Methods for registering and calibrating in vivo terahertz images of cutaneous burn wounds

Abstract

A method to register THz and visible images of cutaneous burn wounds and to calibrate THz image data is presented. Images of partial and full thickness burn wounds in 9 rats were collected over 435 mins. = 7.25 hours following burn induction. A two-step process was developed to reference the unknown structure of THz imaging contrast to the known structure and the features present in visible images of the injury. This process enabled the demarcation of a wound center for each THz image, independent of THz contrast. Threshold based segmentation enabled the automated identification of air (0% reflectivity), brass (100% reflectivity), and abdomen regions within the registered THz images. Pixel populations, defined by the segmentations, informed unsupervised image calibration and contrast warping for display. The registered images revealed that the largest variation in THz tissue reflectivity occurred superior to the contact region at ~0.13%/min. Conversely the contact region showed demonstrated an ~6.5-fold decrease at ~0.02%/min. Exploration of occlusion effects suggests that window contact may affect the measured edematous response.

Application of contrast-enhanced ultrasound in the diagnosis of burn depth

“…Based on the degree of tissue edema, some studies have reported that the use of terahertz imaging could determine the depth of burns (20)(21)(22). However, terahertz imaging cannot observe the tissue structure and the state of the microcirculation, so solely relying on the degree of edema to assess burn depth has obvious limitations.…”

Recent advances in terahertz imaging: 1999 to 2021

“…Such studies have been done both ex vivo [55] and in vivo [56] on various animal models such as Sprague-Dawley rats [57] and Landrace Yorkshire cross pigs [59] whose skin have similarities with humans. Furthermore, differences in the post-burn water accumulation dynamics caused by edema have been well studied with terahertz methods [59,60]. In such studies, an initial depletion of the hydration at the burn site, in the minutes following the injury, produces a decrease of the terahertz reflection at the cutaneous surface.…”

“…[Reprinted] with permission from [60] ©The Optical Society first in vivo measurements of skin [61] were reported in the early 2000s; however, the degree of sophistication required for actual medical applications has maintained interest in the topic up to the present day [62]. As one important example, diabetic foot syndrome, a consequence of diabetes, is a condition for which there is currently no objective diagnostic test, particularly in early stages.…”

Supervised machine learning for automatic classification of in vivo burn injuries using the terahertz Portable Handheld Spectral Reflection (PHASR) scanner

“…Terahertz time-domain spectroscopy (THz-TDS) has emerged as a noninvasive and objective tool for assessment of various biological tissue types, including determining corneal hydration [29][30][31][32] , diagnosis of brain tumors [33][34][35] , diabetic foot syndrome 36 , delineating breast cancer tumor margins [37][38][39][40][41] , and classification of burn injuries 42,43 . In burn diagnosis applications, it was shown that the reflectivity of the full-thickness burns in rodent models is higher compared to the normal skin over a frequency range between 0.2 and 1 THz 44 .…”