Brain surgery uncut

A new approach to brain surgery avoids the use of the surgeon's scalpel and instead exploits advances in magnetic resonance imaging to guide an ultrasound intervention.

Neurosurgeon Daniel Jeanmonod of the Department of Functional Neurosurgery of the Neurosurgical Clinic at the University Hospital Zurich and Ernst Martin, director of the Magnetic Resonance Center at the University Children's Hospital Zurich have successfully demonstrated the safety and efficacy of a revolutionary surgical procedure. The method allows surgeons to carry out fully non-invasive brain interventions even on an out-patient basis using high-intensity focused ultrasound HIFU) guided by magnetic resonance imaging.

HIFU has been used for the treatment of uterine fibroids and tumours of the prostate gland for several years. However, its application to the brain through the intact skull for non-invasive neurosurgery seemed impossible. The researchers have successfully treated ten patients using transcranial HIFU since September 2008.

The HIFU system used, an ExAblate 4000, was developed by the team's cooperation partner InSightec, of Tirat Carmel, Israel, and operates in conjunction with a 3 Tesla high field GE MRI-scanner. The new technology thus opens up procedures for a variety of brain diseases including brain tumours.

The researchers explain that from start to finish, the surgical procedure is mapped out and monitored in real time by MRI, while the HIFU beams pass straight through the patient's skull and are focused within the brain into a point just 3-4 mm in diameter. This allows the surgeon to guide the ultrasound beam and to then ablate tumour or other diseased tissue at a very precise location in the brain. Ablation occurs as the ultrasound beam produced by 1024 transducers raises the temperature of the tissue through a sequence of "sonications", bursts of ultrasound lasting just 10-20 seconds.

The results can be seen on a live MR-temperature map as the ablation takes places. The procedure can last several hours but is performed without anaesthesia, which has two major benefits. First, the patient is fully conscious through the procedure and so can respond to requests to move or speak and so allow the surgeon to double-check that healthy brain tissue is not being damaged. Secondly, it avoids the pre-operative medication, the risks associated with anaesthetics, and reduces the time the patient must spend in hospital following surgery.

The study was carried out as a project within the National Centre of Competence in Research (NCCR) Co-Me (computer aided and image guided medical interventions), in the context of the Swiss National Research Program NCCR. The potential of non-invasive, transcranial MR-guided high-intensity focused ultrasound (tcMRgHIFU) is studied as part of the clinical work of the University Children's Hospital Zurich and the participating scientists ultimately hope to broaden the spectrum of completely non-invasive interventions for functional neurosurgery and for the treatment of brain tumours, stroke and various neurological brain disorders by targeted drug delivery.

Such a significant project relies on a multidisciplinary team and collaboration between the University of Zurich, ETH Zurich, through the Magnetic Resonance Center of the University Children's Hospital, the Department of Functional Neurosurgery of the Neurosurgical Clinic at the University Hospital Zurich, the Medical Image Analysis and Computer Vision Laboratory of ETH Zurich, the Institute of Neuroinformatics, ETH Zurich, and industrial partner InSightec Ltd.

Researchers are also investigating the possibility of using MR-guided HIFU to treat breast, liver, and bone cancers. They are also investigating the potential of cavitation, which can induce much higher temperatures in tissues.

In standard HIFU, the ultrasound wave propagates through the tissue, and is absorbed and its energy released as heat. If a sufficiently high temperature is induced in the tissue, coagulation occurs, the tissue is essentially cooked. At higher acoustic intensities, however, microbubbles can form, this is a phenomenon known as cavitation. Until recently, surgeons have been wary of triggering cavitation as the collapse of the microbubbles is unpredictable and can cause a damaging shock wave that might affect healthy tissue as well as the disease target. Finding a way to enhance HIFU ablation so that cavitation might be brought under control is now the subject of new studies.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.