Koninklijke Philips Corporation N.v.

Philips Intellectual Property & Standards Gmbh

Holger Eggers

Peter Boernert

Kay Nehrke

Steffen Weiss

Ulrich Wolfgang Katscher

Jochen Keupp

Peter Bornert

Peter Börnert

Christoph G Leussler

Johan Samuel Van Den Brink

Volker Rasche

Michael Harald Kuhn

Zhiqiang Hu

Bernhard Johannes Brendel

Ingmar Graesslin

Karsten Sommer

Christian Stehning

Bernd E Aldefeld

Jan Jakob Meineke

Erhard Paul Artur Klotz

Adrianus Joseph Willibrordus Duijndam

Dirk Manke

Friedrich-Karl Beckmann

Clemens Bos

Liesbeth Geerts-Ossevoort

Lingzhi Hu

Nadine Gdaniec

Georg Weidinger

Michael Schar

James Grant Pipe

Hendrik Kooijman

Eveline Alberts

Adri J Duijndam

Tobias Schäffter

Rolf Udo Dieter Kobs

The invention relates to a method of Dixon-type MR imaging. The object () is subjected to at least two shots of an imaging sequence, each shot comprising an excitation RF pulse followed by a series of refocusing RF pulses, wherein at least a pair of phase encoded echoes, a first echo at a first echo time and a second echo at a second echo time, is generated in each time interval between two consecutive refocusing RF pulses. Two sets of echo signal pairs, a first set and a second set, are acquired using bipolar pairs of readout magnetic gradients in two respective shots of the imaging sequence. The bipolar pair of readout magnetic field gradients in the acquisition of the second set has an opposite polarity to that of the bipolar pair of readout magnetic field gradients in the acquisition of the first set. Alternatively or additionally the temporal course of the readout magnetic field gradients in the acquisition of the second set is reversed with respect to the temporal course of the readout magnetic field gradients in the acquisition of the first set. Alternatively or additionally the acquisitions of the first and second sets are different from each other with respect to the gradient areas of magnetic field gradients in the readout direction (M) preceding respectively succeeding the bipolar pair of readout magnetic field gradients. Finally, an MR image is reconstructed from the acquired first and second sets of echo signal pairs, whereby signal contributions from water protons and fat protons are separated. Moreover the invention relates to an MR device () and to a computer program to be run on an MR device ().

Dixon-type water/fat separation MR imaging

The invention relates to a method of Dixon-type MR imaging. The object () is subjected to a dual- or multi-acquisition imaging sequence comprising a series of temporally equidistant RF pulses. An echo signal is generated in the presence of a readout magnetic field gradient in each time interval (TR) between successive RF pulses, with the echo time varying between at least a first value (TE) associated with a first acquisition (ACQ) and a second value (TE) associated with a second acquisition (ACQ). The invention proposes that at least one of the magnetic field gradients preceding and/or succeeding the readout magnetic field gradient in each time interval (TR) is temporally shifted, varied in duration and/or varied in amplitude between time intervals (TR). In this way, a reduction of the acoustic noise generated by the multi-acquisition Dixon sequence and, thus, of the discomfort for patients undergoing a corresponding examination is achieved. The echo signals are recorded and an MR image is reconstructed with separating signal contributions from water and fat based on the recorded echo signals of the at least two acquisitions (ACQ, ACQ). Moreover the invention relates to an MR device () and to a computer program to be run on an MR device ().

The invention relates to a method of Dixon-type MR imaging of an object () placed in an examination volume of a MR device (). It is an object of the invention to provide a method that enables an improved Dixon water/fat separation in combination with a dual-acquisition gradient-echo imaging sequence. The method comprises the steps of: —subjecting the object () to a dual-acquisition gradient-echo imaging sequence comprising a series of temporally equidistant RF excitations, wherein one gradient echo is generated in each repetition time between successive RF excitations with the echo time alternating between a first and a second value (TE, TE), and wherein phase-encoding magnetic field gradients (P, S) are switched in each repetition time to sample a pre-defined region of k-space; —acquiring echo signals from the object (), wherein each gradient echo associated with either the first or the second echo time value (TE, TE) is sampled as a partial echo, and —reconstructing an MR image from the acquired echo signals, whereby signal contributions from water and fat are separated. Moreover the invention relates to an MR device () and to a computer program to be run on an MR device ().

Disclosed herein is a medical system () comprising a memory () storing machine executable instructions () and a convolutional neural network (). The convolutional neural network is configured for receiving an initial Dixon magnetic resonance image () as input. The convolutional neural network is configured for identifying one or more water-fat swap regions () in the initial Dixon magnetic resonance image. The medical system further comprises a processor () for controlling the medical system. Execution of the machine executable instructions causes the processor to: receive () the initial Dixon magnetic resonance image; and receive () the one or more water-fat swap regions from the convolutional neural network in response to inputting the initial Dixon magnetic resonance image into the convolutional neural network.

Automated detection of water-fat swaps in Dixon magnetic resonance imaging

The invention relates to a method of MR imaging of an object positioned in an examination volume of a MR device (). It is an object of the invention to enable efficient silent ZTE imaging with self-refocusing. The method of the invention comprises the steps of:—specification of a set of radial k-space spokes to cover a spherical k-space volume;—selection of subsets of a predetermined number of spokes from the specified set so that the concatenation of the spokes contained in each of the subsets forms a closed trajectory in k-space, wherein the selection of the subsets involves optimizing a cost function;—subjecting the object () to a zero echo time imaging sequence, wherein each of the subsets of spokes is acquired as a sequence of gradient echo signals; and—reconstructing an MR image from the acquired spokes. Moreover, the invention relates to a MR device and to a computer program for a MR device.

Efficient self-refocusing zero echo time MR imaging

A method of magnetic resonance (MR) imaging to enable 'silent' zero echo time (ZTE) imaging in combination with water/fat separation. The method includes subjecting the object to a first self-refocusing zero echo time imaging sequence, wherein a first sequence of gradient echo signals is acquired as a first number Nof radial k-space spokes at a first repetition time TR; subjecting the object to a second self-refocusing zero echo time imaging sequence, wherein a second sequence of gradient echo signals is acquired as a second number Nof radial k-space spokes at a second repetition time TR, wherein N&#x2260;Nand/or TR&#x2260;TR; and reconstructing a MR image from the acquired gradient echo signals. Signal contributions of chemical species (e.g., water and fat) may be separated exploiting the different echo times attributed to the gradient echo signals.

Zero echo time MR imaging with water-fat separation

The invention relates to a method of Dixon-type MR imaging. It is an object of the invention to provide a method that enables efficient and reliable water/fat separation. The method of the invention comprises the following steps: subjecting an object () to an imaging sequence, which comprises at least one excitation RF pulse and switched magnetic field gradients, wherein two echo signals, a first echo signal and a second echo signal, are generated at different echo times (TE, TE), acquiring the echo signals from the object (), reconstructing a water image and/or a fat image from the echo signals, wherein contributions from water and fat to the echo signals are separated using a two-point Dixon technique in a first region of k-space and a single-point Dixon technique in a second region of k-space, wherein the first region is different from the second region. In other words, the invention proposes an adaptive switching between a two-point Dixon technique for water/separation, applied to both the first and second echo signals, and a single-point Dixon technique applied to one of the two echo signals, i.e. the first echo signal data or the second echo signal data, depending on the position in k-space. Moreover, the invention relates to a MR device () and to a computer program to be run on a MR device ().

The invention provides for a medical imaging system (). The medical imaging system comprises a processor (). Execution of machine executable instructions () causes the processor to: receive () magnetic resonance imaging data () comprising a Z-spectrum acquisition () for a set of saturation frequency offsets () and at least one reference saturation frequency offset (); reconstruct () saturation frequency offset complex image data (); reconstruct () a B0 map (), a water image (), and a fat image () according to a Dixon-type magnetic resonance imaging protocol; calculate () a water phase angle () using the water image and/or the fat image; calculate () rotated complex image data () by rotating the phase of the saturation frequency offset complex image data such that the complex water signal is aligned with a real axis for each voxel; perform () a B0 correction by calculating shifted complex image data (); calculate () a frequency dependent phase angle () descriptive of a phase angle between the complex water signal and the complex fat signal for each of the set of saturation frequency offsets using a fat signal model comprising at least two fat species; calculate () a residual fat component correction factor () by projecting the complex fat signal onto the real axis for each of the set of saturation frequency offsets; and calculate () corrected water Z-spectrum image data () by subtracting the residual fat component correction factor for each of the set of saturation frequency offsets from the real component of the shifted complex image data.

Single-point dixon method for fat-water separation in chemical exchange saturation transfer magnetic resonance imaging

The invention provides for a magnetic resonance imaging system (). Machine executable instructions () cause a processor controlling the magnetic resonance imaging system to control () the magnetic resonance imaging system with the pulse sequence commands to acquire two point Dixon magnetic resonance data and single point Dixon magnetic resonance data; calculate () a first resolution magnetic field inhomogeneity map () using the two point Dixon magnetic resonance data; calculate () a second resolution magnetic field inhomogeneity map () by interpolating the first resolution magnetic inhomogeneity map to the second resolution; and calculate () a second resolution water image () and a second resolution fat image () using the single point Dixon magnetic resonance imaging data and the second resolution magnetic field inhomogeneity map. The first resolution is lower than the second resolution.

Dual resolution Dixon magnetic resonance imaging

The invention relates to a method of Dixon-type MR imaging. It is an object of the invention to provide an MR imaging technique using bipolar readout magnetic field gradients with an improved estimation of the main field inhomogeneity to eliminate residual artifacts. In accordance with the invention, a method of MR imaging of an object placed in a main magnetic field within an examination volume of a MR device is proposed, wherein the method comprises the steps of: &#x2014;subjecting the object () to an imaging sequence to generate at least two sets of echo signals at two or more different echo times using bipolar pairs of readout magnetic field gradients, one set of echo signals being generated at a first echo time (TE) and the other set of echo signals being generated at a second echo time (TE), &#x2014;acquiring the echo signals from the object (), &#x2014;reconstructing a first image from the echo signals attributed to the first echo time (TE) and a second image from the echo signals attributed to the second echo time (TE), &#x2014;computing modified first and second images by compensating for a fat shift in the reconstructed first and second images respectively, &#x2014;estimating phase errors in the acquired echo signals on the basis of the first and second images and the modified first and second images using a signal model including the resonance spectra of fat and water and the spatial variation of the main magnetic field, and &#x2014;reconstructing a water image and/or a fat image by separating the signal contributions of fat and water to the acquired echo signals using the estimated phase errors. Moreover, the invention relates to a MR device () and to a computer program to be run on a MR device ().

Dixon type water/fat separation MR imaging with improved fat shift correction

A method of Dixon-type MR imaging includes subjecting the object () to a first imaging sequence () including a series of refocusing RF pulses. A single echo signal is generated in the time interval between two consecutive refocusing RF pulses. The first echo signals from the object () are acquired at a first receive bandwidth using unipolar readout magnetic field gradients. The object () is further subject to a second imaging sequence (), which includes a series of refocusing RF pulses. A pair of second echo signals is generated in each time interval between two consecutive refocusing RF pulses. The pairs of second echo signals from the object () are acquired at a second receive bandwidth using bipolar readout magnetic field gradients. The second receive bandwidth is higher than the first receive bandwidth. Signal contributions from water protons and fat protons are separated and an MR image is reconstructed.

The invention relates to a method of Dixon-type MR imaging. It is an object of the invention to provide a method that enables efficient and reliable water/fat separation using bipolar readout magnetic field gradients and avoids flow-induced leaking and swapping artifacts. According to the invention, an object () is subjected to an imaging sequence, which comprises at least one excitation RF pulse and switched magnetic field gradients, wherein two echo signals, a first echo signal and a second echo signal, are generated at different echo times (TE, TE). The echo signals are acquired from the object () using bipolar readout magnetic field gradients. A first single echo image is reconstructed from the first echo signals and a second single echo image is reconstructed from the second echo signals. A zero echo time image is computed by extrapolating the phase of the first single echo image at each voxel position to a zero echo time using the phase difference between the first and the second single echo image at the respective voxel position. Flow-induced phase errors are identified and estimated in the zero echo time image, and the phase of the first single echo image is corrected according to the estimated flow-induced phase errors. Finally, a water image and/or a fat image are reconstructed from the echo signals, wherein signal contributions from water and fat to the echo signals are separated using the phase-corrected first single echo image and the second single echo image. Moreover, the invention relates to a MR device () and to a computer program to be run on a MR device ().

Dual-echo dixon-type water/fat separation MR imaging

The invention relates to a method of Dixon-type MR imaging. It is an object of the invention to provide a method that enables Dixon water/fat separation with high SNR and with improved noise propagation in the water/fat separation. The method comprises the steps of: &#x2014;subjecting an object () to a first imaging sequence, which generates a number of differently phase encoded first MR echo signals at a first echo time, such that contributions from MR signals emanating from water protons and MR signals emanating from fat protons to the first MR echo signals are essentially in phase, &#x2014;acquiring the first MR echo signals using a first signal receiving bandwidth, &#x2014;subjecting the object () to a second imaging sequence which generates a number of differently phase encoded second MR echo signals at a second echo time, such that contributions from MR signals emanating from water protons and MR signals emanating from fat protons to the second MR echo signals are at least partially out of phase, &#x2014;acquiring the second MR echo signals using a second signal receiving bandwidth which is larger than the first receiving bandwidth, wherein the number of phase encodings of the first imaging sequence is smaller than the number of phase encodings of the second imaging sequence, and &#x2014;reconstructing a MR image from the first and second MR echo signals, whereby signal contributions from water protons and fat protons are separated. Moreover the invention relates to a MR device and to a computer program to be run on a MR device.

MR imaging with Dixon-type water/fat separation

The invention provides for a medical instrument () comprising a magnetic resonance imaging system () for acquiring magnetic resonance data () from a subject () within an imaging zone (). The magnetic resonance imaging system comprises: a main magnet () for generating a B0 magnetic field within the imaging zone; a memory () containing machine executable instructions () and pulse sequence commands (); a processor () for controlling the medical instrument. Execution of the machine executable instructions causes the processor to: acquire () the magnetic resonance data by controlling the magnetic resonance imaging system with the pulse sequence commands; receive () a subject magnetic susceptibility map () of the subject; calculate () a B0 inhomogeneity map () from the magnetic resonance data; calculate () a subject B0 magnetic field perturbation () from the subject magnetic susceptibility map; calculate () a residual B0 magnetic field perturbation () by subtracting the subject B0 magnetic field perturbation from the B0 inhomogeneity map; and calculate () a bone map () from the residual B0 magnetic field perturbation.

Bone MRI using B0 inhomogeneity map and a subject magnetic susceptibility map

The invention provides for a Dixon method of controlling a magnetic resonance imaging () system. Acquiring () Dixon magnetic resonance data (), first calibration magnetic resonance data (), and second calibration magnetic resonance data () using pulse sequence commands (). To cause the magnetic resonance imaging system to execute multiple pulse repetitions (). The multiple pulse repetitions causes the magnetic resonance imaging system to generate a Dixon readout gradient () along a readout direction (). The pulse sequence commands cause the processor to perform one or more first modified pulse repetitions () and one or more second modified pulse repetitions (). The one or more first modified pulse repetitions causes the magnetic resonance imaging system to generate a first modified readout gradient () for acquiring first calibration magnetic resonance data () during the first modified readout gradient during at least one of the one or more first modified pulse repetitions. The first modified readout gradient is the Dixon readout gradient with an amplitude reduced by a predetermined factor (). The one or more second modified pulse repetitions causes the magnetic resonance imaging system to generate a second modified readout gradient () for acquiring second calibration magnetic resonance data () during the second modified readout gradient during at least one of the one or more second modified pulse repetitions. The second modified readout gradient is the Dixon readout gradient with an amplitude reduced by the predetermined factor. The first modified readout gradient or the second modified readout gradient has a reversed polarity with respect to the Dixon readout gradient. First () and second () Fourier transformed data () are calculated () by Fourier transforming the first and second calibration magnetic resonance data in the readout direction, calculating () a phase difference () between the first and the second Fourier transformed data and a corrected phase difference () by interpolating and scaling the phase difference using the predefined factor, calculating () corrected Dixon magnetic resonance data () using the Dixon magnetic resonance data and the corrected phase difference, and calculating () a water signal () and a fat signal () from the corrected Dixon magnetic resonance data.

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Ellerhoop, Germany

Holger Eggers