A closer look at nuclear scanners

A physicist is leading the Mater hospital's fight against cancer with the help of advanced diagnostic equipment, writes Dick …

A closer look: Paddy Gilligan, principal physicist at the Mater hospital's PET/CT Centre: 'It is fantastic to have all these tools'.
A closer look: Paddy Gilligan, principal physicist at the Mater hospital's PET/CT Centre: 'It is fantastic to have all these tools'.

A physicist is leading the Mater hospital's fight against cancer with the help of advanced diagnostic equipment, writes Dick Ahlstrom.

New knowledge and more effective treatments should flow from advanced new medical diagnostic equipment installed at the Mater Misericordia Hospital campus in Dublin. Ironically, the person responsible for making it all go is a physicist and not a doctor.

The development of medical equipment that utilises nuclear radiation has meant that medical physicists have had a role in the modern hospital context for decades.

New types of scanners have accelerated this process, however, according to the principal medical physicist at the Mater public and private diagnostic scanning centre, Paddy Gilligan. There was one physicist at the Mater when he joined 14 years ago; now there are about eight, mostly working in therapeutic nuclear medicine. He works on the diagnostic side and is in charge of the Mater's new PET/CT Centre. Installed at a cost of about €5 million, it handled its first patient last October 10th.

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"It has a very good resolution that can see very small objects," says Gilligan. "This thing can pick up the spread of cancer six months ahead of other modalities. This can help prevent unnecessary surgery."

The new scanner is the latest device to be installed there and joins existing devices including MRI, CT and Dexa scanners. There is also a new nuclear medicine suite where radioactive tracers are injected and clinicians can see 3D images and watch an organ functioning.

"I have been at the Mater for 14 years. It was a very exciting place to come to because it was very research-driven," says Gilligan. "There is an awful lot going on. You have to look at radiation safety for staff and patients, run checks on the equipment and help the radiographers set up scans."

The Mater was among the first hospitals in these islands to install MRI scanners and now is one of only three in Ireland with the new PET/CT device. It is actually two units in one, explains Gilligan.

The PET (positron emission tomography) element allows clinicians to watch tissues as they function. The CT (Computed Tomography) scan adds valuable information to the functional test so the tissues, particularly cancers, to be studied can be seen in position among other tissues.

The new scanner only began coming into service in 2001 so it is very new, says Gilligan. It is one of the most advanced cancer diagnostic systems of its kind in the world and is particularly valuable for diagnosing lymphoma, lung tumours, melanoma, oesophageal and colorectal cancers.

While a CT scanner can show whether a tumour has got bigger or smaller, a PET/CT can detect if the cancer cells are dead or active. The device can provide an early diagnosis of Alzheimer's disease, even before clinical signs are present. It can also be used to study scarring and heart muscle tissue death post-heart attack.

The technology involved is very advanced and relies on the science surrounding particle physics and nuclear radiation, says Gilligan.

It starts with a tracer called fluorodeoxyglucose (FDG), which combines a mildly unstable isotope of fluoride 18 with conventional glucose. Rapidly dividing cancer cells have a higher sugar demand than normal tissues so the FDG when administered tends to accumulate at higher levels in tumours.

The F18 isotope has a half-life of only 110 minutes so it degrades rapidly. As it decays it releases positrons, antimatter electrons which quickly encounter nearby normal electrons. They immediately annihilate one another to release another form of radiation, gamma rays.

These rays are detected by the PET/CT scanner which uses them to build up a picture of the tissues it is imaging. Because there is more F18 in the tumour cells, these stand out from surrounding tissues and the radiographer can get an extremely clear view of the tumour and its position in the surrounding tissue, explains Gilligan.

"It is fantastic to have all of these tools," he says. They are needed for frontline patient care but they "also allow us to do research for the future", he adds.

The Mater runs an MSc programme for radiographers that encourages them to do research using the devices in the centre.

"Not only does it bring benefits in gaining new knowledge, but it can also improve clinical treatments for the patients," Gilligan says.