Year: 2026 | Month: March | Volume: 13 | Issue: 3 | Pages: 408-413
DOI: https://doi.org/10.52403/ijrr.20260346
Comparison of Two Alternative Forced Choice (2-AFC) and Receiver Operating Characteristic (ROC) Methods for Low Contrast Detectability Using the Cathpan 503 Phantom
Yanwar Budhiyarto1, Eko Hidayanto1, Catur Edi Widodo1, Choirul Anam2
1Department of Physics, Faculty of Science and Mathematics, Diponegoro University, Semarang, Indonesia.
Corresponding Author: Yanwar Budhiyarto
ABSTRACT
Detecting small and low-contrast objects in CT-Scan images remains a major challenge in radiological diagnostic practice. The limitations of human visual capabilities and the influence of image quality require objective and reliable quantitative evaluation methods. The effect of object size variation on CT-Scan image detection performance was analyzed using the Two Alternative Forced Choice (2-AFC) and Receiver Operating Characteristic (ROC) psychophysical approaches.
The study was conducted using a Catphan 503 phantom with low-contrast objects measuring 6 mm, 8 mm, and 10 mm in diameter. Image acquisition was performed using a Toshiba Aquilion CT-Scan machine with parameters of 120 kV, 300 mA, axial mode, and a slice thickness of 2 mm. The scanned images were processed using IndoQCT software to generate 2-AFC test stimuli and converted to ROC format. Measurements were performed using Region of Interest (ROI) on the object and background areas. Performance evaluation was conducted by five medical physicist observers. Analysis parameters included sensitivity, specificity, and Area Under Curve (AUC).
This study concluded that there was a consistent correlation between the results of the 2-AFC and ROC methods, indicating that the two methods complement each other in evaluating the detection performance of CT-Scan images. Object size had a significant effect on the accuracy of visual detection in CT-Scan images. The combined approach of the 2-AFC and ROC methods is effective as a quantitative evaluation tool for the detectability of low-contrast objects.
Keywords: CT-Scan, object size, 2-AFC, ROC, low-contrast detectability
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