Final answer:
The x-ray beam must indeed be limited to the size of the image receptor to minimize patient exposure to radiation and to maintain image quality, adhering to the ALARA principle.
Step-by-step explanation:
The x-ray beam must be limited to the size of the image receptor or smaller to ensure that the patient is exposed to the least amount of radiation necessary to obtain the required diagnostic information. Using a beam that is larger than the image receptor not only exposes tissue unnecessarily but can also contribute to increased scatter radiation which can degrade the quality of the image and hence the diagnostic information it provides.
It is a key principle in radiology to use the ALARA principle (As Low As Reasonably Achievable) which includes collimation to the size of the sensor to minimize patient exposure and ensure image quality. In situations where precise imaging is required, such as in CT scanners or when assessing crystal lattices, the property of X-rays to produce detailed images of structures that differ in density is utilized.