MRI quantitative T2* mapping on thrombus to predict recanalization after endovascular treatment for acute anterior ischemic stroke.

BACKGROUND: In anterior acute ischemic stroke (AAIS) treated with endovascular treatment (EVT), the susceptibility vessel sign (SVS+ or SVS-) is related to recanalization results (TICI 2b/3) and clinical outcome. However, a binary qualitative assessment of thrombus using SVS does not reflect its complex composition. Our aim was to assess whether a quantitative MRI marker, Thrombus-T2* relaxation time, may be assessable in clinical routine and may to predict early successful recanalization after EVT, defined as a TICI 2b/3 recanalization obtained in 2 attempts or less. MATERIAL AND METHODS: Thrombus-T2* relaxation time was prospectively obtained from consecutive AAIS patients treated by EVT (concomitant aspiration and stent retriever). Quantitative values were compared between early recanalization and late or unsuccessful recanalization. RESULTS: Thirty patients with AAIS were included and Thrombus-T2* relaxation time was obtained in all patients. Earlier TICI 2b/3 recanalization were obtained in 22 patients (73%) and was significantly associated with SVS+ (1/8 vs. 16/22, P=0.01) and a shorter Thombus-T2* relaxation time (mean SD, range: 257, 18-50ms vs. 45 9, 35-60ms, P<0.001). CONCLUSION: A new quantitative MRI biomarker, the Thrombus-T2* relaxation time is assessable in clinical routine. In a preliminary study of 30 patients, a shorter Thombus-T2* relaxation time is related to earlier recanalization after EVT using combination of stent retriever and aspiration.

Overestimation of moderate carotid stenosis assessed by both Doppler US and contrast enhanced 3D-MR angiography in the CARMEDAS study.

PURPOSE: To evaluate the agreement and diagnostic accuracy of Contrast enhanced magnetic resonance angiography (CE-MRA), Doppler ultrasound (DUS) and Digital subtraction angiography (DSA) in the assessment of carotid stenosis. METHODS: DUS, CE-MRA and DSA were performed in 56 patients included in the Carotide-angiographie par résonance magnétique-échographie-doppler-angioscanner (CARMEDAS) multicenter study with a carotid stenosis ≥ 50%. Three readers evaluated stenoses on CE-MRA and DSA (NASCET criteria). Velocities criteria were used for stenosis estimation on DUS. RESULTS: CE-MRA had a sensitivity and specificity of 96-98% and 66-83% respectively for carotid stenoses ≥ 50% and a sensitivity and specificity of 94% and 76-84% respectively for carotid stenoses ≥ 70%. The interobserver agreement of CE-MRA was excellent, except for moderate stenoses (50-69%). DUS had a sensitivity and specificity of 88 and 75% respectively for carotid stenoses ≥ 50% and a sensitivity and specificity of 83 and 86% respectively for carotid stenoses ≥ 70%. Combined concordant CE-MRA and DUS had a sensitivity and specificity of 100 and 85-90% respectively for carotid stenoses ≥ 50% and a sensitivity and specificity of 96-100% and 80-87% respectively for carotid stenoses ≥ 70%. The positive predictive value of the association CE-MRA and DUS for carotid stenoses ≥ 70% is calculated between 77 and 82% while the negative predictive value is calculated between 97 and 100%. CE-MRA and DUS have concordant findings in 63-72%, and the overestimations cases were recorded only for carotid stenosis ≤ 69%. CONCLUSION: Combined DUS-CE-MRA is excellent for evaluation of severe stenosis but remains debatable in moderate stenosis (50-69%) due to the risk of overestimations.

[Delayed myocardial enhancement and diagnosis of acute coronary syndrome with normal coronarography]. / Rehaussement tardif du myocarde et diagnostic étiologique des syndromes coronariens aigus à coronaires saines.

Cardiac MRI in patients with acute coronary syndrome with elevated troponin levels but normal coronarography can now routinely be performed on most MR units. MRI plays an important role in this clinical setting by its ability to detect myocardial infarction in patients with normal coronarography or suggest a different, potentially severe, alternate diagnosis such as myocarditis or takotsubo cardiomyopathy.

[Cardiac diffusion MRI of recent and chronic myocardial infarction: preliminary results]. / IRM de diffusion cardiaque dans l'infarctus du myocarde récent et chronique: expérience préliminaire.

PURPOSE: To use diffusion weighted MR imaging (DWI), a technique routinely used in patients with stroke, for diagnosis of myocardial infarction (MI). MATERIALS AND METHODS: A breath hold ECG gated DWI sequence (b = 300 sec/mm2) was developped and applied to 7 patients with recent MI (3-15 days), 3 patients with chronic MI (> 6 months) and 4 patients with valvular heart disease without MI (control cases). DWI data were correlated to T2W, first pass perfusion and delayed enhancement data. RESULTS: In all patients with recent MI, DWI showed an area of increased signal with reduction of ADC relative to normal myocardium. Hyperintense lesion on DWI corresponded to areas of delayed enhancement. The diffusion images were normal in patients with chronic MI or no MI. CONCLUSION: Even though no animal model or other reference method is available, these preliminary results indicate that DWI could assist clinicians in detecting recent MI.

In-vitro validation of 4D flow MRI measurements with an experimental pulsatile flow model.

PURPOSE: The purpose of this study was to assess the precision of four-dimensional (4D) phase-contrast magnetic resonance imaging (PCMRI) to measure mean flow and peak velocity (Vmax) in a pulsatile flow phantom and to test its sensitivity to spatial resolution and Venc. MATERIAL AND METHODS: The pulsatile flow phantom consisted of a straight tube connected to the systemic circulation of an experimental mock circulatory system. Four-dimensional-PCMR images were acquired using different spatial resolutions (minimum pixel size: 1.5×1.5×1.5mm3) and velocity encoding sensitivities (up to three times Vmax). Mean flow and Vmax calculated from 4D-PCMRI were compared respectively to the reference phantom flow parameters and to Vmax obtained from two-dimensional (2D)-PCMRI. RESULTS: 4D-PCI measured mean flow with a precision of -0.04% to+5.46%, but slightly underestimated Vmax when compared to 2D-PCMRI (differences ranging from -1.71% to -3.85%). 4D PCMRI mean flow measurement was influenced by spatial resolution (P<0.001) with better results obtained with smaller voxel size. There was no effect of Venc on mean flow measurement. Regarding Vmax, neither spatial resolution nor Venc did influence the precision of the measurement. CONCLUSION: Using an experimental pulsatile flow model 4D-PCMRI is accurate to measure mean flow and Vmax with better results obtained with higher spatial resolution. We also show that Venc up to 3 times higher than Vmax may be used with no effect on these measurements.

MRI Quantitative T2* Mapping to Predict Dominant Composition of In Vitro Thrombus.

BACKGROUND AND PURPOSE: MR imaging quantitative T2* mapping, which provides information about thrombus composition and specifically the red blood cell content, may be obtained in the setting of acute ischemic stroke before treatment. This could be useful to adapt the endovascular strategy. We aimed to analyze the red blood cell content of in vitro thrombi in relation to the thrombus-T2* relaxation time. MATERIALS AND METHODS: Thirty-five thrombus analogs of different compositions were scanned with an MR imaging quantitative T2* mapping sequence. Two radiologists, blinded to thrombus composition, measured the thrombus-T2* relaxation time twice at an interval of 2 weeks. Quantitative histologic evaluations of red blood cell content were performed. Inter- and intraobserver reproducibility of the thrombus-T2* relaxation time was assessed by calculating intraclass correlation coefficients. Finally, a Spearman product moment correlation between the thrombus-T2* relaxation time and red blood cell content was performed. RESULTS: The median thrombus-T2* relaxation time was 78.5 ms (range, 16-268 ms; interquartile range, 60.5 ms). The median red blood cell content was 55% (range, 0%-100%; interquartile range, 75%). Inter- and intraobserver reproducibility of the thrombus-T2* relaxation time was excellent (>0.9). The Spearman rank correlation test found a significant inverse correlation between thrombus-T2* relaxation time and red blood cell content (ρ = -0.834, P < .001). CONCLUSIONS: MR imaging quantitative T2* mapping can reliably identify the thrombus red blood cell content in vitro. This fast, easy-to-use sequence could be implemented in routine practice to predict stroke etiology and adapt devices or techniques for endovascular treatment of acute ischemic stroke.

[Feasibility of percutaneous exclusion of the left atrial appendage: results of 11 cases]. / Faisabilité de l'exclusion percutanée de l'auricule gauche. A propos de 11 cas.

Atrial fibrillation is associated with a risk of cerebral embolism, the only proven effective prevention of which is anticoagulant therapy. There is no known alternative in cases with contra-indications to this treatment. Percutaneous exclusion of the left atrial appendage by the implantation of a prosthesis (PLAATO System, ev3 Inc., Plymouth, Minnesota) is a new approach to the prevention of these complications. The authors report the results observed in a series of 11 consecutive patients (7 men, mean age 72 +/- 9 years) in whom this procedure was proposed. All patients had atrial fibrillation for over 3 months, were at high risk and had contra-indications to oral anticoagulants. The implantation of the prosthesis was performed after treatment with aspirin and clopidogrel, under general anaesthesia radioscopy and transoesophageal echocardiographic guidance with success in 9 cases (1 implantation refused in the catheter laboratory and 1 failure). The only complication observed was transient ST elevation treated by emergency angioplasty. The echographic and angiographic criteria of success of left atrial appendage exclusion were fulfilled in all implanted patients. The hospital course was uncomplicated. One recurrence of stroke was observed at the second month: transoesophageal echocardiography confirmed the absence of thrombosis, of migration of the prosthesis and its impermeability in all the patients. After 7 +/- 5 months' follow-up, no other adverse event was observed. This new procedure is technically feasible. Despite encouraging results, its long-term efficacy in the prevention of thromboembolic complications of atrial fibrillation remains to be demonstrated.

Magnetic resonance imaging permits in vivo monitoring of catheter-based vascular gene delivery.

BACKGROUND: Gene therapy is an exciting frontier in modern medicine. To date, most investigations about the imaging of gene therapy have primarily focused on noncardiovascular systems, and no in vivo imaging modalities are currently available for monitoring vascular gene therapy. The purpose of this study was to develop an in vivo imaging tool to monitor a catheter-based vascular gene delivery procedure. METHODS AND RESULTS: We produced gadolinium/blue dye and gadolinium/gene-vector media by mixing Magnevist with a trypan-blue or a lentiviral vector carrying a green fluorescent protein (GFP) gene. The gadolinium was used as an imaging marker for magnetic resonance (MR) imaging to visualize vessel wall enhancement, and the blue dye/GFP was used as a tissue stain marker for histology/immunohistochemistry to confirm the success of the transfer. Using Remedy gene delivery catheters, we transferred the gadolinium/blue dye (n=8) or gadolinium/GFP lentivirus (n=4) into the arteries of 12 pigs, that were monitored under high-resolution MR imaging. The results showed, in all 12 pigs, the gadolinium enhancement of the target vessel walls on MR imaging and the blue/GFP staining of the target vessel tissues with histology/immunohistochemistry. This study shows the potential of using MR imaging to dynamically visualize (1) where the gadolinium/genes are delivered; (2) how the target portion is marked; and (3) whether the gene transfer procedure causes complications. CONCLUSIONS: We present a technical development that uses high-resolution MR imaging as an in vivo imaging tool to monitor catheter-based vascular gene delivery.

Susceptibility Vessel Sign on MRI Predicts Favorable Clinical Outcome in Patients with Anterior Circulation Acute Stroke Treated with Mechanical Thrombectomy.

BACKGROUND AND PURPOSE: The susceptibility vessel sign on MR imaging has been reported to indicate acute occlusion from erythrocyte-rich thrombus. The purpose of this study was to evaluate the influence of the susceptibility vessel sign seen on MR imaging before treatment on the clinical outcome after mechanical thrombectomy for anterior circulation acute stroke. MATERIALS AND METHODS: We retrospectively included 73 consecutive patients who were treated for anterior circulation acute stroke by mechanical thrombectomy from December 2009 to September 2013. Each patient underwent MR imaging before mechanical thrombectomy. The presence (susceptibility vessel sign+) or absence of the susceptibility vessel sign (susceptibility vessel sign-) was recorded. Mechanical thrombectomy was performed either alone or in association with IV tPA according to the site and time after occlusion. Good functional outcome was defined by an mRS ≤ 2 at 3 months in susceptibility vessel sign+ and susceptibility vessel sign- groups. Patient clinical characteristics, initial NIHSS score and ASPECTS, site of occlusion, time between onset to groin puncture, TICI after mechanical thrombectomy, NIHSS score at day 1, and spontaneous hyperattenuation on CT at day 1 were also analyzed. RESULTS: Fifty-three patients with susceptibility vessel sign+ and 20 with susceptibility vessel sign- were included in our study. mRS ≤ 2 at 3 months occurred in 65% patients in the susceptibility vessel sign+ group and 26% in the susceptibility vessel sign- group (P = .004). On multivariate analysis, the susceptibility vessel sign was the only parameter before treatment that could predict mRS ≤ 2 at 3 months (OR, 8.7; 95% CI, 1.1-69.4; P = .04). CONCLUSIONS: Our study strongly suggests that the susceptibility vessel sign on MR imaging before treatment is predictive of favorable clinical outcome for patients presenting with anterior circulation acute stroke and treated with mechanical thrombectomy.

Contrast-enhanced MR angiography: the effects of k-space truncation on luminal representation in a carotid artery phantom model.

Using carotid bifurcation phantom models with different degrees of stenoses, we evaluated the accuracy of vessel lumen representation on MR images obtained from the inverse Fourier transform of different k-space percentages. Our results show that the lower thresholds of truncated k-space sampling are dictated by the severity of luminal narrowing. The defined thresholds may help improve efficiency of 3D MR imaging of the carotid arteries while maintaining adequate luminal representation.

[Progress in cardiovascular interventional MRI]. / Développement de l'IRM interventionnelle cardiovasculaire.

The purpose of this article is to review recent developments in the field of MR guided vascular interventions. Such interventions require real-time visualization of catheters and guidewires to define their location with regards to the vascular system and surrounding tissues. In the first part of the article, passive and active catheter visualization, real-time angiography, and interactivity techniques that make guidance of intra-vascular instruments possible are described. Subsequently animal coronary and peripheral interventions performed under MR guidance are described. MR guided interventions could potentially open up new applications for the treatment of cardio-vascular disease in the near future.

[Complications of myocardial infarction]. / Complications de l'infarctus du myocarde.

Most acute complications of myocardial infarction do not need emergency imaging, since they often result in death prior to hospital admission: ventricular fibrillation and tachycardia, papillary muscle or septal rupture, fissuration and tamponade. Imaging can play a role at distance of the acute phase (papillary muscle dysfunction, false aneurysm, development of a mural thrombus associated to left ventricular apical dyskinesis, with potential embolic complications).

Efficacy of second intra-tendinous platelet-rich-plasma injection in case of incomplete response of the first injection: three-year follow up experience.

PURPOSE: Tendinopathy is a frequent and ubiquitous disease developing early disorganized collagen fibers with neo-angiogenesis on histology. Peritendinous injection of corticosteroid is the commonly accepted strategy despite the absence of inflammation in tendinopathy. Platelet-rich plasma (PRP) might be a useful strategy to rapidly accelerate healing of the tendinopathy but there is a lack ok knowledge about the amount of PRP to be injected and the opportunity of a second injection in case of partial pain relief. The aim of our study was to assess the potential therapeutic effect of early second PRP intra-tendinous to treat persistent painful tendon tear and tendinosis in a long-term follow-up by ultrasonography (US) and clinical data in case of incomplete efficiency of first PRP treatment injection. MATERIALS AND METHODS: Twenty-four consecutive patients referred for US treatment of tendon tear or tendinosis (T+) were included retrospectively. All had previously received a single intra-tendinous injection of PRP under US guidance (PRPT+) and benefited of a second PRP injection (PRPT2+) under US guidance in order to treat persistent painful. US and clinical data were collected for each anatomic compartment for upper and lower limbs before treatment (D0), 6 weeks (W6) after first treatment, 6 weeks (W12) after second treatment and until 32-month follow-up. We used Mac Nemar test and regression model to compare US and clinical data. RESULTS: The residual US size of lesions was not significantly lower at W12 after PRPT2+ as compared to W6 (P=0.86 in upper and P=NS in lower member) independently of age (P=0.22), gender (P=0.97) and kind of tendinopathy (P=NS). Quick dash test values and WOMAC values were not significantly lower in PRPT+ at W12 (average: 21.5 months) as compared to W6 (P>0.66) and long-term follow-up (P>0.75) independently of age (P=0.39), gender (P=0.63) and kind of tendinopathy (P=NS). Nevertheless, comparison between D0 and long-term follow-up (LTF) functionnal score was statistically significant (p<0.001 in upper and lower member). CONCLUSION: Our study suggests that second early intra-tendinous PRP injection under US guidance does not permit rapid decrease of tendinopathy area in US, nor does it quickly improve clinical pain and functional data in case of incomplete efficiency of first PRP injection. However, in long-term follow-up, patients improved their ability to mobilize pathologic tendons.

Superparamagnetic bifunctional bisphosphonates nanoparticles: a potential MRI contrast agent for osteoporosis therapy and diagnostic.

A bone targeting nanosystem is reported here which combined magnetic contrast agent for Magnetic Resonance Imaging (MRI) and a therapeutic agent (bisphosphonates) into one drug delivery system. This new targeting nanoplatform consists of superparamagnetic γFe(2)O(3) nanoparticles conjugated to 1,5-dihydroxy-1,5,5-tris-phosphono-pentyl-phosphonic acid (di-HMBPs) molecules with a bisphosphonate function at the outer of the nanoparticle surface for bone targeting. The as-synthesized nanoparticles were evaluated as a specific MRI contrast agent by adsorption study onto hydroxyapatite and MRI measurment. The strong adsorption of the bisphosphonates nanoparticles to hydroxyapatite and their use as MRI T2(∗) contrast agent were demonstrated. Cellular tests performed on human osteosarcoma cells (MG63) show that γFe(2)O(3)@di-HMBP hybrid nanomaterial has no citoxity effect in cell viability and may act as a diagnostic and therapeutic system.

Plaque density on CT, a potential marker of ischemic stroke.

The authors sought to determine in a retrospective analysis whether carotid plaque soft TD on CT is associated with recent ischemic neurologic events. Among 141 patients (99 asymptomatic), 106 plaques with more than 50% stenosis were selected for density measurements. They found an odds ratio for neurologic events associated with a 10-point decrease in density of 1.54 (p = 0.002), showing an association between plaque density and neurologic events.

In vivo measurement of pulsewave velocity in small vessels using intravascular MR.

A one-dimensional intravascular MR (IVMR) technique for the measurement of pulsewave velocity in a single cardiac cycle is presented. The technique was used to measure pulsewave velocity in vivo in the intact rabbit model, where its sensitivity to different hemodynamic states was demonstrated using a pharmacological intervention with phenylephrine and nitroprusside. IVMR measurements of pulsewave velocity were found to increase with mean arterial pressure, as expected. Further, IVMR-based pulsewave velocity estimates were in agreement with those measured by pressure catheters and direct distensibility measurement. Because of their rapidity and highly localized nature, these measurements of vessel elasticity may complement the high-resolution vascular imaging information gained in an IVMR examination. This could allow assessment of atherosclerotic plaques and facilitate immediate treatment decisions. Magn Reson Med 45:53-60, 2001.

Toward MRI-guided coronary catheterization: visualization of guiding catheters, guidewires, and anatomy in real time.

The success of x-ray fluoroscopy-guided coronary catheterization depends in part on the ability to obtain simultaneous and real-time visualization of the guidewire, guiding catheter, and anatomy of the chest. The hypothesis explored in this paper is that magnetic resonance imaging (MRI) could provide this ability. This hypothesis was tested with loopless antennas used as the guidewire and a guiding catheter and two surface coils, each connected to four different receiver channels of a GE 1.5-T CV/I MRI scanner. Experiments were conducted on six healthy dogs. Intravascular antennas were inserted in the right carotid artery and maneuvered in the aorta while running a fast gradient-echo sequence (TR/TE 5/1.3 msec, flip angle 7 degrees). Real-time projection images of the chest anatomy, together with the guidewire and guiding catheter, were obtained. Positioning of the MRI guiding catheter either in the descending aorta, ascending aorta, or heart was achieved easily. This study represents a step toward MRI-guided coronary catheterization.

Accuracy of three-dimensional gadolinium-enhanced MR angiography in the assessment of extracranial carotid artery disease.

OBJECTIVE: The purpose of this study was to assess three-dimensional (3D) gadolinium-enhanced MR angiography, used alone or in association with duplex Doppler sonography, with a fast acquisition time (8 sec) for evaluating the extracranial carotid arteries. SUBJECTS AND METHODS: In this prospective study, 48 successive patients with carotid artery stenoses were examined with 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography. Of the 44 eligible patients, conventional angiography was available in 33 and duplex sonography in 27. We used the North American Symptomatic Carotid Endarterectomy Trial technique to quantify stenosis on all angiograms, and a 250 cm/sec threshold at duplex sonography to diagnose stenoses greater than 70%. Image quality of 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography was assessed, as well as sensitivity and specificity for each technique alone and in combination with duplex sonography. Conventional angiography was the gold standard. RESULTS: Three-dimensional gadolinium-enhanced MR angiography yielded good image quality in 90% of cases. When used alone, it yielded a sensitivity and a specificity of 94% and 85%, respectively, in screening stenoses greater than 70% (70-99%). When combined with duplex Doppler sonography, it provided a 100% sensitivity and specificity for detection of stenoses between 70% and 99% and would have obviated 61% of conventional angiography. In comparison, 3D time-of-flight MR angiography used alone yielded a sensitivity of 88% and a specificity of 94%. In combination with duplex Doppler sonography, its use would have obviated conventional angiography in 74% of cases. Three-dimensional gadolinium-enhanced MR angiography provided accurate results in the diagnosis of occlusions and ulcers and can visualize distant stenoses. CONCLUSION: Used alone, 3D gadolinium-enhanced MR angiography is not accurate enough to replace conventional angiography in the evaluation of extracranial carotid arteries. In association with duplex Doppler sonography, however, it is accurate and may obviate a significant number of conventional angiographic examinations.