Introduction  Biliary atresia (BA) is a obstructive disease of intra and extrahepatic biliary ducts, with an unclear etiology. This disease is progressive and always rapidly result in liver cirrhosis and death. The ideal diagnostic and therapeutic method for it is early discovery and biliary duct drainage in time. Low rate of early discovery is the direct cause of BA patients' poor therapeutic effect, but it is difficult for early distinguishing BA from infantile hepatitis. The BA patients always loss good opportunity of operation for their differential diagnosis. The clinical manifestation of most infantile hepatitis is mainly damage of liver function, and operation can increase the difficulty of treatment for increasing liver damage and postoperative complications, so operation is not a suitable therapeutic method for infantile hepatitis. The clinical manifestation of a few infantile hepatitis patient is mainly obstructive jaundice as BA, with grey or light yellow stool, dark green skin and sclera, and high level of direct bilirubin. So the differential diagnosis of this type infantile hepatitis with BA is difficult and nowadays there is no shortcut, specific and reliable differential diagnostic protocol.  Bile canaliculi hyperplasia occurs in the liver pathologic changes of iso-causive infantile obstructive jaundice, but more obvious in BA. The expression form of the subtype of bile canaliculi epithelial cell Cytokeratin (CK) in BA patient is similar with that of fetal bile duct epithelium, the characteristic of epithelial differentiation is a specific CK subtype expression form, and CK is called the marker of epithelial cell family. Amount of bile duct rapidly hyperplasia, induce amount of matrix depositing in the portal area, may be the main cause of rapid progression of BA hepatic fibrosis. Hepatic fibrosis is the result of excess deposition of liver fibrous tissue, and the synthesis of liver Extracellular matrix (ECM) exceed its degradation. Collagen protein is the most important composition of liver ECM. Therefore, the degree of hepatic fibrosis, different content of collagen protein and bile cancaliculus hyperplasia, will result in the changes of liver parenchyma echogenesis during ultrasound examination.  Nestin is a new discovered, high molecular intermediate filament protein, and is localize in the cytoplasm, and mainly express with time order in the cells which is undifferentiated and with splitting ability. And the investigation of nestin is mainly on its localization, distribution and characteristics. Nestin express in muscular tissue, new formational endothelial cells, pancreatic ductus cells and hepatic Kupffer cells. Under the effect of inflammation and trauma, the interstitial fibroblast produced by epithelial cells take part in the formation of tissue fibrosis, increasing the fiber content of the tissue, then result in the hyperlasia of kelaplasty and hyperplastic scar. Also some investigation has observed that some mount of nestin positive cell exist in the liver development process, and the most common location is outside the liver limiting plate and the bile duct periphery, they are maybe more immature than the liver oval cells, possessing the characteristic of migrating generation and advancing differentiation. Nestin positive cells play an important effect in the liver cellular impairment, but there is no report about their relationship with the BA occurance or development.  With the improvement of ultrasonic equipment and high resolution of the transducer, nowadays the sonogram becomes more and more clear, also with the advanced diagnosing experiences of ultrasonic doctors. However, there is no unified diagnostic criteria for biliary atresia(BA). Our investigation is aim at summarize the sonographic features of BA for approaching the clinical diagnostic value of ultrasonic (US) examination in BA; contrast analysis sonogram and magnetic resonance cholangiopancreatogrphy (MRCP) of BA and cholestatic infantile hepatitis; observing diagnostic and differential quality, and improving the diagnostic accuracy of BA. In this study, according to hepatic fibrosis degrading, collagen protein-IV content semi-determination, and the expression of Cytokeratin 7 (CK7) and Proliferating cell nuclear antigen (PCNA) which reflect the hyperplastic degree or activity of bile canaliculi epithelial cells, we can further evaluate the sonogram and liver fibrosis degree, and the correlative pathological changes including intrahepatic canalicular hyperplasia and collagen protein, approaching the clinical significances of ultrasonography in early diagnosis and prognosis of BA. Initial detect the relationship of intrahepatic nidogen positive cell expression in the infant with BA and the occurance or development of BA.   Materials and Methods  1. Investigated objects  42 infants were referred to us for the evaluation of jaundice, including 17 BA and 25 hepatitis (include 15 cholestatic hepatitis and 10 non-cholestatic hepatitis), male 21, female 21, age 22 day～154 day. 20 infants for normal group, male 16 day, female 4 day, age 21 day～240 day. Fasting for 3-4 hours before the US examination, and sedative should be used when crying.  16 infants of BA group (1 infant was deleted for no MRCP examination) and 6 infants with cholestastic infantile hepatitis (called hepatitis for short) among the infants with hepatitis. were performed both US and MRCP examination.  Hepatic tissue biopsy and fibrosis target were done in 16 infants with BA and 5 cases of the cholestastic hepatitis.  2. Equipments and Methods  Ultrasonic examination Used Kretz Voluson730D 3D Color ultrasonic scanner and Neusoft NAS—1000 Color ultrasonograph, with 7.5-10MHz linear array transducers.  US examination contents: infants in supine position, subcostal and intercostals scanning with multiple cross sections. Observe and note the porta hepatis; size of liver (measure the subcostal liver length using transducer vertical to the costal arch on right clavicular median line); the hepatic parenchyma echoes can be divided into uniform, coarse and enhancement; with or without gallbladder (GB), GB size (length X width) and shape; GB contracting function, which referred to GB contracting ratio = the difference of GB size (length X width) before and after meal/GB size (length X width) before meal X 100%; the intercostals thickness and subcostal length of spleen. Store allthe pictures in PACS system.  MRCP used Elscint 2.0T Prestige MRI equipment, somatic coil. Infants in supine position, first scanned cross section with SE array T1WI and FSE array T2WI, then scanned coronal plane with FSE array double T2WI, each layer thickening 3mm, no interlayer space, collecting two times.  Liver biopsy histological investigation: Hepatic fibrosis grading: using Masson collagen stain assessing the collagen fibrous hyperplastic degree, can be divided into S1-4 grades according to "virus hepatitis prevention and cure program ".   Detect the expression of CK7, PCNA and C-IVusing SP immunohistochemical methods, detect the expression of nidogen positive cell using hybridization in situ method.  Measurement of C-IV photodensity average area percent: collect 5 pictures containing ductus collecting area from each section under 40 times objective lens randomly, using microgram analysis system to detect the average area percent of C-IV in the visual field, which is attained buffy by immunohistochemical positive stain.  CK7 cytoplasm positive stain is buffy, PCNA cell nucleus positive stain is buffy, and nestin positive cell in situ hybridization positive signal appeared cytoplasm stained buffy.  3. Statistics methods  Establish the database using SPSS 12.0 software, date were analyzed and managed by computer  Experimental result  US examination was made with 3.5～5.5 MHz convex array transducer, the sonographic imaging rate of triangular cord, GB, resonance of hepatic parenchyma, common bile duct (CBD) and hepatic artery were significantly lower than those using high frequency linear array transducer. Therefore, all the US examinations in our experiment were using 7.5～10 MHz high frequency linear array transducer.  1. Ultrasonographic features  (1) Detecting rate of triangular cord of porta hepatis in BA group (90%) is significantly higher than that in hepatitis group (8%), and 3 cases shown triangular shape, 6 cases shown tabes shape, with clear boundary and high internal echoes. The final diagnostic rate of BA rises from 14.3% to 90% after the comprehension of triangular cord of porta hepatis sonogram.  (2) Length, width and size of GB in BA group were lower than those in normal group, no difference between BA and hepatitis group, but GB of the hepatitis group always with regular shape, smooth and uniform wall. After treatment, the GB size and shape both became normal. GB shown 3 kinds of shapes in BA group, including empty GB, flat GB and normal size GB, with unsmooth and uniform wall. GB contracting rate 1 hour and 2 hour after meal were both <50%, reflecting GB malcontracting or non-contracting. In cholestastic hepatitis group, the GB contracting rate <50% 1 hour after meal, and >50% 2 hour after meal, showing delayed contracting.  (3) There was no statistic difference of hepatic parenchyma and liver enlargement of BA and hepatitis, but the hepatic parenchyma echo in BA group always become coarse comparing with hepatitis group.  (4) The CBD displaying rate in hepatitis group and normal group were 76% and 75%individually, but in BA group except for 3 type I cases showed CBD cystic dilatation, others showed no CBD displaying. There was no statistic difference of spleen enlargement degree in BA group and hepatitis group. A few infants with BA (7 cases) have ascites, and most distributing in the right or left subhepatic or antehepatic spaces (5 cases), no ascites in hepatitis group.  2. Contrast analysis of sonogram and MRCP  (1) No statistic difference of extrahepatic biliary tract MRCP features between BA group and hepatitis group.  (2) Only 3 cases in BA group (19%, 3/16) revealed circumscribed triangular high signal area of porta hepatis in T2WI coronal plane, which is significantly lower than the detection rate of triangular cord of porta hepatis by US examination (90%). No abnormal signal of porta hepatis in hepatitis group.  (3) In BA group, the revealing rates of GB, liver enlargement and coarse hepatic parenchyma by US examination were higher than those by MRCP, which have statistic differences, and indicating that US examination is more active and accurate than MRCP in diagnosing GB, liver enlargement and hepatic parenchyma status.  (4) Comprehension of triangular cord of porta hepatis sonogram has significantly improved US diagnostic rate of BA, and its accurate ratio, positive predictive value and negative predictive value were also obviously higher than those of MRCP.  3. Correlative analysis of sonogram and histological changes  (1) During the operation 12 cases shown triangular cord of porta hepatis and 5 cases without triangular cord. There was obviously difference of hepatic fibrosis grading by liver biopsy histological investigation among BA group, hepatitis group and normal group, but there was no difference between BA and hepatitis group (P>0.05).  (2) The hepatic parenchyma echo is closely correlated with hepatic fibrosis grading, C-IV content and intrahepatic bile canaliculi hyperplasia. The degree of hepatic parenchyma echo coarse and enhancement increase corresponsively along with the increase of intrahepatic collagen protein C-IV content, hepatic fibrosis grading and intrahepatic bile canaliculi hyperplasia.  (3) Intrahepatic bile canaliculi hyperplasia and hepatic fibrosis degree of cholestatic hepatitis were similar with those of BA group, hense it is difficult to differentiat the tow diseases by pathohistomorphologic changes.  (4) Nestin positive cell expression increased in the portal area and mesenchyma area in both BA group and cholestatic hepatitis group comparing with normal group, and which is in accordance with their pathologic changes including fibrous hyperplasia of portal area, bile canaliculi hyperplasia, multiple interstitial fiber and inflammatory cells infiltrating.  Conclusion  1. The sonogram of triangular cord of porta hepatis with thickness≧ 0.25cm may become the specific ultrasonographic diagnostic criteria for BA. The accurate rate of ultrasonic diagnosing BA, and its positive predictive value and negative predictive value were obviously higher than those of MRCP. US examination is a active, economous, convenient, safe, repeatable and noninvasive method for early diagnosis of BA.  2. The ultrasonic changes of GB is a important indirect feature of BA, and BA correct diagnostic rate can be significantly improved combining with GB contracting function and triangular cord of porta hepatis. There were three forms GB displayed in this study, including empty GB, flat GB and normal size GB. Compared with MRCP, US examination is an active, accurate and more dominant method for observing GB size, shape, wall and GB contracting function.  3. The degree of liver echo coarse can reflect the various degrees of hepatic fibrosis and liver enlargement, providing an objective evidence for clinical early diagnosis and judgment of the prognosis and prediction reasonable clinical therapy for the infants with BA.  4. Introduce a suggestive diagnostic flow-sheet for BA for convenient, shortcut and exactly ultrasonic diagnosis.   5. MRCP can reveal the intrahepatic biliary duct and full view of extrahepatic bile duct, which dominant than US examination. But for MRCP long time imaging, difficult for infant persistent sedation and holding breath, the biliary system imaging of infant is far more worse than that of adult.  6. The degree of pathologic hepatic fibrosis, bile duct hyperplasia and ultrasonic changes of hepatic parenchyma in BA were similar with those in cholestatic hepatitis,. US examination can make a correct differential diagnosis according to observing GB shape and contracting function.  7. Nestin positive cell expressed in the portal area and mesenchyma area in both BA and hepatitis group, indicating that it takes part in the process of fibrosis and inflammation, its character and function still remains for further investigation.