Evaluation of hyperspectral imaging to quantify perfusion changes during the modified Allen test

Abstract

Objectives To evaluate the capability of hyperspectral imaging (HSI), a contact‐less and noninvasive technology, to monitor perfusion changes of the hand during a modified Allen test (MAT) and cuff occlusion test. Furthermore, the study aimed at obtaining objective perfusion parameters of the hand. Methods HSI of the hand was performed on 20 healthy volunteers with a commercially available HSI system during a MAT and a cuff occlusion test. Besides gathering red‐green‐blue (RGB) images, the perfusion parameters tissue hemoglobin index (THI), (superficial tissue) hemoglobin oxygenation (StO2), near‐infrared perfusion (NIR), and tissue water index (TWI) were calculated for four different regions of interest on the hand. For the MAT, occlusion (OI; the ratio between the condition during occlusion and before occlusion) and reperfusion (RI; the ratio between the non‐occlusion state and the prior occlusion state) indices were calculated for each perfusion parameter. All data were correlated to the clinical findings. Results False‐color images showed visible differences between the various perfusion conditions during the MAT and cuff occlusion test. THI, StO2, and NIR behaved as expected from physiology, while TWI did not in the context of this study. During rest, mean THI, StO2, and NIR of the hand were 34 ± 2, 72 ± 9, and 61 ± 6, respectively. The RI for THI showed a roundabout threefold increase after reperfusion of both radial and ulnar artery and was thus, distinctly pronounced when compared with StO2 and NIR (~1.25). The OI was lowest for THI when compared with StO2 and NIR. Conclusions HSI with its parameters THI, StO2, and NIR proved to be suitable to evaluate perfusion of the hand. By this, it could complement visual inspection during the MAT for evaluating the functionality of the superficial palmary arch before radial or ulnar artery harvest. The presented RI might deliver useful comparative values to detect pathological perfusion disorders at an early stage. As microcirculation monitoring is crucial for many medical issues, HSI shows potential to be used, besides further applications, in the monitoring of (free) flaps and transplants and microcirculation monitoring of critically ill patients.

Investigation on the influence of the skin tone on hyperspectral imaging for free flap surgery

“…The false color images generated with the HSI-device were transferred into MATLAB (version 2018b The MathWorks Inc., Natick, Massachusetts, USA) to derive the NIR-index, StO 2 , THI and TWI tissue indices. For each body part, a square region of interest (ROI) of 50 × 50 pixels, corresponding to 15 × 15 mm 2 on the skin surface, was selected based on a standardized method adapted from a recently published study 59 . The ROI was defined near the center of the image, and no visible blood vessels or shaded areas at the edge of the skin surface were included in the analyzed area, as this could influence the results for the calculation of the tissue indices and reduce the comparability of the results.…”

Hyperspectral imaging for monitoring of free flaps of the oral cavity: A feasibility study

“…[1][2][3] As HSI provides spectral information about hemoglobin, water and oxygen supply, it has great potential in perfusion monitoring. First studies showed its potential benefit in the microcirculation monitoring in critically ill patients on intensive care units, 4 for the assessment of the superficial palmary arch before radial artery harvest, 5 and in the identification of cutaneous perforators before harvesting an anterolateral thigh flap. 6 Perfusion monitoring is crucial in the postoperative surveillance of flaps.…”