A VECTOR WIENER FILTER FOR DUAL-RADIONUCLIDE IMAGING

The routine use of a single radionuclide for patient imaging in nuclea r medicine can be complemented by studies employing two tracers to exa mine two different processes in a single organ, most frequently by sim ultaneous imaging of both radionuclides in two different energy window s. In addition, simultaneous transmission/emission imaging with dual-r adionuclides has been described, with one radionuclide used for the tr ansmission study and a second for the emission study. There is thus cu rrently considerable interest in dual-radionuclide imaging. A major pr oblem with all dual-radionuclide imaging is the ''crosstalk'' between the two radionuclides. Such crosstalk frequently occurs, because scatt ered radiation from the higher energy radionuclide is detected in the lower energy window, and because the lower energy radionuclide may hav e higher energy emissions which are detected in the higher energy wind ow. We have previously described the use of Fourier-based restoration filtering in single photon emission computed tomography (SPECT) and po sitron emission tomography (PET) to improve quantitative accuracy by d esigning a Wiener or other Fourier filter to partially restore the los s of contrast due to scatter and finite spatial resolution effects. We describe here the derivation and initial validation of an extension o f such filtering for dual-radionuclide imaging that simultaneously 1) improves contrast in each radionuclide's ''direct'' image, 2) reduces image noise, and 3) reduces the crosstalk contribution from the other radionuclide. This filter is based on a vector version of the Wiener f ilter, which is shown to be superior [in the minimum mean square error (MMSE) sense] to the sequential application of separate crosstalk and restoration filters.