Ultrasound represents the primary imaging method used for the evaluation of the biliary tree in patients with cholestatic jaundice. The performance of the method is good in the detection of biliary dilations and satisfactory in the detection of the cause of obstruction. It is highly cost-effective and, when performed by an experienced examiner, it plays a central role in the diagnostic algorithm of extrahepatic cholestasis (1). Depending on the access to other diagnostic means, ultrasound is combined with more effective non-invasive investigations, in the first place cholangio - NMR (which provides highly accurate information on the whole biliary tree, with the visualization of Vater's papilla), as well as retrograde endoscopic cholangiography (an invasive method considered as the gold standard, having a diagnostic and therapeutic value) (1).
The study was prospective and was performed in patients with known pathology. The study group included 35 subjects, of which 26 with the clinical and functional biochemical diagnosis of extrahepatic cholestasis and 9 with no clinical complaints or signs of biliary disease. The group of 26 patients (12 women, 14 men) included: 9 patients with primary bile duct tumors (1 intrahepatic, 1 in the right hepatic duct, 6 in the hilum, 1 in the middle common bile duct, 1 in the lower common bile duct), 5 patients with pancreatic tumors (head of the pancreas), 10 with main bile duct lithiasis (of which 4 cholecystectomized), 2 with congenital cysts of the extrahepatic bile ducts. All patients (except for 1 with a hepatic tumor in the hilum) - underwent retrograde endoscopic cholangiography.
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A General Electric GE7 ultrasound machine equipped with a 2D transducer with variable frequencies (2-7 MHz) and a 3D transducer (frequencies 2-5 MHz) was used. This equipment contains all the usual programs of the 2006 production year and stores the information in a row data system, which allows image processing after the patient has left the department of ultrasonography as if the examination was performed "de novo". The images were processed using the ultrasonographic equipment. All patients were examined under fasting conditions and before noon.
The 2D ultrasound examination was performed using a known procedure: using the right hypocondrium and intercostal spaces as an ultrasound window, the patient was asked to remain in apnea for a convenient time period in order to ensure an as complete and accurate as possible examination.
The 3D ultrasound examination followed immediately the 2D exploration, being intended for the intrahepatic (right, left, hilum) and extrahepatic ducts (the whole main bile duct). The gallbladder was included in the volume examined by scanning, being used as a guide mark in order to certify the correctness of the investigation of the hepatic hilum.
The technique of the sampling and processing of the volume had several steps: a) choice of the area of interest in 2D mode; b) adjustment of the equipment in order to take a medium sized volume, from a depth beyond the area of interest, with a maximum quality of acquisition; c) adjustment of the equipment for the static 3D mode; d) acquisition of the volume (during the acquisition, the patient remained in apnea for a total duration no longer than 10 seconds); e) processing of the information obtained in the volume using the multiplanar mode with the positioning of the area of maximum interest in the center of the image; f) processing of the reference sections and the volume obtained using the correction of the gain and echo threshold; g) correction of the spatial position of the area of interest and its placement in the most intelligible anatomic variant; h) use of the transparent mode, and then, of the inverse mode; i) change from the multiplanar function to the unique volume function; j) interpretation of the voxel with rotation in latero-lateral and cranio-caudal direction and processing for an as good as possible visualization of the bile ducts in terms of spatial position, anatomic pathway, definition of dilation and identification of the obstruction.
In order to interpret the information, the following were taken into consideration: 1. confirmation of bile ducts dilation (existence of parallel / extrahepatic ductal structures that achieve the sign of the "double duct"); 2. identification and definition of the obstruction; 3. relevance of the ultrasound image (visibility and evidence of the bile ducts, gallbladder and the neighbouring structures, with the aim of increasing the reliability of the US image both for the main examiner and for a second examiner, possibly a surgeon). The assessment was performed based on the absence / presence for items (1) and (2), and on a scale very good, good, poor, unsatisfactory, for item (3).
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All the examinations were performed by one examiner, having over 10 years of experience in ultrasonographic practice.
Applying the inverse function over the transparent mode made it easy to evidence the transsonic structures (fig. 1 a.b.).
In the control group (9 patients) the following results were obtained: 2D US evidenced the intra- and extra-hepatic bile ducts and the gallbladder in 9 cases; image relevance was very good in 8 and good in one case; 3D US evidenced the intra- and extra-hepatic bile ducts in 4 cases (gallbladder was evidenced in all the cases), with a very good image relevance in all the 4 cases (figs. 2 a.b. and 3).
The performance of the 2D and 3D ultrasound in the diagnosis and description of extrahepatic cholestasis (26 patients) was assessed based on the site of the obstruction, as related to the insertion of the cystic duct into the common bile duct.
Two subgroups were identified from this point of view:
a. A subgroup with low biliary obstruction - below the cystic - common bile duct junction (17 cases, of which 5 pancreatic head tumours, 2 common bile duct tumours, 10 common bile duct lithiasis). 2 D evidenced the dilated bile ducts in all the cases; image relevance was very good in 11 cases and good in 6 cases; 3D evidenced the dilated bile ducts in 15 cases (figs. 4 a.b., 5, 6 and 7 a.b.) with a very good and good image in 9 and 8 cases respectively.
b. A subgroup with high biliary obstruction - above the cystic - common bile duct junction (9 cases, of which 6 hilum tumours, 1 right hepatic duct tumour, 2 bile duct cysts). 2D evidenced the dilated bile ducts in all the cases, image relevance was very good in 5 and good in 2 cases respectively; 3D evidenced biliary dilations with a very good image relevance in all the cases (figs. 8 a.b; 9 a.b; 10 a.b; 11 a.b.c.d.; 12. a.b.c.d).
Ultrasound is the most widely used imaging method, which is due to its non-invasive and non-radiating character, the absence of documented side effects, its non-painful and non-bleeding nature, as well as to its relatively high accuracy allowing the detection of tumor formations up to 1 mm in size. Conventional ultrasound uses, by definition, planes or sections through the anatomic areas of interest. The limitations of this method are known, the most important one being represented by the planar or two dimensional character (2D). These limitations result in an impossibility to obtain information on the coronal plane for unpaired organs situated on the median line of the body, information which is sometimes required for a better tumor staging or just for a better understanding of normal topography. The two-dimensional character of the investigation also prevents a better representation of the surfaces of normal or pathological structures, information that is frequently "reconstructed" in the examiner's imagination, which confers a marked subjectivity to the ultrasonographic method (2).
The technological improvements of the past 10 years, such as the development of special representation programs, the use of extremely fast processors and the construction of specialized transducers with concomitant two-dimensional scanning, have led to the achievement and implementation of the three-dimensional (3D) technique in ultrasound (3).
Three-dimensional ultrasound can be performed concomitantly with 2D ultrasound or it can be resumed and finalized in a second stage, by the use of an external work station, after the patient has left the department. This is represented by a network computer connected to the ultrasound machine, which functions as a second examining machine.
Information is acquired by manual or automatic scanning. The most used modality of volume acquisition is the automatic scanning technique that uses a special transducer allowing concomitantly the obtaining of two perpendicular planes. Over the whole duration of volume acquisition, the transducer is maintained still focused on the area of interest. The method consists of the selection of an area of interest called reference section that should be of an as good as possible quality on 2D ultrasound; the final ultrasound volume will be centered by this reference area and will consist of an equal number of planes situated on both sides of it.
The quality of the image of the volume obtained depends on the global dimension of the scanned area, the scanning angle, the tissue depth at which scanning is performed and the accuracy of the image (preselected by the user, possible in 5 steps).
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The most numerous applications of 3D ultrasound at present are gynecologic and obstetric (4, 5). Recently, studies have shown that this method can also be useful in abdominal pathology (3, 6). This category includes the applications used for the assessment of functional and morphological pathology (especially tumor staging) in digestive tract diseases (7, 8).
In liver pathology, 3D ultrasound can detect aspects related to the presence and extension of parenchymal restructuring in cirrhosis (9). The method allows, by the cut-out technique, a search for small sized nodules in a preselected hepatic volume. Tumors up to 10 mm in size can be accurately detected and information on their position in relation to the reference vessels: hepatic veins, portal veins, and inferior vena cava, can be obtained. Using the volume function, accurate information on the real size of a tumor mass can be obtained and oncological safety elements can be added, including the application of a parenchymal layer with predetermined thickness that might allow the surgeon to assess the tissue volume to be removed. This information is particularly important, as it may be a decisive element in establishing whether surgery is indicated or for choosing another therapeutic solution such as radiofrequency ablation or percutaneous alcoholization (10). Inverse mode ultrasound combined with the transparent mode allows the evidencing of cystic or hypoechogenic tumors that can be measured in a total volume using the "volume threshold" function, which is extremely useful for the follow-up of the remission of certain hepatic tumors under chemotherapy (10).
In this way, the study of the relation between tumor formations and hepatic vessels becomes considerably easier. Contrast enhanced vascular 3D ultrasound can better characterize spatial distribution, vascular architecture, as well as the type of tumor vascularization, allowing the identification of specific vascular models, in a manner similar to angiographic techniques (11).
The exploration of the gallbladder and bile ducts represents a new challenge for 3D ultrasound. The performance of conventional 2D ultrasound for the evaluation of biliary pathology is well known, this being the first imaging technique carried out in the sick patient, depending on which subsequent investigations are performed. The method has well-known limitations, among which the fact that it depends on the ultrasonographist and the relevance of the diagnostic image varies according to the mode in which this has been obtained (2).
It is extremely useful, for surgeons in particular, to understand the spatial position of a structure at the level of the biliary tree in relation to hepatic segmentation. The operative strategy and the final results often depend on this component.
Three-dimensional ultrasound allows the spatial representation of anatomic structures and facilitates, by means of special software, the spatial rotation of the volume and a cut-out within it. The best known 3D application at the level of the bile ducts is the transparent mode which allows the visualization of the bile ducts within the hepatic parenchyma (12). However, the 3D examination of the bile ducts in this mode is rather difficult because of the similarity between vascular structures and biliary structures, which cannot be differentiated from one another. The hepatic texture that is moulded on the bile ducts adds to this difficulty.
Three-dimensional ultrasound using the transparent mode can be optimized by the use of the inverse mode, which eliminates these inconveniences and may be considered a technical advancement. Thus, the bile ducts and the hepatic vessels are seen much more distinctly and the surrounding hepatic parenchyma is practically eliminated from the image, which makes the investigation considerably easier.
The bile ducts and the hepatic vessels can be relatively easily differentiated by the rotation of the volume around the longitudinal axis, which allows their dissociation. In addition, the rotation of the volume around a transverse axis allows the exploration of the hepatic hilum, the examination being highly similar to intraoperative macroscopic examination.
Normal bile ducts are more visible intrahepatically, over shorter distances. Depending on the patient's status, very convincing images can be obtained related to the appearance of the gallbladder (shape, size, presence of anomalies) and of the intra/extrahepatic bile ducts. A predictable application of 3D ultrasound of normal bile ducts is a better understanding and illustration of biliary anomalies (anatomic variants or malformations).
The diagnostic performance of 3D ultrasound increases when the bile ducts are dilated. The explanation is that cystic aspects are easier to evidence using the transparent and inverse mode software. The spatial disposition of the bile ducts is more eloquent and the distance between the hepatic ducts in the case of a Klatskin tumor is easier to assess by this technique. The best known application of this method is the characterization of biliary cysts whose spatial distribution is extremely easy to evidence (13).
Three-dimensional ultrasound of the bile ducts does not have the same diagnostic value as 2D ultrasound, being in fact complementary to the latter. The diagnosis of biliary lithiasis and the detection of small sized tumors are limited by the still unsatisfactory accuracy of the method. In addition, the investigation of the ampullary region is extremely difficult, the technique being subject to the principle limitations of ultrasound: meteorism, obesity, lack of cooperation. The main contribution of the technique is image relevance for the examiner (increasing confidence in diagnosis) as well as for the surgeon. The use of cut-out software in association with the change of image algorithms such as "threshold" could bring the 3D ultrasound image closer to MRI cholangiography, allowing, at the same time, the navigation within the biliary tree in a manner similar to CT cholangioscopy (14).
The introduction of this technique into clinical practice is relatively recent, therefore more extensive studies over longer periods and on larger patient groups are expected in order to assess its usefulness in routine examinations.
Conclusions. Three-dimensional ultrasound represents a complementary technique to conventional 2D ultrasound, as it provides a spatial representation of the bile ducts and the gallbladder. Its diagnostic value is represented by the confirmation of bile duct dilations, the identification of the site of the obstruction and the superior quality visualization of the cystic formations. The method is highly illustrative and considerably increases confidence in diagnosis. The duration of the procedure is insignificant.