Potential biomedical applications
Terahertz photons are not energetic enough to break chemical bonds or ionize molecules / atoms, and therefore are harmless for living organisms, as opposed to higher energy photons such as x-rays and UV rays. THz radiation is not highly scattered in tissues (unlike optical emission). Besides, due to strong absorption of T-rays by water terahertz imaging can be a useful tool to investigate soft tissues. These unique properties of T-rays make them eligible for use in various medical applications, some of which hold enormous promise for certain aspects of diagnostics as described below.
Non-invasive technique for early detection of cancer
The most recent achievements in the field of medical imaging have dramatically enhanced the early detection and treatment of many pathological conditions. THz imaging systems can help detect the early cancer before it is visible or sensitive to any other identification means
The latest research aimed at examining terahertz properties on skin cancer, breast and colon cancer tissues discovered that refractive index and absorption coefficient of the tumor tissue are higher in comparison to the normal tissue. Such distinction is possible due to higher water content and structural changes that occur in carcinoma (e.g. increased cell and protein density observed in cells affected by disease). Terahertz pulse imaging technique is highly sensitive to water concentration (because of the latter attenuation) and therefore water absorption is evident in the terahertz properties measured for soft tissues, which explains the contrast seen between muscle and adipose tissue, for instance.
Consequently, T-ray images can distinguish between healthy tissue and basal cell carcinoma and therefore help in mapping the exact margins of tumors in earlier stages. (The most promising are such non-invasive terahertz imaging techniques as THz pulse imaging, THz time domain spectroscopy (TDS-THz), continuous wave terahertz (CW-THz), and other THz generation/detection methods).
RTHz Imaging: Biomedical Applications
Mark Stringer, Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering, University of Leeds
Ex-vivo spectroscopy / imaging of tissues (biopsy)
By obtaining both frequency and time domain information, Teraherz imaging can ensure enhanced detection of cancer (and other inflammation areas), and provide sharper imaging and molecular fingerprinting. Each year millions of biopsies of breast tissues are required to compensate for uncertain, inaccurate or negligent diagnoses delivered by means conventional detection methods, which are not always impeccable.
Terahertz time-domain spectroscopy (TDS-THz) can breach the shortcomings of other medical diagnostics in rendering adequate images of the affected tissues or suspected areas. Many researchers confirm that at certain frequency range most tumors have lower absorption than normal tissues. The obvious conclusion here is that THz imaging can ‘distinguish’ the tumors (inflamed areas) from normal tissues. In addition to helping save human lives, such biopsies enhanced by T-ray spectroscopy saves a lot of time and efforts by reducing the number of second surgical procedures in breast and skin cancer treatment cases.
One of the greatest biomedical potential of T-ray imaging is associated with Molecular spectroscopy for diagnostics, which is exponentially advanced and moved closer by the progress.
In-vivo examination of tissue via spectroscopy / imaging
Surgeons during a carcinectomy surgery -just to stay on the safe side — excise the tumor with an ample margin of healthy tissue surrounding it. Such playing-it-safe approach in surgery is often justified but costs dearly to patients and fires back on regeneration/recovery period.
Imaging in THz frequency range can be used to render a real-time imaging during surgical operations to avoid cutting off a lot of healthy tissue, and exclude leaving any part of carcinoma in a patient’s body. This in its turns considerably reduces the likelihood of the need for a repeated invasive operative intervention (s) in the future.
Terahertz imaging (especially THz Pulse Imaging (TPI) can show good contrast between different animal tissue types and, accordingly, can enhance the effectiveness of medical diagnostics and tangibly complement histological analysis. Such diagnostic is believed to allow obtaining the spectrum of each pixel in the image individually.
Please click to see picture «Contribution of THz technology in the future (10 years)» by National Institute of Information and Communication Technology, Japan
Those spectra that represent different tissue types happen to be markedly different. This suggests that the spectral data inherent in T-ray image might be used to distinguishing between soft and hard tissue at each pixel in an image and provide other diagnostic information not afforded by currently available conventional imagine techniques.
In vivo molecular imaging is considered as the next frontier in medical diagnostics, which in the ideal situation, would be performed non-invasively.
A real-time terahertz imaging system consisting of terahertz quantum cascade laser and uncooled microbolometer array detector
Hosako, N. Sekine, N. Oda, M. Sano, S. Kurashina, M. Miyoshi et al., SPIE Vol. 8023, 80230A, doi: 10.1117/12.887 947/
Modern scientific research evidence strongly suggests that THz Pulse Imaging my be used to provide valuable diagnostic information pertaining to the enamel, dentine, and the pump cavity.
Many researchers have consensus that the time-of-flight of THz pulses through the tooth allows to make highly important measurements for a dentist, none the least of which is the thickness of the enamel that can be determined this way. Moreover, it can be used to create an image showing the enamel and dentine regions. Additionally, pulp cavity regions can be identified via absorption of THz pulses in the tooth and allow a dentist to chose the right treatment on the spot.
Preventive healthcare and blood testing
Quite a few medical R&D projects lead to conclusions that terahertz (THz) time-domain spectroscopy (TDS) can be used to characterize the blood. Scientists in this field have already obtained the complex optical constants of blood and its constituents, such as water, plasma, and red blood cells (RBCs) in the THz frequency region. Researcher managed to extract the volume percentage of RBCs in blood and compare it with the conventional RBC counter results. The THz absorption constants proved to vary linearly with the RBC concentration in both normal saline and whole blood. The excellent linearity between the THz signal and the RBC concentration was also confirmed in a polyurethane resin tube using a THz imaging method. These results demonstrate that THz-TDS imaging can facilitate the quantitative analysis of blood.
Additionally, very recent research project in THz emission at the level of a few tens of GHz and at 300 GHz showed sensitivity to the blood glucose level. This invention opened immense opportunities for preventive healthcare (blood analysis) for non-invasive measurement of glucose and other biomedical relevant molecules involving sub-THz and Terahertz ranges, up from aprx. 20GHz on.
It is now evident that different types of biomolecules leave distinctive spectral fingerprints in the THz region, which considerably widens the coverage of THz technologies application to include in-vitro and in-vivo measurements of small molecules (such as glucose, lactate, urea) of clinical importance in PoC and diagnostic systems.
Diagnostics of osteoarthritis, arthritis etc
There are also many other areas in medicine which would benefit from both an intra-operative probe and post-operative analysis of soft tissues sensitive to THz light.
Osteoarthritis (OA) is the most common form of arthritis, caused by the breakdown of cartilage would be one vivid example. It usually affects weight-bearing joints like hip, knee, feet and spine, which causes the joints to degenerate. After cartilage erosion, bone grinding may occur, leading to thickening and forming of osteophytes, and, As a result, pain, stiffness, swelling and reduced range of motion.
OA and many other diseases would be a great medical incentive to investigate the in vivo usage of terahertz imaging.
All in all there are several Terahertz imaging modalities that represent high interest for medicine, in particular, Terahertz pulsed imaging (TPI), THz time domain spectroscopy (TDS-THz), continuous wave terahertz (CW-THz), and a few other THz generation/detection methods.
As it is safe for humans, these Terahertz technologies can open up infinite opportunities for medicine, that like other applications can surely benefit from harmless penetrating capability of Terahertz waves to make the invisible visible and visualize internal information about physical objects.
We must admit that despite numerous reports in the press and internet of successful application of THz imaging in medicine, we have never tested our imaging systems for any medical applications described above. We can only assume that our devices can be useful in some of the areas. We encourage our customers to consider getting our THz imaging systems for respective test in the field and would certainly appreciate any feedback afterworlds.