In this blog post, we will look at the use of CT technology beyond human diagnosis, including its expansion into various fields such as archaeology, industry, and forensic medicine.
The discovery of X-rays in 1895 revolutionized diagnostic medicine. Since then, X-ray photography technology has evolved into CT (computed tomography), which enables three-dimensional imaging through cross-sectional imaging, and has developed into a technology that can accurately diagnose the inside of the human body without dissection. The development of this diagnostic technology has had a major impact not only on medicine but also on various other fields. For example, in archaeology, it has become possible to understand the internal structure of artifacts without damaging them, and in industry, it has become possible to perform more accurate quality inspections of products.
X-ray photographs are obtained by irradiating the human body with X-rays and exposing film to the transmitted X-rays. Some of the irradiated X-rays are absorbed and scattered by the tissue, while the rest pass through the tissue and emerge on the opposite side. The degree of transmission, which indicates the degree to which X-rays pass through, is highest in air and decreases in the order of fat, water, and bone. In addition, the intensity of the transmitted X-rays weakens as the transmission rate of the tissue through which they pass decreases and as the thickness of the tissue increases. The degree of exposure of the X-ray film varies depending on the intensity of the X-rays, allowing black-and-white images of the tissue to be obtained. However, it is difficult to distinguish between tissues with similar transmittance on X-ray images, so X-ray images are mainly used to examine bones and abnormal tissues with large differences in transmittance from other tissues. CT overcomes the limitations of X-ray images.
CT reconstructs cross-sectional images of the human body through the distribution of X-rays that have passed through the body. On one side of the CT scanner is an X-ray generator, and on the other side are several X-ray detectors. When a person lies down on a bed in the center of the CT scanner, X-rays emitted from the X-ray generator pass through the human body and are detected by the X-ray detectors on the opposite side. Through this process, comprehensive image data can be obtained by measuring the X-ray transmission rate from various angles. This goes beyond simple two-dimensional images and is extremely useful for analyzing the three-dimensional structure of the human body.
The X-ray detector detects the intensity of the X-rays that pass through the human body. At this point, the amount of X-rays attenuated by passing through the air must be subtracted to obtain the total amount of X-rays attenuated by passing through the human body tissue. This can be obtained by calculating the difference between the intensity of the X-rays that passed through the air and the intensity of the X-rays that passed through the tissue, which is called the conversion value. In other words, the converted value refers to the total amount of X-rays scattered or absorbed and attenuated as they pass through human tissue in a specific direction. To obtain this value from multiple directions, the CT scanner is rotated. This allows the converted values for each direction of the same cross section to be obtained, which are then used by a computer to reconstruct a cross-sectional image.
The back projection method is used to reconstruct images in CT. Back projection is a method of distributing the conversion values evenly along the path of the X-rays in a given direction. The conversion values obtained from various directions by rotating the CT scanner are back-projected for each path and added together. The sum of the conversion values from various directions is the back-projected value.
When back projection is performed, values from multiple directions are added in tissues that attenuate greatly, such as bones, resulting in larger values than in other tissues. By combining the back-projected values, it is possible to reconstruct images of tissue distribution based on differences in transmission rates.
By repeatedly scanning various cross sections of the human body while the CT scanner moves slightly, continuous cross-sectional images can be obtained, and three-dimensional images can be obtained by combining these cross-sectional images as needed. This has enabled doctors to make more accurate diagnoses and treatment plans, which has had a positive impact on patient outcomes.
Advances in CT technology have greatly improved the accuracy and efficiency of diagnosis. Early CT devices had limited resolution and imaging time, but modern CT devices can now acquire high-resolution images in a short time. This enables rapid diagnosis even in emergency situations and plays an important role in saving patients’ lives. For example, in the case of a stroke patient, CT can be used to quickly check for cerebral hemorrhage and begin appropriate treatment.
CT technology also plays an important role in cancer diagnosis and treatment. Cancer cells have a different density from normal tissue, so they can be detected early with CT, which is also used to monitor the course of treatment. This contributes to increasing patient survival rates and maximizing the effectiveness of treatment.
The application of CT technology is expanding beyond medicine to various other fields. For example, in veterinary medicine, CT can be used to accurately identify and diagnose the internal structure of animals. In forensic medicine, CT is also used to analyze the internal structure of corpses to determine the cause of death. As such, CT technology plays an important role in various fields, and its applications are expected to expand even further in the future.
Along with this, ethical considerations regarding the advancement of CT technology are also important. CT scans use X-rays, so radiation exposure can be a concern. Therefore, it is important to perform scans only when necessary and with minimal exposure. In addition, the protection of personal information and data management using CT data are also emerging as important issues. Continuous research and regulation are necessary to resolve these issues.
In conclusion, advances in X-ray and CT technology have brought about innovations in medical diagnosis and treatment and are playing an important role in various fields. With further technological advances, the range of applications will continue to expand, contributing to the improvement of the quality of life for all humanity.
