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Title: Development of a 0.02 Tesla SQUID Based Benchtop MRI Scanner for Small Samples
Author: Rieger, Sebastian Walter
ISNI:       0000 0001 3518 5146
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2007
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This thesis describes the development of a 20 mT bench top MRI scanner with 25 mm field of view using a receiver based on a superconducting quantum interference device (SQUID). Applications include imaging of finger joints and small animal models. The very low field strength means that magnet costs are greatly reduced and the low fringe field means the system can be installed in areas not available to high field scanners. Also, chemical shift and susceptibility artefacts are negligible, and tissue contrast is potentially increased compared to high field. The imager uses a temperature stabilised, NdFeB permanent magnet with ferrite pole faces to minimise eddy current paths. The magnet does not require a power supply, so the short-term field stability is excellent, and there is no supply-generated interference. The instrument occupies an area of only 0.45 m2 and may be operated without any additional RF shielding. Proton NMR signals are received at 830 kHz using a tuned SQUID amplifier, cooled to 4.2 K in a low noise liquid helium cryostat. Measurements made in a shielded room show that the tuned SQUID receiver's sensitivity exceeds that of a conventional room temperature receiver coil, or an untuned SQUID magnetometer, by at least 6 times at the same frequency. When the receiver is located in the imager; the performance is degraded by magnetically coupled noise from room temperature components. However, this noise already approaches the level of magnetically coupled noise from imaged tissues, and further reductions would be possible by relatively simple modifications to the gradient sub~system. Even so, phantom images acquired with the SQUID receiver exhibit up to 4-fold SNR improvement compared to a room temperature coil, and in vivo-images of human fingers, acquired in less than five minutes, show a high level of anatomical detail with sub-millimetre in-plane resolution. Keywords: MRI, SQUID, bench top, low field, permanent magnet.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available