[Artifact Assessment in the Skull Base Region of Head CT Images with Various Tilt Angles Relative to the Orbitomeatal Line].

Purpose: The aim of this study was to evaluate artifacts in the skull base region of head computed tomography (CT) images with various tilt angles relative to the orbitomeatal line.

Methods: CT images of a head phantom acquired by helical and non-helical scanning with the tilt angles set from 0 to 20 degrees in 5-degree increments were evaluated in this study. Regions of interest (ROIs) were set at the cerebellum, temporal lobe, frontal lobe, and basal ganglia in the phantom images.

[Evaluation of Noise Properties at Nonuniformity Area and Resolution Properties of CT Image Using Iterative Reconstruction Method].

Purpose: The purpose of this study was to investigate the resolution property and the noise properties at the nonuniformity area in the slice plane of iterative reconstruction (IR)-CT image.

Methods: CT images of a phantom with nonuniformity areas including multiple contrast (medium, high, and ultra-high contrast) signals were acquired at various scan dose conditions and reconstructed with different iterative intensity levels. The noise properties at the nonuniformity and the uniformity areas were evaluated by measuring normalized noise power spectra (nNPSs) using subtracted images from sequential scanning data under the same scan conditions.

[Evaluation for Resolution Property of CT Image with Half-reconstruction Algorithm].

Purpose: The aim of this study was to investigate the resolution property in XY-plane for half-reconstruction computed tomography (CT) image by measuring 360° multi-directional modulation transfer functions (MTFs).

Materials And Methods: The 360° multi-directional MTFs were measured by use of a wire method to obtain line spread function with 15° interval in XY-plane. The MTFs of half-reconstruction CT image were measured with 100 mm off-center positions on the X- and Y-axis (X, X, Y, and Y) and compared with those of full-reconstruction CT image.

[Evaluation for Basic Image Qualities Dependence on the Position in XYZ Directions and Acquisition Parameters of the Cone Beam CT for Angiography System with Flat Panel Detector].

The purpose of this study was to investigate the effect of the position in XYZ directions and acquisition parameters on the basic image qualities of for cone beam computed tomography (CBCT) in an angiography system with flat panel detector. The resolution property (modulation transfer function: MTF) and the noise property (Wiener spectrum: WS) of CBCT images in X-Y plane were measured with different acquisition parameters (scan matrix number and projection number) and the effect of the position in XYZ directions. The MTFs with 1024×1024 matrix were higher than those of 512×512 matrix and decreased in the peripheral areas due to the reduction of projection number.

Dose reduction in general radiography for adult patients by use of a dual-side-reading photostimulable phosphor plate in a computed radiography system.

Our purpose in this study was to evaluate the potential of dose reduction in general radiography for adult patients by use of a dual-side-reading (DSR) photostimulable phosphor plate in a computed radiography system. The image quality and low-contrast detectability in terms of the contrast-detail diagram of the DSR system with use of the X-ray beam quality of the RQA 5 defined by the International Electrotechnical Commission 61267 were compared with those of a conventional single-side-reading (SSR) system. The radiographic noise of the DSR system was lower compared to that of the SSR system under the same exposure conditions.

Effect of readout direction in the edge profile on the modulation transfer function of computed radiographic systems by use of the edge method.

We investigated the effect of the readout direction of the edge profile obtained by the edge method on the presampled modulation transfer function (MTF) in various computed radiographic (CR) systems. There were no differences in the MTFs derived from two edge profiles in the sub-scanning direction of four CR systems used in this study. On the other hand, the MTFs measured at a readout direction from the low (edge) to the high (direct exposure) exposure region were higher than those measured at a readout direction from the high to the low exposure region in the laser-beam scanning direction for three of the four CR systems.