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FOUR-ELEMENT BIRDCAGE RADIO FREQUENCY (RF) COIL FOR MAGNETIC RESONANCE IMAGING (MRI) SYSTEMS

IP.com Disclosure Number: IPCOM000199442D
Publication Date: 2010-Sep-04
Document File: 5 page(s) / 31K

Publishing Venue

The IP.com Prior Art Database

Abstract

A technique comprising a four-element birdcage RF coil for large bore Magnetic Resonance Imaging (MRI) systems is disclosed. The technique described herein proposes an RF coil utilized in an MRI scanner employing four or a small number of rung elements. The rungs protrude into the magnet bore and are hidden in the mechanical supports for in-bore lights. The advantage of this technique is that the four-element coil is able to provide a large opening for patients in the bore of the MRI scanner.

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RP13478

FOUR-ELEMENT BIRDCAGE RADIO FREQUENCY (RF) COIL FOR

MAGNETIC RESONANCE IMAGING (MRI) SYSTEMS

BRIEF ABSTRACT

    A technique comprising a four-element birdcage RF coil for large bore Magnetic Resonance Imaging (MRI) systems is disclosed. The technique described herein proposes an RF coil utilized in an MRI scanner employing four or a small number of rung elements. The rungs protrude into the magnet bore and are hidden in the mechanical supports for in-bore lights. The advantage of this technique is that the four-element coil is able to provide a large opening for patients in the bore of the MRI scanner.

KEYWORDS

    Magnetic Resonance Imaging (MRI), Radio frequency (RF), birdcage coil, MRI scanner, Larmor frequency, bore, rungs, magnets, gradient, gyro magnetic ratio

DETAILED DESCRIPTION

    Generally, Magnetic Resonance Imaging (MRI) is a noninvasive medical imaging technique used in radiology to visualize detailed internal structure and limited function of the body. Typically, MRI of a patient undergoing a medical imaging test requires that the patient be placed in a homogeneous magnetic field of a selected strength. Most commercially available MRI scanners utilize field strength between 0.2 and 3.0 Tesla. Research scanners may utilize higher and lower magnetic fields. Patients are also subjected to dynamic magnetic field

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RP13478

gradients during the imaging procedure to encode spatial position. Such magnetic field gradient pulses typically have durations between 0.5 and 10 milliseconds. Usually, it is desirable to make the gradients as strong as possible without inducing physiological stimulation of the patient. Typical gradient coils can create dynamic gradient magnetic fields of the order of 2 to 5 Gauss / centimeter. In addition to the static and dynamic magnetic fields, the patient is exposed to a dynamic magnetic field that rotates at a frequency known as Larmor frequency.

    The Larmor frequency is determined by the gyro magnetic ratio of nuclei of interest and is directly proportional to the static magnetic field. The most abundant element in biological organisms is Hydrogen whose gyro magnetic ratio is 4257 Hz/Gauss. Therefore, for a typical MRI scanner operating at 1.5 Tesla, the Larmor frequency is 63.88 MHz. The creation of a rotating magnetic field at the scanner's Larmor frequency is a function of the MRI scanner's transmitting Radio Frequency (RF) coil.

    Usually the rotating magnetic field creation is accomplished with a large body coil having a 16-element birdcage construction. Such a coil is constructed on the outer surface of a fiberglass cylinder that acts as the patient bore for the magnet. The RF coil is surrounded by an RF shield that is placed on the inner surface of the gradient coils. The gap between the RF coil and RF shield acts as a return path for the RF flux and is a critical aspect of RF coil design. In the construction of an MRI system, the magnetic field gradients are placed within the m...