CT scan: Weighing the benefits and risks The Doctor Says By Dr MILTON LUM

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The CT or CAT scan is an acronym for computerised axial tomography scan, and it’s now a tool regularly used in diagnosis.

THERE have been exponential advances in medicine in the last five decades, both in diagnostics and therapeutics. This has been made possible through technological discoveries or improvements in other fields of human activity. The CT or CAT scan is one such example.

CT or CAT scan is an acronym for computerised axial tomography scan. The images in a CT scan are created through x-rays and a computer system. Anyone who has seen the images of a CT scan, whether in film or digital form, cannot but marvel at its detail and comprehensiveness.

The CT scan is a large ring-shaped medical device which produces a series of x-ray beams as it rotates around the body in small movements. Images are built up of the various parts of the body scanned during this process. These images, which are called tomograms, are of greater detail than that of ordinary x-rays, which uses a single x-ray beam only. The CT scan can produce images of various body parts like the organs in the chest and abdomen, blood vessels and bones.

Full disclosure: Anyone who has seen the images of a CT scan, whether in film or digital form, cannot but marvel at its detail and comprehensiveness.

A more sophisticated CT scan is the spiral or helical scan, which is faster than the standard CT scan. The x-ray beam in this scan rotates around the body part being scanned in a spiral fashion and produces continuous images.

CT scans are used in the diagnosis and evaluation of many conditions as well as the monitoring of treatment. The procedure is painless and the time taken varies, depending on the body part that is scanned and whether a standard or spiral scan is used.

Standard scans usually take between 10 to 30 minutes. Spiral scans take a shorter time.

Preparations

There is a standard operating procedure whenever a CT scan is ordered. The patient will be asked about his or her medical condition, consumption of medicines, history of allergies, and the possibility of pregnancy in women in the reproductive age group.

In general, CT scans are not done in pregnant women unless there are medical or surgical conditions that require evaluation and/or treatment. This is because of the slight possibility that x-rays may harm the developing foetus. Children are more susceptible to radiation risks than adults. As such, CT scans are only done if the child has a serious condition which is of greater risk than the CT scan.

Any jewellery or metal on the body has to be removed because they interfere with the scanning process. Hair clips, dentures, contact lenses and hearing aids will also have to be removed, particularly if the head is to be scanned.

The patient will be asked to change into a hospital gown.

Some people have a fear of being closed in without means of escape (claustrophobia, which is derived from the Latin word claustrum, which means “the shut in place”, and Greek word phobos, which means “fear”). Having a CT scan can be claustrophobic. If one has this problem or an anxiety about the scan, one should inform the staff when making the appointment. This is usually addressed by advice and information or the prescription of a sedative to be taken prior to the scan. It is advisable to arrange for a relative or friend to drive if one is going to take a sedative.

The scan

A patient having a CT scan will be asked to lie on a bed that automatically moves in and out of the hollow part of the CT scanner, which is shaped like a large ring. Images will only be taken of the body part that is inside the ring.

After adjusting the position of the bed to ensure that the exact part of the body is in the ring of the CT scanner, the radiographer or radiologist will leave the examination room. He or she will carry out the scanning from a control room, which has a window with full view of the patient. The reason is to reduce the radiation exposure to staff carrying out x-rays daily. Communication with the staff in the control room during the scan will be through an intercom.

The patient will be requested to be still and breathe normally to prevent any blurring of the images taken. One may be asked to breathe in, breathe out or to hold the breath at certain stage(s) of the procedure.

The x-ray in the ring of the CT scan rotates around the patient, taking images as it does so. With the completion of each rotation, the bed on which the patient is lying is moved forward a little bit and the cycle continues until the examination of the body part required is completed.

Sometimes, a contrast medium may be given to a patient who has a CT scan. The medium contains a dye which enhances the quality of the x-ray images of certain body parts. It may be injected into a blood vessel, swallowed as a drink or inserted into the rectum, depending on the body part that is being scanned.

Some patients experience a warm sensation with the injection of contrast medium. This is not abnormal and will resolve by itself rapidly. The contrast media used in CT scans are usually harmless and are excreted from the body in the urine. However, some patients may develop an allergic reaction to the contrast medium, causing complication; hence the importance of informing the radiologist or radiographer of any previous allergies.

The many x-ray images taken will be stored in a computer system. The radiologist will study and analyse the images taken on a monitor screen from various angles and then write a report for the doctor who ordered the CT scan.

With the completion of the CT scan, one can leave the hospital. It is advisable to ask the staff when to expect the results and to confirm one’s appointment with the doctor who ordered the scan.

Uses

CT scans provide information about various conditions, both in its diagnosis and evaluation as well as the monitoring of treatment. Sometimes, they may help in the diagnosis of an unsuspected condition.

The uses of CT scans are myriad and include:

> Head scans after a stroke and for suspected bleeding, swelling of arteries and tumours;

> Chest scans to assess lung and heart conditions;

> Abdominal scans in conditions affecting the liver, gall bladder, spleen, pancreas, intestines;

> Pelvic scans in conditions affecting the female reproductive tract and intestines;

> Blood vessel scans to assess blood flow in various parts of the body;

> Bone scans in conditions affecting bone;

> Guide for biopsies;

> Planning for radiotherapy; and

> Monitoring effects of treatment.

Risks

The exposure to radiation during a CT scan is generally at levels that are safe and insufficient to cause harm to a patient.

A report from the Clinical Advisory Committee on Diagnostic Imaging of the United Kingdom estimated that a typical CT scan of the abdomen or pelvis of everyone in the population would lead to a theoretical lifetime risk of radiation induced fatal cancer of about one in 2,000 (0.05%). This compares with the normal spontaneous risk of fatal cancer of about one in four (25%).

As with all things in medicine, one has to always consider the benefits and the risks of any intervention. If a CT scan is used in the diagnosis of a medical or surgical condition or to monitor treatment, the benefits will outweigh the potential risk.

However, if one has no symptoms, the risk of a CT scan increases because it may lead to additional tests which are unnecessary. As CT scans are not 100% accurate, there is also the possibility of undue alarm or false reassurance.

The benefits and risks must always be considered before having a CT scan. Doctors recommend that CT scans are done for medical reasons only and not for screening purposes.

Category: Milton's Corner
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