# US 2014/0197836 A1 · Determination of specific absorption rate (sar) in magnetic resonance imaging (mri) > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0197836 A1 - Document ID: US20140197836A1 - Status: Published application - Kind: A1 - Application number: 13/739,236 - Filed: 2013-01-11 - Published: 2014-07-17 - Earliest claimed: 2013-01-11 - Assignees: Toshiba Medical Systems Corporation; Kabushiki Kaisha Toshiba - Applicants: Kabushiki Kaisha Toshiba; Toshiba Medical Systems Corporation - Inventors: YOSHINORI HAMAMURA; XIN CHEN - Web page: https://patentgrep.com/patent/US20140197836A1 ## CPC - G01R 33/44: using nuclear magnetic resonance [NMR] (G01R33/24, G01R33/62 take precedence) - G01R 33/288: {Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room} - G01R 33/36: Electrical details, e.g. matching or coupling of the coil to the receiver - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract A magnetic resonance imaging (MRI) system includes static and gradient magnetic field generators, at least one radio frequency (RF) coil, at least one RF transmitter and at least one RF receiver. At least one power consumption monitor is coupled to locally measure power consumed by the RF coil. The MRI control system has at least one computer configured to determine a specific absorption rate (SAR) for a patient coupled to the RF coil based on at least: (a) RF power transmitted to said RF coil while the RF coil is inductively coupled to the patient, and (b) an electrical signal output from the at least one power consumption monitor while the RF coil is inductively coupled to the patient. ## Claims ### Claim 1 A magnetic resonance imaging (MRI) system comprising: static and gradient magnetic field generators, at least one radio frequency (RF) coil, at least one RF transmitter and at least one RF receiver; at least one power consumption monitor coupled to locally measure power consumed by said RF coil; and an MRI control system having at least one computer configured to: determine a specific absorption rate (SAR) for a patient coupled to said RF coil based on at least: (a) RF power transmitted to said RF coil while the RF coil is inductively coupled to the patient, and (b) an electrical signal output from said at least one power consumption monitor while the RF coil is inductively coupled to the patient. ### Claim 2 (depends on 1) An MRI system as in claim 1, wherein said at least one power consumption monitor comprises plural pickup loops spatially distributed on said RF coil and electrical signals output from said plural pickup loops are combined for use in said determination of a specific absorption rate. ### Claim 3 (depends on 1) An MRI system as in claim 1, wherein said at least one power consumption monitor comprises plural E-field probes spatially distributed on said RF coil and electrical signals output from said plural E-field probes are combined for use in said determination of a specific absorption rate. ### Claim 4 (depends on 3) An MRI system as in claim 3, wherein said E-field probes comprise monopole probes fed by coaxial cable. ### Claim 5 (depends on 3) An MRI system as in claim 3, wherein said E-field probes comprise dipole probes fed by coaxial cable. ### Claim 6 (depends on 1) An MRI system as in claim 1, wherein said at least one power consumption monitor comprises plural voltage measurement connections across capacitors spatially distributed in said R coil and electrical signals from said voltage measurement connections are combined for use in said determination of a specific absorption rate. ### Claim 7 (depends on 1) An MRI system as in claim 1, wherein said at least one power consumption monitor comprises at least one butterfly or figure-eight shaped pickup loop electromagnetically coupled to current flowing in an RF coil conductor. ### Claim 8 (depends on 1) An MRI system as in claim 1, wherein said SAR is calculated using at least: (a) patient weight; (b) RF power transmitted to said RF coil while the RF coil is inductively coupled to the patient; (c) RF power transmitted to said RF coil while the RF coil is not inductively coupled to the patient; and (d) a comparison of power consumption monitor outputs when the RF coil is and is not coupled to the patient. ### Claim 9 (depends on 8) An MRI system as in claim 8, wherein said SAR is calculated using a corrected value for RF power transmitted to said RF coil while the RF coil is not inductively coupled to the patient based on comparison of RF power consumption when the RF coil is inductively coupled to the patient and when the RF coil is not inductively coupled to the patient. ### Claim 10 (depends on 9) An MRI system as in claim 9, wherein said SAR is calculated using a corrected value for RF power transmitted to said RF coil while the RF coil is not inductively coupled to the patient based on comparison of (i) output from at least one power consumption monitor while the RF coil is inductively coupled to the patient, and (ii) output from the at least one power consumption monitor while the RF coil is not inductively coupled to the patient. ### Claim 11 (depends on 1) An MRI system as in claim 1, wherein said SAR is calculated using the following formula: SAR = 1 weight  { P scan - P unloaded   •   ( V scan V unloaded ) 2 } where: weight=patient weight in kilograms; Pscan=RF power transmitted to the RF coil when loaded with the patient for an MRI scan; Punloaded=RF power transmitted to the RF coil when not loaded with the patient for an MRI scan; Vscan=an electrical output from at least one power consumption monitor when RF coil is loaded with patient for an MRI scan; and Vunloaded=an electrical output from at least one power consumption monitor when RF coil is not loaded with patient for an MRI scan. ### Claim 12 (depends on 11) An MRI system as in claim 11, wherein calibration values for Punloaded and Vunloaded are determined and pre-stored in memory for ready use in calculating SAR during subsequent MRI patient imaging procedures. ### Claim 13 A magnetic resonance imaging (MRI) method comprising: configuring and using an MRI system having static and gradient magnetic field generators, at least one radio frequency (RF) coil, at least one RF transmitter, at least one RF receiver, at least one power consumption monitor disposed to measure RF power consumed by said RE coil, and an MRI control system having at least one configurable computer to: determine a specific absorption rate (SAR) for a patient coupled to said RF coil based on at least: (a) RF power transmitted to said RF coil while the RF coil is inductively coupled to the patient, and (b) an output from said power consumption monitor while the RF coil is inductively coupled to the patient. ### Claim 14 (depends on 13) An MRI method as in claim 13, wherein said power consumption monitor comprises plural pickup loops spatially distributed on said RF coil and electrical signals output from said plural pickup loops are combined for use in said determination of a specific absorption rate. ### Claim 15 (depends on 14) An MRI method as in claim 14, wherein said plural pickup loops are symmetrically distributed on said RF coil. ### Claim 16 (depends on 13) An MRI method as in claim 13, wherein said current monitor comprises at least one pickup loop having a butterfly-or figure-eight-shape. ### Claim 17 (depends on 13) An MRI method as in claim 13, wherein said at least one power consumption monitor comprises plural E-field probes spatially distributed on said RF coil and electrical signals output from said plural E-field probes are combined for use in said determination of a specific absorption rate. ### Claim 18 (depends on 17) An MRI method as in claim 17, wherein said E-field probes comprise monopole probes fed by coaxial cable. ### Claim 19 (depends on 17) An MRI system as in claim 17, wherein said E-field probes comprise dipole probes fed by coaxial cable. ### Claim 20 (depends on 13) An MRI system as in claim 13, wherein said at least one power consumption monitor comprises plural voltage measurement connections across capacitors spatially distributed in said R coil and electrical signals from said voltage measurement connections are combined for use in said determination of a specific absorption rate. ### Claim 21 (depends on 13) An MRI method as in claim 13, wherein said SAR is calculated using at least: (a) patient weight; (b) RF power transmitted to said RF coil while the RF coil is inductively coupled to the patient; (c) RF power transmitted to said RF coil while the RF coil is not inductively coupled to the patient; and (d) a comparison of power consumption monitor outputs when the RF coil is and is not coupled to the patient. ### Claim 22 (depends on 21) An MRI method as in claim 21, wherein said SAR is calculated using a corrected value for RF power transmitted to said RF coil while the RF coil is not inductively coupled to the patient based on comparison of RF coil power consumption when the RF coil is inductively coupled to the patient and when the RF coil is not inductively coupled to the patient. ### Claim 23 (depends on 22) An MRI method as in claim 22, wherein said SAR is calculated using a corrected value for RF power transmitted to said RF coil while the RF coil is not inductively coupled to the patient based on comparison of (i) output from at least one power consumption monitor while the RF coil is inductively coupled to the patient, and (ii) output from the at least one power consumption monitor while the RF coil is not inductively coupled to the patient. ### Claim 24 (depends on 13) An MRI method as in claim 13, wherein said SAR is calculated using the following formula: SAR = 1 weight  { P scan - P unloaded   •   ( V scan V unloaded ) 2 } where: weight=patient weight in kilograms; Pscan=RF power transmitted to the RF coil when loaded with the patient for an MRI scan; Punloaded=RF power transmitted to the RF coil when not loaded with the patient for an MRI scan; Vscan=an electrical output from at least one power consumption monitor when the RF coil is loaded with patient for an MRI scan; and Vunloaded=an electrical output from at least one power consumption monitor when the RF coil is not loaded with patient for an MRI scan. ### Claim 25 (depends on 24) An MRI method as in claim 24, wherein calibration values for Punloaded and Vunloaded are determined and pre-stored in memory for ready use in calculating SAR during subsequent MRI patient imaging procedures.