Polymethyl Methacrylate (Perspex) Line Pattern Phantom : A New Gamma Camera Test Pattern for Assessment of Extrinsic Resolution and Linearity

Abstract

Objective: To evaluate the newly designed polymethyl methacrylate (Perspex) line pattern phantom (PLPP) for testing extrinsic resolution and linearity of gamma camera. Method: The phantom was made of 10 mm thick Perspex in which tubes of 1 mm external diameter and 0.5 mm internal diameter were inserted in 1 mm deep grooves, which had been machined in a particular pattern. The final arrangement of lines divided the phantom into four similar quadrants, which encompassed the whole surface of the gamma camera head. Such an arrangement permitted full detection of any change in the linearity and resolution. The tube was filled with technetium-99m (99mTc). Tests were performed on the only two single-headed gamma cameras available in Oman. Results: It was possible to resolve two lines as close as 6 mm. Using the line spread function (LSF) facility, the estimated full width half maximum height (FWHM) value was 4.1 mm. In addition, any distortion in the shape of the lines, used to measure linearity, could be easily detected over the entire surface of the camera head. Conclusion: Data obtained from the PLPP are in agreement with those obtained using the conventional four-quadrant bar pattern phantom (FQBP). The generally accepted relationship that the line profile FWHM is equal to approximately twice the minimal resolvable bar spacing does not apply to the PLPP. However, PLPP gives multi-direction linearity in any one quadrant. In addition, it does not need a flood source for imaging, thus minimizing the test cost.