Which of the following is a common cause of quantum mottle in an image?

Quantum mottle refers to the grainy appearance often seen in radiographic images, which is primarily caused by the statistical nature of photon detection in the imaging process. When there is insufficient radiation exposure to the detector, it becomes more challenging for the system to gather enough photons to produce a clear and uniform image. This lack of adequate exposure results in variations in the number of photons detected across the image, leading to the visible noise characteristic of quantum mottle.

Underexposure to radiation decreases the total number of photons hitting the imaging receptor. As a result, some regions may receive significantly fewer photons than others, creating a pattern of bright and dark spots that manifests as quantum mottle. This is especially pronounced in low-dose imaging situations or when the technical factors applied are not optimized for the patient's body habitus or the specific imaging task.

In contrast, other choices such as overexposure might result in a loss of detail or image contrast but are not directly responsible for quantum mottle. Inconsistent grid usage and improper patient positioning can introduce artifacts or degrade image quality, but they do not inherently cause the statistical fluctuations in photon counts that lead to quantum mottle. Thus, underexposure is the primary factor contributing to this phenomenon.