スピンエコー

WordNet

work natural fibers into a thread; "spin silk"
prolong or extend; "spin out a visit" (同)spin out
the act of rotating rapidly; "he gave the crank a spin"; "it broke off after much twisting" (同)twirl, twist, twisting, whirl
a distinctive interpretation (especially as used by politicians to sway public opinion); "the campaign put a favorable spin on the story"
a short drive in a car; "he took the new car for a spin"
a swift whirling motion (usually of a missile)
revolve quickly and repeatedly around ones own axis; "The dervishes whirl around and around without getting dizzy" (同)spin around, whirl, reel, gyrate
form a web by making a thread; "spiders spin a fine web"
make up a story; "spin a yarn"
stream in jets, of liquids; "The creek spun its course through the woods"
twist and turn so as to give an intended interpretation; "The Presidents spokesmen had to spin the story to make it less embarrassing"
call to mind; "His words echoed John F. Kennedy" (同)recall
the repetition of a sound resulting from reflection of the sound waves; "she could hear echoes of her own footsteps" (同)reverberation, sound reflection, replication
a close parallel of a feeling, idea, style, etc.; "his contention contains more than an echo of Rousseau"; "Napoleon III was an echo of the mighty Emperor but an infinitely better man"
a reflected television or radio or radar beam
an imitation or repetition; "the flower arrangement was created as an echo of a clients still life"
a reply that repeats what has just been said
(of sounds) repeating by reflection; "a hotel with echoing halls" (同)reechoing
(Greek mythology) a nymph who was spurned by Narcissus and pined away until only her voice remained

PrepTutorEJDIC

(羊毛などから)〈糸など〉‘を'『紡ぐ』《+『名』+『out of』+『名』〈羊毛〉》,(糸などに)〈羊毛など〉‘を'紡ぐ《+『名』〈羊毛〉+『into』+『名』》 / 〈クモ・カイコなどが〉〈糸〉‘を'『吐く』;〈巣・繭〉‘を'かける / …‘を'くるくる回す / 〈物語など〉‘を'作る,話す / 『糸を紡ぐ』;〈クモ・カイコなどが〉糸を吐く / 〈こまなどが〉くるくる回る / 〈車などが〉疾走する / 〈頭などが〉くらくらする / 〈C〉〈U〉くるくる回すこと;回転 / 〈C〉《単数形で》(車などの)一走り / 〈C〉(飛行機の)きりもみ降下 / 〈C〉《単数形で》(価値などの)急落
〈C〉〈U〉『反響』[音];『こだま』,山びこ / 〈C〉〈U〉(意見・心情などに対する)共鳴,反応 / 〈C〉〈U〉(他人の行為・意見などの)繰り返し,まね《+『of』+『名』》;(…からの)影響《+『from』+『名』》;〈C〉まねをする人 / 〈場所が〉…‘を'『反響させる』 / 〈人の言葉・意見〉‘を'『そのまま繰り返す』,そっくりまねる / (…で)〈場所・音・声が〉『反響する』《+『with』+『名』(do『ing』)》

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/10/21 01:09:16」(JST)

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Spin echo animation showing the response of spins (red arrows) in the blue Bloch sphere to the green pulse sequence

In magnetic resonance, a spin echo is the refocusing of spin magnetisation by a pulse of resonant electromagnetic radiation.^[1] Modern nuclear magnetic resonance (NMR) and magnetic resonance imaging make use of this effect.

The NMR signal observed following an initial excitation pulse decays with time due to both spin relaxation and any inhomogeneous effects which cause different spins in the sample to precess at different rates. The first of these, relaxation, leads to an irreversible loss of magnetisation. However, the inhomogeneous dephasing can be removed by applying a 180° inversion pulse that inverts the magnetisation vectors.^[2] Examples of inhomogeneous effects include a magnetic field gradient and a distribution of chemical shifts. If the inversion pulse is applied after a period t of dephasing, the inhomogeneous evolution will rephase to form an echo at time 2t. In simple cases, the intensity of the echo relative to the initial signal is given by e^−2t/T₂ where T₂ is the time constant for spin-spin relaxation.

Echo phenomena are important features of coherent spectroscopy which have been used in fields other than magnetic resonance including laser spectroscopy^[3] and neutron scattering. Echoes were first detected in nuclear magnetic resonance by Erwin Hahn in 1950^[4] , and spin echoes are sometimes referred to as Hahn echoes. In nuclear magnetic resonance and magnetic resonance imaging, radiofrequency radiation is most commonly used.^[5]^[6]

In 1972 F. Mezei 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.

Principle

The spin echo effect was discovered by Erwin Hann 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,^[4] and further developed by Carr and Purcell who pointed out the advantages of using a 180° refocusing pulse for the second pulse.^[7] The pulse sequence may be better understood by breaking it down into the following steps:

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 rotating reference frame where the spins are stationary on average.
A 90 degree pulse has been applied that flips the arrow into the horizontal (x-y) plane.
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 field strength and start getting ahead of the others. This makes the signal decay.

A 180 degree pulse is now applied so that the slower spins lead ahead of the main moment and the fast ones trail behind.
Progressively, the fast moments catch up with the main moment and the slow moments drift back toward the main moment.
Complete refocusing has occurred and at this time, an accurate T₂ echo can be measured with all T₂^* effects removed. Quite separately, return of the red arrow towards the vertical (not shown) would reflect the T₁ relaxation. 180 degrees is π radians so 180° pulses are often called π pulses.

Several simplifications are used in this sequence: no decoherence 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 animation below:

Spin echo decay

A Hahn echo decay experiment can be used to measure the spin–spin relaxation 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 exponential decay is measured which is described by the T₂ time.

Stimulated echo

Hahn's 1950 paper^[4] 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 , and then a second 90° pulse is applied such that the “pancake” is now in the x-z plane. After a further time a third pulse is applied and a stimulated echo is observed after waiting a time after the last pulse.

Photon echo

Hahn echos have also been observed at optical frequencies.^[3] For this, resonant light is applied to a material with an inhomogeneously broadened 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.^[8]

Animations and Simulations

http://scratch.mit.edu/projects/nevit/872879 Spin Echo Simulation
The animation show pulse sequences like spin echo sequence

References

^ J. E. Tanner & E. O. Stejskal (2003). "Restricted Self‐Diffusion of Protons in Colloidal Systems by the Pulsed‐Gradient, Spin‐Echo Method". The Journal of Chemical Physics 49: 1768. Bibcode:1968JChPh..49.1768T. doi:10.1063/1.1670306.
^ Malcolm H. Levitt; Ray Freeman (1979). "NMR population inversion using a composite pulse". Journal of Magnetic Resonance 2: 473–476. Bibcode:1979JMagR..33..473L. doi:10.1016/0022-2364(79)90265-8.
^ ^a ^b Kurnit, N. A.; Abella, I. D.; Hartmann, S. R. (1964). "Observation of a photon echo". Physical Review Letters 13: 567–568. Bibcode:1964PhRvL..13..567K. doi:10.1103/PhysRevLett.13.567.
^ ^a ^b ^c Hahn, E.L. (1950). "Spin echoes". Physical Review 80: 580–594. Bibcode:1950PhRv...80..580H. doi:10.1103/PhysRev.80.580.
^ A Awad; R F Spetzler; J A Hodak; C A Awad; et al. (1986). "Incidental subcortical lesions identified on magnetic resonance imaging in the elderly. I. Correlation with age and cerebrovascular risk factors.". Am Heart Assoc 2.
^ Bruce Gelerter. "PEMF Relieves Pain".
^ Carr, H. Y.; Purcell, E. M. (1954). "Effects of Diffusion on Free Precession in Nuclear Magnetic Resonance Experiments". Physical Review 94: 630–638. Bibcode:1954PhRv...94..630C. doi:10.1103/PhysRev.94.630.
^ http://www.physics.montana.edu/oct/web/basics_of_octs.htm

Textbooks

Ray Freeman (1999). Spin Choreography: Basic Steps in High Resolution NMR. Oxford University Press. ISBN 978-0-19-850481-8.

Malcolm H. Levitt (2001). Spin Dynamics: Basics of Nuclear Magnetic Resonance. Wiley. ISBN 978-0-471-48922-1.

Arthur Schweiger; Gunnar Jeschke (2001). Principles of Pulse Electron Paramagnetic Resonance. Oxford University Press. ISBN 978-0-19-850634-8.

UpToDate Contents

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1. 三次元心エコー検査 three dimensional echocardiography
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5. 負荷心エコーの概要 overview of stress echocardiography

English Journal

Tractography of Meyer's Loop asymmetries.

Dreessen de Gervai P1, Sboto-Frankenstein UN2, Bolster RB3, Thind S1, Gruwel ML4, Smith SD3, Tomanek B5.
Epilepsy research.Epilepsy Res.2014 Jul;108(5):872-82. doi: 10.1016/j.eplepsyres.2014.03.006. Epub 2014 Mar 26.
PURPOSE: The purpose of the current study was to use diffusion tensor imaging (DTI) to conduct tractography of the optic radiations (OR) and its component bundles and to assess both the degree of hemispheric asymmetry and the inter-subject variability of Meyer's Loop (ML). We hypothesized that there
PMID 24725809

Ex vivo T2 relaxation: associations with age-related neuropathology and cognition.

Dawe RJ1, Bennett DA2, Schneider JA3, Leurgans SE2, Kotrotsou A4, Boyle PA5, Arfanakis K6.
Neurobiology of aging.Neurobiol Aging.2014 Jul;35(7):1549-61. doi: 10.1016/j.neurobiolaging.2014.01.144. Epub 2014 Feb 6.
The transverse relaxation time constant, T(2), is sensitive to brain tissue's free water content and the presence of paramagnetic materials such as iron. In this study, ex vivo magnetic resonance imaging was used to investigate alterations in T(2) related to Alzheimer's disease (AD) pathology and ot
PMID 24582637

Motor cortex glutathione deficit in ALS measured in vivo with the J-editing technique.

Weiduschat N1, Mao X1, Hupf J2, Armstrong N2, Kang G1, Lange DJ3, Mitsumoto H2, Shungu DC4.
Neuroscience letters.Neurosci Lett.2014 Jun 6;570:102-7. doi: 10.1016/j.neulet.2014.04.020. Epub 2014 Apr 24.
This study compared in vivo levels of the antioxidant glutathione (GSH) in the motor cortex of 11 ALS patients with those in 11 age-matched healthy volunteers (HV). Using the standard J-edited spin-echo difference MRS technique, GSH spectra were recorded on a 3.0T GE MR system from a single precentr
PMID 24769125

Japanese Journal

3D-fast spin echo MRIを用いた頸動脈狭窄患者の狭窄率評価の検討：3DCTAとの比較検討 (第129回成医会総会一般演題)

菅一成,渋谷一敬,北川久,海渡信義,石橋敏寛,村山雄一,阿部俊昭
東京慈恵会医科大学雑誌 127(6), 254-254, 2012-11-15
NAID 120005104568

臨床技術高空間分解能Multiple Echo Planar Imaging Based Signal Targeting and Alternating Radiofrequencyによる頭蓋内非造影Time-resolved MR Angiography

中村理宣,米山正己,田渕隆 [他]
日本放射線技術学会雑誌 68(11), 1525-1532, 2012-11-00
NAID 40019510460

"Hot cross bun" sign in multiple system atrophy with predominant cerebellar ataxia: a comparison between proton density-weighted imaging and T2-weighted imaging.

Kasahara Seiko,Miki Yukio,Kanagaki Mitsunori,Kondo Takayuki,Yamamoto Akira,Morimoto Emiko,Okada Tomohisa,Ito Hidefumi,Takahashi Ryosuke,Togashi Kaori
European journal of radiology 81(10), 2848-2852, 2012-10-00
… Axial unenhanced proton density-weighted imaging and T2-weighted imaging were obtained using a dual-echo fast spin-echo sequence at 3T. …
NAID 120004873778