Magnetic resonance imaging (MRI) has become an important tool for the clinical evaluation of patients with cardiovascular disease. Since its introduction in the late 1980s, 2-dimensional phase contrast MRI (2D PC-MRI) has become a routine part of standard-of-care cardiac MRI for the assessment of regional blood flow in the heart and great vessels. More recently, time-resolved PC-MRI with velocity encoding along all three flow directions and three-dimensional (3D) anatomic coverage (also termed ‘4D flow MRI’) has been developed and applied for the evaluation of cardiovascular hemodynamics in multiple regions of the human body. 4D flow MRI allows for the comprehensive evaluation of complex blood flow patterns by 3D blood flow visualization and flexible retrospective quantification of flow parameters. Recent technical developments, including the utilization of advanced parallel imaging techniques such as k-t GRAPPA, have resulted in reasonable overall scan times, e.g., 8-12 minutes for 4D flow MRI of the aorta and 10-20 minutes for whole heart coverage. As a result, the application of 4D flow MRI in a clinical setting has become more feasible, as documented by an increased number of recent reports on the utility of the technique for the assessment of cardiac and vascular hemodynamics in patient studies. A number of studies have demonstrated the potential of 4D flow MRI to provide an improved assessment of hemodynamics which might aid in the diagnosis and therapeutic management of cardiovascular diseases. The purpose of this review is to describe the methods used for 4D flow MRI acquisition, post-processing and data analysis. In addition, the article provides an overview of the clinical applications of 4D flow MRI and includes a review of applications in the heart, thoracic aorta and hepatic system.

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4D flow imaging with MRI

Background: Pregnancy is associated with considerable changes in the physiological, anatomical and biochemical attributes in women. These may alter the exposure to xenobiotics between pregnant and non-pregnant women who receive similar doses, with implications for different susceptibility to environmental pollutants or therapeutic agents. Physiologically based pharmacokinetic (PBPK) models together with in vitro in vivo extrapolation (IVIVE) of absorption, distribution, metabolism and excretion (ADME) characteristics may capture the likely changes. However, such models require comprehensive information on the longitudinal variations of PBPK parameter values; a set of data that are as yet not available from a singular source. Aim: The aim of this article was to collect, integrate and analyse the available time-variant parameters that are needed for the PBPK modelling of xenobiotic kinetics in a healthy pregnant population. Methods: A structured literature search was carried out on anatomical, physiological and biochemical parameters likely to change in pregnancy and alter the kinetics of xenobiotics. Collated data were carefully assessed, integrated and analysed for trends with gestational age. Algorithms were generated to describe the changes in parameter values with gestational age. These included changes in maternal weight, the individual organ volumes and blood flows, glomerular filtration rates, and some drug-metabolising enzyme activities. Results: Articles were identified using relevant keywords, quality appraised and data were extracted by two investigators. Some parameters showed no change with gestational age and for others robust data were not available. However, for many parameters significant changes were reported during the course of pregnancy, e.g. cardiac output, protein binding and expression/activity of metabolizing enzymes. The trend for time-variant parameters was not consistent (with respect to direction and mono-tonicity). Hence, various mathematical algorithms were needed to describe individual parameter values. Conclusion: Despite the limitations identified in the availability of some values, the collected data presented in this paper provide a potentially useful singular resource for key parameters needed for PBPK modelling in pregnancy. This facilitates the risk assessment of environmental chemicals and therapeutic drug dose adjustments in the pregnant population.

Anatomical, physiological and metabolic changes with gestational age during normal pregnancy: A database for parameters required in physiologically based pharmacokinetic modelling

Drug–drug interactions are a serious clinical issue. An important mechanism underlying drug–drug interactions is induction or inhibition of drug transporters that mediate the cellular uptake and efflux of xenobiotics. Especially drug transporters of the small intestine, liver and kidney are major determinants of the pharmacokinetic profile of drugs. Transporter-mediated drug–drug interactions in these three organs can considerably influence the pharmacokinetics and clinical effects of drugs. In this article, we focus on probe drugs lacking significant metabolism to highlight mechanisms of interactions of selected intestinal, hepatic and renal drug transporters (e.g., organic anion transporting polypeptide [OATP] 1A2, OATP2B1, OATP1B1, OATP1B3, P-gp, organic anion transporter [OAT] 1, OAT3, breast cancer resistance protein [BCRP], organic cation transporter [OCT] 2 and multidrug and toxin extrusion protein [MATE] 1). Genotype-dependent drug–drug interactions are also discussed.

Transporter-mediated drug-drug interactions.

Laparoscopic sleeve gastrectomy (LSG) has a specific morbidity profile in which gastric leak (GL) is the main complication. With a view to defining a standardized protocol for GL management, the present retrospective study sought to describe the clinical patterns of post-LSG GL and treatment of the latter in our university medical center. From July 2004 to December 2010, 25 patients were included. GL was described in terms of clinical presentation, time to onset, and location in the staple line. Treatment of GL with pharmacologic, radiologic, endoscopic, and/or surgical procedures was always validated by a multidisciplinary care team. “Treatment success” was defined as the absence of contrast agent leakage on CT and endoscopy after removal of covered metallic stent or pigtail drains. Systemic inflammation and peritonitis were the main signs for early-onset GL (56%), whereas pulmonary symptoms and intra-abdominal abscesses revealed delayed-onset GL (44%). Surgery was always performed for early-onset GL. In the total study population, the median number of endoscopic procedures was five (range, 1–11) per patient, of covered SEMS was three (range, 1–8), and of pigtail drains was three (range, 1–4). Nine (36%) patients presented endoscopic-related complications. Four (16%) patients with treatment failure underwent radical surgery. The mortality rate was 4% (n=1). The management of post-LSG GL is challenging. Surgery was always performed for early-onset GL, whereas treatment of delayed-onset GL was based on endoscopy. Pigtail drains required fewer procedures per patient, were better tolerated, and had lower morbidity–mortality than covered SEMS.

Is There a Place for Pigtail Drains in the Management of Gastric Leaks After Laparoscopic Sleeve Gastrectomy

Gastrobronchial fistula (GBF) is a serious complication following bariatric surgery, whose treatment by thoracotomy and/or laparotomy involves a high morbidity rate. We present the outcomes of endoscopic management for GBF as a helpful technique for its healing process. This is a multicenter retrospective study of 15 patients who underwent gastric bypass (n = 10) and sleeve gastrectomy (n = 5) and presented GBF postoperatively (mean of 6.7 months). Ten patients developed lung abscess and were treated by antibiotic therapy (n = 10) and thoracotomy (n = 3). Abdominal reoperation was performed in nine patients for abscess drainage (n = 9) and/or ring removal (n = 4) and/or nutritional access (n = 6). The source of the GBF was at the angle of His (n = 14). Furthermore, 14 patients presented a narrowing of the gastric pouch treated by 20 or 30 mm aggressive balloon dilation (n = 11), stricturotomy or septoplasty (n = 10) and/or stent (n = 7). Fibrin glue was used in one patient. We performed, on average, 4.5 endoscopic sessions per patient. Endotherapy led to a 93.3% (14 out of 15) success rate in GBF closure with an average healing time of 4.4 months (range, 1–10 months), being shorter in the stent group (2.5 × 9.5 months). There was no recurrence during the average 27.3-month follow-up. A patient persisted with GBF, despite the fibrin glue application, and decided to discontinue it. GBF is a highly morbid complication, which usually arises late in the postoperative period. Endotherapy through different strategies is a highly effective therapeutic option and should be implemented early in order to shorten leakage healing time.

Gastrobronchial fistula after sleeve gastrectomy and gastric bypass: endoscopic management and prevention

Purpose:

To directly compare and study the variability of parameters related to hepatic blood flow measurements using 3 T phase-contrast magnetic resonance imaging (PC-MRI) and Doppler ultrasound (US).



Materials and Methods:

Nine healthy subjects were studied. Blood velocities and flow rate measurements were performed in the portal vein and the proper hepatic artery. MR studies were performed using a 3 T imager. Gradient-echo fast phase contrast sequences were used with both cardiac and respiratory gating. MR and Doppler flow parameters were extracted and compared. Two methods of calculation were used for Doppler flow rate analysis.



Results:

Compared to Doppler US, PC-MRI largely underestimated hepatic flow data with lower variability and higher reproducibility. This reproducibility was more pronounced in the portal vein than in the proper hepatic artery associated with poorer velocity correlations. Total hepatic flow values were 1239 ± 223 mL/min and 1595 ± 521 mL/min for PC-MRI and Doppler US, respectively.



Conclusion:

Free-breathing PC-MRI can provide reliable noninvasive measurement of hepatic flow parameters compared to Doppler US. The MR technique could help to improve Doppler flow calculations, thereby allowing standardization of protocols, particularly for applications in disease. J. Magn. Reson. Imaging 2010;31:579–588. © 2010 Wiley-Liss, Inc.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jmri.22079

Hepatic vascular flow measurements by phase contrast MRI and doppler echography: A comparative and reproducibility study

Laparoscopic sleeve gastrectomy (LSG) is a new restrictive bariatric procedure increasingly indicated in the treatment of morbid obesity. Postoperative complications are mainly represented by gastric fistula with an occurrence rate of 0% to 5.1% in the literature. This complication is difficult to manage and requires multiple radiological, endoscopic, and surgical procedures. We report herein the case of a 23-year-old woman who underwent LSG for morbid obesity. This patient was reoperated for peritonitis due to a gastric fistula located on the top of the staple line. Five months later, she complained of a cough with fever and expectoration. A methylene blue test and a computed tomography scan diagnosed a postoperative bronchogastric fistula. After failure of aggressive conservative management, radical surgery was performed with total gastrectomy, reconstruction of the diaphragm using the extended latissimus dorsi flap, and a pulmonary lobectomy. This case report highlights the possible issue of the complex management of gastric fistula after LSG.

Case report-complex management of a postoperative bronchogastric fistula after laparoscopic sleeve gastrectomy.

Von Meyenburg complexes (VMC) are a cluster of benign liver malformations including biliary cystic lesions, with congenital fibrocollagenous stroma. This rare entity can mimick multiple secondary hepatic lesions. We report a case of a 56-year-old woman who had multiples liver lesions 12 years after operation for breast cancer. Biopsy of the hepatic lesion confirmed the diagnosis of VMC. Preoperative discovery of multiple gray-white nodular lesions scattered on the surface of the liver should not always contraindicate curative liver resection. The diagnosis of VMC should be known and confirmed with liver biopsy.

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A Pitfall in the Diagnosis of Unresectable Liver Metastases: Multiple Bile Duct Hamartomas (von Meyenburg Complexes).

Background
Meticulous assessment of the left liver for patients scheduled for right hepatectomy is essential. Endoscopic ultrasonography (EUS) is frequently used for the locoregional staging or biopsy of pancreatic tumours and has shown some value in the evaluation of the left liver.

Fabien Demuynck

Papers

Hepatic vascular flow measurements by phase contrast MRI and doppler echography: A comparative and reproducibility study

Case report-complex management of a postoperative bronchogastric fistula after laparoscopic sleeve gastrectomy.

A Pitfall in the Diagnosis of Unresectable Liver Metastases: Multiple Bile Duct Hamartomas (von Meyenburg Complexes).

Is there a role for endoscopic ultrasonography in evaluation of the left liver in colorectal liver metastasis patients selected for right hepatectomy.