Abstract: The shear stiffness of a subject's spleen is measured using elastography techniques such as ultrasound elastography or a magnetic resonance elastography (MRE) acquisition with an MRI system. A relationship between splenic shear stiffness and portal venous blood pressure is modeled and is used to calculate portal venous blood pressure non-invasively from the measured splenic shear stiffness.

Abstract: A driver for applying an oscillating stress to a subject undergoing a medical imaging procedure, such as with magnetic resonance elastography (MRE), includes a passive driver located in the bore of the magnet and in direct contact with the skin of the subject. A remotely located active driver includes a linear motor and a sealed diaphragm that produces acoustic pressure waves in response to an applied current. The pressure waves are directed through a tube and into a chamber formed within the passive driver. Vibrations produced in response to the pressure waves create shear waves that are directed into the subject to aid in the imaging procedure.

Abstract: An acoustic driver system for use in applying an oscillating stress to a subject undergoing a magnetic resonance elastography (MRE) examination includes a flexible passive driver located in the bore of the magnet and in contact with the subject. A remotely located active driver is acoustically coupled to the passive driver and produces acoustic energy in response to an applied current. The passive driver produces shear waves in response to the acoustic energy and are directed into the body of the subject undergoing the MRE examination.

Abstract: A system is configured to produce a stress on a subject while performing a magnetic resonance elastography scan in a magnetic resonance imaging (MRI) system. The system includes an active driver operable to produce an energy configured for a magnetic resonance elastography (MRE) process. A passive actuator is configured to be positioned in the MRI system and to be coupled to the subject. The system includes a tube coupling the active driver to the passive actuator to deliver the energy produced by the active driver to the passive actuator, and a strap coupled to the passive actuator. The strap is configured to be disposed around the subject. The strap includes a substantially inelastic material configured to convert the energy delivered to the passive actuator from the tube into shear waves with the subject for use in the MRE process.

Abstract: A system and method for producing an image of a functional tissue slip interface using MRI. The method includes applying an external stimulus to a subject to impart relative shearing motion at a tissue interface. NMR signals are then acquired from a ROI including the slip interface using a motion encoding gradient to sensitize the acquired NMR signals to the shearing motion. MR images indicative of the degree of mechanical shear connectivity at the tissue interface are reconstructed from the acquired NMR signals in which low-friction shearing motion at the tissue interface is characterized by a loss of magnitude signal due to intravoxel phase dispersion.

Abstract: A magnetic resonance elastography (MRE) scan is performed using an array of transducers for applying a strain wave to tissues in a region of interest. A calibration process is performed prior to the scan in which the strain wave produced by each transducer in the array is imaged using an MRE pulse sequence so that information may be acquired that enables each transducer to be properly driven during a subsequent MRE scan.

Abstract: A driver for use in applying an oscillating stress to a subject undergoing a magnetic resonance elastography (MRE) examination includes a passive actuator located in the bore of the magnet and in contact with the subject. A remotely located acoustic driver produces acoustic energy in response to an applied current and this energy is coupled therethrough a flexible tube to the passive actuator. A movable element in the passive actuator vibrates in response to this acoustic energy.

Abstract: Magnetic resonance acoustography images are acquired in real time using a one-dimensional magnetic resonance elastography (MRE) pulse sequence in which a column of tissue is excited. A spin-echo MRE pulse sequence and a gradient-echo MRE pulse sequence are described which employ a broadband motion sensitizing gradient that enables an asynchronous transducer to be used to produce the oscillatory stress in the subject tissues.

Abstract: Magnetic resonance acoustography images are acquired in real time using a one-dimensional magnetic resonance elastography (MRE) pulse sequence in which a column of tissue is excited. A spin-echo MRE pulse sequence and a gradient-echo MRE pulse sequence are described which employ a broadband motion sensitizing gradient that enables an asynchronous transducer to be used to produce the oscillatory stress in the subject tissues.

Abstract: A scan using an NMR imaging system is carried out while applying an oscillating voltage to the subject being imaged. The applied voltage may produce an electric field which moves charged particles in the subject, or it may produce a current that moves ions in the subject. An alternating magnetic field gradient synchronized with the applied voltage is employed in the NMR imaging pulse sequence to detect and measure synchronous spin motion throughout the field of view. The direction of the alternating gradient and/or the applied voltage may be changed to measure and image the properties of the subject.

Abstract: An MRI image acquired with a phase-array coil is corrected for motion artifacts using an iterative, autocorrection process in which corrections are tried and the quality of the resulting reconstructed image is measured. In one embodiment autocorrections are calculated for the data acquired with one coil element and the same corrections are made to data acquired with the other coil elements. In another embodiment autocorrections are calculated separately for the data acquired with each coil element. In either embodiment, the separate corrected images are combined to form the output image.

Abstract: An MRI image is corrected for motion artifacts using an iterative, autocorrection process in which corrections are tried and the quality of the resulting reconstructed image is measured. Metrics based on the gradient of the reconstructed image are employed to measure image quality.

Abstract: A three-dimensional image data set is acquired with an MRI system and autocorrected to reduce artifacts caused by subject motion during image acquisition. Correction for motion along one or two axes is performed by selecting a 2D slice of data and autocorrecting it to produce phase corrections that are then made to the entire 3D image data set. This may be repeated by autocorrecting an additional 2D slice perpendicular to the first 2D slice to produce phase corrections for the 3D image data set for motion along the third axis.

Abstract: An MRI image is corrected for motion artifacts using an iterative, autocorrection process in which corrections are tried and the quality of the resulting reconstructed image is measured. Different metrics for evaluating image quality are used during the autocorrection process to take advantage of their different attributes.

Abstract: Navigator echo signals are acquired during an MRI scan in which image data is acquired. The navigator echo signals are used to estimate an initial correction of the acquired image data for patient motion during the scan. The initially corrected image data is then autocorrected in an iterative process which measures image quality and makes further corrections to the image data until the measured image quality is within tolerance.

Abstract: Devices for producing an oscillatory shear stress within an object positioned in a polarizing magnetic field of an NMR imaging system are used to perform MR elastography. In one embodiment shear stress is produced within the brain by vibrating the entire skull with a transducer that is gripped by the patient's teeth.

Abstract: A scan using an NMR imaging system is carried out while applying an oscillating stress to the object being imaged. An alternating magnetic field gradient synchronized with the applied stress is employed in the NMR imaging pulse sequence to detect and measure synchronous spin motion throughout the field of view. The direction of the alternating gradient and/or the applied stress may be changed to measure and image the elastic properties of the object.

Abstract: Devices for applying an oscillatory stress to an object positioned in a polarizing magnetic field of an NMR imaging system are used to perform MR elastography. The devices employ electrically energized coils which are connected to drive members and drive plates in a manner to provide various oscillatory forces to an object being imaged. The different oscillatory forces enable different body organs to be imaged using MR elastography methods.

Abstract: The alternating magnetic field gradient used to sensitize an NMR signal to spin motion is modulated in amplitude with a window function to tailor it to the particular NMR measurement. In an MR elastography measurement, the gradient is a sinusoidal waveform having a frequency the same as an applied oscillatory stress, and the window function desensitizes the measurement to spin motions at other frequencies.

Abstract: A dynamic MR angiography technique, MR digital subtraction angiography (MR DSA), based on fast acquisition, contrast enhancement and complex subtraction is described. When a bolus of contrast is injected into a patient, data acquisition begins, dynamically acquiring a thick slab using a fast gradient echo sequence for 1060 sec. Similar to x-ray DSA, a mask is selected from the images without contrast enhancement, and later images are subtracted from the mask to generate angiograms. Complex subtraction is used to overcome the partial volume effects related to the phase difference between the flowing and stationary magnetization in a voxel.