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.
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.
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. No other imaging technique has been shown to reduce the death rate, but breast self-examination (BSE) and physician examination are considered part of regular breast care.
Mammography does not find all cancers. This is partly due to dense tissues obscuring the cancer and the fact that the appearance of cancer on mammograms may overlap with the appearance of normal tissues.
Mammography also finds many abnormalities that are not cancer. Women may be understandably distressed to be called back for a diagnostic mammogram. Most of these recalls will not be cancer, but radiologists would rather be “safe-than sorry,” so try not to worry if you’re called back for extra pictures. Some women even need a needle biopsy to determine whether cancer is present, or not. These are done usually with either ultrasound or mammogram guidance. Local anaesthetic (freezing) is given first. It stings about the same, or less, than the sting when blood is taken from the arm. Once the freezing is in, only dull pressure is felt. So a needle biopsy is only slightly “more glamorous” than a blood test!
A mammogram is a quick and easy X-ray of the breast done in complete privacy by a specially trained female technologist.
Who interprets the results and how do I get them?
A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a signed report to your primary care or referring physician, who will discuss the results with you. You will also be notified of the results by the mammography facility.
Imaging of the breast improves a physician’s ability to detect small tumors. When cancers are small, the woman has more treatment options and a cure is more likely.
Five percent to 10 percent of screening mammograms require more testing such as additional mammograms or ultrasound, etc. Most of these tests turn out to be not cancer. If there is an abnormal finding, a follow-up or biopsy may be recommended.
The risk of the radiation from a mammogram actually causing a breast cancer is negligible. The doses used are very small. It’s estimated that out of a million mammograms performed, that theoretically, one cancer might be caused. The data from the BC Screening Mammography Program show that women who have mammograms have over 40% fewer deaths from breast cancer than women who do not have mammograms, so even if there’s a theoretical risk of one cancer being caused (per million mammograms), the risk of dying from it is less. In other words, the benefit far outweighs the potential risk.
Mammograms are the most important tool doctors have, not only to screen for breast cancer, but also to diagnose, evaluate, and follow people who’ve had breast cancer. They are safe and reasonably accurate, and have been in use for over 50 years.