Concordance of second-order portal venous and biliary tract anatomies on MDCT angiography and MDCT cholangiography

OBJECTIVE: We sought to investigate the concordance between second-order portal venous and biliary tract anatomies using MDCT angiography and MDCT cholangiography. MATERIALS AND METHODS: We retrospectively identified 56 living related potential liver donors who underwent both MDCT angiography and MDCT cholangiography. Two reviewers independently rated axial images and 3D reconstructions of MDCT angiograms and cholangiograms as diagnostic or nondiagnostic with respect to depiction of second-order portal venous and biliary tract anatomies. In images rated as diagnostic, second-order portal venous and biliary tract anatomies were categorized as conventional or variant. The concordance between portal venous and biliary tract anatomies was analyzed using McNemar exact chi-square test. RESULTS: All examinations were diagnostic. Second-order portal venous variants were seen in 10 (18%) and biliary branch variants were seen in 23 (41%) of the 56 patients. Patients with variant portal venous anatomy (6/10, 60%) were more likely to have variant biliary tract anatomy than patients with conventional portal venous anatomy (17/46, 37%; p < 0.01). The sensitivity of variant portal venous anatomy as a marker for variant biliary anatomy was 26% (6/23 patients). CONCLUSION: Concordance between second-order portal venous and biliary tract anatomies is statistically significant. However, in our series, a number of patients with conventional portal venous anatomy had variant biliary anatomy; therefore, the finding of conventional portal venous anatomy does not obviate preoperative biliary tract imaging in patients before liver donation.     

MR angiography and dynamic flow evaluation of the portal venous system

We studied the value of MR angiographic techniques in imaging the portal venous system. Projection angiograms were created by postprocessing a series of two-dimensional, flow-compensated gradient-echo images. Flow velocity was determined by a bolus-tracking method with radiofrequency tagging and multiple data readout periods. Each image was acquired during a breath-hold. MR angiography was applied to six normal subjects and four patients with abnormal hemodynamics in the portal venous system. Flow velocity determined by MR was correlated with the results of duplex sonography. The main portal vein and intrahepatic branches were shown in all cases. Portosystemic collaterals were identified in all patients with portal hypertension. In normal subjects, peak flow velocities (17.9 +/- 2.8 cm/sec) on MR correlated well with values determined by duplex sonography (17.5 +/- 2.2 cm/sec) (r = .846, p less than .04). Reversed portal blood flow was shown in two patients. One patient with portal vein thrombosis had no evidence of flow by MR angiography. Our results indicate that MR angiography can provide a three-dimensional display of normal and abnormal vascular anatomy as well as functional information in the portal venous system.     

Relationship between vascular and biliary anatomy in living liver donors

OBJECTIVE: The objective of our study was to determine whether there is an association between portal venous or hepatic arterial branching patterns (or both) and biliary anatomic variants. MATERIALS AND METHODS: Two radiologists independently reviewed preoperative hepatic CT scans and intraoperative cholangiograms from 39 consecutive living liver donors. The portal venous and hepatic arterial anatomy was classified on the basis of the preoperative CT scans and the biliary anatomy was classified on the basis the intraoperative cholangiograms into one of two groups: conventional or anomalous. Variables were tested for association using Fisher's exact test. RESULTS: Anomalous vascular branching variants were common, being present in 23 (59%) of 39 patients. Hepatic arterial anomalies were present in 18 (46%); portal venous anomalies, in seven (18%); and both, in two (5%). Biliary anomalies were present in 15 (38%) of the 39 patients. Of the 23 patients with anomalous vascular anatomy, seven (30%) had biliary anomalies. Of the 16 patients with conventional vascular anatomy, eight (50%) had biliary anomalies. There was no significant association between hepatic arterial anomalies, portal venous anomalies, or the combination of arterial and portal venous anomalies and anomalous biliary drainage. CONCLUSION: Portal venous and hepatic arterial branching patterns do not correlate well with biliary anatomic variants. In patients with normal hepatic vascular anatomy, biliary anomalies are common.     

Projection arteriography and venography: initial clinical results with MR

Motion currently limits the applications of magnetic resonance (MR) angiography in certain regions of the body. To overcome this problem, a series of breath-hold, two-dimensional, flow-compensated gradient-echo images were acquired. These images were then processed by means of the maximum intensity projection algorithm to produce projection angiograms. The method was evaluated in 10 healthy subjects and in 12 patients and validated by comparing conventional angiograms, contrast material-enhanced computed tomographic scans, and duplex sonograms with MR projection arteriograms and venograms of the chest, abdomen, and pelvis. The aorta and pulmonary arteries and their branches were demonstrated, as was detailed anatomy of the hepatic and portal venous systems and inferior vena cava. Renal arteries and veins could be studied in both native and transplanted kidneys. The method permits determination of flow direction and differentiation of arteries and veins and is superior to three-dimensional acquisition techniques for imaging slow blood flow. Initial results suggest that the method may have clinical applications for a variety of vascular disorders.     

Normal venous anatomy of the brain: demonstration with gadopentetate dimeglumine in enhanced 3-D MR angiography

This investigation evaluates whether gadopentetate dimeglumine enhancement of three-dimensional (3-D) acquisition MR angiography can generate clinically useful images of the normal venous anatomy of the brain. 3-D MR angiography of normal cerebral arterial anatomy has made rapid progress, although demonstration of detailed venous anatomy with similar techniques has been much less revealing. To overcome the limitation of slow venous flow, IV gadopentetate dimeglumine contrast enhancement was used to alter the relaxation times of blood, thus augmenting the venous signal. Several groups of patients were evaluated: we studied eight patients both with and without contrast enhancement, 20 patients and volunteers with multiple techniques to determine optimal technical parameters, and seven patients in whom enhanced MR studies were compared with standard selective biplane cut-film arterial angiograms. Only the large dural sinuses (such as the transverse sinus) could be seen on unenhanced studies owing to the saturation of slowly flowing venous spins. With contrast enhancement, many of the important small and large cerebral venous structures were routinely seen with reasonable scanning times (7 min). The venous anatomy was well seen for approximately one-half hour after injection and correlated well with angiograms. There are several important limitations to this technique, including a limited field of view, variable visibility of specific veins owing to technical and physiologic factors, confusion of enhancing non-flow-related structures, and lack of detailed physiologic information. Single excitation 3-D MR angiograms are insensitive in the evaluation of cerebral venous structures. Enhancement with gadopentetate dimeglumine affords rapid scanning and excellent visualization of the pertinent venous anatomy. The best image quality was obtained with a sequence of 50/7/30 degrees (TR/TE/flip angle).     

Angiography of segmental pancreatic transplants

Arteriography was routinely performed in patients with suspected vascular complications after pancreas transplantation. Dysfunction of the grafts was suggested by 99mTc-DTPA scanning and metabolic tests. Thirty arteriograms obtained in 25 patients were evaluated. Nineteen conventional film angiograms and 11 intraarterial DSA were performed. Five different angiographic patterns were observed: normal vascular anatomy, low-flow phenomenon, arterial or venous thrombosis, and venous neovascularity. On the basis of the angiographic findings, various reasons for graft failure were identified. Recipient venous collaterals or well-functioning grafts without angiographically detectable blood supply were observed in 9 cases, and must be considered to represent neovascularisation by donor and recipient vessels.     

Portal hypertension evaluated by MR imaging

Thirteen patients with portal hypertension were examined by magnetic resonance (MR) imaging, using spin-echo sequences, and by visceral angiography. Data from this group were compared with the MR images and angiograms of 20 patients without portal hypertension. MR imaging demonstrated two of three cases of portal vein occlusion and four of five cases of occlusion of the retropancreatic portion of the superior mesenteric vein. Two thirds of the patients with portal hypertension and patent portal veins had marked MR signal within the main portal vein on MR images. Little or no signal was present in the portal veins of the 20 patients without portal hypertension. Our experience indicates that marked intraportal MR signal can be seen in patients with portal hypertension with or without venous occlusion. In some cases the size and distribution of venous collaterals allow one to distinguish between venous occlusion and other causes of portal hypertension. MR images confirmed the patency of distal splenorenal shunts in two patients studied.     

An improved method of estimating the portal venous fraction of total hepatic blood flow from computerized radionuclide angiography

The measurement of portal venous flow to the liver is important in the evaluation of patients for shunt surgery. A previous report described a method using slope analysis of hepatic radionuclide angiograms to generate an index of relative portal flow, which correlated well with angiographic grades of portal perfusion. The present report describes a refinement in bolus administration and a modification in technique that appear to reflect true portal venous flow more accurately. A total of 109 studies was performed, including seven normal and 80 cirrhotic patients. The method was reproducible (r = 0.998) and showed good correlation with the angiographic grades of perfusion (r = -0.906).     

Hepatic blood supply: comparison of optimized dual phase contrast-enhanced three-dimensional MR angiography and digital subtraction angiography

PURPOSE: To optimize and determine the value of dual-phase contrast material-enhanced three-dimensional (3D) magnetic resonance (MR) angiography for preoperative evaluation of the blood supply to the liver. MATERIALS AND METHODS: Dual phase 3D MR angiography of the hepatic arteries and portal vein was performed in 140 patients. In 80 patients, the value of fat saturation, digital image subtraction, an anticholinergic agent, and a high-caloric meal were evaluated. In the next 60 patients, MR angiographic and digital subtraction angiographic (DSA) image quality and diagnostic value were compared. RESULTS: Fat-saturated images were of significantly better quality (P < .01) than non-fat-saturated images. Digital image subtraction was useful in only 23 of 40 patients. The injection of an anticholinergic agent was superfluous, whereas administration of a high-caloric meal helped in demonstration of the superior mesenteric artery and portal vein. Classification on MR angiograms of the arterial blood supply was correct in 57 of 60 patients. All arterial and portal venous lesions were seen on MR angiograms, and MR angiograms had a significantly higher subjective image-quality ranking than did DSA images in the evaluation of the portal vein (P < .05). CONCLUSION: Fat saturation and use of a high-caloric meal improve the results of MR angiography of hepatic vessels. MR angiography was comparable to DSA for evaluation of the arterial system and was superior for demonstration of the portal vein; therefore, MR angiography could replace intraarterial DSA.     

Multi-detector row CT of relevant vascular anatomy of the surgical plane in split-liver transplantation

PURPOSE: To evaluate relevant arterial and venous anatomy of the hepatectomy plane lateral to segment IV by using multi-detector row computed tomography (CT) with respect to adult living related transplantation of the right lobe of the liver. MATERIALS AND METHODS: In potential liver donors, 100 consecutive hepatic CT angiograms were obtained after intravenous bolus administration of 150-180 mL of nonionic contrast material. Arterial phase images (1.25-mm collimation, 7.5 mm/ 0.8-second table speed) were acquired after test dose injection. Portal phase images were acquired at 60 seconds (2.5-mm collimation, 15 mm/0.8-second table speed). Postprocessing depicted arterial, portal, and hepatic vein anatomy traversing the anticipated surgical hepatectomy plane to the right of the middle hepatic vein (MHV) and separating the right and left lobes of the liver. Two radiologists interpreted the images, and data were agreed on by consensus. Data collected included intrahepatic anatomy and origin of the artery and vein supplying segment IV; the venous drainage from segments V and VIII; and the presence, size, and distance from the right hepatic vein (RHV) confluence of accessory hepatic veins in the surgical plane. RESULTS: Thirty-one donors had conventional hepatic vascular anatomy. Vessels that traversed the hepatectomy plane included the artery supplying segment IV in seven (7%) patients, dominant portal vein supply to segment IV from the right portal vein in two (2%) patients or from both right and left portal vein branches in three (3%) patients, segment VIII draining into the MHV in 67 (67%) patients or both the MHV and RHV in 18 (18%) patients (the major draining vein was >7 mm in diameter in 23%), segment V draining into the MHV in 10 (10%) patients, or both the MHV and RHV in 19 (19%) patients (the major draining vein from segment V was 7-10 mm in diameter in 70 patients, and larger than 10 mm in five). Forty-four accessory hepatic veins were identified in 40 patients; seven drained segment V, while the majority drained segments VI and VII. The mean diameter was 5.3 mm and 45% were larger than 6 mm. The average distance to the RHV-inferior vena cava confluence was 28.7 mm. Of 70 patients with drainage from segment V into RHV, 22 (31%) had an accessory RHV. However, atypical drainage into the MHV was noted in seven (70%) of 10 patients and into the MHV and RHV in 11 (58%) of 19 patients. CONCLUSION: In the majority of potential donors, CT angiography depicted a wide range of vascular anatomic variations that traverse the hepatectomy plane.     

The peribiliary vascular plexus: the microvascular architecture of the bile duct in the rabbit and in clinical cases

The livers of 30 rabbits were perfused with a silicone rubber solution (Microfil), underwent a clearing process, and were examined with a dissection microscope. The study showed distinct vascular plexuses in and around the bile duct, and two concentric vascular layers present within its wall: the inner capillary and the outer venous. Around the bile duct there was a fine arterial network and a larger venous plexus, which communicated with the capillary and venous plexuses of the bile duct, respectively. The venous plexuses drained directly into the sinusoids or indirectly through the portal vein. The microvascular architecture of the rabbit bile duct correlated well with clinical angiograms exhibiting normal and abnormal peribiliary vascular plexuses. The arterial and venous plexuses dilated and provided collateral circulation in both extrahepatic and intrahepatic arterial and portal vein occlusions, respectively. The peribiliary arteries may be dilated or encased in patients with cholangiocarcinoma or hepatocellular carcinoma invading the bile duct. The animal study and observations on angiograms suggest the existence of transplexal arterioportal communication.     

Intracranial vascular lesions: optimization and clinical evaluation of three-dimensional time-of-flight MR angiography

The clinical value of three-dimensional time-of-flight magnetic resonance (MR) angiography was prospectively evaluated in 26 patients with congenital intracranial vascular lesions; 12 had arteriovenous malformations (AVMs), and 14 had venous angiomas. In the initial phase of the study the entire region of interest was imaged with one large acquisition volume (60-120-mm-thick slab). Later, the angiograms were obtained with adjacent but slightly overlapping, 30-mm-thick slabs, which clearly improved vascular detail. Gadolinium enhancement slightly improved depiction of veins but not of arteries. MR angiograms were compared with available conventional angiograms and MR studies. The topography of the AVM nidus was equally well appreciated on the MR as on the conventional angiograms. However, in six of 12 patients the hyperdynamic afferent arteries were incompletely shown on MR angiograms because of incomplete rephrasing. In three patients, venous drainage was also incompletely visualized. Compared with conventional MR studies, MR angiography offered the same detection rate but better anatomic insight. Thirteen of the 14 venous angiomas were also identified on MR angiograms. Detailed imaging, however, necessitated gadolinium enhancement and thin-slab acquisition.     

Congenital and acquired anomalies of the portal venous system.

Knowledge of the normal anatomy, most frequent variants, and congenital and acquired anomalies of the portal venous system is of great importance for liver surgery and interventional procedures such as creation of transjugular intrahepatic portosystemic shunts. Radiologic studies of the portal venous system include color Doppler ultrasonography (US), computed tomography (CT), magnetic resonance imaging, and arterial or direct portography. Among the most common branching variants of the portal vein are trifurcation, right anterior portal branch arising from the left portal vein, and right posterior portal branch arising from the main portal vein. Agenesis of the right or left portal vein is the most frequently reported congenital anomaly. Venous collateral vessels due to portal hypertension and cavernous transformation of the portal vein are best evaluated with cross-sectional imaging. Intrahepatic portosystemic, arterioportal, and arteriosystemic fistulas and associated perfusion anomalies have characteristic features at dual-phase helical CT. Color Doppler US is the single most useful tool for demonstration of aneurysms of the portal venous system and bland or neoplastic portal vein thrombosis. CT is also the best means of evaluating gas in the portal venous system, which is no longer an ominous sign and must be differentiated from aerobilia.     

Preoperative evaluation of the entire hepatic vasculature in living liver donors with use of contrast-enhanced MR angiography and true fast imaging with steady-state precession

PURPOSE: To preoperatively assess the entire hepatic vasculature in living related liver donors with use of a combination of contrast material-enhanced magnetic resonance (MR) angiography and true fast imaging with steady-state precession (FISP). MATERIALS AND METHODS: Twenty-five living potential liver donors were examined preoperatively on a 1.5T Siemens Sonata system. Twenty-four underwent surgery and two had catheter angiography performed to delineate complex anatomy. Contiguous 5-mm-thick, sub-second true FISP images of the liver were initially obtained during breath-holding in axial and coronal planes (repetition time [TR]/echo time [TE], 3.2/1.6; flip angle, 70 degrees ). MR angiography was performed with use of a three-dimensional (3D) gradient-echo fast low-angle shot (FLASH) pulse sequence (TR/TE, 3.0/1.2; flip angle, 25 degrees ), with 40 mL of Gadolinium DTPA injected at a rate of 2 mL/sec. One precontrast and two postcontrast coronal 3D volumes were acquired, each in a 20-second breath-hold, and two subtracted 3D sets were calculated. Arterial anatomy was assessed with use of maximum-intensity projection, volume rendering, and multiplanar reformatting algorithms. Hepatic and portal venous anatomy was evaluated with use of the true FISP images and the venous phase of the MR angiogram. Visualization of hepatic arterial branches was noted. Visualization of portal vein branches was scored on a scale of 0-5. The presence of anatomic variants was noted. Vascular anatomy was confirmed at the time of surgery and at catheter angiography. RESULTS: Segmental branch vessels were visualized on MR angiography in the majority of cases. The segment four branch was identified in 96% patients. Variant arterial anatomy was seen in 50% of patients. MR angiography detected 10 of 11 arterial variants found at surgery and angiography. Visualization of portal vein branches was generally higher with true FISP compared to MR angiography. Twenty-four percent of patients had variant portal venous anatomy. Caudal hepatic veins were identified in 60% of patients, of which eight were significant (>5 mm). Hepatic and portal venous anatomy was accurately predicted by true FISP and MR angiography in all patients who went on to undergo surgery. CONCLUSION: Preoperative imaging with use of a combination of contrast-enhanced MR angiography and true FISP provides a comprehensive assessment of the entire hepatic vasculature in living liver donors.     

Duplex Doppler examination in portal hypertension: technique and anatomy

Three hundred fifty duplex Doppler examinations were performed in 195 patients (150 adults and 45 children) with radiologically and/or clinically proved portal hypertension. In this paper we describe this duplex Doppler technique for the qualitative assessment of splanchnic venous hemodynamics in these patients. The caliber of and the presence and direction of flow in the following veins are assessed: splenic, superior mesenteric, portal and intrahepatic portal, and portasystemic collateral. This examination can be performed on patients of any age without sedation and can establish the diagnosis of clinically significant portal hypertension. Technical success rate was 95%, although 10% of examinations were incomplete because of intestinal meteorism. We conclude that the combined use of Doppler and routine sonography permits precise evaluation of the vascular anatomy in portal venous hypertension.     

Liver transplantation: MR angiography with surgical validation

Thirty patients (mean age, 45 years) were evaluated with magnetic resonance (MR) angiography before liver transplantation to assess the accuracy of MR angiography. A series of breath-hold, two-dimensional images were acquired and subsequently processed to form three-dimensional projection angiograms. Graphic information on blood flow in the portal vein was acquired by using presaturation bolus tracking. Correlative duplex ultrasound (US) was performed in 28 patients, and surgical or autopsy correlation was available in all cases. MR angiography demonstrated patency of the portal vein in 26 (96%) of 27 patients, made possible the diagnosis of portal venous occlusion in three of three patients, depicted reversed portal flow in one patient, and provided clear delineation of the extent of varices and specific portosystemic collateral vessels. When duplex US was successful, there was full agreement with MR angiographic results in assessing portal vein patency and flow direction. All of the MR findings were corroborated at surgical exploration or autopsy. The authors conclude that MR angiography is very accurate in the portal system and is valuable in preoperative assessment for liver transplantation.     

MSCTA对活体右叶供肝血管变异分型的研究

目的：探讨活体肝移植术前多层螺旋CT血管成像对潜在供肝血管系统评估的临床运用及价值。方法：对连续108例潜在右半肝供体行3期CT增强扫描（动脉期、门静脉期和肝静脉期）。根据所有原始图像和重组图像进行供肝的血管变异分型,肝动脉、门静脉以及肝静脉系统分别进行Michels分型、Akgul分型及Nakamura分型。对其中45例行右半肝切除的供体的肝血管变异分型与术中发现进行比较。结果：108例潜在供体的肝动脉、门静脉和肝静脉系统在MSCT上均显示清晰。根据肝动脉Michels分型,Ⅰ型有64例（59.3%）,Ⅱ型9例（8.3%）,Ⅲ型13例（12.0%）,Ⅳ型4例（3.7%）,Ⅴ型11例（10.2%）,Ⅵ型3例（2.8%）,Ⅷ型和Ⅸ型各2例（1.9%）。根据门静脉Akgul分型,A型有87例（80.6%）,B型有15例（13.9%）,C型4例（3.7%）,E型3例（2.8%）。根据肝静脉Nakamura分型,Ⅰ型有73例（67.6%）,Ⅱ型24例（22.2%）,Ⅲ型11例（10.2%）。45例进行手术的供体的术前CT血管分型结果与术中发现一致。结论：多层螺旋CT血管成像可良好地显示潜在供肝的血管系统,对活体肝移植术具有重要的临床应用价值。     

肝内门静脉和肝静脉的解剖与变异(三维动态增强磁共振血管成像分析)

目的用三维动态增强磁共振血管成像（３ｄｉｍｅｎｔｉｏｎａｌｄｙｎａｍｉｃｃｏｎｔｒａｓｔｅｎｈａｎｃｅｄＭＲＡ,３ＤＤＣＥＭＲＡ）前瞻性地观测肝内门静脉（简称门脉）和肝静脉的解剖和变异。方法共进行１４２例门脉和肝静脉３ＤＤＣＥＭＲＡ检查。对肝内门脉和肝静脉的解剖和变异做分型,计算每一型所占总调查人数的比例,并计算右后下肝静脉的显示率。结果１４２次成像中,８例（５．６％）显示门脉呈三分叉状,７例（４．９％）门脉先分出右后支,然后上行分为左支和右前支,４例（２．８％）门脉右前支源于左支,未发现有门脉左支水平段或右支缺如,余下１２３例（８６．６％）显示正常门脉分支。绝大多数情况下（９５．１％）肝中、肝左静脉合并,而三大支肝静脉单独汇入下腔静脉仅占４．９％。右后下肝静脉的显示率为７．７％。结论肝内门脉变异并不少见。肝中和肝左静脉多合并后汇入下腔静脉。部分病人有较为粗大的右后下肝静脉。３ＤＤＣＥＭＲＡ能方便而清楚地显示上述血管的解剖和变异     

Value of an early arteriographic acquisition for evaluating the splanchnic vessels as an adjunct to biphasic CT using a multislice scanner

Our objective was to assess the clinical value of an early arterial scan for assessing the hepatic and mesenteric vasculature in patients with suspected primary or metastatic hypervascular liver disease undergoing multislice computed tomography. In 42 patients a very early arteriographic scan was performed before standard arterial and portal venous scans. Technical parameters of the very early acquisition were: 2.5-mm image thickness; table speed 15 mm/s; pitch 6; 120 kVp; 300 mA; 8.9-s scan time; cranio-caudal acquisition direction; 1.25-mm image interval reconstruction;16-s delay after injection of 110 ml of iodinated contrast agent at 5 ml/s; scan volume focused to image hepatic, splenic, and superior mesenteric arteries (SMA). Standard arterial and portal venous phases were performed with 5-mm image thickness, 15-mm/s table speed, pitch 6, 8- to 10-s scan time, 30- and 70-s delay. The three phases were performed during three different breath-holds. Axial, multiplanar reformatted, maximum intensity projection, and volume-rendering images were evaluated. Image quality was scored, and vascular abnormalities were recorded. Digital subtraction angiography (DSA) was performed in 17 patients. In 36 of 42 patients good-quality CT angiograms were obtained. In 9 patients 12 vascular abnormalities were found, all confirmed at DSA: 3 right hepatic arteries originating from the SMA, 2 left hepatic arteries from the gastric artery, 2 stenoses of the SMA, 1 independent origin of the hepatic and splenic arteries, 2 arteriovenous fistulas, and 2 aneurysms of the common hepatic artery and the SMA. This technique could add important information about vascular splanchnic anatomy which would be particularly useful for surgeons and interventional radiologists. Electronic Publication     

Childhood hepatocellular carcinoma and hepatoblastoma: integrated sonography and dynamic CT.

13 cases of hepatoblastoma and hepatocellular carcinoma are reviewed with respect to the visibility of the tumour margin, hepatic veins, and portal veins on non-contrast, non-dynamic and dynamic computerised scans. In large tumours the accurate interpretation of venous anatomy can be difficult. We found that dynamic scanning followed by a repeat scan of selected slices after a few minutes was the most useful method. If facilities for dynamic scanning are not available then it is suggested that conventional scanning be performed immediately after the intravenous injection so as to avoid the isodense phase of hepatic enhancement.