Question 2935
{"accessible":false,"alternatives":[{"id":14298,"text":"gradient coils"},{"id":14299,"text":"main coils"},{"id":14300,"text":"radiofrequency coils"},{"id":14301,"text":"shim coils"}],"archived":false,"correctAlternativeId":14300,"explanation":"\u003cp\u003eThe radiofrequency coils do not contribute to the magnitude of the main magnetic field. The magnetic field produced by the radiofrequency pulse is perpendicular to the main field. The radiofrequency pulse matches the precession frequency and induces resonance.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe precession frequency of hydrogen atoms is proportional to the main magnetic field strength.\u003c/p\u003e\u003cp\u003eGradient coils create a gradient in the main magnetic field strength across an axis of the field. This will induce changes in precession frequency. Shim coils serve to increase magnetic field homogeneity. By definition, they manipulate the main magnetic field ultimately affecting precession frequency.\u003c/p\u003e","id":2935,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/2963","nextQuestionPath":"/articles/gradient-coils-1/questions/2269","relatedArticles":[{"id":5855,"title":"Larmor frequency","link":"/articles/larmor-frequency?lang=us"},{"id":21769,"title":"Radiofrequency coils","link":"/articles/radiofrequency-coils-1?lang=us"},{"id":60856,"title":"Magnetic shimming","link":"/articles/magnetic-shimming?lang=us"}],"alsoUsedIn":[{"id":1926,"kind":"Course","title":"Imaging Physics: MRI - page 1926","link":"https://radiopaedia.org/courses/imaging-physics-mri/pages/1926"}],"stem":"\u003cp\u003eWhich of the following MRI machine components has \u003cstrong\u003eNO \u003c/strong\u003edirect effect on the precession frequency of hydrogen atoms?\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/2935"}],"attemptsPercentages":[{"alternativeId":"14298","percentage":7},{"alternativeId":"14300","percentage":37},{"alternativeId":"14299","percentage":8},{"alternativeId":"14301","percentage":48}],"promptToLogin":false,"questionManager":false,"articleId":"gradient-coils"}