Elisabeth Schouman-Claeys

Superparamagnetic iron oxides as positive MR contrast agents: In vitro and in vivo evidence

The ability of superparamagnetic iron oxides (SPIO) and ultrasmall superparamagnetic iron oxides (USPIO) to act as positive contrast enhancers due to a marked T1 relaxivity was investigated. At low concentrations, an important signal enhancement was observed in vitro, reaching 120% for SPIO and 140% for USPIO in a spin echo 500/22 sequence. The more heavily the sequence was T1-weighted the greater the enhancement. As the concentration increased, the signal dropped. The in vivo study of USPIO in the rat showed that at low doses (14 mumol Fe/kg), the myocardial signal was enhanced by 30%, whereas at high doses (77 mumol Fe/kg), it fell by -50%. These results indicate that in T1-weighted spin echo sequences, the MR signal can be enhanced by low concentrations of superparamagnetic compounds. This effect could be useful in perfusion imaging, and is also important for a better understanding of any possible paradoxical positive enhancement which could occur in perfused organs.

Basilar Artery Atherosclerotic Plaques in Paramedian and Lacunar Pontine Infarctions A High-Resolution MRI Study

Background and Purpose— Pontine infarction is most often related to basilar artery atherosclerosis when the lesion abuts on the basal surface (paramedian pontine infarction), whereas small medial pontine lesion is usually attributed to small vessel lipohyalinosis. A previous study has found that high-resolution MRI can detect basilar atherosclerotic plaques in up to 70% of patient with paramedian pontine infarction, even in patients with normal angiograms, but none has evaluated the presence of basilar artery plaque by high-resolution MRI in patients with small medial pontine lesion in the medial part of the pons. Methods— Consecutive patients with pontine infarction underwent basilar angiography using time-of-flight and contrast-enhanced 3-dimensional MR angiography to assess the presence of basilar artery stenosis and high-resolution MRI to assess the presence of atherosclerotic plaque. Basilar artery angiogram was scored as “normal,” “irregular,” or “stenosed” ≥30%” and basilar artery by high-resolution MRI was scored as “normal” or “presence of plaque.” Medial pontine infarcts were divided into paramedian pontine infarction and small medial pontine lesion groups. Results— Forty-one patients with pontine infarction were included, 26 with paramedian pontine infarction and 15 with small medial pontine lesion. High-resolution MRI detected basilar artery atherosclerosis in 42% of patients with a pontine infarction and normal basilar angiograms. Among patients with paramedian pontine infarction, 65% had normal basilar angiograms but 77% had basilar artery atherosclerosis detected on high-resolution MRI. Among patients with small medial pontine lesion, 46% had normal basilar angiograms but 73% had basilar artery plaques detected on by high-resolution MRI. Conclusions— This study suggests that medial pontine lacunes may be due to a penetrating artery disease secondary to basilar artery atherosclerosis. High-resolution MRI could help precise stroke subtyping.

In vivo middle cerebral artery plaque imaging by high-resolution MRI

Middle cerebral artery (MCA) atherosclerosis is currently diagnosed by indirect angiographic methods. The authors used high-resolution MRI (HR-MRI) to study MCA stenosis in six patients. At the level of stenosis, an MCA plaque was clearly delineated and significantly measured vs nonatherosclerotic MCA segments, showing that HR-MRI is an accurate direct imaging method.

High-resolution MRI identifies basilar artery plaques in paramedian pontine infarct

Paramedian pontine infarct (PPI) is usually attributed to basilar artery (BA) atherosclerosis. However, this hypothesis has thus far been supported only by post-mortem studies. The authors show that high-resolution MRI is a promising method that can detect BA plaques in patients with PPI at or near the origin of the penetrating artery, whereas MR angiograms may appear normal.

Liver positive enhancement after injection of superparamagnetic nanoparticles: Respective role of circulating and uptaken particles

Superparamagnetic nanoparticles have both high r1 and r2 relaxivities responsible for positive or negative enhancement properties. The aim of this study was to investigate to what extent perfusion (circulating particles) and uptake (clustered particles) mechanisms contribute to liver positive or negative enhancement using two different particles, superparamagnetic iron oxides (ferumoxides, AMI 25) and ultrasmall superparamagnetic iron oxides (ferumoxtran, AMI-227). Uptake kinetics were studied after intravenous injection of 20 micromol Fe/kg ferumoxtran on a washout liver model. Livers of 82 rats were surgically isolated and washed with saline infusion. Imaging was performed ex vivo at 0.5T with T1- and T2-weighted sequences. Enhancement kinetics of the liver were studied in vivo using MRI up to 180 min post injection of 20 micromol Fe/kg ferumoxtran (time response study) or 10, 20, 40 micromol Fe/kg ferumoxtran and 20 micromol Fe/kg ferumoxides (dose response study.) Particle uptake occurred early and resulted in a negative enhancement of the washed livers 15 min after injection of both T1 and T2 sequences. In vivo, a positive enhancement was only seen during the first five min with the lowest dose of ultrasmall superparamagnetic iron oxides and the T1 sequence. Uptake and clustering of the particles induced a negative liver enhancement. During the first minutes after injection, when uptake has not significantly occurred, perfusion imaging of the liver at a dose of 10 micromol Fe/kg results in a positive enhancement with T1-weighted sequences.

Comprehensive evaluation of preoperative patients with aortic valve stenosis: usefulness of cardiac multidetector computed tomography

Background: Preoperative assessment of patients with aortic valve stenosis (AS) relies on the evaluation of AS severity (aortic valve area, AVA) and left ventricular ejection fraction (LVEF) by echocardiography, and of coronary artery anatomy by coronary angiography. Aim: To evaluate the feasibility and accuracy of contrast-enhanced multidetector computed tomography (MDCT), as a single non-invasive preoperative test, for simultaneous evaluation of the AVA, LVEF and coronary status in patients with AS. Methods: 40 consecutive patients with AS scheduled for aortic valve replacement underwent transthoracic echocardiography, electrocardiogram (ECG)-gated MDCT and coronary angiography within a time span of 1 week. Results: MDCT measurements could be performed in all patients. A good correlation but a slight overestimation was observed between mean (SD) AVA measured by MDCT and by echocardiography (0.87 (0.22) vs 0.81 (0.20) cm2, p = 0.01; r = 0.77, p<0.001). Mean difference between methods was 0.06 (0.15) cm2. LVEF measured by MDCT correlated well with, and did not differ from, electrocardiographic measurements (59% (13%) vs 61% (10%), p = 0.34; r = 0.76, p<0.001; mean difference 1% (8%)). Coronary angiography displayed 33 lesions in 13 patients. MDCT correctly identified 26 of these 33 lesions and overestimated three <50% stenosis. On a segment-by-segment analysis, MDCT sensitivity, specificity, positive and negative predictive values were 79%, 99%, 90% and 98%, respectively. For each patient, MDCT had a sensitivity of 85% (11/13 patients), a specificity of 93% (25/27 patients) and positive and negative predictive values of 85% (11/13 patients) and 93% (25/27 patients), respectively. Conclusion: MDCT can provide a simultaneous and accurate evaluation of the AVA, LVEF and coronary artery anatomy in patients with AS. In the near future, with technological improvements, MDCT could achieve an exhaustive and comprehensive preoperative assessment of patients with AS. In addition, for the assessment of AS severity in difficult cases, MDCT could be considered as an alternative to transoesophageal echocardiography or cardiac catheterisation.

Outcomes of mechanical endovascular therapy for acute ischemic stroke: a clinical registry study and systematic review

Background and Purpose— Recanalization is a powerful predictor of stroke outcome in patients with arterial occlusion. Intravenous recombinant tissue plasminogen activator is limited by its recanalization rate, which may be improved with mechanical endovascular therapy (MET). However, the benefit and safety of MET remain to be determined. The aim of this study was to give reliable estimates of efficacy and safety outcomes of MET. Methods— We analyzed data from our prospective clinical registry and conducted a systematic review of all previous studies using MET published between January 1966 and November 2009. Results— From April 2007 to November 2009, 47 patients with acute stroke were treated with MET at Bichat Hospital. The literature search identified 31 previous studies involving a total of 1066 subjects. In the meta-analysis, including our registry data, the overall recanalization rate was 79% (95% CI, 73–84). Meta-analysis of clinical outcomes showed a pooled estimate of 40% (95% CI, 34–46; 27 studies) for favorable outcome, 28% (95% CI, 23–33; 28 studies) for mortality, and 8% (95% CI, 6–10; 27 studies) for symptomatic intracranial hemorrhage. The likelihood of a favorable outcome increased with the use of thrombolysis (OR, 1.99; 95% CI, 1.23–3.22) and with proportion of patients with isolated middle cerebral artery occlusion (OR per 10% increase, 1.14; 95% CI, 1.04–1.25). Conclusions— MET is associated with acceptable safety and efficacy in stroke patients, and it may be a therapeutic option in those presenting with isolated middle cerebral artery occlusion.

Magnetic resonance angiography of intravascular endoprostheses: Investigation of three devices

PurposeTo assess the value of magnetic resonance angiography (MRA) in the evaluation of vascular patency after intravascular endoprosthesis placement.MethodsThree different metallic stents (Wallstent, Strecker, Palmaz) were studied in vitro, and in vivo in six patients with spin-echo (SE) and gradient-echo (GRE) MR imaging. Time-of-flight, two-dimensional (2D) gadolinium-enhanced MRA was performed with GRE and flow-compensation technique, and reconstructed with a maximum-intensity projection (MIP) algorithm. MRA was compared to digital angiograms.ResultsIn vitro studies demonstrated that the signal intensity (SI) within the stent differed according to the device employed, the lowest SI being observed within the Palmaz stent (p = .001). There was no difference in SI or apparent diameter of the stent according to the sequence (SE vs GRE) or length of echo time (TE). In patients, the endoprostheses recorded as a well-defined area of signal void or drop-out (p = 0.004), whereas vessels above and below the stent displayed high signal intensities.ConclusionMRA does not seem as yet to be well suited for evaluating vascular patency after endoprosthesis placement, even if the Strecker and Wallstent endoprostheses provide fewer artifacts than the Palmaz stent.

Blood–brain barrier disruption is associated with increased mortality after endovascular therapy

Objective: To evaluate the incidence, baseline characteristics, and clinical prognosis of blood–brain barrier (BBB) disruption after endovascular therapy in acute ischemic stroke patients. Methods: A total of 220 patients treated with endovascular therapy between April 2007 and October 2011 were identified from a prospective, clinical, thrombolysis registry. All patients underwent a nonenhanced CT scan immediately after treatment. CT scan or MRI was systematically realized at 24 hours to assess intracranial hemorrhage complications. BBB disruption was defined as a hyperdense lesion on the posttreatment CT scan. Results: BBB disruption was found in 128 patients (58.2%; 95% confidence interval [CI], 51.4%–64.9%). Cardioembolic etiology, high admission NIH Stroke Scale score, high blood glucose level, internal carotid artery occlusion, and use of combined endovascular therapy (chemical and mechanical revascularization) were independently associated with BBB disruption. Patients with BBB disruption had lower rates of early major neurologic improvement (8.6% vs 31.5%, p < 0.001), favorable outcome (39.8% vs 61.8%, p = 0.002), and higher rates of 90-day mortality (34.4% vs 14.6%, p = 0.001) and hemorrhagic complications (42.2% vs 8.7%, p < 0.001) than those without BBB disruption. By multivariable analysis, patients with BBB disruption remained with a lower rate of early neurologic improvement (adjusted odds ratio [OR], 0.28; 95% CI, 0.11–0.70) and with a higher rate of mortality (adjusted OR, 2.37; 95% CI, 1.06–5.32) and hemorrhagic complications (adjusted OR, 6.38; 95% CI, 2.66–15.28). Conclusion: BBB disruption has a detrimental effect on outcome and is independently associated with mortality after endovascular therapy. BBB disruption assessment may have a role in prognosis staging in these patients.

Renal carcinoma: diagnosis of venous invasion with Gd-enhanced MR venography

Abstract. The aim of this study was to evaluate the usefulness of gadolinium-enhanced time-of-flight magnetic resonance venography (MRV) in the diagnosis of bland thrombosis/tumoral invasion in the preoperative assessment of renal cell carcinoma. Preoperative precontrast and enhanced GRE fast low-angle shot (FLASH) images of 36 patients with renal adenocarcinoma were reviewed and compared with pre- and post-contrast T1-weighted images. All patients underwent surgery, and MR findings were blindly and prospectively compared with surgical and pathologic data, considered the standard. Renal vein and vena cava were involved in 17 and 9 patients, respectively; right atrial extension was present in one patient. Precontrast spin-echo (SE) and FLASH images were 88 % sensitive and 100 % specific in the detection of venous involvement, respectively, and enhanced FLASH images 100 % sensitive and 96 % specific. The nature of thrombus (neoplastic or bland) was more accurately assessed (McNemars, p < 0.05) with FLASH-enhanced MR images (sensitivity 89 %; specificity 96 %) than with SE and precontrast FLASH images (sensitivity 79 %; specificity 94 %). Our data suggest that use of Gd-enhanced MRV might improve preoperative assessment of vascular involvement in renal carcinoma.