Fast magnetic resonance imaging of intracerebral metastatic disease

The appearance of intracerebral metastases imaged with a multi-slice fast imaging sequence (FLASH) is described. Images were obtained using a Siemens 2.0 T Magnetom operating at 1.5 T. Results of the FLASH imaging sequence at different values of repetition time, different values of "flip angle" and different numbers of acquisitions are described both qualitatively and quantitatively. At low flip angles, both tumour and oedema appear brighter than surrounding white matter. Increasing the flip angle tends to make oedema brighter than both tumour and white matter and increasing the flip angle still further makes tumour and oedema darker than white matter. A major limitation of this technique is that the low flip angle images, in particular, suffer from low signal-to-noise ratios. High flip angle FLASH images have higher signal-to-noise ratios but show similar contrast behaviour to T1-weighted spin-echo images and are likely to be no better as a screening sequence for intracerebral metastases. All the FLASH sequences showed a sensitivity to changes in magnetic susceptibility. This made small intratumoral haemorrhages and basal ganglia "calcification" easier to detect than on spin-echo images but also caused susceptibility artefacts in images around the base of the skull.