PINHOLE SPECT - AN APPROACH TO IN-VIVO HIGH-RESOLUTION SPECT IMAGING IN SMALL LABORATORY-ANIMALS

The performance of pinhole SPECT and the application of this technolog y to investigate the localization properties of radiopharmaceuticals i n vivo in small laboratory animals are presented. Methods: System sens itivity and spatial resolution measurements of a rotating scintillatio n camera system are made for a low-energy pinhole collimator equipped with 1.0-, 2.0- and 3.3-mm aperture pinhole inserts. The spatial detai l offered by pinhole SPECT for in vivo imaging was investigated in stu dies of the brain and heart in Fisher 344 rats by administering (TICI) -T-201, Tc-99m-HMPAO, (TC)-T-99m-DTPA and Tc-99m-MIBI. Image acquisiti on is performed using a rotating scintillation camera equipped with a pinhole collimator; projection data are acquired in conventional step- and-shoot mode as the camera is rotated 360 degrees around the subject . Pinhole SPECT images are reconstructed using a modified cone-beam al gorithm developed from a two-dimensional fanbeam filtered backprojecti on algorithm. Results: The reconstructed transaxial resolution of 2.8 mm FWHM and system sensitivity of 0.086 c/s/kBq with the 2.0-mm pinhol e collimator aperture provide excellent spatial detail and adequate se nsitivity for imaging the regional uptake of the radiopharmaceuticals in tumor, organs and other tissues in small laboratory animals. Conclu sion: The resolution properties of pinhole SPECT are superior to those which have been achieved thus far with conventional SPECT or PET imag ing technologies. Pinhole SPECT provides an important approach for inv estigating localization properties of radiopharmaceuticals in vivo.