431:
424:
echoes. The FSE/TSE pulse sequence superficially resembles a conventional spin-echo (CSE) sequence in that it uses a series of 180Âş-refocusing pulses after a single 90Âş-pulse to generate a train of echoes. The FSE/TSE technique, however, changes the phase-encoding gradient for each of these echoes (a conventional multi-echo sequence collects all echoes in a train with the same phase encoding). As a result of changing the phase-encoding gradient between echoes, multiple lines of k-space (i.e., phase-encoding steps) can be acquired within a given repetition time (TR). As multiple phase-encoding lines are acquired during each TR interval, FSE/TSE techniques may significantly reduce imaging time.
215:
461:
446:
243:
Due to local magnetic field inhomogeneities (variations in the magnetic field at different parts of the sample that are constant in time), as the net moment precesses, some spins slow down due to lower local field strength (and so begin to progressively trail behind) while some speed up due to higher
423:
Fast spin echo (RARE, FAISE or FSE), also called turbo spin echo (TSE) is an MRI sequence that results in fast scan times. In this sequence, several 180 refocusing radio-frequency pulses are delivered during each echo time (TR) interval, and the phase-encoding gradient is briefly switched on between
185:
In 2020 two teams demonstrated that when strongly coupling an ensemble of spins to a resonator, the Hahn pulse sequence does not just lead to a single echo, but rather to a whole train of periodic echoes. In this process the first Hahn echo acts back on the spins as a refocusing pulse, leading to
342:
Hahn's 1950 paper showed that another method for generating spin echoes is to apply three successive 90° pulses. After the first 90° pulse, the magnetization vector spreads out as described above, forming what can be thought of as a "pancake" in the x-y plane. The spreading continues for a time
297:
is included and each spin experiences perfect pulses during which the environment provides no spreading. Six spins are shown above and these are not given the chance to dephase significantly. The spin-echo technique is more useful when the spins have dephased more significantly such as in the
198:
when he applied two successive 90° pulses separated by short time period, but detected a signal, the echo, when no pulse was applied. This phenomenon of spin echo was explained by Erwin Hahn in his 1950 paper, and further developed by
302:
332:
181:
introduced spin-echo neutron scattering, a technique that can be used to study magnons and phonons in single crystals. The technique is now applied in research facilities using triple axis spectrometers.
228:
The vertical red arrow is the average magnetic moment of a group of spins, such as protons. All are vertical in the vertical magnetic field and spinning on their long axis, but this illustration is in a
318:
time, as shown in the animation below. The size of the echo is recorded for different spacings of the two pulses. This reveals the decoherence which is not refocused by the π pulse. In simple cases, an
460:
430:
258:
Progressively, the fast moments catch up with the main moment and the slow moments drift back toward the main moment. At some moment between E and F the sampling of the echo starts.
31:
207:
who pointed out the advantages of using a 180° refocusing pulse for the second pulse. The pulse sequence may be better understood by breaking it down into the following steps:
415:
absorption resonance. Instead of using two spin states in a magnetic field, photon echoes use two energy levels that are present in the material even in zero magnetic field.
445:
92:
at different rates. The first of these, relaxation, leads to an irreversible loss of magnetisation. But the inhomogeneous dephasing can be removed by applying a 180°
401:
361:
381:
785:
Debnath, Kamanasish; Dold, David; Morton, John J. L.; Mølmer, Klaus (2020). "Self-Stimulated Pulse Echo Trains from
Inhomogeneously Broadened Spin Ensembles".
501:
521:
J. E. Tanner & E. O. Stejskal (2003). "Restricted Self-Diffusion of
Protons in Colloidal Systems by the Pulsed-Gradient, Spin-Echo Method".
720:
Weichselbaumer, Stefan; Zens, Matthias; Zollitsch, Christoph W.; Brandt, Martin S.; Rotter, Stefan; Gross, Rudolf; Huebl, Hans (2020).
178:
1180:
1124:
1103:
1078:
1035:
1165:
1160:
846:
Carr, H. Y.; Purcell, E. M. (1954). "Effects of
Diffusion on Free Precession in Nuclear Magnetic Resonance Experiments".
253:
A 180 degree pulse is now applied so that the slower spins lead ahead of the main moment and the fast ones trail behind.
301:
411:
Hahn echos have also been observed at optical frequencies. For this, resonant light is applied to a material with an
496:
1175:
363:, and then a second 90° pulse is applied such that the "pancake" is now in the x-z plane. After a further time
930:"Partial RF echo planar imaging with the FAISE method. I. Experimental and theoretical assessment of artifact"
277:
effects removed. Quite separately, return of the red arrow towards the vertical (not shown) would reflect the
977:"Partial RF echo-planar imaging with the FAISE method. II. Contrast equivalence with spin-echo sequences"
466:
T1-weighted turbo spin echo MRI confirms a fracture, as the surrounding bone marrow has low signal from
1170:
486:
481:
167:
163:
70:
66:
46:
214:
62:
17:
100:
vectors. Examples of inhomogeneous effects include a magnetic field gradient and a distribution of
436:
315:
230:
881:
Melki, Philippe S.; Mulkern, Robert V.; Panych, Lawrence P.; Jolesz, Ferenc A. (May–June 1991).
882:
702:
Mezei, F. (1972), "Neutron spin echo: A new concept in polarized thermal neutron techniques",
1028:
How does MRI work?: An
Introduction to the Physics and Function of Magnetic Resonance Imaging
1023:
976:
929:
331:
855:
804:
743:
677:
637:
572:
530:
386:
346:
204:
77:
8:
112:. In simple cases, the intensity of the echo relative to the initial signal is given by
859:
808:
747:
681:
641:
576:
534:
1004:
957:
910:
828:
794:
767:
733:
366:
139:
628:
Kurnit, N. A.; Abella, I. D.; Hartmann, S. R. (1964). "Observation of a photon echo".
1120:
1099:
1074:
1031:
996:
949:
902:
832:
820:
771:
759:
584:
491:
320:
143:
1008:
961:
914:
383:
a third pulse is applied and a stimulated echo is observed after waiting for a time
988:
941:
894:
863:
816:
812:
755:
751:
722:"Echo Trains in Pulsed Electron Spin Resonance of a Strongly Coupled Spin Ensemble"
685:
645:
580:
538:
244:
field strength and start getting ahead of the others. This makes the signal decay.
81:
721:
238:
A 90° pulse has been applied that flips the arrow into the horizontal (x–y) plane.
1092:
412:
80:
observed following an initial excitation pulse decays with time due to both spin
108:
of dephasing, the inhomogeneous evolution will rephase to form an echo at time 2
1145:
649:
556:
171:
101:
58:
39:
34:
Animation of spin echo, showing the response of spins (red arrows) in the blue
1051:
284:
relaxation. 180 degrees is π radians so 180° pulses are often called π pulses.
1154:
599:
97:
898:
992:
945:
867:
824:
763:
689:
135:
35:
1000:
953:
906:
975:
Melki, Philippe S.; Jolesz, Ferenc A.; Mulkern, Robert V. (August 1992).
928:
Melki, Philippe S.; Jolesz, Ferenc A.; Mulkern, Robert V. (August 1992).
627:
560:
294:
200:
439:
showing a suspected compressive subcapital fracture as a radiodense line
604:
195:
155:
138:
which have been used in fields other than magnetic resonance including
131:) is the time between the excitation pulse and the peak of the signal.
89:
542:
454:
shows the same, atypical for a fracture since the cortex is coherent
1030:(2nd ed.). Springer Science & Business Media. p. 64.
799:
738:
883:"Comparing the FAISE method with conventional dual-echo sequences"
719:
451:
263:
Complete refocusing has occurred and at this time, an accurate
30:
1114:
467:
563:(1979). "NMR population inversion using a composite pulse".
555:
154:
Echoes were first detected in nuclear magnetic resonance by
520:
845:
880:
314:
A Hahn-echo decay experiment can be used to measure the
1021:
784:
293:
Several simplifications are used in this sequence: no
158:
in 1950, and spin echoes are sometimes referred to as
1071:
389:
369:
349:
1117:
Principles of Pulse
Electron Paramagnetic Resonance
1094:
Spin
Dynamics: Basics of Nuclear Magnetic Resonance
123:is the time constant for spin–spin relaxation. The
104:. If the inversion pulse is applied after a period
1091:
974:
927:
597:
395:
375:
355:
134:Echo phenomena are important features of coherent
1089:
713:
1152:
305:A spin echo with more spins and more dephasing
27:Response of spin to electromagnetic radiation
623:
621:
209:
1068:
1022:Weishaupt D, Köchli VD, Marincek B (2008).
88:effects which cause spins in the sample to
778:
667:
233:where the spins are stationary on average.
1115:Arthur Schweiger; Gunnar Jeschke (2001).
1052:"What is Fast (Turbo) Spin Echo imaging?"
798:
737:
618:
29:
323:is measured which is described by the T
194:The spin-echo effect was discovered by
14:
1153:
663:
661:
659:
887:Journal of Magnetic Resonance Imaging
502:Photon echoes in semiconductor optics
61:magnetisation by a pulse of resonant
1146:Spin Echo Simulation scratch.mit.edu
656:
24:
1062:
668:Hahn, E.L. (1950). "Spin echoes".
337:
309:
300:
213:
186:self-stimulated secondary echoes.
25:
1192:
1134:
1024:"Chapter 8: Fast Pulse sequences"
418:
174:radiation is most commonly used.
459:
444:
429:
330:
1181:Electron paramagnetic resonance
1044:
1015:
968:
921:
874:
523:The Journal of Chemical Physics
497:Electron paramagnetic resonance
73:(MRI) make use of this effect.
981:Magnetic Resonance in Medicine
934:Magnetic Resonance in Medicine
839:
817:10.1103/PhysRevLett.125.137702
756:10.1103/PhysRevLett.125.137701
696:
591:
549:
514:
406:
270:echo can be measured with all
13:
1:
565:Journal of Magnetic Resonance
507:
585:10.1016/0022-2364(79)90265-8
189:
7:
1119:. Oxford University Press.
1073:. Oxford University Press.
475:
10:
1197:
1166:Nuclear magnetic resonance
1161:Magnetic resonance imaging
1140:Animations and simulations
1090:Malcolm H. Levitt (2001).
650:10.1103/PhysRevLett.13.567
487:Magnetic resonance imaging
482:Nuclear magnetic resonance
223:
168:magnetic resonance imaging
164:nuclear magnetic resonance
149:
71:magnetic resonance imaging
67:nuclear magnetic resonance
413:inhomogeneously broadened
249:
224:
212:
63:electromagnetic radiation
598:Dan J Bell and J Yeung.
231:rotating reference frame
899:10.1002/jmri.1880010310
787:Physical Review Letters
726:Physical Review Letters
630:Physical Review Letters
250:
96:pulse that inverts the
993:10.1002/mrm.1910260213
946:10.1002/mrm.1910260212
868:10.1103/PhysRev.94.630
704:Zeitschrift fĂĽr Physik
690:10.1103/PhysRev.80.580
403:after the last pulse.
397:
377:
357:
306:
219:
218:The spin-echo sequence
42:
1176:Scientific techniques
398:
396:{\displaystyle \tau }
378:
358:
356:{\displaystyle \tau }
304:
217:
57:is the refocusing of
33:
1069:Ray Freeman (1999).
387:
367:
347:
316:spin–spin relaxation
860:1954PhRv...94..630C
809:2020PhRvL.125m7702D
748:2020PhRvL.125m7701W
682:1950PhRv...80..580H
642:1964PhRvL..13..567K
577:1979JMagR..33..473L
535:1968JChPh..49.1768T
393:
373:
353:
307:
220:
144:neutron scattering
140:laser spectroscopy
47:magnetic resonance
43:
1171:Quantum mechanics
1126:978-0-19-850634-8
1105:978-0-471-48922-1
1080:978-0-19-850481-8
1037:978-3-540-37845-7
710:(2), pp. 146–160.
557:Malcolm H. Levitt
543:10.1063/1.1670306
492:Neutron spin echo
376:{\displaystyle T}
321:exponential decay
298:animation below:
291:
290:
16:(Redirected from
1188:
1130:
1109:
1097:
1084:
1056:
1055:
1048:
1042:
1041:
1019:
1013:
1012:
972:
966:
965:
925:
919:
918:
878:
872:
871:
843:
837:
836:
802:
782:
776:
775:
741:
717:
711:
700:
694:
693:
665:
654:
653:
625:
616:
615:
613:
612:
595:
589:
588:
553:
547:
546:
518:
463:
448:
433:
402:
400:
399:
394:
382:
380:
379:
374:
362:
360:
359:
354:
334:
285:
259:
254:
245:
239:
234:
210:
21:
1196:
1195:
1191:
1190:
1189:
1187:
1186:
1185:
1151:
1150:
1137:
1127:
1106:
1081:
1065:
1063:Further reading
1060:
1059:
1050:
1049:
1045:
1038:
1020:
1016:
973:
969:
926:
922:
879:
875:
848:Physical Review
844:
840:
783:
779:
718:
714:
701:
697:
670:Physical Review
666:
657:
636:(19): 567–568.
626:
619:
610:
608:
596:
592:
554:
550:
519:
515:
510:
478:
471:
464:
455:
449:
440:
434:
421:
409:
388:
385:
384:
368:
365:
364:
348:
345:
344:
340:
338:Stimulated echo
326:
312:
310:Spin-echo decay
283:
276:
269:
262:
257:
252:
242:
237:
227:
192:
152:
122:
102:chemical shifts
28:
23:
22:
15:
12:
11:
5:
1194:
1184:
1183:
1178:
1173:
1168:
1163:
1149:
1148:
1142:
1141:
1136:
1135:External links
1133:
1132:
1131:
1125:
1111:
1110:
1104:
1086:
1085:
1079:
1064:
1061:
1058:
1057:
1043:
1036:
1014:
987:(2): 342–354.
967:
940:(2): 328–341.
920:
893:(3): 319–326.
873:
854:(3): 630–638.
838:
793:(13): 137702.
777:
732:(13): 137701.
712:
695:
676:(4): 580–594.
655:
617:
590:
571:(2): 473–476.
548:
512:
511:
509:
506:
505:
504:
499:
494:
489:
484:
477:
474:
473:
472:
465:
458:
456:
450:
443:
441:
435:
428:
420:
419:Fast spin echo
417:
408:
405:
392:
372:
352:
339:
336:
324:
311:
308:
289:
288:
287:
286:
281:
274:
267:
260:
255:
248:
247:
246:
240:
235:
222:
221:
191:
188:
172:radiofrequency
151:
148:
120:
40:pulse sequence
26:
9:
6:
4:
3:
2:
1193:
1182:
1179:
1177:
1174:
1172:
1169:
1167:
1164:
1162:
1159:
1158:
1156:
1147:
1144:
1143:
1139:
1138:
1128:
1122:
1118:
1113:
1112:
1107:
1101:
1096:
1095:
1088:
1087:
1082:
1076:
1072:
1067:
1066:
1053:
1047:
1039:
1033:
1029:
1025:
1018:
1010:
1006:
1002:
998:
994:
990:
986:
982:
978:
971:
963:
959:
955:
951:
947:
943:
939:
935:
931:
924:
916:
912:
908:
904:
900:
896:
892:
888:
884:
877:
869:
865:
861:
857:
853:
849:
842:
834:
830:
826:
822:
818:
814:
810:
806:
801:
796:
792:
788:
781:
773:
769:
765:
761:
757:
753:
749:
745:
740:
735:
731:
727:
723:
716:
709:
705:
699:
691:
687:
683:
679:
675:
671:
664:
662:
660:
651:
647:
643:
639:
635:
631:
624:
622:
607:
606:
601:
594:
586:
582:
578:
574:
570:
566:
562:
558:
552:
544:
540:
536:
532:
528:
524:
517:
513:
503:
500:
498:
495:
493:
490:
488:
485:
483:
480:
479:
469:
462:
457:
453:
447:
442:
438:
432:
427:
426:
425:
416:
414:
404:
390:
370:
350:
335:
333:
328:
322:
317:
303:
299:
296:
280:
273:
266:
261:
256:
251:
241:
236:
232:
226:
225:
216:
211:
208:
206:
202:
197:
187:
183:
180:
175:
173:
169:
165:
161:
157:
147:
145:
141:
137:
132:
130:
126:
119:
115:
111:
107:
103:
99:
98:magnetisation
95:
91:
87:
86:inhomogeneous
83:
79:
74:
72:
68:
64:
60:
56:
52:
48:
41:
38:to the green
37:
32:
19:
1116:
1093:
1070:
1046:
1027:
1017:
984:
980:
970:
937:
933:
923:
890:
886:
876:
851:
847:
841:
790:
786:
780:
729:
725:
715:
707:
703:
698:
673:
669:
633:
629:
609:. Retrieved
603:
593:
568:
564:
551:
526:
522:
516:
422:
410:
341:
329:
313:
292:
278:
271:
264:
193:
184:
176:
159:
153:
136:spectroscopy
133:
128:
124:
117:
113:
109:
105:
93:
85:
75:
54:
50:
44:
36:Bloch sphere
600:"Echo time"
561:Ray Freeman
529:(4): 1768.
407:Photon echo
295:decoherence
160:Hahn echoes
1155:Categories
800:2004.01116
739:1809.10116
611:2017-09-24
605:Radiopedia
508:References
196:Erwin Hahn
156:Erwin Hahn
82:relaxation
78:NMR signal
69:(NMR) and
1098:. Wiley.
833:214774750
772:119521123
391:τ
351:τ
190:Principle
125:echo time
94:inversion
65:. Modern
55:Hahn echo
51:spin echo
18:Echo time
1009:45145834
962:26351582
915:26083556
825:33034472
764:33034465
476:See also
179:F. Mezei
177:In 1972
84:and any
1001:1513255
954:1513254
907:1802145
856:Bibcode
805:Bibcode
744:Bibcode
678:Bibcode
638:Bibcode
573:Bibcode
531:Bibcode
452:CT scan
205:Purcell
150:History
90:precess
1123:
1102:
1077:
1034:
1007:
999:
960:
952:
913:
905:
831:
823:
770:
762:
327:time.
116:where
1005:S2CID
958:S2CID
911:S2CID
829:S2CID
795:arXiv
768:S2CID
734:arXiv
468:edema
437:X-ray
162:. In
1121:ISBN
1100:ISBN
1075:ISBN
1032:ISBN
997:PMID
950:PMID
903:PMID
821:PMID
760:PMID
203:and
201:Carr
166:and
142:and
76:The
59:spin
49:, a
989:doi
942:doi
895:doi
864:doi
813:doi
791:125
752:doi
730:125
708:255
686:doi
646:doi
581:doi
539:doi
53:or
45:In
1157::
1026:.
1003:.
995:.
985:26
983:.
979:.
956:.
948:.
938:26
936:.
932:.
909:.
901:.
889:.
885:.
862:.
852:94
850:.
827:.
819:.
811:.
803:.
789:.
766:.
758:.
750:.
742:.
728:.
724:.
706:,
684:.
674:80
672:.
658:^
644:.
634:13
632:.
620:^
602:.
579:.
569:33
567:.
559:;
537:.
527:49
525:.
170:,
146:.
129:TE
1129:.
1108:.
1083:.
1054:.
1040:.
1011:.
991::
964:.
944::
917:.
897::
891:1
870:.
866::
858::
835:.
815::
807::
797::
774:.
754::
746::
736::
692:.
688::
680::
652:.
648::
640::
614:.
587:.
583::
575::
545:.
541::
533::
470:.
371:T
325:2
282:1
279:T
275:2
272:T
268:2
265:T
127:(
121:2
118:T
114:e
110:t
106:t
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.