Organ Monitoring
Introduction
Organ sensing for cancer detection relates to the detection and identification of cancer within the specific organ of the body. Cancer is a leading cause of death worldwide and it is estimated that every sixth death in the world is due to cancer. Thereby breast cancer and prostate cancer are the two most common invasive cancers in women and men, respectively. Cancer cells are different from normal cells in those organs. While for example, healthy cells know when to reproduce, where to be in the body, occupy cell death mechanisms and become specialized, cancer cells don´t stop growing and dividing, ignore signals from other cells, don´t specialize, don´t repair themselves and look different. One defining feature of cancer is the rapid creation of abnormal cells that grow beyond their usual boundaries, and which can then invade adjoining parts of the body and spread to other organs. Based on the cancer growth pattern, it can be classified into two broad groups: benign and malignant tumors, where the first has a controlled growth pattern. Whereas, other grows uncontrollably by invading surrounding tissues and spreading across organs.
Moreover, the spreading of cancer cells from a primary site to the rest of the body, better known as cancer metastasis, leads to approximately 90%, mainly cancer-caused moribundity [1]. The primary tumor spreads throughout the body via the bloodstream as circulating tumor cells (CTCs) exploit the blood channel system densely covered over the body for successfully implementing new active malignant tumors at distant sites with metastatic peculiarity/characteristic [2-4]. Hence, early detection and distinction are of significant importance for an appropriate course of treatment, which likely increases the probability of survival with less morbidity [5].
In the context of organ sensing, specifically with less invasive or entirely non-invasive methods, superior advantages can be realized for the early detection of cancer. Based on the detected cancer, the primary goal is to remove the cancer and some healthy tissue around it. A surgery is one of the main treatments for many types of cancers. To Summarize, non-invasive methods for early detection are of critical importance.
State of the Art
Traditional imaging-based non-invasive techniques are mammography, CT, MRI, ultrasound, PET and X-rays [6]. Compared to conventional methods, microwave imaging holds substantial promise in enhancing patient comfort, offering portability, improving cost efficiency, and enabling real-time sensing. Microwave imaging uses low-frequency electromagnetic waves to penetrate the human body and generate images of internal organs. However, the spatial resolution is limited in the microwave spectrum. Whereas, millimeter-wave imaging can provide high-resolution images of soft tissues such as skin, breast tissue, and brain tissue. Further higher frequency spectrum, the THz waves have even shorter wavelengths than microwaves, which is becoming a game changer when it comes to circuit and system integration. For example, a miniaturized THz biosensor could be incorporated into a blood vessel, with a focus on organ sensing.
Given the aforementioned factors of sensing/imaging, the investigation of THz electromagnetic waves interaction with tissues is of significant importance. Due to the larger penetration depth than the mmWave and THz regions, the microwave spectrum is widely adopted in medical applications especially in breast cancer detection [6, 7].
Millimeter waves have been used in dermatology to therapy skin conditions such as warts and corns [8]. Moreover, with imaging techniques at millimeter waves, skin’s superficial properties can be extracted [9]. Just like with any form of electromagnetic radiation exposure, it's crucial to be aware of the duration and strength of the exposure and to employ protective measures when deemed necessary. Typically, cancer cell detection focuses superficially on skin cancer owing to the limited penetration depth. It has been investigated in [10] that cancer tissues are characterized by significantly higher water content when compared to healthy skin. Another example is the detection of breast cancer, in [11] a "Smart-Bra" concept is presented with antennas operating below 10 GHz. For higher-resolution imaging of breast cancer, results at 50 GHz are presented in [12]. Nevertheless, the integration of THz sensors into an organ or blood vessel relies on the miniaturization capabilities available in the THz spectrum to fulfill the goal of being minimally invasive.
Own research
The THz spectroscopy provides reliable results for the identification of degenerated tissue. In our early work on inter-operative biomedical THz near-field imaging, we found that hundreds of near-field sensors can operate concurrently in a THz system-on-chip. The feasibility of THz spectroscopy for breath analysis has been demonstrated in several studies. THz spectroscopy provides reliable and valid results for the analysis of human breath in comparison to gas chromatography with mass spectrometry coupling, the gold standard, and is well suited for clinical application. The main advantages are the high sensitivity, specificity, and selectivity as well as the ability to provide absolute quantities. Human tissue sensing forms the foundation of the "lab-on-skin" concept, which involves collecting diagnostic signals from muscles, blood vessels, nerves, wounds, sweat glands, and the skin itself using soft, flexible, and stretchable sensors in a non-invasive manner. However, the design of these wireless systems requires knowledge of the electrical material parameters and an understanding of potential issues and overall functionality.
Obviously, the reliability is dependent on the penetration losses from transmitter to implanted sensor and vice versa. Due to limited availability and ethical concerns regarding human tissue, our conducted measurements on synthetic tissue phantoms at Ka-Band and D-Band respectively [13], shown in Fig. 1 for a skin and fat phantom respectively. Furthermore, our research targets two sensing applications: A miniaturized THz electronics may enter through the bronchial tubes of the lung and sense the tissue via a reflectometry concept. Another concept revolves around imaging infested tissue to aid in determining the extent that should be excised during surgery. Vital parameter analysis can be employed by extracting information from the blood (e.g., glucose concentration). Referring to the mentioned fundamental limitations regarding skin tissue we investigated additionally a compact THz reflectometry at the fingernail bed as this tissue surface has a less complex morphology, is precisely defined, well perfused and even protected by the (transparent) nail plate [14].
Vision
Our vision for the future of this research is to offer a near-field sensor surface capable of revolutionizing the identification of degenerated tissue live during surgery.
During a surgery the THz system-on-chip can be used to identity the degenerated tissue in order to remove damages tissue as complete as possible. We anticipate this breakthrough will find diverse applications in the field of cancer surgery.
Figures
References
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(10) Arab, H., Chioukh, M., Dashti Ardakani, M., Dufour, S., & Tatu, S. O. (2020). Early-Stage Detection of Melanoma Skin Cancer Using Contactless Millimeter-Wave Sensors. IEEE Sensors Journal 12(13), 7310-7317.
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(12) Bevacqua, M. T., Di Meo, S., Crocco, L., Isernia, T., & M. Pasian. (2021). Millimeter-Waves Breast Cancer Imaging via Inverse Scattering Techniques. IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, 5(3), 246-253.
(13) Prokscha, A et al. (2023). A Look Through Artificial Human Tissues at Ka-Band and D-Band. In Proc. Sixth International Workshop on Mobile Terahertz Systems (IWMTS), 1-5.
(14) Jalali, M et al. (2023). Non-invasive glucose sensing via the fingernail bed using THz radiation. Current Directions in Biomedical Engineering (CDBME), 9(1) 507-510.