Nuclear magnetic resonance (NMR) spectroscopy of small lesions is restricted by the difficulties of localizing the surface coil with respect to the lesion and the problem of ensuring that signal is only obtained from the lesion and not from surrounding tissue. A double-tuned coil has been developed that permits NMR proton images to be obtained from a region of interest, prior to carrying out 31P spectroscopy of the same region with the same coil, without the need for further adjustment. The coil provides a means of accurately localizing the region from which the 31P signal is obtained, whilst offering a means of accurately applying 31P signal localization methods, and the possibility of making corrections for the nonuniform sensitivity of a given surface coil. The coil makes use of two parallel resonant circuits, with independent rf connections, but sharing a common coil. Simulated shorted and open circuit lambda /4 cables are used, respectively, to open circuit each circuit at the resonant frequency of the other circuit and ensure that the simulated lambda /4 line is short circuited for each circuit at the circuit's resonant frequency. At 63.6 MHz, the Q of the coil was 190 unloaded and 90 loaded, and at 25.7 MHz the Q was 210 unloaded and 140 loaded, for a 4-cm-diam coil. The coil has been used to obtain proton images and 31P spectra. A circuit employing only one input was also developed.
Switched array coils (SACs) are a useful tool in local coil imaging since they allow in a user-friendly manner one to make the best choice in the trade-off between field of view and signal-to-noise ratio. This is done by selecting the current path within a conductor array equipped with suitable switches. Since the switching can be controlled by the system, this allows changing of the coil dimensions within multislice sequences. Thus image quality can be improved due to smaller coil dimensions for a given slice and a larger area can be covered by electronically shifting this sensitive area. The principle can be applied to surface--as well as volume--coil designs.
Magnetic resonance (MR) images of the shoulders of a healthy volunteer were obtained in axial, sagittal, and coronal orientations using a 0.5-T imaging system. Multiple high-resolution spin-echo images were generated using an off-center zoom technique and a specially designed surface coil. Several anatomic structures, including the rotator cuff, long biceps tendon, articular capsule, muscles, and bones, were visualized. The coronal and sagittal views were the most useful for demonstrating the rotator cuff. MR imaging has potential as a new non-invasive tool for the evaluation of the shoulder region.
With ECG-gated FLASH-sequences motion of cerebrospinal fluid (CSF) is demonstrated in axial slices of the zervikal vertebral column. The course of the movement is dissolved by signal enhancement of flowing structures in magnitude images and by velocity-dependent phases. It is shown with both methods, that the oscillation of the CSF within the cardiac cycle is superimposed by a directed movement, with is cranial directed in the lateral cervical subarachnoidal spaces and caudal in the ventral subarachnoidal spaces.
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