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PET center in Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea1

JungJin Lim, MT;JaeIl Kim, MT; HongJae Lee, MT;   HyeonJoo Kim, MT1,

Background    and   Purpose    :  The  introduction  of   Fusion  PET    has  brought  a   higher diagnostic  value  compared  to  conventional  PET.  In   particular,  it  not  only   allows accurate determination of  location through CT  images but also accurate  compensation of   attenuation,  which  greatly   improves  image  quality.  This  paper   examines   the differences of SUV in attenuation corrected image according to the tube voltage. Subjects and  Methods :  For patient examination, six sick patients were selected  and

18F-FDG  was intravenously injected. After one hour, under the  same  conditions, the

tube voltage of CT  was changed to 90,  120, and  140  kVp.  Then the CT  and  PET  images were obtained. CT  images with changed tube voltages were applied to the 3D-RAMRA algorithm to produce attenuation corrected  images. ROI  was set for each attenuation corrected image and  the maximum SUV values were measured and  compared.

Results  :  Based  on   the  attenuation  corrected  images with the  tube  voltage  of  CT set  to  120   kVp   which  is  used  now,   at  each  ROI  for  liver  the  SUV   showed  the difference of  +2.08% at 90  kVp,  and  -1.01%  at 140   kVp.

The  SUV  showed the  difference  of  +1.42% at  90   kVp,   and   +0.37%  at  140kVp in the lung.

At  each  ROI  for  bone  the  SUV  showed  the  difference  of  +0.60% at  90   kVp,   and

-0.04%   at  140kVp. In  the  last,  the  SUV   showed  the  difference  of   +1.63%  at  90 kVp,  and  -0.32%  at 140   kVp  in  the lesion.

Conclusion :  The higher the energy of  radiation that penetrates  a  subject, the lower gets   the   attenuation  coefficient  of    the   subject   and    the   lower  the   attenuation correction   value  than  the  actually  measured  value.  Furthermore,  the  higher  the density of  subject for the same penetrated  radiation, the higher gets  the attenuation coefficient  of  the  subject  and   the  higher  the  attenuation  correction  value than  the actually  measured  value.  This  pattern  was  found  in   the  results  of   this  paper  as well.  However  the  changes   in   the  result  values  were  insignificant because  the difference of  changing energy  was too small.

key word :  Fusion PET, CTAC,  attenuation corrected  image, SUV