Question 2946
{"accessible":false,"alternatives":[{"id":14348,"text":"Fourier transformation"},{"id":14349,"text":"frequency encoding gradient"},{"id":14350,"text":"gradient echo"},{"id":14351,"text":"phase encoding gradient"},{"id":14352,"text":"spin echo"}],"archived":false,"correctAlternativeId":14352,"explanation":"\u003cp\u003eSpin echo formation, typically using a 90 degree radiofrequency pulse followed by a 180 degree radiofrequency pulse, compensates for phase incoherence caused by local magnetic field inhomogeneities.\u003c/p\u003e\u003cp\u003eFourier transformation is a mathematical calculation converting time based signal data into frequency based data, and frequency data into location based data. The frequency encoding gradient allows for signal amplitude to be spatially localized along the frequency encoding axis based on differing precession frequencies created by the gradient.\u003c/p\u003e\u003cp\u003eThe application of the frequency encoding gradient causes loss of phase coherence and subsequent signal loss. A gradient echo accounts for this signal loss created by the frequency encoding gradient (but not the local magnetic field inhomogeneities).\u003c/p\u003e\u003cp\u003eThe phase encoding gradient allows for signal localization along the phase encoding axis of the slice.\u003c/p\u003e","id":2946,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/2962","nextQuestionPath":null,"relatedArticles":[{"id":22136,"title":"Spin echo sequences","link":"/articles/spin-echo-sequences?lang=us"},{"id":16504,"title":"Fourier transform","link":"/articles/fourier-transform?lang=us"},{"id":18339,"title":"Gradient echo sequences","link":"/articles/gradient-echo-sequences-1?lang=us"},{"id":21768,"title":"Gradient coils","link":"/articles/gradient-coils-1?lang=us"},{"id":57797,"title":"Inverse Fourier transformation","link":"/articles/inverse-fourier-transformation-1?lang=us"},{"id":57795,"title":"Fourier transformation","link":"/articles/fourier-transformation-1?lang=us"},{"id":60748,"title":"Effect of gradient strength and bandwidth on slice thickness","link":"/articles/effect-of-gradient-strength-and-bandwidth-on-slice-thickness?lang=us"}],"alsoUsedIn":[{"id":1927,"kind":"Course","title":"Imaging Physics: MRI - page 1927","link":"https://radiopaedia.org/courses/imaging-physics-mri/pages/1927"}],"stem":"\u003cp\u003eWhich of the following compensates for signal loss due to magnetic field non-uniformity?\u003c/p\u003e","menuLinks":[{"text":"Report problem with question","url":"https://docs.google.com/forms/d/e/1FAIpQLSfO3soWYhOjJ7yErSysyCe5V4A1CqW7WK3rDA7MtAkecMGqNw/viewform?entry.1624461248\u0026entry.553583435=https://radiopaedia.org/questions/2946"}],"attemptsPercentages":[{"alternativeId":"14350","percentage":11},{"alternativeId":"14352","percentage":68},{"alternativeId":"14348","percentage":8},{"alternativeId":"14351","percentage":6},{"alternativeId":"14349","percentage":7}],"promptToLogin":false,"questionManager":false,"articleId":"fast-spin-echo"}