The purpose of this study is to evaluate the mechanical accuracy of a respiratory-gated radiation system that combines the Linear Indicator-equipped Abches respiration-monitoring device and the Varian Real-time Position Management system (LI-RPM system). This combined configuration, implemented for the first time in Japan, was compared with the stand-alone Varian RPM system (RPM system). The delay times, dose profiles, and output waveforms of the LI-RPM and RPM systems were evaluated using a self-produced dynamic phantom. The delay times for the LI-RPM and RPM systems were both 0.1 s for 4 s and 8 s test periods. The corresponding output waveform correlation factors (R²) for the 4 s and 8 s test periods were 0.9981 and 0.9975, respectively. No difference was observed in the dose profiles of the two systems. Thus, the present results indicate that the proposed LI-RPM combined respiratory-gated radiation system has similar properties to the RPM system. However, it offers several advantages in terms of its versatility, including its alignment assistance capabilities for non-coplanar treatments.

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In this issue, simultaneous differential equations were introduced. These differential equations are often used in the field of medical physics. The methods for solving them were also introduced, which include Laplace transform and matrix methods. Some examples were also introduced, in which Laplace transform and matrix methods were applied to solving simultaneous differential equations derived from a three-compartment kinetic model for analyzing the glucose metabolism in tissues and Bloch equations for describing the behavior of the macroscopic magnetization in magnetic resonance imaging.
In the next (final) issue, partial differential equations and various methods for solving them will be introduced together with some examples in medical physics.

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The way of clinical image viewing has changed dramatically by deploying picture archiving and communication system (PACS) in clinical practices. This change has been caused by the digitization of clinical diagnostic images and based on digital imaging and communications in medicine (DICOM) 3.0 standard published in 1992. In the PACS environment, medical displays such as liquid crystal display (LCD) monitors are applying for soft-copy reading. These changes in the way of the clinical image viewing caused by the PACS resulted in development of a new concept of the clinical image quality. In digital radiography, there are various factors that affect the image quality in the PACS environment. In addition, image quality can practically be classified into 3 classes; Raw data image class, Processed image class, and Display image class. Therefore, we must apply appropriate procedure to evaluate the image quality of digital radiography.

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