CAMRT Radiography Practice Exam

In fluoroscopy, increasing the SID will result in what changes to image detail, OID, magnification, and patient dose?

1. Decrease detail, increase OID

2. Increase detail, decrease OID

3. Decrease detail, decrease OID

4. No change

The correct answer is: Increase detail, decrease OID

In fluoroscopy, increasing the Source-to-Image Distance (SID) leads to several important changes in image quality and patient exposure. When the SID is increased, the image detail actually improves. This occurs because a greater distance helps to reduce the effects of penumbra—a blurring that occurs at the edges of an object due to the radiation source's size and its distance from the film or detector. Additionally, increasing SID results in a decrease in Object-to-Image Distance (OID). A lower OID means that the object being imaged is closer to the imaging receptor relative to the source, which further enhances the sharpness and detail of the image. Moreover, a lower OID minimizes magnification, which is crucial for obtaining accurate measurements and representations of anatomical structures. With respect to patient dose, while the increased SID may require a higher exposure time or technique to maintain image quality, it is often interpreted as a way to effectively reduce the dose to the patient, especially as the imaging system compensates for distance. In summary, increasing the SID is beneficial in terms of improving detail due to reducing penumbra, decreasing OID for sharper images, and can also help in optimizing patient dose management.