• Asia pacific journal of information systems
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• v.19 no.4
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• pp.47-75
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• 2009

Recently, researches on Management Information Systems (MIS) have laid out theoretical foundation and academic paradigms by introducing diverse theories, themes, and methodologies. Especially, academic paradigms of MIS encourage a user-friendly approach by developing the technologies from the users' perspectives, which reflects the existence of strong causal relationships between information systems and user's behavior. As in other areas in social science the use of structural equation modeling (SEM) has rapidly increased in recent years especially in the MIS area. The SEM technique is important because it provides powerful ways to address key IS research problems. It also has a unique ability to simultaneously examine a series of casual relationships while analyzing multiple independent and dependent variables all at the same time. In spite of providing many benefits to the MIS researchers, there are some potential pitfalls with the analytical technique. The research objective of this study is to provide some guidelines for an appropriate use of SEM based on the assessment of current practice of using SEM in the MIS research. This study focuses on several statistical issues related to the use of SEM in the MIS research. Selected articles are assessed in three parts through the meta analysis. The first part is related to the initial specification of theoretical model of interest. The second is about data screening prior to model estimation and testing. And the last part concerns estimation and testing of theoretical models based on empirical data. This study reviewed the use of SEM in 164 empirical research articles published in four major MIS journals in Korea (APJIS, ISR, JIS and JITAM) from 1991 to 2007. APJIS, ISR, JIS and JITAM accounted for 73, 17, 58, and 16 of the total number of applications, respectively. The number of published applications has been increased over time. LISREL was the most frequently used SEM software among MIS researchers (97 studies (59.15%)), followed by AMOS (45 studies (27.44%)). In the first part, regarding issues related to the initial specification of theoretical model of interest, all of the studies have used cross-sectional data. The studies that use cross-sectional data may be able to better explain their structural model as a set of relationships. Most of SEM studies, meanwhile, have employed. confirmatory-type analysis (146 articles (89%)). For the model specification issue about model formulation, 159 (96.9%) of the studies were the full structural equation model. For only 5 researches, SEM was used for the measurement model with a set of observed variables. The average sample size for all models was 365.41, with some models retaining a sample as small as 50 and as large as 500. The second part of the issue is related to data screening prior to model estimation and testing. Data screening is important for researchers particularly in defining how they deal with missing values. Overall, discussion of data screening was reported in 118 (71.95%) of the studies while there was no study discussing evidence of multivariate normality for the models. On the third part, issues related to the estimation and testing of theoretical models on empirical data, assessing model fit is one of most important issues because it provides adequate statistical power for research models. There were multiple fit indices used in the SEM applications. The test was reported in the most of studies (146 (89%)), whereas normed-test was reported less frequently (65 studies (39.64%)). It is important that normed- of 3 or lower is required for adequate model fit. The most popular model fit indices were GFI (109 (66.46%)), AGFI (84 (51.22%)), NFI (44 (47.56%)), RMR (42 (25.61%)), CFI (59 (35.98%)), RMSEA (62 (37.80)), and NNFI (48 (29.27%)). Regarding the test of construct validity, convergent validity has been examined in 109 studies (66.46%) and discriminant validity in 98 (59.76%). 81 studies (49.39%) have reported the average variance extracted (AVE). However, there was little discussion of direct (47 (28.66%)), indirect, and total effect in the SEM models. Based on these findings, we suggest general guidelines for the use of SEM and propose some recommendations on concerning issues of latent variables models, raw data, sample size, data screening, reporting parameter estimated, model fit statistics, multivariate normality, confirmatory factor analysis, reliabilities and the decomposition of effects.

• The Korean Journal of Nuclear Medicine
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• v.11 no.1
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• pp.17-32
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• 1977

The present study was undertaken to evaluate the significance of the insulin and the C-peptide rseponse to oral glucose loads in normal and diabetic subjects and to establish the effects of the obesity. In this study, the authors have measured plasma insulin and C-peptide by means of radioimmunoassay in 10 nonobese normal, 5 obese normal, 13 nonobese moderate diabetic patients, 9 obese moderate diabetic patients and 9 severe diabetic patients. The results obtained were as follows; 1. In 10 nonobese normal subjects, the plasma insulin level at fasting state and at 30, 60, 90, and 120 min after oral glucose loads were $15.7{\pm}3.4,\;48.3{\pm}9.8,\;40.4{\pm}6.7,\;37.4{\pm}6.5\;and\;26.0{\pm}4.2uU/ml(Mean{\pm}S.E.)$ and C-peptide were $1.9{\pm}0.3,\;3.9{\pm}0.6,\;6.3{\pm}0.6,\;5.7{\pm}0.5\;and\;4.0{\pm}0.5ng/ml$. The change of C-peptide was found to go almost parallel with that of insulin and the insulin value reaches to the highest level at 30 min whereas C-peptide reaches to its peak at 60min. 2. The plasma insulin level in 5 obese normal subjects were $38.9{\pm}12.3,\;59.5{\pm}12.3,\;59.2{\pm}17.1,\;56.1{\pm}20.0\;and\;48.4{\pm}17.2uU/ml$ and the C-peptide were $5.5{\pm}0.4,\;6.8{\pm}0.5,\;7.9{\pm}0.8,\;7.9{\pm}0.8\;and\;7.8{\pm}2.0ng/ml$. The insulin response appeared to be greater than nonobese normal subjects. 3. In 13 nonobese moderate diabetic patients, the plasma insulin levels were $27.1{\pm}4.9,\;44.1{\pm}6.0,\;37.3{\pm}6.6,\;35.5{\pm}8.1\;and\;34.7{\pm}10.7uU/ml$ and the C-peptide levels were $2.7{\pm}0.4,\;4.9{\pm}0.7,\;6.5{\pm}0.5,\;7.0{\pm}0.3\;and\;6.7{\pm}1.0ng/ml$. There was little significance compared to nonobese normal groups but delayed pattern is noted. 4. In 9 obese moderated diabetic patients, the plasma insulin levels were $22.1{\pm}7.9,\;80.0{\pm}19.3,\;108.0{\pm}27.0,\;62.0{\pm}17.6\;and\;55.5{\pm}10.1uU/ml$ and the C-peptide levels were $5.2{\pm}0.4,\;8.0{\pm}1.0,\;10.4{\pm}1.6,\;10.4{\pm}1.7\;and\;10.1{\pm}1.0ng/ml$ and its response was also greater than that of nonobese moderate diabetic patients. 5. The plasma insulin concentrations in 9 severe diabetic subjects were $8.0{\pm}3.8,\;12.1{\pm}3.5,\;16.8{\pm}4.6,\;19.6{\pm}5.2\;and\;15.0{\pm}5.0uU/ml$ and the C-peptide levels were $1.6{\pm}0.3,\;2.4{\pm}0.4,\;4.1{\pm}0.6,\;4.0{\pm}0.8\;and\;4.5{\pm}0.7ng/ml$ and the insulin and C-peptide responses were markedly reduced in severe diabetic groups. 6. There were-significant differences between each groups of patients on the magnitude of total insulin or C-peptide areas, the insulinogenic index and the C-peptide index.

• The Korean Journal of Nuclear Medicine
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• v.39 no.1
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• pp.15-20
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• 2005

Purpose: Physiologic intestinal FDG uptake is frequently observed in asymptomatic individuals for cancer screening FDG PET Colonic FDG accumulation is a well-known confusing findings that interfere true cancer detection or cause false positive. The aim of this study was to evaluate the pattern and intensity of colonic uptake in whole body FDG PET in asymptomatic healthy adults and to correlate them with colonoscopic findings. Materials and Methods: We reviewed retrospectively 64 subjects (age: 27-87, M:F=31:33) who underwent both FDG PET and colonoscopy for cancer screening. FDG uptake patterns were classified as focal, segmental and diffuse. Maximum SUV were measured. The PET results were compared with colonoscopic and histologic findings. Results: In 13 patients FDG bowel uptake was interpreted as focal, in 17 patients as segmental and in 34 patients as diffuse uptake. Six adenomas (17.6%, average diameter=5.0 mm) were found in diffuse pattern, 7 adenomas (41.1%, 5.6 mm) in segmental and 4 adenomas and 1 adenocarcinoma (38.5%, 16.4 mm) in focal uptake pattern. In patients with focal uptake, four were non-adenomatous pathologic lesions (30.8%, 2 intestinal tuberculosis, 2 mucosal ulcer). There is no difference of mean SUV between patients with adenoma and with negative colonoscopic results in each group of intestinal FDG pattern (Diffuse: $1.7{\pm}0.1\;vs.\;1.9{\pm}0.5$, Segmental: $4.8{\pm}3.6\;vs.\;4.2{\pm}1.2$, Focal: $6.5{\pm}4.7\;vs.\;3.5{\pm}1.3$). large adenomas (>1 cm) can be detected more in the focal uptake pattern (4 out of 5) rather than in segmental (1 out of 7) or diffuse uptake (none) and had higher SUV ($6.3{\pm}4.8$) than small adenomas ($3.5{\pm}3.0$) (statistically insignificant). Conclusion: focal FDG uptake is associated more often with large adenoma and other pathologic findings in colonoscopy. Segmental uptake cannot discriminate presence of adenoma from negative results, while diffuse pattern may have more chance to be normal.

• The Korean Journal of Nuclear Medicine
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• v.36 no.6
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• pp.325-332
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• 2002

Purpose: Human Na+/I- symporter (hNIS) is known to be expressed in many tissues other than thyroid gland. The breast cancer cells are one of them and the possibility of radioiodine therapy in treatment of the breast cancer may be suggested. We investigated the expression rate of hNIS and the relationship between the expression of hNIS and the finding of 99mTc-MIBI scintimammographv in the breast cancer Materials and Methods: Surgically proved 56 patients with breast cancer were the subjects of this study The expression of hNIS were evaluated by immunohistochemistry and the results were compared to the findings of 99m7c-MIBI scintimammography. Results: Overall expression rate of hNIS was 41.1% in 56 patients. According to the pathologic diagnosis, it was 42.9% in 49 patients with invasive ductal carcinoma and 28.6% in the 7 patients with ductal carcinoma in situ. The expression rate of hNIS in the 41 cases with a focal increased uptake at he breast lesion on 99m7c-MIBI sointimammogram was 31.7%. That in the 15 cases without any abnormal uptake on the scan was significantly higher(65.7%, p<0.05). Conclusion: The expression rate of hNIS in the patients with breast cancer was not so high. The rate was higher in the patients with no increased uptake at the breast lesion on 99m7c-MIBI scintimammography.

• The Korean Journal of Nuclear Medicine
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• v.33 no.4
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• pp.398-404
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• 1999

Purpose: Diabetic nephropathy is the most common cause of end stage renal disease and the incidence is progressively increasing. The aim of this study was to investigate the differences of $^{99m}Tc$-DMSA renal uptake among diabetic patients with normoalbuminuria, microalbuminuria and overt proteinuria, and then to determine the clinical usefulness of $^{99m}Tc$-DMSA in predicting early diabetic nephropathy Materials and Methods: $^{99m}Tc$-DMSA scan was performed and a total renal uptake of $^{99m}Tc$-DMSA was measured in 145 diabetic patients. Patients were divided into 3 groups according to the amount of 24 hour urinary albumin excretion as Group I (normoalbuminuria, 74 cases), Group II (microalbuminuria, 39 cases), and Group III (overt proteinuria, 32 cases). The differences of $^{99m}Tc$-DMSA renal uptake among the 3 groups and the correlation between the renal uptake of $^{99m}Tc$-DMSA and other clinical parameters were analyzed. Results: The total renal uptake of $^{99m}Tc$-DMSA of Group II ($40.8{\pm}11.0%$) was significantly lower than that of Group I ($54.4{\pm}6.3%$, p<0.001). The uptake of Group III ($27.7{\pm}12.0%$) was significantly lower than those of both Group I and Group II (p<0.001). $^{99m}Tc$-DMSA total renal uptakes correlated negatively with serum creatinine level (r=-0.629, p<0.001) and positively correlated with creatinine clearance rate (r=0.102, p<0.001). Conclusion: $^{99m}Tc$-DMSA total renal uptake of diabetic patients with microalbuminuria was significantly decreased compared with that of patients of normoalbuminuria. Therefore, $^{99m}Tc$-DMSA scan can be used as a diagnostic study for early detection of the diabetic nephropathy.

• The Korean Journal of Nuclear Medicine
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• v.34 no.4
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• pp.312-321
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• 2000

Purpose: The aim of this study was to determine whether crossed cerebellar hyperperfusion (CCH) was helpful in discriminating mesial from lateral temporal lobe epilepsy (TLE) and what other factors were related in the development of CCH on ictal brain SPECT. Materials and Methods: We conducted retrospective analysis in 59 patients with TLE (M:41, F:18; $27.4{\pm}7.8$ years old; mesial TLE: 51, lateral TLE: 8), which was confirmed by invasive EEG and surgical outcome (Engel class I, II). All the patients underwent ictal Tc-99m HMPAO brain SPECT and their injection time from ictal EEG onset on video EEG monitoring ranged from 11 sec to 75 sec ($32.6{\pm}19.5sec$) in 39 patients. Multiple factors including age, TLE subtype (mesial TLE or lateral TLE), propagation pattern (hyperperfusion localized to temporal lobes, spread to adjacent lobes or contralateral hemisphere) and injection time were evaluated for their relationship with CCH using multiple logistic regression analysis Results: CCH was observed in 18 among 59 patients. CCH developed in 29% (15/51) of mesial TLE patients and 38% (3/8) of lateral TLE patients. CCH was associated with propagation pattern; no CCH (0/13) in patients with hyperperfusion localized to temporal lobe, 30% (7/23) in patients with propagation to adjacent lobes, 48% (11/23) to contralateral hemisphere. Multiple logistic regression analysis revealed that propagation pattern (p=0.01) and age (p=0.02) were related to the development of CCH. Conclusion: Crossed cerebellar hyperperfusion in ictal brain SPECT did not help differentiate mesial from lateral temporal lobe epilepsy. Crossed cerebellar hyperperfusion was associated with propagation pattern of temporal lobe epilepsy and age.

• The Korean Journal of Nuclear Medicine
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• v.34 no.4
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• pp.322-335
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• 2000

Purpose: For quantitative estimation of cerebrovascular reserve (CVR), we estimated the cerebral blood flow (CBF) using Lassen's nonlinearity correction algorithm and Tc-99m HMPAO brain SPECT images acquired with consecutive acquisition protocol. Using the values of CBF in basal and acetaBolamide (ACZ) stress states, CBF increase was calculated. Materials and Methods: In 9 normal subjects (age; $72{\pm}4$ years), brain SPECT was performed at basal and ACZ stress states consecutively after injection of 555 MBq and 1,110 MBq of Tc-99m HMPAO, respectively. Cerebellum was automatically extracted as reference region on basal SPECT image using threshold method. Assuming basal CBF of cerebellum as 55 ml/100g/min, CBF was calculated lot every pixel at basal states using Lassen's algorithm. Cerebellar blood flow at stress was estimated comparing counts of cerebellum at rest and ACZ stress and Lassen's algorithm. CBF of every pixel at ACZ stress state was calculated using Lassen's algorithm and ACZ cerebellar count. CVR was calculated by subtracting basal CBF from ACZ stress CBF for every pixel. The percent CVR was calculated by dividing CVR by basal CBF. The CBF and percentage CVR parametric images were generated. Results: The CBF and percentage CVR parametric images were obtained successfully in all the subjects. Global mean CBF were $49.6{\pm}5.5ml/100g/min\;and\;64.4{\pm}10.2ml/100g/min$ at basal and ACZ stress states, respectively. The increase of CBF at ACZ stress state was $14.7{\pm}9.6ml/100g/min$. The global mean percent CVR was 30.7% and was higher than the 13.8% calculated using count images. Conclusion: The blood flow at basal and ACZ stress states and cerebrovascular reserve were estimated using basal/ACZ Tc-99m-HMPAO SPECT images and Lassen's algorithm. Using these values, parametric images for blood flow and cerebrovascular reserve were generated.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.4
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• pp.275-284
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• 2008

Purpose: We intended to evaluate myocardial oxygen consumption ($MVO_2)$ by applying recirculation correction and modified one-compartment model to have a reference range of $MVO_2$ in normal young population and to reveal the effect of recirculation on time-activity curve (TAC). Materials and Methods: In nine normal male volunteers with mean age of $26.3{\pm}4.0$, $MVO_2$ was estimated with 925 MBq (25mCi) of $^{11}C$-Acetate (Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Korea) and PET/CT (Biograph 6, Siemens Medical Solution, Germany). Analysis software such as $MATLAB^{(R)}$ v7.1 (Mathworks, Inc., United States), $Excel^{(R)}$ 2007 (Microsoft, United States), and $SPSS^{(R)}$ v12.0 (Apache Software Foundation, United States) were used. Twenty three frames were of $12{\times}10$, $5{\times}60$, $3{\times}120$, $2{\times}300's$ duration, respectively. The modified one-compartmental model and the recirculation correction method were applied. Statistical analysis was performed by using Test of Normality, ANOVA and Post-Hoc (Scheffe's) analysis, and p-value less than 0.05 was considered as significant. Results: The normal reference ranges of $MVO_2$ were presented as $3.18-4.64\;{\times}\;10^{-4}\;ml/g/sec$, $1.91-3.94\;{\times}\;10^{-4}\;ml/g/sec$, $4.31-6.40\;{\times}\;10^{-4}\;ml/g/sec$, $2.84-4.53\;{\times}\;10^{-4}\;ml/g/sec$ and $3.42-5.00\;{\times}\;10^{-4}\;ml/g/sec$ in the septum, the inferior wall, the lateral wall, the anterior wall and the entire wall, respectively. In addition, it was noted that the dual exponentiality of the clearance curve is due to the recirculation effect and that the characteristic of the curve is essentially mono-exponential. Conclusion: $^{11}C$-Acetate is a radiotracer worthwhile to assess $MVO_2$. Re-circulated $^{11}C$ can influence TAC of $^{11}C$ in myocadia and so the recirculation correction must be considered when measuring $MVO_2$.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.4
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• pp.285-291
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• 2008

Purpose: Although automatic quantification software of myocardial perfusion SPECT provides highly objective and reproducible quantitative measurements, there is still some limitation in the direct use of quantitative measurements. In this study we derived parameters using normal variation of perfusion measurements, and tried to test the usefulness of these parameters. Materials and Methods: In order to calculate normal variation of perfusion measurements on myocardial perfusion SPECT, 55 patients (M:F = 28:27) of low-likelihood for coronary artery disease were enrolled and $^{201}TI$ rest/$^{99m}Tc$-MIBI stress SPECT studies were performed. Using 20-segment model, mean (m) and standard deviation (SD) of perfusion were calculated in each segment. As a myocardial viability assessment group, another 48 patients with known coronary artery disease, who underwent coronary artery bypass graft surgery (CABG) were enrolled. $^{201}TI$ rest/$^{99m}Tc$-MIBI stress / $^{201}TI$ 24-hr delayed SPECT was performed before CABG and SPECT was followed up 3 months after CABG. From the preoperative 24-hr delayed SPECT, $Q_{delay}$ (perfusion measurement), ${\Delta}_{delay}$ ($Q_{delay}$ - m) and $Z_{delay}$ (($Q_{delay}$ - m)/SD) were defined and diagnostic performances of them for myocardial viability were evaluated using area under curve (AUC) on receiver operating characteristic (ROC) curve analysis. Results: Segmental perfusion measurements showed considerable normal variations among segments. In men, the lowest segmental perfusion measurement was $51.8{\pm}6.5$ and the highest segmental perfusion was $87.0{\pm}5.9$, and they are $58.7{\pm}8.1$ and $87.3{\pm}6.0$, respectively in women. In the viability assessment $Q_{delay}$ showed AUC of 0.633, while those for ${\Delta}_{delay}$ and $Z_{delay}$ were 0.735 and 0.716, respectively. The AUCs of ${\Delta}_{delay}$ and $Z_{delay}$ were significantly higher than that of $Q_{delay}$ (p = 0.001 and 0.018, respectively). The diagnostic performance of ${\Delta}_{delay}$, which showed highest AUC, was 85% of sensitivity and 53% of specificity at the optimal cutoff of -24.7. Conclusion: On automatic quantification of myocardial perfusion SPECT, the normal variation of perfusion measurements were considerable among segments. In the viability assessment, the parameters considering normal variation showed better diagnostic performance than the direct perfusion measurement. This study suggests that consideration of normal variation is important in the analysis of measurements on quantitative myocardial perfusion SPECT.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.4
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• pp.292-300
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• 2008

Purpose: Our purpose was to evaluate F-18 FDG uptake in pulmonary lymphangitic carcinomatosis (PLC) according to CT findings and histology of lung cancer. Materials and Methods: Thirty-three lung cancer patients with PLC were enrolled in this retrospective study. All the patients had a CT-based diagnosis of PLC. Chest CT findings of PLC were classified on the basis of involvement of axial interstitium. We categorized the involvement of axial interstitium as group 1, and the involvement of peripheral interstitium only as group 2. Visual and semiquantitative analyses by F-18 FDG PET/CT were performed in the PLC lesions. At first, we analyzed the F-18 FDG uptake in the PLC by visual assessment. If abnormal uptake was seen in the PLC, we drew regions of interest in the PLC lesions to obtain the maximum SUVs (maxSUVs). Results: Of the 33 patients, 22 had abnormal F-18 FDG uptake in the visual assessment. There was no significant difference in the frequency of abnormal F-18 FDG uptake between group 1 and group 2 (p=0.17), although the frequency of group 1 tended to be higher than group 2 (15/19 (78.9%) in group 1, 7/14 (50.0%) in group 2). However, group 1 had a higher maxSUV than group 2 (p<0.01, group 1: $2.9{\pm}1.4$, group 2: $1.5{\pm}0.6$). There was no significant difference in the frequency of abnormal F-18 FDG uptake and maxSUV among the histology of the lung cancers. Conclusion: The involvement of axial interstitium in the PLC by lung cancer has a higher maxSUV than the involvement of only peripheral interstitium.