American Registry of Radiologic Technologists (ARRT) Practice Exam

In radiology, "quantity" primarily refers to the amount of radiation produced, which is typically influenced by the milliampere (mA) setting of the x-ray machine. The mA represents the tube current, or the number of electrons flowing from the cathode to the anode in the x-ray tube, which directly correlates with the amount of x-rays that are produced during an exposure. Higher mA settings increase the quantity of radiation and thus the number of photons that reach the image receptor, which can enhance the overall exposure and help in creating a diagnostic image.

In contrast, kVp (kilovolt peak) relates more to the quality and energy of the x-rays produced rather than the quantity. Exposure time impacts how long the x-ray beam is active but does not define the "quantity" of radiation itself; it instead influences the total exposure over a certain duration. Image contrast refers to the difference in density between various areas of the image, which is affected by both the quantity and quality of radiation but is not itself a measure of quantity. Understanding these distinctions clarifies why mA is the correct measure of "quantity" in radiology.