摘要:
A method for providing a volumetrically-rendered projection image using reverse ray casting, uses the steps of: acquiring, from an object volume of interest, a set of data sampled from each volume element (voxel) therein responsive to a selected characteristic of that object volume; storing the data for each object voxel in a corresponding data volume element; scanning sequentially through each data voxel within the data volume corresponding to the object volume of interest; projecting each scanned data voxel to an image plane, at a solid angle determined from the solid angle at which the object volume is viewed; storing a value for each image plane pixel, responsive to a selected criteria, from the values of all projected data voxel values impingent upon that image plane pixel; and then scaling the dimensions of each image plane pixel responsive to the dimensions of the corresponding object volume shape, and the involved projection solid angle, to correct for anisotropy.
摘要:
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.
摘要:
A method for simultaneously obtaining a three-dimensional nuclear magnetic resonance (NMR) angiographic image of moving spins associated with fluid flow in a region of a living organism sample, and a three-dimensional NMR image of stationary tissue in the same sample region, by immersing the sample in a main static magnetic field; nutating, in an excitation subsequence of each of a plurality of NMR sequences, the nuclear spins and the generating a flow-encoding magnetic field gradient selected to cause a resulting NMR response echo signal from the spin of a moving nucleus to be different from the NMR response echo signal from the spin of a substantially stationary nucleus. The acquired response data is processed to provide at least one of (1) a difference data set from which response data obtained from stationary nuclei has been substantially removed, (2) a summation data set from which response data obtained from moving nuclei has been substantially removed, and (3) a set of phase data indicating direction of flow for flow amplitudes obtained in set (1), in order to generate both an angiographic image lying in a selected plane in a three-dimensional volume, and an image of stationary tissue in the same plane.
摘要:
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 is inserted into the patient at or near the root of a vessel tree desired to be imaged. A hydrogen gas is first cooled and condensed into a liquid state, and then passed through the small high-field polarizing magnet where it becomes highly polarized. A contrast fluid is then made by chemically combining the polarized hydrogen with oxygen to obtain highly polarized water. The water is then heated to physiologic temperatures and, if desired, made more physiologically compatible with the addition of substances such as salts. The physiologically conditioned polarized 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 than tissue which has not passed through the polarizing magnet, the fluid produces a much larger MR response signal than other tissue resulting in the vessel tree being imaged with excellent contrast.
摘要:
A magnetic resonance (MR) angiography system employs a Faraday catheter for generating MR angiograms of selected blood vessels. A subject is first placed in a polarizing magnetic field. The Faraday catheter is then inserted into a selected blood vessel of the subject at or near the root of a vessel tree desired to be imaged. An MR imaging pulse sequence is then applied to the subject to obtain image information from the region containing the desired vessel tree. Fluid inside the Faraday catheter is shielded from the RF pulses of the MR imaging sequence allowing the fluid to be in a relaxed state, while tissue outside the Faraday catheter is on a steady-state. As the fluid exits the catheter, and before it reaches steady-state, it produces an increased MR response signal causing the desired vessel tree to be imaged.
摘要:
A three dimensional image of a human brain or other body structure is constructed using a single flow sensitive data array and a flow insensitive data array to generate the contrasts necessary to differentiate among stationary tissues and also between stationary tissues and flowing blood. A plurality of data points from this combined image data are identified to tissue types and used to segregate the remaining data by using a nearest neighbor process in which each data value takes the tissue type of its nearest neighbor data point.
摘要:
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. Linear combinations of the data acquired responsive to the different applied magnetic field gradients are computed to determine the position of the device in three orthogonal dimensions. The position of the device as determined by the tracking system is superimposed upon independently acquired medical diagnostic images.
摘要:
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. Since the fluid has a larger longitudinal magnetization than tissue which has not passed through the polarizing magnet, the fluid produces a much larger MR response signal than other tissue, resulting in vessel tree images with excellent contrast.
摘要:
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.
摘要:
A magnetic resonance (MR) active invasive device system employs a radio-frequency (RF) coil embedded in an invasive device for the purpose of generating MR angiograms of a selected blood vessels. A subject is first placed in a polarizing magnetic field. The invasive device is then placed into a selected blood vessel of the subject such that the RF coil of the invasive device is located at or near the root of a vessel tree desired to be imaged. The RF coil is then used to alter the nuclear spin magnetization of blood flowing within the vessel. This is done by employing an RF excitation signal to the coil at the Larmor frequency of the blood. The nutation of spin magnetization can change the amount of longitudinal spin magnetization or the Amount of magnetization in the transverse plane. Because the size of the radio-frequency coil in the invasive device is small, the change in spin magnetization is limited to blood flowing by the invasive device. An MR imaging pulse sequence is then applied to the subject to obtain image information from the region containing the desired vessel tree. The MR imaging pulse sequence is designed to selectively detect the blood whose spin magnetization has been changed by the MR-active invasive device. Since only blood which the magnetization has modified is detected with the imaging sequence, the vessel tree is imaged.