Development for a novel phantom for evaluating image quality in small-animal single photon emission computed tomography and positron emission tomography.

Objectives The National Electrical Manufacturers Association (NEMA) has released guidelines delineating the performance of positron emission tomography (PET) devices designed for small animals. However, the NEMA NU 4 image quality phantom could not measure the known contrasts of the hot rod images and the recovery coefficient (RC) of cold rod images due to the structure of the phantom. Thus, we have devised novel hot rod and cold rod phantoms capable of evaluating uniformity and RCs for both hot rod and cold rod images. This study aimed to assess uniformity, image contrasts, and RCs in hot rod and cold rod images of single photon emission computed tomography (SPECT) and PET using the newly developed phantom. Methods The new physical phantom consisted of rod and pool sections. To assess image uniformity, the pool section, designed in a cylindrical shape, was utilized. Conversely, the rod section was created in hot rod and cold rod shapes and integrated into a cylindrical phantom with the same design as the pool section. Hot rod and cold rod phantoms were designed with six different 1–6 mm diameter rods. The rod and pool sections of the hot rod phantom were separately filled with ^99m Tc and ¹⁸ F solutions. In the rod section, the cylindrical part was defined as the background (BG), with a radioactive concentration ratio of 4:1 for the hot rod and BG. The cylindrical part containing the cold rod was separately filled with ^99m Tc and ¹⁸ F solutions. The ^99m Tc and ¹⁸ F phantoms were acquired separately over 30 min. A transverse image with a cubic voxels of 0.8 mm length was reconstructed using a pixel-based ordered subset expectation maximization algorithm. Results The contrast of the hot rod for ^99m Tc and ¹⁸ F showed lower values with a decreasing rod diameter. Furthermore, the ^99m Tc image demonstrated a higher contrast than the ¹⁸ F image and approached the true contrast. The cold rod contrasts with ^99m Tc and ¹⁸ F followed a similar trend as the hot rod contrast. The RCs for the hot rods with 4–6 mm diameters were similar, whereas hot rods with diameters ≤ 3 mm revealed lower values as the rod diameter decreased. The inverse RC was lower with a decreasing cold rod diameter. Moreover, the cold rod image with ¹⁸ F demonstrated a lower inverse RC than with the ^99m Tc. The percent coefficient of variation (%CV) for the ^99m Tc and ¹⁸ F images was 4% and 7%, respectively, with the ^99m Tc image displaying a lower %CV compared to the ¹⁸ F image. Conclusion We have developed a new phantom that allows physical phenomenon evaluation in small animal SPECT and PET images, and can evaluate the image contrast, RC, and uniformity of both hot rod and cold rod images.