Magnetic resonance guided focused ultrasound (MRgFUS) ablation procedures have provided relief for thousands of women with uncomfortable uterine fibroids. Now researchers are hoping to apply this non-invasive outpatient procedure to more malignant problems, such as liver cancer, in the near future.
ExAblate 2000, from GE Healthcare and InSightec, integrates Magnetic Resonance Imaging (MRI) with focused ultrasound energy.
The procedure has already proved successful in the removal of benign uterine tumours around the world and at St Mary’s Hospital and Imperial College London, where it is being tested. However, the procedure has yet to be approved for coverage under the National Health Service, although it has been approved by the Food and Drug Administration in the US.
ExAblate 2000 is also undergoing a trial to treat liver cancer at St. Mary’s Hospital Paddington, but the researchers said that adapting the MRgFUS technology for liver treatments is a tricky task.
The technology works by directing high intensity focused ultrasound waves into the body at a specific tissue via a transducer. At the focal point, the ultrasonic ‘beam’ brings the temperature of the targeted tissue to 65-85°C, which destroys the damaged tissue.
The thermal imaging capabilities of the MRI scanner provide three dimensional, real-time images and a temperature map of the targeted tissue, so that a physician has a high degree of control over the outcome of the therapy.
While capturing an MR image of uterine fibroids has been successful, Lynn Golumbic, director of marketing at InSightec, said the liver’s constant movement makes imaging difficult.
‘You take a picture of a liver in one position and then it might move,’ she said. ‘We can’t exactly stop it, but what we can do is stop the breathing for short periods of time so we can treat this.’
Another problem with MRgFUS technology being applied to the liver is that bones absorb ultrasonic energy and much of the liver is located between the rib cages.
Golumbic said the liver is just one example of the design challenges that researchers at InSightec’s headquarters in Israel are facing when trying to apply this technology to various body organs.
‘We have clinical trials going on right now for brain tumours. We also have liver and breast, and we are also developing some technology in order to treat prostate cancer,’ she said. ‘The list is really unlimited but the question is how to develop the combination of the hardware and the software to reach in to all these things.’
Golumbic said that getting the technology to its current stage has been challenging enough.
‘While the concept of focused ultrasound has been around for close to 60 years,’ she said, ‘the idea never really caught on as a clinical modality because there was no way to visualise what was going on inside the body.’
When some of these visualisation techniques developed, especially MRI, researchers such as those at GE Healthcare started to study the idea of combining MRI and ultrasound technology.
According to Dr Yoav Medan, vice-president for advanced development at InSightec, the biggest challenge in designing the MRgFUS device was trying to work out a way to include electronic technology in an MR environment.
‘It is a challenge because it is very easy to ruin a MR image if you put electronics in the room,’ he said.
Medan said that, to get around this technical hurdle, engineers used amplifiers and a synchronisation mechanism with the MR operation.
The only other option for engineers might have been to replace the MRI with another imaging technology, but Medan said InSightec researchers quickly scrapped that idea.
‘There are systems on the market that are ultrasound guided with ultrasound imaging to guide the ultrasound therapy,’ he said. ‘But from a safety point of view, safety to the patient, and from a mobility point of view, it is inferior to MR because with MR not only do we get 3D real time imaging, we also get the temperature map.’
InSightec was founded in 1999 when GE Healthcare (then GE Medical Systems) and Elbit Medical Imaging transferred their proprietary technology to the company to enable it to concentrate on developing the MRgFUS surgery both companies had investigated.
Golumbic said InSightec first carried out clinical research with MRgFUS on breast cancer, but the idea of marketing the technology as an alternative to breast cancer surgery was jettisoned.
‘In order to commercialise a product like that would take so long,’ she said, ‘so we started looking at something more benign that had a very large prevalence, so it affected many people.’
The company decided to focus on treating uterine fibroids because they are the most common tumours found in women and are the number one cause for hysterectomies.
Golumbic said more than 2,000 patients have been treated with ExAblate 2000 at 35 installations around the world.
‘It’s slowly picking up and the reasons are obvious — because if you can go and have a non-invasive treatment that enables you to go back to work and back to normal life immediately, why wouldn’t you?’ she said. ‘With traditional surgery, most of your recovery time is spent recovering from your incision. With this, we are treating the problem while letting you get on with your life.’
MRI combines with focussed ultrasound to treat benign tumours in a non-invasive way.