This report outlines results from an independent study assessing the clinical potential of an emerging, contemporary
imaging technology. Tissue Viability (TiVi) imaging is an easily implemented, non-invasive, and portable technique
which maps the blood circulation in the surface dermal layer. However, its routine clinical implementation awaits the
development of the necessary standardised protocols. Thus the pilot study examines the efficacy of a novel TiVi imaging
device within a localised skin blood flow occlusion protocol. The test was administered to the upper volar forearm of 19
healthy subjects (10:9 Female:Male) for 5 different time periods ranging from 5 to 25 seconds. Dermal areas
corresponding to 100 × 100 pixels (2.89 cm<sup>2</sup>) were monitored for 60 seconds prior to, during and after each occlusal test.
Our results support the relevance of a TiVi occlusion protocol for physiological assessment of the skin microcirculation.
The use of laser Doppler perfusion imaging (LDPI) and laser speckle perfusion imaging (LSPI) is well known in the noninvasive investigation of microcirculatory blood flow. This work compares the two techniques with the recently developed tissue viability (TiVi) imaging system, which is proposed as a useful tool to quantify red blood cell concentration in microcirculation. Three systems are evaluated with common skin tests such as the use of vasodilating and vasoconstricting drugs (methlynicotinate and clobetasol, respectively) and a reactive hyperaemia maneuver (using a sphygmomanometer). The devices investigated are the laser Doppler line scanner (LDLS), the laser speckle perfusion imager (FLPI)-both from Moor Instruments (Axminster, United Kingdom)-and the TiVi imaging system (WheelsBridge AB, Linköping, Sweden). Both imaging and point scanning by the devices are used to quantify the provoked reactions. Perfusion images of vasodilatation and vasoconstriction are acquired with both LDLS and FLPI, while TiVi images are acquired with the TiVi imager. Time acquisitions of an averaged region of interest are acquired for temporal studies such as the reactive hyperaemia. In contrast to the change in perfusion over time with pressure, the TiVi imager shows a different response due its measurement of blood concentration rather than perfusion. The responses can be explained by physiological understanding. Although the three devices sample different compartments of tissue, and output essentially different variables, comparisons can be seen between the three systems. The LDLS system proves to be suited to measurement of perfusion in deeper vessels, while FLPI and TiVi showed sensitivity to more superficial nutritional supply. (Cont'd.)
We review methods applied to imaging and assessment of the microcirculation and document the
recent progress. Visible and near-infrared light, particularly in the wavelength region of 600 nm
to 1100 nm, offer a window into human and animal tissues due to reduced scattering and
absorption. Laser Doppler perfusion imaging (LDPI) and laser speckle perfusion imaging (LSPI)
are used in the non-invasive investigation of the microcirculation. This paper compares the two
techniques with the recently developed Tissue Viability (TiVi) imaging system, which is
proposed as a useful tool to quantify red blood cell concentration in the microcirculation. Both
imaging and point scanning by the devices were used to quantify microvascular reactivity. The
responses can be explained by physiological understanding and subtle differences by technophysiological
knowledge. The resolution, penetration depth and acquisition rate of each
instrument should be taken into account when choosing a system for a particular clinical
This article describes the theoretical development and design of a real-time microcirculation imaging system, an
extension from a previously technology developed by our group. The technology utilises polarisation spectroscopy, a
technique used in order to selectively gate photons returning from various compartments of human skin tissue, namely
from the superficial layers of the epidermis, and the deeper backscattered light from the dermal matrix. A consumer-end
digital camcorder captures colour data with three individual CCDs, and a custom designed light source consisting of a 24
LED ring light provides broadband illumination over the 400 nm - 700 nm wavelength region. Theory developed leads
to an image processing algorithm, the output of which scales linearly with increasing red blood cell (RBC) concentration.
Processed images are displayed online in real-time at a rate of 25 frames s<sup>-1</sup>, at a frame size of 256 x 256 pixels, and is
limited only by computer RAM memory and processing speed. General demonstrations of the technique <i>in vivo</i> display
several advantages over similar technology.
Biomedical optics and photomedicine applications are challenged by the turbid nature of most biological tissue systems.
This nature limits the penetration depth of light into the tissue. Optical clearing improves the penetration depth of light
by the application of optical clearing agents which produce an equalization of refractive indices between tissue
components and causes a decrease in tissue scattering, and thus increase in optical transmittance. In this paper we
examine the effects of optical clearing agents on <i>ex vivo</i> porcine skin using the immersion method. We develop a simple
model that can be used to compare different aspects of optical clearing agents such as the rate at which the clearing
agents enters the tissue and also the reduction in scattering achieved. We examine the change in the reflected light
spectrum over time as the clearing agent enters the skin. This is examined via point probe measurements and also a wide
field imaging technique with a consumer-end digital camera. The consumer-end digital camera offers a cheap and
simple method for analyzing optical clearing agents over a wider field, overcoming the limitations of single point
This paper describes the design and evaluation of a novel easy to use, tissue viability imaging system (TiVi). The system is
based on the methods of diffuse reflectance spectroscopy and polarization spectroscopy. The technique has been developed as
an alternative to current imaging technology in the area of microcirculation imaging, most notably optical coherence
tomography (OCT) and laser Doppler perfusion imaging (LDPI). The system is based on standard digital camera technology,
and is sensitive to red blood cells (RBCs) in the microcirculation. Lack of clinical acceptance of both OCT and LDPI fuels
the need for an objective, simple, reproducible and portable imaging method that can provide accurate measurements related
to stimulus vasoactivity in the microvasculature. The limitations of these technologies are discussed in this paper. Uses of the
Tissue Viability system include skin care products, drug development, and assessment spatial and temporal aspects of
vasodilation (erythema) and vasoconstriction (blanching).
A new technique for the investigation of microvascular tissue blood concentration is presented, based on the method of polarisation spectroscopy of blood in superficial skin tissue. Linearly polarised light incident on the skin is partly reflected by the surface layers, and partly backscattered from the dermal tissue. Use of orthogonal polarisation filters over both a light source and a CCD suppresses the reflections from the surface, and only the depolarised light backscattered from the dermal matrix reaches the CCD array. By separating the colour planes of an image acquired in this manner and applying a dedicated image processing algorithm, spectroscopic information about the amount of red blood cells (RBCs) in the underlying area of tissue can be discovered. The algorithm incorporates theory that utilises the differences in light absorption of RBCs and dermal tissue in the red and green wavelength regions. <i>In vitro </i>fluid models compare well to computer simulations in describing a linear relationship between output signal (called TiVi<sub>index</sub>) and RBC concentration in the physiological range of 0%-4%. <i>In vivo </i>evaluation of the technique via transepidermal application of acetylcholine by iontophoresis displayed a heterogeneity pattern of vasodilation, which is typical of the vasoactive agent. Extension of the technique to capture and process continuous real-time data creates a new possibility of online real-time image processing. Application of tissue viability (<i>TiVi</i>) imaging include skin care products and drug development, as well as investigations of microvascular angiogenesis.