Arterial spin-labeling in routine clinical practice, part 1: technique and artifacts

Brain MRI in status epilepticus: Relevance of findings

Status epilepticus (SE) represents one of the most common neurological emergencies, associated with high mortality and an important risk of functional sequelae in survivors. Magnetic resonance imaging (MRI) offers the possibility of early and noninvasive observation of seizure-induced parenchymal disturbances secondary to the epileptic process. In the present review, we propose a descriptive and comprehensive understanding of current knowledge concerning seizure-induced MRI abnormalities in SE, also called peri-ictal MRI abnormalities (PMAs). We then discuss how PMAs, as a noninvasive biomarker, could be helpful to optimize patient prognostication in SE management. Finally, we discuss alternative promising MRI approaches, including arterial spin labeling (ASL), susceptibility-weighted imaging (SWI), dynamic contrast-enhanced (DCE) MRI and dynamic susceptibility contrast (DSC) MRI that could refine our understanding of SE, particularly in non-convulsive form.

A novel 5-stage visual rating scale for global arterial spin labeling perfusion assessment in the brain: Simplifying evaluation for clinical implementation

Objectives

The aim of this study was to develop and validate a visual rating scale for evaluating global arterial spin labeling (ASL) perfusion changes in the brain, with potential applications in a variety of conditions that impact general brain blood supply and perfusion.

Methods

We employed a five-stage scale (0 being normal and 4 indicating the most severe perfusion decline) to assess 156 patients using a 3D pulsed ASL technique. Three radiologists independently reviewed the images, and inter-rater reliability of the visual rating scale was evaluated.

Results

The ASL stages showed a consistent distribution among the patients. The inter-rater reliability among the three radiologists, as measured by the Intraclass Correlation Coefficient (ICC), was 0.982.

Conclusion

Our findings suggest that this visual rating scale can be effectively implemented in everyday practice to evaluate global perfusion changes in the context of cardiovascular diseases, cerebrovascular diseases, cerebral small vessel disease, and other conditions that alter brain vascularization and perfusion. Further research is needed to explore the full range of clinical applications and to refine the scale for optimal utility.

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

BACKGROUND

 Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI)-based technique using labeled blood-water of the brain-feeding arteries as an endogenous tracer to derive information about brain perfusion. It enables the assessment of cerebral blood flow (CBF).

METHOD

 This review aims to provide a methodological and technical overview of ASL techniques, and to give examples of clinical use cases for various diseases affecting the central nervous system (CNS). There is a special focus on recent developments including super-selective ASL (ssASL) and time-resolved ASL-based magnetic resonance angiography (MRA) and on diseases commonly not leading to characteristic alterations on conventional structural MRI (e. g., concussion or migraine).

RESULTS

 ASL-derived CBF may represent a clinically relevant parameter in various pathologies such as cerebrovascular diseases, neoplasms, or neurodegenerative diseases. Furthermore, ASL has also been used to investigate CBF in mild traumatic brain injury or migraine, potentially leading to the establishment of imaging-based biomarkers. Recent advances made possible the acquisition of ssASL by selective labeling of single brain-feeding arteries, enabling spatial perfusion territory mapping dependent on blood flow of a specific preselected artery. Furthermore, ASL-based MRA has been introduced, providing time-resolved delineation of single intracranial vessels.

CONCLUSION

 Perfusion imaging by ASL has shown promise in various diseases of the CNS. Given that ASL does not require intravenous administration of a gadolinium-based contrast agent, it may be of particular interest for investigations in pediatric cohorts, patients with impaired kidney function, patients with relevant allergies, or patients that undergo serial MRI for clinical indications such as disease monitoring.

KEY POINTS

  · ASL is an MRI technique that uses labeled blood-water as an endogenous tracer for brain perfusion imaging.. · It allows the assessment of CBF without the need for administration of a gadolinium-based contrast agent.. · CBF quantification by ASL has been used in several pathologies including brain tumors or neurodegenerative diseases.. · Vessel-selective ASL methods can provide brain perfusion territory mapping in cerebrovascular diseases.. · ASL may be of particular interest in patient cohorts with caveats concerning gadolinium administration..

The role of fetal-type posterior cerebral artery in mediating occipital and thalamic perfusion: An arterial spin labeling MRI study

BACKGROUND

The posterior cerebral artery (PCA) is key in supplying blood to the occipital lobes and significant portions of the thalamus. Some individuals present with a 'fetal-type' posterior cerebral artery (fPCA), which is associated with a higher risk of neurological disorders such as ischemic stroke. This study investigates the relationship between the presence of fPCA and arterial spin labeling (ASL) hyperperfusion patterns in the medial occipital cortex and thalami.

METHODS

MRI scans from 84 patients with no detectable radiological evidence of brain pathology were retrospectively analyzed. We investigated the association between PCA type (normal vs. fetal) and perfusion pattern (hyperperfused vs. non-hyperperfused) using Fisher's exact test.

RESULTS

Hyperperfusion in the medial occipital cortex and thalami was absent in all patients with fPCA, but present in 69% of those with normal PCA. In patients with unilateral fPCA, hyperperfusion was exclusively observed on the side with the normal PCA.

CONCLUSION

The study suggests a consistent relationship between PCA type and ASL perfusion patterns in the medial occipital cortex and thalami. Further research is warranted to explore the physiological underpinnings of these findings and their potential clinical implications. Understanding this relationship could improve the interpretation of ASL MRI and contribute to a better understanding of pathophysiological mechanisms associated with PCA variants.

Arterial Spin Labeling in Migraine: A Review of Migraine Categories and Mimics

Migraine is a complex headache characterized by changes in functional connectivity and cerebral perfusion. The perfusion changes represent a valuable domain for targeted drug therapy. Arterial spin labeling is a noncontrast imaging technique of quantifying cerebral perfusion changes in the migraine setting. In this narrative review, we will discuss the pathophysiology of the different categories of migraine, as defined by the International Classification of Headache Disorders-3 and describe a category-based approach to delineating perfusion changes in migraine on arterial spin labeling images. We will also discuss the use of arterial spin labeling to differentiate migraine from stroke and/or seizures in the adult and pediatric populations. Our systematic approach will help improve the understanding of the complicated vascular changes that occur during migraines and identify potential areas of future research.

Magnetic resonance imaging arterial spin labeling hypoperfusion with diffusion-weighted image hyperintensity is useful for diagnostic imaging of Creutzfeldt-Jakob disease

Background and objectives

Magnetic resonance imaging with arterial spin labeling (ASL) perfusion imaging is a noninvasive method for quantifying cerebral blood flow (CBF). We aimed to evaluate the clinical utility of ASL perfusion imaging to aid in the diagnosis of Creutzfeldt-Jakob disease (CJD).

Methods

This retrospective study enrolled 10 clinically diagnosed with probable sporadic CJD (sCJD) based on the National CJD Research & Surveillance Unit and EuroCJD criteria and 18 healthy controls (HCs). Diffusion-weighted images (DWIs), CBF images obtained from ASL, N-isopropyl-(123I)-p-iodoamphetamine (123IMP)-single-photon emission computed tomography (SPECT) images, and 18F-fluorodeoxyglucose (18FDG)-positron emission tomography (PET) images were analyzed. First, the cortical values obtained using volume-of-interest (VOI) analysis were normalized using the global mean in each modality. The cortical regions were classified into DWI-High (≥ +1 SD) and DWI-Normal (< +1 SD) regions according to the DWI-intensity values. The normalized cortical values were compared between the two regions for each modality. Second, each modality value was defined as ASL hypoperfusion (< -1 SD), SPECT hypoperfusion (< -1 SD), and PET low accumulation (< -1 SD). The overall agreement rate of DWIs with ASL-CBF, SPECT, and PET was calculated. Third, regression analyses between the normalized ASL-CBF values and normalized SPECT or PET values derived from the VOIs were performed using a scatter plot.

Results

The mean values of ASL-CBF (N = 10), 123IMP-SPECT (N = 8), and 18FDG-PET (N = 3) in DWI-High regions were significantly lower than those in the DWI-Normal regions (p < 0.001 for all); however, HCs (N = 18) showed no significant differences in ASL-CBF between the two regions. The overall agreement rate of DWI (high or normal) with ASL-CBF (hypoperfusion or normal) (81.8%) was similar to that of SPECT (85.2%) and PET (78.5%) in CJD. The regression analysis showed that the normalized ASL-CBF values significantly correlated with the normalized SPECT (r = 0.44, p < 0.001) and PET values (r = 0.46, p < 0.001) in CJD.

Discussion

Patients with CJD showed ASL hypoperfusion in lesions with DWI hyperintensity, suggesting that ASL-CBF could be beneficial for the diagnostic aid of CJD.

A Study to Evaluate the Role of Three-Dimensional Pseudo-Continuous Arterial Spin Labelling in Acute Ischemic Stroke

Introduction Magnetic resonance imaging (MRI) is well known to detect ischemic brain tissue and evaluate the tissue vulnerable to infarction. Diffusion-weighted imaging (DWI) has been a mainstay of stroke evaluation but has a few shortcomings, as it generally indicates only the core of ischemia and does not provide information regarding the tissue at risk or the ischemic penumbra surrounding the infarct. Perfusion imaging identifies brain tissue that has reduced blood flow as a potential target for reperfusion therapy. Arterial spin labelling (ASL) is a new non-invasive, non-contrast MRI perfusion sequence used to detect areas of hypoperfusion qualitatively and quantitatively and also identify the area at risk, i.e., the penumbra, in acute ischemic stroke. The most important component of the imaging is to determine the ischemic penumbra. One of the working definitions of penumbra is brain tissue that is ischemic but not yet infarcted and is at risk of further damage unless the flow is rapidly restored. Hence, perfusion-diffusion mismatch provides a realistic target for potential intervention. The aim of our study is to assess the role of ASL imaging in identifying the penumbra and providing insight into the management of acute ischemic stroke. Materials and methods Patients who presented with symptoms of acute ischemic stroke were included in the study, and an MRI stroke protocol comprising DWI, fluid-attenuated inversion recovery (FLAIR), ASL, and magnetic resonance angiogram (MRA) sequences was done. Post-thrombolysis, a follow-up MRI was done using DWI, ASL, and MRA to see the restoration of perfusion in the ischemic penumbra. Three-dimensional pseudo-continuous ASL (in our study, ASL refers to pseudo-continuous ASL) is included in the stroke protocol in cases of acute ischemic stroke and assessed qualitatively. Results Our study included 43 patients (n = 43), of whom 39.5% (17 patients) belong to the age group of 51-60 years and 2.3% (one patient) are in the age group of 21-30 years. All 43 cases demonstrated DWI-FLAIR mismatch, suggestive of ischemic stroke within the window period, and all 43 cases showed DWI-ASL mismatch, suggestive of a large yet potentially salvageable peri-infarct ischemic penumbra. The most common territory involved was the middle cerebral artery (MCA), and the posterior cerebral artery (PCA) was the least commonly involved territory. We had one case involving the MCA-PCA watershed zone. Conclusion Arterial spin labelling is a novel, non-invasive, non-contrast MRI sequence with the capability to provide qualitative information regarding the salvageable ischemic penumbra, and timely management prevents the progression of the penumbra. The incorporation of ASL as part of the standard neuroimaging protocol aids in the management of acute stroke, giving insight into the prediction of outcome.

Efficacy of repeat arterial spin labeling for angiogram-negative ruptured micro-arteriovenous malformation: A case report

Background:

Diagnosing ruptured micro-arteriovenous malformation (AVM) could be difficult using digital subtraction angiography (DSA) in the acute stage, and a repeat DSA is recommended in DSA-negative cases. Arterial spin labeling (ASL) is a useful noninvasive tool for detecting AVM, but the efficacy of a repeat ASL for DSA and ASL-negative ruptured micro-AVM in the acute stage is unclear. Here, we report a case of ruptured micro-AVM that was not detected in the acute stage by ASL but in the chronic stage by ASL.

Case Description:

A 43-year-old man developed right upper-extremity paralysis, and computed tomography (CT) revealed a left frontal lobe hemorrhage. Magnetic resonance imaging, including ASL, CT angiography, and DSA, showed no abnormal findings associated with hemorrhage in the acute stage. The second ASL 93 days after the hemorrhage showed a high signal on the cortical vein of the left frontal lobe and superior sagittal sinus, and subsequent DSA detected a micro-AVM in the left precentral gyrus.

Conclusion:

Repeat ASL is less invasive and useful for detecting micro-AVMs which showed no findings on ASL and DSA in the acute stage.

Radiological Differentiation Between Intracranial Meningioma and Solitary Fibrous Tumor/Hemangiopericytoma: A Systematic Literature Review

BACKGROUND

Intracranial solitary fibrous tumor (SFT) is characterized by aggressive local behavior and high post-resection recurrence rates. It is difficult to distinguish between SFT and meningiomas, which are typically benign. The goal of this study was to systematically review radiological features that differentiate meningioma and SFT.

METHODS

We performed a systematic review in accordance with PRISMA guidelines to identify studies that used imaging techniques to identify radiological differentiators of SFT and meningioma.

RESULTS

Eighteen studies with 1565 patients (SFT: 662; meningiomas: 903) were included. The most commonly used imaging modality was diffusion weighted imaging, which was reported in 11 studies. Eight studies used a combination of diffusion weighted imaging and T1- and T2-weighted sequences to distinguish between SFT and meningioma. Compared to all grades/subtypes of meningioma, SFT is associated with higher apparent diffusion coefficient, presence of narrow-based dural attachments, lack of dural tail, less peritumoral brain edema, extensive serpentine flow voids, and younger age at initial diagnosis. Tumor volume was a poor differentiator of SFT and meningioma, and overall, there were less consensus findings in studies exclusively comparing angiomatous meningiomas and SFT.

CONCLUSIONS

Clinicians can differentiate SFT from meningiomas on preoperative imaging by looking for higher apparent diffusion coefficient, lack of dural tail/narrow-based dural attachment, less peritumoral brain edema, and vascular flow voids on neuroimaging, in addition to younger age at diagnosis. Distinguishing between angiomatous meningioma and SFT is much more challenging, as both are highly vascular pathologies. Tumor volume has limited utility in differentiating between SFT and various grades/subtypes of meningioma.

MRI assessment of cerebral perfusion in clinical trials

Neurodegenerative mechanisms affect the brain through a variety of processes that are reflected as changes in brain structure and physiology. Although some biomarkers for these changes are well established, others are at different stages of development for use in clinical trials. One of the most challenging biomarkers to harmonize for clinical trials is cerebral blood flow (CBF). There are several magnetic resonance imaging (MRI) methods for quantifying CBF without the use of contrast agents, in particular arterial spin labeling (ASL) perfusion MRI, which has been increasingly applied in clinical trials. In this review, we present ASL MRI techniques, including strategies for implementation across multiple imaging centers, levels of confidence in assessing disease progression and treatment effects, and details of image analysis.

Pseudo-continuous arterial spin labeling with short post-labeling delay time sensitively reflects the hemodynamics of symptomatic patients with permanent large vessel occlusion before and after revascularization

BACKGROUND AND PURPOSE

This study evaluated the feasibility of arterial spin labeling (ASL) for diagnosing hemodynamic stroke due to permanent anterior circulation large vessel occlusion.

METHODS

Three-dimensional pseudo-continuous ASL data at two post-labeling delay (PLD) times (1.5 and 2.5 s) in patients with unilateral permanent middle cerebral artery (MCA) segment 1 (M1) or internal cerebral artery (ICA) occlusion were acquired during routine magnetic resonance angiography. Sixty-one patients with symptomatic occlusion (M1, 24; ICA, 37) and 69 patients with asymptomatic occlusion (M1, 21; ICA, 48) were enrolled. Regions of interest were automatically placed in the MCA region using a template. The respective scans were compared with asymptomatic M1 or ICA occlusion scans. The ratio of signal intensity (occlusion side/non-occlusion side) in the perfusion area of MCA (asymmetry index [AI]) was compared between both groups.

RESULTS

In both PLD groups, AI was significantly lower in symptomatic patients than in asymptomatic patients. The receiver operating characteristic curve showed moderate capacity for the prediction of symptomatic AI in both groups (area under the curve, 0.739 and 0.712, respectively). As a result of extracranial-intracranial bypass operation in 28 symptomatic (M1, eight; ICA, 20) patients, AI was significantly higher postoperatively in the PLD 1.5 s group than in the PLD 2.5 s group.

CONCLUSION

In symptomatic patients with permanent large vessel occlusion, the signal intensity ratio of pseudo-continuous ASL with short PLD sensitively reflects the hemodynamics before and after revascularization; therefore, this technique may be an alternative method in situations where PET or SPECT cannot be performed.

Insights from computational modeling on the potential hemodynamic effects of sinus rhythm versus atrial fibrillation

Atrial fibrillation (AF) is the most common clinical tachyarrhythmia, posing a significant burden to patients, physicians, and healthcare systems worldwide. With the advent of more effective rhythm control strategies, such as AF catheter ablation, an early rhythm control strategy is progressively demonstrating its superiority not only in symptoms control but also in prognostic terms, over a standard strategy (rate control, with rhythm control reserved only to patients with refractory symptoms). This review summarizes the different impacts exerted by AF on heart mechanics and systemic circulation, as well as on cerebral and coronary vascular beds, providing computational modeling-based hemodynamic insights in favor of pursuing sinus rhythm maintenance in AF patients.

Arterial transit artifacts observed on arterial spin labeling perfusion imaging of carotid artery stenosis patients: What are counterparts on symptomatology, dynamic susceptibility contrast perfusion, and digital subtraction angiography?

PURPOSE

To investigate possible relationships between the presence and location of arterial transit artifacts (ATA) and clinical symptoms, digital subtraction angiography (DSA), and dynamic susceptibility contrast (DSC) perfusion imaging abnormalities in patients with carotid artery stenosis (CAS).

METHODS

Forty-seven patients who underwent arterial spin labeling (ASL) and DSC perfusion imaging in the same period diagnosed with > 50% unilateral internal carotid artery (ICA) stenosis by DSA performed 24 h after perfusion imaging were included. The presence of ATA, localization and hypoperfusion were evaluated using ASL interpretation. Maps derived from DSC perfusion, symptomatology, stenosis rates, and collateralization findings observed in DSA were investigated. Probable relationships were evaluated.

RESULTS

ATA on ASL were detected in 68.1% (32/47); 40.6% (13/32) of ATAs were observed in the distal middle cerebral artery (MCA) trace, 50% (16/32) in the intracranial ICA and MCA traces, and 9.4% (3/32) in the intracranial ICA trace. When classifications based on the ATA presence and localization was made, qualitative and quantitative CBF, MTT, and TTP abnormalities, symptomatology, stenosis rates, and collateralization findings significantly differed between groups (p < 0.05).

CONCLUSION

The presence and localization of ATA in patients with CAS may provide essential insights into cerebral hemodynamics and the CAS severity. ATAs observed only in the distal MCA trace may represent early-stage perfusion abnormalities and a moderate level of stenosis. ATA in the ICA trace may related to a more advanced level of perfusion abnormalities, critical stenosis rates, symptom or collateralization presence.

Noninvasive Follow-up Imaging of Ruptured Pediatric Brain AVMs Using Arterial Spin-Labeling

BACKGROUND AND PURPOSE

Brain AVMs represent the main etiology of pediatric intracranial hemorrhage. Noninvasive imaging techniques to monitor the treatment effect of brain AVMs remain an unmet need. In a large cohort of pediatric ruptured brain AVMs, we aimed to investigate the role of arterial spin-labeling for the longitudinal follow-up during treatment and after complete obliteration by analyzing CBF variations across treatment sessions.

MATERIALS AND METHODS

Consecutive patients with ruptured brain AVMs referred to a pediatric quaternary care center were prospectively included in a registry that was retrospectively queried for children treated between 2011 and 2019 with unimodal or multimodal treatment (surgery, radiosurgery, embolization). We included children who underwent an arterial spin-labeling sequence before and after treatment and a follow-up DSA. CBF variations were analyzed in univariable analyses.

RESULTS

Fifty-nine children with 105 distinct treatment sessions were included. The median CBF variation after treatment was -43 mL/100 mg/min (interquartile range, -102-5.5), significantly lower after complete nidal surgical resection. Following radiosurgery, patients who were healed on the last DSA follow-up demonstrated a greater CBF decrease on intercurrent MR imaging, compared with patients with a persisting shunt at last follow-up (mean, -62 [SD, 61] mL/100 mg/min versus -17 [SD, 40.1] mL/100 mg/min; P = .02). In children with obliterated AVMs, recurrences occurred in 12% and resulted in a constant increase in CBF (mean, +89 [SD, 77] mL/100 mg/min).

CONCLUSIONS

Our results contribute data on the role of noninvasive arterial spin-labeling monitoring of the response to treatment or follow-up after obliteration of pediatric AVMs. Future research may help to better delineate how arterial spin-labeling can assist in decisions regarding the optimal timing for DSA.

Multidelay ASL of the pediatric brain

Arterial spin labeling (ASL) is a powerful noncontrast MRI technique for evaluation of cerebral blood flow (CBF). A key parameter in single-delay ASL is the choice of postlabel delay (PLD), which refers to the timing between the labeling of arterial free water and measurement of flow into the brain. Multidelay ASL (MDASL) utilizes several PLDs to improve the accuracy of CBF calculations using arterial transit time (ATT) correction. This approach is particularly helpful in situations where ATT is unknown, including young subjects and slow-flow conditions. In this article, we discuss the technical considerations for MDASL, including labeling techniques, quantitative metrics, and technical artefacts. We then provide a practical summary of key clinical applications with real-life imaging examples in the pediatric brain, including stroke, vasculopathy, hypoxic-ischemic injury, epilepsy, migraine, tumor, infection, and metabolic disease.

Brain Perfusion Alterations on 3D Pseudocontinuous Arterial Spin-Labeling MR Imaging in Patients with Autoimmune Encephalitis: A Case Series and Literature Review

Autoimmune encephalitis is a heterogeneous group of newly identified disorders that are being diagnosed with increasing frequency. Early recognition and treatment of autoimmune encephalitis are crucial for patients, but diagnosis remains challenging and time-consuming. In this retrospective case series, we describe the findings of conventional MR imaging and 3D pseudocontinuous arterial spin-labeling in patients with autoimmune encephalitis confirmed by antibody testing. All patients with autoimmune encephalitis showed increased CBF in the affected area, even when some of them presented with normal or slightly abnormal findings on conventional MR imaging. Additionally, serial 3D pseudocontinuous arterial spin-labeling showed perfusion reduction in 1 patient after therapy. For patients with highly suspected autoimmune encephalitis, 3D pseudocontinuous arterial spin-labeling may be added to the clinical work-up. Further studies and longitudinal data are needed to corroborate whether and to what extent 3D pseudocontinuous arterial spin-labeling improves the diagnostic work-up in patients with autoimmune encephalitis compared with conventional MR imaging.

Arterial Spin Labeling for Pediatric Central Nervous System Diseases: Techniques and Clinical Applications

Dynamic susceptibility contrast (DSC) and arterial spin labeling (ASL) are techniques used to evaluate brain perfusion using MRI. DSC requires dynamic image acquisition with a rapid administration of gadolinium-based contrast agent. In contrast, ASL obtains brain perfusion information using magnetically labeled blood water as an endogenous tracer. For the evaluation of brain perfusion in pediatric neurological diseases, ASL has a significant advantage compared to DSC, CT, and single-photon emission CT/positron emission tomography because of the lack of radiation exposure and contrast agent administration. However, in ASL, optimization of several parameters, including the type of labeling, image acquisition, background suppression, and postlabeling delay, is required, because they have a significant effect on the quantification of cerebral blood flow (CBF).In this article, we first review recent technical developments of ASL and age-dependent physiological characteristics in pediatric brain perfusion. We then review the clinical implementation of ASL in pediatric neurological diseases, including vascular diseases, brain tumors, acute encephalopathy with biphasic seizure and late reduced diffusion (AESD), and migraine. In moyamoya disease, ASL can be used for brain perfusion and vessel assessment in pre- and post-treatment. In arteriovenous malformations, ASL is sensitive to detect small degrees of shunt. Furthermore, in vascular diseases, the implementation of ASL-based time-resolved MR angiography is described. In neoplasms, ASL-derived CBF has a high diagnostic accuracy for differentiation between low- and high-grade pediatric brain tumors. In AESD and migraine, ASL may allow for accurate early diagnosis and provide pathophysiological information.

Preoperative Collateral Perfusion Using Arterial Spin Labeling: A Predictor of Surgical Collaterals in Moyamoya Angiopathy

Objectives

Various degrees of surgical collateral circulation are often found in moyamoya angiopathy (MMA) patients after revascularization. Little is known about arterial spin labeling (ASL) that affects surgical collateral circulation. This study aimed to investigate the effect of ASL on surgical collaterals in patients with MMA after combined bypass surgery.

Methods

MMA patients with complete radiological and clinical information, who had undergone combined bypass, were enrolled in this study. Surgical collaterals were classified as good or poor based on the Matsushima standard. Cerebral perfusion on ASL was quantitatively analyzed as relative cerebral blood flow (rCBF). The qualitative collateral score was calculated using a four-grade scale. Univariable and multivariable logistic regressions were performed to identify the predictors for surgical collaterals after combined bypass.

Results

In total, 66 hemispheres of 61 patients (47 years old ± 8.66) were prospectively included (29 and 37 hemispheres with good and poor surgical collaterals, respectively). The presurgical collateral score was significantly lower in patients with good surgical collaterals (13.72 scores ± 7.83) than in those with poor surgical collaterals (19.16 scores ± 6.65, P = 0.005). The presurgical rCBF and modified Rankin scale (mRS) scores were not significantly different between the two groups (P_rCBF = 0.639, P_mRS = 0.590). The collateral score was significantly elevated (good: 13.72 scores ± 7.83 vs. 20.79 scores ± 6.65, P < 0.001; poor: 19.16 scores ± 6.65 vs. 22.84 scores ± 5.06, P < 0.001), and the mRS was reduced (good: 1.66 scores ± 1.14 vs. 0.52 scores ± 0.83, P < 0.001; poor: 1.49 scores ± 0.90 vs. 0.62 scores ± 0.76, P < 0.001) in patients after revascularization. Multivariable logistic regression showed that preoperative collateral scores [odds ratio (OR): 0.791; 95% confidence interval (CI): 0.695, 0.900; P < 0.001], age (OR: 0.181; 95% CI: 0.039, 0.854; P = 0.031), sex (OR: 0.154; 95% CI: 0.035, 0.676; P = 0.013), and hypertension (OR: 0.167; 95% CI: 0.038, 0.736; P = 0.018) were predictors of surgical collaterals after combined revascularization.

Conclusion

The preoperative collateral score based on ASL could be a predictor for surgical collaterals in patients with MMA after combined bypass surgery. Combined with age, sex, and hypertension, it may have a better predictive effect.

Added Value of Arterial Spin Labeling in Detecting Posterior Reversible Encephalopathy Syndrome as a Stroke Mimic on Baseline Neuroimaging: A Single Center Experience

Differentiating stroke from stroke mimics is a diagnostic challenge in every day practice. Posterior Reversible Encephalopathy Syndrome (PRES) is an important stroke mimic with nonspecific symptomatology, making prompt and accurate diagnosis challenging. Baseline neuroimaging plays a pivotal role in detection and differentiation of stroke from many common mimics and is thus critical in guiding appropriate management. In particular, MR perfusion (MRP) imaging modalities provide added value through detection and quantification of multiple physiological parameters. Arterial Spin Labeling (ASL) is a non-contrast, noninvasive MRP technique increasingly used in clinical practice; however, there is limited description of ASL in PRES in the existing literature. In this single center retrospective pilot study, we investigate the added value of ASL in detecting PRES in the largest series to date. We hope this study can serve as the basis for larger scale investigations exploring the utility of ASL in detecting stroke mimics such as PRES for accurate and efficient management of such patients.

Pearls and Pitfalls in Arterial Spin Labeling Perfusion-Weighted Imaging in Clinical Pediatric Imaging

Characteristic arterial spin labeling (ASL) perfusion patterns are seen in a wide variety of pediatric brain pathologies, highlighting the potential added value and prognostic role of this magnetic resonance imaging (MRI) perfusion-weighted imaging modality. Our objective is to review the basic clinical physics, technical underpinnings, and artifacts and challenges as we highlight some of the most clinically relevant pathologies to the application of ASL in the pediatric setting.

Arterial spin labeling signal ratio between the lesion and contralateral sides for evaluation of acute middle cerebral artery infarct

The purpose of our study was to differentiate arterial transit artifact from post-recanalization luxury perfusion on arterial spin labeling (ASL) image, and obtain the relationship between ASL signal intensity and clinical outcomes in patients with acute ischemic stroke.Thirty-five subjects with an acute middle cerebral artery (MCA) infarct were enrolled (18 with recanalized and 17 with non-recanalized MCAs). ASL images were obtained using pseudo-continuous ASL technique with 1600 ms (millisecond) of post-label delay within 3 days from symptom onset. Signal intensities on color ASL images were classified as high, intermediate, and poor grade visually. The ratio of maximum ASL signal between the ischemic area and contralateral side was calculated and compared between patients with and without MCA recanalization. Among patients with non-recanalized MCA, ASL signal ratios were compared between patients with and without hyperintense vessel sign on fluid attenuated inversion recovery (FLAIR). Also, correlation between the ASL signal ratio and National Institutes of Health Stroke Scale (NIHSS) score was evaluated.High or intermediate grade on color ASL images were more frequently found in patients with recanalized MCA (P < .01). Patients with non-recanalized MCA had higher ASL signal ratio in overall ASL signal grade (P = .010) and intermediate grade (P = .011). Among patients with non-recanalized MCA, those with hyperintense vessel sign on FLAIR had higher ASL signal ratios (P = .049). ASL signal ratio was negatively correlated with both initial (P = .023) and final (P = .003) NIHSS scores.The ASL signal ratio could help to differentiate between the pial collaterals and post-recanalization luxury perfusion. A higher ASL ratio was related with the hyperintense vessel sign on FLAIR and lower NIHSS score.

Efficacy of arterial spin labeling for detection of the ruptured micro-arteriovenous malformation: illustrative cases

BACKGROUND

Diagnosis of a microarteriovenous malformation (micro-AVM) is difficult, especially in the acute stage of rupture because of the small size of the nidus and the existence of hematoma. We report two cases of ruptured micro-AVMs detected by arterial spin labeling (ASL).

OBSERVATIONS

In one case, a 45-year-old male was transported with a complaint of right hemiparesis. Computed tomography (CT) revealed a right parietal lobar hemorrhage. Standard magnetic resonance imaging (MRI) showed no abnormal findings as the cause of the hemorrhage. ASL 23 days after the onset demonstrated high signals on the medial wall of the hematoma. Digital subtraction angiography (DSA) showed a micro-AVM in accordance with the site of high signals on ASL. In another case, a 38-year-old female was transported with a complaint of left hemianopsia. CT on admission revealed a right parietal lobar hemorrhage. Standard MRI showed no abnormal findings as the cause of the hemorrhage. ASL 15 days after the onset demonstrated high signals on the internal wall of the hematoma. DSA showed micro-AVM in accordance with the site of high signaling on ASL. Both cases were successfully treated with open surgery.

LESSONS

ASL can manifest micro-AVMs as high signals within the hematoma. ASL is a useful less-invasive screening tool for the detection of ruptured micro-AVMs.

Feasibility of arterial spin labeling in evaluating high- and low-flow peripheral vascular malformations: a case series

We present a case series highlighting a novel use of arterial spin labeling (ASL), a MRI perfusion technique, to evaluate both high- and low-flow peripheral vascular malformations (PVMs) across a range of anatomical locations. While the role of ASL in assessing intracranial vascular malformations is more established, there is limited evidence for PVMs. Our results provide preliminary evidence for the feasibility of ASL in imaging PVMs and its potential ability to distinguish between high- and low-flow PVMs. In addition, we demonstrate its ability to identify focal high blood flow, which may indicate the nidus in arteriovenous malformations. Together, these findings have important implications for patient management. We also outline the potential benefits and limitations of ASL in the imaging of PVMs, and provide justification for further validation of its diagnostic performance.

A case of recurrent cavernous sinus dural arteriovenous fistula arising after superselective shunt occlusion and detected by venous arterial spin labeling

Background:

Superselective shunt occlusion (SSSO) for cavernous sinus dural arteriovenous fistula (CSDAVF) avoids the risk of cranial nerve palsy, unlike entire sinus packing, but requires paying attention to recurrence. Distinguishing between true and paradoxical worsening of postoperative ophthalmic symptoms using a less-invasive modality is often difficult. Here, we report a case of true worsening of neuro-ophthalmic symptom by recurrent CSDAVF detected by venous-arterial spin labeling (ASL) on magnetic resonance imaging.

Case Description:

A 55-year-old woman with neither contributory medical history nor previous head trauma presented with neuro-ophthalmic symptoms and pulsatile tinnitus. Digital subtraction angiography (DSA) revealed CSDAVF with multiple shunted pouches. She underwent successful transvenous SSSO, but neuroophthalmic symptom worsened after SSSO and venous-ASL revealed increased signal intensity in the right superior orbital vein (SOV). DSA confirmed recurrent CSDAVF and additional transvenous embolization was performed. Neuro-ophthalmic symptoms and venous-ASL hyperintensity on SOV improved postoperatively.

Conclusion:

Venous-ASL is noninvasive and seems useful for detecting true worsening of neuro-ophthalmic symptoms of recurrent CSDAVF.

Advanced Magnetic Resonance Imaging in Pediatric Glioblastomas

The shortly upcoming 5th edition of the World Health Organization Classification of Tumors of the Central Nervous System is bringing extensive changes in the terminology of diffuse high-grade gliomas (DHGGs). Previously "glioblastoma," as a descriptive entity, could have been applied to classify some tumors from the family of pediatric or adult DHGGs. However, now the term "glioblastoma" has been divested and is no longer applied to tumors in the family of pediatric types of DHGGs. As an entity, glioblastoma remains, however, in the family of adult types of diffuse gliomas under the insignia of "glioblastoma, IDH-wildtype." Of note, glioblastomas still can be detected in children when glioblastoma, IDH-wildtype is found in this population, despite being much more common in adults. Despite the separation from the family of pediatric types of DHGGs, what was previously labeled as "pediatric glioblastomas" still remains with novel labels and as new entities. As a result of advances in molecular biology, most of the previously called "pediatric glioblastomas" are now classified in one of the four family members of pediatric types of DHGGs. In this review, the term glioblastoma is still apocryphally employed mainly due to its historical relevance and the paucity of recent literature dealing with the recently described new entities. Therefore, "glioblastoma" is used here as an umbrella term in the attempt to encompass multiple entities such as astrocytoma, IDH-mutant (grade 4); glioblastoma, IDH-wildtype; diffuse hemispheric glioma, H3 G34-mutant; diffuse pediatric-type high-grade glioma, H3-wildtype and IDH-wildtype; and high grade infant-type hemispheric glioma. Glioblastomas are highly aggressive neoplasms. They may arise anywhere in the developing central nervous system, including the spinal cord. Signs and symptoms are non-specific, typically of short duration, and usually derived from increased intracranial pressure or seizure. Localized symptoms may also occur. The standard of care of "pediatric glioblastomas" is not well-established, typically composed of surgery with maximal safe tumor resection. Subsequent chemoradiation is recommended if the patient is older than 3 years. If younger than 3 years, surgery is followed by chemotherapy. In general, "pediatric glioblastomas" also have a poor prognosis despite surgery and adjuvant therapy. Magnetic resonance imaging (MRI) is the imaging modality of choice for the evaluation of glioblastomas. In addition to the typical conventional MRI features, i.e., highly heterogeneous invasive masses with indistinct borders, mass effect on surrounding structures, and a variable degree of enhancement, the lesions may show restricted diffusion in the solid components, hemorrhage, and increased perfusion, reflecting increased vascularity and angiogenesis. In addition, magnetic resonance spectroscopy has proven helpful in pre- and postsurgical evaluation. Lastly, we will refer to new MRI techniques, which have already been applied in evaluating adult glioblastomas, with promising results, yet not widely utilized in children.

Collicular Hyperactivation in Patients with COVID-19: A New Finding on Brain MRI and PET/CT

Hyperactivation of the colliculi has been observed in some patients with coronavirus disease 2019.

Human microvascular reactivity: a review of vasomodulating stimuli and non-invasive imaging assessment

The microvasculature serves an imperative function in regulating perfusion and nutrient exchange throughout the body, adaptively altering blood flow to preserve hemodynamic and metabolic homeostasis. Its normal functioning is vital to tissue health, whereas its dysfunction is present in many chronic conditions, including diabetes, heart disease, and cognitive decline. As microvascular dysfunction often appears early in disease progression, its detection can offer early diagnostic information. To detect microvascular dysfunction, one uses imaging to probe the microvasculature's ability to react to a stimulus, also known as microvascular reactivity (MVR). An assessment of MVR requires an integrated understanding of vascular physiology, techniques for stimulating reactivity, and available imaging methods to capture the dynamic response. Practical considerations, including compatibility between the selected stimulus and imaging approach, likewise require attention. In this review, we provide a comprehensive foundation necessary for informed imaging of MVR, with a particular focus on the challenging endeavor of assessing microvascular function in deep tissues.

Brain perfusion magnetic resonance imaging using pseudocontinuous arterial spin labeling in 314 dogs and cats

Background

Arterial spin labeling (ASL) is a noninvasive brain perfusion magnetic resonance imaging (MRI) technique that has not been assessed in clinical veterinary medicine.

Hypothesis/Objectives

To test the feasibility of ASL using a 1.5 Tesla scanner and provide recommendations for optimal quantification of cerebral blood flow (CBF) in dogs and cats.

Animals

Three hundred fourteen prospectively selected client‐owned dogs and cats.

Methods

Each animal underwent brain MRI including morphological sequences and ≥1 ASL sequences using different sites of blood labeling and postlabeling delays (PLD). Calculated ASL success rates were compared. The CBF was quantified in animals that had morphologically normal brain MRI results and parameters of ASL optimization were investigated.

Results

Arterial spin labeling was easily implemented with an overall success rate of 95% in animals with normal brain MRI. Technical recommendations included (a) positioning of the imaging slab at the foramen magnum and (b) selected PLD of 1025 ms in cats and dogs <7 kg, 1525 ms in dogs 7 to 38 kg, and 2025 ms in dogs >38 kg. In 37 dogs, median optimal CBF in the cortex and thalamic nuclei were 114 and 95 mL/100 g/min, respectively. In 28 cats, median CBF in the cortex and thalamic nuclei were 113 and 114 mL/100 g/min, respectively.

Conclusions and Clinical Importance

Our survey of brain perfusion ASL‐MRI demonstrated the feasibility of ASL at 1.5 Tesla, suggested technical recommendations and provided CBF values that should be helpful in the characterization of various brain diseases in dogs and cats.

Cerebral Hemodynamic Correlates of Transcutaneous Auricular Vagal Nerve Stimulation in Consciousness Restoration: An Open-Label Pilot Study

This study aimed to preliminarily illustrate the cerebral hemodynamic correlates of transcutaneous auricular vagal nerve stimulation (taVNS) in consciousness restoration. Arterial spin labeling (ASL) was adopted with functional magnetic resonance imaging (fMRI) to measure cerebral blood flow (CBF) changes before and after taVNS in 10 qualified patients with disorders of consciousness (DOC). Before taVNS, five patients responded to auditory stimuli (RtAS), and five did not respond to auditory stimuli (nRtAS). The RtAS DOC patients obtained favorable prognoses after the 4-week taVNS treatment, whereas the nRtAS ones did not. Simultaneously, taVNS increased CBF of multiple brain regions in the RtAS DOC patients, but hardly in the nRtAS ones. In conclusion, the preserved auditory function might be the prior key factor of the taVNS responders in DOC patients, and taVNS might alleviate RtAS DOC by activating the salience network, the limbic system, and the interoceptive system.

Visualization of incidentally imaged pituitary gland on three-dimensional arterial spin labeling of the brain

OBJECTIVE

To evaluate the visualization of incidentally imaged normal pituitary gland on three-dimensional (3D) pseudo continuous arterial spin labeling (PCASL) perfusion imaging of the brain.

METHODS

Ninety-three patients with a normal pituitary gland who underwent 3D PCASL for suspected brain diseases were retrospectively included. Visualization of the pituitary gland on PCASL cerebral blood flow (CBF) maps was assessed independently by two observers using a three-point grading system: Grade 1, pituitary CBF ≤ CBF of the cerebral white matter (WM); Grade 2, CBF of WM < pituitary CBF ≤ CBF of the cortical gray matter (GM); and Grade 3, CBF of GM < pituitary CBF. The interobserver agreement of visual grading was determined using weighted κ statistic. The associations of visual grades with age, sex, and pituitary volume were assessed using multivariate logistic regression. Pituitary glands were divided equally into three groups (small, medium, and large) according to their volume for categorization.

RESULTS

The interobserver agreement for visual rating was excellent (weighted κ = 0.823). Of the 93 cases, Grades 1, 2, and 3 included 17 (18.3%), 41 (44.1%), and 35 cases (37.6%), respectively. Medium and large pituitary volume were significantly associated with Grade 3 visualization (p = 0.0153, OR = 4.8323; 95% CI: 1.3525, 17.2649 and p = 0.0009; OR = 9.0299; 95% CI: 2.4663, 33.0614, respectively), whereas there was no significant association for age or sex.

CONCLUSION

The normal pituitary gland is often visualized with higher CBF than cortical GM on 3D PCASL, especially in individuals with larger pituitary volume.

ADVANCES IN KNOWLEDGE

Appearance of the normal pituitary gland on 3D PCASL has been documented for the first time.

Novel Thoracic MRI Approaches for the Assessment of Pulmonary Physiology and Inflammation

Excessive pulmonary inflammation can lead to damage of lung tissue, airway remodelling and established structural lung disease. Novel therapeutics that specifically target inflammatory pathways are becoming increasingly common in clinical practice, but there is yet to be a similar stepwise change in pulmonary diagnostic tools. A variety of thoracic magnetic resonance imaging (MRI) tools are currently in development, which may soon fulfil this emerging clinical need for highly sensitive assessments of lung structure and function. Given conventional MRI techniques are poorly suited to lung imaging, alternate strategies have been developed, including the use of inhaled contrast agents, intravenous contrast and specialized lung MR sequences. In this chapter, we discuss technical challenges of performing MRI of the lungs and how they may be overcome. Key thoracic MRI modalities are reviewed, namely, hyperpolarized noble gas MRI, oxygen-enhanced MRI (OE-MRI), ultrashort echo time (UTE) MRI and dynamic contrast-enhanced (DCE) MRI. Finally, we consider potential clinical applications of these techniques including phenotyping of lung disease, evaluation of novel pulmonary therapeutic efficacy and longitudinal assessment of specific patient groups.

Usefulness of arterial spin labeling in the evaluation for dural arteriovenous fistula of the craniocervical junction

In the diagnosis of an intracranial dural arteriovenous fistula (DAVF), arterial spin labeling (ASL), a sequence of magnetic resonance imaging (MRI) to depict high-blood-flow intracranial lesions, has been reported as a useful and noninvasive tool, not only to predict the presence of cortical venous drainage and draining veins, but also to confirm persistent obliteration after treatment. However, such utility of ASL has not been reported in DAVF of the craniocervical junction (CCJDAVF) because of the rarity of this disease and uncertainty in the acquisition of precise images.

We report a case of CCJDAVF presenting with myelopathy. Preoperative ASL images showed an abnormal high-intensity signal in the craniocervical junction, consistent with the anterior spinal vein and draining veins, which were also identified by digital subtraction angiography. After successful surgical treatment for the disease, MRI and 4-dimensional computed tomography angiography (4DCTA) confirmed complete disappearance of CCJDAVF. The ASL images also showed no abnormal intensity signal. The patient was followed-up using ASL, and no recurrence of high-intensity signal was observed.

As repetitive image examination is mandatory in the follow-up of a patient with DAVF to exclude recurrence, ASL is highly beneficial because of the unnecessity of an exogenous contrast medium and high credibility to depict the disease. The craniocervical junction may be out of the field of view in routine MRI. Special attention must be paid to setting the field of view and post labeling delay (PLD) to obtain precise images of ASL in CCJDAVF.

Increased beat-to-beat variability of cerebral microcirculatory perfusion during atrial fibrillation: a near-infrared spectroscopy study

AIMS

Atrial fibrillation (AFib) is associated with cognitive decline/dementia, independently from clinical strokes or transient ischaemic attacks (TIA). Recent in silico data suggested that AFib may induce transient critical haemodynamic events in the cerebral microcirculation. The aim of this study is to use non-invasive spatially resolved cerebral near-infrared spectroscopy (SRS-NIRS) to investigate in vivo beat-to-beat microcirculatory perfusion during AFib and after sinus rhythm (SR) restoration.

METHODS AND RESULTS

Cerebral SRS-NIRS with high-frequency sampling (20 Hz) and non-invasive systemic haemodynamic monitoring were recorded before and after elective electrical cardioversion (ECV) for AFib or atrial flutter (AFL). To assess beat-to-beat effects of the rhythm status, the frequency distribution of inter-beat differences in tissue haemoglobin index (THI), a proxy of microcirculatory cerebral perfusion, was compared before and after SR restoration. Fifty-three AFib/AFL patients (mean age 69 ± 8 years, 79% males) were ultimately enrolled. Cardioversion was successful in restoring SR in 51 (96%) patients. In front of a non-significant decrease in arterial blood pressure extreme events between pre- and post-ECV measurements, a significant decrease of both hypoperfusive and hyperperfusive/hypertensive microcirculatory events was observed after SR restoration (P < 0.001 and P = 0.041, respectively).

CONCLUSION

The present is the first in vivo demonstration that SR restoration by ECV significantly reduces the burden of extreme single-beat haemodynamic events in cerebral microcirculation. Future studies are needed to assess whether SR maintenance might slow long-term AFib-correlated cognitive decline/dementia.

Spatial dependency and the role of local susceptibility for velocity selective arterial spin labeling (VS-ASL) relative tagging efficiency using accelerated 3D radial sampling with a BIR-8 preparation

PURPOSE

Velocity selective arterial spin labeling (VS-ASL) is a promising approach for non-contrast perfusion imaging that provides robustness to vascular geometry and transit times; however, VS-ASL assumes spatially uniform tagging efficiency. This work presents a mapping approach to investigate VS-ASL relative tagging efficiency including the impact of local susceptibility effects on a BIR-8 preparation.

METHODS

Numerical simulations of tagging efficiency were performed to evaluate sensitivity to regionally varying local susceptibility gradients and blood velocity. Tagging efficiency mapping was performed in susceptibility phantoms and healthy human subjects (N = 7) using a VS-ASL preparation module followed by a short, high spatial resolution 3D radial-based image acquisition. Tagging efficiency maps were compared to 4D-flow, B₁ , and B₀ maps acquired in the same imaging session for six of the seven subjects.

RESULTS

Numerical simulations were found to predict reduced tagging efficiency with the combination of high blood velocity and local gradient fields. Phantom experiments corroborated numerical results. Relative efficiency mapping in normal volunteers showed unique efficiency patterns depending on individual subject anatomy and physiology. Uniform tagging efficiency was generally observed in vivo, but reduced efficiency was noted in regions of high blood velocity and local susceptibility gradients.

CONCLUSION

We demonstrate an approach to map the relative tagging efficiency and show application of this methodology to a novel BIR-8 preparation recently proposed in the literature. We present results showing rapid flow in the presence of local susceptibility gradients can lead to complicated signal modulations in both tag and control images and reduced tagging efficiency.

Disrupted Regional Cerebral Blood Flow and Functional Connectivity in Pontine Infarction: A Longitudinal MRI Study

Abnormal cerebral blood flow (CBF) and resting-state functional connectivity (rs-FC) are sensitive biomarkers of disease progression and prognosis. This study investigated neural underpinnings of motor and cognitive recovery by longitudinally studying the changes of CBF and FC in pontine infarction (PI). Twenty patients underwent three-dimensional pseudo-continuous arterial spin labeling (3D-pcASL), resting-state functional magnetic resonance imaging (rs-fMRI) scans, and behavioral assessments at 1 week, 1, 3, and 6 months after stroke. Twenty normal control (NC) subjects underwent the same examination once. First, we investigated CBF changes in the acute stage, and longitudinal changes from 1 week to 6 months after PI. Brain regions with longitudinal CBF changes were then used as seeds to investigate longitudinal FC alterations during the follow-up period. Compared with NC, patients in the left PI (LPI) and right PI (RPI) groups showed significant CBF alterations in the bilateral cerebellum and some supratentorial brain regions at the baseline stage. Longitudinal analysis revealed that altered CBF values in the right supramarginal (SMG_R) for the LPI group, while the RPI group showed significantly dynamic changes of CBF in the left calcarine sulcus (CAL_L), middle occipital gyrus (MOG_L), and right supplementary motor area (SMA_R). Using the SMG_R as the seed in the LPI group, FC changes were found in the MOG_L, middle temporal gyrus (MTG_L), and prefrontal lobe (IFG_L). Correlation analysis showed that longitudinal CBF changes in the SMG_R and FC values between the SMG_R and MOG_L were associated with motor and memory scores in the LPI group, and longitudinal CBF changes in the CAL_L and SMA_R were related to memory and motor recovery in the RPI group. These longitudinal CBF and accompany FC alterations may provide insights into the neural mechanism underlying functional recovery after PI, including that of motor and cognitive functions.

Arterial Spin Labeling Applications in Pediatric and Adult Neurologic Disorders

Arterial spin labeling (ASL) is a powerful noncontrast magnetic resonance imaging (MRI) technique that enables quantitative evaluation of brain perfusion. To optimize the clinical and research utilization of ASL, radiologists and physicists must understand the technical considerations and age-related variations in normal and disease states. We discuss advanced applications of ASL across the lifespan, with example cases from children and adults covering a wide variety of pathologies. Through literature review and illustrated clinical cases, we highlight the subtleties as well as pitfalls of ASL interpretation. First, we review basic physical principles, techniques, and artifacts. This is followed by a discussion of normal perfusion variants based on age and physiology. The three major categories of perfusion abnormalities-hypoperfusion, hyperperfusion, and mixed patterns-are covered with an emphasis on clinical interpretation and relationship to the disease process. Major etiologies of hypoperfusion include large artery, small artery, and venous disease; other vascular conditions; global hypoxic-ischemic injury; and neurodegeneration. Hyperperfusion is characteristic of vascular malformations and tumors. Mixed perfusion patterns can be seen with epilepsy, migraine, trauma, infection/inflammation, and toxic-metabolic encephalopathy. LEVEL OF EVIDENCE: 4 TECHNICAL EFFICACY STAGE: 3.

A pictorial review of brain arterial spin labelling artefacts and their potential remedies in clinical studies

Arterial spin labelling is an emerging non-invasive magnetic resonance imaging technique for estimating the cerebral perfusion without the requirement for gadolinium-based intravenous contrast agents. Despite the wide range of applications in epilepsy, dementia, brain tumours, vascular malformations and stroke imaging, obtaining clinically useful arterial spin labelling data is technically challenging and prone to numerous artefacts. The objective of this review is to provide a comprehensive pictorial overview of the various artefacts associated with arterial spin labelling, particularly three-dimensional fast spin echo pseudocontinuous arterial spin labelling with spiral readout. These artefacts could be broadly classified as those occurring during the magnetic labelling, arterial transit or image acquisition. Arterial spin labelling artefacts of clinical diagnostic utility are also elaborated. A thorough knowledge of the basis of these artefacts will avoid diagnostic pitfalls while interpreting arterial spin labelling images. Important tips to reduce or overcome these artefacts are also discussed.

Arterial spin-labelling and magnetic resonance spectroscopy as imaging biomarkers for detection of epileptogenic zone in non-lesional focal impaired awareness epilepsy

Background

The proper identification of an epileptic focus is a pivotal diagnostic issue; particularly in non-lesional focal impaired awareness epilepsy (FIAE). Seizures are usually accompanied by alterations of regional cerebral blood flow (rCBF) and metabolism. Arterial spin labeling-MRI (ASL-MRI) and proton magnetic resonance spectroscopy (1H-MRS) are MRI techniques that can, non-invasively, define the regions of cerebral perfusion and metabolic changes, respectively. The aim of the current study was to recognize the epileptogenic zone in patients with non-lesional FIAE by evaluating the interictal changes in rCBF and cerebral metabolic alterations, using PASL-MRI and 1H-MRS.

Results

For identification of the epileptogenic zone, increased ASLAI% assessed by PASL-MRI (at a cut-off value ≥ 5.96%) showed 95.78% accuracy, and increased %AF (at a cut-off value ≥ 9.98%) showed 98.14% accuracy, while decreased NAA/(Cho + Cr) ratio estimated by multi-voxels (MV) 1H-MRS (at a cut-off value ≥ 0.59) showed 97.74% accuracy. Moreover, the combined use of PASL-MRI and MV 1H-MRS yielded 100% sensitivity, 98.45% specificity and 98.86% accuracy.

Conclusion

The combined use of PASL-MRI and MV 1H-MRS can be considered as in-vivo proficient bio-marker for proper identification of epileptogenic zone in patients with non-lesional FIAE.

Crossed cerebellar diaschisis after stroke detected noninvasively by arterial spin-labeling MR imaging

Background

As a noninvasive perfusion-weighted MRI technique, arterial spin-labeling (ASL) was becoming increasingly used to evaluate cerebral hemodynamics in many studies. The relation between ASL-MRI and crossed cerebellar diaschisis (CCD) was rarely discussed. In this study, the aim of our study was to assess the performance of ASL-MRI in the detection of crossed cerebellar diaschisis after stroke in compared with single-photon emission CT (SPECT).

Results

17 of 51(33.3%) patients revealed CCD phenomenon by the SPECT method. In CCD-positive group, CBF_ASL of ipsilateral cerebellar were significantly increased compared with contralateral cerebellar (p < 0.0001) while no significant differences (p = 0.063, > 0.001) in the CCD-negative group. Positive correlation was detected between admission National institute of health stroke scale (NIHSS) and asymmetry index of SPECT (AI_SPECT) (r = 0.351, p = 0.011), AI_ASL (r = 0.372, p = 0.007); infract volume and AI_SPECT (r = 0.443, p = 0.001), AI_ASL (r = 0.426, p = 0.002). Significant correlation was also found between cerebral blood flow of SPECT (CBF_SPECT) and CBF_ASL, AI_SPECT and AI_ASL (r = 0.204, p = 0.04; r = 0.467, p = 0.001, respectively). Furthermore, the area under the receiver operating characteristic (ROC) curve value of AI_ASL was 0.829.

Conclusions

CBF derived from ASL-MRI could be valuable for assessment of CCD in supratentorial stroke patients. Additionally, CCD was significantly associated with larger ischemic volume and higher initial NIHSS score.

Investigation of the new non-invasive semi-quantitative method of 123I-IMP pediatric cerebral perfusion SPECT

In pediatric cases requiring quantification of cerebral blood flow (CBF) using 123I-N-isopropyl-p-iodoamphetamine (123I-IMP) single-photon emission computed tomography (SPECT), arterial blood sampling is sometimes impossible due to issues such as movement, crying, or body motion. If arterial blood sampling fails, quantitative diagnostic assessment becomes impossible despite radiation exposure. We devised a new easy non-invasive microsphere (e-NIMS) method using whole-body scan data. This method can be used in conjunction with autoradiography (ARG) and can provide supportive data for invasive CBF quantification. In this study, we examined the usefulness of e-NIMS for pediatric cerebral perfusion semi-quantitative SPECT and compared it with the invasive ARG. The e-NIMS estimates cardiac output (CO) using whole-body acquisition data after 123I-IMP injection and the body surface area from calculation formula. A whole-body scan was performed 5 minutes after the 123I-IMP injection and CO was estimated by region of interest (ROI) counts measured for the whole body, lungs, and brain using the whole-body anterior image. The mean CBF (mCBF) was compared with that acquired via ARG in 115 pediatric patients with suspected cerebrovascular disorders (age 0-15 years). Although the mCBF estimated by the e-NIMS indicated a slight deviation in the extremely low- or high-mCBF cases when compared with the values acquired using the invasive ARG, there was a good correlation between the two methods (r = 0.799; p < 0.001). There were no significant differences in the mCBF values based on physical features, such as patients' height, weight, and age. Our findings suggest that 123I-IMP brain perfusion SPECT with e-NIMS is the simplest semi-quantitative method that can provide supportive data for invasive CBF quantification. This method may be useful, especially in pediatric brain perfusion SPECT, when blood sampling or identifying pulmonary arteries for CO estimation using the graph plot method is difficult.

Brain moderators supporting the relationship between depressive mood and pain

Pain and depressive mood commonly exhibit a comorbid relationship. Yet, the brain mechanisms that moderate the relationship between dysphoric mood and pain remain unknown. An exploratory analysis of functional magnetic resonance imaging, behavioral, and psychophysical data was collected from a previous study in 76 healthy, nondepressed, and pain-free individuals. Participants completed the Beck Depression Inventory-II (BDI), a measure of negative mood/depressive symptomology, and provided pain intensity and pain unpleasantness ratings in response to noxious heat (49°C) during perfusion-based, arterial spin-labeled functional magnetic resonance imaging. Moderation analyses were conducted to determine neural mechanisms involved in facilitating the hypothesized relationship between depressive mood and pain sensitivity. Higher BDI-II scores were positively associated with pain intensity (R = 0.10; P = 0.006) and pain unpleasantness (R = 0.12; P = 0.003) ratings. There was a high correlation between pain intensity and unpleasantness ratings (r = 0.94; P < 0.001); thus, brain moderation analyses were focused on pain intensity ratings. Individuals with higher levels of depressive mood exhibited heightened sensitivity to experimental pain. Greater activation in regions supporting the evaluation of pain (ventrolateral prefrontal cortex; anterior insula) and sensory-discrimination (secondary somatosensory cortex; posterior insula) moderated the relationship between higher BDI-II scores and pain intensity ratings. This study demonstrates that executive-level and sensory-discriminative brain mechanisms play a multimodal role in facilitating the bidirectional relationship between negative mood and pain.

Molecular and Imaging Biomarkers in Alzheimer's Disease: A Focus on Recent Insights

Alzheimer’s disease (AD) is the most common neurodegenerative disease among the elderly, affecting millions of people worldwide and clinically characterized by a progressive and irreversible cognitive decline. The rapid increase in the incidence of AD highlights the need for an easy, efficient and accurate diagnosis of the disease in its initial stages in order to halt or delay the progression. The currently used diagnostic methods rely on measures of amyloid-β (Aβ), phosphorylated (p-tau) and total tau (t-tau) protein levels in the cerebrospinal fluid (CSF) aided by advanced neuroimaging techniques like positron emission tomography (PET) and magnetic resonance imaging (MRI). However, the invasiveness of these procedures and the high cost restrict their utilization. Hence, biomarkers from biological fluids obtained using non-invasive methods and novel neuroimaging approaches provide an attractive alternative for the early diagnosis of AD. Such biomarkers may also be helpful for better understanding of the molecular mechanisms underlying the disease, allowing differential diagnosis or at least prolonging the pre-symptomatic stage in patients suffering from AD. Herein, we discuss the advantages and limits of the conventional biomarkers as well as recent promising candidates from alternative body fluids and new imaging techniques.

Technical Improvements in Head and Neck MR Imaging: At the Cutting Edge

Head and neck MR imaging is technically challenging because of magnetic field inhomogeneity, respiratory and swallowing motion, and necessity of high-resolution imaging to trace key anatomic structures. These challenges have been answered by advances in MR imaging technology, including isovolumetric three-dimensional imaging, robust fat-water separation techniques, and novel deep learning-based reconstruction algorithms. New applications of MR imaging have been advanced and functional imaging has been improved. Improvements in acquisition and reconstruction technique facilitate novel applications of morphologic and functional imaging. This results in opportunities to improve diagnosis, staging, and treatment selection through application of advanced MR imaging techniques.

Arterial transit artifacts observed by arterial spin labeling in Moyamoya disease

OBJECTIVES

Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI) technique used to assess cerebral perfusion. When tissue perfusion is impaired, such as in Moyamoya disease, a hyperintense band called the arterial transit artifact (ATA) may occur, which interferes with accurate measurements on ASL-MRI. In this study, we evaluated the correlation of ATAs with magnetic resonance angiography (MRA) and single-photon emission computed tomography (SPECT) imaging results in Moyamoya disease. The aim of our study was to elucidate the pathophysiology of ATAs and risk factors for high ATA scores.

MATERIALS AND METHODS

This retrospective study included 28 patients (56 hemispheres) with Moyamoya disease treated at our institution. MRI, MRA, ASL perfusion, and N-isopropyl-[¹²³I] b-iodoamphetamine (¹²³I-IMP) SPECT were performed. In order to semi-quantitatively evaluate the degree of ATA, the ATA scores were measured according to the number of hyperintense signal bands in the cerebral cortex. The relationship between the ATA scores and clinical and radiological factors were analyzed.

RESULTS

Regional cerebral blood flow (rCBF) determined with ASL weakly correlated with that determined by ¹²³I-IMP SPECT (ρ=0.31, p=0.027). There was no significant association between the ATA scores and rCBF values determined with ¹²³I-IMP SPECT (p=0.872, 0.745, 0.743 at PLD1000 (post-labeling delay), 1500, and 2000, respectively). However, there was a significant correlation between ATA scores and MRA scores (ρ=0.427 p=0.001; ρ=0.612 p=0.001; ρ=0.563 p=0.001 at PLD1000, 1500, and 2000, respectively). An analysis of patient background characteristics revealed a significantly higher incidence of high ATA scores in female patients, patients with high MRA scores, and patients with a distinguishable ivy sign. A multivariate analysis confirmed that female sex, high MRA score, and presence of an ivy sign were risk factors for high ATA scores.

CONCLUSION

ATA scores were moderately correlated with MRA scores, and presence of an ivy sign was the most predictive factor for high ATA scores. A high ATA score determined using ASL in a patient with Moyamoya disease might suggest an advanced disease stage and a reduction in cerebrovascular reserve capacity.

Combined Denoising and Suppression of Transient Artifacts in Arterial Spin Labeling MRI Using Deep Learning

BACKGROUND

Arterial spin labeling (ASL) is a useful tool for measuring cerebral blood flow (CBF). However, due to the low signal-to-noise ratio (SNR) of the technique, multiple repetitions are required, which results in prolonged scan times and increased susceptibility to artifacts.

PURPOSE

To develop a deep-learning-based algorithm for simultaneous denoising and suppression of transient artifacts in ASL images.

STUDY TYPE

Retrospective.

SUBJECTS

131 pediatric neuro-oncology patients for model training and 11 healthy adult subjects for model evaluation.

FIELD STRENGTH/SEQUENCE

3T / pseudo-continuous and pulsed ASL with 3D gradient-and-spin-echo readout.

ASSESSMENT

A denoising autoencoder (DAE) model was designed with stacked encoding/decoding convolutional layers. Reference standard images were generated by averaging 10 pairwise ASL subtraction images. The model was trained to produce perfusion images of a similar quality using a single subtraction image. Performance was compared against Gaussian and non-local means (NLM) filters. Evaluation metrics included SNR, peak SNR (PSNR), and structural similarity index (SSIM) of the CBF images, compared to the reference standard.

STATISTICAL TESTS

One-way analysis of variance (ANOVA) tests for group comparisons.

RESULTS

The DAE model was the only model to produce a significant increase in SNR compared to the raw images (P < 0.05), providing an average SNR gain of 62%. The DAE model was also effective at suppressing transient artifacts, and was the only model to show a significant improvement in accuracy in the generated CBF images, as assessed using PSNR values (P < 0.05). In addition, using data from multiple inflow time acquisitions, the DAE images produced the best fit to the Buxton kinetic model, offering a 75% reduction in the fitting error compared to the raw images.

DATA CONCLUSION

Deep-learning-based algorithms provide superior accuracy when denoising ASL images, due to their ability to simultaneously increase SNR and suppress artifactual signals in raw ASL images.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 1.

Perfusion-driven Intravoxel Incoherent Motion (IVIM) MRI in Oncology: Applications, Challenges, and Future Trends

Recent developments in MR hardware and software have allowed a surge of interest in intravoxel incoherent motion (IVIM) MRI in oncology. Beyond diffusion-weighted imaging (and the standard apparent diffusion coefficient mapping most commonly used clinically), IVIM provides information on tissue microcirculation without the need for contrast agents. In oncology, perfusion-driven IVIM MRI has already shown its potential for the differential diagnosis of malignant and benign tumors, as well as for detecting prognostic biomarkers and treatment monitoring. Current developments in IVIM data processing, and its use as a method of scanning patients who cannot receive contrast agents, are expected to increase further utilization. This paper reviews the current applications, challenges, and future trends of perfusion-driven IVIM in oncology.

ExploreASL: An image processing pipeline for multi-center ASL perfusion MRI studies

Arterial spin labeling (ASL) has undergone significant development since its inception, with a focus on improving standardization and reproducibility of its acquisition and quantification. In a community-wide effort towards robust and reproducible clinical ASL image processing, we developed the software package ExploreASL, allowing standardized analyses across centers and scanners. The procedures used in ExploreASL capitalize on published image processing advancements and address the challenges of multi-center datasets with scanner-specific processing and artifact reduction to limit patient exclusion. ExploreASL is self-contained, written in MATLAB and based on Statistical Parameter Mapping (SPM) and runs on multiple operating systems. To facilitate collaboration and data-exchange, the toolbox follows several standards and recommendations for data structure, provenance, and best analysis practice. ExploreASL was iteratively refined and tested in the analysis of >10,000 ASL scans using different pulse-sequences in a variety of clinical populations, resulting in four processing modules: Import, Structural, ASL, and Population that perform tasks, respectively, for data curation, structural and ASL image processing and quality control, and finally preparing the results for statistical analyses on both single-subject and group level. We illustrate ExploreASL processing results from three cohorts: perinatally HIV-infected children, healthy adults, and elderly at risk for neurodegenerative disease. We show the reproducibility for each cohort when processed at different centers with different operating systems and MATLAB versions, and its effects on the quantification of gray matter cerebral blood flow. ExploreASL facilitates the standardization of image processing and quality control, allowing the pooling of cohorts which may increase statistical power and discover between-group perfusion differences. Ultimately, this workflow may advance ASL for wider adoption in clinical studies, trials, and practice.