Search

Resume Introduction L’elastographie dynamique est une methode d’imagerie quantitative non-invasive permettant d’evaluer les proprietes mecaniques des tissus biologiques. Elle est utilisee pour identifier de nouveaux biomarqueurs de processus pathologiques. Son principe repose sur l’introduction d’ondes mecaniques et l’evaluation de la reponse tissulaire. Donnees recentes Plusieurs techniques d’elastographie ultrasonore sont implementees sur des appareils cliniques et sont desormais utilisees en routine. L’elastographie par resonance magnetique s’est developpee plus recemment et l’objectif de cet article est d’exposer ses bases techniques ainsi que de discuter ses avantages et limites par rapport a l’echographie ultrasonore. Conclusion L’elastographie par resonance magnetique est une methode prometteuse pour le diagnostic non-invasif de pathologies fibro-inflammatoires et du cancer.

International audience; Non-alcoholic steatohepatitis (NASH) is characterized at histology by steatosis, hepatocyte ballooning and inflammatory infiltrates, with or without fibrosis. Although diamagnetic material in fibrosis and inflammation can be detected with quantitative susceptibility imaging, fatty acid composition changes in NASH relative to simple steatosis have also been reported. Therefore, our aim was to develop a single magnetic resonance (MR) acquisition and post-processing scheme for the diagnosis of steatohepatitis by the simultaneous quantification of hepatic fat content, fatty acid composition, T 2 * transverse relaxation time and magnetic susceptibility in patients with non-alcoholic fatty liver disease. MR acquisition was performed at 3.0 T using a three-dimensional, multi-echo, spoiled gradient echo sequence. Phase images were unwrapped to compute the B 0 field inhomogeneity (ΔB 0) map. The ΔB 0-demodulated real part images were used for fat-water separation, T 2 * and fatty acid composition quantification. The external and internal fields were separated with the projection onto dipole field method. Susceptibility maps were obtained after dipole inversion from the internal field map with single-orientation Bayesian regularization including spatial priors. Method validation was performed in 32 patients with biopsy-proven, non-alcoholic fatty liver disease from which 12 had simple steatosis and 20 NASH. Liver fat fraction and T 2 * did not change significantly between patients with simple steatosis and NASH. In contrast, the saturated fatty acid fraction increased in patients with NASH relative to patients with simple steatosis (48 ± 2% versus 44 ± 4%; p < 0.05) and the magnetic susceptibility decreased (−0.30 ± 0.27 ppm versus 0.10 ± 0.14 ppm; p < 0.001). The area under the receiver operating characteristic curve for magnetic susceptibility as NASH marker was 0.91 (95% CI: 0.79-1.0). Simultaneous MR quantification of fat content, fatty acid composition, T 2 * and magnetic susceptibility is feasible in the liver. Our preliminary results suggest that quantitative susceptibility imaging has a high diagnostic performance for the diagnosis of NASH.

Resume L’imagerie de perfusion hepatique est une modalite d’etude quantitative et fonctionnelle. La difficulte, dans le cas du foie, vient de son double apport vasculaire, des artefacts lies aux mouvements respiratoires et aux capillaires sinusoides fenetres laissant diffuser le traceur. On peut etudier la perfusion hepatique en echographie, scanner ou IRM et chaque technique presente limites et specificites. Les grandes indications en hepatologie sont l’oncologie (detection, caracterisation et reponse tumorale) et l’exploration non invasive des maladies hepatiques chroniques. Des efforts de standardisation sont necessaires concernant les modalites d’acquisition et la modelisation pour permettre une diffusion des resultats et une utilisation plus large.

Liver perfusion imaging is a quantitative functional investigation. Liver perfusion imaging is complicated because of the liver's dual vascular supply, artefacts due to respiratory movements and the fenestrated sinusoidal capillaries which allow the contrast medium to diffuse out. Liver perfusion can be examined by ultrasound, CT or MRI: each technique has its limitations and specific features. The major indications in hepatology are oncology (detection, characterization and tumor response) and non-invasive investigation of patients with chronic liver disease. Work is needed to standardize acquisition and modeling methods to allow wider use of results and more widespread use of the technique.

Diffusion-weighted MR imaging of the liver Diffusion-weighted imaging studies the motion of water molecules within a given tissue. Initially used for neuroradiological applications, it is now routinely used for abdominal imaging, especially liver imaging. The diffusion pulse sequence is a T2 echo-planar sequence where diffusion gradients are applied. In this article, we will review the sequence itself and the parameters used to optimize the sequence, quantitative and qualitative image evaluation, and the main applications for liver imaging: characterization of focal lesions, detection of focal lesions, evaluation of response to therapy and quantification of liver fibrosis.

The purpose of our study was to assess the effects of intravenous administration of ferumoxides on normal and abnormal vertebral bone marrow T1 and T2 relaxation times. Changes in bulk T1 and T2 relaxation times induced by intravenous administration of ferumoxides were determined in the normal vertebral marrow of two healthy subjects and four patients. In the four patients, changes in bulk T1 and T2 values induced by furomoxides injection were also determined in 12 vertebral metastases. Relative to precontrast relaxation time values, bulk T1 and T2 values of normal bone marrow had declined by a mean of 24% and 19%, respectively, in the two subjects and the four patients 45 minutes after ferumoxides administration. Relative to precontrast values, bulk T1 and T2 values of abnormal bone marrow had decreased by a mean of 16% and 2%, respectively. Decreases in bulk T1 and T2 values in normal bone marrow and in bulk T1 values in metastases were statistically significant (P

Magnetic resonance (MR) elastography is an emerging method for measuring the viscoelastic properties of tissues. Hepatic fibrosis, which increases the elasticity or stiffness of the liver, can be detected and staged by MR elastography. The technique has several advantages compared with transient ultrasound elastography (FibroScan): it can evaluate much larger liver volumes; it can be performed in obese patients and in those with ascites; and it can assess the full three-dimensional displacement vector, allowing a more precise analysis of viscoelastic parameters. These technical advantages mean that MR elastography is more accurate forstaging liver fibrosis than is transient ultrasound elastography. Moreover, it has been shown in animal studies using MR elastography that parameters other than fibrosis can also increase liver elasticity, including inflammation and myofibroblast activation before extracellular matrix deposition. Because of its greater accuracy-but also its higher cost-MR elastography will probably have a complementary role alongside ultrasound elastography. Nevertheless, this role should be further studied, especially in terms of response to treatment and the early detection of chronic liver diseases such as steatohepatitis.

Purpose: To construct an appropriate phantom for quality control use in diffusion-weighted imaging (DWI), to establish ground truth for measurement of apparent diffusion coefficient (ADC) and to characterize measurement linearity across a relevant physiological range of ADC. Methods: Aqueous solutions containing the polymer polyvinylpyrrolidone (PVP) were mixed at concentrations of 0, 10, 20, 30, 40 and 50% by mass PVP. These solutions were placed in 20 mL vials, arranged in concentric inner and outer circles, with a central water vial, and were fixed in a spherical phantom with a diameter of 194 mm, designed to fit into commercially-available MRI head coils. Two prototype phantoms were constructed, and underwent inter-site comparison in the US and EU. The phantoms were filled with an ice-water bath to ensure stable temperature; 0 °C temperature was verified by use of a thermocouple before and after scans. The phantoms were scanned using b-values of 0, 500 and 900 s/mm2 at several sites, using coronal and/or axial orientations and scan planes. Results: ADC values ranged from 0.12 to 1.12 × 10-3 mm2/s, and exhibited a high degree of reproducibility across different scanners and imaging sites (coefficient of variations (CoV) ranged from 1.1 to 2.2% for 0 to 40% PVP, with 50% PVP at 11.3%). Little difference in ADCs was seen between inner and outer ring vials of the same PVP concentration (average CoV< 5% across vials, 10.3% for 50% PVP). Conclusion: The range of ADCs covers a relevant physiological range, most notably in brain white matter. The ADCs of water vials were in excellent agreement with literature values of the diffusion coefficient of water at 0 °C (1.1 × 10-3 mm2/s). The phantom provides a much needed quality control tool for DWI, and provides ground truth with the diffusion coefficient of water at 0 °C.

Bile duct calculi can be classified into primary or secondary stones, depending on their site of origin. The majority of bile duct stones are secondary stones formed in the gallbladder, which then migrate into the extrahepatic biliary tree. These stones reflect the composition of gallbladder stones, i.e. predominantly cholesterol in 80% and black pigment in 20% (Hawes and Sherman 1995) The frequency of common bile duct stones increases with increasing age of the patient. Cystic duct diameter appears to be an important factor in the migration of gallbladder stones into the common bile duct. Primary stones form de novo in the bile ducts. These pigmented stones are brown or black and are often friable. Their pathogenesis depends on two main factors, which are biliary stasis and bacterial or parasitic infection.

The aim of our study was to assess the feasibility of using Doppler sonography for the detection of acute intestinal ischemia due to occlusion of the superior mesenteric artery. Between September 1993 and March 1995, abdominal sonography with Doppler imaging of the mesenteric vessels was performed in 770 patients with emergency admissions for acute abdominal pain. In six cases, the diagnosis, based on surgery or arteriography and computed tomography, was acute intestinal ischemia due to complete or localized occlusion of the superior mesenteric artery. Five cases of occlusion of the superior mesenteric artery were correctly detected by Doppler sonography. These results suggest that Doppler sonography may be a feasible method for detecting acute intestinal ischemia due to proximal superior mesenteric artery occlusion.