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31 Jan 2007



Ever since 1895, X-rays have been used by doctors to detect problems in the body. It took up to eleven minutes to complete a head X-ray then, a procedure that would now take only a few seconds.

Now, medical imaging is used so often that over 400,000 radiology scans were done last year at Singapore General Hospital alone. This includes X-ray tests, CT, MRI, ultrasound and PET scans. All these imaging techniques are used to look inside the body.

Imaging is so vital to cancer treatment that the Ministry of Health will be allowing cancer patients to use Medisave to pay for CT and MRI scans from probably the second half of this year. A 23-year-old student at the National University of Singapore who has lung cancer said that "Medisave will help so that we don't have to come up with cash".

A CT scan can cost anywhere from $300 to $1,300 while a MRI scan costs $500 to $1,900.

Radiology exams such as CT and MRI have been integral in the treatment of patients when making a diagnosis and looking at the spread of cancer, adds Dr Khoo Kei Siong, a consultant medical oncologist at Gleneagles Hospital.

Dr James Khoo, head and senior consultant at the oncologic imaging department of the National Cancer Centre, adds: "For surgical planning or radiotherapy planning, it is important to determine whether vital structures such as blood vessels, nerve and bone can be preserved.

"In follow-up imaging, we determine how the tumour has responded to treatment. Has the tumour been eradicated or is there a hint of residual disease? This is not an easy task and it is best undertaken by radiologists who are familiar with cancer imaging."

Medisave will only cover CT and MRI scans for cancer treatment, as MOH feels that the usage of diagnostic scans is easily abused. However, clinicians, radiologists and radiographers use other procedures to detect and treat various conditions.

Radiologists are medical doctors while radiographers are trained to operate the scanners. Many decisions depend on the judgment of radiographers and radiologists.

"We are essentially medical detectives," says Dr Tan Bien Soo, a senior consultant radiologist with the department of diagnostic radiology at Singapore General Hospital.

While a clinician might request a chest X-ray for a patient who has broken a few ribs, a radiologist might decide that a more specific view of those ribs would be more helpful. The X-ray beam would be aimed specifically at that area.

When to do a scan and what machines to use are also important decisions made by radiographers and radiologists with clinicians. Cost will limit the choices available for some patients, forcing specialists to decide how to be most cost effective.

Doctors have many more options now as medical imaging has greatly progressed.

CT scans, which were invented in 1972, used to require hours to take a picture of one "slice", or cross-section of the heart, and then reconstruct it into an image.

Now CT technology can take images of 64 slices of the heart, or more, in just a few seconds. These slices can be reconstructed into a 3D image of the heart.

Even clearer and more detailed are MRI images, a better choice for detecting a brain tumour.

Radiologists are not only detectives but also the "gatekeepers of radiation", according to Dr Kwek Boon Han, a consultant radiologist at Asia Health Partners.

While the radiation dosage used in X-rays, CT and PET scans are small enough to pose almost no risk of tissue damage to the patient, radiologists still need to be careful when deciding how frequently to perform one of these scans on a patient.

Pregnant women are advised not to undergo any of these scans unless absolutely necessary, as there is a risk of doing damage to the foetus.

A radiologist might do an MRI on a patient who has been undergoing frequent CT scans, as MRI scans hold no risk of tissue damage or cancer for the patient.

According to research done at Columbia University, having a full body CT scan gives you a 1 in 1,200 chance of getting cancer. This suggests that if you have a full body CT scan every year for 30 years, your chances of getting cancer are as high as 1 in 50.

But Dr Khoo Kei Siong says that patients frequently have four or five CT scans a year that look only at a specific area of the body and this is not known to have negative long-term effects.

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Last Modified Date :26 Sep 2013