Parallel, spatial-encoded MRI requires a large number of independent detectors that simultaneously acquire signals. The loop structure and mutual coupling in conventional phased arrays limit the number of coils and therefore the potential reduction in minimum scan time achievable by parallel MRI tchniques. A new near-field MRI detector array, the planar strip array (PSA), is presented that eliminates the coupling problems and can be extended to a very large number of detectors and high MRI frequencies. Its basic structure is an array of parallel microstrips with a high permittivity substrate and overlay. The electromagnetic (EM) wavelength can be adjusted with the permittivity, and the strip lengths tuned to a preselected fraction of the wavelength of the MRI frequency. EM wave analysis and measurements on a prototype four-element PSA reveal that the coupling between the strips vanishes when the strip length is either an integer times a quarter wavelength for a standing-wave PSA, or a half wavelength for a travelling-wave PSA, independent of the spacing between the strips. The analysis, as well as phantom and human MRI experiments performed by conventional and parallel-encoded MRI with the PSA at 1.5 T, show that the decoupled strips produce a relatively high-quality factor and signal-to-noise ratio, provided that the strips are properly terminated, tuned, and matched or coupled to the preamplifiers. Parallel spatial-encoding techniques, such as the simultaneous acquisition of the spatial harmonics method (SMASH (1)), sensitivity encoding (SENSE (2)), and the analytical SMASH procedure (ASP (3)) are practical methods for dramatically reducing the minimum MRI scan time by replacing phase-encoding steps with the encoding inherent in the sensitivity profiles of a set of phased-array detection coils. Conceivably, if pushed to the extreme, these methods could completely replace the MRI phaseencoding gradients, reducing the minimum acquisition time to a single free-induction decay. Accomplishing this would require at least a very large array of detectors, ultimately with sensitivity profiles that match the image resolution in the phase-encoding direction. However, conventional MRI phased-array coil design limits the number of coils in a phased array, mainly due to the practical difficulties associated with the loop structure of the coil elements and the difficulty in decoupling them (4).The loop surface coils that serve as detector elements in MRI phased-arrays (4 -8) currently have higher-quality factors (Q) and lower electric field losses than dipole-type antennas (9). Although linear elements, such as conducting strips combined with lumped reactances, are often integrated into single-channel detectors, such as ladder surface (10) and birdcage coils (11-13), they are not used as independent detectors in multicoil arrays. In high-field MRI scanners, linear elements-including transmission lines (14,15) and slotted tubes (16,17)-take direct advantage of the wave characteristics of the electromagnetic (EM) field for rad...
