Focused Ultrasound Treatment, Present and Future

Abstract

The discovery that ultrasound waves could be focused inside the skull and heated to high temperatures at a focal point goes back to 1944. However, because the skull causes the ultrasound waves to attenuate and scatter, it was believed that application of this technology would be difficult, and that it would be impossible to use this approach in the surgical treatment of intracranial diseases. Eventually, magnetic resonance image guided focused ultrasound (MRgFUS) surgery began being used to treat uterine fibroids, breast cancer and bone metastasis and locally confined prostate cancer. In the first ten years of the 21st century, new developments in this technology have been achieved, broadening the scope of practical application, and treatment is now being performed in various countries around the world. In 2011, third-generation transcranial focused ultrasound made it possible to use thermocoagulation and create intracranial lesions measuring 2 to 6 mm in diameter with a precision of around 1 mm. It was also possible to produce MR images which relay information of temperature changes in real time, enabling a shift from reversible test heating to irreversible therapeutic heating. This gave rise to the possibility of a minimally-invasive treatment with outcomes similar to those of conventional brain surgery. This method is paving the way to a new future not only in functional neurosurgery, but in cranial neurosurgery targeting conditions such as epilepsy and brain tumors, among others. In this paper, we describe the current state and future outlook of magnetic resonance image guided focused ultrasound, which uses computed tomography (CT) bone images in combination with MRI monitoring of brain temperature.

Keywords: blood brain barrier permeability; brain tumor; epilepsy; focused ultrasound; functional neurosurgery.

Fig. 1

Focused ultrasound. Description: Ultrasound waves are shown focused on the left thalamic Vim nucleus.

Fig. 2

No-pass region. Description: The black circle indicates air around the membrane, and the red circle indicates the membrane itself.

Fig. 3

Display of elements that are on, and skull area. Description: This shows elements that are operating, and the permeable surface area of the brain.

Fig. 4

3-dimensional position correction. Description: Sagittal or coronal images are used to correct in the superior/inferior direction (S/I), and axial or sagittal images are used to correct in the anteroposterior direction (A/P). Coronal or axial images are used to correct in the horizontal (left-to-right) direction.