Question 809
{"accessible":false,"alternatives":[{"id":4092,"text":"correct for exponential attenuation"},{"id":4093,"text":"eliminate motion artefacts"},{"id":4094,"text":"increase spatial resolution"},{"id":4095,"text":"reduce scatter effects"},{"id":4096,"text":"sharpen vessel edges"}],"archived":false,"correctAlternativeId":4092,"explanation":"\u003cp\u003eThe density of opacified vessels in the subtraction image may contain artefacts which are dependent on the anatomical details which underlie and overlap the blood vessels within the patient. These artefacts result because of the exponential nature of radiation attenuation in matter. They may be reduced ideally by computing the natural logarithm of the transmitted intensities prior to subtraction. Many DSA systems utilize this reasoning to logarithmically transform both the mask and the live images prior to subtraction.\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":809,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/809","nextQuestionPath":"/articles/spatial-resolution/questions/804","relatedArticles":[{"id":30308,"title":"Compton effect","link":"/articles/compton-effect?lang=us"}],"alsoUsedIn":[],"stem":"\u003cp\u003eDigital subtraction angiography (DSA) images are generally transformed logarithmically prior to subtraction in order to...\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/809"}],"attemptsPercentages":[{"alternativeId":"4095","percentage":18},{"alternativeId":"4096","percentage":16},{"alternativeId":"4094","percentage":19},{"alternativeId":"4092","percentage":34},{"alternativeId":"4093","percentage":12}],"promptToLogin":false,"questionManager":false,"articleId":"spatial-resolution"}