Optical coherence tomography (OCT) and speckle imaging are two coherence-based imaging modalities with burgeoning applications in rapid non-invasive measurement of the skin. Both modalities are sensitive to tissue morphology and have polarization-sensitive augmentations. This study compares Polarization Sensitive OCT (PS-OCT) and Polarization Speckle measurements to better understand the relationship between polarization and coherence properties of skin. Volunteers of Fitzpatrick skin type I through VI were recruited and healthy skin was measured at four body sites (palm, inner forearm, forehead, and eye corner). Preliminary results indicate a strong similarity between the skin surface roughness measurements of PS-OCT and polarization speckle. In regards to tissue depolarization, PS-OCT measurements appear minimally affected by skin color, whereas polarization speckle was strongly affected due to differing measurement wavelengths. Among body sites, the palm and face were found to be generally smoother than the forearm; however the epidermis layer of the palm demonstrated notably greater polarization scrambling.
Polarization-Sensitive Optical Coherence Tomography (PS-OCT) is a real-time 3D imaging technique providing structural and functional contrasts in tissue. Previously, we have quantified multiple contrasts such as back-scattered intensity, accumulated phase retardation, local birefringence, and degree of polarization uniformity in the epidermis and dermis of the skin. Here, we add the Attenuation Coefficient (AC) contrast to quantify light attenuation from absorption and scattering in skin layers. Two techniques are utilized to obtain AC. One involves slope fitting to the logarithm of intensity A-lines, and the other uses a depth-resolved model-based reconstruction of AC. To investigate the effect of skin tone on AC, we first used skin phantoms with various absorption and scattering coefficients. It is found that the color of the phantom directly correlates with the absorption coefficient, while AC correlates with the sum of the absorption and reduced scattering coefficient. Darker objects, indicative of a higher concentration of melanin in the skin tissue, show a higher absorption coefficient. AC is further analyzed on in vivo skin imaging with different skin tones. However, no clear correlation between AC and skin tone is observed. This lack of correlation is likely due to the absorption coefficient being much smaller than the scattering coefficient in skin tissue at the OCT imaging wavelength of 1060nm.
Polarization-sensitive optical coherence tomography (PS-OCT) is a promising tool for non-invasive skin imaging, with its capability for depth-resolved, high-resolution, fast, and polarization-sensitive imaging. Thirty volunteers are recruited for skin imaging on the palm, arm, forehead, and eye corner. A segmentation algorithm based on intensity images will segment the epidermis and dermis layers and also stratum corneum if applicable. Multi-contrast images, including phase retardation, local birefringence, and degree of polarization uniformity, will be obtained from different skin layers. Possible relationships between the optical properties and skin features including layered structure, collagen organization, melanin concertation, and skin roughness will be investigated.
This presentation reports a snapshot polarimetry system, capable of measuring a Stokes vector distribution within a millisecond timescale. The proposed system measures at a perpendicular backscattering angle and features a polarization state analyzer with no moving parts, comprised of a pair of quarter waveplates and pixel polarization cameras. An additional novel design aspect of the system is its capability to register polarization speckle. Polarization speckle contains both polarization and phase information that is not available from conventional techniques. The device’s acquisition speed and small form factor enable future studies of polarization speckle for biomedical applications.
Jones matrix optical coherence tomography (JM-OCT) is a form of polarization-sensitive OCT (PS-OCT) that allows for the simultaneous and high-quality in vivo capture of multiple polarization-based imaging contrasts. Our system allows for the capture of high-sensitivity structural OCT, degree of polarization uniformity (DOPU), and birefringence images. Segmenting the epidermal-dermal junction is a topic of high interest in OCT and dermatology. While others have explored this with traditional OCT, no other groups have used this type of segmentation with JM-OCT. We believe that combining a reliable segmentation procedure with the robust and localized characterization provided by JM-OCT can help fully utilize the strengths of both techniques and allow for a better characterization of the skin layers. Here, we utilize JM-OCT to assess the skin properties of healthy volunteers. Using high-sensitivity OCT, we quantified the epidermal thickness of various locations in vivo and were able to segment the epidermis, dermis, and stratum corneum in thick skin. Polarization imaging is sensitive to specific structures in the skin, such as collagen and melanin, and we were able to quantify the depolarization, and birefringence caused by these structures in different skin layers. In thick skin, localized polarization results showed an average DOPU of 0.89 in the dermis compared to an average of 0.79 in the stratum corneum. However, in both thick and thin skin, DOPU was lower overall in the epidermis compared to the dermis, indicating that most observed depolarization occurs due to the structure of the stratum corneum. Birefringence was found to be higher in the dermis than the epidermis in both cases.
Recently optical imaging is focused on non-invasive methods which could be automated and provide diagnostics in vivo. Coherence and polarization encoding the wave phase transformation create additional channels of information compared with the amplitude-based techniques. The modification of polarization properties like depolarization, birefringence, and diattenuation are the subject of polarimetry. One of the depolarization metrics is the Degree of Polarization (DOP), which represent the fraction of polarized light maintained while light propagates in media, ranging from 1 for fully polarized to 0 for totally depolarized light. After constructing a one-shot Stokes polarimetry probe, we conducted a preliminary clinical trial including 20 benign, 28 malignant skin lesions. Also 59 normal skin sites where tested. Using DOP as a diagnostics criterion we were able to separate Malignant Melanomas against all other lesions. Another depolarization metric tested was the Polarization Memory Rate (PMR) which characterizes the decay of circularly polarized light relative to linearly polarized light as light propagates in a medium. PMR demonstrates a strong diagnostics potential separating all cancer against benign lesions.
Significance: Management of skin cancer worldwide is often a challenge of scale, in that the number of potential cases presented outweighs the resources available to detect and treat skin cancer.
Aim: This project aims to develop a polarimetry probe to create an accessible skin cancer detection tool.
Approach: An optical probe was developed to perform bulk tissue Stokes polarimetry, a technique in which a laser of known polarization illuminates a target, and the altered polarization state of the backscattered light is measured. Typically, measuring a polarization state requires four sequential measurements with different orientations of polarization filters; however, this probe contains four spatially separated detectors to take four measurements in one shot. The probe was designed to perform at a lower cost and higher speed than conventional polarimetry methods. The probe uses photodiodes and linear and circular film polarizing filters as detectors, and a low-coherence laser diode as its illumination source. The probe design takes advantage of the statistical uniformity of the polarization speckle field formed at the detection area.
Results: Tests of each probe component, and the complete system put together, were performed to evaluate error and confirm the probe’s performance despite its low-cost components. This probe’s potential is demonstrated in a pilot clinical study on 71 skin lesions. The degree of polarization was found to be a factor by which malignant melanoma could be separated from other types of skin lesions.
Skin cancer is the most common form of cancer in North America, and melanoma is the most deadly form of skin cancer. Roughness assessment of epidermis has been shown to be valuable in detecting potential skin neoplasia. However, the existing roughness assessment techniques cannot also provide volumetric information. For greater insight, we propose polarization sensitive optical coherence tomography (PS-OCT) for skin assessment. The intensity channel of OCT visualizes the layered structure and surface roughness profile of skin in 3D. Furthermore, PS-OCT can simultaneously conduct polarization related measurements such as the degree of polarization uniformity (DOPU) in a separate imaging channel. Skin phantoms of different surface roughness ranging from 1 to 68 μm have been studied. It was observed that for rougher surfaces, the roughness can be quantified from the surface profile visible in the intensity channel. In smoother surfaces for which the profile is not sensitive, the DOPU decreases with roughness in a quantifiable correlation. The contrast in the DOPU channel is sensitive to polarization and phase fluctuations. Smoother surfaces tend to maintain the polarization state, whereas the height differences in a rougher surface contribute to larger phase shifts between light waves within the coherence volume, leading to greater depolarization. PS-OCT was also applied to in vivo imaging of human skin. The skin at the palm edge shows lower DOPU compared to the skin on the back of the hand, an indication of greater polarization state modification caused by skin roughness. PS-OCT can provide a comprehensive evaluation of skin, which has great potential for detecting melanoma.
Introduction: Management of skin cancer worldwide is often a challenge of scale, in that the resources available to detect and treat skin cancer are outweighed by the number of potential cases presented. This project aims to develop oneshot Stokes polarimetry using low-cost components to create a widely available skin cancer detection tool. Methods: A probe was developed to perform one-shot Stokes polarimetry on skin lesions in-vivo. Stokes polarimetry is an optical technique in which a laser of known polarization is fired at a target, and the altered polarization state of the returning light is measured. Typically, measuring a polarization state requires sequential measurements with four polarizing filters, however this probe contains four separate detectors to take these measurements in one shot. This probe was designed to perform at a lower cost and higher speed than traditional polarization methods. The Stokes vector is assessed as opposed to a Mueller matrix image to reduce the number of optical components and measurements required. The probe uses photodiodes and non-actuating film polarizing filters as detectors, and a partially-coherent laser diode as its illumination source. Results: Validation tests of each probe component, and the complete system put together, were performed to confirm the probe’s performance despite its low-cost components. This probe’s potential is demonstrated in a pilot clinical study on 69 skin lesions. The degree of polarization was found to be a factor by which melanoma could be potentially separated from other types of skin lesions.
Determining the optical polarization properties of a skin lesion is a proposed method to differentiate melanoma from other skin lesions. We developed an in vivo Stokes polarimetry probe that fires a laser of known polarization at the skin and measures the Stokes parameters of the backscattered light in one shot. From these measured Stokes parameters, we can calculate the degree of polarization (DOP). Through testing on rough skin phantoms, a correlation between backscattered DOP and skin roughness was identified for both linear and circular input polarization, the latter of which was found to be more useful. In a pilot clinical trial of 69 skin lesions in vivo, it was found that the mean DOP for melanoma (linear input on melanoma: 0.46 ± 0.09) was greater than that of other lesions (linear input on all other lesions: 0.28 ± 0.01). This separation is greater for circular polarized input light, and it is likely that circular polarized light’s greater sensitivity to surface roughness contributes to this result. In addition, all skin lesions demonstrated a stronger depolarizing effect on circular polarized light than linear polarized light. We have identified DOP as a potentially useful measurement to identify melanoma among other types of skin lesions.
This paper reports on the design of a prototype in-vivo Stokes polarimetry probe for skin lesion evaluation, and preliminary results from skin phantom and clinical trials of this device. The probe releases a single millisecond-long pulse from a laser diode with either linear or circular polarization. It then captures the resulting backscattered far-field polarization speckle and calculates the Stokes parameters. This probe was designed with three novel innovations in mind. First, the Stokes vector is captured quickly, using low-cost components without the use of moving parts. Second, a compact collimated laser diode was used as the light source. Third, the device and detector geometry were designed to produce and capture a uniform speckle field. In the first clinical trial of this device, measurements were taken from a variety of skin lesions, both cancerous and benign. The Stokes vector was measured and used to calculate the degree of polarization (DOP), the azimuth angle, and the ellipticity angle of the polarization ellipse for two input light polarizations. Among other findings, the DOP for circular polarized input light was consistently lower than the DOP for linear polarized input light. These findings indicate the potential for a fast and low-cost in-vivo skin cancer screening tool, and encourages the continuing development of this probe’s techniques.
Polarization speckle is a rapidly developed field. Unlike laser speckle, polarization speckle consists of stochastic interference patterns with spatially random polarizations, amplitudes and phases. We have been working in this exciting research field, developing techniques to generate polarization patterns from skin. We hypothesize that polarization speckle patterns could be used in biomedical applications, especially, for detecting and monitoring skin cancers, the most common neoplasmas for white populations around the world. This paper describes our effort in developing two polarization speckle devices. One of them captures the Stokes parameters So and S1 simultaneously, and another one captures all four Stokes parameters So, S1, S2, and S3 in one-shot, within milliseconds. Hence these two devices could be used in medical clinics and assessed skin conditions in-vivo. In order to validate our hypothesis, we conducted a series of three clinical studies. These are early pilot studies, and the results suggest that the devices have potential to detect and monitor skin cancers.
Skin roughness is an important parameter in the characterization of skin and skin lesions, particularly for the purposes of
skin cancer detection. Our group had previously constructed a laser speckle device that can detect the roughness in
microrelief of the skin. This paper reports on findings made for the further miniaturization of our existing portably-sized
device. These findings include the feasibility of adopting a laser diode without temperature control, and the use of a single
CCD camera for detection. The coherence length of a laser is a crucial criterion for speckle measurements as it must be
within a specific range. The coherence length of a commercial grade 405 nm laser diode was found to be of an appropriate
length. Also, after a short warm-up period the coherence length of the laser was found to remain relatively stable, even
without temperature control. Although the laser’s temperature change during operation may affect its power output and
the shape of its spectrum, these are only minor factors in speckle contrast measurements. Our second finding covers a
calibration curve to relate speckle measurements to roughness using only parallel polarization from one CCD camera. This
was created using experimental data from skin phantoms and tested on in-vivo skin. These improvements are important
steps forward in the ongoing development of the laser speckle device, especially towards a clinical device to measure skin
roughness and evaluate skin lesions.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.