Perthen, Joanna Elizabeth; (2003) Measurement of cerebral perfusion using magnetic resonance techniques. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Measurements of cerebral perfusion are increasingly made using magnetic resonance techniques. The two main MR approaches to perfusion measurement are bolus tracking and arterial spin labelling (ASL), and aspects of both are investigated in the research described in this thesis. Bolus tracking within the adult patient population is becoming common, but its use in young children has so far been relatively limited. Data collected in normal children less than 30 months old are used to assess the reliability and age dependence of perfusion measurements in early childhood. Deconvolution is generally regarded to be the most robust approach to the analysis of bolus tracking data. However, current deconvolution techniques are inappropriate in cases of severe cerebrovascular disease, and an alternative is the use of 'summary parameters' as indicators of tissue perfusion status. These parameters have many theoretical drawbacks, and the reliability of their use is investigated using numerical simulations. ASL techniques are advantageous in that they require no exogenous contrast agents, thus facilitating repeated measurements, and perfusion can potentially be quantified in absolute units. However, the size of the perfusion-related signal means that ASL sequence implementation is not straightforward. The implementation of the FAIR ASL technique at our institution is described, including a discussion of the problems encountered. Current ASL techniques suffer from many inherent problems, including low signal-to- noise ratio and sensitivity to arterial transit times. A new sequence, designed to ameliorate some of these issues, is proposed and implemented. The novel sequence is investigated in vivo, and through numerical simulation. Comparison with a standard ASL technique showed that the novel sequence does lead to improved signal-to-noise ratio and reduced transit times. However, significant problems with the sequence remain to be resolved, and potential solutions to these are described and discussed.

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