Geodesic Length Measurement in Medical Images: Effect of the Discretization by the Camera Chip and Quantitative Assessment of Error Reduction Methods

Ady Naber,Daniel Berwanger,Werner Nahm

doi:10.3390/photonics7030070

Abstract

After interventions such as bypass surgeries the vascular function is checked qualitatively and remotely by observing the blood dynamics inside the vessel via Fluorescence Angiography. This state-of-the-art method has to be improved by introducing a quantitatively measured blood flow. Previous approaches show that the measured blood flow cannot be easily calibrated against a gold standard reference. In order to systematically address the possible sources of error, we investigated the error in geodesic length measurement caused by spatial discretization on the camera chip. We used an in-silico vessel segmentation model based on mathematical functions as a ground truth for the length of vessel-like anatomical structures in the continuous space. Discretization errors for the chosen models were determined in a typical magnitude of 6%. Since this length error would propagate to an unacceptable error in blood flow measurement, counteractions need to be developed. Therefore, different methods for the centerline extraction and spatial interpolation have been tested and compared against their performance in reducing the discretization error in length measurement by re-continualization. In conclusion, the discretization error is reduced by the re-continualization of the centerline to an acceptable range. The discretization error is dependent on the complexity of the centerline and this dependency is also reduced. Thereby the centerline extraction by erosion in combination with the piecewise Bézier curve fitting performs best by reducing the error to 2.7% with an acceptable computational time.

Highlights

Camera-based diagnostic methods, as a subfield of biomedical optics, are becoming increasingly important in many clinical applications and their use is ubiquitous and indispensable, especially when contactless operation is required [1,2,3,4]
We investigate the performance of two centerline extraction methods: Erosion method and Voronoi diagrams
The centerline extraction and spatial interpolation methods were applied on 1204 such images

Summary

Introduction

Camera-based diagnostic methods, as a subfield of biomedical optics, are becoming increasingly important in many clinical applications and their use is ubiquitous and indispensable, especially when contactless operation is required [1,2,3,4]. The aim of this study is to improve the accuracy of quantitative intraoperative FA with the focus on determining the exact length of vessel segments from fluorescence images, as the precise determination of vessel geometry is one of the preconditions for the accurate quantification of blood volume flow. During surgical interventions, such as bypass grafting, the quality of the procedure should be checked before closing the patient’s skull to ensure a low recurrence rate [9].

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Conclusion