Diagnostic Imaging Modality Overview

In modern medical practice, the term Radiology encompasses the techniques used to investigate the architecture and physiological function of the human body. These techniques include tomography, radiography, fluoroscopic, scintigraphic, ultrasonic, Computed Tomography, Magnetic Resonance Imaging and Interventional Radiologic modalities used in conjunction with one another and with a variety of other diagnostic aids available to the physician.

Radiographic and fluoroscopic procedures require the production of an x-ray beam into which the anatomy being evaluated is placed. The portion of the x-ray beam not absorbed by the body, termed remnant radiation, is then used to expose medical x-ray film, thereby producing the diagnostic image. Bone and soft tissue structure require no special preparation for the evaluation. The organ systems and the circulatory system, however, require the administration of a contrast material to enhance the visualization of their characteristic shape, size and position or their related functional status. Iodinated solutions and barium sulfate suspensions are the most common forms used. Computerized Tomography (CT scan) is a special kind of x-ray that produces 3-D pictures of a cross-section of a part of the body.

Scintigraphic, or nuclear medicine, procedures are a diagnostic service which uses isotopes to image organs and study their function. Isotopes are a group of atoms which chemically behave in an identical manner, but differ from one another by their nuclear structure, findings are recorded by camera or scanner, a type of sophisticated geiger counter.

Ultrasonography utilizes a high-frequency sound bean to visualize the structures of interest. The sound beam is directed into the body and the resulting densities of body tissue are analyzed to produce the diagnostic image. The technique is similar to sonar used on submarines.

Magnetic Resonance Imaging is based on the magnetic behavior of hydrogen atoms in human tissues when they are placed in a magnetic field and excited by radio frequency pulses. After the excitation, the hydrogen atoms return to their normal state by emitting energy that is monitored. This process is characterized by relaxation times, which reflect the chemical and physical properties of tissues, such as temperature, flow, etc., and contain a lot of information which cannot be obtained by any other imaging modality using ionizing radiation.

The main applications of MRI in clinical diagnostics are to study the soft tissues of the central nervous system, spine, extremities, bones and joints.

In brain diagnostics, MRI has proven to be a reliable modality for studies of tumors, infarction, hemorrhages and degeneration paenomena (cerebral atrophy-Alzheimer's).

Non-invasive, painless examinations of the spinal cord can be carried out without contrast media. The spinal cord, cerebrospinal fluid (CSF), discs and cavities of the spinal canal are clearly shown on the images.

Other typical MRI-indicated studies in the body and extremity areas are injuries, hemorrhages, cysts, infections and tumors, both in bone marrow and in soft tissue.

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