Pulsed Arterial Spin Labeling MRI Research Articles

Functional Brain Network Connectivity Changes in Children and Adolescents with Attention- Deficit Hyperactivity Disorder: A Resting-State Brain Functional Magnetic Resonance Imaging Study

Background: ADHD is one of the most common psychiatric disorders in children and adolescents. Altered functional connectivity has been associated with ADHD symptoms. This study aimed to investigate abnormal changes in the functional connectivity of resting-state brain networks (RSNs) among children and adolescents with different subtypes of ADHD.
 Methods: This study was performed on 50 participants Group A: included 30 children and adolescents with ADHD Group B: included 20 normal typically developing controls. All participants aged between 7 and 16 years. All study patients. All participants underwent a neuropsychological assessment by applying the DSM-5 criteria to them. All study children and adolescents will undergo a R-fMRI examination, including Blood oxygenation level dependent BOLD-MRI and pulsed Arterial spin labeling MRI (PASL-MRI).
 Results: According to Conner’s Rating scale, there was a significant difference between ADHD subtypes and severity. Children with combined subtype were more likely to have severe degree in both teacher and parent editions of Conner’s Rating Scale. On the other hand, children with inattentive subtype had less severe degrees by both teacher and parent edition. There were a statistically significance difference between both genders as regard ADHD severity according to Conner’s Rating scale (Teacher and parent editions) (P value = 0.049, 0.028 respectively). Males were significantly affected by moderate and severe type compared to females whose affection were mostly mild and moderate. According to CBCL, most of ADHD children had low competence parameters. There was a statistically significant difference (P value < 0.001) on the type of ADHD and social competence in the studied children, where the lowest parameters were found in children with hyperactive type.
 Conclusion: There was a statistically significant difference on the type of ADHD and social competence, where the lowest parameters were found in children with hyperactive type.

Neural correlates of mindfulness meditation-related anxiety relief

Anxiety is the cognitive state related to the inability to control emotional responses to perceived threats. Anxiety is inversely related to brain activity associated with the cognitive regulation of emotions. Mindfulness meditation has been found to regulate anxiety. However, the brain mechanisms involved in meditation-related anxiety relief are largely unknown. We employed pulsed arterial spin labeling MRI to compare the effects of distraction in the form of attending to the breath (ATB; before meditation training) to mindfulness meditation (after meditation training) on state anxiety across the same subjects. Fifteen healthy subjects, with no prior meditation experience, participated in 4 d of mindfulness meditation training. ATB did not reduce state anxiety, but state anxiety was significantly reduced in every session that subjects meditated. Meditation-related anxiety relief was associated with activation of the anterior cingulate cortex, ventromedial prefrontal cortex and anterior insula. Meditation-related activation in these regions exhibited a strong relationship to anxiety relief when compared to ATB. During meditation, those who exhibited greater default-related activity (i.e. posterior cingulate cortex) reported greater anxiety, possibly reflecting an inability to control self-referential thoughts. These findings provide evidence that mindfulness meditation attenuates anxiety through mechanisms involved in the regulation of self-referential thought processes.

The importance of RF bandwidth for effective tagging in pulsed arterial spin labeling MRI at 9.4T

The movement towards MRI at higher field strengths (>7T) has enhanced the appeal of arterial spin labeling (ASL) for many applications due to improved SNR of the measurements. Greater field strength also introduces increased magnetic susceptibility effects resulting in marked B(0) field inhomogeneity. Although B(0) field perturbations can be minimised by shimming over the imaging volume, marked field inhomogeneity is likely to remain within the labeling region for pulsed ASL (PASL). This study highlights a potential source of error in cerebral blood flow quantification using PASL at high field. We show that labeling efficiency in flow-sensitive alternating inversion recovery (FAIR) displayed marked sensitivity to the RF bandwidth of the inversion pulse in a rat model at 9.4T. The majority of preclinical PASL studies have not reported the bandwidth of the inversion pulse. We show that a high bandwidth pulse of > = 15 kHz was required to robustly overcome the field inhomogeneity in the labeling region at high field strength, which is significantly greater than the inversion bandwidth ~2-3 kHz used in previous studies. Unless SAR levels are at their limit, we suggest the use of a high bandwidth labeling pulse for most PASL studies.

Complex relationships between cerebral blood flow and brain atrophy in early Huntington's disease.

Alterations in cerebral blood flow (CBF) may play an important role in the pathophysiology of neurodegenerative disorders such as Huntington's disease (HD). While a few reports have suggested reductions in CBF in HD, little is known about their extent and whether, or how, they might be related to atrophy and to clinical symptoms. We used pulsed arterial-spin labeling MRI in conjunction with high-resolution anatomical MRI to non-invasively measure regional CBF in 17 early stage HD subjects and 41 age- and gender-matched healthy controls. We found profound yet heterogeneous CBF reductions in the cortex, extending to the sensorimotor, paracentral, inferior temporal and lateral occipital regions, with sparing of the neighboring postcentral gyrus, insula and medial occipital areas. As expected, CBF in subcortical regions was also profoundly reduced, and to a similar degree. Unexpectedly, however, the association between CBF reductions and regional atrophy was complex, the two being directly associated in certain areas but not with others. In contrast, CBF was associated with performance on the Stroop, suggesting a potentially important role for alterations in CBF in cognitive deficits in HD. The work described here may have broad-reaching implications for our understanding of HD pathogenesis, progression and emerging therapies.

Differential effects of intranasal insulin and caffeine on cerebral blood flow

Insulin is an important modulator of brain functions such as memory and appetite regulation. Besides the effect on neuronal activity, it is also possible that insulin has a direct vasodilatory effect on cerebral blood flow (CBF). We investigated the impact of increased insulin levels in the central nervous system on basal and task-induced CBF as well as blood oxygenation level-dependent (BOLD) response in the visual cortex using pulsed arterial spin-labeling MRI. An intranasal insulin application was used to avoid peripheral hyperinsulinaemia, which would lead to a cascade of hormonal changes. In a control experiment, caffeine was applied due to its well-known impact on the vasculature of the brain leading to a reliable reduction of CBF. Eight lean subjects were included in the study. On 2 separate days, intranasal human insulin or caffeine tablets were given to the subjects after fasting over night. On each day, basal CBF and task-induced CBF were measured before and 30 min after application of insulin or caffeine in each subject. During the task condition, a flickering checkerboard was presented. Insulin had no effect on basal CBF and task-induced CBF in comparison with drug-free baseline measurement in the visual cortex and control regions. After caffeine application, however, there was a significant decrease of CBF during stimulation in the visual cortex. The BOLD response was not altered by insulin or caffeine between pre- and postdose measurements. In conclusion, we found no evidence for a direct vasodilatory effect of intranasal insulin on the cerebral vascular system in this study.

PW01-74 - Cerebral blood hypoperfusion in mild cognitive impairment and mild dementia in Alzheimer's disease measured with pulsed arterial spin labeling MRI

Pulsed arterial spin labeling (PASL) perfusion imaging is an MRI technique,relying on the detection of magnetically labelled water. The aim of the present study was to determine regional CBF abnormalities in patients with Alzheimer's Disease (AD) and Mild Cognitive Impairment (MCI), the transitional clinical stage between normal cognition and dementia, as compared with cognitively normal elderly controls using PASL.MRI was performed on a 3 T MR scanner. A multislice STAR sequence with WET presaturation and thin slice periodic saturation pulses was used for PASL: readout single-shot EPI; TR/TE/a = 2500ms/17ms/90°; TI1/TI1S/TI2 = 700ms/ 1200ms/1500ms; 11 slices ; 80 pairs of labeled-control; scan time 7min 18sec. For coregistration a single shot EPI and a T1-weighted TFE sequence were acquired. Resting CBF maps were obtained from 15 elderly cognitively normal controls, 13 MCI patients and 7 patients with AD. Analysis of variance was performed across groups using SPM5. Results were thresholded at p< 0.05, corrected for FWE.Lower perfusion was found in the left and right inferior parietal cortex and angular gyrus, in the left middle temporal and posterior cingulate cortex in patients. A small reduction of perfusion was detected in the left caudate in patients as compared with cognitively normal controls.These results confirm previous findings of hypoperfusion in parietal and temporal areas of patients with MCI and AD as compared to age matched controls. In addition, lower perfusion was detected in the left caudate. PASL may be a valuable tool for investigating the transition from normal ageing to dementia.

A fast, effective filtering method for improving clinical pulsed arterial spin labeling MRI

To evaluate the effectiveness of a fully automated postprocessing filter algorithm in pulsed arterial spin labeling (PASL) MRI perfusion images in a large clinical population. A mean and standard deviation-based filter was implemented to remove outliers in the set of perfusion-weighted images (control - label) before being averaged and scaled to quantitative cerebral blood flow (CBF) maps. Filtered and unfiltered CBF maps from 200 randomly selected clinical cases were assessed by four blinded raters to evaluate the effectiveness of the filter. The filter salvaged many studies deemed uninterpretable as a result of motion artifacts, transient gradient, and/or radiofrequency instabilities, and unexpected disruption of data acquisition by the technologist to communicate with the patient. The filtered CBF maps contained significantly (P < 0.05) fewer artifacts and were more interpretable than unfiltered CBF maps as determined by one-tail paired t-test. Variations in MR perfusion signal related to patient motion, system instability, or disruption of the steady state can introduce artifacts in the CBF maps that can be significantly reduced by postprocessing filtering. Diagnostic quality of the clinical perfusion images can be improved by performing selective averaging without a significant loss in perfusion signal-to-noise ratio.

Optimal design of pulsed arterial spin labeling MRI experiments

Quantitative measurement of cerebral blood flow (CBF) using arterial spin labeling (ASL) MRI requires the acquisition of multiple inversion times (TIs) and the application of an appropriate kinetic model. The choice of these sampling times will have an impact on the precision of the estimated parameters. Here, optimal sampling schedule (OSS) design techniques, based on the Fisher Information approach, are applied in order to derive an optimal sampling scheme for pulsed arterial spin labeling (PASL) experiments. Such an approach should improve the precision of parameter estimation from experimental data, and provide a formal framework for optimally selecting a limited number of samples. In this study, we aimed to optimize the estimation precision of CBF and bolus arrival time from the PASL data. The performance of OSS was compared to a more standard evenly distributed sampling schedule (EDS) using both simulated and measured experimental data sets. It was found that OSS was able to significantly improve the precision of parameter estimation in PASL studies that sought to estimate either both CBF and bolus arrival time, or CBF alone.

Theoretical analysis of the effect of imperfect slice profiles on tagging schemes for pulsed arterial spin labeling MRI.

Pulsed arterial spin labeling (ASL) techniques provide a noninvasive method of obtaining qualitative and quantitative perfusion images with MRI. ASL techniques employ inversion recovery and/or saturation recovery to induce perfusion weighting, and thus the performance of these techniques is dependent on the slice profiles of the inversion or saturation pulses. This article systematically examines through simulations the effects of slice profile imperfections on the perfusion signal for nine labeling schemes, including FAIR, FAIRER, and EST (UNFAIR). Each sequence is evaluated for quantitative accuracy, suppression of stationary signal, and magnitude of perfusion signal. Perfusion effects are modeled from a modified Bloch equation and experimentally determined slice profiles. The results show that FAIR, FAIRER, and EST have excellent tissue suppression. The magnitude of the perfusion signal is comparable for FAIR and FAIRER, with EST providing a slightly weaker signal. For quantitative measurements, all three methods underestimate the perfusion signal by more than 20%. Of the additional six ASL techniques examined, only one performed well in this model. This method, which combines inversion and saturation recovery, yields improved signal accuracy (<15% difference from the theoretical value) and tissue suppression similar to that of FAIR and its variants, but has only half the signal. Magn Reson Med 46:141-148, 2001.