Measurement of image quality in nuclear medicine and radiology
The imaging process can be thought of as the acquisition of data and the processing and display of data. The image quality of the acquired data is assessed using objective methods. The spatial transfer characteristic was measured using the MTF, and the noise properties assessed using Wiener spectra for gamma camera and film-screen systems. An overall measure of image quality, noise equivalent quanta, can then be calculated. The image quality of the displayed data is assessed using subjective methods. Contrast detail test objects have been used for film-screen systems and forced choice experiments for nuclear medicine data. The Wiener spectrum noise measurement has been investigated as a measure of uniformity. Simulated and gamma camera flood images were produced. Observer tests were carried out to give a contrast at which the non-uniform flood images could be distinguished from the uniform flood images. Wiener spectra were produced and single number indices derived. Statistical tests were performed to determine the contrast at which the uniform and non-uniform Wiener spectra can be distinguished. Results showed that Wiener spectra measurements can be used as a measure of uniformity under certain conditions. The application of resolution and noise measurements to the evaluation of film-screen systems and radiographic techniques has been considered. The results follow the trends presented in the literature. Provided that the scanning equipment is available tests on film-screen systems are practical to perform and are an important addition to other evaluation tests. Results show the ideal observer approach of measuring the resolution, noise and hence noise equivalent quanta, is a practical method of assessing image quality in a hospital environment.