MENU

Click here to

×

Are you sure ?

Yes, do it No, cancel

Relation Between Deviation Index and Contrast to Noise Ratio in Portable Digital Chest Radiography

J Dave*, E Gingold , B Sundaram , Thomas Jefferson University, Philadelphia, PA

Presentations

(Tuesday, 7/31/2018) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 8

Purpose: To explore the relation between DI and contrast-to-noise ratio (CNR) in portable digital chest radiographs (CXRs).

Methods: IRB approved this retrospective study. Data-log files corresponding to all bedside CXRs acquired over a one-year period using nine Carestream DRX-Revolution x-ray units (DRX1C image receptors) were extracted and analyzed. The vendor-reported DI and normalized CNR (noise estimated from the central mediastinum/spinal region; contrast from log exposure differences of lung region versus mediastinum) were analyzed. Analysis was split for cases falling in ±0.5 range around DI values of 0, ±4 and ±9, representing 0.1 to 7.9 times the target exposure. Rejected CXR data was analyzed separately.

Results: Data was obtained from 31,923 CXRs. Mean (± standard deviation) DI was 0.8±2.1 (median: 0.8). Mean CNR was 0.5±0.2 (median: 0.5). Correlation between vendor-reported DI and CNR was 0.5. For examinations falling in ±0.5 range around DI values of -9, -4, 0, 4 and 9, the CNR was 0.2±0.0, 0.2±0.1, 0.5±0.1, 0.6±0.2 and 0.4±0.1, respectively, indicating a gradual CNR increase with receptor exposure, and then saturation. Strikingly, even at target DI of 0±0.5 (18% of all CXRs) the CNR showed a wide spread ranging from 0 to 1 (partially, this may be due to inherent differences within patients’ CXRs due to underlying disease status, etc.); this spread from 0 to 1 for CNR also extended for DI within a range of ±3 (representing half to double the target exposure). The DI distribution of rejected CXRs overlapped with that of accepted CXRs (mean: 0.4±2.9; median: 0.6); for subset of rejected images due to exposure parameters, the mean DI was -1.6 and median DI was -2.7, indicating insufficient exposure.

Conclusion: The observed wide-range in CNR, even for optimal exposures, suggests wide variability of quantitative image quality in portable CXRs which may be another target for quality improvement.

Keywords

Contrast, Noise, Radiography

Taxonomy

IM- X-ray: Quality Control

Contact Email