Does the 'keyhole' technique improve spatial resolution in MRI perfusion measurements? A study in volunteers

We examined the potential of the 'keyhole' technique to improve spatial res olution in perfusion-weighted MRI on whole-body imagers with standard gradi ent hardware. We examined 15 healthy volunteers. We acquired a high-resolut ion image with 256 phase-encoding steps before a bolus-tracking procedure. For the dynamic series we collected only 34 lines in the center of k-space. Data reconstruction was performed by both zero-filling and keyhole methods . The dynamic datasets, concentration-time curves calculated from user-defi ned regions and maps of the cerebrovascular parameters using both reconstru ction methods were compared. Using keyhole series, anatomical structures co uld easily be defined which were not seen on the original dynamic series be cause of blurring due to ringing artefacts. Comparison of signal-time curve s in large regions yielded no significant difference in signal loss during bolus passage. In the parameter maps truncation artefacts were significantl y reduced using keyhole reconstruction. The keyhole method is appropriate f or enhancing image quality in perfusion-weighted imaging on standard imager s without sacrificing time resolution or information about transitory susce ptibility changes. However, it should be applied carefully, because the spa tial resolution of the dynamic signal change and the cerebrovascular parame ters is less than that afforded by the spatial resolution of the reconstruc ted images.