Sidestream dark-field imaging versus orthogonal polarization spectroscopic imaging: a comparative study

Introduction

Sidestream dark-field (SDF) imaging, a stroboscopic LED ring-based imaging modality for clinical observation of the microcirculation, was validated by quantitative and qualitative comparison with orthogonal polarization spectral (OPS) imaging.

Methods

For OPS imaging a Cytocan-II backfocus type device (Cytometrics, Philadelphia, PA, USA) was used, and for SDF imaging a MicroScan Video Microscope (MicroVision Medical Inc., Amsterdam, The Netherlands) was employed. To validate SDF imaging, nailfold capillary diameters and red blood cell velocities were measured in the exact same capillaries using OPS and SDF imaging. For quantitative comparison of the quality of sublingually acquired microcirculatory images, an image quality quantification system was developed to score venular and capillary contrast and sharpness on scales from 0 to 1.

Results

After introduction of a scaling factor to correct for the slightly higher magnification of the SDF device with respect to the OPS device, equal quantitative results for capillary diameters and red blood cell velocities were obtained. Venular contrast and sharpness were shown to be comparable for OPS and SDF imaging. Capillary sharpness and contrast, however, were shown to be significantly higher using SDF imaging (Figure 1). Venular granularity, in addition, was more clearly observable employing the SDF device.

Figure 1

Sidestream dark-field (SDF) imaging versus orthogonal polarization spectral (OPS) imaging: capillary contrast and sharpness.

Conclusion

SDF imaging provided significantly higher image quality by the use of stroboscopic LED ring-based SDF illumination. It is anticipated that SDF imaging will serve as a reliable imaging modality for the clinical assessment of the microcirculation and will enhance computer-aided image analysis.