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Assessment of fluoroscopic systems with a simple test object
1Medical Physics Department, Westmead Hospital.
Summary
A new non-invasive test protocol and object evaluate fluoroscopic systems under automatic brightness control (ABC). Patient-equivalent absorbers, like water, are recommended for accurate image quality assessment during acceptance testing.
Area of Science:
- Medical Imaging Physics
- Radiological Sciences
- Diagnostic Imaging Technology
Background:
- Evaluating fluoroscopic system image quality is crucial for diagnostic accuracy.
- Existing protocols may focus on individual components, not the complete system under clinical conditions.
- Automatic Brightness Control (ABC) significantly influences image quality parameters like dose rate and kVp.
Purpose of the Study:
- To develop and validate a non-invasive test protocol and object (Westmead test object) for assessing the complete fluoroscopic system, including grid performance, under ABC.
- To compare the efficacy of patient-equivalent absorbers (water) versus traditional absorbers (copper) in simulating clinical conditions for fluoroscopic testing.
Main Methods:
- A novel test object and protocol were designed to evaluate the entire fluoroscopic system under ABC.
- The protocol utilized kVp and dose rate as determined by the ABC.
- Radiographic absorbers (20 cm water and copper sheets) were used to simulate patient scatter, beam quality, and exit beam intensity.
Main Results:
- No single copper thickness provided equivalent beam hardness and absorption compared to 20 cm water under ABC.
- Testing on 23 fluoroscopic systems showed varied results between copper and water absorbers for Threshold Contrast and Contrast-Detail.
- Copper absorbers generally yielded slightly better Contrast-Detail and Threshold Contrast results in this survey, though water provided a wider spread, indicating potential for better discrimination.
Conclusions:
- The Westmead test object and protocol are effective for evaluating fluoroscopic systems under ABC.
- Patient-equivalent absorbers, such as 20 cm water, are recommended for acceptance testing to ensure accurate simulation of clinical conditions.
- Correlating X-ray input dose with test object results, particularly Contrast-Detail, allows for good image quality discrimination between different fluoroscopic units.