Question 2933
{"accessible":false,"alternatives":[{"id":14288,"text":"cause hydrogen atoms to precess in-phase"},{"id":14289,"text":"increase Brownian motion of hydrogen"},{"id":14290,"text":"increase the gyromagnetic ratio of hydrogen"},{"id":14291,"text":"increase the magnetic moment of hydrogen"},{"id":14292,"text":"increase the number of hydrogen atoms in the spin-up energy state"}],"archived":false,"correctAlternativeId":14292,"explanation":"\u003cp\u003eWhen placed in an external magnetic field, hydrogen atoms will align with, and precess around, the axis of the field. Hydrogen atoms will exist in two energy states - spin-up and spin-down. There will be a slight predominance of the spin-up (or parallel) orientation. As the magnetic field strength increases the number of hydrogen atoms in the spin-up orientation will increase (which in turn increases the net magnetization vector of the tissue).\u003c/p\u003e\u003cp\u003eHydrogen atoms will only precess in phase during the application of the perpendicular radiofrequency pulse. Brownian motion is the spontaneous and random movement of particles due to thermal collisions which is not dependent on magnetic field strength. The gyromagnetic ratio is a constant, unique to each atom, and does not change. The magnetic moment is a function of the gyromagnetic ratio and the atomic particle's net spin value - both of which are constant independent of magnetic field strength.\u003c/p\u003e\u003cp\u003e*note: although in classical physics spins are described as existing in two discrete states, spin-up and spin-down, in the quantum realm it is impossible to measure or predict the exact orientation of an individual spin at any given moment in time. However, when observing a group of spins as a whole, there is a defined energy gap which correlates to a specific proportion of spins in the spin-up and spin-down states.\u003c/p\u003e","id":2933,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/2933","nextQuestionPath":"/articles/mri-2/questions/2269","relatedArticles":[{"id":14586,"title":"Gyromagnetic ratio","link":"/articles/gyromagnetic-ratio?lang=us"},{"id":16492,"title":"Nuclear magnetic resonance","link":"/articles/nuclear-magnetic-resonance?lang=us"},{"id":60733,"title":"Magnetic dipole moment","link":"/articles/magnetic-dipole-moment?lang=us"},{"id":178369,"title":"Spin (physics)","link":"/articles/spin-physics?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\u003eIncreasing the strength of the main magnetic field (B0) will...\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/2933"}],"attemptsPercentages":[{"alternativeId":"14290","percentage":12},{"alternativeId":"14291","percentage":25},{"alternativeId":"14289","percentage":6},{"alternativeId":"14292","percentage":44},{"alternativeId":"14288","percentage":13}],"promptToLogin":false,"questionManager":false,"articleId":"mri"}