Final answer:
PBL in radiology stands for Positive Beam Limitation, which is a system that adjusts the X-ray field size to match the size of the cassette, improving patient safety and image quality.
Step-by-step explanation:
In radiology, the acronym PBL (Positive Beam Limitation) stands for Positive Beam Limitation, which is a feature of radiographic systems designed to automatically adjust the X-ray field size to the size of the cassette in order to minimize patient exposure and ensure that only the area of interest is imaged. The use of PBL helps to optimize the quality of the radiographic image by reducing the amount of scatter radiation and ensuring proper collimation. This is crucial in diagnostic imaging procedures like bone scans where a radioactive tracer is used to reveal areas with increased bone activity that may indicate diseases such as bone cancer. For example, Figure 31.6 might depict an image where a radioactive substance like a tracer is administered to a patient, and active bone cells can be identified by the detection of emitted y radiation, which has a sufficient range to leave the body and be measured with an external detector.