Fourier coded-aperture imaging in nuclear medicine

A Fourier aperture (FA) is composed of two sinusoidal gratings in contact. When the two gratings rotate on the same axis in equal angles but opposite directions a clear pattern of difference moire fringes is formed, the moire frequency depending on the angle between the two gratings. This aperture of moire fringes is used as a variable-frequency grating which is able to scan the object spectrum in the frequency domain. The summation-filtered back projection algorithm with three different apodizing functions was introduced in the reconstruction. A ^99mTc gamma ray source and a 1 in-diameter NaI scintillation detector were used in the experiment. The thyroid phantom images showed that spatial resolution of FA agrees with the theoretical prediction. Three dimensional image capability is also discussed. The matrix inversion algorithm was used in the computer simulation of 3-D images. Although the depth resolution of a FA is limited by the restricted view angle of the detector, two plane objects free from noise at different depths were reconstructed.