RAD 120 - Ch 23 Technical Considerations in Digital Imaging - Review Questions

How should a digital exposure technique system be established?

Exposure technique selection is as important as ever when using CR and DR receptors, due to the impact exposure factors have on image quality and patient dose. Although image processing LUTs and rescaling can compensate for exposure variations to some degree, accurate exposure selection is still essential to ALARA compliance and optimum image quality. Most departments adapt their existing technique charts systems as they replace the analog imaging systems with digital equipment. According to the ASRT White Paper on best practice in digital radiography, it is recommended "to use exposure technique charts that are continuously improved and applicable to a wide range of patient sizes" (2012).

What are the two most common factors that affect digital image quality?

Positioning errors and objectionable image noise are the two most common factors that affect digital image quality.

List the five steps in the creation of an exposure technique chart.

Phantom test exposures, extrapolate the chart, clinical trial, clinical fine tuning, and continuous quality assurance.

How does digital imaging latitude compare to that of film-screen systems?

Digital imaging has a wide latitude and can accommodate four to five times overexposure and still produce acceptable image quality. Underexposure latitude, however, has a variance of approximately 25% before objectionable noise impacts the quality of an image.

What is dose creep?

A trend in which errors in technique selection are made on the additive side, resulting in an increased exposure technique to decrease chance of image noise and avoid repeats. This trend is due to the wide exposure latitude associated with digital imaging systems and many medical imaging experts are working to correct it as it does not reflect the standards established by the profession.

What does a DI value of −2 indicate? What is the recommended action for such value?

DI of -2 indicates underexposure to the detector that was 40% below the recommended target value, and an image that will demonstrate noise. Therefore any image with such value should be repeated.

What causes photon starvation?

Inadequate exposure to the detector elements causes photon starvation.

How are data drop and detector saturation related?

Data drop is a condition created by an extreme overexposure and it occurs when data elements in the detector are overwhelmed with photon energy and incapable of recognizing high-energy values. When the image is reconstructed, these saturated data points are dropped from the data set and not part of the image reconstruction. Data drop can occur over an area of the detector, leading to detector saturation. Therefore detector saturation can be described as data drop that involves areas or regions of the detector.

Which technical factor controls the amount of scatter in digital imaging?

mAs controls the amount of scatter in digital imaging.

What is electronic masking? Should electronic masking be used to substitute for exposure collimation?

Electronic masking is a post-processing function that affects the data set by removing undesirable information in an effort to improve image quality. Electronic masking is not a substitute for exposure collimation.

What can cause electronic artifacts on DR images?

Electronic artifacts randomly occur on DR images for a variety of reasons including Bucky motor interference, x-ray tube rotor initiation, extraneous RF signals in the room, AEC noise, etc.