89 results about "Steady state free precession" patented technology

A generalized multi-point fat-water separation process is combined with steady-state free precession (SSFP) to obtain high quality images of articular cartilage with reduced imaging time.

A method that exploits the intrinsic selectivity of steady-state free precession (SSFP) to perform spectral suppression is disclosed. Such a method avoids the need to incorporate additional spectrally selective pulse sequence elements. The scheme is based on breaking the FISP imaging sequence into short trains having, for example, 8–64 RF pulses. At the moment of echo formation (i.e., TE=TR/2) after the last full RF pulse of the train, water signal is z-stored. Residual transverse magnetization, which include isochromats phase-opposed to the on-resonance water, is gradient crushed and RF spoiled. The stored magnetization is subsequently re-excited with little disturbance to the on-resonance steady-state water signal. The additional time required to perform the steady-state interruption is typically as little as a single TR, minimally affecting the efficiency of the imaging process. The sequence can be employed repetitively, greatly reducing the amplitude of fat signals throughout a real-time or cine imaging process.

A method of steady-state free precession MR imaging is provided that includes the steps of: (a) providing a balanced steady-state free precession imaging sequence that includes a plurality of phase encoding steps, wherein each phase encoding step comprises a phase encoding gradient and a slice selection gradient; and (b) acquiring imaging data by performing the plurality of phase encoding steps in sequence, wherein the imaging data is acquired is compensated for one or more effects due to eddy-currents, flow, or motion related artefacts due to the implementation of one or more artefact compensation strategies that consist of (i) “pairing” of consecutive phase encoding steps and of (ii) “through slice equilibration” of eddy-current and motion or flow related signal oscillations.

A method for non-contrast enhanced 4D time resolved dynamic magnetic resonance angiography using arterial spin labeling of blood water as an endogenous tracer and a multiphase balanced steady state free precession readout is presented. Imaging can be accelerated with dynamic golden angle radial acquisitions and k-space weighted imaging contrast (KWIC) image reconstruction and it can be used with parallel imaging techniques. Quantitative tracer kinetic models can be formed allowing cerebral blood volume, cerebral blood flow and mean transit time to be estimated. Vascular compliance can also be assessed using 4D dMRA by synchronizing dMRA acquisitions with the systolic and diastolic phases of the cardiac cycle.

A magnetic resonance imaging (MRI) method for the quantification of the longitudinal (T₁) and/or transverse (T₂) relaxation times in a sample is provided. According to this MRI method a sample is subjected to an unbalanced steady state free precession (SSFP) sequence comprising a series of consecutive radiofrequency (RF) pulses. By means of this unbalanced SSFP sequence, the first order SSFP FID signal (F₁), the lowest order SSFP FID signal (F₀), and the lowest order SSFP Echo signal (F₋₁) are acquired. Based on the F₀-signal, the F₁-signal and the F₋₁-signal the longitudinal (T₁) and/or transverse (T₂) relaxation times of the sample are determined.

A system has been developed for mapping the magnetic field during a balanced steady-state free precession (SSFP) sequence. Field maps are generated by analyzing the magnitude of images acquired using the SSFP imaging sequences with phase increment or frequency shift. The system maps the magnetic field relevant to the imaging sequence and need not rely on phase information. The field maps may be applied to adjust the hardware for correcting the field anomalies contained in the maps. The field maps may also be used for separation of water and fat signals in SSFP imaging.

An MR imaging includes acquiring echoes from the object by implementing a pulse sequence which specifies the conditions which should be established with spins excited in the steady-state free precession (SSFP) method, so that the object can be scanned with an echo induced by water contained in the object and an echo induced by fat contained therein in single quadrature with each other or with a phase difference of 90° between the echoes induced by water and fat, constructing a tomographic image by performing frequency transformation on the acquired echoes, compensating the transformed data for the inhomogeneity in a static magnetic field and reconstructing an image, of which water and fat components are separated from each other, according to the result of the compensation.

Water-fat separated magnetic resonance (MR) images with balanced steady-state free precession (SSFP) are produced. The acquired SSFP signals are isolated into multiple echo components in which the phase arrangements between the water and fat signals are controlled by appropriately selecting the TR and TE values of the SSFP imaging sequence. From the isolated echo components, the effects of the field inhomogeneities are corrected and water and fat images are separated.

The invention relates to a magnetic resonance imaging temperature measuring method on the basis of three-dimensional free motion, comprising the steps as follows: 1) at initial temperature Tb, the repeating time TR, the temperature coefficients a and b, large turnover angle Alpha1 and small turnover angle Alpha 2 of the three-dimensional stable free motion sequence are determined; 2) images I and I of tissue to be measured are collected so as to gain the superposition images Ib=I+I of the tissue to be measured at the initial temperature Tb; 3) at the to-be-measured temperature Th, under the conditions of temperature coefficient Alpha1 and repeating time T determined in the step 1), the image I of the tissue to be measured is collected; subsequently, under the conditions of temperature coefficient Alpha2 and repeating time T, the image I of the tissue to be measured is collected so as to gain the image I=I+I at the to-be-measured temperature Th of the tissue to be measured; 4) standard image I=Ih/Ib is superposed; 5) the temperature image I of the tissue to be measured is calculated; the value of each point on the temperature image I is the Delta T of the tissue to be measured at the point; 6) the to-be-measured temperature Th equal to Tb+Delta T of the tissue to be measured is worked out.

The invention provides a magnetic resonance imaging method based on a steady-state free procession sequence and belongs to the technical field of magnetic resonance imaging. The magnetic resonance imaging method based on the steady-state free procession sequence comprises the steps that excitation pulses and a first-level selection gradient A are applied at the same time; a second-level selection gradient B and a first phase encoding gradient U are applied, and a phase pre-dispersing gradient J is read; a first reading gradient G is applied, and an echo horizontal-movement signal is acquired at the same time; a third-level selection gradient D is applied; a second reading gradient H is applied, and a time reversed steady-state procession signal is acquired at the same time; a reading back-gathering gradient F, a second phase encoding gradient V and a fourth-level selection gradient C are applied, wherein the moment of the gradient A, the moment of the gradient B, the moment of the gradient C and the moment of the gradient D meet the relation: MC=-MA/2 and 2MB-MD=MA; a k space is filled with obtained signals, and Fourier transformation is conducted, so that a magnetic resonance image is obtained. According to the magnetic resonance imaging method based on the steady-state free procession sequence, the time reversed steady-state procession signal and the time reversed steady-state procession signal can be acquired at the same time, and imaging time is shortened.

Artifact reduction in steady state free precession magnetic resonance imaging uses weighting of acquired image data to emphasize higher signals and then establishing an image signal based on the combined weighted signals. In one embodiment, a SSFP imaging sequence uses phase cycling and acquired image data is squared with the squared data then combined. The final image signal is based on the square root of the squared data.

The present invention provides a magnetic resonance imaging apparatus and method. The magnetic resonance imaging apparatus comprises a data acquisition unit and an image generating unit. The data acquisition unit configured to acquire magnetic resonance data according to an imaging condition for obtaining a steady state free precession of nuclear magnetic spins in flowing matter in an object by applying plural excitation pulses having a same flip angle with a constant repetition time (TR) and gradient magnetic fields to the object; wherein respective zero order moments of gradient magnetic field within the repetition time (TR), gradient magnetic field for slice selection from each application time of the plural excitation pulses till a center time of a corresponding echo, gradient magnetic field for readout from each application time of the plural excitation pulses till a center time of a corresponding echo, gradient magnetic field for slice selection from a center time of each echo till an application time of a following excitation pulse, gradient magnetic field for readout from a center time of each echo till an application time of a following excitation pulse are zero while a first order moment of at least one of gradient magnetic field for slice selection and gradient magnetic field for readout within the repetition time is nonzero. The image generating unit is configured to generate an image of the flowing matter based on the magnetic resonance data.

Disclosed is a method and system for steady state free precession based magnetic resonance thermometry that measures changes in temperature on a pixel by pixel basis. The method comprises generating an RF pulse sequence used to find the proton resonance frequency shift, which is proportional to temperature change, processing the resultant MRI data to measure the proton frequency shift, and converting the measured proton frequency shift into change in temperature data. Further disclosed is a method for identifying and compensating for temperature drifts due to core heating of the gradient magnet.

A pulse sequence for use in steady state free precession (SSFP) imaging sequences includes a RF pulse and a time-varying gradient pulse based on a conventional design algorithm such as the Shinnar-LeRoux (SLR) pulse design algorithm and in which amplitude of the RF pulse and gradient pulse are increased while pulse time is decreased thereby reducing imaging time and improving slab profiles.