Quantitative assessment of external carotid artery territory supply with modified vessel-encoded arterial spin-labeling

Assessment of blood supply of the external carotid artery in moyamoya disease using super-selective pseudo-continuous arterial spin labeling technique

OBJECTIVES

To evaluate the diagnostic accuracy of super-selective pseudo-continuous arterial spin labeling (ss-pCASL) at depicting external carotid artery (ECA) perfusion territory in moyamoya disease (MMD).

METHODS

In total, 103 patients with MMD who underwent both ss-pCASL and digital subtraction angiography (DSA, the reference standard) were included. There were 3, 184, and 19 normal, preoperative, and postoperative MMD hemispheres, respectively. The ss-pCASL results were interpreted by two different visual inspection criteria: presence or absence and definite or indefinite ECA perfusion territory. The performance of ss-pCASL at depiction of ECA perfusion territory was compared to that of DSA. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were calculated. The κ statistic was used to assess intermodality and inter-reader agreement.

RESULTS

When interpreted as presence or absence, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of ss-pCASL for depicting ECA perfusion territory were 78.3 %, 79.6 %, 92.5 %, 53.4 %, and 78.6 %, respectively, and the intermodality and inter-reader agreement were κ = 0.49 (CI: 0.43 - 0.55, p < 0.01) and 0.71 (CI: 0.66 - 0.76, p < 0.01), respectively. When interpreted as definite or indefinite, the respective values were 61.1%, 100%, 100%, 44.5%, 70.4%, κ = 0.42 (CI: 0.37 - 0.47, p < 0.01), and 0.90 (CI: 0.87 - 0.93, p < 0.01).

CONCLUSION

ss-pCASL has substantial sensitivity and specificity compared with DSA for depicting the presence versus absence of ECA perfusion territory in MMD. As a noninvasive method in which no ion radiation or contrast medium is needed, ss-pCASL may potentially reduce the need for repeated DSA examination.

KEY POINTS

• Super-selective pseudo-continuous arterial spin labeling (ss-pCASL) is a noninvasive vessel-selective MR technique to demonstrate perfusion territory of a single cerebral artery. • Compared with digital subtraction angiography, ss-pCASL has substantial sensitivity and specificity for depicting the perfusion territory of the external carotid artery in brain parenchyma in moyamoya disease. • ss-pCASL may potentially reduce the need for repeated DSA examination.

Feasibility of MRI based oxygenation imaging for the assessment of acute limb ischemia

Background

Acute limb ischemia (ALI) can lead to death and amputation. Evaluating the severity of ischemia is important but difficult, through current methods of examination. The purpose of this research was to demonstrate the feasibility of magnetic resonance imaging (MRI) susceptibility-based imaging techniques for use in assessing muscle oxygenation alterations in ALI.

Methods

ALI animal models were established in 11 rabbits. Their left iliac arteries were embolized by microspheres. MRI scans were conducted 24 hours before (Pre) and 1 hour (Post 1) and 3 hours (Post 2) after the procedure. A susceptibility model was used to calculate skeletal muscle oxygenation extraction fraction (SMOEF) and relaxation rate (R2’). T2 weighted (T2w) imaging and diffusion-weighted (DW) imaging were performed.

Results

The average calf muscle SMOEF in the embolized hindlimbs increased from 0.43±0.02 (Pre) to 0.48±0.02 (Post 1) and 0.50±0.02 (Post 2), both P<0.05. The R2’ value increased from 13.01±2.31 s⁻¹ (Pre) to 16.78±2.28 s⁻¹ (Post 1) and 17.90±3.29 s⁻¹ (Post 2), both P<0.05. No significant changes of SMOEF and R2’ were found after embolization in the contralateral hindlimbs. Apparent diffusion coefficient (ADC) values derived from DW imaging remained unchanged at different stages compared to before the procedures (all P>0.05). No abnormal signals were observed in the anatomical T2w images at Post 1 and Post 2.

Conclusions

This study demonstrates the feasibility of using SMOEF for the assessment of oxygenation alterations in ALI models. SMOEF is more sensitive than T2w and DW imaging in detecting acute muscle ischemia at an early stage.

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.

Automated analysis of perfusion weighted MRI using asymmetry in vascular territories

PURPOSE

To determine the feasibility of automatic vascular territory region of interest (ROI) construction as a method for standardized quantification of cerebral blood flow (CBF) images.

MATERIALS AND METHODS

An algorithm for automatic construction of vascular territory ROIs was performed on 10 healthy controls and 25 patients with perfusion abnormalities identified by retrospective chart review. The ROIs were used to quantify perfusion asymmetry for each territory, and perfusion asymmetry was compared in the two cohorts and against blinded neuroradiologist interpretation. The algorithm was additionally applied to a separate cohort of 23 prospectively enrolled patients and perfusion asymmetry was correlated against clinical variables.

RESULTS

There was significantly greater perfusion asymmetry in territories graded by neuroradiologists as hypoperfused compared to those graded as normally perfused (p<.05) and compared to healthy volunteers (p<.01). An ROC analysis showed that perfusion asymmetry was sensitive and specific for identifying hypoperfusion in vascular territories (84.9% sensitivity and 90.5% specificity for a threshold asymmetry index of .829). In the prospective cohort, perfusion asymmetry was correlated with initial NIH stroke scale (NIHSS) (p<.01) and length of stay (p<.05).

CONCLUSIONS

Automatic construction of vascular territory ROIs and calculation of perfusion asymmetry is a feasible method for analyzing CBF images. Because the technique is rapid and minimizes bias, it can facilitate analysis of larger scale research studies.

Morphometric, geographic, and territorial characterization of brain arterial trees

Morphometric information of the brain vascularization is valuable for a variety of clinical and scientific applications. In particular, this information is important when creating arterial tree models for imposing boundary conditions in numerical simulations of the brain hemodynamics. The purpose of this work is to provide quantitative descriptions of arterial branches, bifurcation patterns, shape, and geographical distribution of the arborization of the main cerebral arteries as well as estimations of the corresponding vascular territories. For this purpose, subject-specific digital reconstructions of the brain vascular network created from 3T magnetic resonance angiography images of healthy volunteers are used to derive population-averaged morphometric characteristics of the cerebral arterial trees. Copyri

Accuracy of vessel-encoded pseudocontinuous arterial spin-labeling in identification of feeding arteries in patients with intracranial arteriovenous malformations

BACKGROUND AND PURPOSE

Identifying feeding arteries of intracranial AVMs is very important for preoperative evaluation. DSA remains the reference standard for diagnosis but is invasive. Our aim was to evaluate the diagnostic accuracy of vessel-encoded pseudocontinuous arterial spin-labeling in identifying feeding arteries of intracranial AVMs by using DSA as the criterion standard.

MATERIALS AND METHODS

Eighteen patients with AVMs were examined with vessel-encoded pseudocontinuous arterial spin-labeling and DSA. Three postlabeling delays (postlabeling delay = 1, 1.3, and 1.6 seconds) were applied in 6 patients, and a single postlabeling delay (1 second) was applied in the remainder. Perfusion-weighted images were decoded into individual vascular territories with standard and relative tagging efficiencies, respectively. The supply fraction of each feeding artery to the AVM was calculated. The within-subject ANOVA was applied to compare supply fractions acquired across 3 postlabeling delays. Receiver operating characteristic analysis curves were calculated to evaluate the diagnostic accuracy of vessel-encoded pseudocontinuous arterial spin-labeling for identifying the feeding arteries of AVMs.

RESULTS

There were no significant differences in supply fractions of the 3 major arteries to AVMs acquired with 3 postlabeling delays (P > .05). For vessel-encoded pseudocontinuous arterial spin-labeling with standard labeling efficiencies, the area under the receiver operating characteristic analysis curve was 0.942. The optimal cutoff of the supply fraction for identifying feeding arteries was 15.17%, and the resulting sensitivity and specificity were 84.62% and 93.33%, respectively. For vessel-encoded pseudocontinuous arterial spin-labeling with relative labeling efficiencies, the area under the receiver operating characteristic analysis curve was 0.957. The optimal cutoff of the supply fraction was 11.73%, which yielded an 89.74% sensitivity and 93.33% specificity.

CONCLUSIONS

The contribution fraction of each feeding artery of the AVM can be reliably estimated by using vessel-encoded pseudocontinuous arterial spin-labeling. Vessel-encoded pseudocontinuous arterial spin-labeling with either standard or relative labeling efficiencies offers a high level of diagnostic accuracy compared with DSA for identifying feeding arteries.