Jessica C. Ramella-Roman

Imaging skin pathology with polarized light

Linearly polarized light that illuminates skin is backscattered by superficial layers and rapidly depolarized by birefringent collagen fibers. It is possible to distinguish such superficially backscattered light from the total diffusely reflected light that is dominated by light penetrating deeply into the dermis. The method involves acquisition of two images through an analyzing linear polarizer in front of the camera, one image (I(par)) acquired with the analyzer oriented parallel to the polarization of illumination and one image (I(per)) acquired with the analyzer oriented perpendicular to the illumination. An image based on the polarization ratio, Pol=(I(par)-I(per))/(I(par)+I(per)), is created. This paper compares normal light images, represented by I(per), and Pol images of various skin pathologies in a pilot clinical study using incoherent visible-spectrum light. Images include pigmented skin sites (freckle, tattoo, pigmented nevi) and unpigmented skin sites [nonpigmented intradermal nevus, neurofibroma, actinic keratosis, malignant basal cell carcinoma, squamous cell carcinoma, vascular abnormality (venous lake), burn scar]. Images of a shadow cast from a razor blade onto a forearm skin site illustrate the behavior of Pol values near the shadow edge. Near the shadow edge, Pol approximately doubles in value because no I(per) photons are superficially scattered into the shadow-edge pixels by the shadow region while I(par) photons are directly backscattered from the superficial layer of these pixels. This result suggests that the point spread function in skin for cross-talk between Pol pixels has a half-width-half-max of about 390 microm.

Critical Review of Burn Depth Assessment Techniques: Part II. Review of Laser Doppler Technology

The judgment of which wounds are expected to heal within 21 days is one of the most difficult and important tasks of the burn surgeon. The quoted accuracy of 64 to 76% by senior burn surgeons underscores the importance of an adjunct technology to help make this determination. A plethora of techniques have been developed in the last 70 years. Laser Doppler imaging (LDI) is one of the most recent and widely studied of these techniques. The technology provides an estimate of perfusion through the burn wound, the assumption being that a lower perfusion correlates with a deeper wound and, therefore, a longer time to heal. Although some reports suggest accuracy between 96 and 100% and that it does this 2 days ahead of clinical judgment, others have questioned its applicability to clinical practice. This article, the second of a two-part series, has two objectives: 1) a review of the Doppler principle and how the LDI uses it to estimate perfusion; and 2) a critical assessment of the burn literature on the LDI. Part I provides a historical perspective of the different technologies used through the last 70 years to assist in the determination of burn depth. Laser Doppler has brought technology closer to provide a reliable adjuvant to the clinical prediction of healing, yet, caution is warranted. A clear understanding of the limitations of LDI is needed to put the current research in perspective to find the right clinical application for LDI.

Design, testing, and clinical studies of a handheld polarized light camera

Polarized light imaging has been used to detect the borders of skin cancer and facilitate assessment of cancer boundaries. A design for an inexpensive handheld polarized camera is presented and clinical images acquired with this prototype are shown. The camera is built with two universal serial bus (USB) color video cameras, a polarizing beamsplitter cube, and a 4x objective lens. Illumination is provided by three white LEDs and a sheet polarizer. Horizontal and vertical linearly polarized reflected images are processed at 7 frames/s and a resulting polarized image is displayed on screen. We compare the performances of cheap USB camera and a 16-bit electronically cooled camera. Dark noise and image repeatability are compared. In both cases, the 16-bit camera outperforms the USB cameras. Despite these limitations, the results obtained with this USB prototype are very satisfactory. Examples of polarized images of lesions taken prior to surgery are presented.

Measurement of oxygen saturation in the retina with a spectroscopic sensitive multi aperture camera

We introduce a new multi aperture system capable of capturing six identical images of the human fundus at six different spectral bands. The system is based on a lenslet array architecture and is well suited for spectroscopy application. The multi-aperture system was interfaced with a fundus camera to acquire spectroscopic sensitive images of the retina vessel and ultimately to calculate oxygen saturation in the retina in vivo. In vitro testing showed that the system is able to accurately reconstruct curves of partially oxygenated hemoglobin. In vivo testing on healthy volunteers was conducted and yielded results of oxygen saturation similar to the one reported in the literature, with arterial SO(2) approximately 0.95 and venous SO(2) approximately 0.5.

Use of a multi-spectral camera in the characterization of skin wounds

Skin breakdown is a prevalent and costly medical condition worldwide, with the etiologic and healing processes being complex and multifactorial. Quantitative assessment of wound healing is challenging due to the subjective measurement of wound size and related characteristics. We propose that in vivo spectral reflectance measurements can serve as valuable clinical monitoring tool/device in the study of wound healing. We have designed a multi spectral camera able to acquire 18 wavelength sensitive images in a single snapshot. A lenslets array in front of a digital camera is combined with narrowband filters (bandwidth 10 nm) ranging from 460 to 886 nm. Images taken with the spectroscopic camera are composed of 18 identical sub-images, each carrying different spectral information, that can be used in the assessment of skin chromophores. A clinical trial based on a repeated measures design was conducted at the National Rehabilitation Hospital on 15 individuals to assess whether Poly Carboxy Methyl Glucose Sulfate (PCMGS, CACIPLIQ20), a bio-engineered component of the extracellular matrix of the skin, is effective at promoting healing of a variety of wounds. Multi spectral images collected at different wavelengths combined with optical skin models were used to quantify skin oxygen saturation and its relation to the traditional measures of wound healing.

Noninvasive imaging technologies for cutaneous wound assessment: A review.

The ability to phenotype wounds for the purposes of assessing severity, healing potential and treatment is an important function of evidence‐based medicine. A variety of optical technologies are currently in development for noninvasive wound assessment. To varying extents, these optical technologies have the potential to supplement traditional clinical wound evaluation and research, by providing detailed information regarding skin components imperceptible to visual inspection. These assessments are achieved through quantitative optical analysis of tissue characteristics including blood flow, collagen remodeling, hemoglobin content, inflammation, temperature, vascular structure, and water content. Technologies that have, to this date, been applied to wound assessment include: near infrared imaging, thermal imaging, optical coherence tomography, orthogonal polarization spectral imaging, fluorescence imaging, laser Doppler imaging, microscopy, spatial frequency domain imaging, photoacoustic detection, and spectral/hyperspectral imaging. We present a review of the technologies in use or development for these purposes with three aims: (1) providing basic explanations of imaging technology concepts, (2) reviewing the wound imaging literature, and (3) providing insight into areas for further application and exploration. Noninvasive imaging is a promising advancement in wound assessment and all technologies require further validation.

Three-dimensional phantoms for curvature correction in spatial frequency domain imaging

The sensitivity to surface profile of non-contact optical imaging, such as spatial frequency domain imaging, may lead to incorrect measurements of optical properties and consequently erroneous extrapolation of physiological parameters of interest. Previous correction methods have focused on calibration-based, model-based, and computation-based approached. We propose an experimental method to correct the effect of surface profile on spectral images. Three-dimensional (3D) phantoms were built with acrylonitrile butadiene styrene (ABS) plastic using an accurate 3D imaging and an emergent 3D printing technique. In this study, our method was utilized for the correction of optical properties (absorption coefficient μa and reduced scattering coefficient μs′) of objects obtained with a spatial frequency domain imaging system. The correction method was verified on three objects with simple to complex shapes. Incorrect optical properties due to surface with minimum 4 mm variation in height and 80 degree in slope were detected and improved, particularly for the absorption coefficients. The 3D phantom-based correction method is applicable for a wide range of purposes. The advantages and drawbacks of the 3D phantom-based correction methods are discussed in details.

Regenerating matrix-based therapy for chronic wound healing: a prospective within-subject pilot study.

The aim of this study was to determine whether a skin‐specific bioengineered regenerating agent (RGTA) heparan sulphate mimetic (CACIPLIQ20) improves chronic wound healing. The design of this article is a prospective within‐subject study. The setting was an urban hospital. Patients were 16 African‐American individuals (mean age 42 years) with 22 wounds (mean duration 2·5 years) because of either pressure, diabetic, vascular or burn wounds. Two participants each were lost to follow‐up or removed because of poor compliance, resulting in 18 wounds analysed. Sterile gauze was soaked with CACIPLIQ20 saline solution, placed on the wound for 5 min, then removed twice weekly for 4 weeks. Wounds were otherwise treated according to the standard of care. Twenty‐two percent of wounds fully healed during the treatment period. Wounds showed a 15·2–18·1% decrease in wound size as measured by the vision engineering research group (VERG) digital wound measurement system and total PUSH scores, respectively, at 4 weeks (P = 0·014 and P = 0·003). At 8 weeks there was an 18–26% reduction in wound size (P = 0·04) in the remaining patients. Wound‐related pain measured by the visual analogue pain scale and the wound pain scale declined 60% (P = 0·024) and 70% (P = 0·001), respectively. Patient and clinician satisfaction remained positive throughout the treatment period. It is concluded that treatment with CACIPLIQ20 significantly improved wound‐related pain and may facilitate wound healing. Patient and clinician satisfaction remained high throughout the trial.

Quantitative transverse flow measurement using optical coherence tomography speckle decorrelation analysis

We propose an inter-Ascan speckle decorrelation based method that can quantitatively assess blood flow normal to the direction of the optical coherence tomography imaging beam. To validate this method, we performed a systematic study using both phantom and in vivo animal models. Results show that our speckle analysis method can accurately extract transverse flow speed with high spatial and temporal resolution.

Spectroscopic Measurements of Oxygen Saturation in the Retina

We introduce a new type of retinal oximeter able to capture multiple spectroscopic sensitive images of the retina in a single snapshot. The core of our apparatus is a multiaperture camera that can be easily interfaced with a fundus camera system. A lenslet array divides the image collected by a fundus camera into identical subimages. A bandpass filter array in front of the lens system is used to collect the subimages only at the wavelengths of interest. Two different instruments were designed based on this simple principle. The first system can collect six different images, while the second system can collect up to 18 different images in a single snapshot.