Correcting for hysteresis in magnetic resonance imaging

Abstract

An apparatus for controlling at least one gradient coil of a magnetic resonance imaging (MRI) system. The apparatus may include at least one computer hardware processor; and at least one computer-readable storage medium storing processor executable instructions that, when executed by the at least one computer hardware processor, cause the at least one computer hardware processor to perform a method. The method may include receiving information specifying at least one target pulse sequence; determining a corrected pulse sequence to control the at least one gradient coil based on the at least one target pulse sequence and a hysteresis model of induced magnetization in the MRI system caused by operation of the at least one gradient coil; and controlling, using the corrected gradient pulse sequence, the at least one gradient coil to generate one or more gradient pulses for imaging a patient.

What is claimed is: 
     
         1 . An apparatus for controlling at least one gradient coil of a magnetic resonance imaging (MRI) system, the apparatus comprising:
 at least one computer hardware processor; and   at least one computer-readable storage medium storing processor executable instructions that, when executed by the at least one computer hardware processor, cause the at least one computer hardware processor to perform a method comprising:
 receiving information specifying at least one target pulse sequence; 
 determining a corrected pulse sequence to control the at least one gradient coil based on the at least one target pulse sequence and a hysteresis model of induced magnetization in the MRI system caused by operation of the at least one gradient coil; and 
 controlling, using the corrected pulse sequence, the at least one gradient coil to generate one or more gradient pulses for imaging a patient. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the corrected pulse sequence includes a corrected gradient pulse sequence and controlling the at least one gradient coil comprises driving the at least one gradient coil with the corrected gradient pulse sequence such that a strength of a gradient field formed in at least a portion of an imaging region of the MRI system is substantially equal to a target magnetic field strength that the target pulse sequence is designed to achieve. 
     
     
         3 . The apparatus of  claim 1 , wherein determining the corrected pulse sequence is further based on a current state of the hysteresis model. 
     
     
         4 . The apparatus of  claim 1 , wherein the hysteresis model comprises a plurality of weights, a respective plurality of lower magnetic field strength values and a respective plurality of upper magnetic field strength values, wherein each of the plurality of weights is associated with a respective one of the plurality of lower magnetic field strength values and a respective one of the upper magnetic field strength values. 
     
     
         5 . The apparatus of  claim 4 , wherein the hysteresis model comprises a Preisach model. 
     
     
         6 . The apparatus of  claim 4 , wherein each of the plurality of weights is determined using at least one previously-obtained hysteresis measurement obtained with a multi-element probe. 
     
     
         7 . The apparatus of  claim 1 , wherein the MRI system includes a ferromagnetic yoke, and wherein the hysteresis model represents effects of hysteresis induced at least in the ferromagnetic yoke by operation of the at least one gradient coil. 
     
     
         8 . The apparatus of  claim 1 , wherein determining the corrected pulse sequence comprises iteratively determining the corrected pulse sequence. 
     
     
         9 . The apparatus of  claim 8 , wherein iteratively determining the corrected pulse sequence comprises:
 determining an initial corrected pulse sequence based on the target pulse sequence and the hysteresis model; and   determining a final corrected pulse sequence based on the initial corrected pulse sequence and the hysteresis model,   wherein controlling the at least one gradient coil comprises driving the at least one gradient coil with a final gradient pulse sequence of the final pulse sequence such that a strength of a gradient field formed in at least a portion of an imaging region of the MRI system is substantially equal to a target magnetic field strength value.   
     
     
         10 . The apparatus of  claim 1 , wherein determining the corrected pulse sequence comprises adjusting an amplitude of a pulse within a target gradient pulse sequence of the target pulse sequence. 
     
     
         11 . The apparatus of  claim 10 , wherein:
 the target pulse sequence comprises a target gradient pulse sequence comprising a plurality of target gradient pulses;   determining the corrected pulse sequence comprises determining a plurality of corrected pulse amplitudes for a plurality of corrected gradient pulses of a corrected gradient pulse sequence; and   determining a first corrected pulse amplitude of a first corrected gradient pulse is based on at least a second corrected pulse amplitude of a second corrected gradient pulse that occurs earlier in the corrected gradient pulse sequence than the first corrected gradient pulse.   
     
     
         12 . The apparatus of  claim 11 , wherein determining the corrected gradient pulse sequence comprises determining an amplitude of every pulse of the corrected pulse sequence by iterating from a beginning gradient pulse of the corrected gradient pulse sequence to a final gradient pulse of the corrected gradient pulse sequence, wherein the amplitude of a particular corrected gradient pulse of the corrected gradient pulse sequence is based on at least one previous corrected gradient pulse of the corrected gradient pulse sequence. 
     
     
         13 . The apparatus of  claim 1 , wherein determining the corrected pulse sequence comprises determining a corrected transmit radio frequency (RF) pulse sequence used to control a RF transmit coil and/or a corrected receive RF pulse sequence used to control a RF receive coil. 
     
     
         14 . The apparatus of  claim 13 , wherein:
 determining a corrected transmit RF pulse sequence comprises adjusting a center frequency or phase of a transmit RF pulse of the corrected transmit RF pulse sequence; and   determining a corrected receive RF pulse sequence comprises adjusting a center frequency or phase of a receive RF pulse of the corrected receive RF pulse sequence.   
     
     
         15 . The apparatus of  claim 1 , further comprising the MRI system. 
     
     
         16 . The apparatus of  claim 15 , further comprising the at least one gradient coil. 
     
     
         17 . The apparatus of  claim 15 , wherein the MRI system comprises a ferromagnetic yoke. 
     
     
         18 . The apparatus of  claim 17 , wherein the ferromagnetic yoke comprises:
 a first plate comprising ferromagnetic material;   a second plate comprising ferromagnetic material; and   a frame comprising ferromagnetic material coupled to the first plate and the second plate.   
     
     
         19 - 28 . (canceled) 
     
     
         29 . A method of controlling at least one gradient coil of a magnetic resonance imaging (MRI) system, the method comprising, with at least one computer hardware processor:
 receiving information specifying at least one target pulse sequence;   determining a corrected pulse sequence to control the at least one gradient coil based on the at least one target pulse sequence and a hysteresis model of induced magnetization in the MRI system caused by operation of the at least one gradient coil; and   controlling, using the corrected pulse sequence, the at least one gradient coil to generate one or more gradient pulses for imaging a patient.   
     
     
         30 - 54 . (canceled) 
     
     
         55 . At least one computer-readable storage medium storing processor executable instructions that, when executed by at least one computer hardware processor, cause the at least one computer hardware processor to perform a method of controlling at least one gradient coil of a magnetic resonance imaging (MRI) system, the method comprising:
 receiving information specifying at least one target pulse sequence;   determining a corrected pulse sequence to control the at least one gradient coil based on the at least one target pulse sequence and a hysteresis model of induced magnetization in the MRI system caused by operation of the at least one gradient coil; and   controlling, using the corrected pulse sequence, the at least one gradient coil to generate one or more gradient pulses for imaging a patient.   
     
     
         56 - 196 . (canceled)