ABSTRACT
The interest focused on the signal-to-noise ratio comes from X-ray CT, where the only way of increasing the sensitivity is to increase the S/N ratio or to inject a contrast medium. In NMR examinations pulse sequences can be manipulated to achieve the same goal by highlighting the features of interest. High-field systems are supposed to have the advantage of shorter measuring times, which in turn is expected to give more rapid patient throughput. The time needed to produce an image depends on the product of pulse repetition time, the number of pulse repetitions per image scan. The use of low fields offers some practical advantages in installation and patient handling. The low field allows the system to be operated in the vicinity of ferromagnetic materials and with ferromagnetic materials in the patient. Trace amounts of paramagnetic metal ions have been shown to reduce the relaxation time of nuclei in the surrounding environment due to the strong electron-nuclear magnetic moment interaction.
