Real time shear waves elastography monitoring of thermal ablation: in vivo evaluation in pig livers.

BACKGROUND: Thermal ablation is a widely used minimally invasive treatment modality for different cancers. However, lack of a real-time imaging system for accurate evaluation of the procedure is one of the reasons of local recurrences. Shear waves elastography (SWE) is a new ultrasound (US) imaging modality to quantify tissue stiffness. The aim of the study was to assess the feasibility and accuracy of US elastography for quantitative monitoring of thermal ablation and to determine the elasticity threshold predictive of coagulation necrosis. METHODS: A total of 29 in vivo thermal lesions were performed in pig livers with radiofrequency system. SWE and B-mode images were acquired simultaneously. Liver elasticity was quantified by using SWE data and expressed in kilopascal. After the procedure, pathologic analysis of treated tissues was compared with US images. The sensitivity and positive predictive value of the SWE maps of tissue elasticity were calculated and compared with the boundaries of the pale coagulation necrosis areas found at pathology. RESULTS: The liver mean elasticity values before and after thermal therapy were 6.4 ± 0.3 and 38.1 ± 2.5 kPa, respectively (P < 0.0001). For a threshold of 20 kPa, sensitivity (i.e., the rate of pixels correctly detected as necrosed tissue) was 0.8, and the positive predictive value (i.e., the rate of pixels in the elastographic map >20 kPa that actually developed coagulation necrosis) was 0.83. CONCLUSIONS: Tissue areas with coagulation necrosis are significantly stiffer than the surrounding tissue. SWE permits the real-time detection of coagulation necrosis produced by radiofrequency and could potentially be used to monitor US-guided thermal ablation.

In vivo MRI assessment of placental and foetal oxygenation changes in a rat model of growth restriction using blood oxygen level-dependent (BOLD) magnetic resonance imaging.

OBJECTIVES: To evaluate whether changes in BOLD signal intensities following hyperoxygenation are related to intrauterine growth restriction (IUGR) in a rat model. METHODS: IUGR was induced in pregnant rats by ligating the left vascular uterine pedicle at day 16 of gestation. BOLD MR imaging using a balanced steady-state free-precession (balanced-SSFP) sequence on a 1.5-T system was performed on day 19. Signal intensities (SI) before and after maternal hyperoxygenation were compared in the maternal liver and in control and growth-restricted foetoplacental units (FPUs). RESULTS: Maternal hyperoxygenation resulted in a significant increase in SI in all regions of interest (P < 0.05) in the 18 rats. In the control group, the SI (mean ± SD) increased by 21 % ± 15 in placentas (n = 74) and 13 % ± 8.5 in foetuses (n = 53). In the IUGR group, the increase was significantly lower: 6.5 % ± 4 in placentas (n = 36) and 7 %± 5.5 in foetuses (n = 34) (P < 0.05). CONCLUSION: BOLD MRI allows non-invasive assessment of the foetoplacental response to maternal hyperoxygenation in the rat and demonstrates its alteration in an IUGR model. This imaging method may provide a useful adjunct for the early diagnosis, evaluation, and management of human IUGR. KEY POINTS: • Intra-uterine growth restriction is an important cause of perinatal morbidity and mortality. • Blood oxygen level-dependent MRI non-invasively assesses foetoplacental response to maternal hyperoxygenation. • In the rat, foetoplacental response to maternal hyperoxygenation is altered in IUGR. • Functional MRI may help to assess human IUGR.

Shear wave elastography of tumour growth in a human breast cancer model with pathological correlation.

OBJECTIVE: To assess stiffness in a human breast cancer implanted in mice using shear wave elastography (SWE) during tumour growth and to correlate the results with pathology. METHODS: Local ethics committee for animal research approval was obtained. A human invasive ductal carcinoma was implanted subcutaneously in 24 athymic nude female mice. Ultrasound was longitudinally performed in 22 tumours, every 1-2 weeks. Maximum diameter and mean stiffness were collected. Seven tumours were measured both in vivo and ex vivo. Tumours of different sizes were removed for pathological analysis on which the percentages of viable cellular tissue, fibrosis and necrosis were measured. RESULTS: A total of 63 SWE measurements were performed. Stiffness increased during tumour growth with an excellent correlation with size (r = 0.94, P < 0.0001). No differences were found between the values of stiffness in vivo and ex vivo (P = 0.81). There was a significant correlation between elasticity and fibrosis (r = 0.83, P < 0.0001), a negative correlation with necrosis (r = -0.76, p = 0.0004) but no significant correlation with cellular tissue (r = 0.40, p = 0.1). CONCLUSION: Fibrosis plays an important role in stiffness as measured by SWE, whereas necrosis is correlated with softness. KEY POINTS: • In a breast cancer model, ultrasound tumour stiffness is correlated with size. • Stiffness changes with tumour growth are correlated with pathological changes. • Stiffness is very well correlated with proportion of tumour fibrosis. • Stiffness is inversely correlated with proportion of tumour necrosis. • Tumour stiffness measurements are similar in vivo and ex vivo.

SPIO-enhanced magnetic resonance imaging study of placental perfusion in a rat model of intrauterine growth restriction.

OBJECTIVE: To assess placental perfusion with magnetic resonance imaging (MRI) and superparamagnetic iron oxide (SPIO) in a rat model of intrauterine growth restriction (IUGR). DESIGN: Experimental animal study. SETTING: The study complied with US National Institutes of Health recommendations for animal care. POPULATION: Thirty-two rats at day 16 of gestation underwent surgical ligation of the left uterine vessel to induce IUGR. METHODS: Eighteen rats were examined by MRI 3 days later, after bolus injection of ferucarbotran. MAIN OUTCOME MEASURE: Signal intensities were measured in the maternal left ventricle and in the placentas of the two horns. Quantitative microcirculation parameters were calculated and compared between the placentas of the two horns. RESULTS: Fifty-four kinetic curves of placental perfusion were obtained in 11 rats. The mean placental blood flow was significantly lower in the ligated horns than in the normal horns (108.1 versus 159.4 ml/minute/100 ml, p = 0.0004). The mean fractional volume of the maternal vascular placental compartment did not differ significantly between the pathological (42.8%) and normal placentas (39.2%). CONCLUSIONS: Placental perfusion, including changes during experimental IUGR, can be measured in rats by using MRI with SPIO. These findings could have implications for human studies of placental microcirculation and for the management of disorders related to placental dysfunction.

Optimizing the size variation threshold for the CT evaluation of response in metastatic renal cell carcinoma treated with sunitinib.

BACKGROUND: In metastatic renal cell carcinoma (mRCC), antiangiogenic treatments rarely achieve a reduction of -30% in the sum of longest diameters (SLD) of target lesions required by RECIST for an 'objective response', although they objectively improve progression-free survival (PFS). We sought to determine a threshold for the computed tomography evaluation of these patients' best reflecting patient outcome. PATIENTS AND METHODS: In 334 mRCC patients treated with sunitinib, we tested thresholds from -45% to +10%. We classified patients as 'responders' when the best relative variation of the sum of longest diameters (DeltaSLD) reached the tested threshold and as 'nonresponders' otherwise. For each tested threshold, the median PFS of the two groups were compared. Receiver operating characteristic (ROC) analysis was also carried out among the 103 patients that progressed during follow-up. Finally, the 'optimal' threshold was retested on an independent cohort of 39 patients. RESULTS: The DeltaSLD threshold of -10% gave the most significant difference. It divided patients into 256 responders and 78 nonresponders (median PFS 11.1 and 5.6 months). The same -10% threshold was found using the ROC analysis. Results were confirmed on the external validation cohort. CONCLUSION: A variation of -10% in the SLD accurately and rapidly identifies mRCC patients benefiting from sunitinib.

Small bowel polyp resection using device-assisted enteroscopy in Peutz-Jeghers Syndrome: Results of a specialised tertiary care centre.

INTRODUCTION: Enteroscopy resection of small bowel polyps in Peutz-Jeghers syndrome has only been described in small case series. Herein, we aimed to assess the efficacy of enteroscopy resection of small bowel polyps within a specialised tertiary care centre and the impact on intraoperative enteroscopy. METHODS: This was an observational single-centre study. All adult Peutz-Jeghers syndrome patients followed in the Predisposition Digestive Ile-de-France network who underwent an endoscopic resection of at least one small bowel polyp ≥ 1 cm by enteroscopy between 2002-2015 were included. Small bowel polyps were detected under a dedicated screening programme by previous capsule endoscopy and/or magnetic resonance enterography, performed every 2-3 years. Complete treatment was defined as the absence of polyps ≥ 1 cm after conventional endoscopic resection. Intraoperative enteroscopy or surgical resection were indicated in incomplete treatments. The overall complete treatment rate including conventional enteroscopy and intraoperative enteroscopy was also considered. RESULTS: Endoscopic resection of 216 small bowel polyps (median: 8.6 per patient, size: 6-60 mm) was performed by 50 enteroscopies in 25 patients (mean age: 36 years, range: 18-71, 56% male) with small bowel polyp ≥ 1 cm. Twenty-three patients (92%) underwent 42 screening capsule endoscopies and 14 (57%) had 23 magnetic resonance enterographies during a median follow-up of 60 months. Complete treatment was achieved in 76%. Intraoperative enteroscopy and surgical resection were performed in four (16%) and two (8%) patients. Intraoperative enteroscopy improved by 16% the complete treatment rate and the overall rate was 92%. The complication rate was 6%. CONCLUSION: This long-term study confirmed the efficacy and safety of endoscopic resection of small bowel polyps in Peutz-Jeghers syndrome. Intraoperative enteroscopy can be a complementary approach in selected cases.

Fibrin glue sealing in the treatment of a recto-urethral fistula in Crohn's disease: a case report.

Recto-urethral fistulas in Crohn's disease are rare, and managing them is difficult. The various surgical techniques are not reliably effective and are associated with a significant risk of morbidity. The rectal mucosal transposition flap technique, which is used most frequently, requires the rectal mucosa to be in a healthy condition. We report here on a case where treatment was by injecting fibrin glue into a complex fistula with a single anorectal point of origin but combining a median recto-urethrocutaneous tract with two deep lateral rectoperineal tracts. The patient had presented with active rectal Crohn's disease. This treatment produced complete closure, verified by MRI, of all the fistula tracts, which was still maintained after three years, and with normal anal continence. When confronted with this type of fistula, and particularly when the condition of the rectal mucosa is poor, the specialist should be encouraged by this good result to consider the injection of fibrin glue, a technique without risk of morbidity, as a first course of action.

[Imaging of response to treatment in oncology]. / Imagerie de la réponse aux traitements en cancérologie.

Imaging plays a crucial role in oncology to assist in the management of patients and selection of drug regimen. Recent advances in imaging techniques allowing to predict and evaluate response to treatments in oncology will be reviewed. The standard in the evaluation of response to treatment is based on the measurement of lesion size. Functional imaging assesses physiological or molecular processes that may be earlier indicators of early response to treatment. Dynamic imaging of tumor vascularization assesses the biodistribution of a contrast agent within tumoral tissues. Diffusion-weighted MR imaging can differentiate free water from water restricted by tissues, providing an assessment of tumor cellularity. MR spectroscopy assesses the relative quantity of specific chemical components within normal and tumoral tissues. 18 FDG PET imaging provides an assessment of the metabolic activity of tissues. FDG uptake is proportional to cellular proliferation and number of viable cells within a tumor. Results from studies assessing the role of these emerging imaging techniques remain preliminary and the medical community must determine their respective role in the routine evaluation of response to treatment in oncological patients.

Dynamic contrast enhanced MRI of the placenta: A tool for prenatal diagnosis of placenta accreta?

BACKGROUND: Ultrasound (US) is the primary imaging modality for the diagnosis of placenta accreta, but it is not sufficiently accurate. MRI morphologic criteria have recently emerged as a useful tool in this setting, but their analysis is too subjective. Recent studies suggest that gadolinium enhancement may help to distinguish between the stretched myometrium and placenta within a scar area. However, objective MRI criteria are still required for prenatal diagnosis of placenta accreta. The purpose of this study was to assess the diagnostic value of dynamic contrast gadolinium enhancement (DCE) MRI patterns for placenta accreta. MATERIALS AND METHODS: MR images were acquired with a 1.5-T unit at 30-35 weeks of gestation in women with a history of Caesarian section, a low-lying anterior placenta, and US features compatible with placenta accreta. Sagittal, axial and coronal SSFP (Steady State Free Precession) sequences were acquired before injection. Then, contrast-enhanced dynamic T1-weighted images were acquired through the entire cross-sectional area of the placenta. Images were obtained sequentially at 10- to 14-s intervals for 2 min, beginning simultaneously with the bolus injection. Functional analysis was performed retrospectively, and tissular relative enhancement parameters were extracted from the recorded images. The suspected area of accreta (SAA) was placed in the region of the previous scar, and a control area (CA) of similar size was placed on the same image plane, as far as possible from the SAA. Semi-quantitative analysis of DCE-MR images was based on the kinetic enhancement curves in these two regions of interest (ROI). Three tissular relative enhancement parameters were compared according to the pregnancy outcomes, namely time to peak, maximal signal intensity, and area under the enhancement curve. RESULTS: We studied 9 women (43%) with accreta and 12 women (57%) with a normal placenta. All three tissular relative enhancement parameters differed significantly between the two groups (p < 10-3). CONCLUSION: The use of dynamic contrast-enhanced MRI at 30-35 weeks of gestation in women with a high risk of placenta accreta allows the extraction of tissular enhancement parameters that differ significantly between placenta accreta and normal placenta. It therefore provides objective parameters on which to base the diagnosis and patient management.

In vivo dynamic MRI measurement of the noradrenaline-induced reduction in placental blood flow in mice.

PURPOSE: We developed a new model for in vivo placental perfusion measurements based on dynamic MRI in mice. As noradrenaline has been implicated in the pathogenesis of preeclampsia, we examined whether it reduced placental perfusion in mice, and whether such a reduction could be detected with our MRI model. MATERIALS AND METHODS: Mice at 16 days of gestation were injected intramuscularly with saline or noradrenaline solution. A conventional gadolinium chelate was then injected IV, and a single-slice T1-weighed 2D Fast SPGR sequence was acquired for 200 s. Signal intensity was measured on all the images and converted into contrast agent tissue concentrations in the maternal left ventricle (input function) and placentas. A one-compartment model was developed using compartmental and numerical modeling software. Mean blood flow (F) was calculated from a transfer constant. RESULTS: Twenty-six mice were studied, yielding a total of 55 MRI measurements of placental perfusion (29 in the control group and 26 in the noradrenaline group). Mean placental blood flow (F) was significantly lower in the noradrenaline group (0.72+/-0.84 ml/min/g of placenta) than in the control group (1.26+/-0.54 ml/min/g of placenta). CONCLUSION: Noradrenaline reduces placental perfusion in mice. Our MRI dynamic model might be useful for detecting and investigating abnormal placental blood flow, thereby avoiding the need for invasive procedures and animal sacrifice.

[Treatment response evaluation by functional imaging]. / Evaluation de la réponse au traitement par imagerie fonctionnelle.

Imaging in cancer plays a capital role to guide the clinician in his choice of therapies. We will discuss the new techniques available to predict and evaluate treatment response in oncology. The method of reference to evaluate treatment response is based on the measure of lesion size. Functional imaging doesn't evaluate size, but rather a physiological or molecular feature, which is probably modified earlier in response to treatment. Dynamic contrast-enhanced functional imaging of microcirculation follows the biodistribution of a contrast agent and analyses tumour vascularization. Diffusion-weighted Magnetic Resonance Imaging differentiates free and restrained water molecules in tissues, reflecting tumor cellularity. Nuclear Magnetic Resonance spectroscopy is an application of MRI that yields information on the metabolic content of a tissue. It detects relative quantities of various molecules which differ in tumour compared to normal tissue. Positon-emission tomography using (18)FDG is a nuclear medicine technique which gives information on tissue metabolism. Captation of FDG is proportional to the proliferative activity and the number of viable cells in a tumour. Human studies concerning these techniques are still quite preliminary, and the medical community must determine their potential in clinical practice to evaluate treatment response in oncology.

[Placental functional assessment using MRI: mice today, humans tomorrow?]. / L'IRM fonctionnelle pour l'étude de la fonction placentaire: aujourd'hui chez la souris, demain chez l'homme?

Placental insufficiency, a process due to either poor placental perfusion or permeability, may lead to progressive deterioration in placental function and materno-fetal morbidity. Advances in MR contrast media pharmacokinetic studies of transit through tissues and dynamic MRI allow to characterize organs microcirculation in vivo. Placental function assessment might be achieved using analysis of dynamic contrast enhanced MRI of tracers. A murine model of placental assessment has been constructed. Herein, principles, results and limitations of such techniques are discussed as well as their potential interest and weaknesses in humans.

Amygdala atrophy in Alzheimer's disease. An in vivo magnetic resonance imaging study.

OBJECTIVES: To study the ability of magnetic resonance imaging to measure the volume of the amygdala and detect amygdala atrophy in patients with early Alzheimer's disease. DESIGN: Prospective case-control study and "blind" measurements. SETTING: Subjects were ambulatory outpatients selected from an institutional practice in Paris, France. PATIENTS: We studied 11 patients with probable Alzheimer's disease according to National Institute of Neurologic and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) and Consortium to Establish a Registry for Alzheimer's Disease (CERAD) inclusion and exclusion criteria, as well as six age-matched control subjects. INTERVENTION: None. MAIN OUTCOME MEASURE: A 1.5-T magnetic resonance imager was used to acquire the images. Two neuroradiologists independently and blindly measured the volume of the right and left amygdalas on high-resolution contiguous slices. In addition, other cerebral structures, ie, the sylvian fissures, temporal lobes, lateral and third ventricles, corpus callosum, and hippocampal formation, were measured on a single slice. RESULTS: The values obtained by the two observers correlated highly (r = .90), and interrater variability was 13%. The Alzheimer's disease group showed significant (33%, P < .0001) atrophy of the amygdala when compared with the control group. The other structures showed less variation. CONCLUSION: Significant amygdala atrophy can be detected in vivo in patients with early Alzheimer's disease by means of standard magnetic resonance imaging. This technique may be useful in the early diagnosis of Alzheimer's disease.

Phospholipid abnormalities in early Alzheimer's disease. In vivo phosphorus 31 magnetic resonance spectroscopy.

OBJECTIVE: To determine whether changes in phosphomonoester and phosphodiester levels could be detected in vivo with phosphorus magnetic resonance spectroscopy in the early stage of Alzheimer's disease (AD). DESIGN: Survey-type of case-control study using neuropsychological testing as criterion standard with blinded data analysis. SETTING: Patients were from a neurology clinic in Paris, France. The controls were from the community. Magnetic resonance measurements were performed in the prefrontal region of the brain with a clinical 1.5-T scanner. Blinded data analysis. PARTICIPANTS: Twenty-four patients with mild AD and 15 age-matched healthy volunteers. Subjects were separated into two groups, both composed of patients with AD and healthy volunteers. Two successive acquisition protocols were used in the two groups. RESULTS: A significant increase in the phosphomonoester-total phosphorus ratio was found in patients with AD compared with controls. In this series, use of a ratio above 11% as a threshold to test our sample yielded an 83.3% sensitivity and a 73.3% specificity test for AD. Other metabolite ratios (inorganic phosphate, phosphodiesters, phosphocreatine, and nucleotide phosphates to total phosphorus) were not significantly different between patients and controls. No metabolite ratio correlated with the neuropsychological status as assessed by the Mini-Mental State Examination. CONCLUSION: Changes in phospholipid metabolism can be detected in vivo in the early stage of AD. Discrepancies in the literature may be due to differences in technical setting or in subject population types.

Functional MRI during word generation, using conventional equipment: a potential tool for language localization in the clinical environment.

OBJECTIVE: To test the accuracy of bilateral language mapping using a standard clinical magnetic resonance (MR) imaging device during word generation. DESIGN: A study of normal volunteers. SETTING: Volunteers from the Washington, DC, area. PARTICIPANTS: Nine normal, right-handed, native English speakers (four women, five men, mean age 31 years). INTERVENTIONS: During four MR acquisition periods, subjects would alternately rest and silently generate words. Sagittal MR images covered the middle and inferior frontal gyri, insulae, and part of the temporal and parietal lobes bilaterally. MAIN OUTCOME MEASURES: (1) Anatomic maps of task-related signal changes obtained by comparing, in each voxel, the signal during word generation and rest periods, and (2) analysis of the time course of the signal. RESULTS: Maximum responses were in the left hemisphere, mainly in the frontal lobe (Broca's area, premotor cortex, and dorsolateral prefrontal cortex) but also in posterior regions such as Wernicke's area. In agreement with previous studies, some degree of task-related changes was present in a subset of the corresponding regions in the right hemisphere. CONCLUSION: Despite certain limitations, it is possible, using widely available MR equipment, to obtain results consistent with previous studies. The technique may have important implications for assessment of cognitive functions in patients with neurologic disorders in a clinical environment.

Noninvasive assessment of language dominance in children and adolescents with functional MRI: a preliminary study.

BACKGROUND: Assessment of language organization is crucial in patients considered for epilepsy surgery. In children, the current techniques, intra-carotid amobarbital test (IAT) for language dominance, and cortical electrostimulation mapping (ESM), are invasive and risky. Functional magnetic resonance imaging (fMRI) is an alternative method for noninvasive functional mapping, through the detection of the hemodynamic changes associated with neuronal activation. We used fMRI, to assess language dominance in children with partial epilepsy. METHODS: Eleven right handed children and adolescents performed a word generation task during fMRI acquisition focused on the frontal lobes. Areas where the signal time course correlated with the test paradigm (r = 0.7) were considered activated. Extent and magnitude of signal changes were used to calculate asymmetry indices. Seven patients had IAT, ESM, or surgery outcome available for comparison. RESULTS: fMRI language dominance always agreed with IAT (6 cases) and ESM (1 case), showing left dominance in six and bilateral language in one. fMRI demonstrated left dominance in three additional children, and right dominance in one with early onset of left temporal epilepsy. Four children whose initial studies were equivocal due to noncompliance or motion artifacts were restudied successfully. CONCLUSIONS: fMRI can be used to assess language lateralization noninvasively in children. It has the potential to replace current functional mapping techniques in patients, and to provide important data on brain development.

Hepatocyte targeting with Gd-EOB-DTPA: potential application for gene therapy.

RATIONALE AND OBJECTIVES: To evaluate the suitability of the liver-specific MRI contrast agent Gd-EOB-DTPA as a nonviral vector for gene therapy of hepatocellular carcinoma. METHODS: Specific uptake of Gd-EOB-DTPA was quantified by relaxometry in rat cultured hepatocytes and the hepatoma cells HepG2 and Huh7. Nonviral vectors for gene transfer were synthesized by coupling Gd-EOB-DTPA to polyethyleneimine or polylysine as DNA condensing agents, and their efficiency was studied using beta-galactosidase (lacZ) as the reporter gene. RESULTS: Gd-EOB-DTPA was specifically taken up by rat cultured hepatocytes (4.32 vs. 1.08 mmol/L in nonhepatocyte control cells) but not by the hepatoma cells; this uptake was concentration-dependently inhibited by Bromsulphtalein. Polycation linkages were achieved with yields of 0.9 Gd-EOB-DTPA molecule per polyethyleneimine molecule and 10 Gd-EOB-DTPA molecules per polylysine molecule. Incubating the cells with plasmids containing lacZ reporter gene and polyethyleneimine-Gd-EOB-DTPA resulted in a few blue (transfected) cells, whereas no blue cells were observed on incubation with polylysine-Gd-EOB-DTPA. CONCLUSIONS: Gd-EOB-DTPA is taken up by normal hepatocytes but not by HepG2 and Huh7 cells, probably because of the lack of the organic anion transporter in these hepatoma cells. The Gd-EOB-DTPA polycation conjugates, such as polyethyleneimine-Gd-EOB-DTPA, could serve as transfer vectors of interest for gene targeting imagery at the early stage of hepatocarcinogenesis. However, the transfer efficiency of such conjugates is low and requires improvement.

Late contralateral lobectomy after single-lung transplantation for emphysema.

Cases of hyperinflation of native emphysematous lung have been reported in the early period after single-lung transplantation. We report a case of a similar complication that occurred 2 years after transplantation and was successfully treated by lobectomy.

MR imaging of acute spinal cord injury: results of an experimental study in dogs.

A weight-drop model was used to induce 16 acute lesions of varying severity in the spinal cords of eight mongrel dogs. The subsequent 3- to 7-hr postinjury MR images (0.5 T) were assessed. T1-weighted images contributed little information. Injection of gadolinium tetra-azacyclododecane tetraacetic acid did not result in significant enhancement. T2-weighted sequences offered precise detection and delineation of the lesions, displaying fusiform hyperintense signal abnormalities that corresponded to both edema and hemorrhage. In low-impact injuries, abnormalities were small and centrally located, sparing the periphery of the spinal cord. In these cases hemorrhage was minimal and limited to the center of the lesion. In severe-impact injuries, MR showed widespread longitudinal extension with involvement of the periphery of the spinal cord. In the most severe injuries, a central heterogeneous signal component was frequently observed opposite the site of impact because of important hemorrhage within the cord. Overall, hyperintense areas correlated closely with lesion severity, as demonstrated by pathologic findings. T2-weighted MR images obtained at 0.5 T were found to be reliable in the evaluation of acute spinal cord trauma.

Contrast agents in magnetic resonance imaging of the liver: present and future.

New contrast agents are being developed by drug companies to better image the liver magnetic resonance imaging (MRI). They can be divided into hepatobiliary agents (Gd-EOB-DTPA, Gd-BOPTA, Mangafodipir) and nanoparticulate agents directed to the reticulo-endothelial system (ferumoxides, SHU 555A). After intravenous injection, all these agents concentrate in the liver and induce profound signal changes. Particulate agents induce predominantly a darkening of the liver parenchyma, while hepatobiliary agents induce a brightening. In both cases, liver-lesion conspicuity is enhanced, leading to a better visualization of the lesion. After a description of the principal pharmacokinetic characteristics of the compounds, this review paper summarizes the utility of the agents in the detection and characterization of focal liver diseases.