Hye-Kyung Son

ROC analysis of ordered subset expectation maximization and filtered back projection technique for FDG-PET in lung cancer

The purpose of the study was to evaluate the image quality and discriminative ability of FDG-PET images reconstructed by filtered back projection (FBP) and ordered subset expectation maximization (OSEM) in patients with lung cancer. Thirty-six subjects including normal controls and lung cancer patients underwent whole body PET scan (emission 3 min, transmission 1 min) using a GE Advance scanner after the administration of approximately 370 MBq of FDG. The raw data were then reconstructed by conventional FBP and OSEM. The PET images were interpreted by two observers with random exposure of normal and diseased cases for transverse and coronal sections. The results were evaluated using receiver operating characteristic (ROC) curve analysis. The optimal parameters for reconstructing by OSEM involved 2 iterations and 16 subsets. The image quality of thirty-six subjects including normal controls and lung cancer patients reconstructed by OSEM was generally superior to FBP in terms of visual analysis. Though FBP had poor image quality, it had better image contrast than OSEM. The ROC curve plotted for the identification of lung cancer in coronal sections showed better results than in transverse sections by FBP and OSEM, except for the OSEM result of observer 2. ROC analysis showed that OSEM performed better than conventional FBP in terms of its discriminative ability of lung cancer with FDG PET, although there was no significant difference in the area under the ROC curve (p-value >0.05). The results suggest that the simultaneous use of FBP and OSEM images is helpful for the FDG-PET diagnosis of lung cancer.

Improved scatter correction for SPECT images: a Monte Carlo study

We propose the extended triple energy window (ETEW) method that improves quantitation and contrast in SPECT images. ETEW is a modification of the triple energy window (TEW) method which corrects for scatter by using abutted scatter rejection windows, which can overestimate or underestimate scatter. ETEW is compared to TEW using Monte Carlo simulated data for point sources as well as hot and cold spheres in a cylindrical water phantom. Various main energy window widths were simulated. Both TEW and ETEW improved image contrast and recovery coefficients. Estimated scatter components by TEW were not proportional to the true scatter components when main energy window widths of 10%, 15%, and 20% were simulated. ETEW resulted in scatter that was directly proportional to the true scatter. ETEW improves image quantitation and quality of SPECT image data by more accurately correcting for scatter.

Analysis of the heart rate and its variation affecting image quality and optimized reconstruction window in retrospective ECG-gated coronary angiography using multidetector row CT

It is clinically important to examine the effect of the heart rate and its variation on the image quality and selection of the optimized window in coronary angiography using multidetector row CT (MDCT). This study performed contrast-enhanced coronary angiography using MDCT on 83 patients. Fifty-two cases with information on the heart rate available were enrolled in this study. The effect of heart rate and its variation were systemically analyzed. Two radiologists rated the image quality as follows: 4-excellent; 3-good; 2-fair; 1-bad. Cardiac cycle windows at 40% and 70% were routinely selected for image reconstruction. The optimized window was rated as 1 when a 40% reconstruction had a better quality than the 70% reconstruction, as 2 when the 40% reconstruction was the same as the 70% reconstruction, and as 3 when the 70% reconstruction was better than the 40% reconstruction. The image quality was more affected by a variation of the heart rate than by the high heart rate. The selection of the optimized reconstruction window for a good image quality was mostly affected by the heart rate and there was a tendency for the 40% phase reconstruction to have a better image quality than the 70% reconstruction at higher heart rates.It is clinically important to study the effect of heart rate and its variation on image quality, and selection of optimized window in coronary angiography using multi-detector row CT (MDCT). We performed contrast-enhanced coronary angiography using MDCT in 83 patients. Sixty cases with available information of heart rate were enrolled in this study. We systemically analyzed the effect of heart rate and its variation. Two radiologists rated image quality as follows: 4, excellent; 3, good; 2, fair; 1, bad. Cardiac cycle windows at 70 and 40% were routinely selected for image reconstruction. Both of 40% and 70% reconstructed images were available only to fifty-seven cases. Optimized window was rated as 1 when 40% reconstruction was better quality than 70%, as 2 when 40% reconstruction was the same as 70%, and as 3 when 70% reconstruction was better than 40%.

Radiation dose during CT scan with PET/CT clinical protocols

The purpose of this study was to evaluate the radiation doses during CT scans by changing tube voltage and tube current, and to estimate the radiation dose for our clinical protocols during transmission measurement in PET/CT scans. Radiation doses were evaluated for Philips GEMINI 16 slices PET/CT and GE DSTe 8 slices PET/CT systems. A CTDI was measured with standard head and body CT dosimetry phantoms in a variety of CT tube voltage and tube current. A pencil ionization chamber with an active length of 100 mm, and electrometer were used for the CTDI measurement. The measurement is carried out at the free-in-air, center and periphery. The average dose was calculated by the weighted CTDI (CTDIw = 1/3CTDI100,c + 2/3CTDI100,p). Specific organ doses were measured with our clinical protocols for transmission measurement with the Philips PET/CT system and GE PET/CT system with TLDs and anthropomorphic phantom. The TLDs used for measurements were selected for an accuracy of plusmn5% and calibrated in an X-ray radiation field. The organ or tissue was selected by the recommendations of ICRP 60. The radiation dose measured by using standard CTDI phantoms during a CT scan is affected by the tube voltage and the tube current. The measured effective doses with transmission measurements for the Philips system were ranged from 0.14 mSv to 55.54 mSv. The measured effective doses with transmission measurements for GE system were ranged from 0.27 mSv to 24.83 mSv. Radiation dose for clinical protocols during transmission measurements in the PET/CT system can be measured using CTDI phantom with ionization chamber and anthropomorphic phantom with TLDs. Further studies need to be performed to find optimal CT acquisition protocols for reducing the patient exposure with same image quality.

PET imaging and quantitation of Internet-addicted patients and normal controls

Internet addicted patients (IAPs) have widely been increased, as Internet games are becoming very popular in daily life. The purpose of this study was to investigate regional brain activation patterns associated with excessive use of Internet games in adolescents. Six normal controls (NCs) and eight IAPs who were classified as addiction group by adapted version of DSM-IV for pathologic gambling were participated. 18F-FDG PET studies were performed for all adolescents at their rest and activated condition after 20 minutes of each subjects favorite Internet game. To investigate quantitative metabolic differences in both groups, all possible combinations of group comparison were carried out using Statistical Parametric Mapping (SPM 99). Regional brain activation foci were identified on Talairach coordinate. SPM results showed increased metabolic activation in occipital lobes for both groups. Higher metabolisms were seen at resting condition in IAPs than that of in NCs. In comparison to both groups, IAPs showed different patterns of regional brain metabolic activation compared with that of NCs. It suggests that addictive use of Internet games may result in functional alteration of developing brain in adolescents.

Radiation dose for clinical protocols during CT transmission measurement in PET/CT scan

The purpose of this study was to evaluate the radiation doses during CT transmission scan by changing tube voltage and current, and to estimate the radiation dose during our clinical whole body high quality CT scan. Radiation doses were evaluated for Philips GEMINI 16 slices PET/CT system. CTDI was measured with standard head and body CT dosimetry phantoms in a variety of CT tube voltage and current over time measurement. A pencil ionization chamber with an active length of 100 mm and electrometer were used for CTDI measurement. The measurement is carried out at the free-in-air, at the center, and at the periphery. The average dose was calculated by the weighted CTDI (CTDIw = 1/3CTDI100,c + 2/3CTDI100,p). Specific organ dose was measured with clinical whole body high quality CT acquisition protocol using TLDs and Alderson phantom. The TLDs used for measurements were selected for an accuracy of ±5% and calibrated in X-ray radiation field. The organ or tissue was selected by the recommendations of ICRP 60. The weighted CT dose index is affected by the tube voltage and current over time measurements. For the CTDI head phantom, when tube voltage was fixed to 120 kVp, the CTDIw values were ranged from 6.5 mGy to 97.9 mGy by changing the current values from 35 mAs to 500 mAs. When the current value was fixed to 350 mAs, the CTDIw values were ranged from 27.3 mGy to 85.0 mGy by changing the tube voltage from 90 kVp to 140 kVp. For the CTDI body phantom, when tube voltage was fixed to 120 kVp, the CTDIw values were ranged from 4.8 mGy to 35.8 mGy by changing the tube current from 50 mAs to 400 mAs. When the tube current was fixed to 200 mAs, the CTDIw values were ranged from 8.5 mGy to 27.7 mGy by changing the tube voltage from 90 kVp to 140 kVp. The measured specific organ doses were ranged from 23.9 mGy (bone marrow) to 42.3 mGy (skin). Radiation dose during CT scan in the PET/CT system was measured using CT dosimetry phantom with ion chamber and anthropomorphic phantom with TLDs. Further study need to be performed to find optimal CT acquisition protocols for reducing the patient exposure with same image quality.