Dynamic MRI with projection reconstruction and KWIC processing for simultaneous high spatial and temporal resolution

Abstract

A method for dynamic imaging in MRI is presented that enables the acquisition of a series of images with both high temporal and high spatial resolution. The technique, which is based on the projection reconstruction (PR) imaging scheme, utilizes distinct data acquisition and reconstruction strategies to achieve this simultaneous capability. First, during acquisition, data are collected in multiple undersampled passes, with the view angles interleaved in such a way that those of subsequent passes bisect the views of earlier ones. During reconstruction, these views are weighted according to a previously described kspace weighted image contrast (KWIC) technique that enables the manipulation of image contrast by selective filtering. Unlike conventional undersampled PR methods, the proposed dynamic KWIC technique does not suffer from low image SNR or image degradation due to streaking artifacts. Dynamic MRI plays a critical role in numerous MRI applications, such as dynamic contrast-enhancement studies, hyperpolarized gas imaging, and real-time motion tracking. In addition to requirements for rapid data acquisition, many applications also demand high spatial resolution. For example, the kinetics of contrast enhancement (1-4) and lesion morphology (5-7) have both been shown to be valuable in the diagnosis of suspicious breast lesions, and it has been demonstrated that the combined information offers improved lesion characterization (8). High-spatialresolution imaging typically requires long scan times, and determining the enhancement kinetics requires the use of rapid imaging techniques. With conventional methods, the need to trade off spatial and temporal resolution prevents the development of an optimal acquisition that meets both requirements.Several strategies have been investigated as a means of reducing the need to trade off spatial and temporal resolution in dynamic studies. Parallel image acquisitions with sensitivity encoding (SENSE) or simultaneous acquisition of spatial harmonics (SMASH) technology have been proposed for rapid imaging (9,10). These techniques utilize the sensitivity profiles of multiple coils to reduce the scan time. However, certain coil geometries are often required, and most practical implementations result in an improvement by a factor of 2 or 3 in temporal resolution. Keyhole rectilinear k-space acquisitions have also been proposed (11,12). In the keyhole technique, only the low spatial frequencies along the phase-encoding direction are acquired at short intervals, and the full-resolution images are reconstructed with the use of the high spatial frequencies from a reference dataset. However, this acquisition scheme causes the constantly updated low-spatial-frequency data to be mixed with the high-frequency data acquired at different time periods, potentially resulting in blurring of the enhancing structures in the phase-encoding direction. Other related acquisition schemes have been developed to help reduce these artifacts (13-15). However, the inevitable mixing of old and new data tha...

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Prediction of Response to Chemoradiation Therapy in Squamous Cell Carcinomas of the Head and Neck Using Dynamic Contrast-Enhanced MR Imaging

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