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22 March 2010 Dose reduction and lesion delectability in abdominal CT
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The purpose of this study was to quantify how reducing x-ray beam intensity (i.e., mAs) affects lesion detection performance in abdominal CT examinations. A simulation package (Syngo Explorer) was used to reconstruct 4-mm thick CT images of a patient undergoing a standard abdominal exam. Simulations were performed at four x-ray beam intensities of 100%, 70%, 50%, and 25%. Four observers were used to perform a series of two Alternate Forced Choice (2-AFC) experiments that measure the lesion contrast (I92%) corresponding to a detection accuracy of 92%. Four lesion sizes were used ranging from 5 mm to 12 mm. Results were plotted as log(I92%) versus log(mAs) to quantify how changes in x-ray intensity affect lesion detection, as well as log(I92%) versus log(size) to generate contrast-detail curves. The fitted slope of noise in reconstructed images as a function of relative CT x-ray beam intensity was -0.25, which is about half the value of -0.5 expected for an ideal quantum noise limited imaging system. For lesion sizes between 5 mm and 10 mm, slopes of log(I92%) versus log(mAs) curves were very similar for all four observers, and ranged between -0.10 and -0.17. For 5 mm sized lesions, doubling the x-ray beam intensity improved detection performance by about 13%, whereas for 7 and 10 mm lesions, doubling the x-ray intensity improved detection performance by about 7%. For the 12 mm lesion there were no consistent patterns for all four readers, which may be related to the lack of a standardized viewing distance. The average slope for the four contrast detail curves was -0.41 ± 0.09, which is substantially less than the value of -1.0 predicted for an ideal observer operating with a quantum noise limited images. For our abdominal CT images, doubling of the lesion size resulted in improvements in lesion detection of ~ 30%.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Sameer Tipnis, Walter Huda, Andrew Hardie, and Kent Ogden "Dose reduction and lesion delectability in abdominal CT", Proc. SPIE 7622, Medical Imaging 2010: Physics of Medical Imaging, 76222Q (22 March 2010);

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