The assessment of diagnostic image quality for MRI is considered. The assessment of three key image quality determinants is addressed: signal, noise and contrast. There is a distinction between random noise evaluation, for the calculation of the SNR, and structured noise evaluation for the assessment of image artefacts. Specific methods used are correlation techniques and the Wiener spectrum. Contrast is assessed by comparison of experimental data and theoretical predictions. For each assessment, the theory and method of the evaluation strategy are discussed. The discussion is illustrated with analysis results from commercial MR systems. The choice of analysis method and the subsequent derivation of quality indices are shown to be critical in respect of robustness and accuracy.

The spin-lattice relaxation rates (1/T1) were measured at 94.1 MHz for six peaks in the 19F NMR spectrum of the perfluorochemical blood substitute fluosol-DA, which contains a mixed emulsion of perfluorodecalin and perfluorotripropylamine. Each of these rates increased linearly with the percentage of oxygen dissolved in the emulsion. Relative values of the linear increase for different peaks established that, for perfluorotripropylamine in the mixed emulsion, the oxygen-fluorocarbon interaction is loosely but preferentially oriented in a manner similar to that previously established for other pure fluorocarbons. The uncertainty in the oxygen level estimated from T1 measurements is somewhat less than 5% O2 and it is thus established that quantitative non-invasive oxygenation measurements can be made to sufficient precision by this approach, using fluosol-DA and 19F spin-lattice relaxation.

Using CSF/protein solutions as models of vasogenic extracellular fluid, the concentration dependences of longitudinal and transverse proton relaxation rates have been measured at 37 degrees C and 100 MHz for the serum proteins, albumin, IgG, a 2.8:1 mixture of albumin and IgG and human serum itself. These measurements have been used to determine the sensitivity of proton relaxation rates to the amount and the type of the protein in oedema fluid, and to establish the significance of both of these factors in relation to a separation of vasogenic from cytotoxic oedema. An extension of the two-environment rapid-exchange model of solvent relaxation is presented, which accounts for the measurements on protein mixtures and which enables estimates to be made of the number and the transverse relaxation rate of water protons associated with the protein surface.

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The modification of the RF field distribution of a surface coil, which is brought about by both loading and skin effect conditions arising from the proximity of weakly conducting saline samples, is demonstrated. A procedure for the calibration of the depth of the spectral acquisition region in depth-pulse localized in vivo spectroscopy is shown to be acceptable.