[Performance evaluation of computed tomography with equivalent resolution images].

A method of evaluating the performance of computed tomography (CT) with equivalent resolution images was investigated. Generally, in performance evaluations of CT, the resolution property is measured by the wire method, and the noise property is measured from noise images of a cylindrical water phantom. The signal-to-noise ratio (SNR) is then calculated for the integrated evaluation. Our proposed method enabled perceptual integrated evaluation by using equivalent resolution images created with frequency processing. The frequency-processing factor was calculated from the ratio of the modulation transfer factors of two models of CT, and the image of one of the two was processed by the factor. Because these processed images have resolution equivalent to images of the other CT, the perceptual evaluation with noise images becomes effective. In this investigation, images of a water phantom and a middle contrast resolution phantom were employed. Perceptual comparison of the amount of noise with equivalent resolution images could be performed easily, and effective performance evaluation was achieved. Therefore, our proposed method is useful for noise property and performance evaluation of CT.

[MRI-intracranial compliance analysis in patients with NPH].

We devised a method for non-invasively assessing intracranial compliance with retrospective ECG-triggered phase contrast cine MRI. This method was examined in patients with normal pressure hydrocephalus (NPH) group and those with asymptomatic ventricular dilation or brain atrophy (VD group), and in healthy volunteers (control group). Intracranial volume change (DeltaV(max)) was calculated from arterial inflow, venous outflow, cerebrospinal fluid (CSF) flow, and spinal cord motion at the C2 level during a cardiac cycle. Next, craniospinal CSF pressure gradient change (DeltaPG(max)) was calculated from measured CSF flow velocity using a simplified Navier-Stokes equation. Finally, Ci was obtained by dividing Delta V(max) into DeltaPG(max). Ci in the NPH group was significantly smaller and could be differentiated from other groups. This method makes it possible to non-invasively obtain a more detailed determination of the intracranial state and dynamics in NPH and to assist in its diagnosis.

[New method of measuring presampling MTF by fourier transform of square-wave chart image].

We developed an easy method of measuring the presampling modulation transfer function (MTF) using the square wave chart in digital radiography. In this method, the presampling MTF is measured by Fourier transform of image data of the square wave chart. When Fourier analysis of the sampling data of a square wave is carried out, it is generally difficult to find the starting point and terminal point of the periodic data that should be extracted because of an insufficient number of data. To solve this problem, interpolated data were calculated by using a window function of the frequency domain. The aliasing error was avoided using a characteristic such that the square wave has discrete frequency components. The accuracy of this method was investigated by computer simulation study. Actual measurement of the presampling MTF by this method was also performed with a CR system. These studies indicated the effectiveness of our proposed method in terms of accuracy and ease of use.