ACR Appropriateness Criteria® Dizziness and Ataxia: 2023 Update.

Diagnostic evaluation of a patient with dizziness or vertigo is complicated by a lack of standardized nomenclature, significant overlap in symptom descriptions, and the subjective nature of the patient's symptoms. Although dizziness is an imprecise term often used by patients to describe a feeling of being off-balance, in many cases dizziness can be subcategorized based on symptomatology as vertigo (false sense of motion or spinning), disequilibrium (imbalance with gait instability), presyncope (nearly fainting or blacking out), or lightheadedness (nonspecific). As such, current diagnostic paradigms focus on timing, triggers, and associated symptoms rather than subjective descriptions of dizziness type. Regardless, these factors complicate the selection of appropriate diagnostic imaging in patients presenting with dizziness or vertigo. This document serves to aid providers in this selection by using a framework of definable clinical variants. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Incorporating Supramaximal Resection into Survival Stratification of IDH-Wildtype Glioblastoma: A Refined Multi-institutional Recursive Partitioning Analysis.

PURPOSE: To propose a novel recursive partitioning analysis (RPA) classification model in patients with IDH-wildtype glioblastomas that incorporates the recently expanded conception of the extent of resection (EOR) in terms of both supramaximal and total resections. EXPERIMENTAL DESIGN: This multicenter cohort study included a developmental cohort of 622 patients with IDH-wildtype glioblastomas from a single institution (Severance Hospital) and validation cohorts of 536 patients from three institutions (Seoul National University Hospital, Asan Medical Center, and Heidelberg University Hospital). All patients completed standard treatment including concurrent chemoradiotherapy and underwent testing to determine their IDH mutation and MGMTp methylation status. EORs were categorized into either supramaximal, total, or non-total resections. A novel RPA model was then developed and compared to a previous RTOG RPA model. RESULTS: In the developmental cohort, the RPA model included age, MGMTp methylation status, KPS, and EOR. Younger patients with MGMTp methylation and supramaximal resections showed a more favorable prognosis (class I: median overall survival [OS] 57.3 months), while low-performing patients with non-total resections and without MGMTp methylation showed the worst prognosis (class IV: median OS 14.3 months). The prognostic significance of the RPA was subsequently confirmed in the validation cohorts, which revealed a greater separation between prognostic classes for all cohorts compared to the previous RTOG RPA model. CONCLUSIONS: The proposed RPA model highlights the impact of supramaximal versus total resections and incorporates clinical and molecular factors into survival stratification. The RPA model may improve the accuracy of assessing prognostic groups.

Predicting Progression of Intracranial Hemorrhage in the Prehospital TXA for TBI Trial.

Progression of intracranial hemorrhage is a common, potentially devastating complication after moderate/severe traumatic brain injury (TBI). Clinicians have few tools to predict which patients with traumatic intracranial hemorrhage on their initial head computed tomography (hCT) scan will progress. The objective of this investigation was to identify clinical, imaging, and/or protein biomarkers associated with progression of intracranial hemorrhage (PICH) after moderate/severe TBI and to create an accurate predictive model of PICH based on clinical features available at presentation. We analyzed a subset of subjects from the phase II double-blind, multi-center, randomized "Prehospital Tranexamic Acid Use for TBI" trial. This subset was limited to the placebo arm of the parent trial with evidence of hemorrhage on the initial hCT and a follow-up hCT 6 h after. PICH was defined as an increase in hemorrhage size by 30% or more, or the development of new hemorrhage in the intra- and extra-axial intracranial vault between the initial and the follow-up hCT. Two independent radiologists evaluated each hCT, and conflicts were adjudicated by a third. Clinical and radiographic characteristics were collected, along with plasma protein biomarkers at admission. Principal component analysis (PCA) was performed, and each principal component (PC) was interrogated for its association with PICH. Finally, expert opinion and recursive feature extraction (RFE) were used to select input features for the construction of several supervised classification models. Their ability to predict PICH was quantified and compared. In this subset of subjects (n = 104), 46% (n = 48) demonstrated PICH. Univariate analyses showed no association between PICH and age, sex, admission Glasgow Coma Scale (GCS), GCS motor subscore, presence of midline shift, admission platelet count or admission INR. Radiographic severity scores (Marshall score [p = 0.007], Rotterdam score [p = 0.004]), and initial hematoma volume [p = 0.005] were associated with PICH. Higher levels of admission glial fibrillary acidic protein (p < 0.001) and MAP (p = 0.011) were also associated with PICH. Of the PCs, PC1 was significantly associated with PICH (p = 0.0125). Using multimodal data input, machine learning classifiers successfully discriminated patients with or without PICH. Models composed of machine-selected features performed better than models composed of expert-selected variables (reaching an average of 77% accuracy, AUC = 0.78 versus AUC = 0.68 for the expert-selected variables). Predictive models utilizing variables measured at admission can accurately predict PICH, confirmed by the 6-hour follow-up hCT. Our best-performing models must now be externally validated in a separate cohort of TBI patients with low GCS and initial hCT positive for hemorrhage.

ACR Appropriateness Criteria® Headache: 2022 Update.

Headache is an ancient problem plaguing a large proportion of the population. At present, headache disorders rank third among the global causes of disability, accounting for over $78 billion per year in direct and indirect costs in the United States. Given the prevalence of headache and the wide range of possible etiologies, the goal of this document is to help clarify the most appropriate initial imaging guidelines for headache for eight clinical scenarios/variants, which range from acute onset, life-threatening etiologies to chronic benign scenarios. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

ACR Appropriateness Criteria® Cerebrovascular Diseases-Aneurysm, Vascular Malformation, and Subarachnoid Hemorrhage.

Cerebrovascular disease is a broad topic. This document focuses on the imaging recommendations for the varied clinical scenarios involving intracranial aneurysms, vascular malformations, and vasculitis, which all carry high risk of morbidity and mortality. Additional imaging recommendations regarding complications of these conditions, including subarachnoid hemorrhage and vasospasm, are also covered. While each variant presentation has unique imaging recommendations, the major focus of this document is neurovascular imaging techniques. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

ACR Appropriateness Criteria® Head Trauma: 2021 Update.

Head trauma (ie, head injury) is a significant public health concern and is a leading cause of morbidity and mortality in children and young adults. Neuroimaging plays an important role in the management of head and brain injury, which can be separated into acute (0-7 days), subacute (<3 months), then chronic (>3 months) phases. Over 75% of acute head trauma is classified as mild, of which over 75% have a normal Glasgow Coma Scale score of 15, therefore clinical practice guidelines universally recommend selective CT scanning in this patient population, which is often based on clinical decision rules. While CT is considered the first-line imaging modality for suspected intracranial injury, MRI is useful when there are persistent neurologic deficits that remain unexplained after CT, especially in the subacute or chronic phase. Regardless of time frame, head trauma with suspected vascular injury or suspected cerebrospinal fluid leak should also be evaluated with CT angiography or thin-section CT imaging of the skull base, respectively. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

ACR appropriateness criteria head trauma: 2021 update

Head trauma (ie, head injury) is a significant public health concern and is a leading cause of morbidity and mortality in children and young adults. Neuroimaging plays an important role in the management of head and brain injury, which can be separated into acute (0-7 days), subacute (<3 months), then chronic (>3 months) phases. Over 75% of acute head trauma is classified as mild, of which over 75% have a normal Glasgow Coma Scale score of 15, therefore clinical practice guidelines universally recommend selective CT scanning in this patient population, which is often based on clinical decision rules. While CT is considered the first-line imaging modality for suspected intracranial injury, MRI is useful when there are persistent neurologic deficits that remain unexplained after CT, especially in the subacute or chronic phase. Regardless of time frame, head trauma with suspected vascular injury or suspected cerebrospinal fluid leak should also be evaluated with CT angiography or thin-section CT imaging of the skull base, respectively. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Incorporating Immunoproteins in the Development of Classification Models of Progression of Intracranial Hemorrhage After Traumatic Brain Injury.

OBJECTIVE: To define clinical, radiographic, and blood-based biomarker features to be incorporated into a classification model of progression of intracranial hemorrhage (PICH), and to provide a pilot assessment of those models. METHODS: Patients with hemorrhage on admission head computed tomography were identified from a prospectively enrolled cohort of subjects with traumatic brain injury. Initial and follow-up images were interpreted both by 2 independent readers, and disagreements adjudicated. Admission plasma samples were analyzed and principal components (PCs) composed of the immune proteins (IPs) significantly associated with the outcome of interest were selected for further evaluation. A series of logistic regression models were constructed based on (1) clinical variables (CV) and (2) clinical variables + immune proteins (CV+IP). Error rates of these models for correct classification of PICH were estimated; significance was set at P < .05. RESULTS: We identified 106 patients, 36% had PICH. Dichotomized admission Glasgow Coma Scale (P = .004), Marshall score (P = .004), and 3 PCs were significantly associated with PICH. For the CV only model, sensitivity was 1.0 and specificity was 0.29 (95% CI, 0.07-0.67). The CV+IP model performed significantly better, with a sensitivity of 0.93 (95% CI, 0.64-0.99) and a specificity of 1.0 (P = .008). Adjustments to refine the definition of PICH and better define radiographic predictors of PICH did not significantly improve the models' performance. CONCLUSIONS: In this pilot investigation, we observed that composites of IPs may improve PICH classification models when combined with CVs. However, overall model performance must be further optimized; results will inform feature inclusion included in follow-up models.

ACR Appropriateness Criteria® Dementia.

Degenerative disease of the central nervous system is a growing public health concern. The primary role of neuroimaging in the workup of patients with probable or possible Alzheimer disease has typically been to exclude other significant intracranial abnormalities. In general, the imaging findings in structural studies, such as MRI, are nonspecific and have limited potential in differentiating different types of dementia. Advanced imaging methods are not routinely used in community or general practices for the diagnosis or differentiation of forms of dementia. Nonetheless, in patients who have been evaluated by a dementia expert, FDG-PET helps to distinguish Alzheimer disease from frontotemporal dementia. In patients with suspected dementia with Lewy bodies, functional imaging of the dopamine transporter (ioflupane) using SPECT may be helpful. In patients with suspected normal-pressure hydrocephalus, DTPA cisternography and HMPAO SPECT/CT brain may provide assessment. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

ACR Appropriateness Criteria® Movement Disorders and Neurodegenerative Diseases.

Movement disorders and neurodegenerative diseases are a variety of conditions that involve progressive neuronal degeneration, injury, or death. Establishing the correct diagnosis of a movement disorder or neurodegenerative process can be difficult due to the variable features of these conditions, unusual clinical presentations, and overlapping symptoms and characteristics. MRI has an important role in the initial assessment of these patients, although a combination of imaging and laboratory and genetic tests is often needed for complete evaluation and management. This document summarizes the imaging appropriateness data for rapidly progressive dementia, chorea, Parkinsonian syndromes, suspected neurodegeneration with brain iron accumulation, and suspected motor neuron disease. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

ACR Appropriateness Criteria® Seizures and Epilepsy.

Seizures and epilepsy are a set of conditions that can be challenging to diagnose, treat, and manage. This document summarizes recommendations for imaging in different clinical scenarios for a patient presenting with seizures and epilepsy. MRI of the brain is usually appropriate for each clinical scenario described with the exception of known seizures and unchanged semiology (Variant 3). In this scenario, it is unclear if any imaging would provide a benefit to patients. In the emergent situation, a noncontrast CT of the head is also usually appropriate as it can diagnose or exclude emergent findings quickly and is an alternative to MRI of the brain in these clinical scenarios. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Anterior Cervical Arthrodesis With Polyetheretherketone Spacers: What is the Role of the Grafting Material?

STUDY DESIGN: This was a retrospective study of 2 surgeons' use of a single polyetheretherketone (PEEK) device. OBJECTIVE: Our objective was to investigate the fusion adjunct placed within PEEK devices to examine the likelihood of an arthrodesis, regardless of the PEEK interbody device itself. SUMMARY OF BACKGROUND DATA: The effectiveness of PEEK interbody devices in anterior cervical arthrodesis has been questioned. METHODS: The authors retrospectively reviewed the results of 121 patients with demineralized bone matrix (DBM) and 96 with local autograft bone placed within identical PEEK devices for anterior cervical arthrodesis (from 2011 to 2018); 1 surgeon used DBM and another local autograft bone. Arthrodesis was determined independently by a surgeon and 2 blinded neuroradiologists. RESULTS: For DBM versus autograft; mean age was 60 versus 61 years, smoking status 42.1% versus 31%, diabetes mellitus 18.2% versus 28%, mean body mass index 31 versus 30, and follow up averaged 17 months in both groups. For DBM versus autograft; a radiographic arthrodesis was observed in 22.3% versus 76% of patients. Refusion at the index level was required in 5.8% of the DBM and 0% of the autograft patients. CONCLUSIONS: A PEEK interbody device filled with local autograft resulted in a higher radiographic fusion rate and a lower need for reoperation at the index level than an identical device filled with DBM. Caution is warranted in assigning fusion failure to the PEEK device alone in anterior cervical discectomy and fusion surgery.

Morphological changes of the dorsal contour of the corpus callosum during the first two years of life.

BACKGROUND: In the medicolegal literature, focal concavities or notching of the corpus callosum has been thought to be associated with fetal alcohol spectrum disorders. Recent work suggests corpus callosum notching is a dynamic and normal anatomical feature, although it has not yet been defined in early life or infancy. OBJECTIVE: Our purpose was to characterize the dorsal contour of the corpus callosum during the first 2 years of life by defining the prevalence, onset and trajectory of notching on midsagittal T1-weighted images. MATERIALS AND METHODS: We reviewed retrospectively 1,157 consecutive patients between birth and 2 years of age. Corpus callosum morphology was evaluated and described. A notch was defined as a dorsal concavity of at least 1 mm in depth along the dorsal surface of the corpus callosum. Patient age as well as notch depth, location, number and presence of the pericallosal artery in the notch were noted. RESULTS: Two hundred thirty-three notches were identified in 549 patients: 36 anterior, 194 posterior and 3 patients with undulations. A statistically significant (R2=0.53, Beta=0.021, P=0.002) positive correlation between posterior notch prevalence and age in months was noted. A positive correlation between age and depth of the posterior notch was also statistically significant (r=0.32, n=179, P≤0.001). A trend for increased anterior notch prevalence with age was identified with significant correlation between visualized pericallosal artery indentation and anterior notching (r=0.20, n=138, P=0.016). Sub-analysis of the first month of life showed corpus callosum notching was not present. CONCLUSION: The presence of posterior notching increased significantly with age and was more frequent than that of anterior notching. Corpus callosum notching was absent in the first week of life, building on prior studies suggesting corpus callosum notching is acquired. This study provides baseline data on normative corpus callosum notching trajectories by age group during early life, a helpful correlate when associating corpus callosum morphology with disease.

ACR Appropriateness Criteria® Headache.

Headache is one of the most common human afflictions. In most cases, headaches are benign and idiopathic, and resolve spontaneously or with minor therapeutic measures. Imaging is not required for many types of headaches. However, patients presenting with headaches in the setting of "red flags" such as head trauma, cancer, immunocompromised state, pregnancy, patients 50 years or older, related to activity or position, or with a corresponding neurological deficit, may benefit from CT, MRI, or noninvasive vascular imaging to identify a treatable cause. This publication addresses the initial imaging strategies for headaches associated with the following features: severe and sudden onset, optic disc edema, "red flags," migraine or tension-type, trigeminal autonomic origin, and chronic headaches with and without new or progressive features. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Autoidentification of perivascular spaces in white matter using clinical field strength T1 and FLAIR MR imaging.

Recent interest in enlarged perivascular spaces (ePVS) in the brain, which can be visualized on MRI and appear isointense to cerebrospinal fluid on all sequence weightings, has resulted in the necessity of reliable algorithms for automated segmentation to allow for whole brain assessment of ePVS burden. However, several publicly available datasets do not contain sequences required for recently published algorithms. This prospective study presents a method for identification of enlarged perivascular spaces (ePVS) in white matter using 3T T1 and FLAIR MR imaging (MAPS-T1), making the algorithm accessible to groups with valuable sets of limited data. The approach was applied identically to two datasets: 1) a repeated measurement in a dementia-free aged human population (N = 14), and 2) an aged sample of multisite ADNI datasets (N = 30). ePVS segmentation was accomplished by a stepwise local homogeneity search of white matter-masked T1-weighted data, constrained by FLAIR hyperintensity, and further constrained by width, volume, and linearity measurements. Pearson's r was employed for statistical testing between visual (gold standard) assessment and repeated measures in cohort one. Visual ePVS counts were significantly correlated with MAPS-T1 (r = .72, P < .0001). Correlations between repeated measurements in cohort one were significant for both visual and automated methods in the single visually-rated slice (MAPS-T1: r = .87, P < .0001, visual: (r = .86, P < .0001) and for whole brain assessment (MAPS-T1: r = .77, P = .001). Results from each cohort were manually inspected and found to have positive predictive values of 77.5% and 87.5%, respectively. The approach described in this report is an important tool for detailed assessment of ePVS burden in white matter on routinely acquired MRI sequences.

Sex-dependent posterior fossa anatomical differences in trigeminal neuralgia patients with and without neurovascular compression: a volumetric MRI age- and sex-matched case-control study.

OBJECTIVE: The pathophysiology of trigeminal neuralgia (TN) in patients without neurovascular compression (NVC) is not completely understood. The objective of this retrospective study was to evaluate the hypothesis that TN patients without NVC differ from TN patient with NVC with respect to brain anatomy and demographic characteristics. METHODS: Six anatomical brain measurements from high-resolution brain MR images were tabulated; anterior-posterior (AP) prepontine cistern length, cerebellopontine angle (CPA) cistern volume, nerve-to-nerve distance, symptomatic nerve length, pons volume, and posterior fossa volume were assessed on OsiriX. Brain MRI anatomical measurements from 232 patients with either TN type 1 or TN type 2 (TN group) were compared with measurements obtained in 100 age- and sex-matched healthy controls (control group). Two-way ANOVA tests were conducted on the 6 measurements relative to group and NVC status. Bonferroni adjustments were used to correct for multiple comparisons. A nonhierarchical k-means cluster analysis was performed on the TN group using age and posterior fossa volume as independent variables. RESULTS: Within the TN group, females were found to be younger than males and less likely to have NVC. The odds ratio (OR) of females not having NVC compared to males was 2.7 (95% CI 1.3-5.5, p = 0.017). Patients younger than 30 years were much less likely to have NVC compared to older patients (OR 4.9, 95% CI 1.3-18.4, p = 0.017). The mean AP prepontine cistern length and symptomatic nerve length were smaller in the TN group than in the control group (5.3 vs 6.5 mm and 8.7 vs 9.7 mm, respectively; p < 0.001). The posterior fossa volume was significantly smaller in TN patients without NVC compared to those with NVC. A TN group cluster analysis suggested a sex-dependent difference that was not observed in those without NVC. Factorial ANOVA and post hoc testing found that findings in males without NVC were significantly different from those in controls or male TN patients with NVC and similar to those in females (female controls as well as female TN patients with or without NVC). CONCLUSIONS: Posterior fossa volume in males was larger than posterior fossa volume in females. This finding, along with the higher incidence of TN in females, suggests that smaller posterior fossa volume might be an independent factor in the pathophysiology of TN, which warrants further study.

Unilateral anoxic brain injury secondary to strangulation identified on conventional and arterial spin-labeled perfusion imaging.

Anoxic brain injury on magnetic resonance imaging classically demonstrates symmetric diffusion restriction involving the highly metabolic structures including the basal ganglia and cortex and global hyperperfusion on arterial spin labeling perfusion. The pattern of injury is classically diffuse and bilateral owing to global oxygen deprivation from systemic causes, most commonly cardiac arrest. In cases of suspected nonaccidental trauma presenting with a unilateral anoxic injury pattern, strangulation with temporary occlusion of a unilateral carotid artery should be considered. We present 2 cases of unilateral anoxic brain injury due to strangulation identified on magnetic resonance imaging and arterial spin labeling perfusion.