Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-11-25
2001-03-06
Casler, Brian L. (Department: 1911)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C324S318000, C324S322000
Reexamination Certificate
active
06198962
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an RF quadrature detection (QD) for magnetic resonance imaging (MRI) procedures. More specifically, it relates to an MRI quadrature detection coil having an open structural arrangement that allows easy access to body tissues during interventional MRI procedures (e.g., tissue biopsy or surgery).
BACKGROUND OF THE INVENTION
Magnetic resonance (MR) images acquired during surgery assist a surgeon to accurately locate tissue malignancies, obtain a biopsy from desired surgical sites on the patient, and assist in the successful removal of tissue from the patient. Interventional MRI is the magnetic resonance imaging technique (often involving real-time imaging) that allows a surgeon to perform MRI-guided tissue biopsy or surgical procedures.
To provide a surgeon with open access to surgical sites during MR imaging, conventional MR reception coils often have to sacrifice their signal reception performance. For interventional MRI guided surgery, it is desirable that the MR reception coil have a large opening to receive the body part to be imaged and wide-open access to provide a surgeon access to the surgical site with a biopsy needle or other surgical devices. To provide open surgical access, conventional interventional MRI coils generally have had a simplified RF coil structure. These simplified coils have large openings and provide good access during surgery. However, these simple coils also have compromised field homogeneity and signal reception efficiency. Because of these shortcomings, conventional interventional MRI reception coils have had limited usefulness as viable surgical tools.
An example of a simplified coil configuration previously used in interventional MRI is a flat single-loop surface coil arrangement used to image breasts. The flat signal-loop coil typically is placed near the chest wall of the patient, and around all or at least a portion of a single breast. A significant disadvantage of such a single-loop coil is that it has poor field homogeneity, and provides poor signal quality, especially with respect to breast tissue not immediately adjacent the RF reception coil loop. When using a single-loop reception coil, a surgeon experiences difficulty in clearly viewing or positively identifying malignancies of the breast that are more than a short distance from the RF coil.
Improving coil performance, such as the signal-to-noise ratio and uniformity of interventional MR reception coils, would increase the depth to which tissue can be clearly imaged. If the signal reception efficiency could be improved, then signal quality would be improved and good, clear interventional MR images would be available of the surgical site and surrounding tissue. Providing a clear image of a surgical or biopsy site would allow a surgeon to make better informed decisions during MRI guided surgery.
RF quadrature detection coil can improve signal detection efficiencies effectively. A quadrature detection coil arrangement consists of two orthogonal RF reception coils. If the two coils are resonant at the same frequency, then MR signals induced in one coil (channel A) will have a 90° phase shift with respect to the signals induced in the other coil (channel B).
In an MRI quadrature detection arrangement, a pair of MR signals (one from each coil-channel) are processed and combined to obtain one combined MR signal having a better signal-to-noise ratio than either of the single signals from the individual coil-channels of the quadrature arrangement. Where the two coils of the quadrature detection arrangement are identical (except for their orientation), the resultant signal should be about 40% better than that of either coil individually or of an equivalent single-loop coil arrangement.
While quadrature detection coils offer superior signal efficiency, they have in the past been difficult for use in interventional MRI devices. Providing open access to a tissue site is a significant constraint on the design of interventional quadrature detection coil. Compared to open structure single channel RF reception coils, the structure of a quadrature detection coil (having a pair of orthogonal coils) is more complex. The structural constraints of a quadrature coil arrangement present an imposing and perplexing problem which has made quadrature coils less applicable to interventional MRI, at least until the present invention.
SUMMARY OF THE INVENTION
In accordance with the present invention, an interventional MRI quadrature detection coil has been developed that has an open structural arrangement for providing both an opening to receive a breast (or other body part) to be imaged and provides open access to the tissues being imaged during surgery. In addition, the superior efficiency of quadrature coils of the present invention produces the good signal and image qualities that are characteristic of quadrature detection coils.
The quadrature detection coil of the present invention comprises a pair of orthogonal RF reception coils, that together form a generally-rectangular (box-like) shape. Each coil provides one signal channel of the two 90°-phase-shifted signal channels used for quadrature detection. In addition, each conductive-coil is arranged to have a pair of straight parallel sections, where each straight section is formed of two parallel and adjacent conductors. The four straight sections of the pair of coils form the four side edges of the rectangular shape of the quadrature detector. The two side-edges form by each coil are diagonal from each other across the rectangle, and are in a common side-edge plane. The common side-edge plane for one coil is perpendicular to the side-edge plane for the other coil. In addition, the two side-edge sections of each coil are connected by a semi-circular arc-shaped section of the coil. When the pair of coils are arranged together the arc-shaped sections of the pair of coils are in a plane perpendicular to the planes of the straight side-edge sections of the coils.
In the quadrature detection coil of the present invention, the circular opening formed by the arc-shaped portions of the coils provides an opening for a body part (such as a breast) to be imaged. In addition, the open side-walls between the side-edge straight portions of the coils provide large open access portals through which can pass surgical instruments used during interventional MRI procedures. Accordingly, a quadrature detection coil arrangement has been developed that combine superior signal efficiencies and open surgical access through the coils during interventional MRI procedures.
In a second embodiment of the present invention, the coil conductors are arranged to form circular openings on both the top and bottom ends of the rectangular structure formed by the straight side-edges sections of quadrature detection coil. By forming circular openings (aperture) in the top and bottom of the quadrature detection coils, a cylindrical passageway is formed through the entire coil structure. The cylindrical passageway is a highly open structure that facilitates interventional MRI of head, extremities and other body parts, and provides good signal efficiency.
Accordingly, a first embodiment of the invention is an RF quadrature receiving coil apparatus for interventional magnetic resonance imaging (MRI) comprising:
a pair of nested conductive coils each providing one of two channels for the RF quadrature receiving coil apparatus,
an aperture in the nested conductive coils to receive a body part to be imaged;
wherein each coil has two parallel straight coil segments and each straight coil segment includes at least two adjacent coil windings, and the parallel straight coil segments of the nested coils are arranged at ninety degree (90°) intervals around the aperture, and
the windings of the parallel straight coil segments are connected by arc-shaped coil winding segments forming a portion of a periphery of the aperture.
Another embodiment of the invention is an RF quadrature detection coil for interventional MRI, comprising:
a pair of nested conductive coils ea
Casler Brian L.
Nixon & Vanderhye P.C.
Toshiba America MRI Inc.
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