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

Priyamvada Tewari, James Garritano, Neha Bajwa, Shijun Sung, Haochong Huang, Dayong Wang, Warren Grundfest, Daniel B. Ennis, Dan Ruan, Elliott Brown, Erik Dutson, Michael C. Fishbein, and Zachary Taylor

Fig. 1 Burn zones organize as concentric like shells in the depth are hypothesized to appear as projections of the shells on the surface. Skin layers denoted A, B, C and damage zones denoted 1, 2, 3, 4. (a) Cross-sectional view: damage from superficial thickness wounds are limited primarily to the stratum corneum and epidermis, partial thickness burn wounds extend into the epidermis, and full thickness wounds extend into deep dermis. (b) Isometric view providing orientation between (a) and (c). (c) Top down view: The damage zones, and thus variations in surface TWC should present as regions concentric with the center.

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-10-1-322

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.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-THz Imaging System for in vivo Human Cornea

Sunshiny Sung, Skyler Selvin, Neha Bajwa,  Somporn Chantra,   Bryan Nowroozi,  James Garritano, Jacob Goell, Alexander D. Li,   Sophie X. Deng,  Elliott R. Brown,  Warren S. Grundfest,  Zachary D. Taylor

http://ieeexplore.ieee.org/document/8167336/

Terahertz (THz) imaging of corneal tissue water content (CTWC) is a proposed method for early, accurate detection and study of corneal diseases. Despite promising results from ex vivo and in vivo cornea studies, interpretation of the reflectivity data is confounded by the contact between corneal tissue and rigid dielectric window used to flatten the imaging field. This work develops a novel imaging system and image reconstruction methods specifically for nearly spherical targets such as human cornea. A prototype system was constructed using a 650-GHz multiplier source and Schottky diode detector. Resolution and imaging field strength measurement from characterization targets correlate well with those predicted by the quasioptical theory and physical optics analysis. Imaging experiments with corneal phantoms and ex vivo corneas demonstrate the hydration sensitivity of the imaging system and reliable measurement of CTWC. We present successful acquisition of noncontact THz images of in vivo human cornea, and discuss strategies for optimizing the imaging system design for clinical use.

Multidisciplinary team publishes the first study of terahertz imaging based assessment of tissue flap viability

http://www.bioeng.ucla.edu/multidisciplinary-team-publishes-the-first-study-of-terahertz-imaging-based-assessment-of-tissue-flap-viability/

An interdisciplinary collaboration between the UCLA school of engineering and the UCLA school of medicine has produced the first published work describing the assessment of tissue flap viability using terahertz (THz) imaging. The research was led by Professor Taylor and postdoctoral scholar Neha Bajwa in the department of Bioengineering and Professor Maie St. John in the department of Head and Neck Surgery.

Tissue flaps have become a life-saving reconstructive option for patients with breast cancer, head and neck cancer, soft tissue defects, and wounds. A flap includes the harvested skin, muscle, soft tissue or bone, and their corresponding neurovascular supply. This tissue is either surgically resected and rotated or transferred from a donor site to a recipient site. In any flap surgery, the key for flap survival is to maintain or successfully reestablish the blood supply to the flap. Despite the high success rates of flap surgery, a small risk of vascular compromise can lead to devastating consequences and, therefore, necessitates urgent re-exploration for attempted salvage. Early and accurate assessment of flap viability – the most significant predictor of flap salvage outcome – is still an unmet clinical need.

The current gold standard for determining flap viability is clinical examination, in which skin color, capillary refill, turgor, and bleeding patterns are periodically examined. This method, however, is highly operator-dependent, and changes in the appearance of the flap due to microvascular complications are generally delayed by 1 to 2 hours, thus preventing early intervention. Efforts towards achieving more non-invasive and accurate tissue viability measurements have been widespread and include the use of several adjunctive optical technologies such as Laser Doppler Imaging (LDI) and fluorescence angiography. Adoption of these systems in surgical flap assessment have been hampered by a range of clinical constraints.  In the case of LDI, the buildup of significant tissue edema (tissue water content (TWC)) immediately following tissue transplantation prevents the early stage acquisition of data needed to predict flap viability.

In this work, the group investigated the utility of tissue water content (TWC) based contrast in terahertz (THz) imaging for early assessment of flap viability. We obtained longitudinal visible and reflective THz imagery comparing 3 bipedicled flaps (i.e. survival model) and 3 fully excised flaps (i.e. failure model) in the dorsal skin of rats over a postoperative period of 7 days. While visual differences between both models manifested 48 hr after surgery, statistically significant (p < 0.05, independent t-test) local differences in TWC contrast were evident in THz flap image sets as early as 24 hr. Excised flaps, histologically confirmed as necrotic, demonstrated a significant, yet localized, reduction in TWC in the flap region compared to non-traumatized skin. In contrast, bipedicled flaps, histologically verified as viable, displayed mostly uniform, unperturbed TWC across the flap tissue. These results indicate the practical potential of THz TWC sensing to accurately predict flap failure 24 hours earlier than clinical examination

This work was funded by grants from the NIH.

Abstract-Non-invasive terahertz imaging of tissue water content for flap viability assessment

Non-invasive terahertz imaging of tissue water content for flap viability assessment 

Neha Bajwa, Joshua Au, Reza Jarrahy, Shijun Sung, Michael C. Fishbein, David Riopelle, Daniel B. Ennis, Tara Aghaloo, Maie A. St. John, Warren S. Grundfest, and Zachary D. Taylor
https://www.osapublishing.org/boe/abstract.cfm?uri=boe-8-1-460

Accurate and early prediction of tissue viability is the most significant determinant of tissue flap survival in reconstructive surgery. Perturbation in tissue water content (TWC) is a generic component of the tissue response to such surgeries, and, therefore, may be an important diagnostic target for assessing the extent of flap viability in vivo. We have previously shown that reflective terahertz (THz) imaging, a non-ionizing technique, can generate spatially resolved maps of TWC in superficial soft tissues, such as cornea and wounds, on the order of minutes. Herein, we report the first in vivo pilot study to investigate the utility of reflective THz TWC imaging for early assessment of skin flap viability. We obtained longitudinal visible and reflective THz imagery comparing 3 bipedicled flaps (i.e. survival model) and 3 fully excised flaps (i.e. failure model) in the dorsal skin of rats over a postoperative period of 7 days. While visual differences between both models manifested 48 hr after surgery, statistically significant (p < 0.05, independent t-test) local differences in TWC contrast were evident in THz flap image sets as early as 24 hr. Excised flaps, histologically confirmed as necrotic, demonstrated a significant, yet localized, reduction in TWC in the flap region compared to non-traumatized skin. In contrast, bipedicled flaps, histologically verified as viable, displayed mostly uniform, unperturbed TWC across the flap tissue. These results indicate the practical potential of THz TWC sensing to accurately predict flap failure 24 hours earlier than clinical examination.

© 2016 Optical Society of America

Abstract-THz polarization difference imaging of aqueous targets

Shijun Sung; Neha Bajwa; Lucia Ramirez; Warren Grundfest; Zachary Taylor

http://spie.org/Publications/Proceedings/Paper/10.1117/12.2189318

This paper describes the basic design, implementation, and testing of a polarization difference imaging system for use on aqueous targets. The ultimate performance limitation of THz imaging in many active areas of research is clutter from surface geometry. While the signal to nose ratio (SNR) of standard THz imaging systems is quite large, the signal to clutter ratio (SCR) often faced in an imaging application is orders of magnitude lower and, in many cases, lower than the contrast to noise (CNR) resulting in imagery where the contrast mechanism of interest does not significantly contribute to the overall observed contrast. To overcome these limitations we develop a system that uses a circularly polarized source and linearly polarized detectors to acquire images of transverse electric (TE) and transverse magnetic (TM) reflectivities of the target over the same field of view. Geletin based tissue mimicking phantoms are fabricated with spatially varying water content and modified with a range of surface topologies and surface roughness. TE and TM images are combined to yield self-calibrated clutter-suppressed images. The resulting image indicates that the imaging field clutter affected both polarization channels nearly equally allowing the system to resolve differences in phantom water content. This design is a step toward windowless THz imaging capability critical for clinical translation where patient imaging is dominated by clutter.

Abstract-Exploration of the effects of burn parameters on THz wound imaging

Neha Bajwa; Shijun Sung; Michael Fishbein; Warren S. Grundfest; Zachary D. Taylor

http://spie.org/Publications/Proceedings/Paper/10.1117/12.2189295

The high contrast resolution afforded by terahertz (1 THz = 1012 Hz) imaging of physiologic tissue continues to drive explorations into the utility of THz technology for burn wound detection. Although we have previously reported the use of a novel, reflective THz imaging technology to sense spatiotemporal differences in reflectivity between partial and full thickness burn wounds, no evidence exists of a one-to-one correlation between structural damage observed in histological assessments of burn severity and THz signal. For example, varying burn induction methods may all result in a common burn wound severity, however, burn features observed in parallel THz imagery may not be identical. Successful clinical translation of THz technology as a comprehensive burn guidance tool, therefore, necessitates an understanding of THz signal and its relation to wound pathophysiology. In this work, longitudinal THz imagery was acquired with a quartz (n = 2.1, 500 μm) window of cutaneous wounds induced with the same brand geometry and contact pressure but varying contact times (5, 7, and 10 seconds) in in vivo, pre-clinical rat models (n=3) over a period of 3 days. Though all burn wounds were evaluated to be deep partial thickness with histology, THz contrasts observed for each burn contact time were intrinsically unique. This is the first preliminary in vivo evidence of a many-to-one relationship between changes in THz contrast and burn severity as ascertained by histology. Future large-scale studies are required to assess whether these observed changes in THz contrast may be interpreted as physiological changes occurring over time, morphometric changes related to anatomical change, or electromagnetic changes between dielectric substrate windows and the underlying tissue.