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Radiology

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X-ray

Radiology is the medical application of radioactive materials to produce medical imaging. It has been developed over the last hundred years, but the field accelerated dramatically just in the past twenty.

Radiologic technologies contribute to doctors' ability to treat patients by providing relatively low-risk, non-invasive methods of diagnosis. A patient is referred by a doctor for a scan, A technician or technologist will perform the procedure, then a radiologist will interpret the images to send back to the referring doctor. These technologies have become so precise and reliable that they have taken much guesswork out of medical practice.

Radiologic facilities can be found in private outpatient clinics or in hospitals. Private radiology clinics will often specialize in one or two types of scans and be very proficient in their area of expertise. A hospital with a radiology department will have most of the current technology in one place making the scans more convenient and available on shorter notice.

X-ray

Chest X-ray
X-rays are forms of electromagnetic energy carried by photons, just like visible light. The difference is that x-rays have a much shorter wavelength and a higher energy level than light. This high level of energy allows the photons to pass through less dense materials such as soft tissue, but cannot pass as easily through more dense materials such as bone. [1] Medical x-ray imaging was the first internal, non-invasive imaging technique, developed over 100 years ago. The process involves directing x-rays through the scanning area onto a film on the other side which is sensitive to the light photons. Bones and dense tissue will show up on the film as lighter colored areas whereas the soft tissue will show up dark on the film. The soft tissues are less dense allowing the charged x-ray particles to move through easily. The denser tissues show up light because the photon particles collide more readily with the atoms of the tissue which creates the release of light photons that are captured on the film.

The medical X-ray procedure is directed by a certified technician who instructs the patient about how to position themselves depending on what part of the body needs to be imaged. Often the patient will lie on a table while the technician places a film underneath the patient and moves an x-ray photon emitter head over the patient. The technician must have an in-depth knowledge of anatomy in order to work with the patient and to know the equipment for the right patient position and image angle required by the doctor.

X-rays are used to detect anomalies in anatomical structures such as a break in a bone or a dense tumor. They are limited to providing visual images of structures in the body. Since most internal organs consist of soft tissue of about the same density, these organs will not show up on the images.

CT scan

CT scan of the brain
A computed tomography scan is like an x-ray in that it sends radiation through a person to a detector on the opposite side, but it has many major differences as well. A CT scan takes place in a tube with a rotating radiation emitter opposite a receptor that rotates around a patient that is lying on a sliding table that moves through the tube. Where an x-ray sends a short burst of radiation through a patient, a CT scan sends multitudinous amounts of x-rays through in a spiral type pattern.

The detection is different from a conventional x-ray image as well. Opposite of the emitter is a crystal lens that detects the levels of radiation reaching the lens. The detection method along with taking many sequential images allows for precise mapping of even soft tissue organs in the body. The lens then sends the information to a computer which converts the data from the machine into images on a screen for the technician. The rotational pattern of the scan produces many cross-sectional, (slice type) lateral images of a patient. These types of images create a three-dimensional portrayal of the patient, allowing a doctor to pinpoint with accuracy and precision, anything he wishes.

CT technology also offers the ability for specific areas or functions of the body to be highlighted through the use of contrast solutions. Contrast solutions are substances that partially block the radiation, having a similar effect as the tissue density in a conventional x-ray. Contrasts can be introduced through ingestion, injection, intravenous line, or through an enema. These methods of contrasting can help a doctor detect specific functions such as blood flow or digestion efficiency.

Nuclear Medicine

3D heart with nuclear med SPECT scan sliced through
Nuclear medicine is quite different from both x-ray, and computed tomography technologies. Nuclear medicine involves the injection of radioactive isotopes directly into the patient. The same basic principle of capturing the radioactivity data holds true, but the source of the radiation is actually inside the patient unlike x-ray and CT where the radiation source is external. Nuclear medicine procedures reveal the body’s functionality at the cellular level. There are two detection lenses that can rotate around the patient. These lenses do not transmit anything to each other so they do not need to be directly opposite of each other, this lets the technician position each lens independently to get the best angles for the scan. For example: the heart is towards the front and the left of a person, so the lenses can be positioned at a 90 degree angle to each other and be placed above and to the side of the heart to get as close as possible to get the best results.
SPECT image of heart

The way in which the procedure shows the cellular processes is by adding radioactivity to something the body is doing. I will continue with an example of cellular metabolic rate monitoring for cancer screening. A radioactive isotope is added to a glucose injection given to the patient. Cancer cells are more active than normal cells, which means that they will more readily take up glucose for energy. When the radioactivity is added to the glucose the location of the glucose is detected by the scan. Since the cancer cells are more active, they will use more glucose resulting in high concentrations of radioactivity at the site of the cancer giving up its location. The same methods can be applied to look at nearly all cellular functions. Attaching a radioactive isotope to a substance that is normally used by the body to image that part of the body and specifically what is happening.

Because of the extensiveness of the nuclear medicine procedures, patient preparation is arguably the most important aspect. Patients are given a strict diet, exercise, and medication plan by the technologists to prepare for the test. Even the slightest error can skew the test results so that they are rendered useless. For instance, if a person goes running before they get a cancer screening scan as described before, the leg muscles will require the energy from the glucose and so it will be directed away from the cancer. As a result, the leg muscles will show up bright and the cancer might not show up at all. Preparation for a nuclear medicine procedure is often days to weeks of planning by the doctors working together with the patients and the technologists. There is much preparation at the time of the scan as well. The patient's time needs to be managed carefully by the technologist because the body needs time to take in the substances and radioactivity of the substance will decay in a short amount of time, so if a patient is tested either too soon or too late after injection, it will compromise the entire test. Safe levels of radiation must be maintained, so there are no second chances. When a test is not usable, the exam must be rescheduled, stressing the importance of patient cooperation and preparation.

Resources

  1. http://health.howstuffworks.com/x-ray1.htm how stuff works (howstuffworks.com)

Further Reading