8/3/2016
                        MR Pulse Sequences
                        Robert A. Pooley, PhD
                        AAPM 2016, Washington, DC
                        August 3, 2016
                                                                                                            ©2014 MFMER  |  slide-1
                        Disclosure
                        • No conflicts of interest
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                        Outline
                        • Spin echo
                        • Inversion recovery
                        • Gradient echo
                        • Echo planar
                        • K-space trajectories
                                                                                                            ©2014 MFMER  |  slide-3
                        Spin Echo
                        •  Uses 90° and 180° flip angles
                        •  Spin density contrast: short TE, long TR
                        •  T1 contrast: short TE, short TR
                        •  T2 contrast: long TE, long TR
                        •  Rephases effects from B inhomogeneity, chemical shift, and 
                           magnetic susceptibility         0
                        •  Scan time = TR x N x NSA                          TR: Repetition time
                                                    P                        N # phase encodes
                                                                              P: 
                                                                             NSA: # signal averages = 
                                                                             NEX: # excitations
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                          Spin Echo
                                             90°                  180°
                                RF
                            Signal
                              ADC
                              Gslice
                              Gfreq
                            Gphase
                                                                     TE 
                                                                     TR 
                                                                                                            ©2014 MFMER  |  slide-5
                        Filling K-space
                         • The signal from the echo is sampled; the values 
                           are placed in k-space.
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                                        Image space                                                  k-space
                                                                                    FT
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                                Single Slice Spin Echo
                                           1 Slice
                               RF
                            Signal
                             ADC
                             G
                            Gslice
                            Gfreq
                              phase
                                            TE
                                                                                   TR
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