Comparison of tissue viability imaging and colorimetry: skin blanching

The tissue viability imaging system-Suitable method for discovering minimal skin changes in occupational screenings? Results of a cross-sectional field study

BACKGROUND

For early detection of initial skin changes in occupational screenings, only few objective assessment systems are available.

OBJECTIVES

With the aim of assessing an objective measurement method for hand eczema, we trialed the application of the tissue viability imaging (TiVi) system, quantifying erythema non-invasively by polarized light spectroscopy.

MATERIALS AND METHODS

In a field study with 625 employees of a semiconductor production company, 411 were exposed to prolonged wearing of occlusive gloves in the clean room. TiVi system and Hand Eczema Score for Occupational Screenings (HEROS), a quantitative skin score for the hands, were used, supplemented by a standardized personal interview.

RESULTS

TiVi values of 65 up to 246 for each hand (palm or back), for each participant summed to overall 289 up to 848 (median 389), were measured. Higher TiVi values were noted for men, smokers, and with increasing age. Correlation between TiVi and HEROS was only weak. Several factors like skin pigmentation, thickness of the skin, or tattoos seem to influence TiVi results.

CONCLUSIONS

The practical relevance of one-time measurements with the TiVi system in occupational screenings seems to be limited. Specifically, the TiVi system cannot replace dermatological examinations at the workplace. Notwithstanding, the application for other scientific purposes might be useful.

Hypoperfusion following the injection of epinephrine in human forearm skin can be measured by RGB analysis but not with laser speckle contrast imaging

BACKGROUND

The time taken for epinephrine to achieve its optimal effect during local anesthesia has recently become the subject of debate. The time from injection to commencement of surgery is traditionally quoted to be 7 to 10 min, while recent reports claim that it may take 30 min to achieve maximum hypoperfusion, which would prolong the time required for surgical procedures. The discrepancy may be related to difficulties associated with the techniques used to measure blood perfusion. The aim of this study was to test two methods of determining the time to maximum hypoperfusion.

METHODS

Laser speckle contrast imaging (LSCI) and red, green, blue (RGB) analysis of images obtained with a commercial digital camera, were used to monitor the effect of infiltration with commonly used local anesthetic preparations: lidocaine (20 mg/ml) + epinephrine (12.5 μg/ml), lidocaine (10 mg/ml) + epinephrine (5 μg/ml), and lidocaine (20 mg/ml) alone, in healthy subjects.

RESULTS

LSCI showed a paradoxical increase in signal after the injection of local anesthetics containing epinephrine, probably due to a change in the laser penetration depth resulting from blanching of the skin. However, RGB analysis of digital photographs gave more reliable results, showing skin blanching that corresponded to the expected effect of epinephrine in local anesthetics. The time to maximum effect was found to be 7 (range 5-10) minutes for 12.5 μg/ml epinephrine, and 9 (range 7-13) minutes for 5 μg/ml epinephrine in lidocaine.

CONCLUSIONS

RGB analysis of digital images proved to be a valid technique for monitoring the effect of local anesthetics with epinephrine in human skin. The technique requires only a commercial digital camera and constitutes a cheap, simple method. The optimal delay between epinephrine injection and incision, to minimize bleeding, was found to be 7 to 9 min, which is in good agreement with common surgical practice.

Reflectance spectroscopy: to shed new light on the capillary refill test

To use Bioengineering methodology is used to achieve, at five anatomical sites, a detailed, quantitative assessment of the return of blood content to the blanched area, during the Capillary Refill (CR) test. An observational, non-randomized, experimental study on 23 healthy subjects (14 females) was performed in our climate controlled skin physiology laboratory. Our main outcome measures were based on the chronological assessment and quantification of red blood cell concentration (RBC) after the release of blanching pressure in the CR test, using Tissue Viability Imaging (TiVi), a digital photographic technique based on polarisation spectroscopy. TiVi enabled collection of detailed data on skin RBC concentration during the CR test. The results were shown as curves with skin blood concentration (TiVi-value) on the y-axis and the time on the x-axis. Quantitative CR responses showed site and temperature variability. We also suggest possible objective endpoint values from the capillary refill curve. Detailed data on skin RBC concentration during the CR test is easily obtained and allows objective determination of end points not possible to achieve by naked eye assessment. These findings have the potential to place the utility of the CR test in a clinical setting in a new light. Picture: Regular photograph and TiVi Image showing CR test and corresponding graph for the CR response.

Assessment of microcirculation of the skin using Tissue Viability Imaging: A promising technique for detecting venous stasis in the skin

BACKGROUND

Venous occlusion in the skin is difficult to detect by existing measurement techniques. Our aim was to find out whether Tissue Viability Imaging (TiVi) was better at detecting venous occlusion by comparing it with results of laser Doppler flowmetry (LDF) during graded arterial and venous stasis in human forearm skin.

METHODS

Arterial and venous occlusions were simulated in 10 healthy volunteers by inflating a blood pressure cuff around the upper right arm. Changes in the concentration of red blood cells (RBC) were measured using TiVi, while skin perfusion and concentration of moving red blood cells (CMBC) were measured using static indices of LDF during exsanguination and subsequent arterial occlusion, postocclusive reactive hyperaemia, and graded increasing and decreasing venous stasis.

RESULTS

During arterial occlusion there was a significant reduction in the mean concentration of RBC from baseline, as well as in perfusion and CMBC (p<0.008). Venous occlusion resulted in a significant 28% increase in the concentration of RBC (p=0.002), but no significant change in perfusion (mean change -14%) while CMBC decreased significantly by 24% (p=0.02). With stepwise increasing occlusion pressures there was a significant rise in the TiVi index and reduction in perfusion (p=0.008), while the reverse was seen when venous flow was gradually restored.

CONCLUSION

The concentration of RBC measured with TiVi changes rapidly and consistently during both total and partial arterial and venous occlusions, while the changes in perfusion, measured by LDF, were less consistent. This suggests that TiVi could be a more useful, non-invasive clinical monitoring tool for detecting venous stasis in the skin than LDF.

Correcting for possible tissue distortion between provocation and assessment in skin testing: the divergent beam UVB photo-test

BACKGROUND

In tissue viability imaging (TiVi), an assessment method for skin erythema, correct orientation of skin position from provocation to assessment optimizes data interpretation. Image processing algorithms could compensate for the effects of skin translation, torsion and rotation realigning assessment images to the position of the skin at provocation.

METHODS

A reference image of a divergent, UVB phototest was acquired, as well as test images at varying levels of translation, rotation and torsion. Using 12 skin markers, an algorithm was applied to restore the distorted test images to the reference image.

RESULTS

The algorithm corrected torsion and rotation up to approximately 35 degrees. The radius of the erythemal reaction and average value of the input image closely matched that of the reference image's 'true value'.

CONCLUSION

The image 'de-warping' procedure improves the robustness of the response image evaluation in a clinical research setting and opens the possibility of the correction of possibly flawed images performed away from the laboratory setting by the subject/patient themselves. This opportunity may increase the use of photo-testing and, by extension, other late response skin testing where the necessity of a return assessment visit is a disincentive to performance of the test.

Polarized light spectroscopy for measurement of the microvascular response to local heating at multiple skin sites

OBJECTIVE

To evaluate whether TiVi, a technique based on polarized light, could measure the change in RBC concentration during local heating in healthy volunteers.

METHODS

Using a custom-made transparent heater, forearm skin was heated to 42 °C for 40 minutes while the change in RBC concentration was measured with TiVi. The perfusion response during local heating was measured at the same time with Laser Doppler flowmetry.

RESULTS

Mean RBC concentration increased (91 ± 34 vs. 51 ± 34 A.U. at baseline, p < 0.001). The spatial heterogeneity of the RBC concentration in the measured skin areas was 26 ± 6.4% at baseline, and 23 ± 4.6% after 40 minutes of heating. The mean RBC concentrations in two skin sites were highly correlated (0.98 at baseline and 0.96 after 40 minutes of heating). The change in RBC concentration was less than the change in perfusion, measured with LDF. Unlike with LDF, a neurally mediated peak was not observed with TiVi in most of the test subjects.

CONCLUSIONS

TiVi is a valuable technique for measuring the microvascular response to local heating in the skin, and offers a high reproducibility for simultaneous measurements at different skin sites, provided carefully controlled experiments are ensured.

Reflectance measurement using digital camera and a protecting dome with built in light source

The reflectance of the skin reveals the chemical and physical changes of the skin as well as many metabolic changes. The reflectance measurement is an important method for medical diagnosis, follow-up and screening. This article concentrates on designing and validating an imaging system, based on a digital camera. The proposed system can measure the reflectance of the skin with high spatial and currently four channel spectral resolution, in the range of 450 nm to 980 nm. The accuracy of the system is determined by imaging a colour checker board and comparing the obtained values with both given values and spectrometer measurements. The diffuse interreflections of both, the integrating sphere and the lighting dome of the imaging system, is compensated with a correction factor. The accuracy of the proposed system is only slightly weaker than the spectrometer. The imaging system characteristics are independent of the camera characteristics.