Nuclear Magnetic Resonance for Diffusion Imaging Development and evaluation of spin-echo-based pulse sequences for in vivo studies of water self-diffusion

Sara Brockstedt

Research output: ThesisDoctoral Thesis (compilation)

Abstract

The interest in diffusion imaging with nuclear magnetic resonance techniques has increased during the last few years. The main reason is the possibility of early diagnosis of acute ischaemic stroke, at a time when conventional MR techniques and computerised tomography fail. The purpose of this study was to develop and evaluate methods for the measurement of water self-diffusion <i>in vivo</i> using magnetic resonance imaging (MRI). The main objective was to design pulse sequences that allow quantification of the diffusion coefficient, and provide diffusion-weighted (DW) images of high quality. DW-MRI is highly sensitive to macroscopic motion, which causes severe image artifacts and makes quantification difficult. This problem was addressed through pulse sequence design and image post-processing techniques. The use of first-order motion-compensating diffusion-encoding gradients in combination with DW spin-echo (SE) imaging proved to increase image quality and accuracy in quantitative data. Further more, quantitative diffusion imaging was found to be possible with fast-SEs, a method that does not require any high-performance gradient systems. Using a segmented echo-planar imaging (SEPI) technique high-resolution DW-images and ADC maps were obtained, showing no proof of susceptibility artifacts or geometrical distortions, problems normally associated with EPI. Navigator-echo phase-corrections were found to reduce motion artifacts present in images obtained with SE, FSE and SEPI techniques. The use of electro-cardiographic triggering for DW-EPI was also evaluated, and found to be relevant in quantitative measurements. Assessment of the perfusion fraction <i>in vivo</i> from DW-images might be helpful in diagnosis and characterisation of acute stroke and can be performed whenever enough data are available. Finally, the performance of DW-SE and DW-EPI for diagnosis of ischaemic stroke in the acute phase was evaluated. DW-EPI and DW-SE in combination with ADC maps were compared with respect to diagnostic accuracy. It was found that although DW-SE methods suffer from limited diffusion sensitivity and limited numbers of slices, it can be used for diagnosis of acute stroke, but ADC maps are essential in discriminating between acute and chronic infarcts.
Original languageEnglish
QualificationDoctor
Awarding Institution
  • Medical Radiation Physics, Lund
Supervisors/Advisors
  • [unknown], [unknown], Supervisor, External person
Award date1998 Nov 26
Publisher
ISBN (Print)91-628-3234-4
Publication statusPublished - 1998

Bibliographical note

Defence details

Date: 1998-11-26
Time: 09:15
Place: Föreläsningssal F1, Centralblocket, Lunds Universitetssjukhus, Lund

External reviewer(s)

Name: Ericsson, Anders
Title: Docent
Affiliation: Institutionen för onkologi, radiologi och klinisk immunologi, Uppsala Universitet. Akademiska sjukhuset, Röntgendivisionen, 751 85 Uppsala

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Subject classification (UKÄ)

  • Radiology, Nuclear Medicine and Medical Imaging

Keywords

  • perfusion fraction
  • electrocardiographic triggering
  • segmented EPI (SEPI)
  • echo-planar imaging (EPI)
  • fast spin-echo (FSE)
  • spin-echo (SE)
  • navigator echoes
  • phase corrections
  • diffusion
  • Magnetic resonance
  • MRI
  • ischaemic stroke
  • Medicine (human and vertebrates)
  • Medicin (människa och djur)

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