BACKGROUND: Somatostatin receptor scintigraphy (SRS)
is a useful tool in the assessment of GEP-NET (gastroenteropancreatic
neuroendocrine tumor) patients. The choice
of appropriate settings of image reconstruction parameters is
crucial in interpretation of these images. The aim of the study
was to investigate how the GEP NET lesion signal to noise ratio
(TCS/TCB) depends on different reconstruction settings for Flash
3D software (Siemens).

METHODS: SRS results of 76 randomly selected patients with
confirmed GEP-NET were analyzed. For SPECT studies the data
were acquired using standard clinical settings 3–4 h after the
injection of 740 MBq 99mTc-[EDDA/HYNIC] octreotate. To obtain
final images the OSEM 3D Flash reconstruction with different
settings and FBP reconstruction were used. First, the TCS/TCB
ratio in voxels was analyzed for different combinations of the
number of subsets and the number of iterations of the OSEM
3D Flash reconstruction. Secondly, the same ratio was analyzed for different parameters of the Gaussian filter (with FWHM = 2–4
times greater from the pixel size). Also the influence of scatter
correction on the TCS/TCB ratio was investigated.

RESULTS: With increasing number of subsets and iterations, the
increase of TCS/TCB ratio was observed. With increasing settings
of Gauss [FWHM coefficient] filter, the decrease of TCS/TCB ratio
was reported. The use of scatter correction slightly decreases
the values of this ratio.

CONCLUSIONS: OSEM algorithm provides a meaningfully
better reconstruction of the SRS SPECT study as compared to
the FBP technique. A high number of subsets improves image
quality (images are smoother). Increasing number of iterations
gives a better contrast and the shapes of lesions and organs are
sharper. The choice of reconstruction parameters is a compromise
between image qualitative appearance and its quantitative
accuracy and should not be modified when comparing multiple
studies of the same patient.