In early 1980th magnetic resonance imaging (MRI) became utilized practically as a medical diagnostic instrument. MRI has several advantages over computed tomography (CT) in the evaluation of anatomy and pathology of human body. First, contrast resolution obtained by MRI surpasses that of CT, because, with MRI, several parameters such as T1 and T2 relaxation times, mobile proton density, and blood flow affect signal intensity and manipulation of tissue cotrast is achieved by highlighting differences in these parameters, and differences in density on CT is obtained only by attenuation differences of the X-ray beam. Other advantages of MRI include the ability to depict cross-sectional anatomy in any planes without patient manipulation, the lack of artifacts from bony structures and air, and the absence of ionizing-irradiation. Because of these capabilities, MRI has quickly evolved into the premier imaging tool for central nervous system including brain and spinal cord. In addition, usefulness of MRI has been recognized in the spine, heart and great vessels, pelvis and extremities and it will become one of the important diagnostic imaging methods in various organs and parts.
A brief review was made of the recent development of the high critical temperature oxide superconductors from the pioneering work by Bednorz and Muller to the liquid nitrogen temperature superconductor and the magnetic superconductors. The electronic structures and the superconducting properties were discussed from the experimental point of views. The problems associated with the critical current and the microstructures of the oxides were described.
A method of flow visualization in He II was developed by the use of H2-D2 solid particles and hollow glass spheres as tracers which were prepared to be neutral buoyant in He II. Streaks of tracers which follow the normal fluid flow enable us to see flow structure. It is of great importance in fluid dynamics to grasp a flow field as a pattern as well as to take a quantitative measurement. The thermal counterflow jet was investigated by means of this method. A motor-driven 35-mm camera was used to photograph each flow event. Some pictures are examined to recognize flow patterns and others to measure the flow velocity from the lengths of particle streaks. The jet evolution appeared depending on the Reynolds number quite similarly to usual viscous fluids. The traceability was found to be satisfactory at least up to about 6cm/s for both kinds of tracers. The existence of large scale vortical structure in fully developed jets and the occurrence of wide-spread entrainment into main jet from the surroundings were evidently pointed out in the pictures. The calculation of the total momentum flux in jet indicates that the zero-relative-velocity situation is reached in the fully developed stage of turbulent jet.