• The Korean Journal of Nuclear Medicine Technology
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• v.16 no.2
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• pp.68-80
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• 2012

Purpose : More recently, combined PET/MR scanners have been developed in which the MR data can be used for both anatometabolic image formation and attenuation correction of the PET data. For quantitative PET information, correction of tissue photon attenuation is mandatory. The attenuation map is obtained from the CT scan in the PET/CT. In the case of PET/MR, the attenuation map can be calculated from the MR image. The purpose of this study was to assess the quantitative differences between MR-based and CT-based attenuation corrected PET images. Materials and Methods : Using the uniform cylinder phantom of distilled water which has 199.8 MBq of $^{18}F$-FDG put into the phantom, we studied the effect of MR-based and CT-based attenuation corrected PET images, of the PET-CT using time of flight (TOF) and non-TOF iterative reconstruction. The images were acquired from 60 minutes at 15-minute intervals. Region of interests were drawn over 70% from the center of the image, and the Scanners' analysis software tools calculated both maximum and mean SUV. These data were analyzed by one way-anova test and Bland-Altman analysis. MR images are segmented into three classes(not including bone), and each class is assigned to each region based on the expected average attenuation of each region. For clinical diagnostic purpose, PET/MR and PET/CT images were acquired in 23 patients (Ingenuity TF PET/MR, Gemini TF64). PET/CT scans were performed approximately 33.8 minutes after the beginnig of the PET/MR scans. Region of interests were drawn over 9 regions of interest(lung, liver, spleen, bone), and the Scanners' analysis software tools calculated both maximum and mean SUV. The SUVs from 9 regions of interest in MR-based PET images and in CT-based PET images were compared. These data were analyzed by paired t test and Bland-Altman analysis. Results : In phantom study, MR-based attenuation corrected PET images generally showed slightly lower -0.36~-0.15 SUVs than CT-based attenuation corrected PET images (p<0.05). In clinical study, MR-based attenuation corrected PET images generally showed slightly lower SUVs than CT-based attenuation corrected PET images (excepting left middle lung and transverse Lumbar) (p<0.05). And percent differences were -8.01.79% lower for the PET/MR images than for the PET/CT images. (excepting lung) Based on the Bland-Altman method, the agreement between the two methods was considered good. Conclusion : PET/MR confirms generally lower SUVs than PET/CT. But, there were no difference in the clinical interpretations made by the quantitative comparisons with both type of attenuation map.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.10
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• pp.4418-4424
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• 2011

This study is aimed to assess the effect of the gamma ray of 511keV energy which is emitted from phantom where the positron emission radionuclide was injected on X-ray CT image. As a scanning method, the CT number and pixel value of the reference image where water was injected(0 mCi), and those acquired by changing the capacity of 18F(Fluorine), positron emission radionuclide, into 1 mCi, 2 mCi, 5 mCi, and 10 mCi were measured. As a result of measuring the CT number(HU) of the phantom image where the positron emission radionuclide($^{18}F$) was injected, there were reference water ($-7.58{\pm}0.66$ HU), 1 mCi($-9.85{\pm}0.50$ HU), 2 mCi($-10.27{\pm}0.21$ HU), 5 mCi($-11.31{\pm}0.66$ HU), and 10 mCi($-13.47{\pm}0.38$ HU). Compared with the image where it was filled with water, there was a reduction of 5.89 Hu in 10 mCi, 3.73 in 5 mCi, 2.69 HU in 2 mCi, and 2 HU in 1 mCi. As for the pixel value of the phantom image, there were reference water ($-2.70{\pm}0.75$), 1 mCi($-4.72{\pm}0.58$), 2 mCi($-6.01{\pm}0.78$), 5 mCi($-6.10{\pm}0.84$), and 10 mCi($-8.20{\pm}0.60$). Compared with the reference image, there was a reduction of 5.50 in 10 mCi, 3.40 in 5 mCi, 3.10 in 2 mCi, and 2.02 in 1 mCi. Through this experiment, it was indicated that, with the increase in the dose of the positron emission radionuclide($^{18}F$), the CT number and the pixel value of the image reduced proportionally, and the width of reduction showed a similar value, too. Accordingly, according to the degree of change in X-ray CT image due to the positron emission radionuclide in the quality control item of PET/CT, the proper standard should be established and it should be periodically managed.

• Nuclear Medicine and Molecular Imaging
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• v.43 no.5
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• pp.421-428
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• 2009

Purpose: We have evaluated characteristics of adrenal masses incidentally observed in nonenhanced F-18 FDG PET/CT of the oncologic patients and the diagnostic ability of F-18 FDG PET/CT to differentiate malignant from benign adrenal masses. Materials and Methods: Between Mar 2005 and Aug 2008, 75 oncologic patients (46 men, 29 women; mean age, $60.8{\pm}10.2$ years; range, 35-87 years) with 89 adrenal masses incidentally found in PET/CT were enrolled in this study. For quantitative analysis, size (cm), Hounsfield unit (HU), maximum standardized uptake value (SUVmax), SUVratio of all 89 adrenal masses were measured. SUVmax of the adrenal mass divided by SUVliver, which is SUVmax of the segment 8, was defined as SUVratio. The final diagnosis of adrenal masses was based on pathologic confirmation, radiologic evaluation (HU<0 : benign), and clinical decision. Results: Size, HU, SUVmax, and SUVratio were all significantly different between benign and malignant adrenal masses.(P < 0.05) And, SUVratio was the most accurate parameter. A cut-off value of 1.0 for SUVratio provided 90.9% sensitivity and 75.6% specificity. In small adrenal masses (1.5 cm or less), only SUVratio had statistically significant difference between benign and malignant adrenal masses. Similarly a cut-off value of 1.0 for SUVratio provided 80.0% sensitivity and 86.4% specificity. Conclusion: F-18 FDG PET/CT can offer more accurate information with quantitative analysis in differentiating malignant from benign adrenal masses incidentally observed in oncologic patients, compared to nonenhanced CT.

• Journal of the Korean Society of Radiology
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• v.17 no.3
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• pp.297-303
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• 2023

Pediatric Computed Tomography (CT) examinations can often result in exam failures or the need for frequent retests due to the difficulty of cooperation from young patients. Deep Learning Image Reconstruction (DLIR) methods offer the potential to obtain diagnostically valuable images while reducing the retest rate in CT examinations of pediatric patients with high radiation sensitivity. In this study, we investigated the possibility of applying DLIR to reduce artifacts caused by respiration or motion and obtain clinically useful images in pediatric chest CT examinations. Retrospective analysis was conducted on chest CT examination data of 43 children under the age of 7 from P Hospital in Gyeongsangnam-do. The images reconstructed using Filtered Back Projection (FBP), Adaptive Statistical Iterative Reconstruction (ASIR-50), and the deep learning algorithm TrueFidelity-Middle (TF-M) were compared. Regions of interest (ROI) were drawn on the right ascending aorta (AA) and back muscle (BM) in contrast-enhanced chest images, and noise (standard deviation, SD) was measured using Hounsfield units (HU) in each image. Statistical analysis was performed using SPSS (ver. 22.0), analyzing the mean values of the three measurements with one-way analysis of variance (ANOVA). The results showed that the SD values for AA were FBP=25.65±3.75, ASIR-50=19.08±3.93, and TF-M=17.05±4.45 (F=66.72, p=0.00), while the SD values for BM were FBP=26.64±3.81, ASIR-50=19.19±3.37, and TF-M=19.87±4.25 (F=49.54, p=0.00). Post-hoc tests revealed significant differences among the three groups. DLIR using TF-M demonstrated significantly lower noise values compared to conventional reconstruction methods. Therefore, the application of the deep learning algorithm TrueFidelity-Middle (TF-M) is expected to be clinically valuable in pediatric chest CT examinations by reducing the degradation of image quality caused by respiration or motion.

• Korean Journal of Radiology
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• v.2 no.1
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• pp.28-36
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• 2001

Objective: To provide a systematic overview of the effects of various parameters on contrast enhancement within the same population, an animal experiment as well as a computer-aided simulation study was performed. Materials and Methods: In an animal experiment, single-level dynamic CT through the liver was performed at 5-second intervals just after the injection of contrast medium for 3 minutes. Combinations of three different amounts (1, 2, 3 mL/kg), concentrations (150, 200, 300 mgI/mL), and injection rates (0.5, 1, 2 mL/sec) were used. The CT number of the aorta (A), portal vein (P) and liver (L) was measured in each image, and time-attenuation curves for A, P and L were thus obtained. The degree of maximum enhancement (Imax) and time to reach peak enhancement (Tmax) of A, P and L were determined, and times to equilibrium (Teq) were analyzed. In the computed-aided simulation model, a program based on the amount, flow, and diffusion coefficient of body fluid in various compartments of the human body was designed. The input variables were the concentrations, volumes and injection rates of the contrast media used. The program generated the time-attenuation curves of A, P and L, as well as liver-to-hepatocellular carcinoma (HCC) contrast curves. On each curve, we calculated and plotted the optimal temporal window (time period above the lower threshold, which in this experiment was 10 Hounsfield units), the total area under the curve above the lower threshold, and the area within the optimal range. Results: A. Animal Experiment: At a given concentration and injection rate, an increased volume of contrast medium led to increases in Imax A, P and L. In addition, Tmax A, P, L and Teq were prolonged in parallel with increases in injection time The time-attenuation curve shifted upward and to the right. For a given volume and injection rate, an increased concentration of contrast medium increased the degree of aortic, portal and hepatic enhancement, though Tmax A, P and L remained the same. The time-attenuation curve shifted upward. For a given volume and concentration of contrast medium, changes in the injection rate had a prominent effect on aortic enhancement, and that of the portal vein and hepatic parenchyma also showed some increase, though the effect was less prominent. A increased in the rate of contrast injection led to shifting of the time enhancement curve to the left and upward. B. Computer Simulation: At a faster injection rate, there was minimal change in the degree of hepatic attenuation, though the duration of the optimal temporal window decreased. The area between 10 and 30 HU was greatest when contrast media was delivered at a rate of 2 3 mL/sec. Although the total area under the curve increased in proportion to the injection rate, most of this increase was above the upper threshould and thus the temporal window was narrow and the optimal area decreased. Conclusion: Increases in volume, concentration and injection rate all resulted in improved arterial enhancement. If cost was disregarded, increasing the injection volume was the most reliable way of obtaining good quality enhancement. The optimal way of delivering a given amount of contrast medium can be calculated using a computer-based mathematical model.