Low contrast resolution of X-ray CT scanners in the range of 0.1 to 3% is clinically important but difficult to measure accurately. The main obstacle for measurement has been the lack of a proper phantom. Presently available phantoms cannot be used to measure various contrasts, and they also have the problem of reproducibility. We have made a water and polystyrene phantom which overcomes these problems. The new phantom is made of the 3% lower attenuation coefficient of polystyrene in relation to water. By varying the thickness of the polystyrene disk in six different sectors, the partial volume effect of the disk and water allows six contrast differences between 0.3 and 3% to be detected. The disk is also provided with holes of various diameters. By measuring the minimum hole sizes of the phantom images, the threshold of perceptibility for each contrast difference can be determined. A contrast-detail-curve is drawn using the contrast and perceptible hole size as parameters. These curves allow for visualization of varing physical parameters and comparison of the performance of differing X-ray CT scanners.