Quantification of the effect of kVp on edge‐enhancement index in phase‐contrast radiography

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Abstract
This study was performed to measure the dependence of edge‐enhancement in polychromatic phase‐contrast radiography on x‐ray tube operating voltage. Measurements of edge enhancement were made at tube voltages from 40 to 86 kVp using a tungsten anode x‐ray tube with a nominal focal spot size of 100 micrometers. A relatively weak attenuating, sharp edge consisting of a thin lucite sheet (3 mm) in air was imaged utilizing phase‐contrast radiography (PC‐R). PC‐R images were acquired at different radiographic techniques in which x‐ray tube voltage was varied from 40 to 86 kVp. The image receptor was a single emulsion x‐ray mammography cassette. Optical density profiles across the edge of the object were obtained using a film digitizer and edge‐enhancement indices were calculated. Increasing kVp resulted in a gradual decrease of the edge‐enhancement index. Even at the highest kVp (86), however, important edge‐enhancement effects were evident. While there is some degradation in the edge‐enhancement effect of phase‐contrast radiography at higher kVps, the decrease from 40 to 86 kVp is relatively small (11%). Our results suggest that further investigation into the role of phase‐contrast imaging at higher kVp values for the purpose of patient dose reduction while still realizing the advantage of phase‐contrast effects for improved soft‐tissue detectability is warranted.