| [Background]Gastric cancer incidence ranked fourth in all the malignant tumor, with the second mortality rate, seriously endangering human health. Surgery is the most effective treatment, preoperative evaluation of lymph node status and distant metastasis is crucial areas to guide treatment.18F-FDG PET/CT has been routinely used in the diagnosis and clinical staging of malignant tumors, such as lung cancer, lymphoma, colorectal cancer, melanoma, etc. A number of studies have shown that 18F-FDG PET/CT accomplish good in the evaluation of treatment response and prognosis. However, there is a big controversy in the diagnosis of gastric primary tumor and the evaluation of regional lymph node status. Mainly because the conventional PET/CT examination is conducted under fasting state and stomach is always in a state of rhythmic activities, a variety of factors could affect uptake of 18F-FDG and observing PET/CT images. This paper aims to explore the gain value of stomach expansion method in 18F-FDG PET/CT for diagnosis of gastric cancer, through oral milk-diatrizoate contrast agent mixture.[Objective]1. To investigate the value of 18F-FDG PET/CT for diagnosing the gastric cancer using milk and meglumini diatrizoate for filling gastric cavity2. To explore the role of 18F-FDG PET/CT in gastric benign and malignant lesions.3. To discuss the staging value of 18F-FDG PET/CT in patients with gastric cancer.[Materials and Methods]1. Study objectiveSelecting cases with clinical suspicion of gastric cancer examined 18F-FDG PET/CT in the South Hospital PET Center from November 2012 to December 2013. Meet the following conditions are included in the scope of this study: â‘ clinically suspected gastric cancer patients ã‚›ny patients without treatment of gastric cancer â‘¢any patients without previous history of malignancy â‘£all patients were followed up for more than six months 81 patients were eligible for the study after screening, including 50 males and 31 females, with an age range from 23 to 88 years old (average age of 54.3).2. Main equipments and Imaging agentBiography mCTx PET/CT Scanner (Siemens, Germany), PET scanner was 52-ring LSO crystal, and CT was of 128 layers. The imaging agent was 18F-FDG, derived from GE PET trace accelerator (GE, USA), and 18F-FDG was compound by Automatic synthesis (PET Biotechnology Limited Company of Beijing, China) with a radiochemical purity over 95%.3. Imaging methods and conditions3.1 Imaging methodsConventional imaging All the subjects should be fasting more than 6 hours, testing blood glucose level controlled under 10.0mmol/L before the examination, should be injected 5.5MBq/kg 18F-FDG at the hand vein by using the three-way pipe, later lying down in a dark room for around an hour, undergoing PET/CT imaging after urination. The imaging included CT scan and PET scan with a scan range from the head to the middle of the femur,6 to 8 beds. And the CT scanning conditions were: voltage 120kv, current auto-mA, pitch 0.8,0.5 seconds for tube lab rotation,1.2mm collimation width; PET emission scan used 3D acquisition, each scan time was 2 minutes per bed position.Delayed imaging after filling gastric cavity All of patients were orally administrated with the mixture of milk and meglumini diatrizoate for filling the gastric cavity after the finish of routine 18F-FDG PET/CT whole body imaging.10-20 minutes later, regional PET/CT scan for the stomach was performed (since diaphragmatic top scanning a next bed), ensuring adequate coverage of the whole stomach.3.2 Image fusion and Image reconstructionThe PET images were reconstructed by OS-EM method and images attenuation correction used CT data. CT images were reconstructed by the standard reconstruction method. The reconstructed images can be displayed in the cross-section, coronal, sagittal sections and the maximum intensity projection (maximum-intensity image, MIP), with 3.0mm slice thickness. Then PET and CT images were transmitted to the Syngo workstation of Siemens to have the frame to frame image fusion display.4. Image analysis and Diagnostic criteriaPET/CT images were analyzed by two experienced PET center physician blinded simultaneously after understanding of the patient simple history. Determined according to the following image changes:4.1 Qualitative AnalysisMake an evaluation of the primary tumor and metastases according to the location of abnormal uptake, size, shape, number, density changes, distribution and focus radioactive degree of lesions on visual inspection.4.2 Semi-quantitative AnalysisThe uptake lesion used regions of interest uptake foci (ROI) technique, painting the surrounding regions of interest along the lesion, the standard uptake value calculated by the computer (Standardized Uptake Value, SUV), selecting the maximum value (SUVmax).5. Statistical MethodThe statistical analysis adopted SPSS 17.0 software. Categorical data were calculated by chi-square test and measurement data were calculated by t-test. The consistency were calculated by Kappa test. P<0.05 was considered to have significant difference. The SUVmax data was expressed by mean±standard deviation (x±s).[Results]Among the 81 patients, gastric cancer pathologically confirmed were 51 cases, including 4 cases of well differentiated adenocarcinoma,9 cases of moderately differentiated adenocarcinoma,24 cases of poorly differentiated adenocarcinoma,2 cases of malignant gastric ulcer,12 cases of signet-ring cell carcinoma; benign lesions were 30 cases, including 22 cases of gastritis,7 cases of gastric ulcer,1 case of schwannoma.1. The gain value of 18F-FDG PET/CT for diagnosing the gastric cancer using milk and meglumini diatrizoate for filling gastric cavity1.1 The clinical role of PET and PET/CT with and without gastric cavity filling for diagnosing the gastric cancerIn conventional imaging,51 patients with gastric cancer in PET imaging to see 42 cases of gastric high FDG uptake:31 cases were located in the stomach wall,11 cases were difficult to determine for stomach area uptake is caused by gastric cancer or stomach physiological gathering due to the PET image and CT image inaccurate alignment. In the benign group,16 cases show gastric FDG uptake:14 cases difficult to determine due to inaccurate alignment.After filling the gastric cavity,11 cases of gastric cancer group show the lesion of FDG uptake located in the stomach wall. However,9 of 14 cases in the benign group show uptake disappear,3 cases located in the stomach wall,2 cases were still to determine.After the gastric cavity filling, the sensitivity and specificity of PET for gastric cancer improved from 60.7% to 82.3%(χ2=5.829, P=0.016) and from 46.7% to 76.6%(χ2=5.711, P=0.017). However, the sensitivity of PET/CT for the gastric cancer before and after the gastric cavity filling were respectively 88.2%,94.1%, and the specificity were 46.7% and 76.6%, which was not significantly different (χ2 =0.487, P=0.484 and χ2=0.144, P=0.704).1.2 Lesion display differences in gastric cancer patients before and after the gastric cavity fillingThe ratio of lesion display before and after the gastric cavity filling were respectively 4.922±2.753,7.291±3.554. Filling gastric cavity with a mixture of milk and meglumini diatrizoate, the tumor lesion display more clearly (t=6.866, P=0.000).2. The role of 18F-FDG PET/CT image in gastric benign and malignant lesions2.1 In gastric cancer group, the scope of SUVmax was 1.9～23.9, and the average SUVmax was 8.29±4.54. Meanwhile, in gastric benign group, the scope was 2.2～12.7, and the average was 4.24±2.02. The SUVmax of gastric cancer was significantly higher than that of benign lesions (t=5.513, p=0.000)2.2 ROC curve evaluation between gastric cancer and gastric benign lesionROC curve evaluation showed that Area Under the Curve (AUC) between gastric cancer and gastric benign lesion was 0.886 (0.811～0.962). When the cutoff-value was 4.65, the sensitivity and the specificity for the gastric cancer were 82.4%å'Œ86.7%. It was in good consistency with the pathological diagnosis (Kappa=0.667, p=0.000). Compared with SUVmax, the sensitivity and the specificity of PET/CT was no statistical difference (χ2=2.361, P=0.124å'ŒÏ‡2=0.000, P=1.000).2.3 The relationship between 18F-FDG uptake degree and pathological typeThe positive predictive value of 18F-FDG PET in detecting the signet-ring cell carcinoma and other type cell carcinoma were 87.2%(34/39) and 66.7%(8/12) respectively, the difference was no statistically significant (χ2=1.432, P=0.321). However, the difference between the SUVmax of them was statistically significant (t=3.832, P= 0.000)2.4 Analysis of the extent of malignant lesion violations after the gastric cavity fillingIn 48 patients whose PET/CT imaging was positive,43.8%(21/48) gastric lesions appear as focal changed and metabolism significantly higher. These PET and CT images show consistent lesion size. In another 56.2%(27/48) of patients with gastric cancer, the lesion size of PET and CT images are inconsistent:4 cases of them show focal lesions; 23 cases presented as diffuse infiltration. And 19 cases show CT findings range greater than PET, it prompt that CT image change would help to more accurately display and judge the extent of violations, especially in gastric cancer patients with diffuse disease or low 18F-FDG uptake.3. The staging value of 18F-FDG PET/CT in patients with gastric cancer3.1 Gastric primary tumorAmong 81 cases, PET/CT for diagnosing the gastric cancer has 48 true-positive cases,5 false-positive cases,25 true-negative cases,3 false-negative cases. The sensitivity, specificity of PET/CT were 94.1% and 83.3% respectively.5 false-positive cases all showed focal increased metabolism, including 4 cases of radioactivity distribution were significantly higher than the liver. Pathological results were 2 case of gastric ulcer with acute activity and 2 cases of chronic gastric mucosa inflammation. Another 1 case of radioactivity distribution slightly more than liver, was confirmed by endoscopic biopsy to chronic inflammation.3 false-negative cases showed no obvious abnormalities in PET/CT scanning, including 2 cases of early gastric cancer and 1 case of gastric malignant ulcer.There are 42 clear clinical staging cases in 51 patients. The SUVmax of advanced gastric primary foci (8.53±4.56) was significantly higher than that of early gastric primary foci (2.87±0.76)(t=2.134, p=0.038). However,2 cases of 3 early gastric cancer was misdiagnosed.3.2 Lymph nodes metastasesAmong 51 gastric cancer patients,18F-FDG PET/CT discovered 28 cases of regional lymph node metastasis. The sensitivity and specificity of the PET/CT for diagnosing regional lymph node metastasis were 82.3%(28/34) and 82.4%(14/17) respectively.3.3 Distant metastasesAmong 51 gastric cancer patients,21 ones were diagnosed to have metastases in the abdominal cavity and other parts of body.18F-FDG PET/CT detected the metastases in 13 ones (61.9%,13/21). However, PET/CT showed false-negative findings in 8 patients with peritoneal micro-metastases.3.4 The influence of changes in the clinical staging8 cases of 51 patients (15.7%,8/51) dramatically changed the clinical treatment strategies after 18F-FDG PET/CT scanning.6 cases raised to stage IV cancelled the surgery.2 cases exclude clinically suspected liver metastases.[Conclusions]1.18F-FDG PET/CT after filling gastric cavity with milk and meglumini diatrizoate can make up shortage of routine diagnosing the gastric cancer in a fasting state and improve the visualization of the tumor lesion and the scope of tumor invasion.2.18F-FDG PET/CT scanning play an important role in distinguishing gastric malignant lesions from benign lesions. It was in good consistency with the pathological diagnosis.3.18F-FDG PET/CT imaging for part of the signet-ring cell carcinoma and poorly differentiated adenocarcinoma may be false-negative, part of the inflammation may be false-positive. Appropriately raised the threshold of SUVmax can improve the efficacy of PET/CT for diagnosing the gastric cancer.4.18F-FDG PET/CT imaging can provide a comprehensive clinical staging. Due to discovery of more lesions,18F-FDG PET/CT imaging changed the clinical staging, and then affecting the choice of treatment. |
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