Abstract: A local RF antenna assembly for a magnetic resonance imaging (MRI) system includes a conducting RF antenna structure. First and second capacitors are connected in series with the inductance of the RF antenna structure to form a circuit that resonates at a Larmor frequency. An inductor has a first terminal connected to a node between the first and second capacitors and has a second terminal. A photosensitive first semiconductor switch is connected between the second terminal of the inductor and one terminal of the RF antenna inductance. A receive coil control selectively provides illumination that places the photosensitive first semiconductor switch in a conductive state. When the photosensitive first semiconductor switch is conductive, the inductor disables resonance of the RF antenna circuit at the Larmor frequency. This action inhibits the RF receive antenna from interacting with other antennae in the MRI system.

Abstract: An optical coupling is incorporated into an invasive device used in magnetic resonance (MR) imaging. The coupling is incorporated into the invasive device between an imaging or tracking RF coil, and the MR receiver. The optical coupling has a first transducer circuit coupled to the RF which converts between optical and electrical signals. An optical fiber is coupled to the first transducer circuit and extends out of the invasive device to medical imaging equipment. Near this equipment, a second transducer circuit converts optical signals to electrical, and electrical signals to optical, just opposite that of the first transducer circuit. The present invention thereby replaces long lead wires which can cause heating during MR imaging, and may distort an MR image.

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 temperature monitoring system employs a temperature detection means incorporated into an invasive device intended to be placed within a body during a magnetic resonance procedure. The temperature monitoring system is used to monitor temperature rises in tissue arising from the creation of electric fields within the tissue. These electric fields are created by the application of RF pulses during the course of a magnetic resonance procedure which induce electrical current in the invasive device. It the detected temperature rise exceeds a selected threshold, the temperature monitoring system can cause the magnetic resonance imaging system to either reduce RF power or terminate the procedure. An optical coupling may be used between the imaging or tracking RF coil and the MR receiver to eliminate heating induced by the application of RF pulses during the procedure.

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 images of blood perfusion in tissue. 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 supplying blood to a portion of tissue 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 high degree 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 is 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.

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.