RF coil for imaging system

Abstract

An RF coil suitable for use in imaging systems is provided which coil has a dielectric filled cavity formed by a surrounding conducting enclosure, the conducting enclosure preferably being patterned to form continuous electrical paths around the cavity, each of which paths may be tuned to a selected resonant frequency. The patterning breaks up any currents inducted in the coil and shortens path lengths to permit higher frequency, and thus higher field strength operation. The invention also includes improved mechanisms for tuning the resonant frequency of the paths, for selectively detuning the paths, for applying signal to the coil, for shortening the length of the coil and for controlling the field profile of the coil and the delivery of field to the object to the image.

Description

RELATED APPLICATIONS [0001] This application is a continuation of U.S. patent application Ser. No. 11 / 196,131, filed Aug. 3, 2005, entitled “RF Coil for Imaging System,” by J. T. Vaughan, which is a continuation of U.S. patent application Ser. No. 10 / 750,031, filed Dec. 29, 2003, entitled “RF Coil for Imaging System,” by J. T. Vaughan, which is a continuation of U.S. patent application Ser. No. 10 / 367,489, filed Feb. 14, 2003, entitled “RF Coil for Imaging System,” by J. T. Vaughan, which application is a divisional of U.S. patent application Ser. No. 09 / 575,384, filed May 22, 2000, now issued U.S. Pat. No. 6,633,161, (Oct. 14, 2003), entitled “RF Coil for Imaging System,” by J. T. Vaughan, which application claims the benefit of U.S. Provisional Patent Application Ser. No. 60 / 135,269, filed May 21, 1999, entitled “RF Coil for Imaging System,” by J. T. Vaughan, each of which is incorporated herein by reference.FIELD OF THE INVENTION [0002] This invention relates to imaging systems e...

AI Technical Summary

Benefits of technology

This design enhances signal-to-noise ratio, spectral resolution, and imaging speed while reducing radiative losses and eddy currents, enabling higher frequency and field strength operations with improved coil flexibility and efficiency.

Problems solved by technology

A major limitation to higher resolution, and / or faster imaging is an insufficient signal to noise ratio.

However, while conventional birdcage coils in existing MRI and related systems might resonate at a frequency of 170 MHZ (4 T) for example, the conventional birdcage coil with lumped elements (reactance) will operate very inefficiently, radiating much of its energy like an antenna, rather than conserving its energy like a “coil”.

At higher frequencies still, such lumped element coils of human head or body dimensions will not reach the Larmor resonant frequency required, limiting the magnetic field strength at which such MRI or EPR systems can operate.

Further, since frequency is a function of the electrical path lengths (measured in wavelengths) in the RF coil, higher frequency, and thus higher field strength operation, has been previously achievable only with very small coils which are not always useful for imaging a human being or other larger objects.

Still another potential problem in operating these imaging systems, especially at high fields, is in driving the RF coil in a manner so as to achieve a homogeneous RF field, even when a body is positioned in the field, or to achieve some other desired field profile.

However, having both the large transmit coil and the local RF receive coil tuned to the same frequency results in the coils being destructively coupled (by Lenz's Law for example), this defeating enhanced operation from the local receive coil.

While some of the advantages indicated above are achieved by distributed impedance RF coils disclosed in U.S. Pat. Nos. 5,557,247 and 5,744,957, which patents have the same inventor as this invention, the systems taught in these patents, and in particular the RF coils thereof, do not provide optimum performance in all situations, and improvements are possible on various aspects of these RF coils, including eddy current suppression, design of the coil for optimum positioning in a greater number of cases, improved control of field profile, improved tuning options and improved detuning in situations where the use of two or more coils is desired.

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