Mareels G, Poyck PPC, Eloot S, Verdonck PR. In a normal patient, contrast injected from the upper extremity first opacifies the SVC, followed by the right atrium, right ventricle, pulmonary artery, pulmonary vein, left atrium, left ventricle, ascending aorta, and finally the descending thoracic aorta. In. Here we do not consider the very first tube length ratio as no information is provided on the first duct length in Refs19,29. Combining Eq. The peak flow rate that can be achieved also depends on the size of the access vein [9] (Table 4). ACR Manual on Contrast Media discusses the treatment of contrast extravasation [9]. In the absence of more precise data, Eq. In the paper published by Miguel35 in 2016, the equipartition of thermodynamics imperfections concept translates into an equipartition of flow resistances. Further, the right ventricle propels the blood/contrast medium into the pulmonary artery from where it enters the pulmonary vein and then the left atrium. Leading to the sinusoid pressure drop ratio between a square and a hexagonal lobule: Finally, we conclude that the overall pressure losses will be smaller in the case of the assembly of hexagonal lobules (Eq. Ricken, T., Waschinsky, N. & Werner, D. Simulation of steatosis zonation in liver lobuleA continuum mechanical bi-scale, tri-phasic, multi-component approach. The liver is one of the most important organ of the human body. Using contrast enhancement and flow patterns to identify the cause of a non-diagnostic CTA. Privacy If we look into Fig. Also note the differential enhancement in descending aorta. Decreased systolic function of left ventricle can result in dependent contrast pooling and layering in the aorta [25]. Similarly, persistent enhancement of a proximal segment when most of the contrast has washed out from the distal segments is not normal. this patient does have hepatic steatosis and a tiny gallstone or cholesterol polyp. Scanning Electron Microscope images of human liver reveal that the elemental system, the lobule, is entirely vascularized19. In these patients, the contrast is distributed almost entirely in the venous system with no opacification of the right ventricle, pulmonary artery or aorta and indicates circulatory dysfunction (Fig. However, the arrival of contrast media may not always be simultaneous due to different resistance, collaterals, and flow velocities. Models range from the entire circulatory architecture6 to the hepatic micro circulation7,8. We gathered the values of fn from Wechsatol et al.33 They are 13.16, 16.31, 18.67, 20.5, 21.8 and 22.6 for n=2 to 7 respectively, which means that for increasing pairing levels, fn reaches an asymptote close to 25. Analyzing the human liver vascular architecture by combining vascular corrosion casting and micro-CT scanning: a feasibility study. No pleural or pericardial effusion. Why the bigger live longer and travel farther: animals, vehicles, rivers and the winds. The hepatic artery, portal vein and hepatic vein form a compact three-dimensional dendritic architecture within the liver. 3) and length ratios (Eq. The liver vasculature makes its unique among the other organs as it is made of the superimposition of three main networks, two inlets and one outlet. Its generic expression is. For the sake of simplicity, assume that the hepatic artery and the portal vein are one single conduct of diameter d and length Ld, through which the mass flow rate is hence 3mh/6. These are, however, not commonly seen in left atrium or left ventricle, and whenever seen should be considered abnormal (Fig. As the majority of thoracic CTAsare performed with the patients arms raised, compression of the subclavian vein (asymptomatic or symptomatic) can lead to compromises in IV contrast delivery to the central vascular structures, affecting bolus timing and leading to suboptimal opacification due to reductions in flow rate (Fig. In addition, intraluminal abnormalities, including dissection and embolus, may not be readily apparent on the precontrast localizer images and placement of the ROI overlying one of these structures may result in delayed or absent bolus triggering. The flow resistance created in the case of a dendritic design is given by. No abdominal aortic aneurysm. PubMed Central On conventional angiography, the fistula is seen opacifying on the arterial phase (arrow). This is similar to contrast attenuation in SVC. The microcirculation happens through lobules which hexagonal shape corresponds to minimum flow resistances. No body wall masses. Normal caliber intrahepatic and common bile ducts. All the cells of the porous lobule-system fulfill the metabolic and filtering functions. EXAMPLE REPORTING TEMPLATE WITH CHECKLIST: LOWER CHEST: Lung bases are clear. Match. Insights into Imaging Indications for thoracic CTA include pulmonary embolus, acute aortic syndrome, or coronary artery disease. Inappropriate placement of ROI for bolus tracking scan is a common cause of non-diagnostic CT scan. Patient movement between localizer slice selection/ROI placement and the start of contrast administration/imaging can also affect ROI placement (i.e. Contrast opacifies the right portal vein secondary to backflow from hepatic vein into portal vein. WebHepatic vasculature: a conceptual review Author Abstract The hepatic circulation is reviewed with emphasis on the role of hepatic blood vessels in hepatic and homeostatic The shape of the liver as a hemisphere of radius R. By the same token, the flow resistance ratio between the dendritic and radial configurations is: where L1 is the channel length corresponding to the first generation number. Post-threshold delay needs to be increased when using a faster scanner to better opacify the non target vessels. This can lead to variable enhancement pattern (Fig. Two images from a CTPE study obtained in a patient with tricuspid atresia and bidirectional cavopulmonary connection demonstrate poor opacification of right pulmonary artery and non-enhancement of left pulmonary artery (a). Accessibility When using bolus tracker technique, failure to adequately opacify the target vessels to reach the threshold needed for triggering the scan may also be an indication of decreased cardiac pump function. Lucia U, Grisolia G, Astori MR. Constructal law analysis of Cl transport in eyes aqueous humor. large respiratory effort, cardiac motion, and/or the patient physically shifting on the table), leading to premature, delayed or even no bolus triggering. In normal subjects, this is about 6.81.7s [6]. Contrast arrival in the target vessel can be determined by using test bolus or bolus tracker technique [7, 8]. Sequential contrast opacification of central veins and cardiac chambers can be observed when bolus timing technique is used to identify contrast arrival. The authors declare no competing interests. The hexagonal cross section shows 6 portal triads made of the bile duct, the portal vein and the hepatic artery. J Comput Assist Tomogr 34(1):7581, Clough RE, Hussain T, Uribe S, Greil GF, Razavi R, Taylor PR et al (2011) A new method for quantification of false lumen thrombosis in aortic dissection using magnetic resonance imaging and a blood pool contrast agent. In. At the time the case was submitted for publication Michael P Hartung had no recorded disclosures. Debbaut C, et al. The sinusoids tortuous network bathes the entire lobule, supplying the blood to the central vein from the 6 sources (hepatic artery+portal vein). 1Department of Mechanical Engineering, Villanova University, Villanova, PA 19085 USA, 2Departamento de Fsica, Facultad de Ciencias, Universidad Nacional Autnoma de Mxico, Circuito Exterior S/N, Ciudad Universitaria, CP04510 Coyoacn, Ciudad de Mxico, Mexico, 3Centro Mdico 20 de Noviembre, ISSSTE,, Flix Cuevas 540, Del Valle Sur, Benito Jurez, CP03100 Ciudad de Mxico, Mexico. Traditionally, ECG gated CT/MR have been used to define cardiac chamber enlargement. This can lead to differential enhancement in different segments of the aorta, which merely indicates different contrast density at different time points. In this article, wewill review several abnormal contrast enhancement and flow patterns that are encountered in thoracic CTA, including severe abnormalities such as right heart strain, cardiac asystole, and cardiac tamponade. Calculations of the diameter ratio, length ratio and splitting number of branches, data from Debbaut et al.19,29 and Ma et al.22. Note that the predicted tube length ratio is identical to the channel diameter ratio. The sinusoids are uniformly distributed throughout the entire liver volume, and constitute the hepatic microcirculation. Manifestations of focal venous obstruction depend on the location. Obstruction can be, Extrahepatic portal vein thrombosis Portal Vein Thrombosis Portal vein thrombosis causes portal hypertension and consequent gastrointestinal bleeding from varices, usually in the lower esophagus or stomach. This is likely due to decreased stroke volume with resultant contrast blood pooling with dependent layering of the higher viscosity contrast. The two inlet networks, namely the hepatic artery (HA) and the portal vein (PV), run in parallel. Malley-Ernewein, A. Relying on these findings, we write Li+1=kLi, where k is to be discovered. No peripancreatic fluid. If contrast is suboptimal, sometimes it can be amplified by using virtual monoenergetic images from a dual energy scanner. Normal gallbladder morphology. View Michael P Hartung's current disclosures, see full revision history and disclosures, How to read a CT of the abdomen and pelvis, "How to Read an Abdominal CT" Chapter 2 Supplement, #14 Gastrointestinal tract. For each network to be fully determined, we also need to predict the tube lengths ratio, and prove the merit of a dendritic-based architecture as opposed to a radial fluid distribution. However, the contrast injection is typically performed slower than peripheral routes due to safety concerns. 1 for a bird-eye view. It may be diffuse and is often related to alcohol, diabetes, certain drugs and medications, or obesity [16].Occasionally, there may be diffuse fatty infiltration in the liver with focal areas of sparing or focal areas of fatty deposition in an otherwise normal liver [46]. Any disruption of the above-described normal sequence of events should be treated with suspicion. J Comput Assist Tomogr 39(5):794796, Rudski LG, Lai WW, Afilalo J, Hua L, Handschumacher MD, Chandrasekaran K et al (2010) Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography. Raising the affected limb above the level of the heart may reduce swelling and facilitate absorption of extravasated fluid. When using a scanner with shorter acquisition time, non-target vessel enhancement may be less than expected and these vessels should be interpreted with caution. Portal hypertension may be caused by intrinsic liver disease, obstruction, or structural changes that result in increased portal venous flow or increased hepatic resistance. If the patient is not being monitored, and when such a finding is seen on a nondiagnostic CTA, it is imperative to call the code team and immediately begin cardiopulmonary resuscitation rather than planning for a reinjection. Sagittal CECT MIP image demonstrates differential opacification of the aorta proximal and distal to the aortic coarctation with post-stenotic dilatation. Coil embolisation of the varices was performed. Chaturvedi, A., Oppenheimer, D., Rajiah, P. et al. The hepatic veins drain the liver into the inferior vena cava. When portal vein blood flow increases, hepatic artery flow decreases and vice versa (the hepatic arterial buffer response). This dual, reciprocally compensatory blood supply provides some protection from hepatic ischemia in healthy people. The results are di+1/di= 0.74, 0.70, and 0.59 for the hepatic arteria, the portal vein and the hepatic vein respectively according to Debbaut et al.19,29, while a ratio of 0.79 is obtained from the measurements provided by Ma et al.22. Nevertheless, and following the work of Revellin et al.31, Hess-Murrays law remains valid even with a power-law model. Blood is then pushed out when reaching the center of the lobule through the central vein parallel to the portal triad. A less dramatic, but equally important observation may be seen in patients with congestive heart failure with resultant poor or no opacification of left cardiac chambers and aorta during a CT pulmonary angiogram (Fig. Nevertheless considering that the hexagonal shape is close to the circle shape, the same expression was used in this work to predict the order of magnitude of the lobule permeability. For example, if the ROI is placed in the false lumen of a type B aortic dissection (Fig. Cookies policy. Google Scholar, Department of Imaging Sciences, University of Rochester Medical Center, 601 Elmwood Ave, P.O. A 3D porous media liver lobule model: the importance of vascular septa and anisotropic permeability for homogeneous perfusion. This does not have impact in the theoretical approach presented here because the frequency domains relevant to biological flows, as in the case of the liver, correspond to a negligible imaginary contribution in the impedance expression of the fluid flow, leaving a direct proportionality between pressure difference and mass flow rates as provided by the real part of the impedance30. Bejan A, Tondeur D. Equipartition, optimal allocation, and the constructal approach to predicting organization in nature. Insights Imaging 8, 127140 (2017). In addition to target vessel opacification, evaluation of non-target vessels may also contain important clues to the underlying disease that brought the patient to the ED. CTA shows contrast reflux into IVC and dependent hepatic veins and blood-contrast level in the IVC. Considering Darcy flow through the porous elemental system (i.e. (See also Overview of Vascular Disorders of the Liver.) The distribution of contrast medium is now being determined by the push from the power injector and the viscosity of the contrast medium. The outlet flow (hepatic vein) is located at the center of each lobule. In this case we see an altered pattern of contrast flow: first SVC, followed by minimal opacification of the pulmonary artery and ascending aorta, dense opacification of the descending aorta followed by dense opacification of the ascending aorta. On another hand, Debbaut et al.46 reported a value of 0.134 mm3 for 3 human liver lobules. Received 2019 Dec 23; Accepted 2020 Sep 10. The canopy-to-canopy view of the liver vascular system. Systems modeling of developmental vascular toxicity. Axial CECT following the rapid bolus of intravenous contrast in the left upper extremity with the left arm raise (a) shows narrowing of the left subclavian vein at the thoracic inlet and contrast filling multiple small collateral veins in the left shoulder region. In addition, attempts to remove the extravasated contrast via aspiration have not been shown to be consistently beneficial. Repeat injection using high pitch FLASH technique with free breathing (c) shows excellent opacification of the pulmonary artery. WebUltrasound demonstrated a sonographically normal liver without nodularity or cirrhosis and patent hepatic vasculature ( Fig. Pater L, Berg J. Vena portae hepatis. The work unveils the structure of the liver blood flow architecture as a combination of superimposed tree-shaped networks and porous system. Evaluation of these graphs is important in identifying the planned flow rate and any changes to that. A physiologically-based flow network model for hepatic drug elimination I: regular lattice lobule model. Radiographics 26(6):17351750. 16b). A non-diagnostic CTA following the initial contrast injection can be secondary to many causes; these include both extrinsic factors, such as injection technique/equipment failure (iv cannula, power injector), and intrinsic, patient-related factors. The two major venous plexuses that are Normally, vascular Measuring read more , blood-filled cystic spaces develop in the sinusoids (microvascular anastomoses between the portal and hepatic veins). Numerical modeling of oxygen availability in the AMC bioartificial liver. This phase allows more accurate estimation of the extent of the false lumen thrombus and slow flow. This is indicative of poor stroke volume from tamponade. 17 obtained after the ECMO circuit was put on minimal flow status for a short period (25s) to allow for near physiologic circulation. If pain is the main symptom, we use cold compresses, and if the extravasation has occurred in a location where there is a higher likelihood of compartment syndrome, we use hot compresses. Incidentally, the deterministic structure of the body fluid networks was highlighted in the early twentieth century by respectively Hess27 and Murray28 who came to the conclusion that the diameter ratio between mother and daughter branches has a unique value. In addition, use of distal access sites (i.e. 8a and b). Such dependent contrast pooling in descending aorta can also be seen in patients with acute cardiac tamponade, likely due to decreased stroke volume (Fig. Treatment read more due to a hypercoagulable state, a vessel wall lesion (eg, pylephlebitis, omphalitis), an adjacent lesion (eg, pancreatitis Overview of Pancreatitis Pancreatitis is classified as either acute or chronic. There may be retrograde opacification of IVC, hepatic veins, and even portal vein with dependent pooling of the contrast forming a blood-contrast level (Movie 1) [24]. Yet, about 20years ago, A. Bejan25 proved that dendritic configurations can be predicted, and that they exist for a very specific purpose. Below are links to the electronic supplementary material. 2). Accounting for the discrepancy of the measurements from one generation level to the other, we consider the predicted value of 3-1/3 0.69 as reliable. PubMed 6) in order to spend less pumping power for the same fluid volume26. Further downstream, the flow from the two inlet trees is reconstituted into a single stream through the outlet HV tree. The work relies on the fundamentals of fluid mechanics and allows to predict how the blood transport happens through a human liver. An electrical analogue of the entire human circulatory system. Repeat injection with placement of ROI in true lumen resulted in adequate evaluation of dissection. Patients receiving chemotherapy also have an increased risk due to fragile, damaged, and often small caliber vessels. The necessary pumping power is provided by the heart, and is proportional to mp. Use for phrases 18). The lobules dimensions are also difficult to find in the literature. In type B dissection, identification of false lumen thrombus can be overestimated by first pass CTA/MRA. 18 gives a permeability K ranging between 3 1010 m2 and 9 1012 m2. Causes are most often systemic: Impaired hepatic read more ; focal ischemia can cause hepatic infarction or ischemic cholangiopathy Ischemic Cholangiopathy Ischemic cholangiopathy is focal damage to the biliary tree due to disrupted flow from the hepatic artery via the peribiliary arterial plexus. This is called the transit delay (Table 2) and varies from patient to patient and scanner to scanner. WebThe iliac arteries are blood vessels that provide blood to the legs, pelvis, reproductive organs and other organs in the pelvic area. Provided by the Springer Nature SharedIt content-sharing initiative. 2). Normal flow of intravenous contrast through a commonly used upper extremity venous access site follows a pattern; contrast flows first into the brachiocephalic vein, then into the superior vena cava, right atrium, right ventricle, pulmonary artery, pulmonary vein, left atrium, left ventricle, ultimately to opacify the ascending and then the descending aorta. The average values together with their standard deviation are also provided. The initial CTA ROI wasplaced in the false lumen (b). Since the contrast media will directly opacify the lower SVC or the right atrium and the subsequent cardiovascular structures, the upper SVC and other veins will not be adequately opacified in the first pass as with a peripheral route injection. 14). Bolus tracking technique for identification of contrast arrival. 3 predicts that the corresponding diameter ratio should be 31/30.69 in order to minimize the pumping power needed to push the blood in and out the liver. non deterministic. Normal caliber small and large bowel. Provides 80% of blood to the liver. 5b). The portal venous system drains the intestines, pancreas, and spleen with numerous collateral anastomoses to other venous beds of the abdomen. Contrast also opacifies the right portal vein secondary tobackflow from hepatic vein into the portal vein. Normal hepatic anatomy occurs in approximately 80% of cases, for the remaining 20% multiple variations have been described. Diagnosis is based on ultrasonography. where K is the intrinsic permeability of the lobule. Graphs and tables from the power injector: pressure-time and flow rate-time graphs. However these models, regardless their sophistication level14,15, are descriptive. Street network theory of organization in nature. This means that in this configuration, the central vein would be connected to 4 radial branches of diameter dc and length Lc=2LS through which the mass flow rate is mh/4. Axial (a) and coronal reformatted pulmonary CTA (b) subsequently demonstrates a large central pulmonary embolism. Therefore, because the total mass flow rate is a constant, the mass flow rate per element must continue to be mh. PubMedGoogle Scholar. Ma R, et al. There is no solution to this artifact once acquired, but this can be avoided by using spiral instead of axial acquisitions. cannula mismatch the pressure may exceed the threshold, which may limit the flow rate. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. 3b) with abrupt cessation of flow, or contrast medium extravasation. Note the differential enhancement in the right ventricle outflow tract vs. main pulmonary trunk. Thanks to the constructal law we could predict the main geometrical features of the liver: This work establishes the theoretical bases that help to complete the understanding of the results of experimental work carried out since the last century on animal models, as well as the most recent ones on experimental models on silicon scaffolds, organs on chips, and scaffolds of decellularized organs. Total cavopulmonary connection involves a Glenn shunt connecting SVC to the right PA and Fontan shunt connecting IVC to left PA. CT angiography in these patients to visualize the pulmonary arteries or the conduits themselves is challenging since the SVC flow is directed to the right lung and the IVC flow is directed to the lung (Fig. This can help in planning a reinjection and obtain a diagnostic scan. The inlet vasculature is made of the hepatic artery and the portal vein, the outlet vasculature is made of the hepatic vein. Obstruction can occur in the intrahepatic or extrahepatic veins (Budd-Chiari syndrome Budd-Chiari Syndrome Budd-Chiari syndrome is obstruction of hepatic venous outflow that originates anywhere from the small hepatic veins inside the liver to the inferior vena cava and right atrium. To avoid this, the indication of the scan should be well known to the operating technologist. In Eq. In their 2005 paper, Wechsatol et al.33 documented the design of laminar dendritic networks on a fixed disc-shaped area. Conceptually, the liver vascularization can be seen as 2 trees matching canopy-to-canopy bathing a porous architecture made of lobules, as presented in Fig. The central veins, or hepatic veins (HV) collect the blood and lead it to the vena cava inferior. Understanding and controlling the liver portal pressure after surgery would be of the utmost importance to guarantee correct regeneration signals and prevent cell death18. Although there are safety issues related to this such as the risk of catheter rupture, fragmentation, or thromboembolism, these devices can be safely used if appropriate precautions including manufacturer specifications are followed [34]. Calling Ah the area of the hexagon, we have Ah=332Lh2. Size of the cannula used for delivery of contrast medium is important to achieve the desired flow rate for the duration of the injection [9]. https://doi.org/10.1007/s13244-016-0524-3, DOI: https://doi.org/10.1007/s13244-016-0524-3. Plaats AVD, et al. Pattern of opacification of non target vessels can be useful in understanding the hemodynamic status of the patient and correctly identifying life threatening conditions such as tamponade, heart failure, and asystole. Debbaut C, et al. The total pressure difference between the inlet and the outlet of a lobule is given by, Another way to pave entirely the square domain represented in Fig. this is a higher quality study than a standard CT. We showed that the entire liver circulatory architecture is deterministic. Axial CTA shows moderate pericardial effusion and heterogeneous enhancement of descending aorta with blood contrast layering. Blood is a non-Newtonian fluid. Nearly all portal vein disorders obstruct portal vein blood flow and cause portal hypertension Portal Hypertension Portal hypertension is elevated pressure in the portal vein. The flow path is represented on the left hand side of Fig. The trusted provider of medical information since 1899, Overview of Vascular Disorders of the Liver, Last review/revision Jan 2022 | Modified Sep 2022. Radiograph or CT topogram imaging of the affected limb following an extravasation event may be useful to determine the magnitude of infiltration and verify if compartmentation is present (Fig. Optimal time for acquisition would be when both lumens are opacified. 16, 21 and 28. On an average, the measured splitting number is 2.76 for the hepatic artery, 2.80 for the portal vein, and 3.22 for the hepatic vein, which translated into the integer n = 3. True estimation of this false lumen thrombosis after aortic dissection is important as this can be important for prognosis [29]. Location The IVC starts 4b) [15]. Their complexity often forces to reduce the hydrodynamic studies of the liver to its morphofunctional unit, the lobule23,24. Google Scholar, Lakoma A, Tuite D, Sheehan J, Weale P, Carr JC (2010) Measurement of pulmonary circulation parameters using time-resolved MR angiography in patients after Ross procedure. With this end goal in mind, understanding the anatomy and physiology of the cardiovascular system as it pertains to contrast flow dynamics can serve as a useful starting point. The hepatic artery provides oxygenated blood to the liver, while the portal vein brings deoxygenated blood; the two mix in the sinusoids. In the simplest case we assume that the ducts have a round cross section of diameter d and length L. The pulsatile nature of blood flow in the hepatic artery network is classically expressed through an electrical impedance analogy. ADVERTISEMENT: Supporters see fewer/no ads. Portal, splenic, superior mesenteric Ischemia results from reduced blood flow, reduced oxygen delivery, increased metabolic activity, or all 3. This artifact should be considered when there is decreased opacification of multiple bilateral pulmonary arteries at the same level without vessel lumen distention: true pulmonary emboli typically present at various levels and normally expand the vessel lumen acutely [19]. In our experience, slowing the flow of the circuit to the minimal flow rate that would prevent thrombus formation for the duration of the scan (1520s) has worked well in cases of suspected pulmonary embolism (Fig. We demonstrate that the dendritic nature of the hepatic artery, portal vein and hepatic vein can be predicted, together with their geometrical features (diameter ratio, duct length ratio) as the entire blood flow architectures follow the principle of equipartition of imperfections. Fontan shunt is performed as the third stage of ventricular repair and involves anastomosis between the IVC and the left pulmonary artery. Mixing artifacts in the true lumen of the descending aortic aneurysm with Type B aortic dissection which resolve on delayed phase acquisition. 6. Thoracic outlet syndrome (TOS) refers to the effects of dynamic compression of the nerve, artery, and/or vein as these structures cross the thoracic outlet due to changes in arm position, typically induced by elevation of the arms [16].
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