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An approach is described which allows remote tuning of a probe via a length of transmission line, while retaining nearly ideal efficiency relative to the equivalent locally tuned coil. This preservation of efficiency is accomplished through the principle of "partial local matching." In comparison to common methods of remote tuning which involve half-wavelength cables, or in which a length of transmission line is itself utilized as a tuning element, the partial matching method results in a substantial increase in the efficiency of power transfer to the coil, and therefore increased B1 field intensity and signal-to-noise ratio. Applications in which the use of local variable tuning capacitors is made difficult by either space, accessibility, or environmental considerations should benefit from this method.

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In order to overcome the problems that arise from nonuniform B1 fields, there has been interest in developing pulses that are insensitive to large variations in RF power. Pulses derived from adiabatic passage principles that can execute spin inversion, excitation, and 90 degrees and 180 degrees plane rotations in the presence of B1 inhomogeneities have recently been described. When driven with optimized modulation functions, these pulses can execute uniform excitation, refocusing, and slice-selective inversion over a 10-fold or greater variation in B1 magnitude. This insensitivity to B1 strength enables the execution of T1- and/or T2-weighted spin-echo imaging experiments using coils, such as the surface coil, with extremely inhomogeneous B1 profiles. We have successfully acquired images with these pulses at 200 MHz using a single surface coil as the transmitter and receiver. Images of the slice definition, the region over which the excitation and refocusing pulses operate with a surface coil, and brain images obtained with slice planes perpendicular to the plane of the surface coil are presented. Results demonstrate that these pulses can be transmitted with a surface coil to yield high-quality T1- and/or T2-weighted images without B1 artifacts.