# US 12,181,550 B2 · Method for generating a magnetic resonance synthetic computer tomography image > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,181,550 B2 - Document ID: US12181550B2 - Status: Granted - Kind: B2 - Application number: 18/005,047 - Filed: 2021-07-12 - Published: 2024-09-05 - Granted: 2024-12-31 - Earliest claimed: 2020-07-10 - Assignees: Mriguidance B.V. - Applicants: Mriguidance B.V. - Inventors: Peter Roland Seevinck; Frank Zijlstra - Web page: https://patentgrep.com/patent/US12181550B2 ## CPC - G01R 33/4828: {Resolving the MR signals of different chemical species, e.g. water-fat imaging} - G01R 33/5613: {Generating steady state signals, e.g. low flip angle sequences [FLASH]} - G01R 33/4812: {MR combined with X-ray or computed tomography [CT]} - G01R 33/50: based on the determination of relaxation times {, e.g. T1 measurement by IR sequences; T2 measurement by multiple-echo sequences} - G01R 33/5602: {by filtering or weighting based on different relaxation times within the sample, e.g. T1 weighting using an inversion pulse} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract A method is disclosed for generating a contrast image using MRI comprising a four-echo steady state free precession (SSFP) sequence. The method comprises: generating a pulse train of excitation pulses having a repetition time; generating between two subsequent excitation pulses of the pulse train a first S+ echo; a second S+ echo; a first S− echo; and a second S− echo sampling between the two subsequent excitation pulses the first S+ echo; the second S+ echo; the first S− echo; and the second S− echo; generating the contrast image based on the sampled first S+ echo, the sampled second S+ echo, the sampled first S− echo, and the sampled second S− echo. ## Claims ### Claim 1 A method for generating a contrast image using MRI comprising a four-echo steady state free precession (SSFP) sequence, the method comprising: generating a pulse train of excitation pulses having a repetition time; generating between two subsequent excitation pulses of the pulse train a first S+ echo; a second S+ echo; a first S− echo; and a second S− echo; sampling between the two subsequent excitation pulses the first S+ echo; the second S+ echo; the first S− echo; and the second S− echo; generating the contrast image based on the sampled first S+ echo, the sampled second S+ echo, the sampled first S− echo, and the sampled second S− echo, wherein the contrast image comprises a synthetic Computer Tomography, CT, image, and wherein the method comprises, between the two subsequent excitation pulses, generating a readout gradient of the first S+ echo and a readout gradient of the second S+ echo, wherein the readout gradients of the first S+ echo and second S+ echo have opposite polarities, and wherein a time integral of the readout gradient of the first S+ echo and a time integral of the readout gradient of the second S+ echo have a same absolute value, generating a readout gradient of the first S− echo and a readout gradient of the second S− echo, wherein the readout gradients of the first S− echo and second S− echo have opposite polarities, and wherein a time integral of the readout gradient of the first S− echo and a time integral of the readout gradient of the second S− echo have a same absolute value, wherein the readout gradient of a latest of the first and second S+ echo's and the readout gradient of an earliest of the first and second S− echo's have a same polarity and a same value of the time integral, generating a dephasing gradient in a readout direction before an earliest of the first and second S+ echo's, and generating a rephasing gradient in the readout direction after a latest of the first and second S− echo's, wherein a time integral of the readout gradients, the dephasing gradient and the rephasing gradient over the repetition time provides for one cycle of dephasing per voxel. ### Claim 2 (depends on 1) The method according to claim 1, wherein the contrast image further comprises any contrast image from a group of contrast images comprising: a water-fat decomposed image, a quantitative relaxometry map, a phase based map, and a synthetic CT reconstruction. ### Claim 3 (depends on 2) The method according to claim 2, further comprising: providing the sampled first S+ echo, the sampled second S+ echo, the sampled first S− echo, and the sampled second S− echo to a statistical model; generating by the statistical model a synthetic CT image of the object based on one or more images chosen from the sampled first S+ echo, the sampled second S+ echo, the sampled first S− echo, and the sampled second S− echo. ### Claim 4 (depends on 3) The method according to claim 3, wherein the statistical model comprises a machine learning algorithm, wherein the machine learning algorithm is pre-trained using at least one of: provided S+ data and associated CT images, provided S− data and associated CT images, provided S+ data, associated S− data and associated CT images, provided S+ data and/or associated S− data and/or a contrast image from the group of contrast images, and any other MRI data and associated CT images, wherein the machine learning algorithm comprises one of a convolutional neural network, an attention-aware network, a generative adversarial network and a graph convolutional network. ### Claim 5 (depends on 1) The method according to claim 1, wherein the contrast image further comprises any contrast image from a group of contrast images comprising: a water-fat decomposed image, a quantitative relaxometry map, a phase based map, a synthetic CT reconstruction, a T1w image, a T2w image, a mixed T1/T2w image, a water fraction image, a fat fraction image, an in-phase image, an opposed-phase image, a T2 map of a water fraction image, a T2 map of a fat fraction image, a T2 map general, and a T2* map general. ### Claim 6 (depends on 1) The method according to claim 1, wherein the contrast image further comprises any contrast image from a group of contrast images comprising: a water-fat decomposed image, a quantitative relaxometry map, a phase based map, a synthetic CT reconstruction a T1w image, a T2w image, a mixed T1/T2w image, a water fraction image, a fat fraction image, an in-phase image, an opposed-phase image, a T2 map of a water fraction image, a T2 map of a fat fraction image, a T2 map general, a T2* map general a B0 map, and a magnetic susceptibility map. ### Claim 7 (depends on 1) The method according to claim 1, wherein a time between the excitation pulse and an earliest one of the S+ echoes following the excitation pulse is equal to a time between a latest one of the S− echoes preceding the subsequent excitation pulse, and the subsequent excitation pulse, wherein a time between the earliest one of the S+ echoes and a latest one of the S+ echoes is equal to a time between an earliest one of the S− echoes and the latest one of the S− echoes. ### Claim 8 (depends on 7) The method according to claim 7, further comprising determining effective echo times associated with the S+ echoes and the S− echoes from echo times associated with the S+ echoes and the S− echoes and the repetition time; and generating, using the determined effective echo times, at least one T2 map associated with the individual S+ echo images and the individual S− echo images, wherein the at least one T2 map is calculated from an earliest one of the S+ echoes and a latest one of the S− echoes in the repetition time between subsequent excitation pulses and/or from a latest one of the S+ echoes and an earliest one of the S− echoes in the repetition time between subsequent excitation pulses. ### Claim 9 (depends on 1) The method according to claim 1, wherein a time integral of gradients in a readout direction in the repetition time is dimensioned to provide that the gradients in the readout direction in the repetition time induce one cycle of dephasing per voxel. ### Claim 10 (depends on 1) The method according to claim 1, wherein a readout polarity of the first S+ echo is opposite to a readout polarity of the second S+ echo, and a readout polarity of the first S− echo is opposite to a readout polarity of the second S− echo. ### Claim 11 (depends on 1) The method according to claim 1, further comprising at least one of: obtaining first water-fat decomposed signals based on a plurality of sampled first S+ echoes and a plurality of sampled second S+ echoes; and obtaining second water-fat decomposed signals based on a plurality of sampled first S− echoes and a plurality of sampled second S− echoes. ### Claim 12 (depends on 11) The method according to claim 11, wherein the first water-fat decomposed signals and the second water-fat decomposed signals are obtained using Dixon reconstruction. ### Claim 13 (depends on 11) The method according to claim 11, further comprising: generating a first set of water, fat, in-phase and out-phase images based on the first water-fat decomposed signals, wherein the first water, fat, in-phase and out-phase images have a mixed contrast weighting which is predominantly T 1w weighted and is low T2(*) weighted, the method further comprising: generating a second set of water, fat, in-phase and out-phase images based on the second water-fat decomposed signals, wherein the second water, fat, in-phase and out-phase images have an increased T2 weighting and diffusion weighting compared to the first set of water, fat, in-phase and out-phase images. ### Claim 14 (depends on 1) The method according to claim 1, further comprising: calculating effective echo times for a first set of water, fat, in-phase and out-phase images and for a second set of water, fat, in-phase and out-phase images, and calculating T2 maps of the water, fat, in-phase and out-of-phase images using the effective echo time for the first set of water, fat, in-phase and out-phase images and the second set of water, fat, in-phase and out-phase images; or generating images with intermediate contrasts based on combining an image generated from a single one of the echo's with at least one generated contrast image. ### Claim 15 (depends on 1) The method according to claim 1, wherein the contrast image comprises a water-fat separation image, the water-fat separation image being determined using the first and second S+ echo's, wherein the water-fat separation image are determined further using at least one of the first and second S− echo's. ### Claim 16 (depends on 15) The method according to claim 15, wherein a T2w image is derived from at least one of the first and second S− echo's, the synthetic Computer Tomography image being reconstructed from the T2w image and the water-fat separation image. ### Claim 17 (depends on 1) The method according to claim 1, wherein the rephasing gradient in the readout direction is further provided between the latest of the first and second S+ echo's and the earliest of the first and second S− echo's. ### Claim 18 A method for generating a contrast image using MRI comprising a three-echo steady state free precession, SSFP, sequence, the method comprising: generating a pulse train of excitation pulses having a repetition time; generating between two subsequent excitation pulses of the pulse train a first S+ echo; a second S+ echo and a first S− echo; sampling between the two subsequent excitation pulses the first S+ echo; the second S+ echo and the first S− echo; generating the contrast image based on the sampled first S+ echo, the sampled second S+ echo and the sampled first S− echo; wherein the contrast image comprises a synthetic Computer Tomography, CT, image, and wherein the method comprises, between the two subsequent excitation pulses, generating a readout gradient of the first S+ echo and a readout gradient of the second S+ echo, wherein the readout gradients of the first S+ echo and second S+ echo have opposite polarities, and wherein a time integral of the readout gradient of the first S+ echo and a time integral of the readout gradient of the second S+ echo have a same absolute value, generating a readout gradient of the first S− echo, wherein the readout gradient of a latest of the first and second S+ echo's and the readout gradient of the first S− echo have a same polarity and a same value of the time integral, generating a dephasing gradient in a readout direction before an earliest of the first and second S+ echo's, and generating a rephasing gradient in the readout direction after the first S− echo, wherein a time integral of the readout gradients, the dephasing gradient and the rephasing gradient over the repetition time provides for one cycle of dephasing per voxel. ### Claim 19 A control device for controlling a magnetic resonance imaging apparatus, the control device configured to control the magnetic resonance imaging apparatus to: generate a pulse train of excitation pulses having a repetition time; generate between two subsequent excitation pulses of the pulse train a first S+ echo; a second S+ echo; a first S− echo; and a second S− echo; sample between the two subsequent excitation pulses the first S+ echo; the second S+ echo; the first S− echo; and the second S− echo; and generate a contrast image based on the sampled first S+ echo, the sampled second S+ echo, the sampled first S− echo, and the sampled second S− echo, wherein the contrast image comprises a synthetic Computer Tomography, CT, image, and wherein the control device is further configured to control the magnetic resonance imaging apparatus to, between the two subsequent excitation pulses, generate a readout gradient of the first S+ echo and a readout gradient of the second S+ echo, wherein the readout gradients of the first S+ echo and second S+ echo have opposite polarities, and wherein a time integral of the readout gradient of the first S+ echo and a time integral of the readout gradient of the second S+ echo have a same absolute value, generate a readout gradient of the first S− echo and a readout gradient of the second S− echo, wherein the readout gradients of the first S− echo and second S− echo have opposite polarities, and wherein a time integral of the readout gradient of the first S− echo and a time integral of the readout gradient of the second S− echo have a same absolute value, wherein the readout gradient of a latest of the first and second S+ echo's and the readout gradient of an earliest of the first and second S− echo's have a same polarity, generate a dephasing gradient in a readout direction before an earliest of the first and second S+ echo's, and generate a rephasing gradient in the readout direction after a latest of the first and second S− echo's, wherein a time integral of the readout gradients, the dephasing gradient and the rephasing gradient over the repetition time provides for one cycle of dephasing per voxel.