Tomography Applications in Cancer Diagnosis, Prognosis, Treatment, and Research
Tomography is a term derived from the Greek words tomos, which is defined as a section or slice, and graphien, which means to measure or write. While tomography is widely used to advance scientific disciplines such as archeology, oceanography, astrophysics, materials science, and others, the utilization of tomography is best known for Medical Imaging (MI) applications that are today indispensable to cancer physicians and researchers alike. MI tomography joins in the battle against cancer by providing three-dimensional views of internal anatomical structures such as bone and internal organ tissues.
Cancer can present itself in many different forms in myriad parts of the body, and prior to the advent of advanced MI technologies, physicians were extremely limited in their ability to detect many types of cancer without the use of highly invasive exploratory surgeries. Today, having to physically enter the body in order to examine anatomical structures is virtually unheard of due to the countess advances in MI, nearly all of which rely on tomographic images of one type or another.
While the initial diagnosis, ongoing prognosis, and therapeutic treatment of cancer are all areas that have been significantly advanced through tomographic imaging, so, too, have cancer researchers benefited from the technology. Very high resolution, color enhanced, and three-dimensional views of cancer are now invaluable bench and clinical research tools—bringing cancer into ultra-clear focus is a significant step towards an eventual cure for the deadly disease.
Basic X-ray Tomography
X-rays have provided physicians with internal views of the human body since the late 1800’s. First discovered by the German physicist Wilhelm Roentgen in 1895, X-rays are similar to visible light rays—both are electromagnetic forms of energy that are carried by particles known as photons. The chief difference between X-rays and light rays is the energy levels within the ray’s respective photons, a variation that is generally expressed through the precise scientific measurement of wavelengths.
The earliest use of X-rays produced two-dimensional, black and white images of skeletal structures, as well as views of denser tissues such as those that make up the lungs. While the ability to produce basic X-ray images has been hailed as one of the greatest scientific discoveries in all of human history, when used in concert with tomographic technologies, X-ray-based MI is elevated to new heights. In basic X-ray tomography, radiologists and other clinical personnel create a sectional image of anatomical structures by moving an X-ray source and image capturing film in opposite directions during an exposure, and as a result, structures in the focal plane are viewed in high resolution while all others are blurred. MI technicians are able to utilize subtle or distinct variations in the movement of the X-ray source and film to designate specific focal planes that concentrate on the anatomical structure of clinical interest.
First developed by the radiologist, Alessandro Vellabona, in the 1930s, basic X-ray tomography was designed to overcome the superimposition of anatomical structures in conventional projection radiography. The medical images produced through the use of basic X-ray tomography have proven to be invaluable to oncologists who first need to confirm the presence of cancer before deciding on appropriate treatments for the disease. Today, numerous and highly advanced variations of tomography are possible through the application of tomographic reconstruction algorithms that work in concert with a computer.
Computed tomography (CT) was originally referred to as an EMI scan because the technology was first developed at a research department of EMI, a company that is now widely recognized as a leader in the music and recording industry. Today, CT technology is more commonly referred to as computed axial tomography (CAT or CT scan). CT creates high resolution, three-dimensional medical images of the interior of a solid object through the utilization of an extensive series of standard, two-dimensional X-ray images that are captured around a single axis of rotation. This large body of X-ray data is subsequently manipulated through a process known as windowing, which identifies specific anatomical structures based on the object’s ability to resist or block an X-ray beam.
CAT scan machines are very large, circular shaped devices that can cost between $1-2 million, and as a result of this very high price tag, the devices are usually found in major hospitals and cancer centers. Operated by Certified CT Technicians and specially trained physicians, CAT scan machines provide a painless MI examination that requires no use of patient anesthesia or sedation. Additionally, no unpleasant physical side-effects during or subsequent to a CAT scan are known to exist.
During a CAT examination, the patient will lie on a flat table that is moved—in extremely precise increments—further into the circular opening of the machine as an X-ray source revolves around the patient. During this rotation of the X-ray beam, extremely thin, sectioned anatomical images are recorded. Once the extensive collection of sliced images has been compiled, computed algorithms translate the data into the three-dimensional images that provide cancer doctors with precise and highly detailed views of any malignant disease that may be present.
Two additional applications of computed tomography that are widely used in the detection, prognosis, and treatment of cancer are:
- Positron Emission Tomography (PET): A unique tomographic technology that is highly prized for its ability to image the metabolic function of cancer. PET scans can locate a tumor while simultaneously determining if the growth is malignant or benign. Additionally, the effectiveness of specific cancer therapies can also be judged through the prognostic use of PET.
- Single Photon Emission Computed Tomography (SPECT): Tomographic
imaging widely used in the search for cancer in skeletal structures
(bone cancer). SPECT imaging relies on the use of radioactive
isotopes that are injected into the body and later detected in
specific skeletal sites that are suspected of involvement with
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