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Jung Jin Lim1, Sung Wook Jo1, Jin Eui Kim 1 Geon wook Kang1,2

Dept. of Nuclear Medicine, Seoul National Univ. Hospital1

Dept. of Nuclear Medicine, Seoul National Univ.2

[Object] There are several factors that determine image quality in SPECT/CT, such as acquisition time, angle and reconstruction methods.  In this study, we focused on only the  aspect of  acquisition  angles and  evaluated  the  image quality  by  applying four different angles.

[Materials and Methods] This study was carried out with Flangeless Esser PET Phantom (Data Spectrum Corp.,  USA) and NEMA Triple Line Source  Phantom  (Data Spectrum Corp, USA) using a SPECT/CT, Discovery 670 (GE, USA). The interior of the Flangeless Esser PET phantom was filled with 37 kBq/mL of 99mTcO - for  background setting and

4 of cylinders (8, 12, 16, 25 mm) were filled with 296 kBq/mL of 99mTcO -.; The cylinders

to background activity ratio  was regulated as 8:1. The three  lines of the NEMA Triple Line Source Phantom were filled with 3.7 MBq/mL of 99mTcO -. Acquisition angles were varied  as 3°,  4°,  5°  and  6°  with  the  acquisition time  fixed  on  15 sec/Frame.  OSEM algorithm and CT attenuation correction were applied  for  reconstruction. For comparison, contrast noise to ratios(CNR) and contrast recovery ratio  were calculated

from  the images of Flangeless Esser PET phantom. Plus, resolution was also measured from  the images of NEMA Triple Line Source Phantom.

[Results] In the  experiments using Flangeless  Esser  PET Phantom,  there  was not  a significant change  in the contrast recovery  ratio(supplement table  1), however  the contrast  noise   to   ratio  was  decreased   with  the   increase  of   acquisition  angle (supplement table  2). In the  experiments using NEMA Triple Line Source  Phantom, resolution  did   not   change   significantly  with  the   increase  of  acquisition  angle (supplement table 3).

[Conclusion] In SPECT/CT images, the contrast to noise ratio  was found  to be reduced with the increase of acquisition angle while it did not affect the contrast recovery ratio and resolution. Therefore, when performing SPECT/CT, it is necessary  to adjust the acquisition  angle according  to  the  type of  study,  and  it is also recommended to perform additional experiments to find  a suitable acquisition angle.