American Registry of Radiologic Technologists (ARRT) Practice Exam

How does increasing mass affect radiographic density?

1. It decreases density

2. It has no effect on density

3. It increases density

4. It changes exposure time

The correct answer is: It increases density

Increasing mass directly affects radiographic density by increasing it. When imaging with X-rays, the denser the object being imaged, the more X-ray photons are absorbed. This is due to the interaction between the X-rays and the materials that comprise the object, which have different atomic numbers and mass densities. As the mass of an object increases, it has a higher probability of attenuating (or absorbing) the X-ray beam. This results in fewer X-rays reaching the image receptor (like a film or digital detector), producing a darker (or higher density) image in the areas where the increased mass has resulted in greater absorption of X-rays. In radiography, this means that denser materials will appear lighter on a radiograph because they reduce the number of X-ray photons that strike the imaging receptor, while less dense areas will appear darker. Understanding this relationship helps radiologic technologists adjust their techniques, such as increasing exposure time or adjusting the kilovoltage peak (kVp), to ensure that the radiographic images are of adequate density for interpretation.