We can’t hear sound waves of frequencies above 20 kilohertz. Such sound waves, called ultrasound, are traditionally used in imaging foetuses. The ultrasound based diagnostics is fast, non-invasive, and relatively inexpensive. Unlike CT scans and MRI, ultrasound does not use any form of radiation. Many new applications of ultrasound, including cancer detection and brain imaging, are thus emerging.

Ultrasound scanning is commonly used for determining the nature of breast abnormality, and a supplement of mammography for cancer screening. Ultrasound-guided biopsy is used where ultrasound can’t characterise the nature of breast abnormality. The University of Washington researchers claim that for young women, targeted breast ultrasound is safe, reliable and cost-effective alternative to invasive biopsies.

The neurosurgeons at the University of Virginia are studying the ability of using MRI in conjunction with ultrasound to target specific areas of the body more precisely. Researchers at the University of Rome used “second look” ultrasound of the breast after MRI to identify lesions, which could not be detected by conventional mammography and “first look” ultrasound. This ‘second look ultrasound’ procedure can even give clues of malignancy or otherwise to the radiologist.

Ultrasound might provide a new, non-invasive way to control brain activity, writes Technology Review. Researchers of Arizona State University used ultrasound to treat neurological disorders such as deep-brain stimulation (DBS). DBS is used to treat severe cases of Parkinson's disease, dystonia and obsessive-compulsive disorder, and is an invasive procedure. The procedure delivers (via implanted electrode) electric jolt to the brain. Ultrasound gives better spatial focus than DBS, say the researchers. The use of high-intensity, high-frequency ultrasound (HIFU) to essentially burn away uterine fibroids has now been developed. HIFU based technique for treating brain and breast tumours, and prostate cancer are also being developed.

A team of researchers at the Uni­versity of Zurich’s Children’s Hospital used ultrasound to treat neuropathic pain patients. Neuropathic pain is a type of pain, which is caused by damage to or dysfunction of the peripheral or the central nervous system (brain and spinal cord). The transcranial MR-guided focused non-invasive system promises to replace the conventional invasive therapy, which includes drilling a hole in the skull and inserting an electrode in the thalamus. This procedure app­ears to be quite safe as it avoids infection, hemorrhage, and collateral damage to normal brain structures.

One of the challenges of ultrasound technology is targeting the brain in controlled manner. The idea is to send sound waves through the skull. There is no problem in sending ultrasound (frequency ranging from megahertz to gigahertz) through soft tissues. The problem arises when it is passed through the skull as bone gets heated due to the absorption of the ultrasound wave and thus tends to liquefy it.

Ultrasound of frequency less than one megahertz can pass through the skull, say the researchers of Brigham and Women's Hospital in Boston. But “lower the frequency, more difficult it is to focus the energy on a particular point in the brain”. Scientists are generating detailed images of the skull using CT scan and MRI to guide sound waves to the precise site. Instruments companies are also developing capabilities to specifically and precisely target ultrasound energy to the desired site.

The writer is a biotechnologist and ED, Birla Institute of Scientific Research, Jaipur