Application Of High Field MR Diffusion Weighted Imaging In Preoperative Evaluation And Prognosis Evaluation Of Resectable Gastric Cancer

Part one Value of high field MR diffusion weighted imaging in preoperative evaluation of resectable gastric cancerObjective Gastric cancer is one of the most common malignant tumors in human digestive system,and its incidence and mortality are at the top of the list for a long time.In China,80%gastric cancer patients were the advanced stage at diagnosis.The mortality rate was 25.2/10 million,accounting for 23.2%of the total death of malignant tumors.Surgical resection is the most important and effective method for gastric cancer,and the criteria of radical resection are:(1)without liver,peritoneum or other distant metastasis;(2)the tumor can be resected together with the metastatic lymph nodes and the surrounding viscera;(3)no residual cancer cells were found at the end of the fracture.Preoperative accurate medical imaging examinations can help evaluate the extent and degree of invasion of the gastric cancer,and evaluate the exact TNM staging,which is important for clinicians to choose individualized treatment and to evaluate the effect of treatment and prognosis.Moreover,it can avoid unnecessary laparotomy.Endoscopic ultrasonography(EUS)and computed tomography(CT)are the most common imaging examinations to evaluate gastric cancer.For diagnosis of gastric lymph node metastasis,they are mainly based on the size and shape of lymph nodes,and there is lack of uniform standards.Therefore,the sensitivity,specificity and accuracy of the diagnosis are not high.In clinical practice,normal lymph nodes at different sites can be different in size.Swollen lymph nodes are not all metastases,and some may be caused by inflammatory reactions.Metastatic lymph nodes are not always enlarged,and lymph nodes of normal size may also have been metastasized.Magnetic resonance imaging(MRI)has high soft tissue resolution and high spatial resolution,and there is no potential radiation damage and kidney toxicity of iodinated contrast.With the rapid development of MRI imaging equipment and imaging technology,MRI scanning speed,and imaging quality have been greatly improved,which makes MRI more and more widely used in the examination and diagnosis of abdominal diseases.By selecting suitable imaging sequences and parameters,high-quality MRI images of stomach and adjacent organs and tissues can be obtained.It provides a new method for the imaging examination of gastric cancer.Diffusion weighted imaging(DWI)is one of the fMRI imaging,which re:flects the microscopic movement of water molecules.By measuring the degree of diffusion of water molecules in living tissues,it can reflect the function of normal organs and tissues,and the composition and internal structure of diseased tissues.It is a noninvasive method to detect tumor.The dispersion of water molecules in living tissues is expressed mainly by signal intensity and apparent diffusion coefficients(ADC)values on DWI images.Studies have found that ADC can help to differentiate benign and malignant lesions.The cell density of malignant lesions is high,diffusion is limited,and the ADC value is low.Usuda et al study found that DWI was better than PET-CT in both the detection of primary focus and the evaluation of peripheral lymph node metastasis in non-small cell lung cancer.The aim of this study was to compare the pathological findings to the value of DWI combined with conventional MRI in preoperative T staging,lymph node metastasis evaluation and N staging in gastric cancer,in order to integrate DWI into clinical practice,and provide more favorable means and help preoperative staging of gastric cancer.MethodsThe study was reviewed and approved by the medical ethics committee of our hospital.All the patients in the study were informed consent and signed informed consent.From December 2013 to December 2016,68 patients were enrolled in this study.Inclusion criteria:(1)gastric carcinoma was confirmed by pathology;(2)no magnetic resonance imaging contraindication;(3)MRI can show the tumor;(4)no contraindications;(5)the function of heart and liver is basically normal and can tolerate the operation.Exclusion criteria:(1)with other organ metastasis;(2)having the history of malignant tumor or finding malignant tumors at the same time;3)received neoadjuvant chemotherapy before surgery;(4)magnetic resonance imaging is contraindicated;(5)MRI images are poor quality and can not be used for diagnosis.Finally,53 patients(36 males,17 females,age range:38-79 years,mean age 57.25±9.13 years)were included in the study.MRI scan,DWI(b=0,800s/mm2)and dynamic contrast enhanced scan were performed in 53 patients.The MRI scan was performed by T2WI fast recovery fast spin echo(FRFSE)with fat suppression and no fat suppression,with respiratory gated.If the motion artifact was severe,T2WI single-shot fast spin echo(SSFSE)sequence and T1WI fast spoiled gradient recalled echo(FSPGR)were performed.DWI used single-shot echo planar imaging(SS-EPI)sequences,the b values were 0s/mm2 and 800s/mm2,respectively.The enhanced scan was performed with breath holding LAVA dynamic enhanced scan.The elbow vein was injected into Dimeglumine Gadopentetic Acid Injection by a high pressure syringe,with a dose of 0.1mmol/kg and an injection rate of 2ml/s.The MRI image data were independently interpreted by two magnetic resonance diagnostic physicians(with more than 10 years experience in MRI diagnosis)without knowing the histopathological findings.In the case of inconsistent interpretation,diagnoses were made by the third physician with more experienced(with MRI diagnosis experience for more than 15 years).Measurements of lymph node ADC values:First,the lymph nodes were observed on the DWI image,and the location of the target lymph nodes on the ADC map was determined.Draw 3 regions of interest(ROI)manually at the largest cross section of lymph node..ROI was about 3/4 of the maximum cross sectional area;pay attention to avoid the necrosis area,the blood vessel and the edge.The average was recordas the ADCmin value of the lymph node.T staging criteria of gastric cancer MRI:T1:The tumor invades mucous membranes,low signal areas in submucosa is intact or irregular,and no invading the muscularis propria;T2:The tumor invades the muscularis propria,interrupts the low signal area of the submucosa,and shows a slightly lower signal on the outside of the muscularis propria;T3:The tumor invades the lower layer of the tunica propria.The lower part of the muscularis propria is vague and disappears,and the low signal band of the gastric serosa and the surrounding gastric fat is still clear;T4a:The tumor invades the serosal membrane,blurring the low signal band between the gastric serosa and the surrounding stomach fat and separating the fat between the surrounding organs;T4b:The tumor invades adjacent organs.N staging criteria of gastric cancer MRI:N0:no regional lymph node metastasis;N1:1-2 regional lymph nodes have metastasis;N2:3-6 regional lymph nodes have metastasis;N3:7 or more than 7 regional lymph nodes have metastasis,N3a:7-15 regional lymph nodes have metastasis;N3b:16 and even more regional lymph nodes have metastasis.The specimens and lymph nodes of gastric cancer were histopathologically analyzed.By observing the adjacent structures of the lymph nodes and the surrounding structures on the MRI,such as the structures of the blood vessels and bone muscles,the localization was simulated with the surgeons to ensure the localization accuracy of the lymph nodes.The pathological staging adopted the seventh edition UICC international standard for staging of gastric cancer(TNM).ResultsT and N staging were performed according to the seventh edition of UICC international staging criteria for TNM staging of gastric cancer after surgery.There were 4 cases with stage T1,17 cases in stage T2,19 cases in stage T3,13 cases in stage T4,11 cases in stage T4a,2 cases in stage T4b,21 cases in stage N0,6 cases in stage N1,9 cases in stage N2,17 cases in stage N3,among them 12 cases in stage N3a,5 cases in stage N3b.The overall accuracy of T staging of MRI was 86.8%.A total of 7 patients did not agree with the postoperative pathological staging.The accuracy of T1,T2,T3 and T4 was 75%,82.3%,89.5%,and 92.3%,respectively.271 lymph nodes were detected on DWI,including 206 metastatic lymph nodes(76%),which showed high signal or obvious high signal on DWI.Microscopically,the tumor cells were found in normal lymph nodes.The tumor cells showed obvious atypia,large nuclei,small cytoplasm and large volume.There were 65 non metastatic lymph nodes,with a slightly higher signal or higher signal,and slightly lower signal on the ADC map.Microscopically,they showed enlargement of the medullary sinus and enlargement and increas of lymph follicles in normal lymphocytes.The ADCmin value of the metastatic lymph nodes and non metastatic lymph nodes were(1,005±0.057)×10-3mm2/s,and(1.339±0.169)×10-3mm2/s,respectively;there was a significance differece(P<0.001).The ADCmin value determined that the ROC area under the lymph node metastasis of gastric lymph nodes was 0.894.When the optimum threshold was 1.140×10-3mm2/s,the sensitivity and specificity was 87.7%,and 76.2%,respectively.Compared with pathological N staging,the total accuracy of N staging in gastric cancer was 75.4%by ADCmin value.The accuracy of N0,N1,N2 and N3 were 90.4%,66.6%,66.6%and 64.7%.,respectively.ConclusionThe accuracy of DWI combined with conventional MRI to judge T staging of gastric cancer is higher,which can provide an important method for preoperative T staging of gastric cancer;ADCmin is a noninvasive and quantitative biomarker for gastric lymph node metastasis diagnosis,and it can be used to evaluate the preoperative N staging of gastric cancer.Part two Evaluation of invasion and prognosis of resectable gastric cancer by apparent diffusion coefficientObjective Recent advances in diffusion weighted imaging(DWI)have confirmed its potential value in the study of gastrointestinal diseases.In DWI,the pathological tissue is characterized by signals that are significantly higher than normal structures.Through the measurement of apparent diffusion coefficient(ADC)value,DWI reflects the movement of water molecules in biological tissues,and the pathological cell density is high,cell gap is small,resulting in water molecule diffusion limited and low ADC value.As a quantitative parameter,ADC has been of great value in predicting tumor prognosis and evaluating the efficacy of neoadjuvant chemotherapy.This study investigated the value of ADCmin in assessing the aggressiveness and prognosis of resectable gastric cancer by comparing it with pathological findings.MethodsA retrospective analysis of the patient’s imaging data of MRI scan,DWI scan and dynamic contrast enhanced scan in our hospital from December 2013 to December 2016 was performed.A total of 62 patients(40 males,22 females,age range:38-81 years old,mean age:56.13±8.26 years old)were included in our study.Inclusion criteria:(1)the MRI images were clear and clearly showed the tumor;(2)no neoadjuvant chemotherapy was performed before surgery;(3)in accordance with the indications of operation and underwent radical gastrectomy after the complete examinations.MRI scan,DWI(b=0,800s/mm2)and dynamic contrast enhanced scan were performed in 62 patients.The MRI scan was performed by T2WI fast recovery fast spin echo(FRFSE)with fat suppression and no fat suppression,with respiratory gated.If the motion artifact was severe,then T2WI single-shot fast spin echo(SSFSE)sequence,and T1WI fast spoiled gradient recalled echo(FSPGR)were added.DWI used single-shot echo planar imaging(SS-EPI)sequences,and the b values were Os/mm2 and 800s/mm2,respectively.The enhanced scan was performed with fat suppressed breath holding LAVA dynamic enhanced scan.The elbow vein was injected into Magnevist Solution by a high pressure syringe,with a dose of 0.1mmol/kg and an injection rate of 2ml/s.The MRI image data were independently interpreted by two magnetic resonance diagnostic physicians(with more than 10 years experience in MRI diagnosis)without knowing the histopathological findings.In the case of inconsistent interpretation,the third physician with more experienced diagnoses were made(with a magnetic resonance diagnosis experience for more than 15 years).Measurements of gastric cancer ADC values:On the ADC map,the largest level of gastric cancer was selected and the region of interest(ROI)was drawn by hand.Pay attention to avoiding vascular and cystic necrotic areas,and ROI was placed in the lowest signal area of the tumor.Each physician measured 3 times,and recorded the minimum ADC value,taking the mean of the two as the final ADCmin value.In order to accurately identify cancer foci,the DWI sequence and the dynamic enhancement scan sequence were used to draw the ROI.The pathological staging adopted the seventh edition UICC international standard for staging of gastric cancer(TNM).SPSS 18 statistical software was used to analyze the measured data,P<0.05 means statistically significant.Results T and N staging were performed according to the seventh edition of UICC international staging criteria for TNM staging of gastric cancer after surgery.There were 5 cases with stage T1,18 cases in stage T2,22 cases in stage T3,17 cases in stage T4,12 cases in stage T4a,5 cases in stage T4b,23 cases in stage N0,7 cases in stage N1,11 cases in stage N2,21 cases in stage N3,among them 14 cases in stage N3a,7 cases in stage N3b.The ADCmin value decreased with the increase of T staging.The differences between T1-3 and T4,between T2 and T3,and between T1-2 and T3-4 were statistically significant,P<0.001.The ADCmin value decreased with the increase of N staging.The differences between N0 and N1-3,between N0 and N1,and between N2 and N3a were statistically significant,P<0.001.The value of ADCmin decreased with the increase of clinical pathological stages.Moreover,there was a significant difference between stage Ⅰ and stage Ⅱ,stage Ⅱ andⅢ,which was statistically significant,P<0.001.The ADCmin value was determined to be 1.04×10-3mm2/s,which could separate the stage Ⅲ with stage Ⅱ and stage Ⅰ of gastric cancer.The ADCmin value was determined to be 1.2×10-3mm2/s,which could separate the stage Ⅱ with stage Ⅰof gastric cancer.Conclusion As a non-invasive and quantitative biological marker,ADCmin,is of important value in evaluating the invasiveness of gastric cancer.According to the seventh edition of UICC international staging criteria for TNM staging of gastric cancer,the ADCmin value can assist in the risk classification and prognostic evaluation of gastric cancer.