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Seok Hwan Yoon, Seong wook Cho, Jin Eui Kim

Department of Nuclear Medicide, Seoul National University Hospital, Seoul, Korea,

Purpose : Auto exposure control (AEC) in SPECT/CT automatically controls the exposure dose (mA)

according to patient's shape and size. The aim of this study was to evaluate the effect of AEC in SPECT/CT

on exposure dose reduction and image quality. Methods: The model of SPECT/CT used in this study was

Discovery 670 of GE Co.; Smart mA for AEC; and 99mTc as a radioisotope. To compare SPECT and CT

images by CT exposure dose variation, we used a standard technique set at 80/100/120/140kVp,

10/30/50/100/150/200/250mA, and AEC at 80/100/120/140kVp, 10~250mA. To evaluate resolution and contrast

of SPECT images, triple line phantom and flangeless Esser PET phantom were used. For CT images, noise

and uniformity were checked by anthropomorphic chest phantom. For dose evaluation to find DLP value,

anthropomorphic chest phantom was used and the CT protocol of torso was applied by standard technique

(120kVp, 100mA) and AEC (120kVp, 10~250mA).

Results : When standard and AEC were applied, the resolutions at SPECT images with Attenuation

Correction(A.C) were the same as FWHM by Center 3.65㎜ , Left 3.48㎜ , Right 3.61㎜ . Contrasts of

standard and AEC showed no significant difference: standard 53.5/29.8/22.5/15.8/6.0, AEC

53.5/29.6/22.4/15.7/6.1 In CT images, noise values at standard and AEC were 15.4 and 18.5 respectively. The

application of AEC increases noise but the value of coefficient variation were 33.8, 24.9 respectively,

obtaining uniform noise image. The values of DLP at standard and AEC were 426.78 and 352.09 each, which

shows that the application of AEC decreases exposure dose more than standard by approximately 18%.

Conclusions : The results of our study show that there was no difference of A.C in SPECT images based on

the CT exposure dose variation at SPECT/CT images. It was found that the increased CT exposure dose leads

to the improvement of CT image quality but also increases the exposure dose. Thus, the use of AEC in

SPECT/CT contributes to obtaining equal A.C SPECT images, and uniform noise in CT images while

reducing exposure dose.

Key Words : SPECT/CT, AEC(Automatic Exposure Control), Attenuation correction