Magnetic resonance imaging system

摘要

The magnetic resonance imaging system applies a uniform static magnetic field and a gradient magnetic field to an object and further applies an excitation rotating magnetic field to cause magnetic resonance phenomena in the object to detect the induced magnetic resonance signals and then to obtain image data by processing the magnetic resonance signals. The system has a power controller for controlling the transmission power in a transmitter for transmitting the excitation rotating field. The system further has a transmission controller for controlling the power controller in response to the magnetic resonance signal which is received by the receiver from the object. The transmission controller controls the power controller to sequentially change the transmission power and detects the transmission power at which the maximum magnetic resonance signal is obtained in response to the reception signal by the receiver when the excitation rotating field is applied to the object, thereby controlling the power controller in accordance with the detected data. A fraction of the detected maximum power is utilized to generate the excitation field to thereby rotate the spin angle of the nuclei by an amount less than 90 DEG , and preferably 45 DEG , so as to reduce data collection time.