Accuracy of blood flow assessment in cerebral arteries with 4D flow MRI: Evaluation with three segmentation methods

Abstract

Background Accelerated 4D flow MRI allows for high‐resolution velocity measurements with whole‐brain coverage. Such scans are increasingly used to calculate flow rates of individual arteries in the vascular tree, but detailed information about the accuracy and precision in relation to different postprocessing options is lacking. Purpose To evaluate and optimize three proposed segmentation methods and determine the accuracy of in vivo 4D flow MRI blood flow rate assessments in major cerebral arteries, with high‐resolution 2D PCMRI as a reference. Study Type Prospective. Subjects Thirty‐five subjects (20 women, 79 ± 5 years, range 70–91 years). Field Strength/Sequence 4D flow MRI with PC‐VIPR and 2D PCMRI acquired with a 3 T scanner. Assessment We compared blood flow rates measured with 4D flow MRI, to the reference, in nine main cerebral arteries. Lumen segmentation in the 4D flow MRI was performed with k‐means clustering using four different input datasets, and with two types of thresholding methods. The threshold was defined as a percentage of the maximum intensity value in the complex difference image. Local and global thresholding approaches were used, with evaluated thresholds from 6–26%. Statistical Tests Paired t‐test, F‐test, linear correlation (P < 0.05 was considered significant) along with intraclass correlation (ICC). Results With the thresholding methods, the lowest average flow difference was obtained for 20% local (0.02 ± 15.0 ml/min, ICC = 0.97, n = 310) or 10% global (0.08 ± 17.3 ml/min, ICC = 0.97, n = 310) thresholding with a significant lower standard deviation for local (F‐test, P = 0.01). For all clustering methods, we found a large systematic underestimation of flow compared with 2D PCMRI (16.1–22.3 ml/min). Data Conclusion A locally adapted threshold value gives a more stable result compared with a globally fixed threshold. 4D flow with the proposed segmentation method has the potential to become a useful reliable clinical tool for assessment of blood flow in the major cerebral arteries. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:511–518.

Assessment of Cerebral Blood Flow Pulsatility and Cerebral Arterial Compliance With 4D Flow MRI

“…The ROI was kept constant through all time frames. Interrater reliability for these segmentations has previously been shown to be excellent …”

“…The scan protocol was previously described . It included 4D flow MRI followed by multiple 2D PC‐MRI acquisitions, without any contrast agent, performed on a 3T scanner (GE Discovery MR 750, Milwaukee, WI) with a 32‐channel head coil.…”

“…This image was gradually thinned to a one‐voxel‐thick centerline . To avoid a mismatch in spatial location between the 4D flow MRI and 2D PC‐MRI datasets, the center coordinate of each segmented ROI in the 2D PC‐MRI plane was transformed to the corresponding location in the 4D flow MRI data . The centerline voxel closest to the located coordinate was used as the seed point in the segmentation method.…”

“…The centerline voxel closest to the located coordinate was used as the seed point in the segmentation method. All seed points were visually inspected, and manually adjusted in case of mismatch …”

“…In this study, a previously introduced methodology for segmentation, based on local thresholding, was used for quantification of blood flow rates in cerebral arteries. Cut planes were extracted from the CD volume and resampled in the direction of the arteries, perpendicular to the velocity direction of the arterial flow, using the centerline representation of the branches.…”