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BIRDCAGE COIL DRIVEN BY DISTRIBUTED RADIO FREQUENCY AMPLIFIERS

IP.com Disclosure Number: IPCOM000198544D
Publication Date: 2010-Aug-09
Document File: 9 page(s) / 172K

Publishing Venue

The IP.com Prior Art Database

Abstract

A technique for applying excitation multiple relative low radio frequency energy to establish a homogeneous B1 field within the birdcage coil is disclosed. The technique described herein proposes applying excitation by multiple relative low radio frequency energy through multiple drives.

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Page 1 of 9

RP13454

BRIEF ABSTRACT

    A technique for applying excitation multiple relative low radio frequency energy to establish a homogeneous B1 field within the birdcage coil is disclosed. The technique described herein proposes applying excitation by multiple relative low radio frequency energy through multiple drives.

KEYWORDS

    Magnetic resonance imaging (MRI), cascade power, scanner room, RF transmits, birdcage coil, impedances, amplifiers, RF amplifiers.

DETAILED DESCRIPTION

    Generally, Magnetic resonance imaging (MRI) is used as a noninvasive medical imaging technique to visualize detailed internal structure and limited function of the body. Typically, in a conventional MRI system, the radio frequency (RF) power level requirement is up to 35 kilo watt (KW) peak. However, typically in metal oxide semiconductor field effect transistor (MOSFET) module, the power level is normally less then 1kW. Therefore in conventionally used RF amplifier employed for MRI system, a cascade power combiner is used to combine the power from multi MOSFET modules into a desired level, as illustrated in Figure 1.

1

BIRDCAGE COIL DRIVEN BY DISTRIBUTED RADIO FREQUENCY AMPLIFIERS

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RP13454

    Generally, the RF amplifier is placed outside a scanner room. The RF power is transmitted through a long coaxial cable into the scanner room. The power is then split by a hybrid and drives two orthogonal ports on a birdcage coil in which the power is further delivered into each rung through the circuit network. However, power loss occurs at each stage in such a power transmit chain. Depending on the combiner design and power level, the power loss in the combiner stage may be up to 35%. An additional 10%-20% power loss occurs due to the cable and hybrid.

    Therefore, there is a need in the art for a cost-effective and power efficient RF transmit chain for MRI systems.

    A technique for applying excitation multiple relative low radio frequency energy to establish a homogeneous B1 field within the birdcage coil is disclosed. The present technique is directed to applying excitation of multiple relative low radio frequency energy to a birdcage coil through multiple drive ports (more than
4). By removal of most power combination components and decrease in power transmission components, the birdcage coil is directly driven through multiple drive ports with independent RF amplifier modules (more than 4). Further, a substantially circular polarized RF field or an elliptic polarized RF field may be also produced within the birdcage coil through independent phase/amplitude adjustment of two groups of amplifiers to reduce dielectric effect and B1 in homogeneous high field MRI.

    According to the present technique, multiple current sources which have very high output impedances of more than 350 Ohm are selected to drive the birdcage coil. In this manner, the birdcage coil configuration generates a substantially uniform B1 field independent of source impedance asymmetry.

    Further, magnet co...