| BackgroundThere is little free fluid in the abdominal cavity of healthy person, which is less than200mL for lubrication of the abdominal organs. Abnormal free fluid, usually more than200mL, aggregating in the abdominal cavity under pathologic conditions is recognized as ascites. Many diseases can cause ascites. Ascites caused by malignant tumor and its metastases is referred to malignant ascites, and ascites caused by other benign diseases, such as hepatic disease, heart disease, renal disease, and nutritional disease is referred to benign ascites.It is the physician’s responsibility to find out the cause of ascites as soon as possible for the patients with undetermined origin ascites. Malignant cells are suspended in the ascites fluid and can form permanent implantations on the peritoneum or on the surface of the abdominal organs. Ascites cytological examination is considered as the gold standard of diagnosing malignant ascites, but its sensitivity is low (usually between30%and50%). Ultrasound, CT, and MRI are mainly used for regional anatomic structure examination. The shapes of abdominal organs are changeable due to the respiratory movement and enterocinesi, and the metastases in peritoneum are usually small and delitescence. In clinical practice, original diseases of many ascites patients could not be determined by routine tests such as ultrasound, CT, MRI, or cytological examination.With the greatly increased clinical application of positron emission tomography/computed tomography (PET/CT), the clinical value of18F-deoxyglucose (18F-FDG) PET/CT has been highlighted in the diagnosis of tumor diagnosis and staging. Consequently,18F-FDG PET/CT scans might be a useful option for examination of those patients with undetermined origin ascites. However,18F-FDG is a non-specific tracer agent that can be absorbed by malignant tumor or a few benign diseases and sometimes even not be absorbed by some malignant tumors, consequently causing the problem of false-positive or false-negative in tumor localization by18F-FDG PET/CT. Double-phase imaging has proved to be a good method to enhance the diagnostic efficiency of F-FDG PET/CT for many disease such as pulmonary lesions. Some information about FDG metabolism in ascites might be obtained through the measurement of the standard uptake value (SUV) of ascites and the observation of18F-FDG PET/CT images. Nevertheless, little information has been reported on ascites metabolism to date.This study paid main attention to the differential diagnostic value of double-phase imaging and ascites metabolism measurement for ascites patients when performing18F-FDG PET-CT scan. The two parts below were included:1) The diagnostic value of18F-FDG PET-CT double phase imaging in primary tumor and metastasis localization for ascites patients2) Ascites metabolism measurement enhanced diagnostic value and prognostic evaluation in18F-FDG PET/CT for malignant ascites patients. Objective:Recently, accompany with the clinical application of positron emission tomography/computed tomography (PET/CT), the clinical value of18F-deoxyglucose (18F-FDG) PET/CT has been highlighted in the diagnosis and staging of malignant tumors.18F-FDG PET/CT has a high sensitivity that can detect malignant tumors in early stage due to their characteristics of high metabolic rate of glucose (MRGlc). The shapes of abdominal organs are changeable due to the respiratory movement and enterocinesi, and the metastases in peritoneum are usually small and delitescence, consequently causing the problem of false-positive or false-negative in tumor Iocalization by routine F-FDG PET/CT imaging. In this paper, Double-phase imaging and gastrointestinal tract contrast medium were used in18F-FDG PET/CT scan in order to enhance the diagnostic efficiency of primary tumor and metastasis localization for ascites patients.Methods:This was a retrospective study.89patients who were referred for18F-FDG PET/CT double phase imaging to determine the original cause of their ascites in October2010to October2012were reviewed for all their medical records. All patients including68of malignant ascites and21of benign ascites were confirmed by follow up such as CT, MRI, supersound, abdominal speculum, repeated ascites cytology or histopathology. There were no history of malignant tumor exairesis and other treatment for all cases. The interpretation of F-FDG PET/CT images and CT image was based on the consensus of two nuclear medicine physicians and two radiology physicians respectively. The maximum SUV (SUVmax) of primary tumor, metastasis, and the peritoneum of benign ascites patients were measured by elliptic region of interest (ROI) tools in fusion images. Those patients without positive results in primary tumor and metastasis in F-FDG PET/CT localization, the same region of the malignant lesions determined in follow up was used for SUVmax measurement. Statistical analysis was performed by PASW Statistics18software and the result with P<0.05was considered as statistically significant. The sensitivity, specificity and accuracy were calculated and compared by X2-test or Fisher’s analysis among F-FDG PET/CT tumor localization and CT images based on the primary tumor and metastasis in peritoneum respectively. SUVmax of the primary tumor and metastasis or peritoneum were measured and checked by t-test. The value of increased rate of delay imaging (IRDI) was calculated by double phase PET/CT imaging. The ROC curve was used to analyze the diagnostic efficiency of F-FDG PET/CT routing imaging and delay imaging in metastasis of peritoneum according to SUVmax.Results:The sensitivity and accuracy of18F-FDG PET/CT double phase imaging in primary tumor localization of ascites patients were76.5%and74.2%. The sensitivity and accuracy of CT were54.4%and53.9%. The former were higher than the latter (X2=7.31,7.90; P all<0.05). Delay imaging promoted the sensitivity of18F-FDG PET/CT for primary tumor of ascites patients, especially for the patients with primary hepatic carcinoma, gastric cancer, and pancreatic carcinoma.The sensitivity, specificity, accuracy and positive predictive value of F-FDG PET/CT double phase imaging in peritoneum metastasis localization of ascites patients were64.7%,85.7%,69.7%, and93.6%. Those of CT were47.1%,57.1%,49.4%, and78.1%. The former were higher than the latter (X2=4.29,4.20,7.56,4.51; P all<0.05).The IRDI of primary tumors calculated by double phases PET/CT imaging was (45.0±63.1)%, those of peritoneum metastasis and benign lesions in peritoneum were (13.6±41.2)%and (-8.0±27.6)%. The latter was much lower than the two formers (t=3.71,2.22; Pall<0.05).SUVmax>3.0in routine imaging and delay imaging, IRDI>15%in double phases imaging discriminated primary malignant tumor efficiently. SUVmax>2.0in delay imaging, IRDI>10%in double phases imaging discriminated peritoneum metastasis efficiently. The area under ROC curve of SUVmax in delay imaging was the larger than that of routine imaging and IRDI in double phases imaging.Conclusion:18F-FDG PET/CT double phase imaging promoted the diagnostic efficiency in primary tumor localization of ascites patients, which could demonstrate the continuous uptake of FDG in gastrointestinal primary tumor.18F-FDG PET/CT double phase imaging accompany with the use of gastrointestinal tract contrast medium could successfully promote the diagnostic accuracy of peritoneum metastasis for ascites patients.SUVmax>3.0in18F-FDG PET/CT routine or delay imaging or IRDI>15%could be considered as efficient index to promoted the diagnostic efficiency in primary tumor localization of ascites patients.SUVmax measurement in’8F-FDG PET/CT double phase imaging is a good method to promote the diagnostic efficiency of peritoneum metastasis for ascites patients. SUVmax>2.0in delay imaging or IRDI>10%in double phases imaging were good index for peritoneum metastasis discriminated diagnosis. ObjectiveWith the greatly increased clinical application of positron emission tomography/computed tomography (PET/CT), the clinical value of F-deoxyglucose (18F-FDG) PET/CT has been highlighted in the diagnosis of malignant ascites. However, F-FDG is a non-specific tracer agent that can be absorbed by malignant tumor or a few benign diseases and sometimes even not be absorbed by some malignant tumors, consequently causing the problem of false-positive or false-negative in tumor localization by F-FDG PET/CT. To date, little information has been reported on ascites metabolism. Nevertheless, some information about FDG metabolism in ascites might be obtained through the measurement of the standard uptake value (SUV) of ascites and the observation of F-FDG PET/CT images. This study aimed to evaluate the role of ascites metabolism measurement in F-FDG PET/CT for auxiliary diagnosis and prognostic evaluation of malignant ascites.MethodsThis study reviewed all the medical records of55patients that underwent F-FDG PET/CT to determine the original cause of ascites. Among these55cases of ascites patients,36cases were malignant ascites and19cases were benign ascites. All patients underwent ascites CEA, ascites CA125, ascites CA199and ascites cytology examinations before or within two weeks after F-FDG PET/CT scans. The patients with negative results of ascites cytology were confirmed by clinical follow-up (including CT, MRI, supersound, abdominal speculum, repeated ascites cytology or histopathology). F-FDG PET/CT scan was performed on a PET/CT system. The scan field ranged from the head to middle of the thigh. Seven to8bed positions were usually required and the emission images were acquired for2.5min per bed position. Delayed imaging was performed50to90min after the first PET/CT scan according to the requirements of diagnosis.The mean SUV (SUVmean) of ascites and liver were measured by elliptic region of interest (ROI) tools in fusion images. The SUV ratio of ascites and liver, denoted as T/NT, was calculated based on the SUVmean. The interpretation of18F-FDG PET/CT images was based on the consensus of two nuclear medicine physicians. Ascites metabolism measurement was based on the value of T/NT and the experience of nuclear medicine physicians. Ascites metabolism measurement was defined as positive if the ascites was found to increase the radioactivity uptake or the shapes of the liver and spleen were vague in maximum intensity projection (MIP) images. Otherwise, it was defined as negative. If definite lumps or abnormal metabolic foci were not found in F-FDG PET/CT images or they were found but interpreted as benign disease or no definite diagnosis was given, the18F-FDG PET/CT tumor localization was defined as negative. On the contrary, if definite abnormal metabolic foci or abnormal lumps were found and an interpretation of malignant tumor or metastasis was given, the F-FDG PET/CT tumor localization was defined as positive.Ascites cytology examination was performed before the first18F-FDG PET/CT or two weeks after. If malignant tumor cells were found, the result of ascites cytology examination was defined as positive. On the contrary, it was defined as negative.Statistical analysis was performed by PASW Statistics18software and the result with P<0.05was considered as statistically significant. The sensitivity, specificity and accuracy were calculated and compared by X2-test or Fisher’s analysis among F-FDG PET/CT ascites metabolism measurement, tumor localization, and ascites cytology examination. SUVmean of the ascites and liver were measured and the T/NT value was calculated and checked by t-test. The ROC curve was used to analyze the diagnostic efficiency of ascites T/NT, ascites CEA, ascites CA125, and ascites CA199. And the linear regression was used to analyze the relationship between ascites T/NT and the survival time of patients.Results In cases of malignant ascites, the characteristics of immersed liver and spleen could be seen in those patients with widespread tiny metastasis in peritoneum in MIP images. In slice images of those patients, increased radioactive uptake was seen around peritoneum and intestinal canal, and the ascites metabolic level was lower in center and higher on verge. The sensitivity and accuracy of ascites metabolism measurement were higher than those of ascites cytology examination (X2=6.98,4.58; P all<0.05). The specificity of ascites metabolism measurement was higher than that of18F-FDG PET/CT tumor localization (X2=5.70, P<0.05).The SUVmean of malignant ascites in routine imaging wasl.37±0.38. That of benign ascites was0.72±0.22. the former was higher than the latter (i=6.82, P<0.05). Based on the criteria of SUVmean>1.0, the sensitivity, specificity and accuracy were77.8%,84.2%, and81.8%respectively. The T/NT values of benign and malignant ascites were0.38±0.10and0.68±0.17, respectively, indicating that the latter was higher than the former (t=7.21, P<0.05). Nevertheless, the T/NT value of malignant ascites patients with positive results of ascites cytology examination was0.76±0.14, and that with negative results was0.62±0.16, indicating that the former was higher than the latter (t=2.80; P<0.05). Based on the criteria of T/NT>0.5, the sensitivity, specificity and accuracy were86.1%,78.9%, and83.6%respectively.The area under ROC curve of T/NTmean in routine imaging, T/NTmean in delay imaging, SUVmean in routine imaging, SUVmea,in delay imaging, ascites CEA, ascites CA125and ascites CA199was0.837(P<0.01),0.871(P<0.01),0.805(P<0.01),0.836(P<0.01),0.707(P<0.05),0.561(P=0.463) and0.664(P<0.05), respectively. The area under ROC curve of SUVmean and T/NTmean were the larger than others. The area under ROC curve of ascites CA125was lower due to its abnormal increase in some benign ascites such as hepatic cirrhosis ascites and tuberculous ascites. There was a negative correlation between the survival of patients with malignant ascites and ascites T/NT (r=-0.647, P<0.01). The higher the ascites metabolism level was, the shorter survival time the patient would have.Conclusion1. In cases of malignant ascites, the characteristics of immersed liver and spleen could be seen in those patients with widespread tiny metastasis in peritoneum in18F-FDG PET/CT MIP images.Ascites metabolism measurement was good for differential diagnosis of malignant ascites, and has an important auxiliary diagnostic value for ascites patients.2. The SUV ratio of ascites and liver in18F-FDG PET/CT imaging, denoted as T/NT, was helpful to determine the nature of ascites diagnosis. SUVmean>1.0and T/NTmean>0.5were good index for differential diagnosis of ascites. The T/NT and SUVmean of ascites were better than ascites CEA, ascites CA125, and ascites CA199in differential diagnosis of ascites.3. There was a negative correlation between the survival of patients with malignant ascites and ascites T/NTmean, which may be a good index for prognostic evaluation of malignant ascites... |
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