Question 2837
{"accessible":false,"alternatives":[{"id":13843,"text":"decreasing pulse repetition frequency"},{"id":13844,"text":"moving the probe across a wide scanning area"},{"id":13845,"text":"reducing scanning time"},{"id":13846,"text":"reducing transducer gain"},{"id":13847,"text":"scanning a tissue with reduced perfusion"}],"archived":false,"correctAlternativeId":13847,"explanation":"\u003cp\u003eBlood flow in a tissue reduces the chance of thermal bioeffects by removing ‘heated’ blood and replacing it with blood that has not been exposed to any wave intensity. When a tissue is poorly perfused this does not occur and can increase the risk of thermal bioeffects.\u003c/p\u003e\u003cp\u003eMoving the probes spreads the energy over a wider area reducing beam intensity. Thermal bioeffects are cumulative so reducing scanning time decreases their likelihood. A reduction in pulse repetition frequency increases receive time, which reduces temporal average intensity – reducing thermal bioeffect risk. Intensity is proportional to wave amplitude\u003csup\u003e \u003c/sup\u003esquared and reducing transducer gain will reduce intensity.\u003c/p\u003e","id":2837,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/2837","nextQuestionPath":"/articles/mechanical-index/questions/2836","relatedArticles":[{"id":32611,"title":"Thermal index","link":"/articles/thermal-index?lang=gb"},{"id":54038,"title":"Ultrasound transducer","link":"/articles/ultrasound-transducer?lang=gb"},{"id":64450,"title":"Pulse repetition frequency","link":"/articles/pulse-repetition-frequency?lang=gb"}],"alsoUsedIn":[{"id":1620,"kind":"RestrictedPage","title":"Page 1620 (in no courses)","link":"https://radiopaedia.org/admin/restricted_pages/1620"},{"id":1984,"kind":"Course","title":"Imaging Physics: Ultrasound Peer Review - page 1984","link":"https://radiopaedia.org/courses/imaging-physics-ultrasound-peer-review/pages/1984"},{"id":1984,"kind":"Course","title":"Imaging Physics: Ultrasound - page 1984","link":"https://radiopaedia.org/courses/imaging-physics-ultrasound/pages/1984"}],"stem":"\u003cp\u003eWhich of the following increases the likelihood of thermal bioeffects in ultrasound imaging?\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/2837"}],"attemptsPercentages":[{"alternativeId":"13845","percentage":2},{"alternativeId":"13847","percentage":69},{"alternativeId":"13843","percentage":16},{"alternativeId":"13846","percentage":4},{"alternativeId":"13844","percentage":8}],"promptToLogin":false,"questionManager":false,"articleId":"mechanical-index"}