# US 2019/0377044 A1 · Determination of higher order terms of the three-dimensional gradient impulse response function > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0377044 A1 - Document ID: US20190377044A1 - Status: Published application - Kind: A1 - Application number: 16/391,457 - Filed: 2019-04-23 - Published: 2019-12-12 - Earliest claimed: 2018-06-12 - Assignees: Koninklijke Philips N.V. - Applicants: Koninklijke Philips N.V. - Inventors: JUERGEN RAHMER; TIM NIELSEN; PETER BOERNERT - Web page: https://patentgrep.com/patent/US20190377044A1 ## CPC - G01R 33/3852: {Gradient amplifiers; means for controlling the application of a gradient magnetic field to the sample, e.g. a gradient signal synthesizer} - G01R 33/56518: {due to eddy currents, e.g. caused by switching of the gradient magnetic field} - A61B 5/055: involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging - G01R 33/443: {Assessment of an electric or a magnetic field, e.g. spatial mapping, determination of a B0 drift or dosimetry} - G01R 33/4808: {Multimodal MR, e.g. MR combined with positron emission tomography [PET], MR combined with ultrasound or MR combined with computed tomography [CT]} - G01R 33/4835: {of multiple slices} - G01R 33/5611: {Parallel magnetic resonance imaging, e.g. sensitivity encoding [SENSE], simultaneous acquisition of spatial harmonics [SMASH], unaliasing by Fourier encoding of the overlaps using the temporal dimension [UNFOLD], k-t-broad-use linear acquisition speed-up technique [k-t-BLAST], k-t-SENSE (structural details of arrays of sub-coils G01R33/3415)} - G01R 33/56572: {caused by a distortion of a gradient magnetic field, e.g. non-linearity of a gradient magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence)} - G01R 33/58: Calibration of imaging systems, e.g. using test probes {, Phantoms; Calibration objects or fiducial markers such as active or passive RF coils surrounding an MR active material} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract The invention provides for a medical instrument comprising a magnetic resonance imaging system with an imaging zone. The magnetic resonance imaging system comprises a gradient coil system with three orthogonal gradient coils. The execution of the machine executable instructions causes a processor controlling the medical instrument to: repeatedly control the magnetic resonance imaging system with the calibration pulse sequence commands to acquire the magnetic resonance calibration data for multiples slices using at least one of the three orthogonal gradient coils to generate the slice select gradient magnetic field; compute a Fourier transform of the magnetic resonance calibration data for each of the voxels of the multiple slices in the phase encoding directions; compute an expansion of the Fourier transformed magnetic resonance calibration data into spherical harmonics; and calculate a three-dimensional gradient impulse response function for the at least one of the three orthogonal gradient coils using the expansion into spherical harmonics. The calibration pulse sequence commands are configured for acquiring magnetic resonance calibration data from a magnetic resonance imaging phantom within the imaging zone according to a calibration magnetic resonance imaging protocol with two-dimensional phase encoding perpendicular to a slice select gradient magnetic field. The calibration magnetic resonance imaging protocol is configured for acquiring slices divided into voxels by the two-dimensional phase encoding. ## Claims ### Claim 1 A medical instrument comprising a magnetic resonance imaging system with an imaging zone, wherein the magnetic resonance imaging system comprises: a gradient coil system for generating a gradient magnetic field within the imaging zone, wherein the gradient coil system comprises three orthogonal gradient coils; a memory for storing machine executable instructions and calibration pulse sequence commands, wherein the calibration pulse sequence commands are configured for acquiring magnetic resonance calibration data from a magnetic resonance imaging phantom within the imaging zone according to a calibration magnetic resonance imaging protocol with two-dimensional phase encoding perpendicular to a slice select gradient magnetic field, wherein the calibration magnetic resonance imaging protocol is configured for acquiring slices divided into voxels by the two-dimensional phase encoding; a processor for controlling the magnetic resonance imaging system, wherein execution of the machine executable instructions causes the processor to: repeatedly control the magnetic resonance imaging system with the calibration pulse sequence commands to acquire the magnetic resonance calibration data for multiples slices using at least one of the three orthogonal gradient coils to generate the slice select gradient magnetic field; compute a Fourier transform of the magnetic resonance calibration data for each of the voxels of the multiple slices in the phase encoding directions; compute an expansion of the Fourier transformed magnetic resonance calibration data into spherical harmonics; and calculate a three-dimensional gradient impulse response function for the at least one of the three orthogonal gradient coils using the expansion into spherical harmonics. ### Claim 2 (depends on 1) The medical instrument of claim 1, wherein the memory further contains imaging pulse sequence commands for acquiring magnetic resonance imaging data from the imaging zone according to an imaging magnetic resonance imaging protocol, wherein execution of the machine executable instructions further causes the processor to: control the magnetic resonance imaging system with the imaging pulse sequence commands to acquire the magnetic resonance imaging data; and reconstruct a magnetic resonance image from the magnetic resonance imaging data. ### Claim 3 (depends on 2) The medical instrument of claim 2, wherein the reconstruction of the magnetic resonance image comprises correcting the magnetic resonance image using higher order terms of the three-dimensional gradient impulse function. ### Claim 4 (depends on 2) The medical instrument of claim 2, wherein execution of the machine executable instructions further causes the processor to correct the imaging pulse sequence commands using the three-dimensional gradient impulse response function for the at least one of the three orthogonal gradient coils by driving orthogonal gradient coils for suppression of cross terms or by adjusting higher order shim coils for the suppression of unwanted higher order response terms. ### Claim 5 (depends on 1) The medical instrument of claim 1, wherein the magnetic resonance imaging comprises a radio frequency system with multiple receive coils. ### Claim 6 (depends on 5) The medical instrument of claim 5, wherein the calibration magnetic resonance imaging protocol is a SENSE magnetic resonance imaging protocol using the multiple receive coils. ### Claim 7 (depends on 5) The medical instrument of claim 5, wherein execution of the machine executable instructions causes the processor to adjust a number of the multiple slices and a number of two-dimensional phase encoding steps according to a planned magnetic resonance imaging protocol. ### Claim 8 (depends on 1) The medical instrument of claim 1, wherein the calibration pulse sequence commands are configured for exciting two or more of the multiples slices simultaneously using multi-band thin-slice excitation. ### Claim 9 (depends on 1) The medical instrument of claim 1, wherein the magnetic resonance imaging system comprises a dedicated receive coil that is used for acquiring the magnetic resonance calibration data to account for effects of the dedicated receive coil in the three-dimensional gradient impulse response function. ### Claim 10 (depends on 1) The medical instrument of claim 1, wherein execution of the machine executable instructions further causes the processor to receive a B0 homogeneity map of the imaging zone, wherein the computation of the Fourier transform of the magnetic resonance calibration data for each voxel of the multiple slices in phase encoding directions is corrected using the B0 homogeneity map. ### Claim 11 (depends on 1) The medical instrument of claim 1, wherein the medical instrument further comprises any one of the following: a nuclear medicine imaging system, a positron emission tomography system, a single photon emission tomography system, a computed tomography imaging system, a radio therapy system, and a LINAC system. ### Claim 12 (depends on 1) The medical instrument of claim 1, wherein the calibration magnetic resonance imaging protocol is any one of the following: a thin slice magnetic resonance imaging protocol, a gradient pulse magnetic resonance imaging protocol, and combinations thereof. ### Claim 13 (depends on 12) The medical instrument of claim 12, wherein the gradient pulse magnetic resonance imaging protocol comprises a read out gradient generated by the slice select gradient, wherein the read out gradient is any one of the following: a chirp read out gradient, a triangular read out gradient, an alternating combination of a chirp readout gradient and a triangular read out gradient, and a dedicated waveform computed to achieve maximal spectral intensity at a chosen bandwidth of interest. ### Claim 14 A method of operating a medical instrument comprising a magnetic resonance imaging system with an imaging zone, wherein the magnetic resonance imaging system comprises a gradient coil system for generating a gradient magnetic field within the imaging zone, wherein the gradient coil system comprises three orthogonal gradient coils, wherein the method comprises: repeatedly controlling the magnetic resonance imaging system with calibration pulse sequence commands to acquire the magnetic resonance calibration data for multiples slices using at least one of the three orthogonal gradient coils to generate the slice select gradient magnetic field, wherein the calibration pulse sequence commands are configured for acquiring magnetic resonance calibration data from a magnetic resonance imaging phantom within the imaging zone according to a calibration magnetic resonance imaging protocol with two-dimensional phase encoding perpendicular to a slice select gradient magnetic field, wherein the calibration pulse sequence commands are configured for acquiring slices divided into voxels by the two-dimensional phase encoding; computing a Fourier transform of the magnetic resonance calibration data for each of the voxels of the multiple slices in the phase encoding directions; computing an expansion of the Fourier transformed magnetic resonance calibration data into spherical harmonics; and calculating a three-dimensional gradient impulse response function for the at least one of the three orthogonal gradient coils using the expansion into spherical harmonics. ### Claim 15 A computer program product comprising machine executable instructions for execution by a processor configured for controlling a medical instrument, wherein the medical instrument comprises a magnetic resonance imaging system with an imaging zone, wherein the magnetic resonance imaging system comprises a gradient coil system for generating a gradient magnetic field within the imaging zone, wherein the gradient coil system comprises three orthogonal gradient coils, wherein execution of the machine executable instructions causes the processor to: repeatedly control the magnetic resonance imaging system with the calibration pulse sequence commands to acquire magnetic resonance calibration data for multiples slices using the at least one of the three orthogonal gradient coils to generate the slice select gradient magnetic field, wherein the calibration pulse sequence commands are configured for acquiring magnetic resonance calibration data from a magnetic resonance imaging phantom within the imaging zone according to a calibration magnetic resonance imaging protocol with two-dimensional phase encoding perpendicular to a slice select gradient magnetic field, wherein the calibration magnetic resonance imaging protocol is configured for acquiring slices divided into voxels by the two-dimensional phase encoding; compute a Fourier transform of the magnetic resonance calibration data for each of the voxels of the multiple slices in the phase encoding directions; compute an expansion of the Fourier transformed magnetic resonance calibration data into spherical harmonics; and calculate a three-dimensional gradient impulse response function for the at least one of the three orthogonal gradient coils using the expansion into spherical harmonics.