Tomography refers to the reconstruction of objects from projections. Tomography has had a revolutionary impact on diagnostic medicine, providing a non-invasive approach in which doctors can examine internal organs and metabolic activity. Modern computing technologies are essential tools to interpret the vast amounts of data and calculations required in tomography, and computerized tomography (CT) encompasses many disciplines including, electrical engineering, mathematics, computer science, physics, mechanics and biomedical sciences. Tomography, however, is not only limited to the medical field. Its principles have been applied to numerous and diverse arenas such as industrial evaluation, airport screening, micro tomography, geophysics, oceanography, astronomy, and optical tomography and diffraction tomography. The concept of tomography was first published in 1826 by a Norwegian physicist named Able.
In 1917, J. Radon, an Austrian mathematician, furthered Abel’s ideas to prove than an arbitrary image of a three-dimensional object could be projected from its mathematical projections. However, it was in 1972 that the current excitement over tomographic imaging began, when Godfrey Hounsfield constructed the first experiment X-ray CT scanner in 1972. [This technique is also known as computerized axial tomography or CAT scans because the first CT machines were only capable of axial tomography. ] Another man, Allan Cormack, made important contributions to the mathematics of X-ray CT, now the most prominent example of computerized tomography. [Though their work in the field of X-ray tomography was done independently of one another, Hounsfeld and Cormack shared the 1979 Nobel Prize in science for their contributions to computer-assisted tomography.
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] Essentially, the process involves a series of X-ray “slices” through the body that are then analyzed by a computer that constructs a cross-image from the data. CAT scans are used in the structural imaging of internal organs and in the detection of tumors. It can show the precise location and shape of a tumor, determine whether a tumor is solid or hollow, and even give clues as to whether or not a tumor is cancerous. However, a CAT scan is not reliable in detecting tumors less than two centimeters in size. CAT scans are also used in neuroimaging, and is used to detect abnormalities in the brain of patients suffering from bipolar disorders or schizophrenia. Magnetic Resonance Imaging (MRI) scans are also used to produce images of the body.
However, unlike CAT scans, MRIs use strong magnets and radio waves to produce the image. The strength of the magnetic field causes the body’s atoms to respond, and the emissions are detected by the scanner, which then analyze the data and produce and image. Modern MRI machines are capable of producing images down to one millimeter, and provide clearer images and detail than a CAT scan in most tissues. Disadvantages of the MRI include greater costs, increased difficulty in differentiating between inflammation and scar tissue, and the general inability to use the technique on those with metal implants. Another chemical imaging technique, Magnetic Resonance Spectroscopy (MRS) works similarly to MRI but is capable of measuring the amount of different chemicals in the brain, depending on the type of scan, providing a spectrum (rather than an image) of the brain. CT and MRI scans are helpful in looking at the structures in the body.
However, another technique, Positron Emission Tomography (PET), looks at function. PET scans use radioactive positrons to detect differences in chemical and metabolic activity in the body, producing a colored image in areas of increased activity. During the procedure, a radioisotope called a tracer is inhaled or injected into the vein of a patient. Because the radioactive atom is attached to a chemical that will bind to only a certain receptor, it is possible to see where body receptors (example: serotonin receptors on the brain) are located and whether the receptors are functioning or not. PET scans are used extensively in differentiating between malignant and benign tumor goths, corn ory heart diseases, and disease of the brain such as Alzheimer’s, Huntington’s and Parkinson’s disease. Most drawbacks to PET scans involve accessibility and costs.
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Until recently PET was used mainly for research. They are very expensive and are not always covered by insurance. The image is also not as clear or easier to read than CT scans and MRIs. The future of tomography includes the combinations of CT and PET technologies with the capability of detecting both the anatomical detail of CT scanning and the functional abilities of PET. It is quite evident that the images tomography provides will provide a useful tool in understanding more about the human body.