Overview
Topic status: We're looking for students to study this topic.
In Nuclear Magnetic Resonance (NMR), manipulation of spin magnetisation is achieved via a specified sequence of RF pulses, gradient pulses and delays (the pulse sequence). The pulse sequence used is determined by the nature of the intended measurement: For example, in measurements of transverse relaxation the Spin Echo pulse sequence is used, while measurements of longitudinal relaxation are done using the Inversion-Recovery pulse sequence. Different pulse sequences sensitise the NMR signal to different physical characteristics of the system (e.g., spin relaxation, diffusion, flow, microscopic alignment order...). The ability to selectively measure these characteristics enables NMR to be used for quantitative physical analysis of materials and tissues, as well as molecular structure determination.
For a pulse sequence to work correctly, its parameters (durations, amplitudes, phases and frequency offsets of the pulses and durations of the delays) must be set to the 'correct' values in order to select the desired coherence transfer pathway (CTP) to the exclusion of all other CTPs. In practise, setting the required parameters to their exact ideal values is not possible; as a result, the NMR signal inevitably contains some systematic errors. This, in turn, can result in distortion of the measured physical quantities (e.g. the diffusion coefficient). Some pulse sequences are less sensitive to the mis-setting of parameters than others. The more robust pulse sequences allow a relatively large window for parameter variation without significantly affecting the signal.For example, in the measurement of diffusion the double spin-echo pulse sequence is less sensitive to a mis-set duration of the RF pulses than the single spin-echo.
Hypotheses/Aims: Analysis of the performance of NMR pulse sequences in the presence of imperfect parameter calibration.
Approach: Using the quantum-mechanical density matrix formalism, the sensitivity of NMR signal to parameter variation will be analysed for commonly used NMR experiments with a focus on diffusion and spin relaxation measurements. The results of experimental NMR measurements of diffusion and spin relaxation will be used as the starting point for the theoretical analysis. General insight into pulse sequence performance will be gained from analytic density-matrix treatment, and numerical simulations will be used for verification of the analytic theory. The ultimate aim is the development of new robust techniques for the measurement of molecular diffusion and spin relaxation.
This is a fundamental research project with wide-ranging applications in clinical Magnetic Resonance Imaging, analysis of materials, molecular structure determination and chemical analysis. You will acquire knowledge of advanced quantum mechanics, numerical computational techniques and state-of-the-art experimental applications of magnetic resonance spectroscopy and imaging.
- Study level
- Honours
- Supervisors
- QUT
- Organisational unit
Science and Engineering Faculty
- Research area
- Contact
- Please contact the supervisor.
Dr Konstantin Momot
