ARRT - American Registry of Radiologic Technologists Image Acquisition and Evaluation Questions and Answers

Question 1

In computed radiography (CR), what is the primary function of the photostimulable phosphor (PSP) within the imaging plate?

Accepted Answer

To absorb the remnant beam energy and store it as a latent image.

Answer

The photostimulable phosphor (PSP) layer, typically made of barium fluorohalide, absorbs the energy from the x-ray photons that pass through the patient. This energy excites electrons within the phosphor, which then become trapped in 'F-centers'. This pattern of trapped electrons forms the latent, or invisible, image.

Question 2

A radiograph of an AP abdomen appears grainy and mottled. The exposure indicator value is significantly lower than the target range. Which of the following technical adjustments would be most effective in correcting this quantum mottle artifact on a repeat exposure?

Accepted Answer

Increase the mAs.

Answer

Quantum mottle, or quantum noise, is a grainy appearance on a radiograph that results from an insufficient number of x-ray photons reaching the image receptor. Increasing the mAs directly increases the number of photons produced, which will improve the signal-to-noise ratio and eliminate the quantum mottle, leading to a smoother, higher-quality image.

Question 3

When changing from an 8:1 ratio grid to a 12:1 ratio grid for a particular examination, which of the following consequences should the technologist anticipate?

Accepted Answer

An increase in image contrast.

Answer

A higher grid ratio, such as 12:1, has taller and/or more closely spaced lead strips compared to a lower ratio grid like 8:1. This makes the grid more efficient at absorbing scatter radiation before it reaches the image receptor. By removing more scatter, which degrades the image, the resulting radiograph will exhibit higher (or improved) image contrast. However, this comes at the cost of increased patient dose, as mAs must be increased to compensate for the primary radiation that is also absorbed.

Question 4

A technologist is performing a lateral lumbar spine using an Automatic Exposure Control (AEC) system. The patient is positioned correctly, but the resulting image is significantly underexposed. Which of the following is the most likely cause of this error?

Accepted Answer

The backup timer was set too low.

Answer

The backup timer is a safety feature that terminates the exposure after a certain time to prevent extreme overexposure to the patient and tube overload. If the backup time is set too short, it may terminate the exposure before the AEC system has received enough radiation to create an optimal image, resulting in underexposure. This is especially common in large or dense anatomy where longer exposure times are needed.

Question 5

While reviewing a portable chest radiograph acquired with a DR flat-panel detector, the technologist notices a faint, reversed image of the detector's electronic wiring superimposed over the patient's anatomy. This artifact is known as:

Accepted Answer

Backscatter

Answer

Backscatter is an artifact that occurs when radiation is scattered back towards the detector from objects behind it, such as the bed or cassette holder. This scattered radiation can be strong enough to create an image of the internal components of the detector's backing, which then appears superimposed on the diagnostic image. This is more common with higher exposure factors needed for larger patients or when collimation is insufficient.

ARRT - American Registry of Radiologic Technologists Practice Test

ARRT - American Registry of Radiologic Technologists Practice Test

ARRT - American Registry of Radiologic Technologists Image Acquisition and Evaluation Questions and Answers