Tomographic Imaging by a Si/CdTe Compton Camera for ¹¹¹In and ¹³¹I Radionuclides

Tomographic imaging with radionuclides commonly used in nuclear medicine, such as
¹¹¹
In (171 and 245 keV) and
¹³¹
I (364 keV), is in high demand for medical applications and small animal imaging. The Si/CdTe Compton camera with its high angular and high energy resolutions is an especially promising detector to extend the energy coverage for imaging to the range that covers gamma ray emitted from these radionuclides. Here, we take the first steps toward short-distance imaging by conducting experiments using 3-D phantoms composed of multiple sphere-like solutions of
¹¹¹
In and
¹³¹
I with a diameter of 2.7 mm, placed at a distance of 41 mm. Using simple back-projection (SBP) methods, the positions of the sources are reproduced with a spatial resolution of 11.5 and 9.0 mm (FWHM) for
¹¹¹
In and
¹³¹
I, respectively. We found that a list-mode maximum-likelihood expectation maximization (LM-MLEM) method gives a better resolution of 4.0 and 2.7 mm (FWHM). We resolve source positions of a tetrahedron structure with a source-to-source separation of 28 mm. These findings demonstrate that Compton Cameras have the potential of close-distance imaging of radioisotopes distributions in the energy range below 400 keV.