Turbo-FLASH based arterial spin labeled perfusion MRI at 7 T.

Motivations of arterial spin labeling (ASL) at ultrahigh magnetic fields include prolonged blood T1 and greater signal-to-noise ratio (SNR). However, increased B0 and B1 inhomogeneities and increased specific absorption ratio (SAR) challenge practical ASL implementations. In this study, Turbo-FLASH (Fast Low Angle Shot) based pulsed and pseudo-continuous ASL sequences were performed at 7T, by taking advantage of the relatively low SAR and short TE of Turbo-FLASH that minimizes susceptibility artifacts. Consistent with theoretical predictions, the experimental data showed that Turbo-FLASH based ASL yielded approximately 4 times SNR gain at 7T compared to 3T. High quality perfusion images were obtained with an in-plane spatial resolution of 0.85×1.7 mm(2). A further functional MRI study of motor cortex activation precisely located the primary motor cortex to the precentral gyrus, with the same high spatial resolution. Finally, functional connectivity between left and right motor cortices as well as supplemental motor area were demonstrated using resting state perfusion images. Turbo-FLASH based ASL is a promising approach for perfusion imaging at 7T, which could provide novel approaches to high spatiotemporal resolution fMRI and to investigate the functional connectivity of brain networks at ultrahigh field

ASL lexicon and reporting recommendations: A consensus report from the ISMRM Open Science Initiative for Perfusion Imaging (OSIPI)

The 2015 consensus statement published by the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group and the European Cooperation in Science and Technology ( COST) Action ASL in Dementia aimed to encourage the implementation of robust arterial spin labeling (ASL) perfusion MRI for clinical applications and promote consistency across scanner types, sites, and studies. Subsequently, the recommended 3D pseudo-continuous ASL sequence has been implemented by most major MRI manufacturers. However, ASL remains a rapidly and widely developing field, leading inevitably to further divergence of the technique and its associated terminology, which could cause confusion and hamper research reproducibility. On behalf of the ISMRM Perfusion Study Group, and as part of the ISMRM Open Science Initiative for Perfusion Imaging (OSIPI), the ASL Lexicon Task Force has been working on the development of an ASL Lexicon and Reporting Recommendations for perfusion imaging and analysis, aiming to (1) develop standardized, consensus nomenclature and terminology for the broad range of ASL imaging techniques and parameters, as well as for the physiological constants required for quantitative analysis; and (2) provide a community-endorsed recommendation of the imaging parameters that we encourage authors to include when describing ASL methods in scientific reports/papers. In this paper, the sequences and parameters in (pseudo-)continuous ASL, pulsed ASL, velocity-selective ASL, and multi-timepoint ASL for brain perfusion imaging are included. However, the content of the lexicon is not intended to be limited to these techniques, and this paper provides the foundation for a growing online inventory that will be extended by the community as further methods and improvements are developed and established

Recommended implementation of arterial spin‐labeled perfusion MRI for clinical applications: A consensus of the ISMRM perfusion study group and the European consortium for ASL in dementia

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109790/1/mrm25197.pd

Cerebral blood flow estimation from Arterial Spin Labeling MRI with Look-Locker readout: a bayesian approach

Arterial Spin Labeling (ASL) è una tecnica MRI che permette di misurare la perfusione in maniera completamente non invasiva. Diversi modelli sono stati proposti in letteratura per la quantificazione della perfusione (CBF) da acquisizioni ASL. In questo lavoro viene proposto un approccio bayesiano alla quantificazione, in grado di indirizzare al meglio le conoscenze disponibili sui parametri inclusi nel modello. Il modello standard, conosciuto anche come modello di Buxton, è stato consideratoopenEmbargo per motivi di priorità nella ricerca previo accordo con terze part

Recommendations for quantitative cerebral perfusion MRI using multi-timepoint arterial spin labeling:Acquisition, quantification, and clinical applications

Accurate assessment of cerebral perfusion is vital for understanding the hemodynamic processes involved in various neurological disorders and guiding clinical decision-making. This guidelines article provides a comprehensive overview of quantitative perfusion imaging of the brain using multi-timepoint arterial spin labeling (ASL), along with recommendations for its acquisition and quantification. A major benefit of acquiring ASL data with multiple label durations and/or post-labeling delays (PLDs) is being able to account for the effect of variable arterial transit time (ATT) on quantitative perfusion values and additionally visualize the spatial pattern of ATT itself, providing valuable clinical insights. Although multi-timepoint data can be acquired in the same scan time as single-PLD data with comparable perfusion measurement precision, its acquisition and postprocessing presents challenges beyond single-PLD ASL, impeding widespread adoption. Building upon the 2015 ASL consensus article, this work highlights the protocol distinctions specific to multi-timepoint ASL and provides robust recommendations for acquiring high-quality data. Additionally, we propose an extended quantification model based on the 2015 consensus model and discuss relevant postprocessing options to enhance the analysis of multi-timepoint ASL data. Furthermore, we review the potential clinical applications where multi-timepoint ASL is expected to offer significant benefits. This article is part of a series published by the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group, aiming to guide and inspire the advancement and utilization of ASL beyond the scope of the 2015 consensus article.</p

The Role of Arterial Spin Labelling (ASL) in Classification of Primary Adult Gliomas

Currently, the histological biopsy is the gold standard for classifying gliomas using the most recent histomolecular features. However, this process is both invasive and challenging, mainly when the lesion is in eloquent brain regions. Considering the complex interaction between the presence of the isocitrate dehydrogenase (IDH)-mutation, the upregulation of the hypoxia-induced factor (HIF), the neo-angiogenesis and the increased cellularity, perfusion MRI may be used indirectly for gliomas staging and further to predict the presence of key mutations, such as IDH. Recently, several studies have reported the subsidiary role of perfusion MRI in the prediction of gliomas histomolecular class. The three most common perfusion MRI methods are dynamic susceptibility contrast (DSC), dynamic contrast enhancement (DCE) and arterial spin labelling (ASL). Both DSC and DCE use exogenous contrast agent (CA) while ASL uses magnetically labelled blood water as an inherently diffusible tracer. ASL has begun to feature more prominently in clinical settings, as this method eliminates the need for CA and facilitates quantification of absolute cerebral blood flow (CBF). As a non-invasive, CA-free test, it can also be performed repeatedly where necessary. This makes it ideal for vulnerable patients, e.g. post-treatment oncological patients, who have reduced tolerance for high rate contrast injections and those suffering from renal insufficiency. This thesis performed a systematic review and critical appraisal of the existing ASL techniques for brain perfusion estimation, followed by a further systematic review and meta-analysis of the published studies, which have quantitatively assessed the diagnostic performance of ASL for grading preoperative adult gliomas. The repeatability of absolute tumour blood flow (aTBF) and relative TBF (rTBF) ASL-derived measurements were estimated to investigate the reliability of these ASL biomarkers in the clinical routine. Finally, utilising the radiomics pipeline analysis, the added diagnostic performance of ASL compared with CA-based MRI perfusion techniques, including DSC and DCE, and diffusion-weighted imaging (DWI) was investigated for glioma class prediction according to the WHO-2016 classification

Functional Evaluation of the Peripheral Vasculature Using Magnetic Resonance Imaging

Akin to cardiac stress testing, functional integrity of the peripheral vasculature can be interrogated by measuring the response to a stimulus. Recent reports suggest that the reactive hyperemia response, the physiologic reaction following induced ischemia, is associated with disease presence, correlated with disease severity, and may be a sensitive biomarker of pre-clinical disease. In this dissertation, an innovative, interleaved magnetic resonance imaging method is developed, termed Perfusion, Intravascular Venous Oxygen saturation, and T2* (PIVOT), which simultaneously measures microvascular perfusion, venous oxygen saturation (SvO2), and the blood-oxygen-level dependent (BOLD) signal. PIVOT is first applied in healthy subjects to demonstrate its ability to measure reactive hyperemia response dynamics. Next, reactive hyperemia perfusion is compared between the more temporally efficient pulsed arterial spin labeling (PASL) used in PIVOT and the more recently developed and preferred method for the brain, pseudo-continuous ASL (pCASL). Assessment of the impact of blood flow variability throughout the ischemia-reperfusion paradigm on pCASL perfusion quantification is investigated. Then, both PASL and pCASL sequences are used to measure reactive hyperemia perfusion in healthy subjects. No significant differences were detected between perfusion measured with PASL or pCASL despite different labeling strategies, temporal resolutions, and perfusion quantification models. Subsequently, PIVOT is combined with a velocity-encoded dual-echo GRE to create an interleaved three-slice sequence that provides quantification of bulk blood flow in the arteries and veins in addition to the traditional PIVOT measures. This new sequence, termed Velocity and PIVOT (vPIVOT) is used to investigate the relationship of blood flow in the macro- and microvasculature and muscle oxygen consumption during the transition from exercise to rest. Finally, PIVOT is applied clinically in a cohort of patients with varying degrees of severity of peripheral artery disease. Increasing disease severity was correlated with a prolongation of the hyperemic response time, measured as a lengthening of time to peak perfusion, SvO2 washout time, and time to peak T2*. In addition, peak perfusion and SvO2 upslope were significantly different between patients with PAD and healthy controls. These results suggest the potential for PIVOT to evaluate disease severity and may present a tool to assess response to therapeutic intervention

Recommendations for quantitative cerebral perfusion MRI using multi-timepoint arterial spin labeling:Acquisition, quantification, and clinical applications

Accurate assessment of cerebral perfusion is vital for understanding the hemodynamic processes involved in various neurological disorders and guiding clinical decision-making. This guidelines article provides a comprehensive overview of quantitative perfusion imaging of the brain using multi-timepoint arterial spin labeling (ASL), along with recommendations for its acquisition and quantification. A major benefit of acquiring ASL data with multiple label durations and/or post-labeling delays (PLDs) is being able to account for the effect of variable arterial transit time (ATT) on quantitative perfusion values and additionally visualize the spatial pattern of ATT itself, providing valuable clinical insights. Although multi-timepoint data can be acquired in the same scan time as single-PLD data with comparable perfusion measurement precision, its acquisition and postprocessing presents challenges beyond single-PLD ASL, impeding widespread adoption. Building upon the 2015 ASL consensus article, this work highlights the protocol distinctions specific to multi-timepoint ASL and provides robust recommendations for acquiring high-quality data. Additionally, we propose an extended quantification model based on the 2015 consensus model and discuss relevant postprocessing options to enhance the analysis of multi-timepoint ASL data. Furthermore, we review the potential clinical applications where multi-timepoint ASL is expected to offer significant benefits. This article is part of a series published by the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group, aiming to guide and inspire the advancement and utilization of ASL beyond the scope of the 2015 consensus article.</p

Recommendations for quantitative cerebral perfusion MRI using multi-timepoint arterial spin labeling: acquisition, quantification, and clinical applications

Accurate assessment of cerebral perfusion is vital for understanding the hemodynamic processes involved in various neurological disorders and guiding clinical decision-making. This guidelines article provides a comprehensive overview of quantitative perfusion imaging of the brain using multi-timepoint arterial spin labeling (ASL), along with recommendations for its acquisition and quantification. A major benefit of acquiring ASL data with multiple label durations and/or post-labeling delays (PLDs) is being able to account for the effect of variable arterial transit time (ATT) on quantitative perfusion values and additionally visualize the spatial pattern of ATT itself, providing valuable clinical insights. Although multi-timepoint data can be acquired in the same scan time as single-PLD data with comparable perfusion measurement precision, its acquisition and postprocessing presents challenges beyond single-PLD ASL, impeding widespread adoption. Building upon the 2015 ASL consensus article, this work highlights the protocol distinctions specific to multi-timepoint ASL and provides robust recommendations for acquiring high-quality data. Additionally, we propose an extended quantification model based on the 2015 consensus model and discuss relevant postprocessing options to enhance the analysis of multi-timepoint ASL data. Furthermore, we review the potential clinical applications where multi-timepoint ASL is expected to offer significant benefits. This article is part of a series published by the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group, aiming to guide and inspire the advancement and utilization of ASL beyond the scope of the 2015 consensus article

Quantification of cerebral perfusion and cerebrovascular reserve using Turbo‐QUASAR arterial spin labeling MRI

PurposeTo compare cerebral blood flow (CBF) and cerebrovascular reserve (CVR) quantification from Turbo‐QUASAR (quantitative signal targeting with alternating radiofrequency labeling of arterial regions) arterial spin labeling (ASL) and single post‐labeling delay pseudo‐continuous ASL (PCASL).MethodsA model‐based method was developed to quantify CBF and arterial transit time (ATT) from Turbo‐QUASAR, including a correction for magnetization transfer effects caused by the repeated labeling pulses. Simulations were performed to assess the accuracy of the model‐based method. Data from an in vivo experiment conducted on a healthy cohort were retrospectively analyzed to compare the CBF and CVR (induced by acetazolamide) measurement from Turbo‐QUASAR and PCASL on the basis of global and regional differences. The quality of the two ASL data sets was examined using the coefficient of variation (CoV).ResultsThe model‐based method for Turbo‐QUASAR was accurate for CBF estimation (relative error was 8% for signal‐to‐noise ratio = 5) in simulations if the bolus duration was known. In the in vivo experiment, the mean global CVR estimated by Turbo‐QUASAR and PCASL was between 63% and 64% and not significantly different. Although global CBF values of the two ASL techniques were not significantly different, regional CBF differences were found in deep gray matter in both pre‐ and postacetazolamide conditions. The CoV of Turbo‐QUASAR data was significantly higher than PCASL.ConclusionBoth ASL techniques were effective for quantifying CBF and CVR, despite the regional differences observed. Although CBF estimated from Turbo‐QUASAR demonstrated a higher variability than PCASL, Turbo‐QUASAR offers the advantage of being able to measure and control for variation in ATT