3. Biodistribution of needle-injections and needle-free jet-injections visualized by a 3D- Fluorescent Imaging Cryomicrotome System 86 Considering the 3D biodistribution shape of TCA, we noticed substantial heterogeneity. These variable patterns of 3D TCA shapes contribute to the observation of the large heterogeneity in TCA biodistribution and ultimately clinical response. There are several strengths to this study. To the best of our knowledge, there are no similar studies assessing the 3D biodistribution of TCA in keloids. Moreover, several drug delivery methods were studied, including needle injection, perforation technique, and jet injection. Furthermore, an innovative 3D imaging technique was used. Various imaging techniques may be used for assessing layers of the skin, including confocal microscopy, optical coherence tomography and high frequency ultrasound. In contrast to these imaging techniques, the custom-built 3D-FICS can be used for high resolution segmentation of large 3D volumes [11]. This novel imaging technique has previously been used in other medical specialties including cardiology to visualize the perfusion distribution within the heart and in neurology for imaging fluid distribution in brain structures [12, 13]. However, there are also several limitations to this study. Firstly, the sample size was limited, because keloids are excised infrequently. Secondly, differentiation in keloid characteristics such as anatomical location, tissue density and prior treatment was not performed due to the small sample size. Moreover, the included keloids were selected for excision and adjuvant brachytherapy, and differ from the usually smaller, thinner and less rigid keloids in clinical practice. Additionally, we visualized the fluorescent marker that was labeled to the TCA suspension, being a proxy for the TCA suspension. Although the fluorescent TCA volumes are not equivalent to the actual injected TCA volumes, they enabled comparison of the fluorescent biodistribution between samples. Furthermore, the observed fluorescent TCA volume and 3D biodistribution shape could be affected by the optical properties of tissue types, which may be different for normal and keloid tissue. Finally, inherent to the exploratory design of the study, in-vivo conditions such as blood flow, skin turgor, and hydration of the skin could not be taken into consideration.
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