22 Dec 2011
By: LEA WEE
Getting a magnetic resonance imaging (MRI) scan can be a traumatising experience, which some have described as being pushed into a coffin alive.
The patient lies on a moving table, which slides into a dark narrow bore or tube. There, he has to keep still for 30 minutes to an hour as he is bathed in a magnetic field which creates images of the insides of his body.
He needs to wear earplugs because the machine makes hammering sounds of up to 120 decibels, as loud as that of the engine of a plane during take-off.
But at least one hospital here has a new American-made MRI machine which allows patients to sit back in a reclining chair.
This machine, which is smaller than a full-body scanner and has a smaller magnet, allows them to have their limbs scanned in a cosy well-lit room. The process is also less noisy.
Unlike previous MRI machines that scan extremities, the new scanner has the same magnetic field power, and can produce images just as sharp, as a full-body MRI scanner.
The Khoo Teck Puat Hospital (KTPH) will start using this new machine next month.
It hopes the new addition to its full-body scanner will shorten the waiting time for patients to have their limbs scanned.
About one quarter of the MRI scans at the hospital are for the extremities, said Professor Wilfred Peh, head and senior consultant at the hospital’s Department of Diagnostic Radiology.
From July last year to November this year, it has done more than 8,100 MRI scans, of which about 1,800 were on extremities.
Most are done to check the painful ankles and knees seen by the doctors at the hospital’s sports clinic, one of the biggest in Singapore.
MRI uses a strong magnetic field to create cross-sectional images of the body’s soft tissues and bone marrow. It can be used to diagnose injuries and tumours that may be found in the body.
With a full-body MRI machine, to have just the wrist or elbow scanned, the patient would still need to lie down with his upper body inside the tube and his arms outstretched towards the centre of the magnetic field.
The new scanner reduces the claustrophobia felt by one in 10 patients inside the narrow bore of the full-body MRI scanner.
The new scanner can scan all parts of the arms and legs but not the shoulder and hips.
It is suitable for patients with limb injuries, who are relatively fit and prefer to sit in a chair rather than lie on a table. It is also suitable for those with back problems and who may have problems lying down for more than 30 minutes at a stretch.
And as the new scanner is only a third of the size of its predecessor, it can be housed in a smaller room. A family member can sit with the patient and keep him company.
Prof Peh said: “This can help make the patient less anxious and reduce his risk of moving excessively, which will affect the quality of the image.”
A family member can also keep the patient company when a full-body scanner is used but the long bore of the magnet often poses a barrier to communication, he said.
Scanning an extremity using the new scanner would cost the same – about $800 – as scanning it with the full-body scanner.
The new machine, by General Electric, costs between $900,000 and a million, half the price of the full-sized scanner, and is currently used in at least 15 centres in Europe and the United States.
Although extremity scanners have been around for a decade, their magnetic field strength has been limited to 0.1 to 0.3 tesla (a unit to measure magnetic field strength), thus resulting in low-quality images.
The new scanner is a technological breakthrough. It has a magnetic field strength of 1.5 teslas, equal to that of the standard full-sized MRI scanner, said Prof Peh.
In recent years, advances have also been made for full-sized scanners. Now, some of them have a magnetic field as strong as 3 teslas, which produces even sharper images.
They also come with a bigger bore which measures 70cm in diameter, instead of the usual 50cm to 60cm.
KTPH has acquired one such machine and will start using it in February next year, in addition to its existing 1.5-tesla machine.
The National University Hospital started using its 3-tesla machine in January this year.
The hospital already has two 1.5-tesla machines, but has no plans to acquire an extremity scanner for now.
A spokesman said: “A 3-tesla scanner can help those with anxiety and mild claustrophobia.”
Those who require MRI scans of their lower limbs can have their upper body outside the scanner, just as they would if they were using an older full-body MRI machine, she added.
The Singapore General Hospital, too, started using its two 3-tesla machines a couple of years ago. It has three other 1.5-tesla full-body MRI scanners.
The hospital may consider an extremity MRI scanner if there is a growth in demand for MRI scans of the limbs over other parts of the body, said Dr Chan Lai Peng, a senior consultant at the department of diagnostic radiology.
She said: “For now, however, we prefer to have an MRI scanner that is more versatile and can scan all parts of the body.
“In some centres, radiologists and surgeons are moving towards imaging small joints like the wrist at 3 teslas as it gives better details.”
Email: leawee@sph.com.sg
Click for jpeg format
« Back to previous
page
back to top