Development and validation of the effective CNR analysis method for evaluating the contrast resolution of CT images.

Contrast resolution is an important index for evaluating the signal detectability of computed tomographic (CT) images. Recently, various noise reduction algorithms, such as iterative reconstruction (IR) and deep learning reconstruction (DLR), have been proposed to reduce the image noise in CT images. However, these algorithms cause changes in the image noise texture and blurred image signals in CT images. Furthermore, the contrast-to-noise ratio (CNR) cannot be accurately evaluated in CT images reconstructed using noise reduction methods. Therefore, in this study, we devised a new method, namely, "effective CNR analysis," for evaluating the contrast resolution of CT images. We verified whether the proposed algorithm could evaluate the effective contrast resolution based on the signal detectability of CT images. The findings showed that the effective CNR values obtained using the proposed method correlated well with the subjective visual impressions of CT images. To investigate whether signal detectability was appropriately evaluated using effective CNR analysis, the conventional CNR analysis method was compared with the proposed method. The CNRs of the IR and DLR images calculated using conventional CNR analysis were 13.2 and 10.7, respectively. By contrast, those calculated using the effective CNR analysis were estimated to be 0.7 and 1.1, respectively. Considering that the signal visibility of DLR images was superior to that of IR images, our proposed effective CNR analysis was shown to be appropriate for evaluating the contrast resolution of CT images.

Determination of rare-earth elements in a limestone geological standard reference material by ICP-MS following solvent extraction.

Rare-earth elements in a limestone geological standard (JLs-1) were determined by inductively coupled plasma mass spectroscopy (ICP-MS) using phosphoric acid 2-ethylhexyl ester solvent extraction, which had been established for seawater analysis. First, the limestone sample was divided into two fractions: acetic acid soluble (carbonate fraction) and insoluble (residue). A modification of the method was undertaken to achieve quantitative recovery. With this method most of the REEs in the carbonate fraction were quantitatively recovered, except for the heaviest three REEs (Tm, Tb and Lu). The reason for the poor recoveries of the three elements was investigated, but still remained unclear. The mass-spectroscopic interference of BaO with Eu made an accurate determination of both lighter REEs and Eu at the same time impossible. The precision of this method was better than 20%. The data adopted after analytical consideration were consistent with those previously reported.