans, in which we drove large changes in total CBV by neuronal burst-suppression under anesthesia or by transient global vasodilation in a hypercapnic challenge. We indirectly monitored CBV changes with a high temporal resolution based on associated changes in total brain volume by functional MRI (fMRI) and measured cerebral blood flow by arterial spin-labeling. Relating CBV-sensitive signals to fMRI-derived measures of macroscopic CSF flow across the basal cisternae, we demonstrate that increasing total CBV extrudes CSF from the skull and decreasing CBV allows its influx. Moreover, CSF largely stagnates when CBV is stable. Together, our results establish the direct coupling between total CBV changes and CSF-flux.

Vasomotor dynamics at the infra-slow frequencies (∼0.1 Hz), driven by synchronized oscillation of smooth muscle cells in vessel walls, play an important role in regulating cerebral perfusion and constitute a physiological basis for resting-state functional connectivity (FC). Invasive animal studies have demonstrated that vasomotor activity contributes to coherent blood oxygenation-dependent level (BOLD) signal fluctuations. However, in humans, it remains challenging to non-invasively detect this contribution due to the limited spatiotemporal sensitivity of functional magnetic resonance imaging (fMRI) to vasomotion. Leveraging internal carotid artery stenosis (ICAS) as a natural lesion model of impaired vasomotion, we examined whether impaired vasomotor activity influences inter-hemispheric BOLD coherence at ∼0.1 Hz. Using a multi-modal fMRI framework that integrates resting-state fMRI with quantitative multi-parametric mapping of cerebral blood volume, blood flow, oxygen metabolism, and BOLD time lag, we compared BOLD coherence in patients with unliteral ICAS to healthy controls. Frequency-specific coherence analysis revealed significantly diminished inter-hemispheric BOLD coherence at the vasomotor frequency range (∼0.1 Hz) across canonical resting-state networks in ICAS patients, whereas ultra-slow (<0.05 Hz) coherence remains largely preserved. This reduction was spatially widespread and particularly pronounced inside watershed areas, i.e., border zones between major vascular perfusion territories that are especially vulnerable to hypoperfusion and associated with a significantly increased lateralization in cerebral blood volume (p < 0.01) inside watershed areas. Notably, coherence-based FC patterns at ∼0.1 Hz were heterogeneous inside watershed areas and homogeneous outside watershed areas, suggesting an interplay between compensatory mechanisms and vasomotion impairment. Taken together, our findings demonstrate that frequency-resolved, region-specific analysis can capture presumably vasomotion-related oscillatory signals at ∼0.1 Hz and detect subtle differences in inter-hemispheric FC, offering a non-invasive biomarker for early cerebrovascular dysfunction, particularly in patients with ICAS and other vasomotion-related neuropathologies. ### Competing Interest Statement S.K. is an employee of Philips GmbH Market DACH, Hamburg, Germany. X.Y. is a co-founder of MRIBOT LLC. The remaining authors declare no conflict of interest. Deutsche Forschungsgemeinschaft, https://ror.org/018mejw64, 395030489 Evangelisches Studienwerk Villigst, personal grant to Gabriel Hoffmann

BACKGROUND AND PURPOSE:Hemodynamic impairment may contribute to stroke risk and cognitive decline in asymptomatic internal carotid artery stenosis (ICAS). Therefore, multimodal MRI-based quantification of hemodynamic impairment could inform improved treatment decisions. While gross interhemispheric hemodynamic imbalances have been reported in ICAS, identifying more spatially resolved patterns of disease-related alterations may be promising to harness the full potential of hemodynamic MRI. METHODS:In this feasibility study, we investigated the spatial topography of ICAS-related impairments by applying scaled subprofile model principal component analysis (SSM-PCA) to cerebral blood flow (CBF), relative oxygen extraction fraction (rOEF), and oxygen extraction capacity (OEFmax) data of 21 unilateral ICAS patients and 25 healthy controls (HC). RESULTS:We found spatially extended, partly overlapping disease-related patterns for CBF and OEFmax, but not rOEF. CBF (area under the curve [AUC] = 0.95) but not OEFmax (AUC = 0.72) SSM-PCA scores distinguished ICAS patients and HC better than interhemispheric lateralizations (AUC = 0.75/0.73). SSM-PCA scores were only partly explained by interhemispheric lateralization (R2 = -0.27/0.38), indicating complementary information. Critically, ICAS patients with higher OEFmax SSM-PCA scores (z ≥ 1) demonstrated higher stenotic degrees and lower cognitive performance (p < 0.05) without differing in interhemispheric lateralization (p > 0.05). CONCLUSIONS:We demonstrated the feasibility of SSM-PCA in ICAS and obtained novel insights into complex hemodynamic impairment patterns and their association with cognitive function.

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:

Atherosclerosis can underly internal carotid artery stenosis (ICAS), a major risk factor for ischemic stroke, as well as small vessel disease (SVD). This study aimed to investigate hemodynamics and structural alterations associated with SVD in ICAS patients. 28 patients with unilateral asymptomatic ICAS and 30 age-matched controls underwent structural (T1-/T2-weighted and diffusion tensor imaging [DTI]) and hemodynamic (pseudo-continuous arterial spin labeling and dynamic susceptibility contrast) magnetic resonance imaging. SVD-related alterations were assessed using free water (FW), FW-corrected DTI, and peak-width of skeletonized mean diffusivity (PSMD). Furthermore, cortical thickness, cerebral blood flow (CBF), and capillary transit time heterogeneity (CTH) were analyzed. Ipsilateral to the stenosis, cortical thickness was significantly decreased in the posterior dorsal cingulate cortex (p = 0.024) and temporal pole (p = 0.028). ICAS patients exhibited elevated PSMD (p = 0.005), FW (p < 0.001), and contralateral alterations in FW-corrected DTI metrics. We found significantly lateralized CBF (p = 0.011) and a tendency for lateralized CTH (p = 0.067) in the white matter (WM) related to ICAS. Elevated PSMD and FW may indicate a link between SVD and WM changes. Contralateral alterations were seen in FW-corrected DTI, whereas hemodynamic and cortical changes were mainly ipsilateral, suggesting SVD might influence global brain changes concurrent with ICAS-related hemodynamic alterations.

Arterial spin labeling (ASL) is a non-invasive magnetic resonance imaging (MRI) method for the assessment of cerebral blood flow (CBF). This review summarizes recent ASL-based investigations in adult and pediatric patients with migraine with aura, migraine without aura, and chronic migraine. A systematic search according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was conducted within PubMed and reference sections of articles identified from April 2014 to November 2022. Out of 236 initial articles, 20 remained after filtering, encompassing data from 1155 subjects in total. Cross-sectional studies in adults showed inconsistent results, while longitudinal studies demonstrated that cerebral perfusion changes over the migraine cycle can be tracked using ASL. The most consistent findings were observed in ictal states among pediatric migraine patients, where studies showed hypoperfusion matching aura symptoms during early imaging followed by hyperperfusion. Overall, ASL is a useful but currently underutilized modality for evaluating cerebral perfusion in patients with migraine. The generalizability of results is currently limited by heterogeneities regarding study design and documentation of clinical variables (e.g., relation of attacks to scanning timepoint, migraine subtypes). Future MRI studies should consider augmenting imaging protocols with ASL to further elucidate perfusion dynamics in migraine.

Arterial spin labeling (ASL) is a contrast agent-free magnetic resonance imaging (MRI) technique to measure cerebral blood flow (CBF). We sought to investigate effects of CBF within the infarct on outcome and risk of hemorrhagic transformation (HT). In 111 patients (median age: 74 years, 50 men) who had undergone mechanical thrombectomy (MT) for ischemic stroke of the anterior circulation (median interval: 4 days between MT and MRI), post-stroke %CBF difference from pseudo-continuous ASL was calculated within the diffusion-weighted imaging (DWI)-positive infarct territory following lesion segmentation in relationship to the unaffected contralateral side. Functional independence was defined as a modified Rankin Scale (mRS) of 0-2 at 90 days post-stroke. %CBF difference, pre-stroke mRS, and infarct volume were independently associated with functional independence in a multivariate regression model. %CBF difference was comparable between patients with and without HT. A subcohort of 10 patients with decreased infarct-CBF despite expanded Treatment in Cerebral Infarction (eTICI) 2c or 3 recanalization was identified (likely related to the no-reflow phenomenon). Outcome was significantly worse in this group compared to the remaining cohort. In conclusion, ASL-derived %CBF difference from the DWI-positive infarct territory independently predicted functional independence, but %CBF difference was not significantly associated with an increased risk of HT.

Vessel-selective imaging is promising to examine collateral blood supply in asymptomatic internal carotid artery stenosis (ICAS). Established modalities like digital subtraction angiography are invasive, not quantitative and associated with potential complication risks. A viable non-invasive alternative is super-selective arterial spin labelling, providing perfusion territories of individual arteries. We present data from seven asymptomatic ICAS patients and four age-matched healthy controls. We compared individual perfusion territory maps to an atlas of vascular territories and evaluated intra-hemispheric differences, allowing for quantitative assessment of stenotic mal-perfusion as well as compensatory collateral blood supply from the contralateral ICA.

Motivation: Internal carotid artery stenosis (ICAS) accounts for ≈10% of strokes. Individual watershed areas (iWSA) are especially susceptible to hemodynamic impairments. Currently, iWSA are segmented from contrast agent-based time-to-peak (TTP), limiting applicability. Goal(s): We aimed towards non-invasive iWSA segmentation based on arterial transit time (ATT) from Hadamard-encoded pseudo-continuous ASL. Approach: Overlap of iWSA from ATT and TTP was investigated and agreement of extracted hemodynamic parameter values such as cerebrovascular reactivity (CVR) was evaluated and ICAS-induced parameter-lateralization was investigated. Results: ATT-based and TTP-based iWSAs overlapped well, with excellent agreement in quantitative parameters and significant lateralization of hemodynamic parameters in ICAS within both iWSA delineation approaches. Impact: We successfully segmented iWSA from non-invasive ATT and demonstrated sensitivity to ICAS-related impairments, in agreement with TTP-based iWSA segmentation. ATT-based iWSAs facilitate longitudinal investigation without contrast application in cerebrovascular diseases such as ICAS or Moyamoya.

Motivation: A driver of macroscopic CSF flux across ventricles and basal cisternae is hypothesized to be global cerebral blood volume, possibly induced by changes in brain-wide neuronal activity. Goal(s): We intended to test this hypothesis experimentally in healthy human subjects. Approach: We performed two experiments: (1) electro-encephalography and functional MRI (fMRI) during burst-suppression anesthesia, and (2) arterial spin labeling and fMRI during transient hypercapnic challenges in wakefulness. Results: Changes in brain blood volume, induced by neuronal activity switches during burst-suppression or brain blood flow during hyper-normocapnia transitions, cause fMRI signal changes in the basal cisternae which represent CSF flux from or into the brain. Impact: Two distinct experiments revealed a consistent and direct coupling between macroscopic CSF flux and brain blood volume, which can be induced by changes in global neuronal activity. This may contribute to perivascular CSF flow and facilitate brain waste clearance.

Motivation: Glioma-induced blood-brain barrier (BBB) disruptions can be characterized by dynamic susceptibility contrast MRI via the leakage parameter K2. However, it may lack sensitivity to subtle impairments. Recently, non-invasive ASL-based water-exchange measurements (Tex) were proposed to measure even subtle BBB-impairments. Goal(s): We hypothesized correlations of Tex with K2 in contrast-enhancing tissue (CET). Approach: K2 & Tex were compared in 22 patients with brain tumors and 19 healthy controls. Results: Tex agreed well with K2 in CET and was sensitive to pathophysiologically impaired BBB. Moreover, results indicate superior sensitivity to subtle impairments, which may improve therapy planning and progress monitoring. Impact: ASL-based Tex allows non-invasive detection of the pathophysiologically impaired blood-brain barrier in tumors. Whereas its sensitivity to subtle impairments may improve treatment planning in tumors, it could also impact diagnosis of neurodegenerative diseases such as Alzheimer's or Parkinson’s.

Motivation: Standard low-resolution 2D-GRE acquisition for T2* mapping in mqBOLD MRI may suffer from long scan durations and insufficient quantification accuracy. Goal(s): Improving quantification accuracy by switching from 2D to high-resolution 3D multi-echo GRE while simultaneously reducing scan duration by applying compressed sensing (CS) acceleration with deep-learning-based reconstruction. Approach: T2* maps from low-resolution 2D-GRE and high-resolution 3D-GRE with different acceleration factors were compared in 11 healthy volunteers based on visual inspection and VOI-analyses. Results: 3D-GRE yields high-resolution parameter maps with improved T2* values for GM/WM in less than half the scan duration compared to standard 2D-GRE when using CS acceleration with DL-based reconstruction. Impact: High-resolution 3D-GRE with compressed sensing acceleration and deep-learning-based reconstruction was compared to standard 2D-GRE visually and quantitatively. 3D-GRE enables clinically feasible scan durations with improved and reliable T2* mapping, which may add to the clinical applicability of oxygenation-sensitive mqBOLD MRI.