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INTRODUCTION: Cerebral amyloid angiopathy (CAA) is a main cause of cognitive dysfunction in the elderly. We investigated specific cognitive profiles, cognitive function in the stage before intracerebral hemorrhage (ICH), and the association between magnetic resonance imaging (MRI) based cerebral small vessel disease (cSVD) burden in CAA because data on these topics are limited. METHODS: We included Dutch‐type hereditary CAA (D‐CAA) mutation carriers with and without ICH, patients with sporadic CAA (sCAA), and age‐matched controls. Cognition was measured with a standardized test battery. Linear regression was performed to assess the association between MRI‐cSVD burden and cognition. RESULTS: D‐CAA ICH− mutation carriers exhibited poorer global cognition and executive function compared to age‐matched controls. Patients with sCAA performed worse across all cognitive domains compared to D‐CAA ICH+ mutation carriers and age‐matched controls. MRI‐cSVD burden is associated with decreased processing speed. DISCUSSION: CAA is associated with dysfunction in multiple cognitive domains, even before ICH, with increased MRI‐cSVD burden being associated with slower processing speed. Highlights: Cognitive dysfunction is present in early disease stages of cerebral amyloid angiopathy (CAA) before the occurrence of symptomatic intracerebral hemorrhage (sICH).Presymptomatic Dutch‐type CAA (D‐CAA) mutation carriers show worse cognition than age‐matched controls.More early awareness of cognitive dysfunction in CAA before first sICH is needed.Increased cerebral small vessel disease CAA‐burden on magnetic resonance imaging is linked to a decrease in processing speed. [ABSTRACT FROM AUTHOR]

Arterial spin labeling (ASL) and dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI) have shown potential for differentiating tumor progression from pseudoprogression. For pseudocontinuous ASL with a single postlabeling delay, the presence of delayed arterial transit times (ATTs) could affect the evaluation of ASL‐MRI perfusion data. In this study, the influence of ATT artifacts on the perfusion assessment and differentiation between tumor progression and pseudoprogression were studied. This study comprised 66 adult patients (mean age 60 ± 13 years; 40 males) with a histologically confirmed glioblastoma who received postoperative radio (chemo)therapy. ASL‐MRI and DSC‐MRI scans were acquired at 3 months postradiotherapy as part of the standard clinical routine. These scans were visually scored regarding (i) the severity of ATT artifacts (%) on the ASL‐MRI scans only, scored by two neuroradiologists; (ii) perfusion of the enhancing tumor lesion; and (iii) radiological evaluation of tumor progression versus pseudoprogression by one neuroradiologist. The final outcome was based on combined clinical and radiological follow‐up until 9 months postradiotherapy. ATT artifacts were identified in all patients based on the mean scores of two raters. A significant difference between the radiological evaluation of ASL‐MRI and DSC‐MRI was observed only for ASL images with moderate ATT severity (30%–65%). The perfusion assessment showed ASL‐MRI tending more towards hyperperfusion than DSC‐MRI in the case of moderate ATT artifacts. In addition, there was a significant difference between the prediction of tumor progression with ASL‐MRI and the final outcome in the case of severe ATT artifacts (McNemar test, p = 0.041). Despite using ASL imaging parameters close to the recommended settings, ATT artifacts frequently occur in patients with treated brain tumors. Those artifacts could hinder the radiological evaluation of ASL‐MRI data and the detection of true disease progression, potentially affecting treatment decisions for patients with glioblastoma. [ABSTRACT FROM AUTHOR]

Over the last decade, it has become evident that cerebrospinal fluid (CSF) plays a pivotal role in brain solute clearance through perivascular pathways and interactions between the brain and meningeal lymphatic vessels. Whereas most of this fundamental knowledge was gained from rodent models, human brain clearance imaging has provided important insights into the human system and highlighted the existence of important interspecies differences. Current gold standard techniques for human brain clearance imaging involve the injection of gadolinium‐based contrast agents and monitoring their distribution and clearance over a period from a few hours up to 2 days. With both intrathecal and intravenous injections being used, which each have their own specific routes of distribution and thus clearance of contrast agent, a clear understanding of the kinetics associated with both approaches, and especially the differences between them, is needed to properly interpret the results. Because it is known that intrathecally injected contrast agent reaches the blood, albeit in small concentrations, and that similarly some of the intravenously injected agent can be detected in CSF, both pathways are connected and will, in theory, reach the same compartments. However, because of clear differences in relative enhancement patterns, both injection approaches will result in varying sensitivities for assessment of different subparts of the brain clearance system. In this opinion review article, the "EU Joint Programme – Neurodegenerative Disease Research (JPND)" consortium on human brain clearance imaging provides an overview of contrast agent pharmacokinetics in vivo following intrathecal and intravenous injections and what typical concentrations and concentration–time curves should be expected. This can be the basis for optimizing and interpreting contrast‐enhanced MRI for brain clearance imaging. Furthermore, this can shed light on how molecules may exchange between blood, brain, and CSF. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Cerebral blood flow (CBF) is reduced in cognitively impaired (CI) Alzheimer's disease (AD) patients. We checked the sensitivity of time‐encoded arterial spin labeling (te‐ASL) in measuring CBF alterations in individuals with positive AD biomarkers and associations with relevant biomarkers in cognitively unimpaired (CU) individuals. METHODS: We compared te‐ASL with single‐postlabel delay (PLD) ASL in measuring CBF in 59 adults across the AD continuum, classified as CU amyloid beta (Aβ) negative (−), CU Aβ positive (+), and CI Aβ+. We sought associations of CBF with biomarkers of AD, cerebrovascular disease, synaptic dysfunction, neurodegeneration, and cognition in CU participants. RESULTS: te‐ASL was more sensitive at detecting CBF reduction in the CU Aβ+ and CI Aβ+ groups. In CU participants, lower CBF was associated with altered biomarkers of Aβ, tau, synaptic dysfunction, and neurodegeneration. DISCUSSION: CBF reduction occurs early in the AD continuum. te‐ASL is more sensitive than single‐PLD ASL at detecting CBF changes in AD. Highlights: Lower CBF can be detected in CU subjects in the early AD continuum.te‐ASL is more sensitive than single‐PLD ASL at detecting CBF alterations in AD.CBF is linked to biomarkers of AD, synaptic dysfunction, and neurodegeneration. [ABSTRACT FROM AUTHOR]

The blood–brain barrier (BBB) is a barrier protecting the brain and a milieu of continuous exchanges between blood and brain. There is emerging evidence that the BBB plays a major role in epileptogenesis and drug‐resistant epilepsy, through several mechanisms, such as water homeostasis dysregulation, overexpression of drug transporters, and inflammation. Studies have shown abnormal water homeostasis in epileptic tissue and altered aquaporin‐4 water channel expression in animal epilepsy models. This review focuses on abnormal water exchange in epilepsy and describes recent non‐invasive MRI methods of quantifying water exchange. Plain Language Summary: Abnormal exchange between blood and brain contribute to seizures and epilepsy. The authors describe why correct water balance is necessary for healthy brain functioning and how it is impacted in epilepsy. This review also presents recent MRI methods to measure water exchange in human brain. These measures would improve our understanding of factors leading to seizures. [ABSTRACT FROM AUTHOR]

Metabolite‐weighted chemical exchange saturation transfer MRI can be used to indirectly image metabolites such as creatine and glutamate. This study aims to further explore the contrast of CEST at 2 ppm in the human brain at 7T and investigate the metabolite correlates of CEST at 2 ppm via correlations with magnetic resonance spectroscopy (MRS). Simulations were performed to establish the optimal acquisition parameters, such as total saturation time (tsat) and B1 root mean squared (B1rms) for CEST at 2 ppm in the human brain. Parameters were validated via in vitro phantom studies at 7T using concentrations, pH and temperature comparable to what is found in the human brain. Finally, 10 healthy volunteers were scanned at 7T for comparison with MRS. Our results show that the optimal parameters to acquire CEST at 2 ppm images are: B1rms = 2.14 μT & tsat = 1500 ms, respectively. Comparison with MRS showed no significant correlation between CEST at 2 ppm and total Creatine measured by MRS (R = 0.19; p‐value = 0.273). However, a significant correlation was found between CEST at 2 ppm and Glu (R = 0.39; p‐value = 0.033), indicating the broad Glutamate‐weighted CEST as the main measurable contributor to CEST at 2 ppm. We identified and confirmed optimal CEST at 2 ppm sequence parameters and validated CEST at 2 ppm measurements in a controlled in vitro environment. Our findings suggest that glutamate is a substantial contributor to the CEST at 2 ppm contrast observed in the human brain, whereas the creatine contribution to CEST at 2 ppm in the brain did not show a measurable contribution. [ABSTRACT FROM AUTHOR]

Background: Magnetic Resonance acquisition is a time consuming process, making it susceptible to patient motion during scanning. Even motion in the order of a millimeter can introduce severe blurring and ghosting artifacts, potentially necessitating re‐acquisition. Magnetic Resonance Imaging (MRI) can be accelerated by acquiring only a fraction of k‐space, combined with advanced reconstruction techniques leveraging coil sensitivity profiles and prior knowledge. Artificial intelligence (AI)‐based reconstruction techniques have recently been popularized, but generally assume an ideal setting without intra‐scan motion. Purpose: To retrospectively detect and quantify the severity of motion artifacts in undersampled MRI data. This may prove valuable as a safety mechanism for AI‐based approaches, provide useful information to the reconstruction method, or prompt for re‐acquisition while the patient is still in the scanner. Methods: We developed a deep learning approach that detects and quantifies motion artifacts in undersampled brain MRI. We demonstrate that synthetically motion‐corrupted data can be leveraged to train the convolutional neural network (CNN)‐based motion artifact estimator, generalizing well to real‐world data. Additionally, we leverage the motion artifact estimator by using it as a selector for a motion‐robust reconstruction model in case a considerable amount of motion was detected, and a high data consistency model otherwise. Results: Training and validation were performed on 4387 and 1304 synthetically motion‐corrupted images and their uncorrupted counterparts, respectively. Testing was performed on undersampled in vivo motion‐corrupted data from 28 volunteers, where our model distinguished head motion from motion‐free scans with 91% and 96% accuracy when trained on synthetic and on real data, respectively. It predicted a manually defined quality label ('Good', 'Medium' or 'Bad' quality) correctly in 76% and 85% of the time when trained on synthetic and real data, respectively. When used as a selector it selected the appropriate reconstruction network 93% of the time, achieving near optimal SSIM values. Conclusions: The proposed method quantified motion artifact severity in undersampled MRI data with high accuracy, enabling real‐time motion artifact detection that can help improve the safety and quality of AI‐based reconstructions. [ABSTRACT FROM AUTHOR]

Purpose: Multi‐shot diffusion‐weighted EPI allows an increase in image resolution and reduced geometric distortions and can be combined with chemical‐shift encoding (Dixon) to separate water/fat signals. However, such approaches suffer from physiological motion‐induced shot‐to‐shot phase variations. In this work, a structured low‐rank‐based navigator‐free algorithm is proposed to address the challenge of simultaneously separating water/fat signals and correcting for physiological motion‐induced shot‐to‐shot phase variations in multi‐shot EPI‐based diffusion‐weighted MRI. Theory and Methods: We propose an iterative, model‐based reconstruction pipeline that applies structured low‐rank regularization to estimate and eliminate the shot‐to‐shot phase variations in a data‐driven way, while separating water/fat images. The algorithm is tested in different anatomies, including head–neck, knee, brain, and prostate. The performance is validated in simulations and in‐vivo experiments in comparison to existing approaches. Results: In‐vivo experiments and simulations demonstrated the effectiveness of the proposed algorithm compared to extra‐navigated and an alternative self‐navigation approach. The proposed algorithm demonstrates the capability to reconstruct in the multi‐shot/Dixon hybrid space domain under‐sampled datasets, using the same number of acquired EPI shots compared to conventional fat‐suppression techniques but eliminating fat signals through chemical‐shift encoding. In addition, partial Fourier reconstruction can also be achieved by using the concept of virtual conjugate coils in conjunction with the proposed algorithm. Conclusion: The proposed algorithm effectively eliminates the shot‐to‐shot phase variations and separates water/fat images, making it a promising solution for future DWI on different anatomies. [ABSTRACT FROM AUTHOR]

INTRODUCTION: We aimed to investigate the association between white matter hyperintensity (WMH) shape and volume and the long‐term dementia risk in community‐dwelling older adults. METHODS: Three thousand seventy‐seven participants (mean age: 75.6 ± 5.2 years) of the Age Gene/Environment Susceptibility (AGES)‐Reykjavik study underwent baseline 1.5T brain magnetic resonance imaging and were followed up for dementia (mean follow‐up: 9.9 ± 2.6 years). RESULTS: More irregular shape of periventricular/confluent WMH (lower solidity (hazard ratio (95% confidence interval) 1.34 (1.17 to 1.52), p <.001) and convexity 1.38 (1.28 to 1.49), p <.001); higher concavity index 1.43 (1.32 to 1.54), p <.001) and fractal dimension 1.45 (1.32 to 1.58), p <.001)), higher total WMH volume (1.68 (1.54 to 1.87), p <.001), higher periventricular/confluent WMH volume (1.71 (1.55 to 1.89), p <.001), and higher deep WMH volume (1.17 (1.08 to 1.27), p <.001) were associated with an increased long‐term dementia risk. DISCUSSION: WMH shape markers may in the future be useful in determining patient prognosis and may aid in patient selection for future preventive treatments in community‐dwelling older adults. [ABSTRACT FROM AUTHOR]

Cerebral vascular reactivity quantified using blood oxygen level‐dependent functional MRI in conjuncture with a visual stimulus has been proven to be a potent and early marker for cerebral amyloid angiopathy. This work investigates the influence of different postprocessing methods on the outcome of such vascular reactivity measurements. Three methods for defining the region of interest (ROI) over which the reactivity is measured are investigated: structural (transformed V1), functional (template based on the activation of a subset of subjects), and percentile (11.5 cm3 most responding voxels). Evaluation is performed both in a test–retest experiment in healthy volunteers (N = 12), as well as in 27 Dutch‐type cerebral amyloid angiopathy patients and 33 age‐ and sex‐matched control subjects. The results show that the three methods select a different subset of voxels, although all three lead to similar outcome measures in healthy subjects. However, in (severe) pathology, the percentile method leads to higher reactivity measures than the other two, due to circular analysis or "double dipping" by defining a subject‐specific ROI based on the strongest responses within each subject. Furthermore, while different voxels are included in the presence of lesions, this does not necessarily result in different outcome measures. In conclusion, to avoid bias created by the method, either a structural or a functional method is recommended. Both of these methods provide similar reactivity measures, although the functional ROI appears to be less reproducible between studies, because slightly different subsets of voxels were found to be included. On the other hand, the functional method did include fewer lesion voxels than the structural method. [ABSTRACT FROM AUTHOR]

For better quantification of perfusion with arterial spin labeling (ASL), partial volume correction (PVC) is used to disentangle the signals from gray matter (GM) and white matter within any voxel. Based on physiological considerations, PVC algorithms typically assume zero signal in the cerebrospinal fluid (CSF). Recent measurements, however, have shown that CSF‐ASL signal can exceed 10% of GM signal, even when using recommended ASL labeling parameters. CSF signal is expected to particularly affect PVC results in the choroid plexus. This study aims to measure the impact of CSF signal on PVC perfusion measurements, and to investigate the potential use of PVC to retrieve pure CSF‐ASL signal for blood–CSF barrier characterization. In vivo imaging included six pCASL sequences with variable label duration and post‐labeling delay (PLD), and an eight‐echo 3D‐GRASE readout. A dataset was simulated to estimate the effect of CSF‐PVC with known ground‐truth parameters. Differences between the results of CSF‐PVC and non‐CSF‐PVC were estimated for regions of interest (ROIs) based on GM probability, and a separate ROI isolating the choroid plexus. In vivo, the suitability of PVC‐CSF signal as an estimate of pure CSF was investigated by comparing its time course with the long‐TE CSF signal. Results from both simulation and in vivo data indicated that including the CSF signal in PVC improves quantification of GM CBF by approximately 10%. In simulated data, this improvement was greater for multi‐PLD (model fitting) quantification than for single PLD (~1–5% difference). In the choroid plexus, the difference between CSF‐PVC and non‐CSF‐PVC was much larger, averaging around 30%. Long‐TE (pure) CSF signal could not be estimated from PVC CSF signal as it followed a different time course, indicating the presence of residual macrovascular signal in the PVC. The inclusion of CSF adds value to PVC for more accurate measurements of GM perfusion, and especially for quantification of perfusion in the choroid plexus and study of the glymphatic system. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the feasibility of spatio‐temporal encoding (SPEN) readout for pseudo‐continuous ASL (pCASL) in brain, and its robustness to susceptibility artifacts as introduced by aneurysm clips. Methods: A 2D self‐refocused T2*‐compensated hybrid SPEN scheme, with super‐resolution reconstruction was implemented on a 1.5T Philips system. Q (=BWchirp*Tchirp) was varied and, the aneurysm clip‐induced artifact was evaluated in phantom (label‐images) as well as in vivo (perfusion‐weighted signal (PWS)‐maps and temporal SNR (tSNR)). In vivo results were compared to gradient‐echo EPI (GE‐EPI) and spin‐echo EPI (SE‐EPI). The dependence of tSNR on TR was evaluated separately for SPEN and SE‐EPI. SPEN with Q ˜ 75 encodes with the same off‐resonance robustness as EPI. Results: The clip‐induced artifact with SPEN decreased with increase in Q, and was smaller compared to SE‐EPI and GE‐EPI in vivo. tSNR decreased with Q and the tSNR of GE‐EPI and SE‐EPI corresponded to SPEN with a Q‐value of approximately ˜85 and ˜108, respectively. In addition, SPEN perfusion images showed a higher tSNR (p < 0.05) for TR = 4000 ms compared to TR = 2100 ms, while SE‐EPI did not. tSNR remained relatively stable when the time between SPEN‐excitation and start of the next labeling‐module was more than ˜1000 ms. Conclusion: Feasibility of combining SPEN with pCASL imaging was demonstrated, enabling cerebral perfusion measurements with a higher robustness to field inhomogeneity (Q > 75) compared to SE‐EPI and GE‐EPI. However, the SPEN chirp‐pulse saturates incoming blood, thereby reducing pCASL labeling efficiency of the next acquisition for short TRs. Future developments are needed to enable 3D scanning. [ABSTRACT FROM AUTHOR]

The purpose of this study was to develop a self‐navigation strategy to improve scan efficiency and image quality of water/fat‐separated, diffusion‐weighted multishot echo‐planar imaging (ms‐EPI). This is accomplished by acquiring chemical shift‐encoded diffusion‐weighted data and using an appropriate water‐fat and diffusion‐encoded signal model to enable reconstruction directly from k‐space data. Multishot EPI provides reduced geometric distortion and improved signal‐to‐noise ratio in diffusion‐weighted imaging compared with single‐shot approaches. Multishot acquisitions require corrections for physiological motion‐induced shot‐to‐shot phase errors using either extra navigators or self‐navigation principles. In addition, proper fat suppression is important, especially in regions with large B0 inhomogeneity. This makes the use of chemical shift encoding attractive. However, when combined with ms‐EPI, shot‐to‐shot phase navigation can be challenging because of the spatial displacement of fat signals along the phase‐encoding direction. In this work, a new model‐based, self‐navigated water/fat separation reconstruction algorithm is proposed. Experiments in legs and in the head–neck region of 10 subjects were performed to validate the algorithm. The results are compared with an image‐based, two‐dimensional (2D) navigated water/fat separation approach for ms‐EPI and with a conventional fat saturation approach. Compared with the 2D navigated method, the use of self‐navigation reduced the shot duration time by 30%–35%. The proposed algorithm provided improved diffusion‐weighted water images in both leg and head–neck regions compared with the 2D navigator‐based approach. The proposed algorithm also produced better fat suppression compared with the conventional fat saturation technique in the B0 inhomogeneous regions. In conclusion, the proposed self‐navigated reconstruction algorithm can produce superior water‐only diffusion‐weighted EPI images with less artefacts compared with the existing methods. [ABSTRACT FROM AUTHOR]

Microvascular function is an important component in the physiology of muscle. One of the major parameters, blood perfusion, can be measured noninvasively and quantitatively by arterial spin labeling (ASL) MRI. Most studies using ASL in muscle have only reported data from a single slice, thereby assuming that muscle perfusion is homogeneous within muscle, whereas recent literature has reported proximodistal differences in oxidative capacity and perfusion. Here, we acquired pulsed ASL data in 12 healthy volunteers after dorsiflexion exercise in two slices separated distally by 7 cm. We combined this with a Look‐Locker scheme to acquire images at multiple postlabeling delays (PLDs) and with a multiecho readout to measure T2*. This enabled the simultaneous evaluation of quantitative muscle blood flow (MBF), arterial transit time (ATT), and T2* relaxation time in the tibialis anterior muscle during recovery. Using repeated measures analyses of variance we tested the effect of time, slice location, and their interaction on MBF, ATT, and T2*. Our results showed a significant difference as a function of time postexercise for all three parameters (MBF: F = 34.0, p <.0001; T2*: F = 73.7, p <.0001; ATT: F = 13.6, p <.001) and no average differences between slices over the total time postexercise were observed. The interaction effect between time postexercise and slice location was significant for MBF and T2* (F = 5.5, p = 0.02, F = 6.1, p = 0.02, respectively), but not for ATT (F = 2.2, p =.16). The proximal slice showed a higher MBF and a lower ATT than the distal slice during the first 2 min of recovery, and T2* showed a delayed response in the distal slice. These results imply a higher perfusion and faster microvascular response to exercise in the proximal slice, in line with previous literature. Moreover, the differences in ATT indicate that it is difficult to correctly determine perfusion based on a single PLD as is commonly performed in the muscle literature. [ABSTRACT FROM AUTHOR]

This review article provides an overview of a range of recent technical developments in advanced arterial spin labeling (ASL) methods that have been developed or adopted by the community since the publication of a previous ASL consensus paper by Alsop et al. It is part of a series of review/recommendation papers from the International Society for Magnetic Resonance in Medicine Perfusion Study Group. Here, we focus on advancements in readouts and trajectories, image reconstruction, noise reduction, partial volume correction, quantification of nonperfusion parameters, fMRI, fingerprinting, vessel selective ASL, angiography, deep learning, and ultrahigh field ASL. We aim to provide a high level of understanding of these new approaches and some guidance for their implementation, with the goal of facilitating the adoption of such advances by research groups and by MRI vendors. Topics outside the scope of this article that are reviewed at length in separate articles include velocity selective ASL, multiple‐timepoint ASL, body ASL, and clinical ASL recommendations. [ABSTRACT FROM AUTHOR]

This review article provides an overview of the current status of velocity‐selective arterial spin labeling (VSASL) perfusion MRI and is part of a wider effort arising from the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group. Since publication of the 2015 consensus paper on arterial spin labeling (ASL) for cerebral perfusion imaging, important advancements have been made in the field. The ASL community has, therefore, decided to provide an extended perspective on various aspects of technical development and application. Because VSASL has the potential to become a principal ASL method because of its unique advantages over traditional approaches, an in‐depth discussion was warranted. VSASL labels blood based on its velocity and creates a magnetic bolus immediately proximal to the microvasculature within the imaging volume. VSASL is, therefore, insensitive to transit delay effects, in contrast to spatially selective pulsed and (pseudo‐) continuous ASL approaches. Recent technical developments have improved the robustness and the labeling efficiency of VSASL, making it a potentially more favorable ASL approach in a wide range of applications where transit delay effects are of concern. In this review article, we (1) describe the concepts and theoretical basis of VSASL; (2) describe different variants of VSASL and their implementation; (3) provide recommended parameters and practices for clinical adoption; (4) describe challenges in developing and implementing VSASL; and (5) describe its current applications. As VSASL continues to undergo rapid development, the focus of this review is to summarize the fundamental concepts of VSASL, describe existing VSASL techniques and applications, and provide recommendations to help the clinical community adopt VSASL. [ABSTRACT FROM AUTHOR]

Background suppression (BGS) in arterial spin labeling (ASL) magnetic resonance imaging leads to a higher temporal signal‐to‐noise ratio (tSNR) of the perfusion images compared with ASL without BGS. The performance of the BGS, however, depends on the tissue relaxation times and on inhomogeneities of the scanner's magnetic fields, which differ between subjects and are unknown at the moment of scanning. Therefore, we developed a feedback loop (FBL) mechanism that optimizes the BGS for each subject in the scanner during acquisition. We implemented the FBL for 2D pseudo‐continuous ASL scans with an echo‐planar imaging readout. After each dynamic scan, the acquired ASL images were automatically sent to an external computer and processed with a Python processing tool. Inversion times were optimized on the fly using 80 iterations of the Nelder–Mead method, by minimizing the signal intensity in the label image while maximizing the signal intensity in the perfusion image. The performance of this method was first tested in a four‐component phantom. The regularization parameter was then tuned in six healthy subjects (three males, three females, age 24–62 years) and set as λ = 4 for all other experiments. The resulting ASL images, perfusion images, and tSNR maps obtained from the last 20 iterations of the FBL scan were compared with those obtained without BGS and with standard BGS in 12 healthy volunteers (five males, seven females, age 24–62 years) (including the six volunteers used for tuning of λ). The FBL resulted in perfusion images with a statistically significantly higher tSNR (2.20) compared with standard BGS (1.96) (p<5x10−3, two‐sided paired t‐test). Minimizing signal in the label image furthermore resulted in control images, from which approximate changes in perfusion signal can directly be appreciated. This could be relevant to ASL applications that require a high temporal resolution. Future work is needed to minimize the number of initial acquisitions during which the performance of BGS is reduced compared with standard BGS, and to extend the technique to 3D ASL. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Velocity-selective arterial spin labeling perfusion MRI: A review of the state of the art and recommendations for clinical implementation." The correction addresses an error in the fifth paragraph of Section 9.1, where a statement about FT-VSI (Fourier Transform Velocity-Selective Imaging) was incorrect. The corrected statement provides the accurate definition of Vcut for FT-VSI, clarifying the assumptions and conditions involved. The authors apologize for the error. [Extracted from the article]

Dynamic susceptibility contrast (DSC) MRI is clinically used to measure brain perfusion by monitoring the dynamic passage of a bolus of contrast agent through the brain. For quantitative analysis of the DSC images, the arterial input function is required. It is known that the original assumption of a linear relation between the R2(*) relaxation and the arterial contrast agent concentration is invalid, although the exact relation is as of yet unknown. Studying this relation in vitro is time‐consuming, because of the widespread variations in field strengths, MRI sequences, contrast agents, and physiological conditions. This study aims to simulate the R2(*) versus contrast concentration relation under varying physiological and technical conditions using an adapted version of an open‐source simulation tool. The approach was validated with previously acquired data in human whole blood at 1.5 T by means of a gradient‐echo sequence (proof‐of‐concept). Subsequently, the impact of hematocrit, field strength, and oxygen saturation on this relation was studied for both gradient‐echo and spin‐echo sequences. The results show that for both gradient‐echo and spin‐echo sequences, the relaxivity increases with hematocrit and field strength, while the hematocrit dependency was nonlinear for both types of MRI sequences. By contrast, oxygen saturation has only a minor effect. In conclusion, the simulation setup has proven to be an efficient method to rapidly calibrate and estimate the relation between R2(*) and gadolinium concentration in whole blood. This knowledge will be useful in future clinical work to more accurately retrieve quantitative information on brain perfusion. [ABSTRACT FROM AUTHOR]

Purpose: Current challenges of in vivo CEST imaging include overlapping signals from different pools. The overlap arises from closely resonating pools and/or the broad magnetization transfer contrast (MTC) from macromolecules. This study aimed to evaluate the feasibility of variable delay multipulse (VDMP) CEST to separately assess solute pools with different chemical exchange rates in the human brain in vivo, while mitigating the MTC. Methods: VDMP saturation buildup curves were simulated for amines, amides, and relayed nuclear Overhauser effect. VDMP data were acquired from glutamate and bovine serum albumin phantoms, and from six healthy volunteers at 7T. For the in vivo data, MTC removal was performed via a three‐pool Lorentzian fitting. Different B1 amplitudes and mixing times were used to evaluate CEST pools with different exchange rates. Results: The results show the importance of removing MTC when applying VDMP in vivo and the influence of B1 for distinguishing different pools. Finally, the optimal B1 and mixing times to effectively saturate slow‐ and fast‐exchanging components are also reported. Slow‐exchanging amides and rNOE components could be distinguished when using B1 = 1 μT and tmix = 10 ms and 40 ms, respectively. Fast‐exchanging components reached the highest saturation when using a B1 = 2.8 μT and tmix = 0 ms. Conclusion: VDMP is a powerful CEST‐editing tool, exploiting chemical exchange‐rate differences. After MTC removal, it allows separate assessment of slow‐ and fast‐exchanging solute pools in in vivo human brain. [ABSTRACT FROM AUTHOR]

Purpose: In this paper, the ability to quantify cerebral blood flow by arterial spin labeling (ASL) was studied by investigating the separation of the macrovascular and tissue component using a 2‐component model. Underlying assumptions of this model, especially the inclusion of dispersion in the analysis, were studied, as well as the temporal resolution of the ASL datasets. Methods: Four different datasets were acquired: (1) 4D ASL angiography to characterize the macrovascular component and to study dispersion modeling within this component, (2) high temporal resolution ASL data to investigate the separation of the 2 components and the effect of dispersion modelling on this separation, (3) low temporal resolution ASL dataset to study the effect of the temporal resolution on the separation of the 2 components, and (4) low temporal resolution ASL data with vascular crushing. Results: The model that included a gamma dispersion kernel had the best fit to the 4D ASL angiography. For the high temporal resolution ASL dataset, inclusion of the gamma dispersion kernel led to more signal included in the arterial blood volume map, which resulted in decreased cerebral blood flow values. The arterial blood volume and cerebral blood flow maps showed overall higher arterial blood volume values and lower cerebral blood flow values for the high temporal resolution dataset compared to the low temporal resolution dataset. Conclusion: Inclusion of a gamma dispersion kernel resulted in better fitting of the model to the data. The separation of the macrovascular and tissue component is affected by the inclusion of a gamma dispersion kernel and the temporal resolution of the ASL dataset. [ABSTRACT FROM AUTHOR]

Purpose: To develop a new water–fat separation and B0 estimation algorithm to effectively suppress the multiple resonances of fat signal in EPI. This is especially relevant for DWI where fat is often a confounding factor. Methods: Water–fat separation based on chemical‐shift encoding enables robust fat suppression in routine MRI. However, for EPI the different chemical‐shift displacements of the multiple fat resonances along the phase‐encoding direction can be problematic for conventional separation algorithms. This work proposes a suitable model approximation for EPI under B0 and fat off‐resonance effects, providing a feasible multi‐peak water–fat separation algorithm. Simulations were performed to validate the algorithm. In vivo validation was performed in 6 volunteers, acquiring spin‐echo EPI images in the leg (B0 homogeneous) and head‐neck (B0 inhomogeneous) regions, using a TE‐shifted interleaved EPI sequence with/without diffusion sensitization. The results are numerically and statistically compared with voxel‐independent water–fat separation and fat saturation techniques to demonstrate the performance of the proposed algorithm. Results: The reference separation algorithm without the proposed spatial shift correction caused water–fat ambiguities in simulations and in vivo experiments. Some spectrally selective fat saturation approaches also failed to suppress fat in regions with severe B0 inhomogeneities. The proposed algorithm was able to achieve improved fat suppression for DWI data and ADC maps in the head–neck and leg regions. Conclusion: The proposed algorithm shows improved suppression of the multi‐peak fat components in multi‐shot interleaved EPI applications compared to the conventional fat saturation approaches and separation algorithms. [ABSTRACT FROM AUTHOR]

Purpose: Multislice arterial spin labeling (ASL) MRI acquisitions are currently challenging in skeletal muscle because of long transit times, translating into low‐perfusion SNR in distal slices when large spatial coverage is required. However, fiber type and oxidative capacity vary along the length of healthy muscles, calling for multislice acquisitions in clinical studies. We propose a new variant of flow alternating inversion recovery (FAIR) that generates sufficient ASL signal to monitor exercise‐induced perfusion changes in muscle in two distant slices. Methods: Label around and between two 7‐cm distant slices was created by applying the presaturation/postsaturation and selective inversion modules selectively to each slice (split‐label multislice FAIR). Images were acquired using simultaneous multislice EPI. We validated our approach in the brain to take advantage of the high resting‐state perfusion, and applied it in the lower leg muscle during and after exercise, interleaved with a single‐slice FAIR as a reference. Results: We show that standard multislice FAIR leads to an underestimation of perfusion, while the proposed split‐label multislice approach shows good agreement with separate single‐slice FAIR acquisitions in brain, as well as in muscle following exercise. Conclusion: Split‐label FAIR allows measuring muscle perfusion in two distant slices simultaneously without losing sensitivity in the distal slice. [ABSTRACT FROM AUTHOR]

Background: Dynamic contrast‐enhanced (DCE) MRI is the most sensitive method for detection of breast cancer. However, due to high costs and retention of intravenously injected gadolinium‐based contrast agent, screening with DCE‐MRI is only recommended for patients who are at high risk for developing breast cancer. Thus, a noncontrast‐enhanced alternative to DCE is desirable. Purpose: To investigate whether velocity selective arterial spin labeling (VS‐ASL) can be used to identify increased perfusion and vascularity within breast lesions compared to surrounding tissue. Study Type: Prospective. Population: Eight breast cancer patients. Field Strength/Sequence: A 3 T; VS‐ASL with multislice single‐shot gradient‐echo echo‐planar‐imaging readout. Assessment: VS‐ASL scans were independently assessed by three radiologists, with 3–25 years of experience in breast radiology. Scans were scored on lesion visibility and artifacts, based on a 3‐point Likert scale. A score of 1 corresponded to "lesions being distinguishable from background" (lesion visibility), and "no or few artifacts visible, artifacts can be distinguished from blood signal" (artifact score). A distinction was made between mass and nonmass lesions (based on BI‐RADS lexicon), as assessed in the standard clinical exam. Statistical Tests: Intra‐class correlation coefficient (ICC) for interobserver agreement. Results: The ICC was 0.77 for lesion visibility and 0.84 for the artifact score. Overall, mass lesions had a mean score of 1.27 on lesion visibility and 1.53 on the artifact score. Nonmass lesions had a mean score of 2.11 on lesion visibility and 2.11 on the artifact score. Data Conclusion: We have demonstrated the technical feasibility of bilateral whole‐breast perfusion imaging using VS‐ASL in breast cancer patients. Evidence Level: 1 Technical Efficacy: Stage 1 [ABSTRACT FROM AUTHOR]

Purpose: Velocity-selective arterial spin labeling (VSASL) has been proposed for renal perfusion imaging to mitigate planning challenges and effects of arterial transit time (ATT) uncertainties. In VSASL, label generation may shift in the vascular tree as a function of cutoff velocity. Here, we investigate label dynamics and especially the ATT of renal VSASL and compared it with a spatially selective pulsed arterial spin labeling technique, flow alternating inversion recovery (FAIR). Methods: Arterial spin labeling data were acquired in 7 subjects, using free-breathing dual VSASL and FAIR with five postlabeling delays: 400, 800, 1200, 2000, and 2600 ms. The VSASL measurements were acquired with cutoff velocities of 5, 10, and 15 cm/s, with anterior--posterior velocity-encoding direction. Cortical perfusion-weighted signal, temporal SNR, quantified renal blood flow, and arterial transit time were reported. Results: In contrast to FAIR, renal VSASL already showed fairly high signal at the earliest postlabeling delays, for all cutoff velocities. The highest VSASL signal and temporal SNR was obtained with a cutoff velocity of 10 cm/s at postlabeling delay = 800 ms, which was earlier than for FAIR at 1200 ms. Fitted ATT on VSASL was ≤ 0 ms, indicating ATT insensitivity, which was shorter than for FAIR (189 ± 79 ms, P < .05). Finally, the average cortical renal blood flow measured with cutoff velocities of 5 cm/s (398 ± 84 mL/min/100 g) and 10 cm/s (472 ± 160 mL/min/100 g) were similar to renal blood flow measured with FAIR (441 ± 84 mL/min/100 g) (P > .05) with good correlations on subject level. Conclusion: Velocity-selective arterial spin labeling in the kidney reduces ATT sensitivity compared with the recommended pulsed arterial spin labeling method, as well as if cutoff velocity is increased to reduce spurious labeling due to motion. Thus, VSASL has potential as a method for time-efficient, single-time-point, freebreathing renal perfusion measurements, despite lower tSNR than FAIR. [ABSTRACT FROM AUTHOR]

Purpose: To determine whether sacrificing part of the scan time of pseudo‐continuous arterial spin labeling (PCASL) for measurement of the labeling efficiency and blood T1 is beneficial in terms of CBF quantification reliability. Methods: In a simulation framework, 5‐minute scan protocols with different scan time divisions between PCASL data acquisition and supporting measurements were evaluated in terms of CBF estimation variability across both noise and ground truth parameter realizations taken from the general population distribution. The entire simulation experiment was repeated for a single‐post‐labeling delay (PLD), multi‐PLD, and free‐lunch time‐encoded (te‐FL) PCASL acquisition strategy. Furthermore, a real data study was designed for preliminary validation. Results: For the considered population statistics, measuring the labeling efficiency and the blood T1 proved beneficial in terms of CBF estimation variability for any distribution of the 5‐minute scan time compared to only acquiring ASL data. Compared to single‐PLD PCASL without support measurements as recommended in the consensus statement, a 26%, 33%, and 42% reduction in relative CBF estimation variability was found for optimal combinations of supporting measurements with single‐PLD, free‐lunch, and multi‐PLD PCASL data acquisition, respectively. The benefit of taking the individual variation of blood T1 into account was also demonstrated in the real data experiment. Conclusions: Spending time to measure the labeling efficiency and the blood T1 instead of acquiring more averages of the PCASL data proves to be advisable for robust CBF quantification in the general population. [ABSTRACT FROM AUTHOR]

Purpose: For free‐breathing renal perfusion imaging using arterial spin labeling (ASL), retrospective image realignment has been found essential to reduce subtraction artifacts and, independently, background suppression has been demonstrated to reduce physiologic noise. However, negative results on ASL precision and accuracy have been reported for the combination of both. In this study, the effect of background suppression ‐level in combination with image registration on free‐breathing renal ASL signal quality, with registration either on ASL‐images themselves or guided by additionally acquired fat‐images, was investigated. The results from free‐breathing acquisitions were compared with the reference paced‐breathing motion compensation strategy. Methods: Pseudocontinuous ASL (pCASL) data with additional fat‐images were acquired from 10 subjects at 1.5T with varying background suppression levels during free‐breathing and paced‐breathing. Images were registered using the ASL‐images themselves (ASLReg) or using their corresponding fat‐images (FatReg). Temporal signal‐to‐noise ratio (tSNR) served to evaluate precision and perfusion weighted signal (PWS) to assess accuracy. Results: In combination with image registration, background suppression significantly improved tSNR by 50% (P <.05). For heavy suppression, ASLReg and FatReg showed similar performance in terms of tSNR and PWS. Background suppression with two inversion pulses induced a small, nonsignificant (P >.05) PWS reduction, but increased PWS accuracy. When applying heavy background suppression, free‐breathing acquisitions resulted in similar ASL‐quality to paced‐breathing acquisitions. Conclusion: Background suppression was found beneficial for free‐breathing renal pCASL precision without compromising accuracy, despite motion challenges. In combination with ASLReg or FatReg, background suppression enabled clinically viable free‐breathing renal pCASL. [ABSTRACT FROM AUTHOR]

Purpose: In vessel‐encoded pseudo‐continuous arterial spin labeling (ve‐pCASL), vessel‐selective labeling is achieved by modulation of the inversion efficiency across space. However, the spatial transition between the labeling and control conditions is rather gradual, which can cause partial labeling of vessels, reducing SNR‐efficiency and necessitating complex postprocessing to decode the vessel‐selective signals. The purpose of this study is to optimize the pCASL labeling parameters to obtain a sharper spatial inversion profile of the labeling and thereby minimizing the risk of partial labeling of untargeted arteries. Methods: Bloch simulations were performed to investigate how the inversion profile was influenced by the pCASL labeling parameters: the maximum (Gmax) and mean (Gmean) labeling gradient were varied for ve‐pCASL with unipolar and bipolar gradients. The findings in the simulation study were subsequently confirmed in an in vivo volunteer study. Moreover, conventional and optimized settings were compared for 4D‐MRA using four‐cycle Hadamard ve‐pCASL; the visualization of arteries and the presence of the partial labeling were assessed by an expert observer. Results: When using unipolar gradient, lower Gmean resulted in a steeper spatial transition, whereas the width of the control region was broader for higher Gmax. The in vivo study confirmed these findings. When using bipolar gradients, the control region was always very narrow. Qualitative comparison of the 4D‐MRA demonstrated lower occurrence of partial labeling when using the optimized gradient parameters. Conclusion: The shape of the ve‐pCASL inversion profile can be optimized by changing Gmean and Gmax to reduce partial labeling of untargeted arteries. [ABSTRACT FROM AUTHOR]

In the above referenced article, we would like to correct the error of the misplaced SI SB B sb term and update the Equation (1) as well as the first sentence of Section 9.5 as below: 9.5 Quantification of VSASL The blood flow (BF, in mL/100 g/min) can be quantified based on the kinetic model as: 1 HT ht Erratum to: Velocity-selective arterial spin labeling perfusion MRI: A review of the state of the art and recommendations for clinical implementation (Magn Reson Med. [Extracted from the article]

The volume transfer constant Ktrans, which describes the leakage of contrast agent (CA) from vasculature into tissue, is the most commonly reported quantitative parameter for dynamic contrast‐enhanced (DCE‐) MRI. However, the variation in reported Ktrans values between studies from different institutes is large. One of the primary sources of uncertainty is quantification of the arterial input function (AIF). The aim of this study is to determine the influence of the CA injection duration on the AIF and tracer kinetic analysis (TKA) parameters (i.e. Ktrans, kep and ve). Thirty‐one patients with prostate cancer received two DCE‐MRI examinations with an injection duration of 5 s in the first examination and a prolonged injection duration in the second examination, varying between 7.5 s and 30 s. The DCE examination was carried out on a 3.0 T MRI scanner using a transversal T1‐weighted 3D spoiled gradient echo sequence (300 s duration, dynamic scan time of 2.5 s). Data of 29 of the 31 were further analysed. AIFs were determined from the phase signal in the left and right femoral arteries. Ktrans, kep and ve were estimated with the standard Tofts model for regions of healthy peripheral zone and tumour tissue. We observed a significantly smaller peak height and increased width in the AIF for injection durations of 15 s and longer. However, we did not find significant differences in Ktrans, kep or ve for the studied injection durations. The study demonstrates that the TKA parameters Ktrans, kep and ve, measured in the prostate, do not show a significant change as a function of injection duration. [ABSTRACT FROM AUTHOR]

Purpose: Both dynamic magnetic resonance angiography (4D‐MRA) and perfusion imaging can be acquired by using arterial spin labeling (ASL). While 4D‐MRA highlights large vessel pathology, such as stenosis or collateral blood flow patterns, perfusion imaging provides information on the microvascular status. Therefore, a complete picture of the cerebral hemodynamic condition could be obtained by combining the two techniques. Here, we propose a novel technique for simultaneous acquisition of 4D‐MRA and perfusion imaging using time‐encoded pseudo‐continuous arterial spin labeling. Methods: The time‐encoded pseudo‐continuous arterial spin labeling module consisted of a first subbolus that was optimized for perfusion imaging by using a labeling duration of 1800 ms, whereas the other six subboli of 130 ms were used for encoding the passage of the labeled spins through the arterial system for 4D‐MRA acquisition. After the entire labeling module, a multishot 3D turbo‐field echo‐planar‐imaging readout was executed for the 4D‐MRA acquisition, immediately followed by a single‐shot, multislice echo‐planar‐imaging readout for perfusion imaging. The optimal excitation flip angle for the 3D turbo‐field echo‐planar‐imaging readout was investigated by evaluating the image quality of the 4D‐MRA and perfusion images as well as the accuracy of the estimated cerebral blood flow values. Results: When using 36 excitation radiofrequency pulses with flip angles of 5 or 7.5°, the saturation effects of the 3D turbo‐field echo‐planar‐imaging readout on the perfusion images were relatively moderate and after correction, there were no statistically significant differences between the obtained cerebral blood flow values and those from traditional time‐encoded pseudo‐continuous arterial spin labeling. Conclusions: This study demonstrated that simultaneous acquisition of 4D‐MRA and perfusion images can be achieved by using time‐encoded pseudo‐continuous arterial spin labeling. Magn Reson Med 79:2676–2684, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

The cerebral blood flow (CBF) is a potential biomarker for neurological disease. However, the arterial transit time (ATT) of the labeled blood is known to potentially affect CBF quantification. Furthermore, ATT could be an interesting biomarker in itself, as it may reflect underlying macro‐ and microvascular pathologies. Currently, no optimized magnetic resonance imaging (MRI) sequence exists to measure ATT in mice. Recently, time‐encoded labeling schemes have been implemented in rats and humans, enabling ATT mapping with higher signal‐to‐noise ratio (SNR) and shorter scan time than multi‐delay arterial spin labeling (ASL). In this study, we show that time‐encoded pseudo‐continuous arterial spin labeling (te‐pCASL) also enables transit time measurements in mice. As an optimal design that takes the fast blood flow in mice into account, time encoding with 11 sub‐boli of 50 ms is proposed to accurately probe the inflow of labeled blood. For perfusion imaging, a separate, traditional pCASL scan was employed. From the six studied brain regions, the hippocampus showed the shortest ATT (169 ± 11 ms) and the auditory/visual cortex showed the longest (284 ± 16 ms). Furthermore, ATT was found to be preserved in old wild‐type mice. In a mouse with an induced carotid artery occlusion, prolongation of ATT was shown. In conclusion, this study shows the successful implementation of te‐pCASL in mice, making it possible, for the first time, to measure ATT in mice in a time‐efficient manner. [ABSTRACT FROM AUTHOR]

Purpose Applications of intravoxel incoherent motion (IVIM) imaging in the brain are scarce, whereas it has been successfully applied in other organs with promising results. To better understand the cerebral IVIM signal, the diffusion properties of the arterial blood flow within different parts of the cerebral vascular tree (i.e., different generations of the branching pattern) were isolated and measured by employing an arterial spin labeling (ASL) preparation module before an IVIM readout. Methods ASL preparation was achieved by T1-adjusted time-encoded pseudo-continuous ASL (te-pCASL). The IVIM readout module was achieved by introducing bipolar gradients immediately after the excitation pulse. The results of ASL-IVIM were compared with those of conventional IVIM to improve our understanding of the signal generation process of IVIM. Results The pseudo-diffusion coefficient D* as calculated from ASL-IVIM data was found to decrease exponentially for postlabeling delays (PLDs) between 883 ms and 2176 ms, becoming relatively stable for PLDs longer than 2176 ms. The fast compartment of the conventional IVIM-experiment shows comparable apparent diffusion values to the ASL signal with PLDs between 1747 ms and 2176 ms. At the longest PLDs, the observed D* values (4.0 ± 2.8 × 10−3 mm2/s) are approximately 4.5 times higher than the slow compartment (0.90 ± 0.05 × 10−3 mm2/s) of the conventional IVIM experiment. Conclusion This study showed much more complicated diffusion properties of vascular signal than the conventionally assumed single D* of the perfusion compartment in the two-compartment model of IVIM (biexponential behavior). Magn Reson Med 79:723-729, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Purpose Noncontrast 4D-MR-angiography (MRA) using arterial spin labeling (ASL) is beneficial because high spatial and temporal resolution can be achieved. However, ASL requires acquisition of labeled and control images for each phase. The purpose of this study is to present a new accelerated 4D-MRA approach that requires only a single control acquisition, achieving similar image quality in approximately half the scan time. Methods In a multi-phase Look-Locker sequence, the first phase was used as the control image and the labeling pulse was applied before the second phase. By acquiring the control and labeled images within a single Look-Locker cycle, 4D-MRA was generated in nearly half the scan time of conventional ASL. However, this approach potentially could be more sensitive to off-resonance and magnetization transfer (MT) effects. To counter this, careful optimizations of the labeling pulse were performed by Bloch simulations. In in-vivo studies arterial visualization was compared between the new and conventional ASL approaches. Results Optimization of the labeling pulse successfully minimized off-resonance effects. Qualitative assessment showed that residual MT effects did not degrade visualization of the peripheral arteries. Conclusion This study demonstrated that the proposed approach achieved similar image quality as conventional ASL-MRA approaches in just over half the scan time. Magn Reson Med 79:224-233, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Purpose: To compare registration strategies to align arterial spin labeling (ASL) with 3D T1-weighted (T1w) images, with the goal of reducing the between-subject variability of cerebral blood flow (CBF) images.Materials and Methods: Multi-center 3T ASL data were collected at eight sites with four different sequences in the multi-center GENetic Frontotemporal dementia Initiative (GENFI) study. In a total of 48 healthy controls, we compared the following image registration options: (I) which images to use for registration (perfusion-weighted images [PWI] to the segmented gray matter (GM) probability map (pGM) (CBF-pGM) or M0 to T1w (M0-T1w); (II) which transformation to use (rigid-body or non-rigid); and (III) whether to mask or not (no masking, M0-based FMRIB software library Brain Extraction Tool [BET] masking). In addition to visual comparison, we quantified image similarity using the Pearson correlation coefficient (CC), and used the Mann-Whitney U rank sum test.Results: CBF-pGM outperformed M0-T1w (CC improvement 47.2% ± 22.0%; P < 0.001), and the non-rigid transformation outperformed rigid-body (20.6% ± 5.3%; P < 0.001). Masking only improved the M0-T1w rigid-body registration (14.5% ± 15.5%; P = 0.007).Conclusion: The choice of image registration strategy impacts ASL group analyses. The non-rigid transformation is promising but requires validation. CBF-pGM rigid-body registration without masking can be used as a default strategy. In patients with expansive perfusion deficits, M0-T1w may outperform CBF-pGM in sequences with high effective spatial resolution. BET-masking only improves M0-T1w registration when the M0 image has sufficient contrast.Level Of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:131-140. [ABSTRACT FROM AUTHOR]

An association between cerebral blood flow ( CBF) and cardiac output ( CO) has been established in young healthy subjects. As of yet it is unclear how this association evolves over the life span. To that purpose, we continuously recorded mean arterial pressure ( MAP; finger plethysmography), CO (pulse contour; CO-trek), mean blood flow velocity in the middle cerebral artery ( MCAV; transcranial Doppler ultrasonography), and end-tidal CO2 partial pressure (Pet CO2) in healthy young (19-27 years), middle-aged (51-61 years), and elderly subjects (70-79 years). Decreases and increases in CO were accomplished using lower body negative pressure and dynamic handgrip exercise, respectively. Aging in itself did not alter dynamic cerebral autoregulation or cerebrovascular CO2 reactivity. A linear relation between changes in CO and MCAVmean was observed in middle-aged ( P < 0.01) and elderly ( P = 0.04) subjects but not in young ( P = 0.45) subjects, taking concurrent changes in MAP and Pet CO2 into account. These data imply that with aging, brain perfusion becomes increasingly dependent on CO. [ABSTRACT FROM AUTHOR]

Background and uroses. The 320-detector row CT scanner enables visualization of whole-brain hemodynamic information (dynamic CT angiograhy (CTA) derived from CT erfusion scans). However, arterial image quality in dynamic CTA (dCTA) is inferior to arterial image quality in standard CTA. This study evaluates whether the arterial image quality can be imroved by using a total bolus extraction (ToBE) method. Materials and Methods. DCTAs of 15 atients, who resented with signs of acute cerebral ischemia, were derived from 320-slice CT erfusion scans using both the standard subtraction method and the roosed ToBE method. Two neurointerventionalists blinded to the scan tye scored the arterial image quality on a 5-oint scale in the 4D dCTAs in consensus. Arteries were divided into four categories: (I) large extradural, (II) intradural (large, medium, and small), (III) communicating arteries, and (IV) cerebellar and ohthalmic arteries. Results. Quality of extradural and intradural arteries was significantly higher in the ToBE dCTAs than in the standard dCTAs (extradural = 0.001, large intradural p < 0.001, medium intradural p < 0.001, and small intradural < 0.001). Conclusion. The 4D dCTAs derived with the total bolus extraction (ToBE) method rovide hemodynamic information combined with imroved arterial image quality as comared to standard 4D dCTAs. [ABSTRACT FROM AUTHOR]

Recently, a new method for perfusion territory imaging named superselective pseudo-continuous arterial spin labeling was introduced. The method uses additional time-varying gradients to create a circular labeling spot that can be adjusted in size and thus adapted to individual arteries. In this study, the additional gradients are adjusted in such a way that an elliptical labeling spot is formed, which can be applied to label the blood in multiple vessels simultaneously in conjunction with an increased labeling efficiency compared with the original superselective approach. When compared with other selective multivessel strategies, the proposed technique allows for an improved and flexible adaption of the labeling focus to different anatomical variations of the arteries in the neck so that a total of five perfusion territories from the data acquired in three measurements can be recalculated in a reduced scan time. These include not only the perfusion territories of the cerebrum but also the perfusion territories in the cerebellum fed by individual vertebral arteries. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Diffusion weighted spectroscopy can provide microstructural information that is specific to compartmental geometry. So far, in human brain, apparent diffusion coefficients (ADCs) of only the metabolites N-acetyl aspartate, creatine (tCr) and choline (tCho) have been assessed. High field MR at 7 T allows the collection and analysis of diffusion weighted spectroscopy data of additional metabolites of interest such as glutamate (Glu), N-acetyl aspartyl glutamate, and glutamine (Gln), which are of interest due to their different compartmentalization and role in brain physiology. In this study, we performed 1H diffusion weighted spectroscopy at 7 T using a diffusion-weighted PRESS sequence in parietal white matter ( n = 6) and occipital grey matter ( n = 7). Data were analyzed using the LCmodel. ADCs could reliably be obtained of N-acetyl aspartate, tCr, tCho, Glu, Gln in grey and white matter, and N-acetyl aspartyl glutamate in white matter. Significant differences in ADC values were observed between grey and white matter for all metabolites. ADCs in grey matter were consistently lower than in white matter. These differences can probably be attributed to different compartmentalization as well as to the differential impact of diffusion time on ADC of different molecules under conditions of restricted diffusion. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Correct arterial input function (AIF) measurements in dynamic susceptibility contrast-MRI are crucial for quantification of the hemodynamic parameters. Often a single global AIF is selected near a large brain-feeding artery. Alternatively, local AIF measurements aim for voxel-specific AIFs from smaller arteries. Because local AIFs are measured higher in the arterial-tree, it is assumed that these will reflect the true input of the microvasculature much better. However, do the measured local AIFs reflect the true concentration-time curves of small arteries? To answer this question, in vivo data were used to evaluate local AIF candidates selected based on two different types of angiograms. For interpretation purposes, a 3D numerical model that simulated partial-volume effects in local AIF measurements was created and the simulated local AIFs were compared to the ground truth. The findings are 2-fold. First, the in vivo data showed that the shape-characteristics of local AIFs are similar to the shape-characteristics of gray matter concentration-time curves. Second, these findings are supported by the simulations showing broadening of the measured local AIFs compared to the ground truth. These findings are suggesting that local AIF measurements do not necessarily reflect the true concentration-time curve in small arteries. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Dynamic contrast-enhanced (DCE) MRI is useful for diagnosis, treatment monitoring and follow-up of prostate cancer. However, large differences have been reported in the parameter range of the transfer constant Ktrans, making longitudinal studies and comparison of DCE-MRI findings between studies difficult. Large part of this inconsistency in Ktrans values can be attributed to problems with the accurate measurement of the arterial input function (AIF) from the magnitude signal (AIFMAGN). Phase-based AIF measurements (AIFPHASE) have been proposed as a more robust alternative to AIFMAGN measurements. This study compares AIFPHASE with AIFs measured with DCE-CT (AIFCT), and the corresponding Ktrans maps in 12 prostate cancer patients. The shape of AIFPHASE and AIFCT are similar, although differences in the peak height and peak width exist as a result of differences in injection protocol. No significant differences in Ktrans values were found between the DCE-MRI and DCE-CT exams, with median Ktrans values of 0.10 and 0.08 min−1 for healthy peripheral zone tissue and 0.44 and 0.36 min−1 for regions suspected of tumor respectively. Therefore, robust quantification of Ktrans values from DCE-MRI exams in the cancerous prostate is feasible with the use of AIFPHASE. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The article proposes a criterion that detects shape errors based on tracer kinetic principles to compute cerebral blood volume. It describes an arterial input function (AIF) selection criterion based on tracer kinetic theory that detects AIF measurements corrupted by partial volume effects (PVEs). It investigates both the reference ration value of tissue and the ratio value of AIF measurements with or without PVEs.

A new technique for the imaging of flow territories of individual extra- and intracranial arteries is presented. The method is based on balanced pseudocontinuous arterial spin labeling but employs additional time-varying gradients in between the radiofrequency pulses of the long labeling train. The direction of the additional gradient vector is perpendicular to the selected artery and its azimuthal angle is switched after every radiofrequency pulse. The phases of the radiofrequency pulses are adopted to cancel out the phase accrual of the spins at the center of the target vessel due to the extra applied gradients. This results in efficient inversion at the targeted position, whereas elsewhere time-varying phase changes will result in marginal inversion efficiency. By changing the moment of the added gradients, the size of the labeling focus can be adjusted. Influence of the temporal order of the additional gradients on the labeling efficiency and on the selectivity was investigated by simulations and experimental measurements. In a volunteer study, the acquisition of high signal-to-noise ratio flow territory images of small branches of the anterior cerebral artery distal to the circle of Willis was demonstrated. This shows the method's flexibility for dealing with complicated arterial geometries and its ability to superselectively label small intracranial arteries. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

In dynamic susceptibility contrast perfusion MRI, arterial input function (AIF) measurements using the phase of the MR signal are traditionally performed inside an artery. However, phase-based AIF selection is also feasible in tissue surrounding an artery such as the middle cerebral artery, which runs approximately perpendicular to B0 since contrast agents also induce local field changes in tissue surrounding the artery. The aim of this study was to investigate whether phase-based AIF selection is better performed in tissue just outside the middle cerebral artery than inside the artery. Additionally, phase-based AIF selection was compared to magnitude-based AIF selection. Both issues were studied theoretically and using numerical simulations, producing results that were validated using phantom experiments. Finally, an in vivo experiment was performed to illustrate the feasibility of phase-based AIF selection. Three main findings are presented: first, phase-based AIF selections are better made in tissue outside the middle cerebral artery, rather than within the middle cerebral artery, since in the latter approach partial-volume effects affect the shape of the estimated AIF. Second, optimal locations for phase-based AIF selection are similar for different clinical dynamic susceptibility contrast MRI sequences. Third, phase-based AIF selection allows more locations in tissue to be chosen that show the correct AIF than does magnitude-based AIF selection. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

In the past decade, MRI perfusion imaging has become increasingly important in the radiological clinic. Herein, arterial spin labeling (ASL) represents a truly noninvasive method for assessment of hemodynamic changes. Recently, whole body scanners that operate at a field strength of 7 Tesla or above have become available, carrying the promise of higher signal to noise ratio. In this article, we discuss the basic ASL methods that are available today and the problems that may be encountered when implementing ASL on a high field scanner. Particularly, B0 and B1 field inhomogeneities and fluctuations in precession frequency due to respiration were measured at the level of the brain feeding arteries. The effect of these disturbances on ASL is being discussed as are other issues such as specific absorption rate and relaxation rates. It can be concluded that implementation of ASL on MRI systems with high field strength is not trivial, although the feasibility of ASL measurements has been demonstrated at 7 Tesla. Further improvements can be expected, for example by the use of local labeling coils and improved shimming and preparation methods. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 62–70, 2010 [ABSTRACT FROM AUTHOR]

Perfusion imaging with pulsed arterial spin labeling techniques, like flow-sensitive alternating inversion recovery (FAIR), may suffer from inflow of fresh, i.e., unlabeled, spins. Inflow of fresh spins is caused by the arrival of unlabeled spins in the image slice and can lead to underestimation of the perfusion if not taken into account. In this study it was shown that a decrease in B1 field strength toward the edge of the transmit coil and the consequent reduction in the inversion efficiency leads to a narrowing of the arterial delivery function and a reduction in FAIR signal. Increasing the B1 amplitude of the adiabatic inversion pulse from 2.3 to 5.7 times its minimum amplitude requirement resulted in an observed increase of 40 to 80% in the rat brain FAIR signal at inflow times longer than 0.65 s. For coils with limited dimensions and significant B1 inhomogeneity over the perfusion labeling slab, the application of an excessively large B1 amplitude in combination with adiabatic inversion is recommended to optimize the FAIR perfusion contrast. Magn Reson Med 53:1355-1362, 2005. © 2005 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]