| 摘要 |
A magnetic resonance imaging apparatus creates images by exciting magnetic resonance in selected nuclei disposed within an image region. Through the image region a main magnetic field (B0) is applied and transverse gradients are produced. At selected times a high power RF pulse is applied to the imaging region causing the selected nuclei to resonate. These magnetic resonance signals are detected by a receive coil (D1, D2) and converted into an image representation viewable on a display (24). Images are obtained by repeating the transmit and receive portions until enough image data is received to produce an image. The receive coil (D1, D2) includes first decoupler circuits (28) arranged about the coil. During the transmit portion of the cycle, the decoupler circuits sense the high power RF pulse and decouple the coil. High speed switching diodes or PIN diodes are excited by the transmit RF pulse to switch inductors (40) into the coil to decouple the receive coil. During a receive portion of a cycle in which the coil is not used, a DC bias is selectively applied to the coil forcing the diodes on, actively decoupling the coil. The DC bias also biases a diode switch (50, 50') to short the input of a preamplifier element (48, 48') providing protection.
|
