Abstract: In an MRI apparatus, the amplification factor of a high-frequency amplifier incorporated in the transmission system for generating RF pulses is automatically controlled in accordance with the input/output characteristic between the signal input to the amplifier and the signal output therefrom. Hence, the amplifier can perform a linear amplification of the input signal, regardless of the level of the input signal. Hence, the transmission system can generate RF pulses having a spectral distribution representing a predetermined intensity in only a specified frequency domain, using the signal output from the amplifiers.

Abstract: A magnetic resonance imaging apparatus has a first surface coil for detecting a magnetic resonance signal induced in an object under examination. An induction current flows through the first surface coil by the magnetic resonance signal. A second surface coil is arranged to oppose the first surface coil through the object to be examined. The second surface coil is electrically endless. Therefore, a magnetic field is generated by the induction current. The magnetic field changes in accordance with a change in magnetic resonance signal. An eddy current flows through the second surface coil without flowing through the object to be examined in order to interfere with a change in magnetic field. As a result, an eddy current can be prevented from flowing through the object to be examined.

Abstract: In MRI, in order to provide accurate position data of a subject to an MR signal, the characteristics of the gradient magnetic fields are controlled. The characteristics, i.e., rise time T.sub.r of the waveform of a current signal required in generating a gradient magnetic field is described as: T.sub.r =(Z.sub.l /Z.sub.r) ln (V/V-I.sub.out .multidot.Z.sub.r)), where Z.sub.l is an inductance part of a gradient field generating coil, Z.sub.r is a resistance part of a gradient field generating coil, V is a power source voltage of a gradient field generating power source, and I.sub.out is a current supplied to the gradient field generating coil. As impedances of the gradient field generating coils are different from one another, the characteristics, for example, rise time periods, of the gradient magnetic fields are controlled by regulating the power source voltage of a gradient magnetic field generating power source.