Magnetic Resonance Imaging Systems Equipment Hardware Today and Tomorrow

MR is undoubtedly the most revolutionary imaging technology of the century. The clinical jsefulness of MRI has been widely accepted in the CNS, spine and certain body areas and the future vision of MR includes wide-ranging morphological and functional applications in cardiology, oncology, orthopaedics, obstetrics and sports medicine. In order to accommodate this wide range of clinical applications, Picker has developed the Vista MR2055 HP system which delivers maximum clinical imaging flexibility at field strengths from 0.5 Tesla to 1.5 Tesla and spectroscopic capability at 1.5 or 2.0 Tesla. Five primary subsystems are integrated to produce an MR imager capable of high resolution proton images in axial, coronal, sagittal or oblique planes. These primary subsystems include the magnet, gradient, radiofrequency and control subsystems which in turn are driven by a powerful, multi-tasking computer. Magnet: Superconductive magnet options include field strength variability between 0.5T and 2.0 Tesla. The magnet design provides a high degree of uniformity during imaging overthe imaging volume. Superconducting niobium titanium windings are immersed in liquid helium and thermally insulated by liquid nitrogen to maintain a stable operating temperature of 4.2? Kelvin. Electronically adjusted cryogenic and resistive shim coils maintain field uniformity during imaging sequences. When the magnet is at field liquid nitrogen boils off at 1.0 litre/hour and liquid helium at 0.5 litre/hour. The wide bore of today's magnets, 60 cm in the centre of the magnet, minimises claustrophobic effects. New active shield magnets reduce the fringe magnetic field by up to 95% and enable MR systems to be sited in locations previously thought impossible. Patient Couch: The patient couch is capable of both horizontal and vertical movement to facilitate easy patient loading and unloading. Patient positioning is by laser index and a single operator can easily manage patients of any size in or out of the static field. A decorative facade surrounds the magnet to make the environment pleasing to the patient. Safety features for the patient include a hand activated patient alarm, two way voice communication between the patient and the operator at the console, magnet bore illumination, ventilation and visual indications for cardiac and respiratory monitoring. Gradient Subsystem: The X, Y and Z multicore gradient coils are located between the shim and patient tube and a special mounting minimises acoustic noise. Gradient coils are designed to allow the best combination of linearity, switching rate and gradient strength to provide