Laser scanner gives 3D view inside tumours

时间:2019-03-01 12:01:01166网络整理admin

By David Robson (Image: Paul Beard) An ultrasound scanner that provides more detailed 3D images of the deformed blood vessels within a tumour could help doctors determine the boundary between cancerous and healthy tissue during surgery. The scanner uses a novel form of non-invasive imaging called photoacoustic tomography. This uses laser light to “twang” cells so they emit an ultrasound wave, which is then detected and used to form a 3D image. Existing ultrasound scanners capture images by aiming high-frequency sound waves at the body. These waves reflect whenever the density of tissue changes, for example at the boundary between muscle and bone. The resulting “echoes” are then used to create a picture. Such scanners are good at capturing images of high-contrast subjects like antenatal scans, but produce only low-contrast images of the inside of a tumour, because the density of blood vessels is similar to that of the surrounding tissue. Paul Beard and colleagues at University College London, UK, have now developed a high-resolution photoacoustic tomography scanner that offers a solution. This shoots very short pulses of non-harmful near-infrared laser light at a tumour. As the light is absorbed by tissue, the cells heat up and expand very slightly, creating an ultrasound wave that can then be detected by a sensor. The intensity of the ultrasound wave depends on how well the tissue absorbs the near-infrared radiation, which produces high-contrast images of blood vessels because haemoglobin is very absorbent at these wavelengths (see image, top right). “It’s very scalable,” Beard told New Scientist. “Our scanner is best suited to providing high-resolutions images at a short range, but the technique could be used to image tumours a few centimetres into the breast.” In order to convert the reflected ultrasound into a high-resolution 3D image the team had to create a new ultrasound sensor as well. This consists of a thin layer of a polymer sandwiched between two reflective layers. The outer layers only reflect certain wavelengths of light and the laser light used to penetrate a patient’s tissue shines straight through all three layers. The acoustic signal generated using the infrared is then picked up by the polymer layer. “This work demonstrates progress,” says Hao Zhang, an expert on medical imaging at Washington University in St Louis, US. “In my opinion, it is important for more precise quantitative measurements.” However, Zhang points out two potential problems. At the moment it takes a relatively long time to capture the image, while the laser scans each reflective surface. In addition, the sensor is flat making it difficult to scan images over curved parts of the body. But Jeremy Skepper, a physiologist at the University of Cambridge in the UK says the ability to image blood vessels at this resolution is very attractive. “It’s less expensive and more portable than other solutions,” he says. “It’s a powerful additional tool to the ones we already have.” Skepper also suggest that advances in laser diode technology could make the device highly portable in future. Cancer – Learn more about one of the world’s biggest killers in our comprehensive special report. More on these topics: