The Online Encyclopedia and Dictionary







Radiology is the branch of medical science dealing with the medical use of x-ray machines or other such radiation devices. It is also the examination of the inner structure of opaque objects using X rays or other penetrating radiation.



As a medical specialty, radiology can be classified into two subfields. Diagnostic radiology is concerned with the use of various imaging modalities to aid in the diagnosis of disease. Interventional radiology uses these imaging modalities to guide minimally invasive surgical procedures.

Radiation therapy uses radiation to treat diseases such as cancer. While originally encompassed within radiology, therapeutic radiology — or, as it is now called, radiation oncology — is now a separate field.

Diagnostic radiology

Commonly used imaging modalities include plain radiography, computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and nuclear imaging techniques. These techniques are usually non-invasive. Each of these modalities has strengths and limitations which dictate its use in diagnosis.


Radiographs are often used to for quick evaluation of bony structures. Fluoroscopy, angiography and barium contrast studies are special applications of X-ray imaging, where an X-ray video camera allows the imaging of structures in motion or augmented with a radiocontrast agent. Often, chemicals are injected, swallowed or otherwise administered into the body of the patient to help delineate certain parts of the body such as the blood vessels and gastrointestinal tract. These contrast materials, which strongly absorb X-ray radiation, also help to demonstrate dynamic processes, such as the motion of the digestive tract.

CT scanning

CT imaging uses X-rays in conjunction with computing algorithms to image a variety of soft tissues in the body. X-ray contrast is often used with CT as well. CT can generate much more detailed images than plain X-rays, but exposes the patient to more ionizing radiation.


Medical ultrasonography uses ultrasound (high-frequency sound waves) to vizualize soft tissue structures in the body in real time. No radiation is involved, but the quality of the images obtained using ultrasound is highly dependent on the skill of the person performing the exam.


MRI uses strong magnetic fields to align spinning atomic nuclei (usually hydrogen protons) within body tissues, then disturbs the axis of rotation of these nuclei and observes the radio frequency signal generated as the nuclei return to their baseline states. MRI scans give the best soft tissue contrast of all the imaging modalities. With advances in scanning speed and spatial resolution, and improvements in computer 3D algorithms and hardware, MRI has great potential for development in the next few years. One disadvantage is that the patient has to hold still for long periods of time in a noisy, cramped space while the imaging is performed.

Nuclear medicine

Nuclear medicine imaging involves the administration into the patient of substances labelled with radioactive tracers which have affinity for particular tissues. The heart, lungs, thyroid, liver, gallbladder, and bones are commonly evaluated for particular conditions using these techniques. While anatomical detail is limited in these studies, nuclear medicine is useful in displaying physiological function. As such, processes such as the growth of a tumor can often be monitored, even when the tumor cannot be adequately visualized using any of the other modalities. The principle imaging device is the gamma camera which detects the tracer in the body and displays it as an image. Often the information is converted into a series of slices through the body. In the most modern devices Nuclear Medicine images can be fused with a CT scan taken at the same time so that the physiological information can be overlayed on the anatomical structures to improve diagnostic accuracy.

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Last updated: 05-10-2005 13:37:56
Last updated: 09-12-2005 02:39:13