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Radiological test equipment, measurement, and practice


The radiographic and fluoroscopic imaging chains have many interlinked components.  For example, radiographic systems require an x-ray generator, x-ray tube and focal spot, and a screen-film or digital imaging system. Screen-film systems and require a knowledge of sensitometry and densitometry, and the associated instrumentation.  All test equipment must be calibrated on a periodic basis and properly maintained.

Important Principles

The medical physicist must be able to evaluate each link in the radiographic and fluoroscopic imaging chains. This starts with both invasive and non-invasive (preferred method) of kilovoltage measurements, the use of clamp-on current meters to measure tube current, and measurement of the x-ray tube focal spot using different methods (pinhole camera, star test pattern, and resolution pattern).
Sensitometry and densitometry are used to characterize the components of the screen-film imaging system. Understanding the issues with film processing, including the impact of time and temperature of development on the contrast and speed of the X-ray film, are essential even in facilities that use primarily digital imaging systems.  

Each link in the imaging chain, i.e., x-ray generator, x-ray tube focal spot, screen-film system, and photographic processor, impact the quality of the radiographic image and, therefore, the quality of the clinical image and the dose to the patient and staff. Consequently, it is important to optimize each link in the medical imaging chain.

Introduction to References

Both the IAEA Handbook on the Physics of Diagnostic Radiology and the AAPM Report #74 “Quality Control in Diagnostic Imaging” (both available on line at no cost) provide the broadest coverage of these topics. Haus and the Kodak online publications are good references for the theory behind sensitometry and densitometry while Gray, et al., provides details of clinical applications. Bushberg, et al., provide a broad background in medical imaging technology and applications.