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유병혁,지광훈 대한원격탐사학회 2009 大韓遠隔探査學會誌 Vol.25 No.3
Multi-temporal satellite imagery can be changed into a transform image that emphasizes the changed area only through the application of various change detection techniques. From the transform image, an automated change detection model calculates the optimal threshold value for classifying the changed and unchanged areas. However, the model can cause undesirable results when the histogram of the transform image is unbalanced. This is because the model uses a single threshold value in which the sign is either positive or negative and its value is constant (e.g. -1, 1), regardless of the imbalance between changed pixels. This paper proposes an advanced method that can improve accuracy by applying separate threshold values according to the increased or decreased range of the changed pixels. It applies multiple threshold values based on the cumulative producer? and user? accuracies in the automated binary change detection model, and the analyst can automatically extract more accurate optimal threshold values. Multi-temporal IKONOS satellite imagery for the Daejeon area was used to test the proposed method. A total of 16 transformation results were applied to the two study sites, and optimal threshold values were determined using accuracy assessment curves. The experiment showed that the accuracy of most transform images is improved by applying multiple threshold values. The proposed method is expected to be used in various study fields, such as detection of illegal urban building, detection of the damaged area in a disaster, etc.
Prognostic Factors in Stage IB Gastric Cancer after Surgical Resection
유병혁,박지연,박기범,권오경,이승수,정호영 대한위암학회 2020 Journal of gastric cancer Vol.20 No.3
Purpose: The standard treatment for stage IB gastric cancer is curative surgery alone, but some patients show poor survival with disease recurrence after curative surgery. The aim of this study was to identify prognostic factors of recurrence and long-term survival in patients with stage IB gastric cancer after surgery. Materials and Methods: We retrospectively reviewed data from 253 patients with stage IB gastric cancer who underwent gastrectomy between 2011 and 2016 at Kyungpook National University Chilgok Hospital and analyzed the clinicopathological characteristics associated with recurrence and survival. Results: Fourteen patients experienced recurrence with a mean follow-up of 54.1 months. Two of these patients had locoregional recurrence and 12 patients had systemic recurrence. The median interval between the operation day and the day of recurrence was 11 months (range 4–56 months). Multivariate analysis revealed that lymphatic vessel invasion (LVI) (hazard ratio [HR], 3.851; 95% confidence interval [CI], 1.264–11.732) and the elderly (age≥65) (HR, 3.850; 95% CI, 1.157–12.809) were independent risk factors for recurrence after surgery. The LVI (HR, 3.630; 95% CI, 1.105–11.923) was the independent prognostic factors for disease-specific survival (DSS). The 5-year DSS rates were 96.8% in patients who did not have LVI, and 89.3% in patients who had LVI. Conclusions: This study shows that LVI was associated with recurrence and poor survival in patients with stage IB gastric cancer after curative gastrectomy. Patients diagnosed with LVI require careful attention for systemic recurrence during the follow-up period.