rayDiagnostic Radiology

Diagnostic Radiology is the medical specialty that uses several different forms of imaging technology (imaging modalities) to aid in the diagnosis of disease. These different modalities or imaging techniques include “plain” x-rays, CT scanning, MRI, ultrasound and nuclear medicine. Most or all of these modalities are available in hospital radiology departments and community radiology clinics.



X-rays were discovered in 1895, and within a very few years the use of x-rays to provide simple images of the lungs and the bones had spread around the world. X-rays were originally used to develop images on film, much like a photograph. Increasingly in developed countries film is being replaced by detector plates that transmit a digitized image to a computer screen. This form of technology is now known as either computed radiography (CR) or digital radiography (DR). Fluoroscopy uses pulses of low-dose x-rays to provide images in real time that can be used to guide diagnostic and therapeutic procedures such as angiography (detailed x-rays of the blood vessels), biopsies, and the placement of drainage tubes or stents.

Computed Tomography (CT)

A CT scanner consists of an x-ray tube and x-ray detectors mounted on opposite sides of a circular gantry that are linked to a very powerful computer. The x-ray tube emits radiation while the patient passes through the hole in the centre of the gantry. The X-ray detectors on the other side of the patient’s body relay detailed information about the body part that has been scanned to the computer. The computer uses this information to construct multiple cross sectional images or “slices” of the body. There has been continual development in CT technology in the years since its invention in 1971, and state-of-the-art scanners can now generate very detailed images of the body in multiple planes. CT scanners can detect many abnormalities that “plain” x-rays cannot, although usually with a higher x-ray dose.
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Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging uses a combination of an extremely powerful magnet, radio waves and powerful computers to generate cross sectional images of the body. No X-rays are involved. The powerful magnetic field can however interfere with the function of certain devices such as pacemakers and implanted stimulators or pumps, making MRI generally unsafe for patients with these devices. Patients with certain types of older aneurysm clips used to treat brain aneurysms also cannot undergo MRI for safety reasons.

The MRI gantry fits more tightly around the patient than a CT scanner, and some patients with claustrophobia may have difficulty having an MRI. Claustrophobic patients should request a prescription for an oral sedative from their doctor before the MRI examination.

MRI is often the procedure of choice to evaluate certain diseases involving the soft tissues. MRI examinations are generally more expensive than CT however, and require more time to perform (30 to 60 minutes or even longer). As MRI does not use x-rays, there is no concern about radiation dose.


Ultrasound uses high frequency sound waves that are directed into the body using a transducer. The sound waves are reflected back toward the transducer by tissues, and a computer uses the information in the reflected waves to generate an image. The study is generally performed by a highly trained technologist called an ultrasonographer. Because it does not use x-radiation, it is very useful if medical imaging is required during pregnancy. It can be used to provide images of the soft tissues and blood vessels, and also to guide intervention such as biopsies and drainages. It cannot provide images through air or bone however, and therefore cannot be used to image the lungs and cannot see through air-filled bowel loops.


Mammography is the process of using low-dose X-rays to examine the human breast. The goal of mammography is the early detection of breast cancer, typically through detection of characteristic masses, architectural distortion and/or microcalcifications. Mammography reduces mortality from breast cancer.
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Nuclear Medicine

Nuclear medicine uses small doses of radioactive drugs to look for diseases and examine function of various organ systems. Different drugs (usually injected intravenously) are used to study different organs. For example certain drugs look at heart blood flow, others at kidney function. A gamma camera detects radioactivity in the body and forms an image. Advantages include rapid whole body images and high sensitivity of detecting disease. PET is a nuclear medicine technique used mainly in cancer patients.

Should I be concerned about radiation?

Plain x-rays (computed radiography and digital radiography) as well as CT scanning and angiography all use x-rays. X-rays are a form of electromagnetic radiation, which comes in a variety of forms. Low energy electromagnetic radiation includes radio waves, micro waves that are used in cooking, and visible light. Higher energy electromagnetic radiation includes the ultraviolet rays that cause sun burn, X-rays and gamma rays, which are produced by stars like the sun.

In high enough doses, X-rays can damage tissue, and doctors make use of this effectradiation to treat certain kinds of cancer. At the same time, X-rays can cause damage to the DNA of normal cells that leads to cancer. The chances of this happening at low radiation doses are extremely small, but the risks become greater with increased radiation dose. dose.

We are all exposed to radiation in low doses that comes from radioactive substances in the ground as well as from the sun. The amount of natural or background radiation received by an individual in one year is approximately equivalent to the dose received in a single CT scan of the head. Plain X-rays of the chest or bones use much lower X-ray doses, whereas a CT scan of the chest or abdomen provides the equivalent of three to four years of background radiation.

The information provided by imaging studies that use X-rays can be invaluable in diagnosing disease and monitoring treatment. Because of the low risk of cancer produced by x-rays however, these tests should never be performed needlessly. Alternative imaging modalities that do not use x-radiation, such as ultrasound or MRI, should be considered wherever possible.