# US 5,347,218 A · Method and apparatus for rapid spin echo magnetic resonance imaging > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,347,218 A - Document ID: US5347218A - Status: Granted - Kind: A - Application number: 08/052,302 - Filed: 1993-04-23 - Granted: 1994-09-13 - Earliest claimed: 1992-04-24 - Assignees: U.S. Philips Corporation - Inventors: Gerrit H. Van Yperen - Web page: https://patentgrep.com/patent/US5347218A ## CPC - G01R 33/561: by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences - G01R 33/565: Correction of image distortions, e.g. due to magnetic field inhomogeneities - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract In a spin-echo magnetic resonance sequence a phase encoding gradient magnetic field (39) is applied after the 180.degree. rephasing pulse (32.sub.1). After detection of the spin-echo signal (33) the position dependent phases are compensated for by applying a further gradient magnetic field (39'), identical in size but opposite in sign. The phase difference (.phi..sub.32,1 -.phi..sub.31,1) between the RF-pulses (31.sub.1,32.sub.1) applied within a sequence is constant over the sequences. With no position dependent effects left at the end of a sequence the next sequence can be started immediately following the earlier one. A repetition time TR substantially shorter than the spin-spin relaxation time T.sub.2 is feasible, thereby developing a steady state of the magnetization. A TR of 50 ms or less can be obtained, as well as strong signals for long T.sub.2 substances and good T.sub.2 contrast. RF spoiling by changing phases of RF-pulses in subsequent sequences can destroy the T.sub.2 signal and provide images with pure T.sub.1 contrast. ## Claims ### Claim 1 Method for magnetic resonance imaging of a body placed in a stationary and substantially homogeneous main magnetic field, the method comprising repeated execution, with a repetition time TR, of a sequence including the following steps: application of a first RF-pulse for excitation of at least a portion of the body, application of at least a first gradient magnetic field for phase encoding of the excited portion, application of a second RF-pulse at a time .tau. after the first RF-pulse, detection of a magnetic resonance spin-echo signal around a time 2.tau. after the first RF-pulse, wherein: the repetition time TR between the first RF-pulses in subsequent sequences is shorter than a transverse relaxation time T.sub.2 of a relevant substance of the body, said first gradient magnetic field is applied after the application of the second RF-pulse, and a second gradient magnetic field for compensation of the phase encoding caused by the first gradient magnetic field is applied in the interval after occurrence of the magnetic resonance spin-echo signal and before application of the first RF-pulse in a next sequence. ### Claim 2 (depends on 1) Method as claimed in claim 1, characterised in that a selection gradient magnetic field is applied during application of the first RF-pulse for selection of a slice of the body, and in that a third gradient magnetic field is applied during detection of the magnetic resonance spin-echo signal for frequency encoding. ### Claim 3 (depends on 1) Method as claimed in claim 1 characterised in that phase differences between the first RF-pulse and the second RF-pulses within a sequence are equal over the sequences. ### Claim 4 (depends on 3) Method as claimed in claim 3, characterised in that the first RF-pulses in subsequent sequences have zero phase difference and in that the second RF-pulses in subsequent sequences have zero phase difference. ### Claim 5 (depends on 3) Method as claimed in claim 3, characterised in that the phases of the first and second RF-pulses in subsequent sequences are mutually different, thereby forming an RF-spoiling scheme. ### Claim 6 (depends on 5) Method as claimed in claim 5, characterised in that the phases of the first and second RF-pulses are changed from one sequence to another according to a non-repetitive scheme. ### Claim 7 (depends on 6) Method as claimed in claim 6, characterised in that the phases of the first and second RF-pulses in successive sequences differ with a linear increasing or decreasing value proportional to a rank number of the sequence. ### Claim 8 (depends on 1) Method as claimed in claim 1, characterised in that the repetition time TR is about 50 milliseconds or less. ### Claim 9 Apparatus for magnetic resonance imaging comprising means for establishing a stationary and substantially homogeneous main magnetic field, means for generating gradient magnetic field superimposed upon the main magnetic field, means for radiating RF-pulses towards a body placed in the main magnetic field, control means for controlling the generation of the gradient magnetic fields and the RF-pulses, and means for receiving and sampling magnetic resonance signals generated by sequences of RF-pulses and switched gradient magnetic fields, said control means being meant for: applying a first radio-frequency pulse for excitation of at least a portion of the body, applying at least a first gradient magnetic field for phase encoding of the excited portion, applying a second RF-pulse at a time .tau. after the first RF-pulse, and detecting a magnetic resonance spin-echo signal around a time 2.tau. after the first RF-pulse, in a sequence which is repeatedly executed with a repetition time TR between first RF-pulses in subsequent sequences that is shorter than a transverse relaxation time T.sub.2 of a relevant substance of the body, characterised in that the control means are further arranged for applying said first gradient magnetic field after the application of the second RF-pulse, and applying a second gradient magnetic field in the interval after occurrence of the magnetic resonance spin-echo signal and before application of the first RF-pulse in a next sequence, the second gradient magnetic field compensating the phase encoding caused by the first gradient magnetic field. ### Claim 10 (depends on 2) Method as claimed in claim 2, characterized in that phase differences between the first RF-pulse and the second RF-pulses within a sequence are equal over the sequences. ### Claim 11 (depends on 10) Method as claimed in claim 10, characterized in that the first RF-pulses in subsequent sequences have zero phase difference and in that the second RF-pulses in subsequent sequences have zero phase difference. ### Claim 12 (depends on 10) Method as claimed in claim 10, characterized in that the phases of the first and second RF-pulses in subsequent sequences are mutually different, thereby forming an RF-spoiling scheme. ### Claim 13 (depends on 12) Method as claimed in claim 12, characterized in that the phases of the first and second RF-pulses are changed from one sequence to another according to a non-repetitive scheme. ### Claim 14 (depends on 13) Method as claimed in claim 13, characterized in that the phases of the first and second RF-pulses in successive sequences differ with a linear increasing or decreasing value proportional to a rank number of the sequence. ### Claim 15 (depends on 2) Method as claimed in claim 2, characterised in that the repetition time TR is about 50 milliseconds or less. ### Claim 16 (depends on 3) Method as claimed in claim 3, characterised in that the repetition time TR is about 50 milliseconds or less. ### Claim 17 (depends on 4) Method as claimed in claim 4, characterised in that the repetition time TR is about 50 milliseconds or less. ### Claim 18 (depends on 11) Method as claimed in claim 11, characterised in that the repetition time TR is about 50 milliseconds or less. ### Claim 19 (depends on 12) Method as claimed in claim 12, characterised in that the repetition time TR is about 50 milliseconds or less. ### Claim 20 (depends on 1) Method as claimed in claim 1 wherein said first RF-pulse has a flip-angle substantially greater than 90.degree. and less than 180.degree. and said second RF-pulse has a flip-angle substantially equal to 180.degree..