| Part One Feasibility of Material Suppressed Iodine Images Derived from Spectral CT in Evaluating Gastric Tumors Objective:To assess the feasibility of VNE images derived from single-source fast k Vp-switching dual-energy CT, namely MSI images in evaluating gastric tumors. Materials and Methods:The institutional review board of the first affiliated hospital of Zhengzhou university approved this prospective study; all patients provided written informed consent. From December 2013 to June 2015, 103 patients(63 men, 40 women; age range 20-87, median age 54) with gastric tumors underwent preoperative enhanced CT that included TNE with conventional 120 k Vp mode, AP and VP with GSI mode on Discover GSI CT scanner. MSI images were acquired from enhanced images of AP. Two abdominal radiologists independently evaluated the image quality of TNE and MSI images using a 5-point scale. Interobserver agreement was accessed by kappa value. The sensitivity for lesions on TNE and MSI images were evaluated. The CT number of various regions and image noise was measured on TNE and MSI images. The relative enhancement CT value of lesions, CNR of gastric tumors and effective radiation doses for triple-phase and dual-phase protocol were calculated. Differences were tested for statistical significance using Wilcoxon signed rank test and paired t-test. Results:The diagnoses of these 103 patients were confirmed by endoscopic biopsy or surgical pathology(gastric cancer, n=86; gastric stromal tumor, n=9; gastric lymphoma, n=6; gastric schwannoma, n=2). Interobserver agreement about image quality was excellent. No significant difference in image subjective quality score and definition was found between TNE(4.32±0.53),(3.86±0.50) and MSI(4.21±0.51),(3.73±0.55) images(both P>0.05). Neither in the sensitivities for gastric tumors, lymph node and liver metastasis. The CT number of gastric tumors, liver metastasis and aorta, image noise on MSI images were slightly higher than on TNE images(P<0.05). The CT number of lymph nodes, liver and muscle, CT relative enhancement value of gastric tumors, lymph nodes and liver metastasis had no significant difference between TNE and MSI images(all P>0.05). The CNR of gastric tumor on MSI images was higher than that on TNE images(P<0.001). The effective dose for triple-phase was 25.1 m Sv±6.2 and that for dual-phase was 17.7m Sv±4.1. The dose saving by removing the TNE was 7.5 m Sv(30.5%). Conclusion:1.In patients with gastric tumors, the MSI images derived from single-source fast k Vp-switching dual-energy CT can provide comparable image quality to TNE images and reliable diagnostic information.2.MSI images replacing TNE images will lower radiation dose by 30.5%.Part Two Multivariate Analysis of Spectral CT in Predicting Lymph Node Metastasis in Gastric Cancer Objective:To evaluate the features of primary gastric cancer and lymph nodes in spectral CT images and to investigate the relevant features of gastric cancer which are associated with lymph node metastasis. We attempted to predict lymph nodes metastasis in patients with gastric cancer by multi-factors logistic regression and to investigate the diagnosis threshold and diagnostic efficiency of each factor. Materials and Methods:From December 2013 to June 2015, 86 patients(53 men, 33 women; age range 22-87, median age 53) with gastric cancer confirmed by gastroscope pathology underwent preoperative enhanced CT that included nonenhanced CT with conventional 120 k Vp mode, AP and VP with GSI mode on Discover GSI CT scanner.The raw data were transfered to ADW4.6 postprocessing workstation to reconstruct the monochromatic images at 70 ke V and iodine based images in AP and VP with 1.25 mm thickness. The locations of primary gastric cancer, growth pattern, maximum diameter of tumors, infiltration of peritumor fat, the CT attenuation and iodine value of primary of gastric cancer were evaluated and recorded. The short diameter, long diameter, the ratio of short to long diameter, the CT attenuation and iodine value of lymph nodes were measured and recorded. The relationship between lymph nodes metastasis of gastric cancer patients and the spectral CT features of primary gastric cancer and lymph nodes itself were evaluated by c2 test, multi-factor logistic regression analysis, t test and ROC curves. Results:Among these 86 gastric cancer patients, which diagnosis was confirmed by surgical pathology, 64 cases had lymph nodes metastasis and 22 without. Among 1072 lymph nodes found in operation, 412 nodes were positive and 660 were negative. Among 552 lymph nodes found in CT images, 338 nodes were positive and 214 were negative. Single factor analysis showed that the gender and age of patients, the location of gastric cancer, the CT number of gastric cancer in nonenhanced and AP, the iodine value of gastric cancer in AP had no significant difference between positive and negative lymph nodes. The growth pattern, maximum diameter of tumors, infiltration of peritumor fat, differentiation types, the CT attenuation and iodine value of primary of gastric cancer in VP had obvious relationship with the lymph nodes metastasis of gastric cancer. The infiltration of peritumor fat was the main risk factor, which OR value was 13.154.The results of t test showed that the short diameter, the ratio of short to long diameter, the CT attenuation and iodine value in every phase of positive lymph nodes were higher than these of negative lymph nodes. The area under curve of ROC of the short diameter, the ratio of short to long diameter, the CT attenuation in precontrast, AP and VP, the iodine value in AP and VP of lymph nodes were 0.600, 0.880, 0.648, 0.832, 0.755, 0.864, 0.835, respectively. Taking the ratio of short to long diameter over 0.725 as diagnosis standard, the sensitivity was 75.6% and the specificity was 93.5%. Taking the CT number in AP over 49.75 HU as diagnosis standard, the sensitivity was 66.9% and the specificity was 88.8%. Taking the CT number in VP over 59.80 HU as diagnosis standard, the sensitivity was 69.9% and the specificity was 77.6%. Taking the iodine value in AP over 9.65(100ug/cm3) as diagnosis standard, the sensitivity was 80.4% and the specificity was 82.2%. Taking the iodine value in VP over 15.65(100ug/cm3) as diagnosis standard, the sensitivity was 69.9% and the specificity was 86.9%. Combined the ratio of short to long diameter with the iodine value in AP, the sensitivity was 95.2% and the specificity was 76.9%. Conclusion:1.Some parameters of primary gastric cancer in spectral CT images, including tumor growth pattern, maximum diameter of tumors, infiltration of peritumor fat, differentiation types, the CT attenuation and iodine value of primary of gastric cancer in VP can predict the lymph node metastasis, and the infiltration of peritumor fat was the main risk factor.2.The ratio of short to long diameter, the iodine value in AP and VP and the CT attenuation in AP and VP of lymph nodes are important criteria to evaluate the lymph nodes metastasis of gastric cancer patients. |
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