For Julia Robertson, the only thing possibly worse than being told she might have a brain tumour was having the scan to confirm the diagnosis.

Key points: Experts say the system of licencing MRI machines for Medicare rebates is distorting the market.

Experts say the system of licencing MRI machines for Medicare rebates is distorting the market. It means people with conditions like claustrophobia have to pay to use newer, wide-diametre machines.

It means people with conditions like claustrophobia have to pay to use newer, wide-diametre machines. The struggle to find wide machines eligible for bulk billing also affects the overweight and those in regional areas.

For people with serious illness who need an MRI scan, the process of having the scan can sometimes be the most traumatic procedure of all.

Magnetic Resonance Imaging (MRI) scans involve a patient being put on a bed and fed into a coffin-like narrow tube where patients lie perfectly still for about half an hour.

Ms Robertson's first MRI scan was the most distressing and came after the sudden onset of unexplained headaches and nausea.

"It feels like you can't breathe because you can feel your breath on your own face. I freaked out," she said.

Ms Robertson had to have a general anaesthetic to get through the scan.

"I didn't realise I was claustrophobic until I had my first MRI," she said.

"It can just add that extra layer of stress to what's already a pretty horrendous situation."

Specialists are worried people in regional areas or who are overweight need to travel long distances for bulk-billed MRI scans. ( ABC News: Alison Branley )

The mother-of-two was diagnosed with a rare brain tumour and needed surgery to have it removed.

A decade later, she still needs MRIs up to twice a year to check the tumour hasn't returned.

She frequently experiences what patients refer to as "scan-xiety": the anxiety related to the potential results of the scan mixed the experience of the scan itself.

"I still get really anxious in the days leading up to the scan," she said.

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Too many scans aborted: experts

The University of Adelaide Joanna Briggs Institute associate professor Zachary Munn looked at the issue of MRI claustrophobia after working in medical radiation.

He said Ms Robertson was not alone.

"When I was doing these scans, a lot of people people struggled," he said.

"People really did have a full-on panic attack where they would just crawl their way out."

His team found about two out of every 100 MRI scans were cancelled because the patient could not cope.

The researchers found many people continued to be haunted by the experience.

"They talk about experiences like being buried alive or placed in a coffin, and even thinking back on their experience can cause them pain," Dr Munn said.

In other cases, if the patient moved during the scan the final images were flawed and the scan had to be repeated.

Julia Robertson is not alone in her fear of MRI scans. ( ABC News: Supplied )

The stress experienced by patients such as Ms Robertson can be reduced if they go have their scans in newer machines.

These modern "wide bore" scanners have diameters of 70cm, compared to a width of 60cm in older machines.

Other new machines have things like openings at both ends, shorter scan times and can blow air over the face of patients, making the experience more tolerable.

However, Australia's system of licensing MRI machines for Medicare rebates mean patients are typically only bulk-billed when they go to older machines.

There can be waiting lists of up to six months to use these machines and patients often have to travel further to use them.

The Royal Australia and New Zealand College of Radiologists president, Lance Lawler, said the challenge faced by people with claustrophobia was just one example of the way Australia's system of licensing distorted the market.

"Its an issue of access," he said.

"It's less likely a new machine would have a licence because new licences are dished out infrequently."

No other scanning machine, such as a CT scanner or PET scanner, needs a government licence for Medicare rebates, he said.

Dr Lawler said it also meant older, licensed machines were constantly in use, while newer machines with better capacity sat idle.

"It puts more pressure on the people with licenced machines — they have to staff them for longer shifts."

Julia Robertson says claustrophobia makes her regular MRIs traumatic. ( ABC News: Marc Smith )

Children, overweight and regional patients suffer

Another unintended consequence of the licensing system, Dr Lawler said, was that some doctors referred patients for a CT scan instead of an MRI because it was easier to find one that bulk-billed.

This is a problem because CT scans involve a dose of radiation, compared to an MRI, which just uses magnets.

This puts patients, particularly children, at greater risk.

MRIs also produce a better quality image, meaning conditions were more likely to be accurately diagnosed.

MRI's at a glance: MRI's use magnetic imaging to produce high-quality scans compared to radiation-based scanners

MRI's use magnetic imaging to produce high-quality scans compared to radiation-based scanners There are 212 fully licensed MRI machines in Australia,157 partially licensed machines, and about 160 don't have a licence at all

There are 212 fully licensed MRI machines in Australia,157 partially licensed machines, and about 160 don't have a licence at all Licensed machines include 130 in NSW, 85 (Vic), 79 (Qld), 23 (SA), 33 (WA), 9 (ACT), 7 (Tas) and 3 (NT)

The college said patients in regional or remote areas who needed a bulk-billed MRI also had to travel longer distances.

The newer machines were then only available to those who could afford the out-of-pocket costs.

"It's not just in the rural and remote areas that access is a problem," Dr Lawler said.

"You can live in Sydney and be right next to a magnet, which is perfectly adequate for your needs, but you have to travel across the city to the next one which has got a licence."

A Senate inquiry last year heard upgrading some MRI machines with partial licences to bulk bill selected procedures, to full licences, would lost $150 million.

Licensing all MRI machines would cost $400 million

The College of Radiologists disputed those figures and said removing the licensing system would not lead to more MRI scans.

They argue it won't change the number of doctors who order MRIs or the number of people who need them.

Rather, they believe the work will just be distributed more evenly.

"All you're doing is spreading out the referrals over a wider number of magnets," Dr Lawler said.

Experts fear Australia's system of licensing MRI machines is distorting the market. ( ABC News: Alison Branley )

At the moment, 369 machines are licenced nationally, and 157 of those only have a partial licence, meaning they can only bulk bill scans for some conditions.

It's estimated about 160 are not licenced at all.

In a statement, a Health Department spokesman said they didn't take scanner width into account when it came to dispensing licences and a full list of bulk-billing machines was available online.

Ms Robertson said finding an appropriate facility to have the scan added further stress for people like her.