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Articles on Medical Matters:

Scans Explained

The sign above the doors says, "warning". It is a familiar sight in hospitals. Behind these doors lie X-ray, CT, PET and many other scanners which radiologists, doctors who specialise in radiology, and radiographers, health-care professionals who produce the x-ray, use to look inside our bodies.

The images produced by these are vital to doctors and help them diagnose and treat many diseases and conditions. Diagnostic imaging can be divided into procedures using ionising radiation, which includes nuclear medicine, and procedures using non-ionising radiation.

Ionising Radiation

X-ray
What it is: A typical test that produces a still two-dimensional picture by sending an x-ray beam, a form of electromagnetic radiation, through an area of your body.

Dense tissue, such as bone, shows up as white in the image because it absorbs more of the radiation. Less dense tissue, such as the lungs, absorbs less of the radiation, so it shows up as grey in the image. Air shows up as black.

What it is used for: It can be used to look at bones or internal organs to detect abnormalities and is the most frequently used form of medical imaging.

A common x-ray test is the mammogram, which is designed to look at the breasts. It is recommended that women form the age of 40 to 49 have a mammogram every year, while those above the age of 50 have a mammogram once every two years.

How it is done: The patient may have to lie or stand still depending on the part of the body being x-rayed. The procedure usually takes only a few seconds and it is painless. A dye that acts as a contrast material may have to be injected into the patient to produce a clearer picture.

Costs: X-ray tests can cost anywhere from $15 to $300, depending on where the scan is done, whether contrast material is used and what part of the body the scan is done on. Costs are lower for government-subsidised patients.

Fluoroscopy
What it is: A test similar to an x-ray, except the area of the body viewed appears as a moving image on a TV screen. This can be recorded.

What it is used for: It is used to look at internal organs in motion such as the gastrointestinal tract, uterus, fallopian tubes and bladder. It is also used to guide catheter angiography, a procedure used to view or treat damaged or blocked blood vessels. This is done by inserting a long thin tube into a blood vessel and up to the area being looked at. A dye is then injected and a balloon, stent or drugs may be placed in the vessel.

How it is done: The procedure is similar to an x-ray, but takes longer. Patients may be sedated when having catheter angiography, as it is an invasive procedure. Patients may also have to ingest or be injected with a contrast material.

Costs: Fluoroscopy can cost anywhere from $90 to $500, depending on where the scan is done, whether contrast material is used and what part of the body the scan is done on. Costs are lower for government-subsidised patients.

Computed Tomography (CT) Scan
What it is: What is also called a CAT scan produces two-dimensional detailed images using x-rays. These images can be reconstructed into three-dimensional images. The scanner works bt sending beams of x-rays from several different angles through the body to get cross-sections of the area of interest.

What it is used for: CT scans help doctors look for abnormalities in the body such as tumors. The pictures are considerably clearer than normal x-ray pictures.

How it is done: Patients lie flat on a bed and are sent through a hole in a doughnut-shaped machine. It is very fast, and the procedure can be done within seconds. Patients may have to be injected with a dye that acts as a contrast material is injected to view movement in the blood vessels.

Patients undergoing a cardiac CT may have to take drugs to slow down their heart rate.

Costs: Commonly done CT scans can costs anywhere from $300 to $1,300, depending on where the scan is done, whether contrast material is used and what part of the body it is performed on. Costs are lower for government-subsidised patients.

X-rays, fluoroscopy and CT scans all use ionising radiation, so there is a slight risk of cell and tissue damage. Overall, they are safe procedures. Protective garments, such as to cover a woman's ovaries, are provided when needed.

However, there is a risk to unborn children, so women should tell their doctors if they are pregnant or think that they might be. There is also a small chance of being allergic to the dye injected or ingested.

On the whole, patients need to talk to their doctor about the risks and benefits. If a pregnant woman needs to have a scan to save her life, then that may outweigh the risk to the child.

Non-Ionising Radiation

Magnetic Resonance Imaging (MRI) Scan
What it is: A scan that uses magnetic and radio waves to produce detailed two-dimensional images. These can be reconstructed into three-dimensional images.

What it is used for: MRI scans are very similar to CT scans. However MRI scans do not use harmful radiation and generally, provide more detailed images than CT scans do. An image produced from an MRI scan would give a doctor a better sense than from a CT scan if, for example, a mass is a tumor or just water or fat. They are not as effective as CTs when looking at the lungs or the coronary arteries of the heart.

How it is done: Patients lie down and are sent into a tunnel in a large cylindrical machine. They must lie still and may have to spend more than 30 minutes in the machine. The MRI scanner can also make loud banging noises.

Patients may have to be injected with a dye that acts as a contrast material, such as in MRI angiography, where contrast material is injected to view movement in the blood vessels.

Risks: Patients may feel claustrophobic from lying in the MRI tube. There might be risk to unborn children, through MRI scans are not known to cause any damage.

Costs: Commonly done MRI scans can cost anywhere from around $500 to $1,900 depending on where it is done, whether contrast material is used, and what aprt of the body it is being performed on. Costs are lower for government-subsidised patients.

Ultrasound
What it is: A scan where sound waves are sent through the body to form a real-time two-dimensional image. The image is then shown on a TV screen. The images can be reconstructed into three-dimensional images.

What it is used for: The ultrasound poses no risk to unborn children, so it is safe to use during pregnancy. It is also commonly used to look at the heart in an electrocardiogram (ECG). However it cannot penetrate deep organs as well as other imaging technologies.

How it is done: A scanner that looks like a paint roller is rubbed across the patient's skin once a gel has been spread on the area. During the first weeks of pregnancy, a probe may be placed in the vagina instead of being rubbed across the skin.

Costs: Ultrasound scans can cost anywhere from $50 to $500, depending on where the scan is done and what part of the body it is done on. Costs are lower for government- subsidised patients.

Nuclear medicine is a relatively new field of medicine. When doing imaging, the procedure invulves injecting patients with radioactive tracers that migrate to a certain area of the body and show how active the cells are in that area. The most common form is the PET scan.

Positron Emission Tomography (PET) Scan
What it is: A scan that shows the rate of activity of certain cells in the body. Different rates of activity show up in different colours on the image.

What it is used for: The PET scan is used most often to detect and look at tumors in patients. It can determine whether a tumor is active or inactive, or what portions of a tumor are active. The PET scan is used with CT scans, so the CT scan forms a backdrop for the PET image.

Risks: The radioactive tracers are used in such small quantities that the risk of tissue and cell damage from radiation is very low. The PET scan is even used on children, though there might be a risk to an unborn child.

Costs: Commonly doen PET or CT scans can cost from around $2,000 to $4,000 depending on where the scan is done, whether contrast material is used and what parts of the body the scan is performed on. Costs for government-subsidised patients are lower.

Shelagh Mahbubani
Singapore
16 Mar 2007

This article is an abstract from Mind Your Body, The Straits Times, January 31, 2007.