ARRT - American Registry of Radiologic Technologists Equipment Operation and QA Questions and Answers

Question 1

A radiograph of the pelvis exhibits a uniform loss of density across the entire image. The technologist used a focused grid and suspects grid cutoff. Which of the following errors is the MOST likely cause?

Accepted Answer

Off-level grid error

Answer

An off-level grid error, where the X-ray beam is angled across the lead strips or the grid is tilted, results in the absorption of the primary beam across the entire surface of the grid. This causes a uniform decrease in radiographic density or a light, underexposed image. An upside-down focused grid would cause severe cutoff on the lateral edges but not in the center. Off-center and off-focus errors also result in a non-uniform density loss, typically more pronounced on one side or toward the edges.

Question 2

A quality control test is performed on a single-phase, full-wave rectified x-ray unit. A spinning top test is used to evaluate timer accuracy with an exposure time of 0.1 seconds. How many dots should appear on the finished radiograph?

Accepted Answer

12

Answer

For a single-phase, full-wave rectified generator, there are 120 pulses of x-ray production per second (2 pulses per cycle x 60 Hz). To find the expected number of dots, multiply the pulses per second by the exposure time: 120 pulses/second * 0.1 seconds = 12 dots. A half-wave rectified unit would produce 6 dots, and other values would indicate a different rectification or timer malfunction.

Question 3

Which of the following describes the primary function of a falling load generator?

Accepted Answer

To use the maximum heat capacity of the tube to achieve the shortest possible exposure time.

Answer

A falling load generator starts the exposure with the highest possible mA and then drops the mA to lower levels as the tube's heat loading capacity is reached. This process is designed to deliver the desired mAs in the shortest time possible, which is crucial for minimizing motion artifacts.

Question 4

A digital radiograph of a knee appears grainy and mottled. The technologist confirms that positioning and collimation were accurate. Which of the following is the MOST likely cause of this appearance and how should it be corrected?

Accepted Answer

Quantum mottle; increase the mAs.

Answer

A grainy or mottled appearance on a digital image, often described as quantum mottle or noise, is typically caused by an insufficient number of photons reaching the image receptor (underexposure). The primary way to correct for this is to increase the quantity of photons, which is achieved by increasing the mAs. Grid cutoff would likely present as a more uniform or localized loss of density, not a grainy texture throughout the image. Saturation is an effect of overexposure, and processor artifacts are less common in digital radiography.

Question 5

Which of the following is a key component of the NEMA XR-29 (MITA Smart Dose) standard for CT scanners?

Accepted Answer

Automatic Exposure Control (AEC).

Answer

The NEMA XR-29 standard, also known as MITA Smart Dose, includes four key features to help manage radiation dose in CT. These are: Automatic Exposure Control (AEC), DICOM Radiation Dose Structured Reporting, CT Dose Check features, and reference adult and pediatric protocols. While iterative reconstruction is a dose-saving technology, it is not a required component of the XR-29 standard itself.

ARRT - American Registry of Radiologic Technologists Practice Test

ARRT - American Registry of Radiologic Technologists Practice Test

ARRT - American Registry of Radiologic Technologists Equipment Operation and QA Questions and Answers