Arterial spin-labeled MR perfusion imaging: clinical applications

Perfusion Imaging in Neuro-Oncology: Basic Techniques and Clinical Applications

Perfusion imaging is a method for assessing the flow of blood occurring at the tissue level and can be accomplished by both CT and MR perfusion techniques. The use of perfusion imaging has increased substantially in the past decade, particularly in neuro-oncologic imaging, where it is has been used for brain tumor grading and directing biopsies or targeted therapy, as well as for the evaluation of treatment response and disease progression. This article discusses the basic principles and techniques of perfusion imaging, as well as its applications in neuro-oncology.

Brain Perfusion and Diffusion Abnormalities in Children Treated for Posterior Fossa Brain Tumors

OBJECTIVE

To compare cerebral perfusion and diffusion in survivors of childhood posterior fossa brain tumor with neurologically normal controls and correlate differences with cognitive dysfunction.

STUDY DESIGN

We analyzed retrospectively arterial spin-labeled cerebral blood flow (CBF) and apparent diffusion coefficient (ADC) in 21 patients with medulloblastoma (MB), 18 patients with pilocytic astrocytoma (PA), and 64 neurologically normal children. We generated ANCOVA models to evaluate treatment effects on the cerebral cortex, thalamus, caudate, putamen, globus pallidus, hippocampus, amygdala, nucleus accumbens, and cerebral white matter at time points an average of 5.7 years after original diagnosis. A retrospective review of patient charts identified 12 patients with neurocognitive data and in whom the relationship between IQ and magnetic resonance imaging variables was assessed for each brain structure.

RESULTS

Patients with MB (all treated with surgery, chemotherapy, and radiation) had significantly lower global CBF relative to controls (10%-23% lower, varying by anatomic region, all adjusted P?<?.05), whereas patients with PA (all treated with surgery alone) had normal CBF. ADC was decreased specifically in the hippocampus and amygdala of patients with MB and within the amygdala of patients with PA but otherwise remained normal after therapy. In the patients with tumor previously evaluated for IQ, regional ADC, but not CBF, correlated with IQ (R²?=?0.33-0.75).

CONCLUSIONS

The treatment for MB, but not PA, was associated with globally reduced CBF. Treatment in both tumor types was associated with diffusion abnormalities of the mesial temporal lobe structures. Despite significant perfusion abnormalities in patients with MB, diffusion, but not perfusion, correlated with cognitive outcomes.

Neuroimaging in Central Nervous System Lymphoma

Primary central nervous system lymphoma (PCNSL) is a rare aggressive high-grade type of extranodal lymphoma. PCNSL can have a variable imaging appearance and can mimic other brain disorders such as encephalitis, demyelination, and stroke. In addition to PCNSL, the CNS can be secondarily involved by systemic lymphoma. Computed tomography and conventional MRI are the initial imaging modalities to evaluate these lesions. Recently, however, advanced MRI techniques are more often used in an effort to narrow the differential diagnosis and potentially inform diagnostic and therapeutic decisions.

Understanding the Neurophysiology and Quantification of Brain Perfusion

Newer neuroimaging technology has moved beyond pure anatomical imaging and ventured into functional and physiological imaging. Perfusion magnetic resonance imaging (PWI), which depicts hemodynamic conditions of the brain at the microvascular level, has an increasingly important role in clinical central nervous system applications. This review provides an overview of the established role of PWI in brain tumor and cerebrovascular imaging, as well as some emerging applications in neuroimaging. PWI allows better characterization of brain tumors, grading, and monitoring. In acute stroke imaging, PWI is utilized to distinguish penumbra from infarcted tissue. PWI is a promising tool in the assessment of neurodegenerative and neuropsychiatric diseases, although its clinical role is not yet defined.

Neuroimaging of Peptide-based Vaccine Therapy in Pediatric Brain Tumors: Initial Experience

The potential benefits of peptide-based immunotherapy for pediatric brain tumors are under investigation. Treatment-related heterogeneity has resulted in radiographic challenges, including pseudoprogression. Conventional MR imaging has limitations in assessment of different forms of treatment-related heterogeneity, particularly regarding distinguishing true tumor progression from efficacious treatment responses. Advanced neuroimaging techniques, including diffusion magnetic resonance (MR), perfusion MR, and MR spectroscopy, may add value in the assessment of treatment-related heterogeneity. Observations suggest that recent delineation of specific response criteria for immunotherapy of adult brain tumors is likely relevant to the pediatric population and further validation in multicenter pediatric brain tumor peptide-based vaccine studies is warranted.

Cerebral blood flow and vasoreactivity in aging: an arterial spin labeling study

Regional cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) in young and elderly participants were assessed using pulsed arterial spin labeling (ASL) and blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) techniques in combination with inhalation of CO2. Pulsed ASL and BOLD-MRI were acquired in seventeen asymptomatic volunteers (10 young adults, age: 30±7 years; 7 elderly adults, age: 64±8 years) with no history of diabetes, hypertension, and neurological diseases. Data from one elderly participant was excluded due to the incorrigible head motion. Average baseline CBF in gray matter was significantly reduced in elderly (46±9 mL·100 g-1·min-1) compared to young adults (57±8 mL·100 g-1·min-1; P=0.02). Decreased pulsed ASL-CVR and BOLD-CVR in gray matter were also observed in elderly (2.12±1.30 and 0.13±0.06 %/mmHg, respectively) compared to young adults (3.28±1.43 and 0.28±0.11 %/mmHg, respectively; P<0.05), suggesting some degree of vascular impairment with aging. Moreover, age-related decrease in baseline CBF was observed in different brain regions (inferior, middle and superior frontal gyri; precentral and postcentral gyri; superior temporal gyrus; cingulate gyri; insula, putamen, caudate, and supramarginal gyrus). In conclusion, CBF and CVR were successfully investigated using a protocol that causes minimal or no discomfort for the participants. Age-related decreases in baseline CBF and CVR were observed in the cerebral cortex, which may be related to the vulnerability for neurological disorders in aging.

SAR Simulations & Safety

At ultra-high fields, the assessment of radiofrequency (RF) safety presents several new challenges compared to low-field systems. Multi-channel RF transmit coils in combination with parallel transmit techniques produce time-dependent and spatially varying power loss densities in the tissue. Further, in ultra-high-field systems, localized field effects can be more pronounced due to a transition from the quasi stationary to the electromagnetic field regime. Consequently, local information on the RF field is required for reliable RF safety assessment as well as for monitoring of RF exposure during MR examinations. Numerical RF and thermal simulations for realistic exposure scenarios with anatomical body models are currently the only practical way to obtain the requisite local information on magnetic and electric field distributions as well as tissue temperature. In this article, safety regulations and the fundamental characteristics of RF field distributions in ultra-high-field systems are reviewed. Numerical methods for computation of RF fields as well as typical requirements for the analysis of realistic multi-channel RF exposure scenarios including anatomical body models are highlighted. In recent years, computation of the local tissue temperature has become of increasing interest, since a more accurate safety assessment is expected because temperature is directly related to tissue damage. Regarding thermal simulation, bio-heat transfer models and approaches for taking into account the physiological response of the human body to RF exposure are discussed. In addition, suitable methods are presented to validate calculated RF and thermal results with measurements. Finally, the concept of generalized simulation-based specific absorption rate (SAR) matrix models is discussed. These models can be incorporated into local SAR monitoring in multi-channel MR systems and allow the design of RF pulses under constraints for local SAR.

Prospective motion correction for 3D pseudo-continuous arterial spin labeling using an external optical tracking system

Head motion is an unsolved problem in magnetic resonance imaging (MRI) studies of the brain. Real-time tracking using a camera has recently been proposed as a way to prevent head motion artifacts. As compared to navigator-based approaches that use MRI data to detect and correct motion, optical motion correction works independently of the MRI scanner, thus providing low-latency real-time motion updates without requiring any modifications to the pulse sequence. The purpose of this study was two-fold: 1) to demonstrate that prospective optical motion correction using an optical camera mitigates artifacts from head motion in three-dimensional pseudo-continuous arterial spin labeling (3D PCASL) acquisitions and 2) to assess the effect of latency differences between real-time optical motion tracking and navigator-style approaches (such as PROMO). An optical motion correction system comprising a single camera and a marker attached to the patient's forehead was used to track motion at a rate of 60fps. In the presence of motion, continuous tracking data from the optical system was used to update the scan plane in real-time during the 3D-PCASL acquisition. Navigator-style correction was simulated by using the tracking data from the optical system and performing updates only once per repetition time. Three normal volunteers and a patient were instructed to perform continuous and discrete head motion throughout the scan. Optical motion correction yielded superior image quality compared to uncorrected images or images using navigator-style correction. The standard deviations of pixel-wise CBF differences between reference and non-corrected, navigator-style-corrected and optical-corrected data were 14.28, 14.35 and 11.09mL/100g/min for continuous motion, and 12.42, 12.04 and 9.60mL/100g/min for discrete motion. Data obtained from the patient revealed that motion can obscure pathology and that application of optical prospective correction can successfully reveal the underlying pathology in the presence of head motion.

Arterial Spin-Labeling to Discriminate Pediatric Cervicofacial Soft-Tissue Vascular Anomalies

BACKGROUND AND PURPOSE

Differentiating major subtypes of cervicofacial vascular lesions is crucial for appropriate management. The aim of our study was to evaluate the performance of an MR imaging arterial spin-labeling perfusion sequence in discriminating pediatric cervicofacial soft-tissue vascular anomalies.

MATERIALS AND METHODS

We conducted a retrospective analysis of data from a prospectively maintained registry including pediatric patients at a tertiary pediatric center between January 2012 and January 2014. We included pediatric patients with a final diagnosis of soft-tissue vascular anomalies and an MR imaging, including an arterial spin-labeling sequence at presentation. We performed an analysis of lesion perfusion, blinded to clinical data, by using concurrent spiral 3D pseudocontinuous arterial spin-labeling (1.5T magnet; spiral matrix, 512 × 8 mm; postlabeling delay, 1025 ms). Lesional flow was recorded with calibrated intralesional ROIs. Perfusion characteristics were compared among lesion subtypes with the Mood Median test.

RESULTS

Among 840 patients screened, 46 matched the inclusion criteria and were included (median age, 1.45 years; interquartile range, 0.4-5.1 years; 27 females). Hemangiomas, including infantile hemangiomas (n = 18 patients) and noninvoluting (n = 2) and rapidly involuting (n = 1) congenital types, demonstrated marked hyperperfusion (median flow, 436 mL/min/100 g; interquartile range, 212.5-603 mL/min/100 g), significantly higher than that of lymphatic malformations (median, 22.5 mL/min/100 g; interquartile range, 16-60 mL/min/100 g; P < .001) or venous malformations (median, 25 mL/min/100 g; interquartile range, 15-66.5 mL/min/100 g; P = .003).

CONCLUSIONS

MR imaging arterial spin-labeling is a valuable tool for the assessment of soft-tissue vascular anomaly hemodynamics and for the classification of major lesion subtypes.

A meta-analysis of arterial spin labelling perfusion values for the prediction of glioma grade

AIM

To investigate the ability of arterial spin labelling (ASL) perfusion parameters to distinguish high-grade from low-grade gliomas.

MATERIALS AND METHODS

The PubMed and EMBASE databases were systematically searched for relevant articles published up to September 2015. Studies that evaluated both high- and low-grade gliomas using ASL were included. The random effect model was used to calculate the standardised mean difference (SMD) of maximum mean absolute tumour blood flow values (aTBF_max, aTBF_mean) and maximum mean relative tumour blood flow (rTBF_max, rTBF_mean) between high- and low-grade gliomas.

RESULTS

Nine studies encompassing 305 patients with high- and low-grade gliomas, met all inclusion and exclusion criteria and were included in the study. Compared with low-grade gliomas, high-grade gliomas had a significant increase in all ASL perfusion values: aTBF_max (SMD=0.70, 95% confidence interval [CI]: 0.22-1.19, p=0.0046); aTBF_mean (SMD=0.86, 95% CI: 0.2-1.52, p=0.01); rTBF_max (SMD=1.08, 95% CI: 0.54-1.63, p=0.0001) and rTBF_mean (SMD=0.88, 95% CI: 0.35-1.4, p=0.0011).

CONCLUSIONS

The current study results indicate that tumour blood flow from ASL differs significantly with respect to the glioma grade. Despite some limitations, there is evidence that ASL may be useful to distinguish high- and low-grade gliomas. Further larger-scale studies are necessary to examine the utility of ASL to distinguish tumour grade.

Monitoring cardiac and respiratory physiology during FMRI

This article will consider how physiological monitoring can be used both as an intrinsic part of an experiment, or for removing unwanted physiological signals from the FMRI time series. As functional MRI is used for a wide variety of applications beyond the identification of regions involved in a task, different sources of noise in the time series become important. The use of arterial spin labelling sequences, either in isolation or combined with BOLD imaging, means that temporal noise must be dealt with differently. Moreover, when these are combined with global cerebrovascular stimuli, such as respiratory challenges, the standard analysis tools must be employed with great care so as not to detrimentally distort the data. Acquiring and analysing physiological data is sometimes more art than science, and this article attempts to provide some insight into common techniques as well as advice on identifying and correcting some of the problems that may be encountered.

Evaluation of Renal Blood Flow in Chronic Kidney Disease Using Arterial Spin Labeling Perfusion Magnetic Resonance Imaging

Introduction

Chronic kidney disease (CKD) is known to be associated with reduced renal blood flow. However, data in humans are limited to date.

Methods

In this study, noninvasive arterial spin labeling magnetic resonance imaging data were acquired in 33 patients with diabetes and stage 3 CKD as well as in 30 healthy controls.

Results

A significantly lower renal blood flow in both the cortex (108.4 ± 36.4 vs. 207.3 ± 41.8; P < 0.001, d = 2.52) and medulla (23.2 ± 8.9 vs. 42.6 ± 15.8; P < 0.001, d = 1.5) was observed. Both cortical (ρ = 0.67, P < 0.001) and medullary (ρ = 0.62, P < 0.001) blood flow were correlated with estimated glomerular filtration rate, and cortical blood flow was found to be confounded by age and body mass index. However, in a subset of subjects who were matched for age and body mass index (n = 6), the differences between CKD patients and control subjects remained significant in both the cortex (107.4 ± 42.8 vs. 187.51 ± 20.44; P = 0.002) and medulla (15.43 ± 8.43 vs. 39.18 ± 11.13; P = 0.002). A threshold value to separate healthy controls and CKD patients was estimated to be a cortical blood flow of 142.9 and a medullary blood flow of 24.1.

Discussion

These results support the use of arterial spin labeling in the evaluation of renal blood flow in patients with a moderate level of CKD. Whether these measurements can identify patients at risk for progressive CKD requires further longitudinal follow-up.

Quantitative Perfusion and Permeability Biomarkers in Brain Cancer from Tomographic CT and MR Images

Dynamic contrast-enhanced perfusion and permeability imaging, using computed tomography and magnetic resonance systems, are important techniques for assessing the vascular supply and hemodynamics of healthy brain parenchyma and tumors. These techniques can measure blood flow, blood volume, and blood-brain barrier permeability surface area product and, thus, may provide information complementary to clinical and pathological assessments. These have been used as biomarkers to enhance the treatment planning process, to optimize treatment decision-making, and to enable monitoring of the treatment noninvasively. In this review, the principles of magnetic resonance and computed tomography dynamic contrast-enhanced perfusion and permeability imaging are described (with an emphasis on their commonalities), and the potential values of these techniques for differentiating high-grade gliomas from other brain lesions, distinguishing true progression from posttreatment effects, and predicting survival after radiotherapy, chemotherapy, and antiangiogenic treatments are presented.

Comparison between dynamic susceptibility contrast magnetic resonance imaging and arterial spin labeling techniques in distinguishing malignant from benign brain tumors

OBJECTIVES

The purpose of this study was to preliminarily compare unenhanced arterial spin-labeled (ASL) imaging, dynamic susceptibility contrast-enhanced cerebral blood volume (DSCE-CBV) magnetic resonance imaging (MRI) for evaluation of tumor perfusion in patients with brain tumors.

MATERIALS AND METHODS

A total of 27 patients with brain tumors were examined in 1,5T MRI. Single phase and multiphase ASL, DSCE-CBV examinations were assessed by both qualitative and quantitative analysis for the detection of malignancy. Imaging results were correlated with a histopathology or follow-up.

RESULTS

Based on 31 studies in 27 patients with brain tumors, the visual inspection sensitivities for ASL and dynamic DSC perfusion imaging were 88% and 94%, respectively, with 100% specificity for both. On qualitative evaluation, sensitivities for ASL and DSC perfusion imaging perfusions were 88% and 94%, respectively, with 100% specificity for both. The highest sensitivity values for quantitative ASL imaging were obtained using a normalized cut-off ratio of 1.65, resulting in sensitivity of 94% for ASL imaging and cut-off ratio of 1.95 and sensitivity 94% for DSCE-CBV imaging.

CONCLUSION

The present study revealed similar sensitivity and specificity for both multhiphase ASL and DSC MRI. Thus, we suggest that ASL perfusion can be used in daily clinical practice.

Capability of arterial spin labeling MR imaging in localizing seizure focus in clinical seizure activity

PURPOSE

The purpose of this study was to evaluate cerebral blood flow using arterial spin labeling (ASL) perfusion magnetic resonance (MR) imaging in patients with clinical seizure activity and determine its diagnostic performance in identifying seizure focus.

MATERIALS AND METHODS

Institutional Review Board of our hospital approved this retrospective study. Informed consent was waived. Clinical seizure focus was determined by a neurologist based on seizure semiology, electroencephalography, and conventional imaging modalities. The diagnostic performance of ASL perfusion MR imaging to identifying seizure focus compared to clinical seizure focus was analyzed.

RESULTS

Clinical seizure focus was localized in 95% (42/44) of patients. The sensitivity and specificity of ASL perfusion MR imaging for identifying seizure focus were 74% (95% CI: 58%, 86%) (clinical seizure focus was localizable in 31 of 42 patients, including complete concordance in 10 patients and partial concordance in 21 patients) and 0% (95% CI: 0%, 84%) (for the two patients whose clinical seizure foci were not localizable, they were identified by ASL perfusion MR imaging), respectively. Thus, the overall accuracy of ASL perfusion MR imaging for localizing seizure focus was 70% (33/44). For 4 patients who had abnormal perfusion on ASL, their seizure foci based on ASL perfusion MR imaging were discordant with clinical seizure foci.

CONCLUSION

ASL perfusion MR imaging can provide information about perfusion status and important diagnostic clue in localizing seizure focus in patients with clinical seizure activity. It has the potential as a non-invasive complementary diagnostic tool for patients with clinical seizure activity.

Application of Arterial Spin Labelling in the Assessment of Ocular Tissues

Arterial spin labelling (ASL) is a noninvasive magnetic resonance imaging (MRI) modality, capable of measuring blood perfusion without the use of a contrast agent. While ASL implementation for imaging the brain and monitoring cerebral blood flow has been reviewed in depth, the technique is yet to be widely used for ocular tissue imaging. The human retina is a very thin but highly stratified structure and it is also situated close to the surface of the body which is not ideal for MR imaging. Hence, the application of MR imaging and ASL in particular has been very challenging for ocular tissues and retina. That is despite the fact that almost all of retinal pathologies are accompanied by blood perfusion irregularities. In this review article, we have focused on the technical aspects of the ASL and their implications for its optimum adaptation for retinal blood perfusion monitoring. Retinal blood perfusion has been assessed through qualitative or invasive quantitative methods but the prospect of imaging flow using ASL would increase monitoring and assessment of retinal pathologies. The review provides details of ASL application in human ocular blood flow assessment.

Arterial Spin Labeling Techniques 2009-2014

PURPOSE

Arterial spin labeling (ASL) techniques have been implemented across a diverse range of clinical and experimental applications. This review aims to evaluate the current feasibility of ASL in clinical neuroradiology based on recent improvements to ASL sequences and highlight areas for potential clinical applications.

METHODS AND MATERIALS

In December 2014, a literature search was conducted on PubMed Central, EMBASE, and Scopus using the search terms: "arterial spin labeling, neuroradiology," for studies published between 2009 and 2014 (inclusive). Of 483 studies matching the inclusion criteria, the number of studies using continuous, pseudocontinuous, pulsed, and velocity-selective ASL sequences was 42, 209, 226, and 3, respectively. Studies were classified based on several common clinical applications according to the type of ASL sequence used. Studies using pulsed ASL and pseudo-continuous ASL were grouped based on common sequences.

RESULTS

The number of clinical studies was 264. Numerous studies applied ASL to stroke management (43 studies), drug testing (21 studies), neurodegenerative diseases (40 studies), and psychiatric disorders (26 studies).

CONCLUSIONS

This review discusses several factors hindering the implementation of clinical ASL and ASL-related radiofrequency safety issues encountered in clinical practice. However, a limited number of search terms were used. Further development of robust sequences with multislice imaging capabilities and reduced radiofrequency energy deposition will hopefully improve the clinical acceptance of ASL.

Reproducibility of Kidney Perfusion Measurements With Arterial Spin Labeling at 1.5 Tesla MRI Combined With Semiautomatic Segmentation for Differential Cortical and Medullary Assessment

Magnetic resonance imaging with arterial spin labeling (ASL) is a noninvasive approach to measure organ perfusion. The purpose of this study was to evaluate the reproducibility of ASL kidney perfusion measurements with semiautomatic segmentation, which allows separate quantification of cortical and medullary perfusion. The right kidneys of 14 healthy volunteers were examined 6 times on 2 occasions (3 times at each occasion). There was a 10-minute pause between each examination and a 14-day interval between the 2 occasions. Cortical, medullary, and whole kidney parenchymal perfusion was determined with customized semiautomatic segmentation software. Coefficient of variances (CVs) and intraclass correlations (ICCs) were calculated. Mean whole, cortical, and medullary kidney perfusion was 307.26 ± 25.65, 337.10 ± 34.83, and 279.61 ± 26.73 mL/min/100 g, respectively. On session 1, mean perfusion for the whole kidney, cortex, and medulla was 307.08 ± 26.91, 336.79 ± 36.54, and 279.60 ± 27.81 mL/min/100 g, respectively, and on session 2, 307.45 ± 24.65, 337.41 ± 33.48, and 279.61 ± 25.94 mL/min/100 g, respectively (P > 0.05; R² = 0.60/0.59/0.54). For whole, cortical, and medullary kidney perfusion, the total ICC/CV were 0.97/3.43 ± 0.86%, 0.97/4.19 ± 1.33%, and 0.96/4.12 ± 1.36%, respectively. Measurements did not differ significantly and showed a very good correlation (P > 0.05; R² = 0.75/0.76/0.65). ASL kidney measurements combined with operator-independent semiautomatic segmentation revealed high correlation and low variance of cortical, medullary, and whole kidney perfusion.

Renal perfusion imaging with two-dimensional navigator gated arterial spin labeling

PURPOSE

To develop a navigator technique enabling free-breathing acquisition to afford sufficient signal averaging for quantitative renal perfusion measurement using arterial spin labeling MRI.

METHODS

A novel two-dimensional (2D) navigator technique was implemented in concert with flow-sensitive alternating inversion recovery (FAIR) preparation and true fast imaging with steady precession (True-FISP) readout. The navigator images were obtained with a low-resolution fast low angle shot readout at end of each arterial spin labeling acquisition. A retrospective algorithm was developed to automatically detect respiratory motion for selective signal averaging. The 2D navigator-gated FAIR True-FISP sequence was performed in ten healthy volunteers and five patients with chronic kidney disease.

RESULTS

Excellent image quality and comparable cortical perfusion rates (healthy: 276 ± 28 mL/100 g/min, patients: 155 ± 25 mL/100 g/min) to literature values were obtained. An average of 3-fold signal-to-noise ratio improvement was obtained in the 2D navigator-gated approach compared with the breath-hold acquisition in healthy volunteers. Good image quality was achieved in patients while the results from breath-hold acquisition were unusable. The quantitative perfusion rates were significantly lower in chronic kidney disease patients compared with the healthy volunteers.

CONCLUSION

2D navigator-gated free breathing arterial spin labeling is feasible and is a noninvasive method to evaluate renal perfusion both in healthy subjects and those with chronic kidney disease.

Brain perfusion evaluated by perfusion-weighted magnetic resonance imaging before and after stenting internal carotid artery stenosis in asymptomatic and symptomatic patients

PURPOSE

To evaluate the brain perfusion with MRI perfusion weighted imaging (PWI) before and after ICA stenting in asymptomatic and symptomatic patients.

MATERIALS AND METHODS

PWI was performed 3-21 days before and 3 days after ICA stenting in 31 asymptomatic patients with ICA >70% stenosis - Group I, and in 14 symptomatic patients with ICA >50% stenosis - Group II. PWI was evaluated qualitatively and quantitatively in 5 cerebral territories with: mean transit time (MTT), cerebral blood volume (CBV) and cerebral blood flow (CBF). Mean values of perfusion parameters were measured before and after stenting ΔMTT, ΔCBV, ΔCBF were calculated as subtraction of after-treatment values from those before treatment.

RESULTS

In qualitative evaluation after ICA stenting perfusion was normalized in 21 patients (80.8%) in Group I and in 8 patients (80%) in Group II. In quantitative estimation MTT decreased significantly after CAS on stented side vs. non-stented side in all examined patients regardless of the group, p<0.05. MTT decreased more in Group II than in Group I in all territories (p<0.05) with the exception of temporal lobe. CBV and CBF have shown insignificant differences.

Functional imaging of the human placenta with magnetic resonance

Abnormal placentation is responsible for most failures in pregnancy; however, an understanding of placental functions remains largely concealed from noninvasive, in vivo investigations. Magnetic resonance imaging (MRI) is safe in pregnancy for magnetic fields of up to 3 Tesla and is being used increasingly to improve the accuracy of prenatal imaging. Functional MRI (fMRI) of the placenta has not yet been validated in a clinical setting, and most data are derived from animal studies. FMRI could be used to further explore placental functions that are related to vascularization, oxygenation, and metabolism in human pregnancies by the use of various enhancement processes. Dynamic contrast-enhanced MRI is best able to quantify placental perfusion, permeability, and blood volume fractions. However, the transplacental passage of Gadolinium-based contrast agents represents a significant safety concern for this procedure in humans. There are alternative contrast agents that may be safer in pregnancy or that do not cross the placenta. Arterial spin labeling MRI relies on magnetically labeled water to quantify the blood flows within the placenta. A disadvantage of this technique is a poorer signal-to-noise ratio. Based on arterial spin labeling, placental perfusion in normal pregnancy is 176 ± 91 mL × min(-1) × 100 g(-1) and decreases in cases with intrauterine growth restriction. Blood oxygen level-dependent and oxygen-enhanced MRIs do not assess perfusion but measure the response of the placenta to changes in oxygen levels with the use of hemoglobin as an endogenous contrast agent. Diffusion-weighted imaging and intravoxel incoherent motion MRI do not require exogenous contrast agents, instead they use the movement of water molecules within tissues. The apparent diffusion coefficient and perfusion fraction are significantly lower in placentas of growth-restricted fetuses when compared with normal pregnancies. Magnetic resonance spectroscopy has the ability to extract information regarding metabolites from the placenta noninvasively and in vivo. There are marked differences in all 3 metabolites N-acetyl aspartate/choline levels, inositol/choline ratio between small, and adequately grown fetuses. Current research is focused on the ability of each fMRI technique to make a timely diagnosis of abnormal placentation that would allow for appropriate planning of follow-up examinations and optimal scheduling of delivery. These research programs will benefit from the use of well-defined sequences, standardized imaging protocols, and robust computational methods.

Childhood extracranial neoplasms: the role of imaging in drug development and clinical trials

Cancer is the leading cause of death in children older than 1 year of age and new drugs are necessary to improve outcomes. Imaging is crucial to the drug development process and assessment of therapeutic response. In adults, tumours are often assessed with CT using size criteria. Unfortunately, techniques established in adults are not necessarily applicable in children due to differing pathophysiology, ability to cooperate and increased susceptibility to ionising radiation. MRI, in particular quantitative MRI, has to date not been fully utilised in children with extracranial neoplasms. The specific challenges of imaging in children, the potential for functional imaging techniques to inform upon and their inclusion in clinical trials are discussed.

Arterial Spin Labeling Magnetic Resonance Perfusion for Traumatic Brain Injury: Technical Challenges and Potentials

Traumatic brain injury (TBI), including concussion, is a public health concern, as it affects over 1.7 million persons in the United States per year. Yet, the diagnosis of TBI, particularly mild TBI (mTBI), can be controversial, as neuroimaging findings can be sparse on conventional magnetic resonance and computed tomography examinations, and when present, often poorly correlate with clinical signs and symptoms. Furthermore, the discussion of TBI, concussion, and head impact exposure is immediately complicated by the many differing opinions of what constitutes each, their respective severities, and how the underlying biomechanics of the inciting head impact might alter the distribution, severity, and prognosis of the underlying brain injury. Advanced imaging methodologies hold promise in improving the sensitivity and detectability of associated imaging biomarkers that might better correlate with patient outcome and prognostication, allowing for improved triage and therapeutic guidance in the setting of TBI, particularly in mTBI. This work will examine the defining symptom complex associated with mTBI and explore changes in cerebral blood flow measured by arterial spin labeling, as a potential imaging biomarker for TBI, and briefly correlate these observations with findings identified by single photon emission computed tomography and positron emission tomography imaging.

Advanced Noncontrast MR Imaging in Musculoskeletal Radiology

Multiple nonmorphologic magnetic resonance sequences are available in musculoskeletal imaging that can provide additional information to better characterize and diagnose musculoskeletal disorders and diseases. These sequences include blood-oxygen-level-dependent (BOLD), arterial spin labeling (ASL), diffusion-weighted imaging (DWI), and diffusion-tensor imaging (DTI). BOLD and ASL provide different methods to evaluate skeletal muscle microperfusion. The BOLD signal reflects the ratio between oxyhemoglobin and deoxyhemoglobin. ASL uses selective tagging of inflowing blood spins in a specific region for calculating local perfusion. DWI and DTI provide information about the structural integrity of soft tissue including muscles and fibers as well as pathologies.

Perfusion imaging in neuro-oncology: basic techniques and clinical applications

Perfusion imaging is a method for assessing the flow of blood occurring at the tissue level and can be accomplished by both CT and MR perfusion techniques. The use of perfusion imaging has increased substantially in the past decade, particularly in neuro-oncologic imaging, where it is has been used for brain tumor grading and directing biopsies or targeted therapy, as well as for the evaluation of treatment response and disease progression. This article discusses the basic principles and techniques of perfusion imaging, as well as its applications in neuro-oncology.

ASFNR recommendations for clinical performance of MR dynamic susceptibility contrast perfusion imaging of the brain

MR perfusion imaging is becoming an increasingly common means of evaluating a variety of cerebral pathologies, including tumors and ischemia. In particular, there has been great interest in the use of MR perfusion imaging for both assessing brain tumor grade and for monitoring for tumor recurrence in previously treated patients. Of the various techniques devised for evaluating cerebral perfusion imaging, the dynamic susceptibility contrast method has been employed most widely among clinical MR imaging practitioners. However, when implementing DSC MR perfusion imaging in a contemporary radiology practice, a neuroradiologist is confronted with a large number of decisions. These include choices surrounding appropriate patient selection, scan-acquisition parameters, data-postprocessing methods, image interpretation, and reporting. Throughout the imaging literature, there is conflicting advice on these issues. In an effort to provide guidance to neuroradiologists struggling to implement DSC perfusion imaging in their MR imaging practice, the Clinical Practice Committee of the American Society of Functional Neuroradiology has provided the following recommendations. This guidance is based on review of the literature coupled with the practice experience of the authors. While the ASFNR acknowledges that alternate means of carrying out DSC perfusion imaging may yield clinically acceptable results, the following recommendations should provide a framework for achieving routine success in this complicated-but-rewarding aspect of neuroradiology MR imaging practice.

Arterial spin labeling perfusion cardiovascular magnetic resonance of the calf in peripheral arterial disease: cuff occlusion hyperemia vs exercise

BACKGROUND

Assessment of calf muscle perfusion requires a physiological challenge. Exercise and cuff-occlusion hyperemia are commonly used methods, but it has been unclear if one is superior to the other. We hypothesized that post-occlusion calf muscle perfusion (Cuff) with pulsed arterial spin labeling (PASL) cardiovascular magnetic resonance (CMR) at 3 Tesla (T) would yield greater perfusion and improved reproducibility compared to exercise hyperemia in studies of peripheral arterial disease (PAD).

METHODS

Exercise and Cuff cohorts were independently recruited. PAD patients had an ankle brachial index (ABI) between 0.4-0.9. Controls (NL) had no risk factors and ABI 0.9-1.4. Subjects exercised until exhaustion (15 NL-Ex, 15 PAD-Ex) or had a thigh cuff inflated for 5 minutes (12 NL-Cuff, 11 PAD-Cuff). Peak exercise and average cuff (Cuff mean ) perfusion were compared. Six participants underwent both cuff and exercise testing. Reproducibility was tested in 8 Cuff subjects (5 NL, 3 PAD).

RESULTS

Controls had greater perfusion than PAD independent of stressor (NL-Ex 74 ± 21 vs. PAD-Ex 43 ± 10, p = 0.01; NL-Cuff mean 109 ± 39 vs. PAD-Cuff mean 34 ± 17 ml/min-100 g, p < 0.001). However, there was no difference between exercise and Cuff mean perfusion within groups (p > 0.6). Results were similar when the same subjects had the 2 stressors performed. Cuff mean had superior reproducibility (Cuff mean ICC 0.98 vs. Exercise ICC 0.87) and area under the receiver operating characteristic curve (Cuff mean 0.992 vs. Exercise 0.905).

CONCLUSIONS

Cuff hyperemia differentiates PAD patients from controls, as does exercise stress. Cuff mean and exercise calf perfusion values are similar. Cuff occlusion hyperemia has superior reproducibility and thus may be the preferred stressor.

Assessment of functional and structural damage in brain parenchyma in patients with vitamin B12 deficiency: A longitudinal perfusion and diffusion tensor imaging study

INTRODUCTION

Vitamin B12 deficiency may cause neural tissue damage. Even in advanced stages, conventional imaging of brain usually appears normal in vitamin B12 deficient patients. The aim of this study was to assess the structural and functional changes in brain of patients with vitamin B12 deficiency before and after six weeks of vitamin B12 supplementation using diffusion tensor imaging and pseudo-continuous arterial spin labelling (PCASL).

METHODS

MR imaging including DTI and PCASL and neuropsychological tests (NPT) were performed in 16 patients with vitamin B12 deficiency and 16 controls before and after 6weeks of therapy. Cerebral blood flow (CBF) derived from PCASL and DTI indices was calculated in brain of patients with vitamin B12 deficiency and controls.

RESULTS

Patient with vitamin B12 deficiency showed altered neuropsychological scores and altered CBF as well as fractional anisotropy (FA) values in various brain regions as compared with controls. Both CBF values and neuropsychological scores showed complete reversibility at 6weeks post therapy. Though FA values showed significant recovery, it failed to show complete recovery.

CONCLUSION

Our results suggest that micro-structural recovery lags behind functional recovery in patients with vitamin B12 deficiency following therapy and CBF change may be used as an early predictor of complete recovery in patients with B12 deficiency.

Old wine in new bottles: validating the clinical utility of SPECT in predicting cognitive performance in mild traumatic brain injury

The neural underpinnings of cognitive dysfunction in mild traumatic brain injury (TBI) are not fully understood. Consequently, patient prognosis using existing clinical imaging is somewhat imprecise. Single photon emission computed tomography (SPECT) is a frequently employed investigation in this population, notwithstanding uncertainty over the clinical utility of the data obtained. In this study, subjects with mild TBI underwent (99m)Tc-ECD SPECT scanning, and were administered a brief battery of cognitive tests and self-report symptom scales of concussion and emotional distress. Testing took place 2 weeks (n=84) and 1 year (n=49) post-injury. Multivariate analysis (i.e., partial least squares analysis) revealed that frontal perfusion in right superior frontal and middle frontal gyri predicted poorer performance on the Stroop test, an index of executive function, both at initial and follow-up testing. Conversely, SPECT scans categorized as normal or abnormal by radiologists did not differentiate cognitively impaired from intact subjects. These results demonstrate the clinical utility of SPECT in mild TBI, but only when data are subjected to blood flow quantification analysis.

Heritability and genetic association analysis of neuroimaging measures in the Diabetes Heart Study

Patients with type 2 diabetes are at increased risk of age-related cognitive decline and dementia. Neuroimaging measures such as white matter lesion volume, brain volume, and fractional anisotropy may reflect the pathogenesis of these cognitive declines, and genetic factors may contribute to variability in these measures. This study examined multiple neuroimaging measures in 465 participants from 238 families with extensive genotype data in the type 2 diabetes enriched Diabetes Heart Study-Mind cohort. Heritability of these phenotypes and their association with candidate single-nucleotide polymorphisms (SNPs), and SNP data from genome- and exome-wide arrays were explored. All neuroimaging measures analyzed were significantly heritable (ĥ(2) = 0.55-0.99 in unadjusted models). Seventeen candidate SNPs (from 16 genes/regions) associated with neuroimaging phenotypes in prior studies showed no significant evidence of association. A missense variant (rs150706952, A432V) in PLEKHG4B from the exome-wide array was significantly associated with white matter mean diffusivity (p = 3.66 × 10(-7)) and gray matter mean diffusivity (p = 2.14 × 10(-7)). This analysis suggests genetic factors contribute to variation in neuroimaging measures in a population enriched for metabolic disease and other associated comorbidities.

Inter-study reproducibility of arterial spin labelling magnetic resonance imaging for measurement of renal perfusion in healthy volunteers at 3 Tesla

BACKGROUND

Measurement of renal perfusion is a crucial part of measuring kidney function. Arterial spin labelling magnetic resonance imaging (ASL MRI) is a non-invasive method of measuring renal perfusion using magnetised blood as endogenous contrast. We studied the reproducibility of ASL MRI in normal volunteers.

METHODS

ASL MRI was performed in healthy volunteers on 2 occasions using a 3.0 Tesla MRI scanner with flow-sensitive alternating inversion recovery (FAIR) perfusion preparation with a steady state free precession (True-FISP) pulse sequence. Kidney volume was measured from the scanned images. Routine serum and urine biochemistry were measured prior to MRI scanning.

RESULTS

12 volunteers were recruited yielding 24 kidneys, with a mean participant age of 44.1 ± 14.6 years, blood pressure of 136/82 mmHg and chronic kidney disease epidemiology formula estimated glomerular filtration rate (CKD EPI eGFR) of 98.3 ± 15.1 ml/min/1.73 m2. Mean kidney volumes measured using the ellipsoid formula and voxel count method were 123.5 ± 25.5 cm3, and 156.7 ± 28.9 cm3 respectively. Mean kidney perfusion was 229 ± 41 ml/min/100 g and mean cortical perfusion was 327 ± 63 ml/min/100 g, with no significant differences between ASL MRIs. Mean absolute kidney perfusion calculated from kidney volume measured during the scan was 373 ± 71 ml/min. Bland Altman plots were constructed of the cortical and whole kidney perfusion measurements made at ASL MRIs 1 and 2. These showed good agreement between measurements, with a random distribution of means plotted against differences observed. The intra class correlation for cortical perfusion was 0.85, whilst the within subject coefficient of variance was 9.2%. The intra class correlation for whole kidney perfusion was 0.86, whilst the within subject coefficient of variance was 7.1%.

CONCLUSIONS

ASL MRI at 3.0 Tesla provides a repeatable method of measuring renal perfusion in healthy subjects without the need for administration of exogenous compounds. We have established normal values for renal perfusion using ASL MRI in a cohort of healthy volunteers.

Arterial spin-labeling evaluation of cerebrovascular reactivity to acetazolamide in healthy subjects

BACKGROUND AND PURPOSE

Arterial spin-labeling MR imaging permits safe, repeated CBF measurement. We investigated the potential and technical factors of arterial spin-labeling imaging in assessing cerebrovascular reactivity to acetazolamide.

MATERIALS AND METHODS

The regional CBF was measured in 8 healthy volunteers by use of a 3D pseudocontinuous arterial spin-labeling sequence. Arterial spin labeling imaging was performed at rest and every 2 minutes after intravenous acetazolamide injection. To evaluate repeatability, regional CBF measurements were repeated without acetazolamide within an imaging session and on a separate day. Additionally, arterial spin-labeling imaging was performed at rest and after acetazolamide injection with different postlabeling delays, and regional cerebrovascular reactivity was calculated.

RESULTS

The regional CBF started to increase immediately after acetazolamide injection and peaked at approximately 10 minutes, followed by a slow decrease. Favorable intrasession repeatability was demonstrated, especially when scanner tuning was omitted between scans. Rest regional CBF was slightly lower with a postlabeling delay of 2525 ms than with a postlabeling delay of 1525 ms, and the postlabeling delay-dependent difference was more evident for regional CBF after acetazolamide injection and regional cerebrovascular reactivity.

CONCLUSIONS

Arterial spin-labeling imaging allows evaluation of the distribution, magnitude, and time course of cerebrovascular response to acetazolamide. The influence of the postlabeling delay on the estimated cerebrovascular reactivity should be noted.

The Cerebral Blood Flow Biomedical Informatics Research Network (CBFBIRN) database and analysis pipeline for arterial spin labeling MRI data

Arterial spin labeling (ASL) is a magnetic resonance imaging technique that provides a non-invasive and quantitative measure of cerebral blood flow (CBF). After more than a decade of active research, ASL is now emerging as a robust and reliable CBF measurement technique with increased availability and ease of use. There is a growing number of research and clinical sites using ASL for neuroscience research and clinical care. In this paper, we present an online CBF Database and Analysis Pipeline, collectively called the Cerebral Blood Flow Biomedical Informatics Research Network (CBFBIRN) that allows researchers to upload and share ASL and clinical data. In addition to serving the role as a central data repository, the CBFBIRN provides a streamlined data processing infrastructure for CBF quantification and group analysis, which has the potential to accelerate the discovery of new scientific and clinical knowledge. All capabilities and features built into the CBFBIRN are accessed online using a web browser through a secure login. In this work, we begin with a general description of the CBFBIRN system data model and its architecture, then devote the remainder of the paper to the CBFBIRN capabilities. The latter part of our work is divided into two processing modules: (1) Data Upload and CBF Quantification Module; (2) Group Analysis Module that supports three types of analysis commonly used in neuroscience research. To date, the CBFBIRN hosts CBF maps and associated clinical data from more than 1,300 individual subjects. The data have been contributed by more than 20 different research studies, investigating the effect of various conditions on CBF including Alzheimer’s, schizophrenia, bipolar disorder, depression, traumatic brain injury, HIV, caffeine usage, and methamphetamine abuse. Several example results, generated by the CBFBIRN processing modules, are presented. We conclude with the lessons learned during implementation and deployment of the CBFBIRN and our experience in promoting data sharing.

Reduced cerebral arterial spin-labeled perfusion in children with neurofibromatosis type 1

BACKGROUND AND PURPOSE

Neurofibromatosis type 1 is associated with increased risk for stroke, cerebral vasculopathy, and neurocognitive deficits, but underlying hemodynamic changes in asymptomatic children remain poorly understood. We hypothesized that children with neurofibromatosis type 1 have decreased cerebral blood flow.

MATERIALS AND METHODS

Arterial spin-labeled CBF was measured in 14 children with neurofibromatosis type 1 (median age, 9.7 years; mean, 10.2 years; range, 22 months to 18 years) and compared with age-matched control subjects on 3T MR imaging. Three-dimensional pseudocontinuous spin-echo arterial spin-labeled technique was used. Measurements were obtained at cortical gray matter of bilateral cerebral hemispheres and centrum semiovale by use of the ROI method. Comparison by Mann-Whitney test was used, with Bonferroni-adjusted P values ≤.004 judged as significant.

RESULTS

We identified 7 of 12 areas with significantly diminished arterial spin-labeled CBF in patients with neurofibromatosis type 1 compared with control subjects. These areas included the anterior cingulate gyrus (P = .001), medial frontal cortex (P = .004), centrum semiovale (P = .004), temporo-occipital cortex (P = .002), thalamus (P = .001), posterior cingulate gyrus (P = .002), and occipital cortex (P = .001). Among patients with neurofibromatosis type 1, there were no significant differences in these regions on the basis of the presence of neurofibromatosis type 1 spots or neurocognitive deficits.

CONCLUSIONS

Reduced cerebral perfusion was seen in children with neurofibromatosis type 1, particularly in the posterior circulation and the vascular borderzones of the middle and posterior cerebral arteries.

Clinical applications of arterial spin labeling

MR arterial spin labeling is primarily applied as a neuroimaging method to measure cerebral blood flow. As this technique becomes more widely available, a basic understanding of the clinical applications is necessary for optimal utilization in the setting of patient care. This review focuses on the use of arterial spin labeling imaging for the evaluation of cerebrovascular disease, brain tumors and neuropsychiatric illness.

Atlas-based and DTI-guided quantification of human brain cerebral blood flow: feasibility, quality assurance, spatial heterogeneity and age effects

Accurate and noninvasive quantification of regional cerebral blood perfusion (CBF) of the human brain tissue would advance the study of the complex interplay between human brain structure and function, in both health and disease. Despite the plethora of works on CBF in gray matter, a detailed quantitative white matter perfusion atlas has not been presented on healthy adults using the International Consortium for Brain Mapping atlases. In this study, we present a host of assurance measures such as temporal stability, spatial heterogeneity and age effects of regional and global CBF in selected deep, cortical gray matter and white matter tracts identified and quantified using diffusion tensor imaging (DTI). We utilized whole brain high-resolution DTI combined with arterial spin labeling to quantify regional CBF on 15 healthy adults aged 23.2-57.1years. We present total brain and regional CBF, corresponding volume, mean diffusivity and fractional anisotropy spatial heterogeneity, and dependence on age as additional quality assurance measures to compare with published trends using both MRI and nuclear medicine methods. Total CBF showed a steady decrease with age in gray matter (r=-0.58; P=.03), whereas total CBF of white matter did not significantly change with age (r=0.11; P=.7). This quantitative report offers a preliminary baseline of CBF, volume and DTI measurements for the design of future multicenter and clinical studies utilizing noninvasive perfusion and DT-MRI.

Feasibility of MR perfusion-weighted imaging by use of a time-spatial labeling inversion pulse

Perfusion-weighted imaging (PWI) by use of arterial spin labeling (ASL) has been introduced to the clinical setting. However, it is not widely available because it requires specialized pulse sequences. Imaging using a time-spatial labeling inversion pulse (time-SLIP), which is a magnetic resonance angiography (MRA) technique that is based on ASL, can be used in various situations. In this study, we examined the feasibility of time-SLIP PWI. Two types of time-SLIP sequences were evaluated: (1) a single inversion recovery (IR) pulse sequence, which is the same as that used in conventional time-SLIP MRA except for the timing of data acquisition, and (2) a dual IR pulse sequence, where a second, non-selective, IR pulse was added during the inflow time to suppress background signals. Subtraction processing is performed between the "on" and "off" settings of the first IR pulse (time-SLIP tag) to obtain PWI. The average signal intensity was measured in a uniform phantom as the residual of the background, and in five healthy subjects as the perfusion signal. The average signal-to-noise ratio (SNR) was also measured in the five subjects. All imaging was performed with a 1.5-T MR scanner. Images using the dual IR method showed lower background signals and higher perfusion signals compared with images using the single IR method. However, the SNR was lower in images with the dual IR method. These results demonstrate that a time-SLIP, which is an MRA method, can be used for obtaining cerebral PWI simply by adjusting the imaging parameters.

Arterial spin labeling MR imaging reproducibly measures peak-exercise calf muscle perfusion: a study in patients with peripheral arterial disease and healthy volunteers

OBJECTIVES

This study hypothesized that arterial spin labeling (ASL) magnetic resonance (MR) imaging at 3-T would be a reliable noncontrast technique for measuring peak exercise calf muscle blood flow in both healthy volunteers and patients with peripheral arterial disease (PAD) and will discriminate between these groups.

BACKGROUND

Prior work demonstrated the utility of first-pass gadolinium-enhanced calf muscle perfusion MR imaging in patients with PAD. However, patients with PAD often have advanced renal disease and cannot receive gadolinium.

METHODS

PAD patients had claudication and an ankle brachial index of 0.4 to 0.9. Age-matched normal subjects (NL) had no PAD risk factors and were symptom-free with exercise. All performed supine plantar flexion exercise in a 3-T MR imaging scanner using a pedal ergometer until exhaustion or limiting symptoms and were imaged at peak exercise with 15 averaged ASL images. Peak perfusion was measured from ASL blood flow images by placing a region of interest in the calf muscle region with the greatest signal intensity. Perfusion was compared between PAD patients and NL and repeat testing was performed in 12 subjects (5 NL, 7 PAD) for assessment of reproducibility.

RESULTS

Peak exercise calf perfusion of 15 NL (age: 54 ± 9 years) was higher than in 15 PAD patients (age: 64 ± 5 years, ankle brachial index: 0.70 ± 0.14) (80 ± 23 ml/min - 100 g vs. 49 ± 16 ml/min/100 g, p < 0.001). Five NL performed exercise matched to PAD patients and again demonstrated higher perfusion (84 ± 25 ml/min - 100 g, p < 0.002). As a measure of reproducibility, intraclass correlation coefficient between repeated studies was 0.87 (95% confidence interval [CI]: 0.61 to 0.96). Interobserver reproducibility was 0.96 (95% CI: 0.84 to 0.99).

CONCLUSIONS

ASL is a reproducible noncontrast technique for quantifying peak exercise blood flow in calf muscle. Independent of exercise time, ASL discriminates between NL and PAD patients. This technique may prove useful for clinical trials of therapies for improving muscle perfusion, especially in patients unable to receive gadolinium.

Comparison of regional cerebral blood flow responses to hypoglycemia using pulsed arterial spin labeling and positron emission tomography

Different brain regions sense and modulate the counterregulatory responses that can occur in response to declining plasma glucose levels. The aim of this study was to determine if changes in regional cerebral blood flow (rCBF) during hypoglycemia relative to euglycemia are similar for two imaging modalities–pulsed arterial spin labeling magnetic resonance imaging (PASL-MRI) and positron emission tomography (PET). Nine healthy non-diabetic participants underwent a hyperinsulinemic euglycemic (92±3 mg/dL) – hypoglycemic (53±1 mg/dL) clamp. Counterregulatory hormone levels were collected at each of these glycemic levels and rCBF measurements within the previously described network of hypoglycemia-responsive regions (thalamus, medial prefrontal cortex and globus pallidum) were obtained using PASL-MRI and [¹⁵O] water PET. In response to hypoglycemia, rCBF was significantly increased in the thalamus, medial prefrontal cortex, and globus pallidum compared to euglycemia for both PASL-MRI and PET methodologies. Both imaging techniques found similar increases in rCBF in the thalamus, medial prefrontal cortex, and globus pallidum in response to hypoglycemia. These brain regions may be involved in the physiologic and symptom responses to hypoglycemia. Compared to PET, PASL-MRI may provide a less invasive, less expensive method for assessing changes in rCBF during hypoglycemia without radiation exposure.