• The Korean Journal of Nuclear Medicine Technology
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• v.16 no.2
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• pp.44-48
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• 2012

Purpose : Arm motion can give rise to striking cold artifact on PET/CT. We investigated that evaluation of scatter-limit correction and correct the patient arm motion artifact in Discovery 600 PET/CT. Materials and Methods : To evaluate a radioactivity uptake (Bq/ml) and a standard uptake value (SUV), the scatter limit correction and scatter correction were compared using 1994 NEMA Phantom$^{TM}$ in Discovery 600 PET/CT (GE Healthcare, Mi, We). Arm motion phantom study was involved a central 20 cm diameter cylinder simulating the neck and 2 peripheral 10 cm diameter cylinders simulating arms. The positions of the arms were altered so as to introduce different amounts of misalignment. The evaluation of arm motion phantom study used the radioactivity uptake and SUV in scatter correction and scatter limit correction. Results : The statistical significance of radioactivity uptake and SUV did not show the differences in comparisons of the scatter limit correction and the scatter correction that not show (p<0.05). Radioactivity uptake of the scatter correction was up to 3.1 kBq/ml in the 0.04 kBq/ml. It was approximately 98.7% undervalued in the arm motion phantom study. However, Radioactivity uptake of the scatter limit correction was up to 3.0 kBq/ml in the 2.11 kBq/ml. It was approximately 30% undervalued in arm motion phantom study. SUV of the scatter correction was 1.05 to 0.006 and underestimated about 98%. However, an applying SUV of the scatter limit correction changed the value as 0.67 which is underestimated about 25%. Radioactivity uptake and SUV of the scatter limit correction was increased approximately 60%, or more than the scatter correction. Conclusion : It is considered that if the patient arm motion artifact was occurred the scatter limit correction will be applicable to give an accurate diagnosis.

• The Korean Journal of Nuclear Medicine Technology
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• v.21 no.2
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• pp.55-64
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• 2017

Purpose Recently, with the spread of SPECT/CT, various image correction methods can be applied quickly and accurately, which enabled us to expect quantitative accuracy as well as image quality improvement. Among them, the Collimator Detector Response(CDR) recovery is a correction method aiming at resolution recovery by compensating the blurring effect generated from the distance between the detector and the object. The purpose of this study is to find out quantitative change depending on the change in detection distance in SPECT/CT images with CDR recovery applied. Materials and Methods In order to find out the error of acquisition count depending on the change of detection distance, we set the detection distance according to the obit type as X, Y axis radius 30cm for circular, X, Y axis radius 21cm, 10cm for non-circular and non-circular auto(=auto body contouring, ABC_spacing limit 1cm) and applied reconstruction methods by dividing them into Astonish(3D-OSEM with CDR recovery) and OSEM(w/o CDR recovery) to find out the difference in activity recovery depending on the use of CDR recovery. At this time, attenuation correction, scatter correction, and decay correction were applied to all images. For the quantitative evaluation, calibration scan(cylindrical phantom, $^{99m}TcO_4$ 123.3 MBq, water 9293 ml) was obtained for the purpose of calculating the calibration factor(CF). For the phantom scan, a 50 cc syringe was filled with 31 ml of water and a phantom image was obtained by setting $^{99m}TcO_4$ 123.3 MBq. We set the VOI(volume of interest) in the entire volume of the syringe in the phantom image to measure total counts for each condition and obtained the error of the measured value against true value set by setting CF to check the quantitative accuracy according to the correction. Results The calculated CF was 154.28 (Bq/ml/cps/ml) and the measured values against true values in each conditional image were analyzed to be circular 87.5%, non-circular 90.1%, ABC 91.3% and circular 93.6%, non-circular 93.6%, ABC 93.9% in OSEM and Astonish, respectively. The closer the detection distance, the higher the accuracy of OSEM, and Astonish showed almost similar values regardless of distance. The error was the largest in the OSEM circular(-13.5%) and the smallest in the Astonish ABC(-6.1%). Conclusion SPECT/CT images showed that when the distance compensation is made through the application of CDR recovery, the detection distance shows almost the same quantitative accuracy as the proximity detection even under the distant condition, and accurate correction is possible without being affected by the change in detection distance.