Farman Ali of the Chalmers Department of Signals and Systems, Division of Biomedical Engineering and the Department of Microtechnology and Nanoscience -- MC2, will present his masters thesis "Rapid heating and cooling of superconducting films with infrared lasers for ultra low field magnetic resonance imaging".
Date: Wednesday 18th of January 2012
Time: 10:00-11:00
Place: Luftbryggan, Department of Microtechnology and Nanoscience -- MC2, Kemivägen 9, Chalmers Johanneberg Campus
Abstract:
Ultra low field magnetic resonance imaging (ULF MRI) is a promising technique in medical imaging. It is still in its initial stage of experiments around the world. Unlike normal MRI (1.3-3 tesla or higher), ULF MRI works in extremely low magnetic fields in the range of micro tesla. The weakness of this low field limits the output signal on magnetic field sensor and leads to a very low signal to noise ratio (SNR). In order to increase the SNR researchers uses pre-polarizing pulses. The high transition temperature Superconducting quantum interference device (SQUID) is an ultrasensitive magnetic field sensor this is the heart of our ULF MRI system. Our SQUIDs are fabricated from high transition temperature superconducting films, in particular, YBCO that has a high tendency to trap flux when exposed to strong magnetic fields. Flux trapping together with the Meissner effect can be used for magnetic levitation, and is very useful in many applications. However, this phenomenon is problematic in the case of ULF MRI use. The pre-polarization pulses that are applied to the sample in order to optimize the SNR of ULF MRI system induces flux trapping in the SQUID sensor i.e. pinning vortices in it, that result noise in the signal and dramatically reduces sensitivity.
Therefore, the purpose of this project is to minimize the negative effects of flux trapping on our SQUIDs. The end goal is the demonstrated capability to heat the SQUID above its critical temperature with an Infra red laser pulse and subsequently cool it within a few milli to microseconds.
