翻訳と辞書 Words near each other ・ Ernst Adolf Coccius ・ Ernst Ahl ・ Ernst Aigner ・ Ernst Albert Gäumann ・ Ernst Albrecht ・ Ernst Albrecht (footballer) ・ Ernst Albrecht (politician) ・ Ernst Alex ・ Ernst Alexander Rauter ・ Ernst Alexanderson ・ Ernst Alm ・ Ernst Anders ・ Ernst Andersson ・ Ernst Andres ・ Ernst Angel ・ Ernst angle ・ Ernst Anrich ・ Ernst Anschütz ・ Ernst Antevs ・ Ernst Antoft ・ Ernst Anton Henrik Sinding ・ Ernst Anton Nicolai ・ Ernst Anton Wülfing ・ Ernst Arndt ・ Ernst Arndt (actor) ・ Ernst Articus ・ Ernst August Friedrich Klingemann ・ Ernst August Girschner ・ Ernst August Köstring ・ Ernst August Wagner Dictionary Lists mini英和辞書 mini和英辞書 Webster 1913 Latin-English FOLDOC Wikipedia English ウィキペディア

翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Ernst angle ： ウィキペディア英語版 Ernst angle In nuclear magnetic resonance spectroscopy and magnetic resonance imaging, the Ernst angle is the flip angle (a.k.a. "tip" or "nutation" angle) for excitation of a particular spin that gives the maximal signal intensity in the least amount of time when signal averaging over many transients. In other words the highest signal-to-noise ratio can be achieved in a given amount of time. This relationship was described by Richard R. Ernst, winner of the 1991 Nobel Prize in Chemistry. Consider a single pulse sequence consisting of (1) an excitation pulse with flip angle $\backslash theta\_E$, (2) the recording of the time domain signal (Free induction decay, FID) for a duration known as acquisition time $a\_t$, and (3) a delay until the next excitation pulse (here called interpulse delay $d\_1$). This sequence is repeated back-to-back many times and the sum or the average of all recorded FIDs ("transients") is calculated. If the longitudinal relaxation time $T\_1$ of the specific spin in question is short compared to the sum of $a\_t$ and $d\_1$, the spins (or the spin ensembles) are fully or close to fully relaxed. Then a 90° flip angle will yield the maximum signal intensity (or signal-to-noise ratio) per number of averaged FIDs. For shorter intervals between excitation pulses compared to the longitudinal relaxation, partial longitudinal relaxation until the next excitation pulse leads to signal loss in the subsequent FID. This signal loss can be minimized by reducing the flip angle. The optimal signal-to-noise ratio for a given combination of longitudinal relaxation time and delay between excitation pulses is obtained at the Ernst angle $\backslash cos(\backslash theta\_E)\; =\; e^$ For example, to obtain the highest signal-to-noise ratio for a signal with $d\_1\; +\; a\_t$ set to match the signal's $T\_1$, the optimal flip angle is 68°. An NMR spectrum or an in vivo MR spectrum most of the time consists of signals of more than one spin species which can exhibit different longitudinal relaxation times. Therefore the calculated Ernst angle may apply only to the selected one of the many signals in the spectrum and other signals may be less intense than at their own Ernst angle. In contrast in standard MRI, the detected signal of interest is predominantly that of a single spin species, the water 1H spins. This relationship is especially important in magnetic resonance imaging where the sum of interscan delay $d\_1$ and acquisition time $a\_t$ is often short relative to the signal's $T\_1$ value. In the MRI community, this sum is often known as repetition time $T\_R\; =\; d\_1\; +\; a\_t$, thus $\backslash cos(\backslash theta\_E)=e^$ and consequently $$ \theta_E=\arccos\left(e^}\right). ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ernst angle」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.