Recently, cancer patients were told they can withdraw a few hundred dollars each year from their Medisave accounts to pay for scans.

This, to me, is recognition of the important role that imaging scans play in cancer management - from diagnosis and determining its stage to evaluating treatment response and follow-up surveillance.

When a doctor suspects cancer, some form of imaging will be needed.

There are several types of scans or radiological investigations. The most basic is the common X-ray - like a chest X-ray or abdominal X-ray. But these have limitations: The images are two-dimensional, so many abnormalities may be hidden.

Then, there are more sophisticated imaging tools such as CT (computer tomography) scans.

Today, the use of CT scans is common. But it was not so when I was a medical student in the late 1970s. The first CT scan was just being introduced at Singapore General Hospital. To order a CT scan was such a big deal. I still remember waiting in line to see the overloaded Head of Radiology to justify, on behalf of my clinical consultants, why the patient needed a CT scan.

Things have since changed. There must be at least 50 CT scanners in Singapore. Every hospital, big or small, public or private, will likely have a few CT scanners.

In the 'bad' old days, no one would consider a CT scan for suspected acute appendicitis. But some surgical colleagues say they now use a CT scan to confirm an appendicitis before proceeding with surgery.

The big advantage of a CT scan is that it allows us to 'see' the insides of the body three-dimensionally. I often explain to a patient that it allows us to digitally slice up the body - like cutting a loaf of bread. Once the loaf is sliced, we can see whether the bread has been properly baked or is full of holes within.

The CT scan allows us to check the body for abnormalities. For lung cancer, the CT scan allows us to see the cancer in the lung and determine whether it has spread to other parts, like the lymph nodes, the liver or the brain.

A third type - the MRI (Magnetic Resonance Imaging) - also allows us to look inside the body. But the difference is that it uses magnetic waves instead of X-rays to create the images.

The latest addition to our repertoire of machines for medical imaging is the PET-CT scan. PET stands for positron emission tomography.

As an oncologist, I find such scans invaluable.

I remember a patient who came to see me for a second opinion. She was found to have what was thought to be a tumour in the lung, as shown by a chest X-ray and a CT scan during a routine check-up. Despite a normal biopsy, there was concern as to whether this was a cancer (Sometimes, cancers are missed because of sampling errors). Her oncologist suggested surgery to have the 'tumour' removed.

I suggested instead that she go for a PET-CT scan. I referred her to Hong Kong for this, since it was not available in Singapore at that time.

Thankfully, the lung tumour did not 'light up' like a cancer. The interesting twist to the story was that the PET-CT scan picked up a small tumour in her breast. This was surgically removed and to this day - more than five years on - she has remained cancer-free.

If a patient has metastatic cancer, where a cancer spreads from its original site to another area of the body, many scans - CT, MRI and even PET-CT scans - are needed, which also document the full extent of cancer spread. After every two to three cycles of chemotherapy, the scans are repeated to assess the response to treatment.

But while there is no question that imaging plays an important role in medicine, it is the human factor that makes the real difference.

For example, scans guide the surgeon in his decision to remove a lump or not. Many women have breast lumps - the large majority of which are benign. In most instances, a good radiologist can help sort out which are benign and which are definitely cancerous. The benign ones can be left alone.

Some surgeons suggest having benign lumps removed 'for fear that the lumps may turn cancerous'. That is utter rubbish. Benign lumps cannot turn cancerous. The cancer can arise anywhere in the breast, so the only way to be sure one does not get breast cancer is to have both breasts removed.

Appropriate use of medical technology makes the real difference to the patient. At the end of the day, this is the province of good doctors, not super machines.

E-mail: angpt@parkwaycancercentre.com

The medical director of Parkway Cancer Centre has been treating cancer patients for nearly 20 years.

In 1996, he was awarded Singapore's National Science Award for his outstanding contributions to medical research.

He also recently published a book of patient stories, Doctor, I Have Cancer. Can You Help Me?, which has been translated into four languages.

This story was first published in the Mind Your Body supplement on Feb 27, 2008.