Administrators, Editors, Administrators
3,484
edits
Changes
Jump to navigation
Jump to search
'''Geometric unsharpness''' is a decrease in the spatial resolution of an image because the X-rays from the generator comes from an area rather than a single dot, and is decreased by having the object closer to the detector.
→Interpretation: Integrated
==Interpretation==
[[File:Focal spot size and unsharpness in X-ray.jpg|thumb|340px|Source-object distance (SOD), and source-detector distance (SDD) and geometric unsharpness.<ref>{{cite journal|title=Digital radiography for the inspection of small defects|author=Bruce Blakeley, Konstantinos Spartiotis|url=http://www.twi-global.com/technical-knowledge/published-papers/digital-radiography-for-the-inspection-of-small-defects-february-2006/|journal=Insight|volume=48|issue=2|year=2006}}</ref>This image also shows '''geometric unsharpness''', which is a decrease in the spatial resolution of an image because the X-rays from the generator comes from an area rather than a single dot, and is decreased by having the object closer to the detector.]]
Because of '''geometric magnification''', distances measured on a projection become larger than the actual size of the imaged object:
*Size<sub>Object</sub> = Size<sub>Projection</sub> * Source-object distance (SOD) / Source-detector distance (SDD).<ref>{{cite web|last=DICOM|title=DICOM PS3.3 - Information Object Definitions - Table C.8-30. XA Positioner Module Attributes|url=http://dicom.nema.org/medical/dicom/current/output/chtml/part03/sect_C.8.7.5.html#table_C.8-30|accessdate=2017-01-23|date=2016-11-21}}</ref>
Alternative names for ''source-detector distance''(SDD) are ''source''<ref name=SID>{{cite web|url=http://medical-dictionary.thefreedictionary.com/source-to-image-receptor+distance|title=source-to-image-receptor distance|website=Farlex medical dictionary, in turn citing Mosby's Medical Dictionary, 9th edition.|accessdate=2018-01-28}}</ref>/''focus'' to ''detector''/''image-receptor''<ref name=SID/>/''film'' distance (SID<ref name=SID/>, FID or FRD). On lumbar and [[chest radiograph]]s, it is anticipated that the magnification factor is between 1.05 and 1.40.<ref>{{cite web|title=Implementation of unsharpness and noise into the model of the imaging system: Applications to chest and lumbar spine screen-film radiography|url=https://www.diva-portal.org/smash/get/diva2:327957/FULLTEXT01.pdf|author=M Sandborg, D R Dance, and G Alm Carlsson|website=Faculty of Health Sciences, Linköping University}} Report 90. Jan. 1999. ISRN: LIU-RAD-R-090</ref> Because of the uncertainty of the true size of objects seen on projectional radiography, their sizes are often compared to other structures within the body, such as dimensions of the [[vertebra]]e, or empirically by clinical experience.<ref>[https://books.google.se/books?id=JaL3AAAAQBAJ&pg=PA788 Page 788] in: {{cite book|title=Neuroimaging, Part 2 Volume 136 of Handbook of Clinical Neurology|author=Joseph C. Masdeu, R. Gilberto Gonzalez |publisher=Newnes|year=2016|isbn=9780702045387}}</ref>
==Diseases==
*[[X-ray of fractures]]
