| 摘要 |
An NMR apparatus and method in which the S/N ratio is improved in reception of FID signals. An oscillator includes a pre-amplifier, a driver amplifier, a final power amplifier and a bias control circuit. The operation modes of the final power amplifier can be changed by controlling the biasing voltage to the final power amplifier which is applied by the bias control circuit. While the selective exciting pulse is applied to the slice portion of the patient, the final power amplifier is being operated in class A i.e., high gain mode. Immediately after an application of the selective exciting pulse is accomplished, the operation class of the amplifier is switched to "C" e.g., low gain mode in order to receive FID signal from the excited slice portion by suppressing noise signals.
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