Abstract

A new parallel imaging technique was implemented which can result in reduced image acquisition times in MRI. MR data is acquired in parallel using an array of receiver coils and then reconstructed simultaneously with multiple processors. The method requires the initial estimation of the 2D sensitivity profile of each coil used in the receiver array. These sensitivity profiles are then used to partially encode the images of interest. A fraction of the total number of k-space lines is consequently acquired and used in a parallel reconstruction scheme, allowing for a substantial reduction in scanning and display times. This technique is in the family of parallel acquisition schemes such as simultaneous acquisition of spatial harmonics (SMASH) and sensitivity encoding (SENSE). It extends the use of the SMASH method to allow the placement of the receiver coil array around Despite the many advances in ultrafast MRI, there is always a need for further increases in the speed of image acquisition. Dynamic imaging applications like cardiac and interventional imaging would be greatly served with an order of magnitude reduction in scan time without sacrificing spatial resolution and signal to noise ratio (SNR). Conventional multiecho imaging techniques such as RARE and EPI (1,2) are currently very fast. The new field of parallel imaging can be combined with these methods to further increase imaging speed. In previous work on parallel imaging, Hutchinson and Raff (3) demonstrated the theoretical feasibility of fast data acquisitions using multiple detectors in MRI. In a subsequent work, Kwiat et al. (4) investigated methods to solve the inverse source problem on MR signals received in multiple RF receiver coils. Their technique required the use of a number of RF coils equal to the number of pixels in the image, as well as greatly increased receiver coil sensitivities. These requirements are quite impractical in conventional MR imaging, where the usual number of pixels in an image is on the order of 256 ϫ 256, hence the technique was never successfully used in medical imaging. A number of more promising parallel imaging techniques have been described in the literature (5-7) which use the sensitivity profiles of RF receiver coils for spatial encoding. Ra and Rim (5) described a method that uses sets of equally spaced k-space lines from multiple receiver coils and combines them with sensitivity profile information in order to remove the aliasing that occurs due to the undersampling. A 4-fold decrease in the image acquisition time of a water phantom was shown using an array of four coils, although no biological images were shown. The SMASH method proposed by Sodickson and Manning (6) has proven more practical, yielding good results in volunteers with clinical implementations. SMASH is designed to enhance imaging speed by using multiple receiver RF coils. It is based on the computation of the sensitivity profiles of the coils in one direction. These profiles are then weighted appropriately and combined linearly in order to form sinusoidal harmonics which are used to generate the k-space lines that are missing due to undersampling. This technique showed an 8-fold increase in imaging speed. SMASH has some inflexibility in the choice of imaging planes due its restriction on the placement of receiver coils along one direction. The SENSE method proposed by Pruessmann et al. A generalization of SENSE was introduced by Pruessmann et al. In this article, we present a parallel imaging and reconstruction technique which attempts to generalize the SMASH approach by allowing for the arbitrary placement of RF receiver coils around the object to be imaged as well as for the use of any combination of k-space lines as opposed to regularly spaced ones. In addition, our reconstruction technique is completely parallel, allowing for