Purpose: A simplified linear model approach was proposed to accurately model
Purpose: A simplified linear model approach was proposed to accurately model the response of a flat panel detector utilized for breast CT (bCT). (80 kVp, 500 views total, 30 framesMs), in the low gain mode, additive noise contributes 21% of the total pixel noise variance for any 10 cm object and 44% for any 17 cm object. With the dynamic gain mode, additive noise only represents approximately 2.6% of the total pixel noise variance for any 10 cm object and 7.3% for any 17 cm object. Conclusions: The living of the signal-independent additive noise is the main cause for any quadratic relationship between bCT noise variance and the inverse of radiation dose in the detector. With the knowledge of the additive noise contribution to experimentally acquired images, system modifications can be made to reduce the effect of additive noise and improve the quantum noise efficiency of the bCT system. ideals of 4.37 analog to digital units (ADU) for a fixed high gain mode and 3.14 ADU for a fixed low gain mode. Inside a earlier study,10 the additive noise variance of the same detector used in the bCT software was measured from 500 offset (no x 66085-59-4 IC50 rays) images as 15.11.3 ADU2 for the entire detector in the fixed low gain mode and 20.72.2 ADU2 in the fixed high gain mode. In that study, due to different experimental conditions, it was hard to confirm the results with those extrapolated from measurements using x-ray exposure. 66085-59-4 IC50 However, that study clearly shown that after the logarithmic preprocessing required for reconstruction, there exists a quadratic relationship between the image noise variance and the inverse of the event kerma in the detector. The presence of additive electronic noise is the main cause of this quadratic relationship.11 There are 66085-59-4 IC50 several key questions remaining unanswered from that study, including why the additive noise could not be consistently extrapolated from measurements using x-ray exposure, and what is the exact manifestation of the fit coefficients for the quadratic relationship? The purpose of this study was first to explore a consistent experimental approach to evaluate the linear components of the imply transmission and variance for a flat panel detector, with the bCT software driving the need for low dose, low noise flat panel overall performance. Following earlier efforts,10 the effects of different experimental conditions on the measured results were then examined. The efficacy of the dynamic mode of a Varian PaxScan detector in reducing additive noise contribution was also shown. METHODS AND MATERIALS Experimental setup and data analysis The experiments were conducted on the second prototype bCT scanner built in our laboratory, codename Bodega. The x-ray focal spot was located 511 mm from your isocenter and 1037 mm from your detector aircraft. Projection images were acquired using 66085-59-4 IC50 a CsI centered flat panel detector system (PaxScan 4030CB, Varian Medical Systems, Palo Alto, CA) with the revolving bCT gantry kept stationary. The detector panel used a coating of 600 m columnar CsI(Tl) scintillator (having a nominal denseness of 4.51 gMcm3) over amorphous silicon TFT arrays. This detector managed inside a 22 pixel binning mode (388388 m2 detector element size) with Col3a1 1024768 pixels per framework at 30 framesMs. Two different gain modes are currently available at this frame rate and pixel binning establishing: Fixed low gain and dynamic gain (detailed in Sec. 2C). As analyzed previously,10 image lag will impact the measured transmission imply and variance. To avoid the effect from image lag, each acquisition arranged was performed at least 20 min apart from each additional. An 18 s preacquisition radiation exposure was also applied to the detector immediately before the start of each acquisition arranged. This allowed charge trapping (i.e., transmission build-up phenomenon which is a component of lag) to reach a relative stable state or lag equilibrium operation mode. Five hundred projection images were acquired for each set and confirmed to be in the lag equilibrium stage (the pixel imply and variance remain constant through these 500 images). Different air flow kerma levels were studied by modifying the tube current (mA) from 1 to 7 mA at 80 kVp. The air kerma level for each measurement was identified in the isocenter with no object present and then converted to the event kerma within the detector surface (in the central ray) using the inverse.