Repeat rate analysis is federally (USA) mandated in mammography and recommended by both the federal government and the American Association of Physicists in Medicine in Radiography (AAPM).[1,2,3]
For the tomographic modalities (i.e. MRI, PET, CT) no repeat/reject metric exists. Repeats are usually the fault of technologists, faulty protocols, or uncooperative patients. Repeats/rejects often represent waste or deficiencies such as decreased scanner utilization, poor technologist training, poor CT protocols, wasted Iodine contrast, increased patient ionizing dose, and decreased patient satisfaction.
Figure 1 reviews the causes, effects and impacts of repeat scanning in CT. In short, repeats in CT represent
- a needless 100% increase in patient dose
- longer exam times
- often a double dose of CT contrast agent
What is a repeat?
At right, we show examples of repeats (Figure 2). In the clinic, a technologist may repeat many different types of acquisitions: localizers, bolus tracking phases, axial/sequential scan, helical/spiral scans. A technologist may also need to "add on" a small amount of anatomy they missed in the first scan, for example a few extra centimeters to cover the entire liver.
Sometimes repeats are needed and represent a well-trained technologist. Patient motion in some uncooperative patients cannot be avoided. To produce an image with diagnostic utility, repeats in many motion cases are appropriate.
Sometimes repeats represent poor technologist performance. For example, a technologist may not deliver adequate patient breathing instructions. This may motivate respiratory motion artifacts.
Sometimes a protocol may not be set-up properly. For example, a cardiac protocol may not be using the proper gating options, resulting in gating issues that motivate repeat scans.