Pinhole single photon emission computed tomography (SPECT) offers attractio
ns for thyroid imaging, but acquisition must be limited to 180 degrees. Vil
e have mounted a 3.2 mm pinhole collimator on a rotating gamma camera, magn
ification 2.1, and characterized its response in the 10 cm field-of-view (F
OV) by imaging points, lines, and a Picker thyroid phantom. We compared bot
h full and half-circle data acquisition. Image reconstruction was done with
a new Discrete Vertex Set (DVS) algorithm and the Feldkamp (FDK) algorithm
.
For full-circle acquisition, spatial resolution is quite uniform across the
FOV, averaging 5.3 mm FWHM, and the reconstructed images show an intensity
variation less than 5% in all directions; the FDK and DVS algorithms perfo
rm similarly. For half-circle reconstruction, spatial resolution shows more
variation across the FOV, averaging 5.4 mm FWHM, and the maximum intensity
variation is +/- 20%. Some differences between the FDK and DVS algorithms
are apparent. The point response at non-centered positions along the horizo
ntal transverse axis shows tails in the horizontal transverse direction for
the FDK-half reconstruction, whereas for the DVS-half reconstruction there
is blurring in the vertical direction at these positions.
The thyroid phantom with its 6, 9, and 12 mm cold spots and 12 mm hot spot
can be visualized in both full and half-circle reconstructions, allowing si
ze determination.