B. Van Beers

Assessment of hepatic perfusion parameters with dynamic MRI

Quantification of hepatic perfusion parameters greatly contributes to the assessment of liver function. The purpose of this study was to describe and validate the use of dynamic MRI for the noninvasive assessment of hepatic perfusion parameters. The signal from a fast T1‐weighted spoiled gradient‐echo sequence preceded by a nonslice‐selective 90° pulse and a spoiler gradient was calibrated in vitro with tubes filled with various gadolinium concentrations. Dynamic images of the liver were obtained after intravenous bolus administration of 0.05 mmol/kg of Gd‐DOTA in rabbits with normal liver function. Hepatic, aortic, and portal venous signal intensities were converted to Gd‐DOTA concentrations according to the in vitro calibration curve and fitted with a dual‐input one‐compartmental model. With MRI, hepatic blood flow was 100 ± 35 mL min‐1 100 mL‐1, the arterial fraction 24 ± 11%, the distribution volume 13.0 ± 3.7%, and the mean transit time 8.9 ± 4.1 sec. A linear relationship was observed between perfusion values obtained with MRI and with radiolabeled microspheres (r = 0.93 for hepatic blood flow [P < 0.001], r = 0.79 for arterial blood flow [P = 0.01], and r = 0.91 for portal blood flow [P < 0.001]). Our results indicate that hepatic perfusion parameters can be assessed with dynamic MRI and compartmental modeling. Magn Reson Med 47:135–142, 2002.

Inadequate detection of accessory spleens and splenosis with laparoscopic splenectomy. A shortcoming of the laparoscopic approach in hematologic diseases

AbstractBackground: The ultimate goal of surgery for hematological disorders is the complete removal of both the spleen and accessory spleens in order to avoid recurrence of the disease. Whereas splenectomy by open surgery provides excellent results, the validity of laparoscopic splenectomy in this regard remains unknown. Objective: The purpose of this study was to evaluate the detection of accessory spleens during laparoscopic splenectomy for hematologic diseases. Methods: We therefore evaluated the pre-, intra-, and postoperative detection of accessory spleens in a consecutive series of 18 patients treated by elective laparoscopic splenectomy for hematological diseases by using computed tomography (CT) and denatured red blood cell scintigraphy (DRBCS). Results: Preoperative CT, DRBCS, and laparoscopic exploration detected 25%, 25%, and 75% of accessory spleens, respectively. At time of laparoscopy, 16 accessory spleens were detected in seven of the 18 patients (41%). In two patients (11%), laparoscopic exploration failed to detect accessory spleens, whereas preoperative CT (one case) and DRBCS (one case) did reveal them. Postoperatively, during a mean follow-up of 28 months (median, 24; range, 12–44 months), nine patients (50%) showed persistence of splenic tissue by DRBCS, and three of them had signs of disease recurrence. Conclusions: This prospective clinical study suggests that elective laparoscopic surgery for hematological diseases does not allow complete detection of accessory spleens. Moreover, after such a laparoscopic approach, residual splenic tissue is detectable in half of the patients during the follow-up.

The surgical management of congenital liver cysts.

BackgroundMost series that report the results of surgical treatment for congenital liver cysts focus more on the technical aspects of the operation than on the late outcome of these patients. In this paper, we emphasize the importance of appropriate patient selection and adequate surgical technique for successful long-term outcome.MethodsTwenty-four consecutive patients with congenital liver cysts were selected for surgical treatment. According to our own classification, 13 patients had simple liver cysts, nine had multicystic liver disease, and two had type I polycystic liver disease. All of these patients were treated by the fenestration technique. An open approach was used for five patients (group 1) treated between 1984 and 1990. In 19 patients (group 2) treated since 1991, a laparoscopic approach was used. The incidence of complicated liver cysts was 40% in group 1 and 68% in group 2.ResultsThere were no treatment-related deaths in this series. The mean postoperative hospital stay was significantly shorter for patients who underwent successful laparoscopic fenestration (p < 0.05). In the open group (group 1), there were no postoperative complications, and all patients were alive and free of symptoms during a mean follow-up of 130 months, without any sign of cyst recurrence. In the laparoscopic group (group 2), four patients were converted to open surgery. One of these patients had an inaccessible posterior cyst; another had bile within the cystic cavity. A further two cases had complicated liver cysts with an uncertain diagnosis between congenital and neoplastic cysts. Four patients (21%) developed peri- or postoperative complications. During a mean follow-up time of 38.5 months, none of the patients with simple liver cysts incurred late symptoms or signs of cyst recurrence. In the six patients with multicystic liver disease, one developed disease-related cyst progression (17%) and required reoperation. One of the two patients with type I polycystic liver disease (50%) developed asymptomatic disease-related cyst progression.ConclusionsWhen patients are carefully selected and a proper surgical technique is employed, excellent long-term results with a low morbidity rate can be achieved in patients with congenital liver cysts. Patients with multicystic liver disease or type I polycystic liver disease are more prone to late cyst recurrence. A tailored approach is thus indicated for patients with congenital liver cystic disease. However, the laparoscopic approach appears to be the gold standard for the treatment of highly symptomatic or complicated simple liver cysts.

Calculation of the renal perfusion and glomerular filtration rate from the renal impulse response obtained with MRI

The aim of this study was to assess the importance of deconvolution for the calculation of renal perfusion and glomerular filtration rate (GFR) on the basis of concentration–time curves as measured with perfusion MRI. Six rabbits were scanned dynamically after injection of a gadolinium chelate. Concentration–time curves were generated by manually drawing regions of interest in the aorta and the renal cortex. To remove the dependency on the arterial input function, a regularized structured total least‐squares deconvolution algorithm was used to calculate the renal impulse response. This curve was fitted by the sum of two gamma variate functions, corresponding to the passage of the contrast agent in the glomeruli and the proximal convoluted tubules. Tracer kinetics models were applied to these two functions to obtain the renal perfusion and GFR. For comparison, these two parameters were also calculated on the basis of the renal concentration–time curve before deconvolution. The renal perfusion values correlated well (r = 0.9, P = 0.014) with the values calculated by a validated upslope method. The GFR values correlated well (r = 0.9, P = 0.014) with the values obtained from the clearance of 51Cr‐EDTA. A comparison of the values obtained with and without deconvolution demonstrated the necessity of deconvolution. Magn Reson Med 51:1017–1025, 2004.

Laparoscopic treatment of gallbladder duplication - A plea for removal of both gallbladders

AbstractBackground: Gallbladder duplication is a rare congenital condition, which can now be detected preoperatively by imaging studies. Methods: We report a case of duplicated gallbladder with symptomatic unilobar gallstones. Appropriate biliary workup (ultrasound, oral cholecystography, and intravenous cholangiography) allowed a correct preoperative diagnosis. Results: Laparoscopic treatment included selective removal of the diseased accessory gallbladder. However, postoperative acute cholecystitis and symptomatic gallstone occurred in the remaining main gallbladder, and laparoscopic reintervention was required 27 months later. Conclusions: This case illustrates the need for complete removal of both gallbladders during initial surgery. Precise intraoperative recognition of vascular and biliary anatomy—including abnormalities—is highlighted to avoid mistakes during surgery.

Analysis of contrast-enhanced MR images to assess renal function.

The image analysis and kinetic modeling methods used in dynamic contrast-enhanced magnetic resonance imaging of the kidney are reviewed. Image analysis includes various techniques of coregistration and segmentation. Few methods have been completely implemented. Nevertheless, the use of coregistration may become a standard to decrease the effect of motion on abdominal images and improve the quality of the renal signals. Kinetic models are classified into three categories: enhancement-based, external and internal representations. Enhancement-based representations are limited to a basic analysis of the tracer concentration curves in the kidneys. Their relationship to the underlying physiology is complex and undefined. However, they can be used to evaluate the split renal function. External representations assess the kidney input and output. An external representation based on the up-slope of the renal enhancement to calculate the renal perfusion is commonly used because of its simplicity. In contrast, external representation based on deconvolution or identification methods remain underexploited. For glomerular filtration, an internal representation based on a two-compartmental model is mostly used. Internal representations based on multi-compartmental models describe the renal function in a more realistic way. Because of their numerical complexity, these models remain rarely used.

Imagerie par résonance magnétique de l’angiogenèse tumorale

Tumor angiogenesis induces the proliferation of immature blood vessels that are both heterogeneous and leaky. These characteristics can be demonstrated by measuring the perfusion parameters with MRI. Perfusion MRI is usually performed with in T1-weighted dynamic imaging after bolus injection of an exogenous contrast agent such as gadolinium chelate. The perfusion parameters are obtained by semi-quantitative or quantitative analysis of the enhancement curves in the tumor and the arterial input. Perfusion can also be assessed without injecting a contrast agent using arterial spin labeling techniques, diffusion MRI, or BOLD (blood oxygen level dependent) MRI. However, these latter methods are limited by a low signal-to-noise ratio and problems with quantification. The main indication for perfusion MRI is the assessment of antiangiogenic and antivascular treatments. New possibilities for demonstrating angiogenic blood vessels are being opened by molecular imaging.

Experimental31p nmr study of the influence of ionic strength on the apparent dissociation constant of mgatp

The classical method for31P NMR determination of intracellular free magnesium concentration ([Mgfree2+]) requires an accurate knowledge of the apparent dissociation constant (KD) of MgATP. There is a large difference between the previously determined values ofKD. Although the value of 50 µM, determined by a31P NMR method, is now largely accepted, a value of 86 µM has more recently been measured with a fitting method derived from the original one, and with a different ionic strength. The purpose of our study was to assess if the cause of the difference between these two previously reportedKD values was due to the measuring method or to the ionic strength value used.Working at pH=7.2,T=37°C, and [KCl]=0.25 M, we performedKD measurements with the original31P NMR method and with the fitting method. The results (67±13 µM and 61±20 µM, respectively) were not significantly different. Then, with the first method, we measured KD at [KCl]=0.12 M and found a value of 19±5 µM. We conclude that the main cause of difference between theKD values measured by31P NMR reside in the disparity of ionic strength values used for their measurement. OurKD measurements at [KCl]=0.25 and 0.12 M demonstrate the importance of the ionic strength value used for imitating the intracellular medium on the absolute value of ([Mgfree2+]) measured by31P NMR spectroscopy.

Indinavir Calculi: Diagnosis with Magnetic Resonance Urography

Indinavir sulfate is a protease inhibitor of the human immunodeficiency virus (HIV) type 1, that is widely used to treat patients with HIV infection. Indinavir therapy is associated with a significant incidence of crystalluria and urolithiasis [1]. These calculi are not opaque and consist of monohydrate indinavir crystals. Computed tomographic findings of ureteral calculi in patients with HIV receiving indinavir sulfate have recently been reported [2, 3]. Diagnosis is difficult with unenhanced computed tomography, and images after intravenous injection of an iodinated contrast agent may need to be performed to identify the cause of obstruction. We report a case of bilateral ureteral calculi demonstrated by magnetic resonance (MR) urography in an HIV-infected patient treated with indinavir sulfate.

Oncologie : abdomen et foie

Objectifs Connaitre les particularites de la diffusion hepatique. Savoir realiser les sequences de diffusion hepatique. Connaitre l’interet de la diffusion dans les pathologies diffuses et en detection et caracterisation de lesions focales. Messages a retenir Les sequences de diffusion font partie du protocole d’acquisition des lesions focales du foie en IRM. Les protocoles d’acquisition dependent des questions cliniques : detection ou caracterisation. La detection des tumeurs hepatiques est accrue par les sequences de diffusion. Resume Le foie est un organe isotropique. Il est souhaitable de faire une sequence a multiples valeurs de b. La valeur maximale du b est comprise entre 500 et 1000. On privilegie les sequences sans synchronisation respiratoire. Le coefficient d’ADC diminue avec la fibrose hepatique. Les tumeurs hepatiques benignes ont un ADC plus eleve que les tumeurs hepatiques malignes. Les sequences de diffusion sont aussi utiles pour la detection de lesions hepatiques notamment lors de la recherche de metastases hepatiques.