PTB unites magnetic resonance and radar technology in one prototype

Don't move a muscle! Patients certainly have to take this request to heart if they have to lie in a magnetic resonance tomography (MRT) device – otherwise movement artefacts result on the images produced by the MRT.

These are distorting elements in the image which show the movement of the body, but not the body itself. Movement is a disturbing factor which leads to blurring and “ghosting” in the MRT image. Patients, however, have to have not only a lot of patience but also endurance, as a magnetic resonance imaging (MRI) test can take up to 30 minutes. But even if the patient does not move once during the whole time, movement artefacts cannot be ruled out.

Some parts of the body are always moving – for example the lungs expand when you breathe in and the chest goes up and down. The movement of the heart muscle also leads to distortions in the image – as it changes shape during the pumping cycle. With the aid of an ultra-broadband radar device, these vital movements during measurement can be taken into consideration and the MRI measurements can be corrected.

The joint use of both technologies is being tested with the aid of a prototype developed at the Physikalisch Technische Bundesanstalt (PTB, Germany's national metrology institute), which arose in co-operation with Ilmenau University of Technology. This project is funded by the Deutsche Forschungsgemeinschaft (DFG, the German Research Foundation) in the frame of a priority programme running for six years.

The interdisciplinary research project ultraMEDIS within the DFG priority programme 1202 “Ultra wide-band radio technologies for communication, localisation and sensor technology” is aimed at using ultra-wideband (UWB) radar techniques for the detection of tumours, as well as for navigation technology in magnetic resonance (MR) imaging.

Ultra-wideband electromagnetic pulses (spectral bandwidth up to 10 GHz) generated by an UWB radar and transmitted by an antenna are able to probe the human body with low integral power (~ 1 mW), because electromagnetic waves can propagate through the body and are reflected at interfaces between materials with different dielectric properties. The receiving antenna detects the reflected signals coming from different depths of the body.

The high temporal and spatial resolution of radar sensors, their compatibility to existing narrow-band systems, the low integral power of the probing signals and their ability to penetrate objects are thereby exploited. Especially the latter one is the very property which makes UWB radar so attractive for medical applications.

At PTB, a demonstrator for the evaluation of the principal feasibility of an MR-UWB combination has been realised [1, 2]. With an MR-compatible UWB radar, the characteristic landmarks of the heart muscle during breathing could be followed without disturbing the actual MR measurement. Thus both, a real-time adjustment of the MR frequency according to the current position of the heart or a retrospective position correction of the MR data could be carried out.

The Project is carried out in cooperation with the Technical University of Ilmenau and with medical partners from University of Jena, whose special attention lies on tumor detection.