Question

On a multi-row detector scanner, a radiation penumbra may be found:

a. on every other slice
b. only on the trailing edges of the slices
c. on every slice
d. only on the first and last slices of the slice volume

Answer 1

A radiation penumbra on a multi-row detector scanner is found only on the trailing edges of the slices. This effect is due to the dispersion of the radiation beam and is mitigated by technologies like SPECT and PET scans using advanced detectors and collimators.

Step-by-step explanation:

On a multi-row detector scanner, a radiation penumbra may be found only on the trailing edges of the slices. The penumbra is an area of partial shadow that occurs because, although detectors are designed to measure incoming radiation accurately, there can be some dispersion or spread of the beam which affects the edges of each slice, leading to less precise imaging at those points. The penumbra effect is particularly noticeable on the trailing edges of the slices as the radiation beam moves across the detector field. Nevertheless, the central areas of the slices are typically unaffected by this phenomenon, resulting in clearer, more accurate imaging in those regions.

Modern scanner technologies, such as single-photon-emission computed tomography (SPECT) and positron emission tomography (PET scans), have sophisticated ways to mitigate the effects of radiation penumbra to improve imaging accuracy. For instance, solid-state radiation detectors and collimators are used to better focus the radiation, reducing the spread that causes the penumbra.