Advancements in Dermatological Imaging Modalities

Abnormal body temperature is a natural indicator of illness. Infrared thermography (IRT) is a fast, passive, non-contact and non-invasive alternative to conventional clinical thermometers for monitoring body temperature. Besides, IRT can also map body surface temperature remotely. Last five decades witnessed a steady increase in the utility of thermal imaging cameras to obtain correlations between the thermal physiology and skin temperature. IRT has been successfully used in diagnosis of breast cancer, diabetes neuropathy and peripheral vascular disorders. It has also been used to detect problems associated with gynecology, kidney transplantation, dermatology, heart, neonatal physiology, fever screening and brain imaging. With the advent of modern infrared cameras, data acquisition and processing techniques, it is now possible to have real time high resolution thermographic images, which is likely to surge further research in this field. The present efforts are focused on automatic analysis of temperature distribution of regions of interest and their statistical analysis for detection of abnormalities. This critical review focuses on advances in the area of medical IRT. The basics of IRT, essential theoretical background, the procedures adopted for various measurements and applications of IRT in various medical fields are discussed in this review. Besides background information is provided for beginners for better understanding of the subject.

Photoacoustic imaging (or optoacoustic imaging) is an upcoming biomedical imaging modality availing the benefits of optical resolution and acoustic depth of penetration. With its capacity to offer structural, functional, molecular and kinetic information making use of either endogenous contrast agents like hemoglobin, lipid, melanin and water or a variety of exogenous contrast agents or both, PAI has demonstrated promising potential in a wide range of preclinical and clinical applications. This review provides an overview of the rapidly expanding clinical applications of photoacoustic imaging including breast imaging, dermatologic imaging, vascular imaging, carotid artery imaging, musculoskeletal imaging, gastrointestinal imaging and adipose tissue imaging and the future directives utilizing different configurations of photoacoustic imaging. Particular emphasis is placed on investigations performed on human or human specimens.

Optical coherence tomography (OCT) is a non-invasive technique for morphological investigation of tissue. Since its development in the late 1980s it is mainly used as a diagnostic tool in ophthalmology. For examination of a highly scattering tissue like the skin, it was necessary to modify the method. Early studies on the value of OCT for skin diagnosis gave promising results. The OCT technique is based on the principle of Michelson interferometry. The light sources used for OCT are low coherent superluminescent diodes operating at a wavelength of about 1300 nm. OCT provides two-dimensional images with a scan length of a few millimeters (mm), a resolution of about 15 microns and a maximum detection depth of 1.5 mm. The image acquisition can be performed nearly in real time. The measurement is non-invasive and with no side effects. The in vivo OCT images of human skin show a strong scattering from tissue with a few layers and some optical inhomogeneities. The resolution enables the visualization of architectural changes, but not of single cells. In palmoplantar skin, the thick stratum comeum is visible as a low-scattering superficial well defined layer with spiral sweat gland ducts inside. The epidermis can be distinguished from the dermis. Adnexal structures and blood vessels are low-scattering regions in the upper dermis. Skin tumors show a homogenous signal distribution. In some cases, tumor borders to healthy skin are detectable. Inflammatory skin diseases lead to changes of the OCT image, such as thickening of the epidermis and reduction of the light attenuation in the dermis. A quantification of treatment effects, such as swelling of the horny layer due to application of a moisturizer, is possible. Repeated measurements allow a monitoring of the changes over time. OCT is a promising new bioengineering method for investigation of skin morphology. In some cases it may be useful for diagnosis of skin diseases. Because of its non-invasive character, the technique allows monitoring of inflammatory diseases over time. An objective quantification of the efficacy and tolerance of topical treatment is also possible. Due to the high resolution and simple application, OCT is an interesting addition to other morphological techniques in dermatology.