Intra- and multicenter reproducibility of pulsed, continuous and pseudo-continuous arterial spin labeling methods for measuring cerebral perfusion

Quantifying the test-retest reliability of cerebral blood flow measurements in a clinical model of on-going post-surgical pain: A study using pseudo-continuous arterial spin labelling

Arterial spin labelling (ASL) is increasingly being applied to study the cerebral response to pain in both experimental human models and patients with persistent pain. Despite its advantages, scanning time and reliability remain important issues in the clinical applicability of ASL. Here we present the test–retest analysis of concurrent pseudo-continuous ASL (pCASL) and visual analogue scale (VAS), in a clinical model of on-going pain following third molar extraction (TME). Using ICC performance measures, we were able to quantify the reliability of the post-surgical pain state and ΔCBF (change in CBF), both at the group and individual case level. Within-subject, the inter- and intra-session reliability of the post-surgical pain state was ranked good-to-excellent (ICC > 0.6) across both pCASL and VAS modalities. The parameter ΔCBF (change in CBF between pre- and post-surgical states) performed reliably (ICC > 0.4), provided that a single baseline condition (or the mean of more than one baseline) was used for subtraction. Between-subjects, the pCASL measurements in the post-surgical pain state and ΔCBF were both characterised as reliable (ICC > 0.4). However, the subjective VAS pain ratings demonstrated a significant contribution of pain state variability, which suggests diminished utility for interindividual comparisons. These analyses indicate that the pCASL imaging technique has considerable potential for the comparison of within- and between-subjects differences associated with pain-induced state changes and baseline differences in regional CBF. They also suggest that differences in baseline perfusion and functional lateralisation characteristics may play an important role in the overall reliability of the estimated changes in CBF. Repeated measures designs have the important advantage that they provide good reliability for comparing condition effects because all sources of variability between subjects are excluded from the experimental error. The ability to elicit reliable neural correlates of on-going pain using quantitative perfusion imaging may help support the conclusions derived from subjective self-report.

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Test-retest reliability of pCASL is considered in a post-surgical pain model.

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Pain-state and ∆CBF measurements were reliable at the group and individual level.

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Single or average baseline measurements improve reliability of ∆CBF.

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pCASL is a reliable technique for detecting cerebral responses to on-going pain.

Partial volume correction in arterial spin labeling using a Look-Locker sequence

PURPOSE

Partial volume (PV) effects are caused by limited spatial resolution and significantly affect cerebral blood flow investigations with arterial spin labeling. Therefore, accurate PV correction (PVC) procedures are required. PVC is commonly based on PV maps obtained from segmented high-resolution T1 -weighted images. Segmentation of these images is error-prone, and it can be difficult to coregister these images accurately with the single-shot ASL images such as those created by echo-planar imaging (EPI). In this paper, an alternative method for PV map generation is proposed.

METHODS

The Look-Locker EPI (LL-EPI) acquisition is used for analyzing the T1 -recovery curve and for subsequent PV map generation. The new method was evaluated in five healthy volunteers (mean age 30 ± 3.7 years).

RESULTS

By applying a linear regression method for PVC, a 12% decrease in regression error was reached with the new method.

CONCLUSION

PV maps extraction from LL-EPI is a viable, possibly superior alternative to the standard approach based on segmentation of high-resolution T1 -weighted images.

Cerebral blood flow is diminished in asymptomatic middle-aged adults with maternal history of Alzheimer's disease

Cerebral blood flow (CBF) provides an indication of the metabolic status of the cortex and may have utility in elucidating preclinical brain changes in persons at risk for Alzheimer's disease (AD) and related diseases. In this study, we investigated CBF in 327 well-characterized adults including patients with AD (n = 28), patients with amnestic mild cognitive impairment (aMCI, n = 23), older cognitively normal (OCN, n = 24) adults, and asymptomatic middle-aged adults (n = 252) with and without a family history (FH) of AD. Compared with the asymptomatic cohort, AD patients displayed significant hypoperfusion in the precuneus, posterior cingulate, lateral parietal cortex, and the hippocampal region. Patients with aMCI exhibited a similar but less marked pattern of hypoperfusion. Perfusion deficits within the OCN adults were primarily localized to the inferior parietal lobules. Asymptomatic participants with a maternal FH of AD showed hypoperfusion in hippocampal and parietofrontal regions compared with those without a FH of AD or those with only a paternal FH of AD. These observations persisted when gray matter volume was included as a voxel-wise covariate. Our findings suggest that having a mother with AD might confer a particular risk for AD-related cerebral hypoperfusion in midlife. In addition, they provide further support for the potential utility of arterial spin labeling for the measurement of AD-related neurometabolic dysfunction, particularly in situations where [18F]fluorodeoxyglucose imaging is infeasible or clinically contraindicated.

Simultaneous PET/MR imaging of the brain: feasibility of cerebral blood flow measurements with FAIR-TrueFISP arterial spin labeling MRI

BACKGROUND

Hybrid positron emission tomography/magnetic resonance imaging (PET/MRI) with simultaneous data acquisition promises a comprehensive evaluation of cerebral pathophysiology on a molecular, anatomical, and functional level. Considering the necessary changes to the MR scanner design the feasibility of arterial spin labeling (ASL) is unclear.

PURPOSE

To evaluate whether cerebral blood flow imaging with ASL is feasible using a prototype PET/MRI device.

MATERIAL AND METHODS

ASL imaging of the brain with Flow-sensitive Alternating Inversion Recovery (FAIR) spin preparation and true fast imaging in steady precession (TrueFISP) data readout was performed in eight healthy volunteers sequentially on a prototype PET/MRI and a stand-alone MR scanner with 128 × 128 and 192 × 192 matrix sizes. Cerebral blood flow values for gray matter, signal-to-noise and contrast-to-noise ratios, and relative signal change were compared. Additionally, the feasibility of ASL as part of a clinical hybrid PET/MRI protocol was demonstrated in five patients with intracerebral tumors.

RESULTS

Blood flow maps showed good delineation of gray and white matter with no discernible artifacts. The mean blood flow values of the eight volunteers on the PET/MR system were 51 ± 9 and 51 ± 7 mL/100 g/min for the 128 × 128 and 192 × 192 matrices (stand-alone MR, 57 ± 2 and 55 ± 5, not significant). The value for signal-to-noise (SNR) was significantly higher for the PET/MRI system using the 192 × 192 matrix size (P < 0.01), the relative signal change (δS) was significantly lower for the 192 × 192 matrix size (P = 0.02). ASL imaging as part of a clinical hybrid PET/MRI protocol could successfully be accomplished in all patients in diagnostic image quality.

CONCLUSION

ASL brain imaging is feasible with a prototype hybrid PET/MRI scanner, thus adding to the value of this novel imaging technique.

Mapping serotonergic dysfunction in MDMA (ecstasy) users using pharmacological MRI

3,4-Methylenedioxymethamphetamine (MDMA or ecstasy) is a popular recreational drug that has been shown to induce loss of brain serotonin (5-HT) neurons. The purpose of this study was to determine the usefulness of pharmacological magnetic resonance imaging (phMRI) in assessing 5-HT dysfunction by examining the hemodynamic response evoked by infusion with the selective 5-HT reuptake inhibitor citalopram. We studied the effects of MDMA on brain hemodynamics using arterial spin labeling (ASL) based phMRI following a citalopram challenge (7.5mg/kg, i.v.), combined with [¹²³I]β-CIT SPECT imaging in ten male MDMA users and seven healthy non-users. Single photon emission computed tomography (SPECT) imaging was used to assess the availability of 5-HT transporters (SERT). Imaging results were compared with the results of behavioral measures and mood changes following drug administration, in both groups (using the Beck Depression Inventory, Barratt Impulsiveness Scale and a visual analog scale). Reductions in SERT binding were observed in the occipital cortex of MDMA users. In line with this, citalopram induced decreases in cerebral blood flow (CBF) in the occipital cortex of MDMA users. ASL based phMRI also detected a CBF decrease in the thalamus of MDMA users. In concordance with imaging findings, behavioral measures differed significantly between MDMA users and controls. MDMA users had higher impulsivity scores and felt more uncomfortable after citalopram infusion, compared with control subjects. Our findings indicate that phMRI is very well suited for in-vivo assessment of 5-HT dysfunction.

Arterial spin labelling: final steps to make it a clinical reality

Since its inception in the early 1990s, arterial spin labelling (ASL) has been developed in numerous variants. Tremendous improvements in both pulse sequences and hardware have allowed improved image quality and reduced scan time, to the point where the technique might be ready for clinical application. However, although now routinely used in research centres and universities, its application in daily clinical routine remains restricted to a few centres. Its popularity in magnetic resonance imaging (MRI) research centres and among physicists may have contributed to the lack of enthusiasm from the clinical community, as the variety of possible sequences available might deter even the most die-hard technology-driven neuroradiologist from using this technique. Therefore, a joint action directed towards the harmonisation of all the existing ASL pulse sequences and the development of a reliable and common post-processing pipeline to provide guidance for the major MRI manufacturers was recently endeavoured and dubbed the 'ASL Network' ( http://www.asl-network.org ). This network was established to provide a communication platform among physicists, engineers and clinicians who are keen to see this technique finally make it to daily clinical practice. Finally, a networking European Grant from the COST Office was secured to help fund some of the activities of the ASL Network, in particular as they pertain to the application of ASL in dementia ( http://www.cost.eu/domains_actions/bmbs/Actions/BM1103 ). Here, both the ASL Network and the COST Action are described, with their respective goals and aspirations.

Arterial Spin Labeling (ASL) fMRI: advantages, theoretical constrains, and experimental challenges in neurosciences

Cerebral blood flow (CBF) is a well-established correlate of brain function and therefore an essential parameter for studying the brain at both normal and diseased states. Arterial spin labeling (ASL) is a noninvasive fMRI technique that uses arterial water as an endogenous tracer to measure CBF. ASL provides reliable absolute quantification of CBF with higher spatial and temporal resolution than other techniques. And yet, the routine application of ASL has been somewhat limited. In this review, we start by highlighting theoretical complexities and technical challenges of ASL fMRI for basic and clinical research. While underscoring the main advantages of ASL versus other techniques such as BOLD, we also expound on inherent challenges and confounds in ASL perfusion imaging. In closing, we expound on several exciting developments in the field that we believe will make ASL reach its full potential in neuroscience research.

Arterial spin labeling measurement of cerebral perfusion in children with sickle cell disease

PURPOSE

To evaluate the applicability of arterial spin labeling (ASL) cerebral blood flow (CBF) measurements in children with sickle cell disease (SCD).

MATERIALS AND METHODS

We included 12 patients and five controls. Conventional magnetic resonance imaging (MRI) (T2, fluid attenuated inversion recovery [FLAIR], and MR angiography) was performed to diagnose silent infarcts, vasculopathy, or leukoencephalopathy. Pseudo-continuous ASL was performed to measure CBF using two postlabeling delays to identify transit-time effects. Perfusion estimates were corrected for hematocrit and blood velocity in the labeling plane and compared to phase-contrast MR. CBF asymmetries between the flow maps of the left and right internal carotid arteries were tested for significance using paired t-tests. Significant asymmetries were expressed in terms of an asymmetry ratio (AR = absolute difference/mean). An AR >10% was considered clinically relevant.

RESULTS

Mean CBF was higher in patients than in controls. Agreement between CBF and flow improved after applying hematocrit and velocity corrections. At a 2100 msec postlabeling delay one patient had a clinically relevant asymmetry. No association was observed between CBF asymmetries and silent infarcts.

CONCLUSION

Care must be taken in the interpretation of ASL-CBF measurements in SCD patients. A long postlabeling delay with blood velocity correction anticipates overestimation of CBF asymmetries.

Cerebral perfusion long term after therapeutic occlusion of the internal carotid artery in patients who tolerated angiographic balloon test occlusion

BACKGROUND AND PURPOSE

Therapeutic carotid occlusion is an established technique for treatment of large and giant aneurysms of the ICA, in patients with synchronous venous filling on angiography during BTO. Concern remains that hemodynamic alterations after permanent occlusion will predispose the patient to new ischemic injury in the ipsilateral hemisphere. The purpose of this study was to assess whether BTO with synchronous venous filling is associated with normal CBF long term after carotid sacrifice.

MATERIALS AND METHODS

Eleven patients were included (all women; mean age, 50.5 years; mean follow-up, 38.5 months). ASL with single and multiple TIs was used to assess CBF and its temporal characteristics. Selective ASL was used to assess actual territorial contribution of the ICA and BA. Collateral flow via the AcomA or PcomA or both was determined by time-resolved 3D PCMR. Paired t tests were used to compare CBF and timing parameters between hemispheres.

RESULTS

Absolute CBF values were within the normal range. There was no significant CBF difference between hemispheres ipsilateral and contralateral to carotid sacrifice (49.4 ± 11.2 versus 50.1 ± 10.1 mL/100 g/min). Arterial arrival time and trailing edge time were significantly prolonged on the occlusion side (816 ± 119 ms versus 741 ± 103 ms, P = .001; and 1765 ± 179 ms versus 1646 ± 190 ms, P < .001). Two patients had collateral flow through the AcomA only and were found to have increased timing parameters compared with 9 patients with mixed collateral flow through both the AcomA and PcomA.

CONCLUSIONS

In this small study, patients with synchronous venous filling during BTO had normal CBF long term after therapeutic ICA occlusion.