Holography Goes Brainy.
Researchers at the Polytechnic University of Valencia in Spain have developed a technique for 3D printing holographic lenses that focus ultrasonic sound waves in the brain. It is hoped the new concept will lead to low cost brain imaging and potentially improved drug delivery.
Ultrasound is an acoustic wave that is widely used in diagnostics and for imaging soft tissue and is frequently used to monitor the developing foetus. Furthermore, it can also be used as a non-invasive therapeutic technique to destroy cancerous tissue. However, in the case of the brain, this method is unsatisfactory as the skull blocks and distorts the ultrasound, thereby preventing focus on brain tissue.
In the past researchers have tried using phased arrays to control the incoming ultrasound to correct for aberrations on penetrating the skull but these have a number of disadvantages as well as being costly. Using a new approach researchers have produced a 3D printed plastic lens that can generate complex patterns and diffract ultrasound waves. When the ultrasound waves interfere, a hologram is produced which enables the ultrasound beam to refocus thereby penetrating the skull, allowing it to effectively target brain regions and image more clearly.
The researchers developed a multi-step process to test their approach involving the use of X-ray images from computerised axial tomography (CAT) scans. They then examined soft tissue information from the brain itself, using data from magnetic resonance imaging (MRI) which allowed them to produce a computer model of the patient's skull and brain. The team then devised a method to bend ultrasonic waves inside the skull prior to modelling the sound waves required to create an ultrasonic hologram within the brain.
Finally, using the previously acquired CAT scan and MRI data, they manufactured a 3D printed skull phantom (a realistic brain replica), which they used to test the holographic lens. The data they obtained from the skull phantom showed good agreement with theory and simulations.
It is hoped that this new approach will lead to low cost therapy and brain imaging. Moreover, the approach could also have implications for new drug delivery techniques. For example, it has the potential to observe the blood-brain barrier, which typically blocks therapeutic drugs in the treatment of Alzheimer's disease.