Orthogonal polarization spectral imaging: A new method for study of the microcirculation

Abstract

Fig. 1 a, Orthogonal polarization spectral imaging probe. b, Optical schematic of the OPS imaging probe. A typical magnification of ×10 is maintained between the target and its image. This results in a resolution of approximately 1 µm/pixel, which is limited by the dimension of the CCD pixel. The probe can be focused from the target surface to 1.0-mm depth, depending on the type of target and the optics used. In vivo, the typical depth of focus is approximately 0.2 mm. c, Optical density of a graduated gray scale (catalog number 152-7662; Kodak) was measured in the presence of the polarization analyzer (b) or with a 0.5 OD neutral density filter (ć) used in place of the analyzer. Average light intensity for each gray level was converted to OD by the following formula: OD = log 10 ((I m -I d )/(I max -I d )) where I m = measured light intensity, I d = dark light intensity (obtained using a black velvet target), I max = intensity of white target. NEW TECHNOLOGYDifferent disease states, including diabetes, hypertension and coronary heart disease, produce distinctive microvascular pathologies. So far, imaging of the human microcirculation has been limited to vascular beds in which the vessels are visible and close to the surface (for example, nailfold, conjunctiva). We report here on orthogonal polarization spectral (OPS) imaging, a new method for imaging the microcirculation using reflected light that allows imaging of the microcirculation noninvasively through mucus membranes and on the surface of solid organs. In OPS imaging, the tissue is illuminated with linearly polarized light and imaged through a polarizer oriented orthogonal to the plane of the illuminating light. Only depolarized photons scattered in the tissue contribute to the image. The optical response of OPS imaging is linear and can be used for reflection spectrophotometry over the wide range of optical density typically achieved by transmission spectrophotometry. A comparison of fluorescence intravital microscopy with OPS imaging in the hamster demonstrated equivalence in measured physiological parameters under control conditions and after ischemic injury. OPS imaging produced high-contrast microvascular images in people from sublingual sites and the brain surface that appear as in transillumination. The technology can be implemented in a small optical probe, providing a convenient method for intravital microscopy on otherwise inaccessible sites and organs in the awake subject or during surgery for research and for clinical diagnostic applications.At present, the use of microvascular imaging in diagnosis and treatment of human disease is limited. Use has been made of nailfold capillaroscopy in the diagnosis and treatment of peripheral vascular diseases, diabetes and hematological disorders 1-3 . Problems with movement have restricted the use of the bulbar conjunctiva for clinical applications in opthalmology 4-6 . Other locations observed by intravital microscopy include the microcirculation of the skin, lip, gingival tissue and tongue 4 . Laser-sca...

Femur window—a new approach to microcirculation of living bone in situ

“…Several studies of indirect microcirculatory measurements have been performed using laser Doppler flowmetry, MRI and orthogonal polarization imaging lacking either spatial resolution or the variety to evaluate the microcirculatory environment adequately [20,29,59]. The application of intravital microscopy has proven to be a successful approach to investigate microcirculatory properties in various tissues at a high spatial resolution [1, 4,14,21,31,48,57,62].…”

Orthogonal polarisation spectral imaging as a new tool for the assessment of antivascular tumour treatment in vivo: a validation study

“…Orthogonal polarisation spectral TM (OPS) imaging is a novel technique which has been introduced recently to visualise microvessels in vivo where tissue is illuminated with linearly polarised light and imaged through a polariser oriented orthogonal to the plane of the illuminating light (Groner et al, 1999). Using this technique close to wavelengths within the haemoglobin absorption spectrum, microvessels containing red blood cells can be visualised.…”

Microcirculatory dysfunction and tissue oxygenation in critical illness

“…The microcirculation in the sublingual mucosa of septic patients has been studied by orthogonal polarization spectral (OPS) imaging50 or side‐stream dark‐field (SDF) imaging51 at some institutions, and reported according to the standardized scores 52. Patients with sepsis show reductions in the proportion of perfused capillaries,53 and in animal models of normotensive sepsis, the density of capillaries with either intermittent or no flow is elevated, while the normal response to vasodilators is reduced 54, 55.…”