Abstract
Sidestream dark field (SDF) imaging enables direct visualisation of the microvasculature from which quantification of key variables is possible. The new MicroScan USB3 (MS-U) video-microscope is a hand-held SDF device that has undergone significant technical upgrades from its predecessor, the MicroScan Analogue (MS-A). The MS-U claims superior quality of sublingual microcirculatory image acquisition over the MS-A, however, this has yet to be robustly confirmed. In this manuscript, we therefore compare the quality of image acquisition between these two devices. The microcirculation of healthy volunteers was visualised to generate thirty video images for each device. Two independent raters, blinded to the device type, graded the quality of the images according to the six different traits in the Microcirculation Image Quality Score (MIQS) system. Chi-squared tests and Kappa statistics were used to compare not only the distribution of scores between the devices, but also agreement between raters. MS-U showed superior image quality over MS-A in three of out six MIQS traits; MS-U had significantly more optimal images by illumination (MS-U 95% optimal images, MS-A 70% optimal images (p-value 0.003)), by focus (MS-U 70% optimal images, MS-A 35% optimal images (p-value 0.002)) and by pressure (MS-U 72.5% optimal images, MS-A 47.5% optimal images (p-value 0.02)). For each trait, there was at least 85% agreement between the raters, and all the scores for each trait were independent of the rater (all p-values > 0.05). These results show that the new MS-U provides a superior quality of sublingual microcirculatory image acquisition when compared to old MS-A
Highlights
Sublingual video-microscopy is becoming an increasingly important clinical technique used for real-time assessment of the in-vivo microcirculation [1]
MicroScan USB3 (MS-U) was rated as having superior image quality over MicroScan Analogue (MS-A) in three of out six Microcirculation Image Quality Score (MIQS) traits (Table 2)
There was no significant difference between the content capture of the two video-microscopes (MS-U 77.5% optimal images, MS-A 80% optimal images (p-value 0.79)), and both techniques demonstrated 100% optimal images acquisition in terms of duration and stability (Table 3)
Summary
Sublingual video-microscopy is becoming an increasingly important clinical technique used for real-time assessment of the in-vivo microcirculation [1]. The technology permits evaluation of several variables including vessel density, perfusion indices (such as the proportion of perfused vessels and microvascular flow index), and the heterogeneity of the blood flow throughout the capillary bed Through measuring these variables, sublingual video-microscopy directly quantifies the microcirculation, and this is essential given that it can bear no resemblance to common ‘macro-circulation’—variables such as blood pressure which we usually quantify and make microcirculatory inferences from [2]. The technique exploits the process of incident dark field illumination, whereby blood vessels < 100 μm in diameter, and < 1000 μm below the surface of the organ, are illuminated and visualised in a two-dimensional plane Both SDF and IDF illuminate the microcirculation using a series of concentrically placed light emitting diodes (LEDs) surrounding a central light guide that contains the lens system. Pulsed green light (wavelength 540 ± 10 nm) that is in synchrony with the video camera frame rate, performs intra-vital stroboscopy, with short illumination times used to help to prevent the smearing of moving objects such as flowing red cells, and the motion-induced blurring of capillaries [10]
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