Terahertz (THz) sensing has shown potential as a novel imaging modality in medical applications due to
its high water sensitivity. The design of medical THz sensing systems and their successful application to
<i>in vivo</i> settings has attracted recent interest to the field, and highlighted the need for improved
understanding of the interaction of THz waves with biological tissues. This paper explores the modeling
of composite materials which combine strongly-interacting water with weakly-interacting species such as
those that are common to biological tissues. The Bruggeman, Maxwell-Garnett, and power law effective
media models are introduced and discussed. A reflection-mode 100 GHz Gunn diode sensing system was
used to measure the reflectivity of solutions of water and dioxane as a function of relative concentration,
and the results were compared with the predictions of the Maxwell-Garnett, power law, and Bruggeman
mixing theories. The Maxwell-Garnett model fit poorly to experimental data on near-equal mixtures of
water and dioxane and improved when the concentration of water exceeded ~55% or was below ~15%.
The first-order power law model fit poorly to experimental data across the entire range except at nearpure
solutions. Power law models employing 1/2 and 1/3 terms improved goodness of fit, but did not
match the accuracy of the Bruggeman model. The Bruggeman provided the best fit to experimental data
model as compared to Maxwell-Garnett and the power models and accurately predicted the solution
reflectivity through the whole range of concentrations. This analysis suggests that the Bruggeman model
may offer improved accuracy over more conventional dielectric mixing models when developing
simulation tools for THz reflectometry of hydrated biological tissues.
Terahertz corneal hydration sensing has shown promise in ophthalmology applications and was recently shown to be capable of detecting water concentration changes of about two parts in a thousand in ex vivo corneal tissues. This technology may be effective in patient monitoring during refractive surgery and for early diagnosis and treatment monitoring in diseases of the cornea. In this work, Fuchs dystrophy, cornea transplant rejection, and keratoconus are discussed, and a hydration sensitivity of about one part in a hundred is predicted to be needed to successfully distinguish between diseased and healthy tissues in these applications. Stratified models of corneal tissue reflectivity are developed and validated using ex vivo spectroscopy of harvested porcine corneas that are hydrated using polyethylene glycol solutions. Simulation of the cornea's depth-dependent hydration profile, from 0.01 to 100 THz, identifies a peak in intrinsic reflectivity contrast for sensing at 100 GHz. A 100 GHz hydration sensing system is evaluated alongside the current standard ultrasound pachymetry technique to measure corneal hydration in vivo in four rabbits. A hydration sensitivity, of three parts per thousand or better, was measured in all four rabbits under study. This work presents the first in vivo demonstration of remote corneal hydration sensing.
A reflective, pulsed terahertz (THz) imaging system was used to acquire high-resolution (d10-90/λ ∼ 1.925) images of deep, partial thickness burns in a live rat. The rat's abdomen was burned with a brass brand heated to ∼ 220°C and pressed against the skin with contact pressure for ∼ 10 sec. The burn injury was imaged beneath a Mylar window every 15 to 30 min for up to 7 h. Initial images display an increase in local water concentration of the burned skin as evidenced by a marked increase in THz reflectivity, and this likely correlates to the post-injury inflammatory response. After ∼ 1 h the area of increased reflectivity consolidated to the region of skin that had direct contact with the brand. Additionally, a low reflecting ring of tissue could be observed surrounding the highly reflective burned tissue. We hypothesize that these regions of increased and decreased reflectivity correlate to the zones of coagulation and stasis that are the classic foundation of burn wound histopathology. While further investigations are necessary to confirm this hypothesis, if true, it likely represents the first in vivo THz images of these pathologic zones and may represent a significant step forward in clinical application of THz technology.
THz medical imaging has been a topic of increased interest recently due largely to improvements in source and detector
technology and the identification of suitable applications. One aspect of THz medical imaging research not often
adequately addressed is pixel acquisition rate and phenomenology. The majority of active THz imaging systems use
translation stages to raster scan a sample beneath a fixed THz beam. While these techniques have produced high
resolution images of characterization targets and animal models they do not scale well to human imaging where
clinicians are unwilling to place patients on large translation stages. This paper presents a scanned beam THz imaging
system that can acquire a 1 cm<sup>2</sup> area with 1 mm<sup>2</sup> pixels and a per-pixel SNR of 40 dB in less than 5 seconds. The system
translates a focused THz beam across a stationary target using a spinning polygonal mirror and HDPE objective lens.
The illumination is centered at 525 GHz with ~ 125 GHz of response normalized bandwidth and the component layout is
designed to optically co-locate the stationary source and detector ensuring normal incidence across a 50 mm × 50 mm
field of view at standoff of 190 mm. Component characterization and images of a test target are presented. These
results are some of the first ever reported for a short standoff, high resolution, scanned beam THz imaging system and
represent an important step forward for practical integration of THz medical imaging where fast image acquisition times
and stationary targets (patients) are requisite.
This work introduces the potential application of terahertz (THz) sensing to the field of ophthalmology, where it is uniquely suited due to its nonionizing photon energy and high sensitivity to water content. Reflective THz imaging and spectrometry data are reported on ex-vivo porcine corneas prepared with uniform water concentrations using polyethylene glycol (PEG) solutions. At 79% water concentration by mass, the measured reflectivity of the cornea was 20.4%, 14.7%, 11.7%, 9.6%, and 7.4% at 0.2, 0.4, 0.6, 0.8, and 1 THz, respectively. Comparison of nine corneas hydrated from 79.1% to 91.5% concentration by mass demonstrated an approximately linear relationship between THz reflectivity and water concentration, with a monotonically decreasing slope as the frequency increases. The THz-corneal tissue interaction is simulated with a Bruggeman model with excellent agreement. THz applications to corneal dystrophy, graft rejection, and refractive surgery are examined from the context of these measurements.
THz and millimeter wave technology have shown the potential to become a valuable
medical imaging tool because of its sensitivity to water and safe, non-ionizing photon
energy. Using the high dielectric constant of water in these frequency bands, reflectionmode
THz sensing systems can be employed to measure water content in a target with
high sensitivity. This phenomenology may lead to the development of clinical systems to
measure the hydration state of biological targets. Such measurements may be useful in
fast and convenient diagnosis of conditions whose symptoms can be characterized by
changes in water concentration such as skin burns, dehydration, or chemical exposure. To
explore millimeter wave sensitivity to hydration, a reflectometry system is constructed to
make water concentration measurements at 100 GHz, and the minimum detectable water
concentration difference is measured. This system employs a 100 GHz Gunn diode
source and Golay cell detector to perform point reflectivity measurements of a wetted
polypropylene towel as it dries on a mass balance. A noise limited, minimum detectable
concentration difference of less than 0.5% by mass can be detected in water
concentrations ranging from 70% to 80%. This sensitivity is sufficient to detect hydration
changes caused by many diseases and pathologies and may be useful in the future as a
diagnostic tool for the assessment of burns and other surface pathologies.
This study describes terahertz (THz) imaging of hydration changes in physiological tissues with high water concentration sensitivity. A fast-scanning, pulsed THz imaging system (centered at 525 GHz; 125 GHz bandwidth) was utilized to acquire a 35 mm x 35 mm field-of-view with 0.5 mm x 0.5 mm pixels in less than two minutes. THz time-lapsed images were taken on three sample systems: (1) a simple binary system of water evaporating from a polypropylene towel, (2) the accumulation of fluid at the site of a sulfuric acid burn on <i>ex vivo</i> porcine skin, and (3) the evaporative dehydration of an ex vivo porcine cornea. The diffusion-regulating behavior of corneal tissue is elucidated, and the correlation of THz reflectivity with tissue hydration is measured using THz spectroscopy on four ex vivo corneas. We conclude that THz imaging can discern small differences in the distribution of water in physiological tissues and is a good candidate for burn and corneal imaging.
This paper presents the fabrication of a conformal, ring-annular ultrasound imaging array. Two-dimensional
(2D) ultrasound scanning is possible with ring-annular array transducers in which a number of piezoelectric
elements are arranged in a circle. The 2D scanning technique can be realized through time delays, potentially
allowing for 3D imaging. Ring-annular array transducers have previously been shown to have increased
bandwidth, better signal-to-noise, and uniform scanning in space in contrast to 2D matrix arrays of an equal
number elements and aperture size. Conformal, ring-annular transducers have the ability to match the curvature
of body surfaces, and have the additional advantage that the flexible array elements can be mechanically focused
to provide enhanced focusing capabilities relative to rigid ring-annular arrays. The process developed for the
fabrication of conformal, ring-annular ultrasound array is presented. A microfabrication approach is used to
produce ring-annular arrays featuring flexible joints with high durability, and capable of scaling in size and
element architectures. The fabrication process yields a ring of piezoelectric transducer elements held together with polyimide, which is the basis of the flexible joints that enable conformal ultrasonography. The described fabrication process is used to produce a ring-annular array with a single ring containing piezoelectric elements, but the process can be extended to form arrays with multiple annular-rings of varying sizes. The transducer had a fundamental thickness-mode resonant frequency of 12 MHz, a 6 dB bandwidth of 23%, and an acoustic pulse width of 1.8 μs in water.
A reflective terahertz (THz) system has been under development for imaging and monitoring of skin hydration, and
through consideration of attenuation, scattering, spatial resolution and measurement of sensitivity, the frequency band
0.4 - 0.7 THz has been determined optimal for operation. THz, typically defined as the frequency range between 0.1-10
THz, has been proposed for skin hydration imaging and monitoring primarily due to being non-ionizing radiation and
highly sensitivity to water concentrations. While it is important to maximize measurement sensitivity to changes in water
concentration, the optimal operational frequency band must simultaneously minimize the scattering from the targets (i.e.
skin) and attenuation, as well as maximize the spatial resolution. In terms of atmospheric attenuation, from 0.4 to 1 THz,
there are broad absorption lines at 556 GHz and 750 GHz, and large transmission windows centered at 500, 650, and 870
GHz. Scattering of the energy reflected from skin was show, using modeling, that as the frequency increased there was a
considerable decrease in the power fraction reflected in the specular direction. For measurement sensitivity, it was
shown that a change in reflectivity per change in water volume at 100 GHz was nearly an order of magnitude higher at 1
THz. Finally, as should be expected, higher frequencies were better for spatial resolution. In consideration of the above
criteria, the motivation for using the 0.4-0.7 THz band will be presented as well as an overview the developed THz pulse
reflective imaging system for imaging of skin hydration.
Due to their increased angular coverage around body surfaces, conformal ultrasound transducers may potentially provide
increased signal acquisition relative to rigid medical ultrasound probes and eliminate the need for mechanical scanning.
This paper describes a novel, high efficiency, and robust conformal ultrasound transducer array based on a flexible
substrate of silicon islands joined together using polyimide joints. The array incorporated diced bulk lead zirconate
titanate (PZT) mounted atop the silicon islands as its piezoelectric material for its desirable electromechanical coupling
factor and high piezoelectric coefficients. Parylene thin films deposited over the array reinforced the bendable joints,
encapsulated the metal film interconnects, and formed, in conjunction with the silicon, an acoustical match between the
PZT and soft tissue. Eight element linear arrays were fabricated with a pitch of 3.5 mm, operating at a center frequency
of 12 MHz with a 6dB bandwidth of 27%. The robustness of the transducer was demonstrated by iterative bending
around a 1 cm diameter cylinder, and the durability of the electrical traces and the frequency performance was measured
using a vector network analyzer. This paper presents a robust, durable conformal ultrasound array with the versatility to
scale to enable new applications in diagnostic ultrasound imaging.
The decrease in reimbursement rates for radiology procedures has placed even more pressure on radiology departments
to increase their clinical productivity. Clinical faculties have less time for teaching residents, but with the advent and
prevalence of an electronic environment that includes PACS, RIS, and HIS, there is an opportunity to create electronic
teaching files for fellows, residents, and medical students. Experienced clinicians, who select the most appropriate
radiographic image, and clinical information relevant to that patient, create these teaching files. Important cases are
selected based on the difficulty in determining the diagnosis or the manifestation of rare diseases. This manual process of
teaching file creation is time consuming and may not be practical under the pressure of increased demands on the
radiologist. It is the goal of this research to automate the process of teaching file creation by manually selecting key
images and automatically extracting key sections from clinical reports and laboratories. The text report is then processed
for indexing to two standard nomenclatures UMLS and RADLEX. Interesting teaching files can then be queried based
on specific anatomy and findings found within the clinical reports.