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1. WO2014118559 - APPARATUS AND METHOD FOR CORRECTING SUSCEPTIBILITY ARTEFACTS IN A MAGNETIC RESONANCE IMAGE

Publication Number WO/2014/118559
Publication Date 07.08.2014
International Application No. PCT/GB2014/050268
International Filing Date 31.01.2014
IPC
G01R 33/44 2006.1
GPHYSICS
01MEASURING; TESTING
RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
33Arrangements or instruments for measuring magnetic variables
20involving magnetic resonance
44using nuclear magnetic resonance
G01R 33/56 2006.1
GPHYSICS
01MEASURING; TESTING
RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
33Arrangements or instruments for measuring magnetic variables
20involving magnetic resonance
44using nuclear magnetic resonance
48NMR imaging systems
54Signal processing systems, e.g. using pulse sequences
56Image enhancement or correction, e.g. subtraction or averaging techniques
G01R 33/565 2006.1
GPHYSICS
01MEASURING; TESTING
RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
33Arrangements or instruments for measuring magnetic variables
20involving magnetic resonance
44using nuclear magnetic resonance
48NMR imaging systems
54Signal processing systems, e.g. using pulse sequences
56Image enhancement or correction, e.g. subtraction or averaging techniques
565Correction of image distortions, e.g. due to magnetic field inhomogeneities
CPC
G01R 33/24
GPHYSICS
01MEASURING; TESTING
RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
33Arrangements or instruments for measuring magnetic variables
20involving magnetic resonance
24for measuring direction or magnitude of magnetic fields or magnetic flux
G01R 33/5608
GPHYSICS
01MEASURING; TESTING
RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
33Arrangements or instruments for measuring magnetic variables
20involving magnetic resonance
44using nuclear magnetic resonance [NMR]
48NMR imaging systems
54Signal processing systems, e.g. using pulse sequences ; , Generation or control of pulse sequences
56Image enhancement or correction, e.g. subtraction or averaging techniques ; , e.g. improvement of signal-to-noise ratio and resolution
5608Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels
G01R 33/5616
GPHYSICS
01MEASURING; TESTING
RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
33Arrangements or instruments for measuring magnetic variables
20involving magnetic resonance
44using nuclear magnetic resonance [NMR]
48NMR imaging systems
54Signal processing systems, e.g. using pulse sequences ; , Generation or control of pulse sequences
56Image enhancement or correction, e.g. subtraction or averaging techniques ; , e.g. improvement of signal-to-noise ratio and resolution
561by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
5615Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
5616using gradient refocusing, e.g. EPI
G01R 33/565
GPHYSICS
01MEASURING; TESTING
RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
33Arrangements or instruments for measuring magnetic variables
20involving magnetic resonance
44using nuclear magnetic resonance [NMR]
48NMR imaging systems
54Signal processing systems, e.g. using pulse sequences ; , Generation or control of pulse sequences
56Image enhancement or correction, e.g. subtraction or averaging techniques ; , e.g. improvement of signal-to-noise ratio and resolution
565Correction of image distortions, e.g. due to magnetic field inhomogeneities
G01R 33/56536
GPHYSICS
01MEASURING; TESTING
RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
33Arrangements or instruments for measuring magnetic variables
20involving magnetic resonance
44using nuclear magnetic resonance [NMR]
48NMR imaging systems
54Signal processing systems, e.g. using pulse sequences ; , Generation or control of pulse sequences
56Image enhancement or correction, e.g. subtraction or averaging techniques ; , e.g. improvement of signal-to-noise ratio and resolution
565Correction of image distortions, e.g. due to magnetic field inhomogeneities
56536due to magnetic susceptibility variations
G01R 33/56545
GPHYSICS
01MEASURING; TESTING
RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
33Arrangements or instruments for measuring magnetic variables
20involving magnetic resonance
44using nuclear magnetic resonance [NMR]
48NMR imaging systems
54Signal processing systems, e.g. using pulse sequences ; , Generation or control of pulse sequences
56Image enhancement or correction, e.g. subtraction or averaging techniques ; , e.g. improvement of signal-to-noise ratio and resolution
565Correction of image distortions, e.g. due to magnetic field inhomogeneities
56545caused by finite or discrete sampling, e.g. Gibbs ringing, truncation artefacts, phase aliasing artefacts
Applicants
  • UCL BUSINESS PLC [GB]/[GB]
Inventors
  • OURSELIN, Sebastien
  • DAGA, Pankaj
Agents
  • DAVIES, Simon
Priority Data
1301795.901.02.2013GB
Publication Language English (en)
Filing Language English (EN)
Designated States
Title
(EN) APPARATUS AND METHOD FOR CORRECTING SUSCEPTIBILITY ARTEFACTS IN A MAGNETIC RESONANCE IMAGE
(FR) APPAREIL ET PROCÉDÉ PERMETTANT DE CORRIGER DES ARTEFACTS DE SUSCEPTIBILITÉ DANS UNE IMAGE DE RÉSONANCE MAGNÉTIQUE
Abstract
(EN) An apparatus and method are provided for performing phase unwrapping for an acquired magnetic resonance (MR) image. The method includes modelling the MR phase in the MR image using a Markov random field (MRF) in which the true phase φ(t) and the wrapped phase φ(w) are modelled as random variables such that at voxel i of said MR image φ(t)(i)=φ(w)(i)+2πn(i), where n(i) is an unknown integer that needs to be estimated for each voxel i. The method further includes constructing a graph consisting of a set of vertices V and edges E and two special terminal vertices representing a source s and sink t, where there is a one-to-one correspondence between cuts on the graph and configurations of the MRF, a cut representing a partition of the vertices V into disjoint sets S and T such that s ∈ S and t ∈ T. The method further includes finding the minimum energy configuration, E(n(i)| φ(w)) of the MRF on the basis that the total cost of a given cut represents the energy of the corresponding MRF configuration, where the cost of a cut is the sum of all edges going from S to T across the cut boundary. The method further includes using the values of n(i) in the minimum energy configuration to perform the phase unwrapping from φ(w) to φ(t) for the MR image. A confidence may be computed for each voxel using dynamic graph cuts. The unwrapped phase from two MR images acquired at different times may be used to estimate a field map from the phase difference between the two MR images. The field map may be converted into a deformation field which is then used to initialise a non-rigid image registration of the acquired MR image against a reference image. The deformation field of the non-rigid registration is controlled to be smoother where the confidence is high.
(FR) L'invention concerne un appareil et un procédé permettant d'effectuer un déroulement de phase pour une image de résonance magnétique acquise (MR). Ledit procédé consiste à modéliser la phase MR dans l'image MR au moyen d'un champ aléatoire de Markov (MRF) dans lequel la phase réelle φ(t) et la phase déroulée φ(w) sont modelées en tant que variables aléatoires de sorte qu'au voxel i de ladite image MR φ(t)(i)=φ(w)(i)+2πn(i), où n(i) est un nombre entier inconnu qui doit être estimé pour chaque voxel i. Le procédé consiste également à construire un graphique comprenant un ensemble de sommets V et d'arêtes E et deux sommets terminaux spéciaux représentant une source s et un puits t, où il existe une correspondance univoque entre les coupes sur le graphique et les configurations du MRF, une coupe représentant une partition des sommets V en ensembles disjoints S et T de sorte que s ∈ S et t ∈ T. Le procédé consiste également à trouver la configuration énergétique minimale, E(n(i)| φ(w)) du MRF en s'appuyant sur le fait que le coût total d'une coupe donnée représente l'énergie de la configuration MRF correspondante, le coût d'une coupe étant la somme de toutes les arêtes allant de S à T au-delà de la limite de coupe. Le procédé consiste également à utiliser les valeurs de n(i) dans la configuration énergétique minimale pour effectuer le déroulement de phase de φ(w) à φ(t) pour l'image MR. Une confiance peut être calculée pour chaque voxel au moyen de coupes de graphiques dynamiques. La phase déroulée des deux images MR acquises à différents instants peut servir à estimer une carte de champ à partir de la différence de phase entre les deux images MR. La carte de champ peut être convertie en un champ de déformation qui sert ensuite à initialiser un enregistrement d'image non rigide de l'image MR acquise par rapport à une image de référence. Le champ de déformation de l'enregistrement non rigide est contrôlé pour être plus régulier lorsque la confiance est élevée.
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