Aberdeen Biomedical Imaging Centre
Research Facilities: Novel MR Hardware
We have developed novel equipment to carry out our research on PEDRI free radical imaging, field-cycled MRI (FC-MRI) and continuous-wave MRI (CW-MRI) of solid materials. Many of these MR systems are unique in the world, and offer unprecedented facilities for research in these areas, an for their use in applications. The techniques themselves are described elsewhere on this site.
Field-Cycled PEDRI / FC-MRI Imagers
We have built two field-cycled MRI systems, both of which can be used for field-cycled PEDRI and for FC-MRI.
In our whole-body field-cycled MRI system, the detection magnetic field is provided by a permanent magnet which generates a vertical field of 59 mT. Just inside the bore of the permanent magnet is a resistive magnet, made from copper conductor in a saddle configuration.
When electric current is sent through the resistive magnet windings they generate a field of up to 59 mT, in opposition to the permanent magnet's field. In this way, switching on and off the current switches the total field in the centre of the magnet down and up in value, and the precise field value can be selected by choosing the correct current to send through the resistive magnet coils.
Our second-generation imager uses the same technique, but here the primary magnetic field is provided by a 0.45 tesla superconducting magnet. A resistive secondary magnet coil is again used to oppose the field from the primary (it takes an 880 Ampere current to do this!), but in this case it is also necessary to have a third magnet coil called an 'active shield' coil between the primary and secondary, in order to avoid eddy currents while switching the field.
In both systems the typical switching time between magnetic field levels is 40 ms, which is significantly shorter than the T1 relaxation times in most biological samples or in the human body.
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The whole-body FC-PEDRI system (with its screening covers removed) |
Second-generation 0.45T FC-PEDRI imager |
High-field CW-MRI System
Our CW-MRI equipment uses a 7 Tesla superconducting magnet, with an internal bore of 183 mm. The proton NMR frequency at this field strength is 300 MHz. In order to perform CW-MRI a coil assembly is used which comprises two solenoids and three gradient coils, all water-cooled. One solenoidal coil is used to generate the 'ramp' component of the applied field, parallel to the 7-tesla field. The other generates an amplitude-modulated field at about 1 kHz, used together with lock-in signal detection to improve the signal-to-noise ratio. The gradient coils are designed for CW (rather than pulsed) operation, and can generate continuous gradients up to 300 mT/m gradients. A birdcage resonator is used to apply CW RF to the samples. Imager control software runs on a PC and is written in LabView.
Contact: Professor D Lurie
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Prototype home-built gradient coil set used for CW-MRI |
300 MHz birdcage resonator used in CW-MRI system (i/d 50 mm) |
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7 Tesla superconducting magnet used for CW-MR |
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