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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.

The ability to reversibly and non-invasively modulate region-specific brain activity in vivo suggests Low Intensity Focused Ultrasound (LIFU) as potential therapeutics for neurological dysfunctions such as epilepsy and Parkinson’s disease. While in vivo studies provide evidence of the bioeffects of LIFU on neuronal activity, they merely hint at potential mechanisms but do not fully explain how this technology achieves these effects. One potential hypothesis is that LIFU produces local membrane depolarization by mechanically perturbing the neuronal cell membrane, or activating channels or other proteins embedded in the membrane. Proteins that sense mechanical perturbations of the membrane, such as those gated by membrane tension, are prime candidates for activating in response to LIFU and thus leading to the neurological responses that have been measured. Here we use the bacterial mechanosensitive channel MscL, which has been purified and reconstituted in liposomes, to determine how LIFU may affect the activation of this membrane-tension gated channel. Two bacterial voltage-gated channels, KvAP and NaK2K F92A channels were also studied. Surprisingly, the results suggest that ultrasound modulation and membrane perturbation does not induce channel gating, but rather induces pore formation at the membrane protein-lipid interface. However, in vesicles with high MscL mechanosensitive channel concentrations, apparent decreases in pore formation are observed, suggesting that this membrane-tension-sensitive protein may serve to increase the elasticity of the membrane, presumably because of expansion of the channel in the plane of the membrane independent of channel gating.

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 non-contact THz images of in vivo human cornea, and discuss strategies for optimizing the imaging system design for clinical use.

Reflection-mode 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 dielectric windows used to flatten the imaging field. Herein, we present an optical design for noncontact THz imaging of cornea. A beam-scanning methodology performs angular normal incidence sweeps of a focused beam over the corneal surface while keeping the source, detector, and patient stationary. A quasi-optical analysis method is developed to analyze the theoretical resolution and imaging field intensity profile. These results are compared to the electric field distribution computed with a physical optics analysis code. Imaging experiments validate the optical theories behind the design and suggest that quasi-optical methods are sufficient for designing of THz corneal imaging systems. Successful imaging operations support the feasibility of noncontact in vivo imaging. We believe that this optical system design will enable the first, clinically relevant, in vivo exploration of CTWC using THz technology.

Introduction Persistent bacterial infection prolongs hospitalizations, leading to increased healthcare costs. Treatment of these infections costs several billion dollars annually. Biofilm production is one mechanism by which bacteria become resistant. With the help of biofilms, bacteria withstand the host immune response and are much less susceptible to antibiotics. Currently, there is interest in the use of laser-generated shockwaves (LGS) to delaminate biofilm from infected wound surfaces; however, the safety of such an approach has not yet been established. Of particular concern are the thermal and mechanical effects of the shockwave treatment on the epidermis and the underlying collagen structure of the dermis. The present study is a preliminary investigation of the effect of LGS on freshly harvested ex vivo porcine skin tissue samples. Materials and Methods Tissue samples for investigation were harvested immediately post-mortem and treated with LGS within 30 minutes. Previous studies have shown that laser fluences between 100 and 500 mJ/pulse are capable of delaminating biofilms off a variety of surfaces, thus our preliminary investigation focused on this range of laser energy. For each sample, LGS were produced via laser irradiation of a thin layer (0.5 µm) of titanium sandwiched between a 50 and 100 µm thick layer of water glass and a 0.1 mm thick sheet of Mylar. The rapid thermal expansion of the irradiated titanium film generates a transient compressive wave that is coupled through a liquid layer to the surface of the ex vivo pigskin sample. Shocked samples were immediately fixed in formalin and prepared for histological analysis. A blinded pathologist evaluated and scored each section on the basis of its overall appearance (O) and presence of linear/slit-like spaces roughly parallel to the surface of the skin (S). The scores were given on a scale of 0–3. Results The present investigation revealed no visible difference between the tissue sections of the control sample and those that were subjected to laser-generated shockwaves. There was no relationship between the scores received by the samples and the energy with which they were shocked. Conclusion Preliminary investigation into the safety of the LGS treatment for biofilm delamination appears promising. Additional investigation will continue on ex vivo porcine samples, followed by an in vivo animal trial to better understand the physiological response to LGS treatment. Lasers Surg. Med. 46:620–627, 2014. © 2014 Wiley Periodicals, Inc.

Whole-body stiffness in fishes has important consequences for swimming mode, speed and efficiency, but the contribution of vertebral column stiffness to whole-body stiffness is unclear. In our opinion, this lack of clarity is due in part to the lack of studies that have measured both in vitro mechanical properties of the vertebral column as well as in vivo vertebral kinematics in the same species. Some lack of clarity may also come from real variation in the mechanical role of the vertebral column across species. Previous studies, based on either mechanics or kinematics alone, suggest species-specific variation in vertebral column locomotor function that ranges from highly stiff regimes that contribute greatly to whole-body stiffness, and potentially act as a spring, to highly compliant regimes that only prohibit excessive flexion of the intervertebral joints. We review data collected in combined investigations of both mechanics and kinematics of three species, Myxine glutinosa, Acipenser transmontanus, and Morone saxatilis, to illustrate how mechanical testing within the context of the in vivo kinematics more clearly distinguishes the role of the vertebral column in each species. In addition, we identify species for which kinematic data are available, but mechanical data are lacking. We encourage further investigation of these species to fill these mechanical data gaps. Finally, we hope these future combined analyses will identify certain morphological, mechanical, or kinematic parameters that might be associated with certain vertebral column functional regimes with respect to body stiffness.

The northern spearnose poacher, Agonopsis vulsa, is a benthic, heavily armored fish that swims primarily using pectoral fins. High-speed kinematics, whole-body lift measurements, and flow visualization were used to study how A. vulsa overcomes substantial negative buoyancy while generating forward thrust. Kinematics for five freely swimming poachers indicate that individuals tend to swim near the bottom (within 1cm) with a consistently small (less than 1 degrees ) pitch angle of the body. When the poachers swam more than 1cm above the bottom, however, body pitch angles were higher and varied inversely with speed, suggesting that lift may help overcome negative buoyancy. To determine the contribution of the body to total lift, fins were removed from euthanized fish (n=3) and the lift and drag from the body were measured in a flume. Lift and drag were found to increase with increasing flow velocity and angle of attack (ANCOVA, p0.0001 for both effects). Lift force from the body was found to supply approximately half of the force necessary to overcome negative buoyancy when the fish were swimming more than 1cm above the bottom. Lastly, flow visualization experiments were performed to examine the mechanism of lift generation for near-bottom swimming. A vortex in the wake of the pectoral fins was observed to interact strongly with the substratum when the animals approached the bottom. These flow patterns suggest that, when swimming within 1cm of the bottom, poachers may use hydrodynamic ground effect to augment lift, thereby counteracting negative buoyancy.

SUMMARYMantis shrimp (Stomatopoda) generate extremely rapid and forceful predatory strikes through a suite of structural modifications of their raptorial appendages. Here we examine the key morphological and kinematic components of the raptorial strike that amplify the power output of the underlying muscle contractions. Morphological analyses of joint mechanics are integrated with CT scans of mineralization patterns and kinematic analyses toward the goal of understanding the mechanical basis of linkage dynamics and strike performance. We test whether a four-bar linkage mechanism amplifies rotation in this system and find that the rotational amplification is approximately two times the input rotation, thereby amplifying the velocity and acceleration of the strike. The four-bar model is generally supported, although the observed kinematic transmission is lower than predicted by the four-bar model. The results of the morphological, kinematic and mechanical analyses suggest a multi-faceted mechanical system that integrates latches, linkages and lever arms and is powered by multiple sites of cuticular energy storage. Through reorganization of joint architecture and asymmetric distribution of mineralized cuticle, the mantis shrimp's raptorial appendage offers a remarkable example of how structural and mechanical modifications can yield power amplification sufficient to produce speeds and forces at the outer known limits of biological systems.

IntroductionThe aims of this study were to evaluate (1) grasping forces with the application of a tactile feedback system in vivo and (2) the incidence of tissue damage incurred during robotic tissue manipulation. Robotic-assisted minimally invasive surgery has been shown to be beneficial in a variety of surgical specialties, particularly radical prostatectomy. This innovative surgical tool offers advantages over traditional laparoscopic techniques, such as improved wrist-like maneuverability, stereoscopic video displays, and scaling of surgical gestures to increase precision. A widely cited disadvantage associated with robotic systems is the absence of tactile feedback.Methods and procedureNineteen subjects were categorized into two groups: 5 experts (six or more robotic cases) and 14 novices (five cases or less). The subjects used the da Vinci with integrated tactile feedback to run porcine bowel in the following conditions: (T1: deactivated tactile feedback; T2: activated tactile feedback; and T3: deactivated tactile feedback). The grasping force, incidence of tissue damage, and the correlation of grasping force and tissue damage were analyzed. Tissue damage was evaluated both grossly and histologically by a pathologist blinded to the sample.ResultsTactile feedback resulted in significantly decreased grasping forces for both experts and novices (P0.05 in all subjects).ConclusionThe in vivo application of integrated tactile feedback in the robotic system demonstrates significantly reduced grasping forces, resulting in significantly less tissue damage. This tactile feedback system may improve surgical outcomes and broaden the use of robotic-assisted minimally invasive surgery.

A pulsed terahertz (THz) imaging system and millimeter-wave reflectometer were used to acquire images and point measurements, respectively, of five rabbit cornea in vivo. These imaging results are the first ever produced of in vivo cornea. A modified version of a standard protocol using a gentle stream of air and a Mylar window was employed to slightly dehydrate healthy cornea. The sensor data and companion central corneal thickness (CCT) measurements were acquired every 10–15 min over the course of two hours using ultrasound pachymmetry.. Statistically significant positive correlations were established between CCT measurements and millimeter wave reflectivity. Local shifts in reflectivity contrast were observed in the THz imagery; however, the THz reflectivity did not display a significant correlation with thickness in the region probed by the 100 GHz and CCT measurements. This is explained in part by a thickness sensitivity at least 10 $\times$ higher in the mm-wave than the THz systems. Stratified media and effective media modeling suggest that the protocol perturbed the thickness and not the corneal tissue water content (CTWC). To further explore possible etalon effects, an additional rabbit was euthanized and millimeter wave measurements were obtained during death induced edema. These observations represent the first time that the uncoupled sensing of CTWC and CCT have been achieved in vivo.

© 2015 IEEE. Terahertz (THz) spectral properties of human cornea are explored as a function of central corneal thickness (CCT) and corneal water content, and the clinical utility of THz-based corneal water content sensing is discussed. Three candidate corneal tissue water content (CTWC) perturbations, based on corneal physiology, are investigated that affect the axial water distribution and total thickness. The THz frequency reflectivity properties of the three CTWC perturbations were simulated and explored with varying system center frequency and bandwidths (Q-factors ). The modeling showed that at effective optical path lengths on the order of a wavelength the cornea presents a lossy etalon bordered by air at the anterior and the aqueous humor at the posterior. The simulated standing wave peak-to-valley ratio is pronounced at lower frequencies and its effect on acquired data can be modulated by adjusting the bandwidth of the sensing system. These observations are supported with experimental spectroscopic data. The results suggest that a priori knowledge of corneal thickness can be utilized for accurate assessments of corneal tissue water content. The physiologic variation of corneal thickness with respect to the wavelengths spanned by the THz band is extremely limited compared to all other structures in the body making CTWC sensing unique amongst all proposed applications of THz medical imaging.

Bacteria biofilms in chronically infected wounds significantly increase the burden of healthcare costs and resources for patients and clinics. Because biofilms are such an effective barrier to standard antibiotic treatment, new methods of therapy need to be developed to combat these infections. Our group has demonstrated the potential of using Laser Generated Shockwaves as a potential therapy to mechanically disrupt the bacterial biofilms covering the wound. Previous studies have used rigid silica glass as the shockwave propagation medium, which is not compatible with the intended clinical application. This paper describes the exploration of five candidate flexible plastic films to replace the glass substrate. Each material measured 0.254 mm thick and was used to generate shockwaves of varying intensities. Shockwave characterization was performed using a high-speed Michelson displacement interferometer and peak stress values obtained in the flexible substrates were compared to glass using one-way nested Analysis of Variance and Tukey HSD post-hoc analysis. Results demonstrate statistically significant differences between substrate material and indicate that polycarbonate achieves the highest peak stress for a given laser fluence suggesting that it is optimal for clinical applications.

THz imaging system design will play an important role making possible imaging of targets with arbitrary properties and geometries. This study discusses design consideration and imaging performance optimization techniques in THz quasioptical imaging system optics. Analysis of field and polarization distortion by off-axis parabolic (OAP) mirrors in THz imaging optics shows how distortions are carried in a series of mirrors while guiding the THz beam. While distortions of the beam profile by individual mirrors are not significant, these effects are compounded by a series of mirrors in antisymmetric orientation. It is shown that symmetric orientation of the OAP mirror effectively cancels this distortion to recover the original beam profile. Additionally, symmetric orientation can correct for some geometrical off-focusing due to misalignment. We also demonstrate an alternative method to test for overall system optics alignment by investigating the imaging performance of the tilted target plane. Asymmetric signal profile as a function of the target plane’s tilt angle indicates when one or more imaging components are misaligned, giving a preferred tilt direction. Such analysis can offer additional insight into often elusive source device misalignment at an integrated system. Imaging plane tilting characteristics are representative of a 3-D modulation transfer function of the imaging system. A symmetric tilted plane is preferred to optimize imaging performance.

Terahertz (THz) detection has been proposed and applied to a variety of medical imaging applications in view of its unrivaled hydration profiling capabilities. Variations in tissue dielectric function have been demonstrated at THz frequencies to generate high contrast imagery of tissue, however, the source of image contrast remains to be verified using a modality with a comparable sensing scheme. To investigate the primary contrast mechanism, a pilot comparison study was performed in a burn wound rat model, widely known to create detectable gradients in tissue hydration through both injured and surrounding tissue. Parallel T2 weighted multi slice multi echo (T2w MSME) 7T Magnetic Resonance (MR) scans and THz surface reflectance maps were acquired of a full thickness skin burn in a rat model over a 5 hour time period. A comparison of uninjured and injured regions in the full thickness burn demonstrates a 3-fold increase in average T2 relaxation times and a 15% increase in average THz reflectivity, respectively. These results support the sensitivity and specificity of MRI for measuring in vivo burn tissue water content and the use of this modality to verify and understand the hydration sensing capabilities of THz imaging for acute assessments of the onset and evolution of diseases that affect the skin. A starting point for more sophisticated in vivo studies, this preliminary analysis may be used in the future to explore how and to what extent the release of unbound water affects imaging contrast in THz burn sensing.

There is continuing interest in targeted transcranial stimulation of deep brain structures using techniques such as low intensity focused ultrasound (LIFU). Accurate transcranial targeting and dosage of acoustic energy onto target neural structure requires quantification of the acoustic effect the skull has on the ultrasound wave. The objective of this work is to assess the effect of transcranial passage, both in terms of attenuation and orientation of an incident acoustic wave, in the gyrencephalic Gottingen minipig. Precision measurements of the acoustic transit of the stereotactically addressed intact-skulls resulted in a consistently measured acoustic loss of about 8.5 dB from the skull transition, corresponding to an intensity transmission coefficient of 0.1298 ± 0.00990. Negligible spatial shift in the acoustic focus was observed. These results indicate that the Gottingen minipig may be suitable for studies of targeted transcranial neuromodulation due to the predictable acoustic transmission measured from the intact skull.

Peripheral neuropathy (PN) is a significant public health concern, resulting in abnormal gait biomechanics, diminished postural stability, and increased risk of falls. A wearable tactile feedback system previously developed for sensory augmentation of prosthetic limbs has been adapted for individuals with PN and evaluated in a pilot group of 4 participants with idiopathic bilateral PN, as well as one with Charcot-Marie-Tooth Disease. Participants were assessed both for their abilities to perceive tactile stimuli, and for the effect of tactile biofeedback on their gait. Preliminary data indicate that most participants could localize tactile stimuli and make meaningful modifications to their gait in real time, but that the effect of feedback on gait was highly variable from subject to subject, demanding further investigation.

This paper presents novel a first pass on the thorough analysis of THz optical designs intended for image acquisition of burn wounds in animal models. Current THz medical imaging research typically employs and fixed source detector architecture coupled by a train of off-axis parabolic mirrors. When used individually, parabolic mirrors have near diffraction limited focusing properties, extremely low loss, and are dispersion free. However, when a combination or train of multiple parabolic mirrors are utilized geometric errors can be generated early in the train and exacerbated as the beam propagates to the detector. These errors manifest as significant increases in spot size, asymmetries about the optical axis in beam irradiance and polarization, and the generation of cross polarization components. This work presents a novel configuration of off-axis parabolic mirrors designed to maximize the practicality of beam alignment and image acquisition. Quasi-physical optics simulations of the optical performance are described and significant perturbations in polarization symmetry were observed. The configuration can be described as in between two canonical parabolic mirror configurations. The performance of three different pairs of off-axis parabolic mirror pairs coupled to the novel configuration are presented herein.

Peripheral neuropathy (PN) is a significant public health concern, giving rise to abnormal gait biomechanics, diminished postural stability, and increased risk of falls. A wearable tactile feedback system previously developed for sensory augmentation of prosthetic limbs has been adapted for individuals with PN and evaluated in a pilot group of four subjects with idiopathic bilateral PN. Subjects were assessed both for their abilities to perceive and distinguish tactile stimuli, and for the effect of tactile biofeedback on gait, using optical motion capture and embedded force plate technology. Preliminary data indicate that participants could adequately perceive and localize tactile stimuli, as well as make meaningful modifications to their gait in real time, with minimal training. Observed gait modifications with feedback active included increases in walking speed, step cadence, step length, and peak joint powers. However, the variability of biofeedback's effect on gait from subject to subject demands further investigation with the peripheral neuropathy patient population.

Variations in water volume fraction have been investigated as a possible source of contrast in several reflective THz medical imaging applications including corneal hydration sensing and burn wound severity diagnosis. Due to surface roughness and non-planar geometry most reflective systems employ low loss windows such as quartz or sapphire to minimize the effects of the specimen's topology. This creates a multilayer system consisting of the dielectric substrate window between the tissue medium and free space. Multilayer systems have interference effects due to internal reflections that vary periodically with frequency. To investigate the effects of interference on THz hydration sensing, we implemented an electromagnetic model that computes sensitivity metrics given a window index, window thickness, and incidence angle.

A novel reflective THz imaging objective mirror design is presented and characterized that can switch between pairs of numerical aperture and focal length while maintaining a fixed back focal distance (BFD). This allows the user to easily explore the effect of varying spot size, depth of field and working distance paremter during medical imaging studies without the need for optical realignment. The objective assembly design employs conjugate pairs of off axis parabolic (OAP) mirrors that accept and output parallel, collimated beams. Three pairs of effective focal length (EFL) mirrors were evaluated using a pulsed THz imaging system operating at an effective center frequency of 525 GHz with 125 GHz of 3 dB bandwidth. For the 25.4 mm 50.8 mm, and 76.2 mm EFL mirror pairs, the objective mirror design achieves a 10%–90% edge response measurements of 0.6 mm, 1.3 mm, and 2.1 mm and depth of field of 0.86 mm, 4.0 mm, and 11.7 mm, respectively. Investigation of the propagation of Gaussian THz beam profile from the photoconductive source, through the objective, and to the detector are presented. The knife-edge measurements agree with the predicted focused illumination spot size at the target and the predicted power at the detector focal plane, suggesting the entirety of focused THz beam profiles are effectively captured at the detector plane. Furthermore simulations show that the beam spot walks away from the detector aperture in the detection plane as the target plane is moved in and out of the system focal plane. This suggests that the system is operating in a regime that resembles confocal optical setup. Additionally, the off-axis distortion of field energy distribution and introduction of cross-polarization components is analyzed and the differences to optimal configurations analyzed. We conclude that the deviation of our systems optical setup from the optimal “ortho” conjugate configuration results in minimal degradation in optical performance. This suggests that OAP mirror setups can be designed to maximize practicality with marginal reductions in performance.

THz medical imaging has made significant advances in the years since the first results were published in the late 1990s. The field has benefited significantly from advances in source/detector technology, room temperature component operation, and extensive spectroscopic studies of the THz properties of tissue. Additionally, clinical translation of THz medical imaging technology has been aided by the establishment of the National Institute of Biomedical Imaging and Bioengineering (NIBIB) in December of 2000. This institute has shown interest in THz medical technology and been the funding source for a large portion of NIH sponsored THz projects.

Research in THz imaging is generally focused on three primary application areas: medical, security, and nondestructive evaluation (NDE). While work in THz security imaging and personnel screening is populated by a number of different active and passive system architectures, research in medical imaging in is generally performed with THz time-domain systems. These systems typically employ photoconductive or electro-optic source/detector pairs and can acquire depth resolved data or spectrally resolved pixels by synchronously sampling the electric field of the transmitted/reflected waveform. While time-domain is a very powerful scientific technique, results reported in the literature suggest that desired THz contrast in medical imaging may not require the volume of data accessible from time-resolved measurements and that a simpler direct detection, active technique may be sufficient for specific applications. In this talk we discuss an active direct detection reflectometer system architecture operating at a center frequency of ~ 525 GHz that uses a photoconductive source and schottky diode detector. This design takes advantage or radar-like pulse rectification and novel reflective optical design to achieve high target imaging contrast with significant potential for high speed acquisition time. Results in spatially resolved hydration mapping of burn wounds are presented and future outlooks discussed.

Terahertz (THz) hydration sensing continues to gain traction in the medical imaging community due to its unparalleled sensitivity to tissue water content. Rapid and accurate detection of fluid shifts following induction of thermal skin burns as well as remote corneal hydration sensing have been previously demonstrated in vivo using reflective, pulsed THz imaging. The hydration contrast sensing capabilities of this technology were recently confirmed in a parallel 7 Tesla Magnetic Resonance (MR) imaging study, in which burn areas are associated with increases in local mobile water content. Successful clinical translation of THz sensing, however, still requires quantitative assessments of system performance measurements, specifically hydration concentration sensitivity, with tissue substitutes. This research aims to calibrate the sensitivity of a novel, reflective THz system to tissue water content through the use of hydration phantoms for quantitative comparisons of THz hydration imagery.Gelatin phantoms were identified as an appropriate tissue-mimicking model for reflective THz applications, and gel composition, comprising mixtures of water and protein, was varied between 83% to 95% hydration, a physiologically relevant range. A comparison of four series of gelatin phantom studies demonstrated a positive linear relationship between THz reflectivity and water concentration, with statistically significant hydration sensitivities (p < .01) ranging between 0.0209 - 0.038% (reflectivity: %hydration). The THz-phantom interaction is simulated with a three-layer model using the Transfer Matrix Method with agreement in hydration trends. Having demonstrated the ability to accurately and noninvasively measure water content in tissue equivalent targets with high sensitivity, reflective THz imaging is explored as a potential tool for early detection and intervention of corneal pathologies.

Applications for terahertz (THz) medical imaging have proliferated over the past few years due to advancements in source/detector technology and vigorous application development. While considerable effort has been applied to improving source output power and detector sensitivity, significantly less work has been devoted to improving image acquisition method and time. The majority of THz medical imaging systems in the literature typically acquire pixels by translating the target of interest beneath a fixed illumination beam. While this single-pixel whiskbroom methodology is appropriate for in vitro models, it is unsuitable for in vivo large animal and patient imaging due to practical constraints. This paper presents a scanned beam imaging system based on prior work that enables for reduced image acquisition time while allowing the source, target and detector to remain stationary. The system employs a spinning polygonal mirror and a set of high-density polyethylene (HDPE) objective lenses, and operates at a center illumination frequency of 525GHz with ~125GHz of 3dB bandwidth. The system achieves a focused beam diameter of 1.66mm and a large depth of field of

Terahertz (THz) imaging is an expanding area of research in the field of medical imaging due to its high sensitivity to changes in tissue water content. Previously reported in vivo rat studies demonstrate that spatially resolved hydration mapping with THz illumination can be used to rapidly and accurately detect fluid shifts following induction of burns and provide highly resolved spatial and temporal characterization of edematous tissue. THz imagery of partial and full thickness burn wounds acquired by our group correlate well with burn severity and suggest that hydration gradients are responsible for the observed contrast. This research aims to confirm the dominant contrast mechanism of THz burn imaging using a clinically accepted diagnostic method that relies on tissue water content for contrast generation to support the translation of this technology to clinical application. The hydration contrast sensing capabilities of magnetic resonance imaging (MRI), specifically T2 relaxation times and proton density values N(H), are well established and provide measures of mobile water content, lending MRI as a suitable method to validate hydration states of skin burns. This paper presents correlational studies performed with MR imaging of ex vivo porcine skin that confirm tissue hydration as the principal sensing mechanism in THz burn imaging. Insights from this preliminary research will be used to lay the groundwork for future, parallel MRI and THz imaging of in vivo rat models to further substantiate the clinical efficacy of reflective THz imaging in burn wound care.

Unlike mammalian, disc-shaped intervertebral joints (IVJs), the IVJs in fishes are biconid structures, filled with fluid and thought to act as hydrostatic hinge joints during swimming. However, it remains unclear which IVJ structures are dominant in mechanical resistance to forces in fishes, and whether variation in these tissues might impact the function of the vertebral column along its length. Here, we measured the dynamic mechanical behaviour of IVJs from striped bass,Morone saxatilis. During lateral bending, angular stiffness was significantly lower in the caudal and cervical regions, relative to the abdominal region. The neutral zone, defined as the range of motion (ROM) at bending moments less than 0.001 Nm, was longer in the caudal relative to the abdominal IVJs. Hysteresis was 30–40% in all regions, suggesting that IVJs may play a role in energy dissipation during swimming. Cutting the vertical septum had no statistically significant effect, but cutting the encapsulating tissues caused a sharp decline in angular stiffness and a substantial increase in ROM and hysteresis. We conclude that stiffness decreases and ROM increases from cranial to caudal in striped bass, and that the encapsulating tissues play a prominent role in mechanical variation along the length of the vertebral column.

The vertebral column of fishes has traditionally been divided into just two distinct regions, abdominal and caudal. Recently, however, developmental, morphological, and mechanical investigations have brought this traditional regionalization scheme into question. Alternative regionalization schema advocate the division of the abdominal vertebrae into cervical, abdominal, and in some cases, transitional regions. Here, we investigate regional variation at the level of the vertebrae and intervertebral joint (IVJ) tissues in the striped bass, Morone saxatilis. We use gross dissection, histology, and polarized light imaging to quantify vertebral height, width, length, IVJ length, IVJ tissue volume and cross-sectional area, and vertical septum fiber populations, and angles of insertion. Our results reveal regional differences between the first four (most rostral) abdominal vertebrae and IVJs and the next six abdominal vertebrae and IVJs, supporting the recognition of a distinct cervical region. We found significant variation in vertebral length, width, and height from cranial to caudal. In addition, we see a significant decline in the volume of notochordal cells and the cross-sectional area of the fibrous sheath from cranial to caudal. Further, polarized light imaging revealed four distinct fiber populations within the vertical septum in the cervical and abdominal regions in contrast with just one fiber population found in the caudal region. Measurement of the insertion angles of these fiber populations revealed significant differences between the cervical and abdominal regions. Differences in vertebral, IVJ, and vertical septum morphology all predict greater range of motion and decreased stiffness in the caudal region of the fish compared with the cervical and abdominal regions.

Low Intensity Focused Ultrasound (LIFU) continues to gain traction in the field of non-invasive neuromodulation. Recent in vivo rat studies suggest that LIFU can be used to modulate region-specific brain activity in the motor cortex, leading investigators to conclude that LIFU may be a better alternative to more prominent, and more invasive, mechanisms of neuromodulation for conditions such as Parkinson’s disease, Epilepsy, and applications such as drug delivery applications. Despite these recent successes, a comprehensive understanding of beam patterns within the skull remains elusive.