Interobserver Reproducibility of Signal Intensity Ratio on Magnetic Resonance Angiography for Hemodynamic Impact of Intracranial Atherosclerosis

Abstract

Background Changes of signal intensities (SIs) across intracranial atherosclerosis (ICAS) on magnetic resonance angiography (MRA) may reflect hemodynamic impact of the lesion. We evaluated the interobserver reproducibility of an index termed signal intensity ratio (SIR), developed in a previous study to represent the changes of SIs across ICAS on MRA. Methods Symptomatic ICAS on MRA were retrospectively recruited. Two observers respectively evaluated the images and calculated the SIR as follows, blinded to each other’s readings: SIR = (mean poststenotic SI − mean background SI)/(mean prestenotic SI − mean background SI). Statistical analyses were performed to evaluate the interobserver reproducibility of this index. Results A total of 102 symptomatic ICASs were enrolled, with 36 (35.3%) lesions of 50%–69% MRA stenoses and others being 70%–99% stenoses or flow void on MRA. Overall, mean SIRs were not significantly different between the 2 observers (.92 ± .17 versus .93 ± .17; mean difference −.006 ±.09; P =.496 for paired t test). Pearson correlation coefficients were >.80 for all analyses, indicating strong linear correlations between SIRs by the 2 observers. Bland–Altman analysis for SIRs of all cases showed no systematic bias between the 2 observers. For different cut-points ranging from .75 to 1.00, the kappa statistics were mostly greater than .6 and interobserver agreements were all greater than 80%, implying substantial agreement between observers. Conclusions SIR was demonstrated to be highly reproducible between observers in the present study. Future studies are warranted to further explore the role of this index in comprehensive evaluation and risk stratification of symptomatic ICAS.

Diminished Signal Intensities Distal to Intracranial Arterial Stenosis on Time-of-Flight MR Angiography Might Indicate Delayed Cerebral Perfusion

“…The index SIR of ICAS on TOF-MRA has been demonstrated to be of high inter-observer reproducibility, as reported in our previous study [12]. In theory, SIR across an ICAS may reflect hemodynamic features of the stenosis, and has been proven to be associated with recurrent stroke in the relevant territory in patients with symptomatic ICAS [11,14,17].…”

“…1) [11,12,14]. In brief, SIs proximal or distal to a target lesion were measured on MRA by outlining a 3-mm-length region of interest (ROI) covering the arterial lumen.…”

“…Based on this theory, diminished SI across a stenosis is believed to reflect reduced blood flow or turbulence downstream of the lesion [10,11]. In our previous studies, SI ratio (SIR), defined as the ratio of distal and proximal SIs across an ICAS lesion, was developed to represent the relative changes of the SIs across the lesion [11,12]. SIR of ICAS lesions on TOF-MRA has been found to be related to stroke recurrence in patients with symptomatic ICAS.…”

Noninvasive Fractional Flow on MRA Predicts Stroke Risk of Intracranial Stenosis

“…Feasibilityand intra-rater agreement of 0.975 (Pearson correlation coefficient) have been previously reported[13], with an associated inter-observer variability of 0.847 (Pearson correlation coefficient). [14]…”

Time-of-Flight MR Angiography for Detection of Cerebral Hyperperfusion Syndrome after Superficial Temporal Artery-Middle Cerebral Artery Anastomosis in Moyamoya Disease

“…The degree of enhancement in flowing blood on MRA images, referred to as SI within the vessel lumen, increases nonlinearly with increasing absolute flow velocity. 17,18 MIP images are frequently used for TOF-MRA. However, because the target blood vessels in the present study were thin and were depicted as having a low SI, they were difficult to assess on MIP images.…”