Question 800
{"accessible":false,"alternatives":[{"id":4047,"text":"decreased by a factor of 2"},{"id":4048,"text":"decreased by about 40%"},{"id":4049,"text":"increased by a factor of 2"},{"id":4050,"text":"increased by about 40%"},{"id":4051,"text":"unchanged"}],"archived":false,"correctAlternativeId":4050,"explanation":"\u003cp\u003eThe image subtraction process is highly sensitive to the presence of noise in images - noise being increased by about 40%, theoretically, as a direct consequence of the subtraction process, due to the quadratic addition of noise variances.\u003c/p\u003e\u003cp\u003eThe major sources of noise in DSA images are Quantum Noise - which results from the random nature of x-ray production and System Noise - which results from the electronic components of the imaging system.\u003c/p\u003e\u003cp\u003eAdapted from\u0026nbsp;\u003ca href=\"https://en.wikibooks.org/wiki/Basic_Physics_of_Digital_Radiography\"\u003eBasic Physics of Digital Radiography\u003c/a\u003e\u0026nbsp;by\u0026nbsp;Kieran Maher,\u0026nbsp;with author's permission (License:\u0026nbsp;\u003ca href=\"https://creativecommons.org/licenses/by-sa/3.0/\"\u003eCreative Commons\u0026nbsp;BY-SA 3.0\u003c/a\u003e).\u003c/p\u003e","id":800,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/2955","nextQuestionPath":"/articles/signal-to-noise-ratio-mri/questions/643","relatedArticles":[{"id":12937,"title":"Noise","link":"/articles/noise?lang=us"}],"alsoUsedIn":[],"stem":"\u003cp\u003eWhen two images are subtracted, the noise is...\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/800"}],"attemptsPercentages":[{"alternativeId":"4047","percentage":21},{"alternativeId":"4051","percentage":20},{"alternativeId":"4048","percentage":15},{"alternativeId":"4049","percentage":18},{"alternativeId":"4050","percentage":25}],"promptToLogin":false,"questionManager":false,"articleId":"signal-to-noise-ratio-mri"}