Question 2953
{"accessible":false,"alternatives":[{"id":14381,"text":"halve acquisition time"},{"id":14382,"text":"have NO effect on image contrast"},{"id":14383,"text":"increase signal-to-noise"},{"id":14384,"text":"decrease spatial resolution"}],"archived":false,"correctAlternativeId":14381,"explanation":"\u003cp\u003eAcquisition time is inversely proportional to ETL. Therefore, doubling ETL halves acquisition time.\u003c/p\u003e\u003cp\u003eMore echoes in a single TR increase the TE for later echoes, which changes the overall image contrast. Each echo sample signal is being lost at the rate of the transverse decay curve. Doubling the number of echoes means that later echoes will have very little signal to sample, which decreases the signal-to-noise ratio.\u003c/p\u003e\u003cp\u003eSpatial resolution should remain unchanged as we are not changing the matrix size (contrast resolution may decrease).\u003c/p\u003e","id":2953,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/2967","nextQuestionPath":"/articles/acquisition-time/questions/2951","relatedArticles":[{"id":14045,"title":"Signal-to-noise ratio (MRI)","link":"/articles/signal-to-noise-ratio-mri?lang=us"},{"id":22136,"title":"Spin echo sequences","link":"/articles/spin-echo-sequences?lang=us"},{"id":60745,"title":"Fast spin echo","link":"/articles/fast-spin-echo?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\u003eWhat will doubling the echo train length (ETL) in fast spin echo do?\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/2953"}],"attemptsPercentages":[{"alternativeId":"14381","percentage":60},{"alternativeId":"14383","percentage":21},{"alternativeId":"14384","percentage":13},{"alternativeId":"14382","percentage":7}],"promptToLogin":false,"questionManager":false,"articleId":"acquisition-time"}