Room: AAPM ePoster Library
Purpose: evaluate Image-Quality based on x-ray unit design characteristics.
Methods: detector (FD-henceforth) characteristic-response (linear) data was acquired under conditions satisfying RQA-5 (70kVp,20mm Aluminum-Filter(HVL6.9mm-Al),For-Processing Flat-Field images) using SID of 59-inches on a GE-Definium 8000 radiographic unit (a-Si(CsI),41cmx41cm,200µmx200µm pixels,no-grid).Measured (ROI-size 2cmx2cm,image-center) standard-deviation was squared and plotted (Excel-2016 Micro-Soft Inc) as a function of Image-Receptor Incident Air-Kerma (IRIAK-hereafter),(Range,3.57-31.08µGy,9-exposures) and a power-fit (s² equals c1(IRIAK?²)) was applied. c1 and c2 are constants. IRIAK at which c2 approximates 1 (representing Poisson image-noise) was used for quantitative high-contrast spatial-resolution measurements using Type 1-83 (Super-Tech,0.05mm-Pb) precision patterns at three different spatial-frequencies,below the detector Nyquist-frequency,using Square-Wave-Transfer-Function (SWTF(f)) method,under the same set-up.Patterns were placed at three degrees to FD x-axis and y-axis.Tests were conducted thrice to demonstrate repeatability at detector center and four quadrants.
Low-contrast performance (LC) test was conducted on a Siemens Agile-Max FD(Pixium 34553,35cm x 43cm;a-Si(CsI)) radiographic unit using an Aluminum Contrast-Detail phantom (Sun Nuclear) with 0.5-inch Aluminum attenuator at 70 kVp, 115cm (Grid-focus) SID and mAs values corresponding to an IRIAK of 0.4,0.85,1.1,2.43,3.50,5,7.1 and 10.1µGy. System Automatic Exposure-Control (AEC) is designed to deliver 0.89,1.25,2.5,3.57,5 and 7.14µGy,depending on users direct selection.Minimum (0.4µGy) and maximum (10.1µGy) IRIAKs used for testing are based on lowest and highest IRIAK selection (0.89µGy and 7.14µGy) with the most negative and positive density settings, respectively.
Results: application of FD dose-dependent noise-response analysis to determine optimal IRIAK (14.5µGy) unique to imager for further image-quality assessment.
System design-dose dependent contrast characterization using the entire constellation of clinically employable IRIAKs.
User-subjectivity related limitations of contrast-detail phantom without automated-scoring during routine testing,particularly at lower IRIAK levels.
Conclusion: Quality control tests accounting for system characteristics yield results that can improve performance monitoring, by providing unit design specific data.
Simple phantoms that produce reliably reproducible results are critical to track low-contrast performance over a range of clinical IRIAK values.