Usefulness of Ag Additional Filter on Image Quality and Radiation Dose for Low-Dose Chest Computed Tomography.

OBJECTIVE: This study aimed to evaluate the effect of a silver (Ag) additional filter on dose characteristics and image quality in low-dose chest computed tomography (CT). METHODS: A dose evaluation phantom, physical evaluation phantom, and chest phantom were scanned with and without an Ag additional filter. The doses were adjusted so that the displayed the volume CT dose indexes (CTDI vol ) were from 0.3 to 1.6 mGy. For dose characteristics, the spectrum of photon energies and the measured CTDI vol were calculated for each scanning condition. For task-based image quality analysis, task transfer function, noise power spectrum, and system performance were evaluated. Streak artifacts, image noise, and contrast-to-noise ratio were quantified using a chest phantom. RESULTS: With the Ag additional filter, mean energy was 22% higher and the CTDI vol was approximately 30% lower than those without the Ag additional filter. The task transfer function and noise power spectrum with the Ag additional filter were lower than those without the Ag additional filter. The system performance with the Ag additional filter was similar to that without the Ag additional filter. The Ag additional filter reduced streak artifact near the lung apex and image noise in the lung fields. The contrast-to-noise ratio was slightly higher with the Ag additional filter than that without the Ag additional filter. CONCLUSIONS: The output dose and spatial resolution with the Ag additional filter were lower than those without the Ag additional filter. However, this filter helped reduce the radiation dose, image noise, and streak artifacts, particularly when scanning at ultralow doses.

EVALUATION OF ORGAN DOSE BASED ON PATIENT DATA IN EAST ASIAN DESCENT PEDIATRIC HEAD CT EXAMINATIONS.

The purpose of this study was to investigate other indices estimating absorbed dose for eye lens and brain, using clinical images of East Asian pediatric patients. We simulated head computed tomography (CT ) examinations in 104 pediatric patients. Effective diameter (deff) and water equivalent diameter (dw) were measured on clinical images. Various size metrics and age were compared with absorbed dose normalised by CTDIvol (nD). The nD was estimated for eye and brain. The nD tended to decrease with advancing age. R2 between age and nD were 0.38 and 0.31 for eye and brain, respectively. Increasing head diameters decreased each nD. R2 between deff and dw, and nD were 0.20-0.24 and 0.51-0.53 for eye and brain, respectively. Head sizes allowed us to estimate absorbed dose in brain CT on East Asian pediatric patients. Scanning parameters for pediatric head CT may need to be based on individual patient information.

A method for evaluating luminance non-uniformity of displays by use of a commercially available digital camera.

The luminance uniformity of liquid-crystal displays (LCDs) deteriorates with their prolonged use. In this paper, we present a method for evaluating the degree of luminance non-uniformity of LCDs with the use of a commercially available digital camera. In this study, seven monochrome LCDs, which were used during various operating times ranging from 5000 to 25,000 h, were evaluated with use of a camera. The maximum luminance deviation (MLD) was measured on the two-dimensional (2D) images obtained with the camera. In addition, an index of the luminance non-uniformity was calculated as the ratio of the area exhibiting luminance non-uniformity to the area of the entire LCD screen. We determined the area with the luminance non-uniformity by setting the allowable luminance deviation as the judgment criterion to evaluate the degree of luminance non-uniformity. The MLD values were less than 20% for all conditions, and they varied depending on the locations of the luminance measurement. The area ratios of the luminance non-uniformity based on 2D luminance distributions tended to increase with the duration of use of LCDs, and they indicated the degree of luminance non-uniformity of the LCDs regardless of the measurement locations. Our approach of using a commercially available digital camera showed its potential usefulness for providing more detailed and consistent evaluations of the degree of luminance non-uniformity of LCDs based on the 2D luminance distributions.