In their experiments, the scientists magnetised a water droplet inside an MRI scanner. The researchers claim they could detect even the tiniest variations of the magnetic field strength within the droplet. These changes were said to be up to a trillion times smaller than the 7T field strength of an MRI scanner.
"Until now, it was possible only to measure such small variations in weak magnetic fields," said Klaas Prüssmann, Professor of Bioimaging at ETH Zurich and the University of Zurich.
To measure the variations, the scientists had to incorporate a digital radio receiver into a high precision sensor.
"This allowed us to reduce background noise to an extremely low level during the measurements," explained doctorate student Simon Gross.
In the case of nuclear magnetic resonance (NMR), radio waves are used to excite atomic nuclei in a magnetic field. This causes the nuclei to emit weak radio waves of their own, which are measured using a radio antenna.
The scientists have to position the sensor close to the water droplet but as the radio antenna is made of copper it becomes magnetised in the strong magnetic field, causing a change in the magnetic field inside the droplet.
The researchers therefore cast the droplet and antenna in a specially prepared polymer so that its magnetisability matched that of the copper antenna. In this way, the scientists could eliminate the detrimental influence of the antenna on the water sample.
"The new sensor is so sensitive that we can use it to measure mechanical processes in the body; for example, the contraction of the heart with the heartbeat," Gross described.
Direct measurement of all three nuclear spin components could pave the way for future developments in NMR spectroscopy for applications in biological and chemical research.
