Optical Coherence Tomography
Like ultrasound imaging, optical coherence tomography (OCT) produces cross-sectional imaging in situ of biological tissue. Instead of sound, however, OCT utilizes light to produce high-resolution images. Currently, optical coherence tomography angiography (OCTA) of skin is limited to imaging perfusion in blood vessels to produce a temporary image of surface microvasculature. Standard OCTA identifies the momentary capillary perfusion at the time of imaging without providing information about the actual anatomy of the cutaneous microvasculature. Often OCT images of the same location at different times vary significantly, are not reproducible, and do not allow for the determination of the maximum capacity of the capillary bed. However, OCT is a non-invasive form of imaging and produces high resolution maps of perfusion in vivo, and therefore is a useful tool for dermatological investigations. Since it is also a more efficient procedure compared to histology and does not compromise image resolution, the Manstein Lab developed a procedure using OCT to observe morphological changes in the cutaneous capillary bed.
Human Clinical Study
Factors like aging, smoking, and disease may cause changes in the cutaneous capillary bed such as stiffening of the vascular wall, decreased permeability, and overall variation in vessel network density. These differences in the vessel network can be analyzed by applying and releasing pressure to the skin to result in rapid reperfusion of the capillaries. This so-called capillary refill effect allows for the observation of the entire capillary bed with OCTA. Differences between the baseline and maximum perfusion images are described by the Relative Capillary Capacity (RCC) metric which gives further insight into the character of the imaged blood vessels. Currently, the Manstein Lab is conducting a human clinical study to develop the OCTA/RCC technique for studying factors that may affect the characteristics and/or health of the peripheral vasculature.
In mice, the adipose tissue layer is thin enough to image using OCT. The Manstein Lab has a significant mouse research effort examining the effects of cooling and/or cryolipolysis on fat in mice. We are examining the mechanisms of adipose tissue loss, the browning of adipose tissue as a result of localized cooling, and effects on metabolic activity after cryolipolysis.
Kepp, T., Droigk, C., Casper, M., Evers, M., Hüttman, G., Salma, N., Manstein, D., Heinrich, M.P., Handels, H. Segmentation of mouse skin layers in optical coherence tomography image data using deep convolutional neural networks. Biomedical Optics Express. 2019 Jun 21;10(7):3484-3496. doi: 10.1364/BOE.10.003484. eCollection 2019 Jul 1.
Casper, M., Schulz-Hildebrandt, H., Evers, M., Birngruber, R., Manstein, D., Hüttman, G. Optimization-based vessel segmentation pipeline for robust quantification of capillary networks in skin with optical coherence tomography angiography. Journal of Biomedical Optics. 2019 Apr;2494):1-11. doi: 10.1117/1.JBO.24.4.046005.
Fluorescence Lifetime Imaging Microscopy (FLIM)
FLIM is a well-established imaging method that analyzes the lifetime of a fluorophore rather than its intensity. The Manstein Lab is focused on using this technique for evaluating adipose tissue metabolism. There are three types of fat cells that have metabolic functions in the body; white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue (BeAT). We are looking at BAT and BeAT as targets for treating obesity due to their ability to dissipate energy as heat via nonshivering thermogenesis. By stimulating and activating BAT and BeAT, lipolysis and metabolic activity is increased, resulting in higher whole-body energy expenditure and a reduction in fat. However, traditional metabolic analysis faces many difficulties evaluating the activation of brown fat in a heterogeneous environment and monitoring metabolic activity over time. Two-photon FLIM is used to identify the naturally occurring auto-fluorescent molecule nicotinamide adenine dinucleotide (NADH) for label-free quantification of metabolic activity. Compared to traditional FLIM analysis that utilizes a two-lifetime model of NADH, the Manstein Lab expanded to a four-lifetime model of NADH resulting in superior metabolic assessment. The four-lifetime components can be mapped to specific cellular compartments to create a novel optical biomarker named the mitochondrial-cytoplasmic-ratio (MCR) that accurately reflects the shifts in mitochondrial and cytoplasmic NADH distribution and binding states. Additionally, the new MCR metric correlates very well with the oxygen consumption rate as measured by traditional methods such as an extracellular flux analyzer. This widely applicable approach constitutes a powerful tool for monitoring cellular metabolism, and we are currently using it for wound healing and stem cell differentiation studies.
Evers, M., Salma, N., Osseiran, S., Casper, M., Birngruber, R., Evans, C.L., Manstein, D. Enhanced quantification of metabolic activity for individual adipocytes by label-free FLIM. Scientific Reports. 2018 Jun 8;8(1):8757. doi: 10.1038/s41598-018-27093-x.
Fractional laser technology was co-invented by Dieter Manstein and it utilizes non-ablative or ablative laser treatments to create microscopic treatment zones (MTZs) in skin. Laser exposures thermally damages the target skin within small areas of diameters, generally less than 0.5 mm. Tissue surrounding the MTZs remains unexposed to the laser and thermal damage, increasing the speed and efficacy of wound healing in the MTZs. Fractional laser technology is commonly used for the treatment of photodamaged skin, pigmentation disorders, actinic keratosis, rhytides, and wrinkles. It is also vital in restoring scarred skin caused by acne, surgery, and burns. CO2 lasers are commonly used during fractional ablation as the tissue is immediately evaporated without causing significant thermal damage. However, there is a need to optimize the settings of the CO2 laser, such as wavelength, energy per pulse, pulse duration, pulse number, and temporal pulse shape, without causing significant thermal damage for improved treatment of dermatological conditions. Current research in the Manstein Lab is focused on developing new laser systems that improve upon the feasibility of the CO2 laser for improved dermal ablation and maximum skin tightening.
Alternative lasers like CO lasers and Thulium fiber lasers have the potential to enhance treatment of dermatological conditions. Though less renowned than CO2 lasers, literature has suggested that adaptations to CO lasers would allow smaller spot sizes than those feasible in CO2 lasers. Additionally, Thulium fiber lasers, which are currently used in non-ablative treatments of melasma and mild to moderate photodamage, might also be useful for ablative treatments. Current research focuses on the effect of these lasers on skin specimens to evaluate differences in etch depth, thermal damage, and ablation-to-coagulation ratio (ACR). Laser characteristics such as wavelength, beam diameter, radiant exposure, pulse duration, and temporal pulse shape are altered to establish corresponding changes in etch depth, thermal damage, and ACR on the skin. Further fractional technology research focuses on enhancing skin rejuvenation without causing adverse side effects, as well as adapting laser parameters to create smaller ablation diameters in the skin for increased wound healing.
Evers, M., Ha, L., Casper, M., Welford, D., Kositratna, G., Birngruber, R., Manstein, D. Assessment of skin lesions produced by focused, tunable, mid-infrared chalcogenide laser radiation. Lasers in Surgery and Medicine. 2018 Sep;50(9):961-972. doi: 10.1002/lsm.22935. Epub 2018 May 25.
Kositratna, G., Hibert, M.L., Jaspan, M., Welford, D., Manstein, D. Effects of deviation from focal plane on lesion geometry for ablative fractional photothermolysis. Lasers in Surgery and Medicine. 2016 Jul;48(5):555-61. doi: 10.1002/lsm.22481. Epub 2016 Feb