National Research Council of Canada

David Ian Hoult

Garnette Roy Sutherland

Jarod Matwiy

John K Saunders

Franklin A Roberts

An apparatus for detecting a potentially dangerous ferromagnetic object carried inadvertently by a person approaching the magnet of a magnetic resonance imaging system () uses the fringe field () of the magnet and provides guide members () defining a path along which the person is prescribed to pass. The path () is generally or approximately parallel to the field the path. At least one sense coil and generally two sets of sense coils () are located on respective sides of the path () s the movement of the ferromagnetic object in the field of the magnet causes a voltage to be generated in the sense coil.

Detection of ferromagnetic objects approaching a magnet

In nuclear magnetic resonance experiments, Cartesian electronic feedback is used to reduce substantially in transmission and/or reception the deleterious effects of sample-mediated and direct interactions between coils in an array of transmitting and/or receiving coils. The feedback is also used with single or multiple coils to maintain at essentially constant values the relationship between an input transmitter voltage and the magnetic resonance flip angle, and the relationship between transverse nuclear magnetisation and the strength of the free induction decay signal presented by a receiver for analysis, regardless of factors such as sample electrical conductivity.

Method of effecting nuclear magnetic resonance experiments using Cartesian feedback

There is described a quadrature radio frequency (RF) coil design to be used with appropriate magnetic resonance imaging (MRI) hardware to obtain images of the human body. The design provides good RF field homogeneity over a volume suitable for thoracic diagnostic imaging, and operates in quadrature mode as a transmit and/or receive coil. The design is for use with a 0.33 tesla permanent, C shaped magnet with a vertical main field but is of general applicability. The coil includes two parallel annular coils connected at top and bottom by two plate conductors. The plates are split longitudinally and transversely and connected across the splits by capacitors to define two modes of resonant oscillation which can be tuned separately and independently to the same frequency, where the modes define fields which are mutually orthogonal. The fields are at right angles to the magnetic field and to the plate conductors so that the sample can be inserted through the openings at right angles to the plates.

Quadrature RF field coil for use in magnetic resonance

In an MRI system including a source of a high frequency oscillating current having a required characteristic impedance and a probe having an impedance different from said required characteristic impedance and an adjustment circuit for adjusting the impedance of the probe to the required characteristic impedance there is provided an automatic circuit for matching and tuning the impedances: The circuit includes a first adjustable element and a second adjustable element arranged such that adjustment of the first and second elements causes adjustment of both a resistive component and a reactive component of the impedance and such that, over at least a part of a range, adjustment of the first element while the second element remains constant generates a change in the impedance which is substantially orthogonal to a change in the impedance obtained by adjustment of the second element while the first element remains constant and such that adjustment of the first element to a first required adjustment position and adjustment of the second element to a second required adjustment position causes the impedance of the probe to be adjusted to said required characteristic impedance. A detection circuit provides two separate output values which are orthogonal to one another and which are indicative of a difference in the impedance of the probe from said required characteristic impedance. The output values are indicative of a difference of the first element from the first required adjustment position and a difference of the second element from the second required adjustment position. The values are used for controlling respectively the first and second elements.

Tuning and matching an impedance

Apparatus is provided for use in surgical procedures comprising an operating table for receiving a patient for surgery and a magnetic resonance imaging system for obtaining images of a part of the patient at a series of times through the surgical procedure for analysis by the surgical team to allow the surgical team to monitor the progress of the surgery. The high field magnet and the operating table are shaped and arranged for positioning of the part of the patient into the magnetic field while the patient remains in place on the table and the magnet is mounted for movement between a first position spaced from the table and the patient thereon to allow the surgical team to carry out the surgical procedure and a second position for applying the magnetic field to the part of the patient. The table remains substantially stationary and only the magnet is moved to a position spaced from an adjacent end of the table to allow the surgical team to move around the adjacent end of table and to each side of the table to access the patient.

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Winnipeg, Canada

David Ian Hoult