Model-based analysis of flow-mediated dilation and intima-media thickness

G Bartoli, G Menegaz, M Lisi, G Di Stolfo, S Dragoni, T Gori, G Bartoli, G Menegaz, M Lisi, G Di Stolfo, S Dragoni, T Gori

Abstract

We present an end-to-end system for the automatic measurement of flow-mediated dilation (FMD) and intima-media thickness (IMT) for the assessment of the arterial function. The video sequences are acquired from a B-mode echographic scanner. A spline model (deformable template) is fitted to the data to detect the artery boundaries and track them all along the video sequence. The a priori knowledge about the image features and its content is exploited. Preprocessing is performed to improve both the visual quality of video frames for visual inspection and the performance of the segmentation algorithm without affecting the accuracy of the measurements. The system allows real-time processing as well as a high level of interactivity with the user. This is obtained by a graphical user interface (GUI) enabling the cardiologist to supervise the whole process and to eventually reset the contour extraction at any point in time. The system was validated and the accuracy, reproducibility, and repeatability of the measurements were assessed with extensive in vivo experiments. Jointly with the user friendliness, low cost, and robustness, this makes the system suitable for both research and daily clinical use.

Figures

Figure 1
Figure 1
Typical FMD image resulting from the echo scanner.
Figure 2
Figure 2
Preprocessing. (a) Original image; (b) after histogram stretching; (c) after sharpening.
Figure 3
Figure 3
Search region for positioning the spline curve.
Figure 4
Figure 4
Results: the modeling splines corresponding to the upper and lower boundaries are represented as red curves.
Figure 5
Figure 5
FMD analysis. (a) Correlation between manual (gold standard, horizontal axis) and automatic (vertical axis) analyses; (b) Bland and Altman plot: difference between software and manual measurements versus their average.
Figure 6
Figure 6
Correlation between repeated measurements in 25 healthy subjects studied twice with a delay of 24 hours. (a) Resting diameter; (b) FMD. The interclass correlation coefficients are ICC = 0.85 and ICC = 0.63, respectively.
Figure 7
Figure 7
Repeatability. (a) FMD; (b) IMT.
Figure 8
Figure 8
Bland and Altman plots of repeated measurements. The horizontal axis reports the average of two consecutive measurements, the vertical axis their difference. The dotted lines represent 1.96 standard deviation from the mean. (a) Diameter; (b) FMD.
Figure 9
Figure 9
Reference frame: ROI selection.
Figure 10
Figure 10
The first window of the software presents an “average frame” derived as an average of all frames in the video and is used to manually set the ROI. The second window requires the operator to click on two calibration marks to calibrate the images.
Figure 11
Figure 11
FMD data. Thin line: artery diameter as a function of frame index. Thick line: artery diameter after smoothing. Red line: frame selection.

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