CAMRT Radiography Practice Exam

What does the Reciprocity Law state?

1. Only one mA can be used to achieve mAs

2. Any combination of mA and time that gives the same mAs

3. mA and time must always be kept constant

4. Longer exposure times require higher mA

The correct answer is: Any combination of mA and time that gives the same mAs

The Reciprocity Law states that any combination of milliamperes (mA) and exposure time that yields the same milliampere-seconds (mAs) will produce a similar exposure on the radiographic image. This principle underlines the flexibility in radiographic technique, allowing radiographers to adjust the mA (tube current) and time (duration of exposure) depending on the situation, while still achieving the desired radiation dose and image quality. For instance, if a particular radiographic technique calls for 100 mAs, it can be achieved through various combinations, such as 100 mA for 1 second, 200 mA for 0.5 seconds, or 50 mA for 2 seconds. As long as the product of mA and exposure time equals 100 mAs, the resultant exposure to the image receptor will be equivalent, following the law of reciprocity. Understanding this law is crucial for radiographers because it allows them to make adjustments to optimize patient safety and image quality, accommodating different equipment capabilities and clinical scenarios.