Abstract: Techniques for correcting temperature measurement in MR thermometry are disclosed. In particular, phase shifts that arise from factors other than temperature changes are detected, facilitating correction of temperature measurements.

Abstract: A magnetic resonance system has been developed for actively tracking the three-dimensional positions of numerous coils provided on one or more medical devices. One particular example of a novel magnetic resonance system of the present invention is capable of simultaneously tracking the positions of up to 32 coils or more, which may be provided on the medical device(s). As an example, catheter devices having a large number of independent tracking coils have been constructed, in which each coil has a direct connection to one at least the same number of receivers in the magnetic resonance system. Accordingly, physicians can obtain real-time visualization of the positions of medical devices using a magnetic resonance system, with sufficient frame-rates to guide the manipulation of the medical devices within the body of a patient. The medical devices may include catheters and guidewires.

Abstract: A method and apparatus for producing an imaging plane on an image of a structure of interest, such as an anatomical structure, positioned in an MRI system. An operator interactively pages through real-time, planar sections of the structure of interest. Using an input device, the operator selects three separate points in a planar section of the structure under study. Within approximately one second of selection of the third point, the method of the present invention determines the imaging plane containing the three selected points, determines the centroid of the imaging plane centered on a triangle defined by the three selected points, sends such imaging geometry and in-plane offsets of the imaging plane directly to the MRI system to generate a new imaging plane optimally positioned with respect to the selected points on the structure of interest and displaying such new imaging plane. The operator can also selectively maneuver the imaging plane on the image of the structure of interest.

Abstract: A magnetic resonance (MR) active invasive device system employs a small, high-field polarizing magnet, and a large, possibly low-field magnetic resonance (MR) imaging magnet for the purpose of generating MR angiograms of selected blood vessels. A subject is positioned in a large MR imaging magnet. A catheter is inserted into the patient at or near the root of a vessel tree to be imaged. A fluid, intended to be used as a contrast agent is first cooled and frozen, and then passed through the small high-field polarizing magnet where it becomes highly polarized. The frozen fluid is then heated and melted to physiologic temperatures and introduced into the subject through the catheter. Radiofrequency (RF) pulses and magnetic field gradients are then applied to the patient as in conventional MR imaging.

Abstract: A magnetic resonance (MR) active invasive device system employs a small, high-field polarizing magnet, and a large magnetic resonance (MR) imaging magnet for the purpose of generating MR images of selected body cavities. A subject is positioned in a large low-field MR imaging magnet. A substance, intended to be used as a contrast agent is first cooled, and then passed through the small high-field polarizing magnet where it becomes highly polarized. The substance is then heated to physiologic temperatures, vaporized, and introduced into the subject through a transfer conduit as a vapor. Radiofrequency (RF) pulses and magnetic field gradients are then applied to the patient as in conventional MR imaging. Since the vapor is highly polarized, it can be imaged even though it has a much lower density than the surrounding tissue.

Abstract: A magnetic resonance (MR) active invasive device system employs a small, high-field polarizing magnet having a toroidal geometry, and a large low-field magnetic resonance (MR) imaging magnet for the purpose of generating MR angiograms of selected blood vessels. A subject is positioned in a large low-field MR imaging magnet. A catheter is inserted into the patient at or near the root of a vessel tree to be imaged. A fluid, intended to be used as a contrast agent is first passed through the small high-field polarizing magnet, causing a great deal of net longitudinal magnetization to be produced in the fluid. The fluid is then introduced into the subject through the catheter. Radiofrequency (RF) pulses and magnetic field gradients are then applied to the patient as in conventional MR imaging.

Abstract: Imaging parameters, such as the location, orientation and field of view of an imaging plane are selected. These parameters are provided to a pulse sequencer of a magnetic resonance (MR) scanner which modifies an MR pulse sequence to acquire an image at the selected imaging plane. The pulse sequencer controls an RF transmitter and gradient amplifiers to cause an MR image of the subject at an imaging plane to be acquired. The MR image is displayed on a display device. An interface device receives and reduces the MR image to an image icon and saves the image icon along with the corresponding imaging parameters. The image icons are displayed on the periphery of the screen around an MR image. An operator may then view and select one of the image icons, employing the pointing device. This causes the imaging parameters corresponding to the selected image icon to be sent to the pulse sequencer thereby causing an MR image to be acquired with these imaging parameters.

Abstract: A tracking system monitors the position of a device within a subject and superimposes a graphic symbol on a diagnostic image of the subject. Registration of the tracked location with the diagnostic image is maintained in the presence of subject motion by monitoring subject motion and adjusting the display to compensate for subject motion. Motion monitoring can be performed with ultrasonic, optical or mechanical methods. The display can be adjusted by modifying the displayed location of the device or it can be adjusted by translating, rotating or distorting the diagnostic image.

Abstract: A magnetic resonance system employs a sequence of radio frequency pulses and magnetic field gradients to generate a flow-compensated image of a selected portion of a sample. Flow-compensation is performed with an oscillating readout gradient waveform which is comprised of two components. The first component is a constant amplitude gradient waveform whose amplitude is determined by the desired field-of-view and the bandwidth of the imaging system. The second component is an oscillating waveform whose amplitude, frequency and phase are chosen to obtain the desired degree of flow-compensation. The frequency of the oscillating waveform is typically chosen to match the sampling frequency of the imaging system. In effect, each acquired data point is preceded by the application of a bi-polar magnetic field gradient pulse which causes a phase shift in the acquired signal which is proportional to nuclear spin velocity.

Abstract: An interactive display system superimposes images of internal structures on a semi-transparent screen through which a surgeon views a patient during a medical procedure. The superimposed image is derived from image data obtained with an imaging system. An invasive device is also tracked and displayed on the semi-transparent screen. A ray extending through the invasive device can also be displayed which shows the intended path of the invasive device. The image is registered with the surgeon's view of the patient and displayed in real-time during a medical procedure. This allows the surgeon to view internal and external structures, the relation between them, the proposed path of the invasive device, and adjust the procedure accordingly. A second embodiment employs stereoscopic viewing methods to provide three-dimensional representations of the radiological images superimposed on the semi-transparent screen through which the surgeon views the patient.

Abstract: A newly acquired MR image of an imaging subject is displayed on a display device. An operator interactively manipulates the imaging plane during imaging, by using a button, a rocker switch, a knob, and a trackball. The button enables or disables interactive scan-plane control. The rocker switch chooses between "translate", and "rotate" modes. In "translate" mode, the knob pushes the imaging plane deeper or shallower relative to the most recently displayed image, while the trackball slides the plane sideways and/or up and down. In "rotate" mode, the knob spins the imaging plane about the center of the most recently displayed image without changing the tilt of the plane, while the trackball tumbles or tilts the imaging plane. Colored icons displayed over the image change location, size, and/or shape to indicate the direction and extent of the translation or rotation.

Abstract: An MR image of a subject is displayed on a display device. Scan-control icons are displayed over this image. An operator interacts with an interface device to select imaging plane parameters during imaging. This is performed by selecting one of the icons with a pointing device, and dragging. Interface device then provides a display which indicates the motion of the imaging plane as well as the extent of the motion. Once selected, the location and orientation information transformed to global coordinates and is provided to a pulse sequencer of a magnetic resonance (MR) imaging system. The pulse sequencer controls an RF transmitter and gradient amplifiers to cause an MR image of the subject at an imaging plane to be acquired. This allows fast, accurate imaging plane selection, which may be selected by an operator who is searching for structures within the subject, or who is simultaneously performing a medical procedure on the subject.

Abstract: A magnetic resonance (MR) active invasive device system employs a small, high-field polarizing magnet, and a large low-field magnetic resonance (MR) imaging magnet for the purpose of generating MR angiograms of selected blood vessels. A subject is positioned in a large low-field MR imaging magnet. A catheter in inserted into the patient at or near the root of a vessel tree desired to be imaged. A fluid, intended to be used as a contrast agent is first passed through the small high-field polarizing magnet, causing a great deal of net longitudinal magnetization to be produced in the fluid. The fluid is then introduced into the subject through the catheter. Radiofrequency (RF) pulses and magnetic field gradients are then applied to the patient as in conventional MR imaging. Since the fluid has a larger longitudinal magnetization, before the MR imaging sequence, the fluid produces a much larger MR response signal than other tissue resulting in the vessel tree being imaged with excellent contrast.

Abstract: An invasive imaging system employs a self-contained RF transmitter attached to an invasive device which allows tracking of the invasive device within a subject without physical connections to a tracking/display system and without the use of ionizing rays. An imaging system obtains a medical diagnostic image of the subject. The self-contained RF transmitter is comprised of a power generator, a power conversion means such as an oscillator which converts the generated power to a radiofrequency (RF) signal, and a broadcasting means such as a tuned transmit coil for radiating the RF signal. The radiated RF signal is received by receive coils of a tracking/display means which calculates the location of the RF transmitter. The tracking/display means displays the medical diagnostic image on a monitor and superimposes a symbol on the image at a position corresponding to the calculated location of the RF transmitter.

Abstract: A method of magnetic resonance (MR) fluid flow measurement within a subject employs an invasive device with an RF transmit/receive coil and an RF transmit coil spaced a known distance apart. The subject is positioned in a static magnetic field. The invasive device is positioned in a vessel of a subject in which fluid flow is desired to be determined. A regular pattern of RF transmission pulses are radiated through the RF transmit/receive coil causing it to cause a steady-state MR response signal. Intermittently a second RF signal is transmitted from the RF coil positioned upstream which causes a change in the steady-state MR response signal sensed by the downstream transmit/receive coil. This is detected a short delay time later at the RF receive coil. The time delay and the distance between the RF coils leads directly to a fluid velocity. By exchanging the position of the RF transmit and transmit/receive coils, retrograde velocity may be measured. In another embodiment, more RF coils are employed.

Abstract: An invasive imaging system employs a self-contained RF transmitter attached to an invasive device which allows tracking of the invasive device within a subject without physical connections to a tracking/display system and without the use of ionizing rays. An imaging system obtains a medical diagnostic image of the subject. The self-contained RF transmitter is comprised of a power generator means, a power conversion means such as an oscillator which converts the generated power to a radiofrequency (RF) signal, and a broadcasting means such as a tuned transmit coil for radiating the RF signal. The radiated RF signal is received by receive coils of a tracing/display means which calculates the location of the RF transmitter. The tracking/display means displays the medical diagnostic image on a monitor and superimposes a symbol on the image at a position corresponding to the calculated location of the RF transmitter.

Abstract: RF tracking system employs a RF invasive device coupled to surgical tracking equipment for tracking the invasive device. An inductive coupling permits the device to be quickly coupled to, and decoupled from, the equipment. The coupling comprises an inducting coil which transmits a signal from the surgical tracking equipment to a communicating coil in the invasive device. The signal received by the communicating coil passes along leads to a tracked coil in a distal end of the invasive device. The tracked coil transmits the signal as RF energy which is received by the surgical tracking equipment which superimposes the position of the distal end of the invasive device on an X-ray image and displays it on a monitor A sterile shield is employed as a sterile barrier between the inducting coil and the equipment end of the invasive device to prevent contamination of the invasive device by the inducting coil.

Abstract: A tracking system in which radiofrequency signals emitted by an invasive device such as a catheter, are detected and used to measure the position and orientation of the invasive device. The invasive device has a transmit coil attached near its end and is driven by a low power RF source to produce a dipole electromagnetic field that can be detected by an array of receive coils distributed around a region of interest. The position and orientation of the device as determined by the tracking system are superimposed upon independently acquired Medical Diagnostic images, thereby minimizing the radiographic exposure times. One or more invasive devices can be simultaneously tracked.

Abstract: A magnetic resonance (MR) imaging system for use in a medical procedure employs an open main magnet allowing access to a portion of a patient within an imaging volume, for producing a main magnetic field over the imaging volume; a set of open gradient coils which provide magnetic fields gradients over the imaging volume without restricting access to the imaging volume; a radiofrequency coil set for transmitting RF energy into the imaging volume to nutate nuclear spins within the imaging volume and receive an MR response signal from the nuclear spins; and a pointing device for indicating the position and orientation of a plane in which an image is to be acquired; an image control means for operating power supplies for the gradient coils and the RF coils to acquire an MR signal from the desired imaging plane; and a computation unit for constructing an image of the desired imaging plane.

Abstract: A tracking system employs magnetic resonance signals to monitor the position of a device such as a catheter within a subject. The device has a receiver coil which is sensitive to magnetic resonance signals generated in the subject. These signals are detected in the presence of magnetic field gradients and thus have frequencies which are substantially proportional to the location of the coil along the direction of the applied gradient. Signals are detected responsive to applied magnetic gradients to determine the position of the device in several dimensions. Sensitivity of the measured position to resonance offset conditions such as transmitter frequency misadjustment, chemical shift and the like is minimized by repeating the process a plurality of times with selected amplitudes and polarities for the applied magnetic field gradient.