We have developed novel equipment to carry out our research on fast field-cycling MRI (FFC-MRI). Many of these MR systems are unique in the world, and offer unprecedented facilities for research, and for their use in applications. The techniques themselves are described elsewhere on this site.
In our first-generation whole-body field-cycling MRI system (shown below), the detection magnetic field was provided by a permanent magnet which generated a vertical field of 59 mT. Just inside the bore of the permanent magnet was a resistive magnet, made from copper conductor in a saddle configuration. When electric current was sent through the resistive magnet windings they generated a field of up to 59 mT, in opposition to the permanent magnet's field. In this way, switching on and off the current switched the total field in the centre of the magnet down and up in value, and the precise field value could be selected by choosing the correct current to send through the resistive magnet coils.
The typical switching time between magnetic field levels was 20-30 ms, significantly shorter than the T1 relaxation times found in most biological samples or in the human body.
The original 59 mT whole-body FFC-MRI system (with its copper RF screening removed)
More recently, we have built a whole-body FFC-MRI scanner based on a single-magnet design. The use of a single resistive magnet makes the pulse sequence more flexible, as the detection field can be altered as well as the polarisation and evolution magnetic fields. However, this flexibility comes at the expense of potential instability of the magnetic field during the detection period. Therefore, particular attention must be paid to the design and implementation of the control circuitry and the magnet power supplies.
|0.2 T whole-body magnet for FFC-MRI||0.2 T FFC-MRI system, including 3-axis square Helmoltz coils for environmental field correction|
|Service end of 0.2 T FFC-MRI magnet, showing water and electrical connections||Power supply cabinets (3 x 650 A) for 0.2 T FFC-MRI scanner (International Electric Co., Finland)|
In addition to the home-built scanners described above, we have a commercial bench-top field-cycling relaxometer (Stelar SMARtracer), capable of making T1 dispersion measurements from 10 kHz to 10 MHz proton Larmor frequency on small (~1 ml) samples.
|Our lab's benchtop field-cycling relaxometer|