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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


(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.


Contrast, Noise, Radiography


IM- X-ray: Quality Control

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