Optimizing Contrast Resolution in Digital Chest Radiography by Varying Copper Filtration and kVp.

PURPOSE: To measure the effect of increasing kilovoltage peak (kVp) and copper filtration thickness on entrance skin exposure and contrast resolution for chest radiography performed using digital flat-panel detectors. METHODS: A phantom-based experiment was conducted in which 24 radiographs of a quality control chest phantom were obtained at varying kVp levels and copper filtration thicknesses. The entrance skin exposure was measured and analyzed for each exposure. All radiographs were analyzed based on measured pixel values and contrast:noise ratio (CNR) and using subjective analysis, which focused on contrast resolution assessment performed by 4 radiologists. RESULTS: The results from the subjective image analysis showed that increasing copper filtration in increments of 0.1 mm resulted in less of a decrease in contrast resolution compared with increasing the kVp by 10 kVp, and that contrast resolution is more dependent on energy level than on filtration. The results from objective image analysis indicated that CNR decreased when kVp increased at all filtration thicknesses, but consistent dependency between CNR and filtration was not evident. Exposure data analysis showed an average 46% decrease in entrance skin exposure for each increase of 0.1 mm in copper filtration thickness. DISCUSSION: Although subjective and objective data analysis results indicated that increases of copper filtration are more beneficial to maintaining contrast resolution and reducing entrance skin exposure compared with increases of kVp, objective image data analysis showed a greater reduction in contrast resolution when kVp is increased. These results validate previous research that concluded that copper filtration should be considered as a dose-reduction and image-optimization strategy in digital radiography departments. CONCLUSION: Although entrance skin exposure reduction can be accomplished using higher kVp and copper filtration, increasing copper filtration thickness could be considered to minimize the loss of contrast resolution for routine chest imaging when digital flat-panel detectors are used.

Establishing Standardized Terminology for Digital Image Analysis: A Pilot Study.

PURPOSE: To point out the need for standardized terminology for digital image analysis and to collect data by surveying radiologic technology professionals for a more comprehensive, national-breadth study. METHODS: A mixed-method pilot study was conducted, in which a survey was emailed to 4 Joint Review Committee on Education in Radiologic Technology-accredited radiography programs in July and August 2019. Eight educators and 28 radiologic technologists responded, and acceptance was evaluated on 3 of the proposed terms: signal, signal value, and signal variance (later changed to signal differences). Quantitative data results were analyzed in Microsoft Forms and percentage of acceptance rates calculated. Respondents who did not accept the proposed terms were asked to provide reasoning in open-ended responses, which were analyzed using manual coding and categorization. RESULTS: The term signal received an 88% acceptance rate among educators and a 96% rate among radiographers. Signal value was accepted by 88% of educators and 79% of radiographers. The lowest acceptance rate was for the term signal variance (educators, 63%; radiographers, 79%). Open-ended responses were categorized into themes revealing respondent concerns about the use of signal value, which might result in forgetting about radiation dose (4 respondents) and how signal value relates to image receptor exposure and exposure indicator value (2 respondents). Concerns about signal variance involved contrast being easier to understand because it is visible (2 respondents), confusion with the usage of the proposed term (2 respondents), and preference for contrast because of its current use (2 respondents). DISCUSSION: Recent history indicates confusion regarding which terms effectively describe the new image quality factors that dictate proper use of digital radiography. The proposed terms evaluated in this pilot study received a mean acceptance rate of 83.5%, suggesting understanding of terms related to digital image analysis from participating educators and radiographers. CONCLUSION: The findings of this pilot study indicate a need to standardize terminology related to digital image quality factors. However, these preliminary results should be interpreted with caution because of the low response rate. Readers can participate in helping to establish a universal language for digital image analysis by scanning the quick response (QR) code or clicking the link at the end of the article and completing the survey.