Semi-quantification of the minimum detectable difference of imaging quality of gamma camera SPET for four radionuclides via an innovative PMMA phantom with a V-shaped slit: interpretation of a feasibility study.

OBJECTIVE: An indigenous polymethyl metacrylate (PMMA) phantom with a V-shaped slit and a correlated technique for semi-quantifying the minimum detectable difference (MDD) of single photon emission tomography (SPET) via gamma camera scanning are proposed and validated using four radionuclides.

MATERIALS AND METHODS: Radio-actinide solutions of gallium-67 (67 Ga), technetium-99m (99m Tc), iodine-131 (131 I) and thallium-201 (201 Tl) were diluted to 11c.c. and thoroughly injected into the continuous zig zag slit of the PMMA phantom. Either depth or edge of the slit between two lines of the V-shape was customized from deep or wide to change into shallow or narrow gradually. Thus, the quantified MDD could be easily evaluated, according to the revised Student's t-test evaluation. The revised Student's t-test was calculated by both full width at half maximum (FWHM) and edge width between two adjacent peaks that were acquired from the original data matrix of SPET. The derived MDD was indicated as for radionuclide, depth, width in mm: For 67 Ga, 2.9, 2.13, for 99m Tc, 2.5, 0.66, for 131 I, 4.7, 2.38 and for 201 Tl, 3.3, 2.00, respectively.

RESULTS: Technetium-99m had the highest and 131 I had the lowest MDD among the four radionuclides. Furthermore, two adjacent peaks of 67 Ga could be easily identified with fewer counts than for 201 Tl (depth, 2.9 vs. 3.3mm), but its MDD was poorer (width: 2.13 vs.2.00mm). The revised Student's t-test analysis proved to be an acceptable technique for the MDD identification.

CONCLUSION: The proposed new combination of PMMA phantom with a V-slit and the revised Student's t-test proved to be instrumental in the MDD of SPET optimization analysis.