The ability to discern malignant from benign tissue in excised human breast specimens in Breast Conservation Surgery (BCS) was evaluated using a prototype single frequency terahertz radiation. Terahertz (THz) images of the specimens in reflection mode were obtained by employing a gas laser source and mechanical scanning. The images were correlated with optical histological micrographs of the same specimens, and a mean discrimination of 73% was found for five out of six samples using Receiver Operating Characteristic (ROC) analysis. This result is similar to what has previously been obtained using Terahertz pulsed imaging (TPI) techniques. We will discuss the specific advantages of Single frequency THz imaging (SFTI) compared with TPI for potentially allowing the development of much faster, more compact and less expensive cancer imaging systems that could be adapted for employment in the operating room. The system design and characterization of the prototype SFTI system are discussed in detail. The initial results are encouraging but further development of the technology and clinical evaluation is needed to evaluate its feasibility in the clinical environment.
In breast conservation surgery, surgeons attempt to remove malignant tissue along with a surrounding margin of
healthy tissue. Subsequent pathological analysis determines if those margins are clear of malignant tissue, a process that
typically requires at least one day. Only then can it be determined whether a follow-up surgery is necessary. This
possibility of re-excision is undesirable in terms of reducing patient morbidity, emotional stress and healthcare.
It has been shown that terahertz (THz) images of breast specimens can accurately differentiate between breast
carcinoma, normal fibroglandular tissue, and adipose tissue. That study employed the Time-Domain Spectroscopy (TDS)
technique. We are instead developing a new technique, Frequency-Domain Terahertz Imaging (FDTI).
In this joint project between UMass/Amherst and UMass Medical School/Worcester (UMMS), we are investigating
the feasibility of the FDTI technique for THz reflection imaging of breast cancer margins. Our system, which produces
mechanically scanned images of size 2cm x 2cm, uses a THz gas laser. The system is calibrated with mixtures of water
and ethanol and reflection coefficients as low as 1% have been measured. Images from phantoms and specimens cut
from breast cancer lumpectomies at UMMS will be presented. Finally, there will be a discussion of a possible transition
of this FDTI setup to a compact and inexpensive CMOS THz camera for use in the operating room.
In this paper we describe a project for designing, developing and translating a THz imaging
device for monitoring margins from extracted tissue during surgical breast cancer conservation
procedures. In this application, the reflective and transmission properties of extracted tissue
are monitored, in near real-time using a fine-beam THz signal which is sensitive to the
presence of liquid and bound water content. In this way, it is intended that the extracted tissue
will be studied in the operating theatre to determine during surgery, whether or not the region
of malignant tissue has been fully excised from the patient. In the early stages of this project,
we are determining to what degree an existing THz system at the University of Massachusetts
(UMass) in Amherst is able to differentiate between breast carcinoma, normal fibroglandular
and adipose tissues. This is achieved through close collaboration with a surgical and
radiological team at the UMass-Worcester medical school and involves post-surgical
recovered tissues. As part of this work, we are describing the system, measurement
methodology, and first results that were obtained to calibrate the imaging system.
Imaging and spectroscopy at terahertz frequencies (defined roughly as 300 GHz - 3 THz) have great potential for both healthcare and homeland security applications. Terahertz frequencies correspond to energy level transitions of important molecules in biology and astrophysics. Terahertz radiation (T-rays) can penetrate clothing and, to some extent, can also penetrate biological materials, and because of their shorter wavelengths they offer higher spatial resolution than microwaves or millimeter waves. We describe the development of a novel two-dimensional scanning, passive, terahertz imaging system based on a hot electron bolometer (HEB) detector element. HEB mixers are near quantum noise limited heterodyne detectors operating over the entire terahertz spectrum. HEB devices absorb terahertz radiation up to the visible range due to the very short momentum scattering times. The terahertz imaging system consists of a front-end heterodyne detector integrated with a state-of-the-art monolithic microwave integrated-circuit low-noise amplifier (MMIC LNA) on the same mixer block. The terahertz local oscillator (LO) signal is provided by a commercial harmonic multiplier source.
We have achieved the first demonstration of a low-noise heterodyne array operating at a frequency above 1 THz (1.6 THz). The prototype array has three elements, consisting of NbN hot electron bolometer (HEB) detectors on silicon substrates. We use a quasi-optical design to couple the signal and local oscillator (LO) power to the detector. We also demonstrate, for the first time, how the HEB detectors can be intimately integrated in the same block with monolithic microwave integrated circuit (MMIC) IF amplifiers. Such focal plane arrays can be increased in size to a few hundred elements using the next generation fabrication architecture for compact and easy assembly. Future HEB-based focal plane arrays will make low-noise heterodyne imaging systems with high angular resolution possible from 500 GHz to several terahertz. Large low-noise HEB arrays are well suited for real-time video imaging at any frequency over the entire terahertz spectrum. This is made possible by virtue of the extremely low local oscillator power requirements of the HEB detectors (a few hundred nanowatts to a microwatt per pixel). The operating temperature is 4 to 6 K, which can be provided by a compact and mobile cryocooler system, developed as a spin-off from the space program. The terahertz HEB imager consists of a computer-controlled optical system mounted on an elevation and azimuth scanning translator which provides a two-dimensional image of the target. We present preliminary measured data at the symposium for a terahertz security system of this type.
The next generation of hot electron bolometric (HEB) mixer receivers for terahertz frequencies is under development. In order to improve sensitivity and integration time, terahertz focal plane arrays with HEB elements are required. We have designed, fabricated, and tested a three-element focal plane array with HEB devices. We implemented a quasi-optical power coupling scheme using three elliptical silicon lenses. Recently developed wideband (0.5 GHz to 12 GHz) MMIC low noise amplifiers were directly integrated with HEB devices in a single block. The array was tested using an FIR laser as the LO source and a side band generator as the signal source. This is the first heterodyne array for a frequency above 1 THz, and the suitability of HEB elements in a terahertz FPA has thus been demonstrated. This development is also geared toward investigating new architectures for much larger arrays utilizing HEB elements. Additional issues to be resolved include an improved antenna design for efficient LO injection, compact and low power IF amplifiers, and cryogenic optimization.
Based on the excellent performance of NbN HEB mixer receivers at THz frequencies which we have established in the laboratory, we are building a Terahertz REceiver with NbN HEB Device (TREND) to be installed on the 1.7 meter diameter AST/RO submillimeter wave telescope at the Amundsen/Scott South Pole Station. TREND is scheduled for deployment during the austral summer season of 2002/2003. The frequency range of 1.25 THz to 1.5 THz was chosen in order to match the good windows for atmospheric transmission and interstellar spectral lines of special interest. The South Pole Station is the best available site for THz observations due to the very cold and dry atmosphere over this site. In this paper, we report on the design of this receiver. In particular, we report on HEB mixer device performance, the quasi-optical coupling design using an elliptical silicon lens and a twin-slot antenna, the laser local oscillator (LO), as well as the mixer block design and the plans for coupling the TREND receiver to the sky beam and to the laser LO at the AST/RO telescope site.
Hot electron bolometric (HEB) detectors and mixers for the THz frequency range, which use thin-film superconductors, have been developed recently. They have short response times due to efficient cooling of ht hot electrons by either (i) phonon transmission from the film to the substrate, or (ii) diffusion of the electrons into the contacts. We have previously demonstrated a 2DEG detector which uses the heated 2D electron gas medium, as well as phonon-cooling. Here we propose and analyze a new version of this detector which employs diffusion cooling. A response time of 1 ps and responsivity of 3,000 V/W are calculated for a device which is 0.8 (mu) l long. This response time is considerably shorter than for any of the superconducting HEB detectors. The predicted double sideband receiver noise temperature for the mixer version is in the range 1,000 K to 2,000 K at 1 THz, with a 100 GHz intermediate frequency bandwidth. The new detector could be operated at 77K and the local oscillator power is estimated to be about 1 (mu) W.
HEB technology continues to extend the sate-of-the-art for THz low-noise receivers. This talk discusses recent measured noise temperatures for NbN HEB receivers form which we infer intrinsic noise temperatures which approach the quantum noise limit within a factor of 3-5. We discuss the feasibility of achieving noise temperatures even close to the quantum limit noting that this limit has been reached both at lower frequencies and at higher frequencies. Another approach for considerably enhancing the speed with which THz receivers collect data is to employ a focal plane array system. We will discuss our design approach and general constraints for such a system.
We have developed prototype HEB receivers using thin film superconducting NbN devices deposited on silicon substrates. The devices are quasi-optically coupled through a silicon lens and a self-complementary log-specific toothed antenna. We measured DSB receiver noise temperatures of 500 K (13 X hf/2k) at 1.56 THz and 1,100 K (20 X hf/2k) at 2.24 THz. Noise temperatures are expected to fall further as devices and quasi-optical coupling methods are being optimized. The measured 3 dB IF conversion gain bandwidth for one device was 3 GHz, and it is estimated that the bandwidth over which the receiver noise temperature is within 3 dB of its minimum value is 6.5 GHz which is sufficient for a number of practical applications. We will discuss our latest results and give a detailed description of our prototype setup and experiments. We will also discuss our plans for developing focal plane arrays with tens of Hot Electron Bolometric mixer elements on a single silicon substrate which will make real time imaging systems in the THz region feasible.