# US 2013/0278255 A1 · System and method of receive sensitivity correction in mr imaging > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0278255 A1 - Document ID: US20130278255A1 - Status: Published application - Kind: A1 - Application number: 13/449,387 - Filed: 2012-04-18 - Published: 2013-10-24 - Earliest claimed: 2012-04-18 - Assignees: General Electric Company - Inventors: Mohammad Mehdi Khalighi; Brian Rutt - Web page: https://patentgrep.com/patent/US20130278255A1 ## CPC - G01R 33/246: {Spatial mapping of the RF magnetic field B1} - G01R 33/5659: {caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence)} - G01R 33/56563: {caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 (G01R33/56509, G01R33/56518, G01R33/56536 take precedence)} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract A magnetic resonance imaging (MRI) apparatus includes a magnetic resonance imaging (MRI) system having a plurality of gradient coils positioned about a bore of a magnet, and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images, and a computer programmed to generate an original image of an object, generate a proton density weighted image of the object, generate a B1+ field map of the object, generate a transmit-corrected image based on the B1+ field map and based on the proton density weighted image, electronically filter the transmit-corrected image to generate a receive sensitivity map, and revise the original image using the receive sensitivity map. ## Claims ### Claim 1 A magnetic resonance imaging (MRI) apparatus comprising: a magnetic resonance imaging (MRI) system having a plurality of gradient coils positioned about a bore of a magnet, and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images; and a computer programmed to: generate an original image of an object; generate a proton density weighted image of the object; generate a B1+ field map of the object; generate a transmit-corrected image based on the B1+ field map and based on the proton density weighted image; electronically filter the transmit-corrected image to generate a receive sensitivity map; and revise the original image using the receive sensitivity map. ### Claim 2 (depends on 1) The MRI apparatus of claim 1 wherein the computer is programmed to calculate a transmit sensitivity at each voxel of the B1+ field map based on a signal equation for a Bloch-Siegert (B-S) magnitude signal, and generate the transmit-corrected image using the transmit sensitivity. ### Claim 3 (depends on 2) The MRI apparatus of claim 2 wherein the signal equation is given by: S n = R n  M 0   sin  ( α )  1 - E 1 1 - E 1   cos  ( α ) , where Sn is a signal from an n-th coil, Rn is a receive sensitivity of the n-th coil, M0 is a proton density, α is a flip angle, and E1=exp(−TR/T1), wherein TR is a repetition time and T1 is a time constant pertaining to longitudinal relaxation. ### Claim 4 (depends on 2) The MRI apparatus of claim 2 wherein the signal equation is given by Sn=RnM0 sin(α), where Sn is a signal from an n-th coil, Rn is a receive sensitivity of the n-th coil, M0 is a proton density, a is a flip angle. ### Claim 5 (depends on 1) The MRI apparatus of claim 1 wherein the computer is programmed to execute a B-S sequence to generate the proton density weighted image and to generate the B1+ field map of the object. ### Claim 6 (depends on 5) The MRI apparatus of claim 5 wherein the computer is programmed to execute the B-S sequence and generate the proton density weighted image from a single B-S image derived therefrom. ### Claim 7 (depends on 5) The MRI apparatus of claim 5 wherein the computer is programmed to: execute the B-S sequence by being programmed to obtain a positive off-resonance B-S image and a negative off-resonance B-S image; combine the positive and the negative off-resonance B-S images to generate the proton density weighted image; and combine the positive and negative off-resonance B-S images to generate the B1+ field map. ### Claim 8 (depends on 1) The MRI apparatus of claim 1 wherein the computer is programmed to: electronically filter the transmit-corrected image by low-pass filtering the transmit-corrected image having a cutoff frequency of approximately σ=0.4 cm−1. ### Claim 9 A method of magnetic resonance imaging (MRI) comprising: generating a proton density weighted image of an object; determining a transmit sensitivity map from a B1+ field map of the object; generating a transmit-corrected image of the object based on the transmit sensitivity map and based on the proton density weighted image; low-pass filtering the transmit-corrected image to generate a receive sensitivity map; and correcting an MR image using the receive sensitivity map. ### Claim 10 (depends on 9) The method of claim 9 comprising generating the B1+ field map of the object and generating a proton weighted image of the object using a Bloch-Siegert (B-S) mapping sequence. ### Claim 11 (depends on 10) The method of claim 10 wherein using the B-S mapping sequence comprises obtaining a positive off-resonance B-S image and a negative off-resonance B-S image; and further comprises: combining the positive and the negative off-resonance B-S images to generate the proton density weighted image; and generating the B1+ field map from the positive and the negative off-resonance B-S images. ### Claim 12 (depends on 9) The method of claim 9 wherein determining the transmit sensitivity map comprises calculating a transmit sensitivity at each voxel of the B1+ field map based on a signal equation for a B-S magnitude signal. ### Claim 13 (depends on 9) The method of claim 9 wherein low-pass filtering the transmit-corrected image comprises electronically filtering the transmit-corrected image using a cutoff frequency of approximately σ=0.4 cm−1. ### Claim 14 A computer readable storage medium having stored thereon a computer program comprising instructions, which, when executed by a computer, cause the computer to: generate an original image of an object; obtain an MR image of an object; obtain a proton density weighted image of the object; obtain a B1+ field map of the object; generate a transmit-corrected image based on the B1+ field map and based on the proton density weighted image; electronically filter the transmit-corrected image to generate a receive sensitivity map; and refine the original image using the receive sensitivity map. ### Claim 15 (depends on 14) The computer readable storage medium of claim 14 wherein the computer is programmed to control a magnetic resonance imaging (MRI) system in order to: generate the MR image of the object; and execute a Bloch-Siegert (B-S) sequence in order to: generate the proton density weighted image; and generate the B1+ field map. ### Claim 16 (depends on 15) The computer readable storage medium of claim 15 wherein the computer is programmed to: execute the B-S sequence by being programmed to obtain a positive off-resonance B-S image and a negative off-resonance B-S image; derive the proton density weighted image from the positive and the negative off-resonance B-S images; and derive the B1+ field map from the positive and negative off-resonance B-S images. ### Claim 17 (depends on 16) The computer readable storage medium of claim 16 wherein the proton density weighted image is an average of the positive and negative off-resonance B-S images. ### Claim 18 (depends on 14) The computer readable storage medium of claim 14 wherein the computer is programmed to calculate a transmit sensitivity at each voxel of the B1+ field map based on a signal equation for a Bloch-Siegert (B-S) magnitude signal. ### Claim 19 (depends on 18) The computer readable storage medium of claim 18 wherein the signal equation is estimated as Sn=Rn=M0 sin(α), where Sn is a signal from an n-th coil, Rn is a receive sensitivity of the n-th coil, M0 is a proton density, α is a flip angle. ### Claim 20 (depends on 14) The computer readable storage medium of claim 14 wherein the computer is programmed to electronically filter the transmit-corrected image by low-pass filtering the transmit-corrected image having a cutoff frequency of approximately σ=0.4 cm−1.