RADIOLOGIE ET IMAGERIE MEDICALE : Cardiovasculaire - Thoracique - Cervicale - Epreuve corrigee par l'auteur. Disponible en ligne depuis le 18/07/2018

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/mm(2)) 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.

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.

L’IRM est un examen très performant pour le bilan des valvulopathies. Le but de ce travail est de définir les plans d’acquisition nécessaires à la réalisation de cet examen. L’IRM est réalisée à l’aide d’une séquence ciné synchronisée à l’ECG T2/T1 à sang blanc monocoupe multiphases dans les différents plans d’acquisition des valves. Les 3 plans du cœur sont utilisés pour étudier les valves cardiaques ainsi que des plans spécifiques pour les valves artérielles. La séquence ciné T2/T1 permet d’obtenir une étude dynamique des valves dans les différents plans d’acquisition. Cette présentation a pour objectif de donner une base anatomique suffisante des différents plans d’acquisition, nécessaire à la bonne réalisation du bilan dynamique des valvulopathies.

Les séquences ciné IRM en apnée sont capables d’évaluer la fonction contractile du cœur. Les volumes télésystoliques, télédiastoliques et la fraction d’éjection ainsi que la mesure de la masse cardiaque sont mesurables en routine clinique à l’aide de logiciels de détection automatisée des contours. L’IRM est réalisée à l’aide de séquences ciné T2/T1 à sang blanc multicoupes multiphases synchronisées à l’ECG. Les séquences sont acquises dans les plans long axe, petit axe et 4 cavités du cœur. Les logiciels de reconstruction cardiaque permettent de réaliser les mesures du volume ventriculaire gauche à l’aide d’un contourage manuel ou automatique des surfaces endo/épicardiques. Il est important de connaître le poids et la taille du patient pour indexer les résultats à la surface corporelle, gage de la plus grande reproductibilité. Grâce au développement des logiciels de détection automatisé des contours, l’IRM donne des mesures non invasives et robuste de la fonction ventriculaire gauche.

Objective— Ferumoxtran-10 is an MRI contrast agent, which accumulates in macrophages and induces magnetic susceptibility artifacts (MSAs). We evaluated the ability of ferumoxtran-10–enhanced MRI to quantify focal macrophage infiltration in the aortic wall of hypercholesterolemic rabbits. Methods and Results— Six weeks after a double-balloon injury of the infrarenal aorta, 12 hypercholesterolemic rabbits underwent MRI of the aorta before (first MRI) and after (second MRI) intravenous injection of ferumoxtran-10 (n=10) or saline (n=2). A third MRI was performed 5 days later to detect ferumoxtran-10–induced MSA in the aortic wall. Aortas were subsequently processed for histology, immunohistochemistry, and gelatin zymography studies. Injured aortas displayed a macrophage-rich neointima with high-matrix metalloproteinase 2 and 9 activities. Iron stain of injured aortas showed massive accumulation of ferumoxtran-10 in neointimal macrophages. Five days after the injection of ferumoxtran-10, MSAs were detected only in the injured aortas by in vivo MRI and were quantified indirectly using the percentage reduction of luminal area attributable to the extension of these MSAs in the aortic lumen. This parameter correlated with macrophage infiltration on corresponding aortic cross-sections ( r =0.82; P <0.05). Conclusion— Ferumoxtran-10–enhanced MRI allows quantitative assessment of macrophage infiltration induced by balloon angioplasty in the aorta of hypercholesterolemic rabbits.

L’IRM du plancher pelvien est devenue un examen de routine dans le service pour le bilan des prolapsus. Le but de ce travail est de revoir l’anatomie du plancher pelvien et de définir les plans de références nécessaires à la réalisation de l’acquisition dynamique. L’IRM est réalisée en décubitus dorsal à l’aide de séquences Fast Spin Écho (FSE) à contraste T2 pour l’étude statique et de séquences cinétiques en écho de gradient T2/T1. La séquence T2 FSE permet de faire le bilan anatomique du plancher pelvien. La séquence écho de gradient T2/T1 cinétique permet d’obtenir une étude dynamique du plancher pelvien dans les 3 plans de l’espace. Ce travail a pour principal objectif de donner une base anatomique suffisante, nécessaire à la bonne réalisation du bilan dynamique du plancher pelvien par IRM.

Purpose: To evaluate the diagnostic value of contrast-enhanced (CE) delayed cine steady-static free precession (SSFP) sequences in the assessment of apparent infarct size after acute myocardial infarction (MI).Materials and Methods: Contrast-enhanced (CE) balanced cine-SSFP sequences were compared with delayed-enhancement (DE) T1 sequences for their ability to detect segmental abnormal enhancement in 29 consecutive patients with recent successfully reperfused acute MI.Results: The extent of myocardial involvement revealed by postcontrast cine-SSFP sequences and DE Images was closely correlated (Spearman r = 0.86, P < 0.001). There was no significant difference between the two sequences in assessing subendocardial or transmural involvement.Conclusion: In addition to DE sequences, CE cine-SSFP sequences should play a role in assessing necrotic and jeopardized myocardium after acute MI.

L’IRM, aujourd’hui, a un champ d’application et un rôle reconnu en imagerie cardiaque. Il s’agit surtout de réaliser une étude de la fonction cardiaque et de la perfusion myocardique. Le but de cette étude est de bien connaître l’anatomie du cœur et de définir les plans d’acquisition dans les axes vrais du cœur pour assurer des examens reproductibles et comparables aux autres techniques (échocardiographie, médecine nucléaire). L’IRM cardiaque est réalisée à l’aide de séquences à contraste sang noir et sang blanc dans les 3 plans du cœur, le « long axe », le « petit axe » et le plan « 4 cavités ». Une coupe axiale de thorax passant par le cœur permet de repérer le « long axe ». La coupe « long axe » permet de repérer le « faux 4 cavités » du cœur. La coupe « faux 4 cavités » permet de repérer le « petit axe » du cœur. La coupe « petit axe » permet de repérer le « vrai 4 cavités » du cœur. Les appareillages bénéficient aujourd’hui de progrès extrêmement rapides, et, de ce fait, l’IRM cardiaque est devenue un examen de routine. Ce travail à pour objet d’optimiser la réalisation de cet examen par une meilleure connaissance de l’anatomie et des différents plans d’acquisition du cœur.

En IRM, les plans d’acquisitions sont multiples et les contrastes peuvent faire apparaître les vaisseaux en hypo ou en hypersignal. Certains plans et certaines séquences permettent de bien visualiser les coronaires en IRM. L’artère coronaire droite et l’artère interventriculaire postérieure irriguent le cœur droit mais aussi la partie inféroseptale du ventricule gauche. L’artère coronaire gauche, qui est composée du tronc commun, de l’interventriculaire antérieure et de la circonflexe, irriguent la partie antéroseptale et latérale du ventricule gauche. L’IRM des coronaires est réalisée à l’aide d’une séquence 3D Fiesta fat sat offrant un contraste à sang blanc. L’acquisition de chaque plan de coupe peut être réalisée en apnée ou en respiration libre avec échonavigateur. Le plan axial du thorax permet de repérer la coronaire droite et la coronaire gauche. Le plan petit axe du cœur permet de visualiser la coronaire droite et la circonflexe. Le plan long axe du cœur permet de visualiser l’interventriculaire antérieure et l’interventriculaire postérieure. L’IRM cardiaque est devenue aujourd’hui un examen courant, se prolongeant souvent, pour certains cas, par une étude des coronaires. Ce travail à pour objet de mieux connaître l’anatomie et les différents plans d’acquisitions qui nous permettront de bien localiser les coronaires.

The purpose of this study was to evaluate the potential reversibility of kidney lesions in an experimental model of acute renal failure using ultra-small particles of iron oxide (USPIO)-enhanced magnetic resonance (MR) imaging. This study was conducted in 21 uninephrectomized rats using a model of iodinated contrast media-induced renal failure. Thirteen rats received selective intraarterial renal administration of diatrizoate (370 mg/ml) and were compared with two control groups, including six animals injected with saline and two noninjected animals. MR imaging was performed 28 hours, 8 days, and 22 days after the procedure. Each MR session included axial and coronal T1- and coronal T2-weighted images before and after intravenous administration of 60 micromol Fe/kg of USPIO. The rats were sacrificed immediately after the last MR session for pathologic evaluation. MR images were qualitatively and quantitatively interpreted with respect to pathologic data, and differences were statistically studied. At day 22, histology showed 4 severely diseased kidneys with focal areas of necrosis, 5 mildly diseased kidneys with tubular vacuolization, and 12 normal kidneys. On quantitative data, a high correlation between the percentage of negative enhancement and histologic data was observed (P < 0.05). Qualitative interpretation showed a sensitivity and specificity of USPIO-enhanced T2-weighted MR images of 88% and 91%, respectively. Follow-up enhancement curves showed a constant increase of intrarenal USPIO negative enhancement in normal kidneys between day 1 and day 22, whereas all severely involved kidneys displayed higher USPIO negative enhancement at day 1 without significant changes over time until day 22. USPIO may be useful for in vivo follow-up of the reversibility of experimentally induced iodinated contrast media renal impairment in animals.

RATIONALE AND OBJECTIVES:To assess the abilities of dynamic diffusion-weighted MRI to demonstrate the effects in vivo of a high-viscosity iodinated contrast agent on medullary and cortical blood flow in the rat kidney. METHODS:Dynamic diffusion-weighted, echoplanar MR images obtained from five b-value single-shot acquisitions and their isotropic apparent diffusion coefficient maps were obtained from nine rats anesthetized by pentobarbital sedation, before and after intravenous injection of a high-viscosity, dimeric iso-osmolar iodinated contrast medium (iodixanol), and compared with those obtained from four control rats that received saline. RESULTS:The mean baseline apparent diffusion coefficient values were 1.64 +/- 0.05 x 10(-3) mm2/s for the cortex and 1.75 +/- 0.06 x 10(-3) mm2/s for the medulla. In the iodixanol group, a significant decrease in renal diffusion was observed at 12 minutes and lasted at least until 24 minutes. The decrease in diffusion occurred earlier for the cortex and lasted less than for the medulla. There was no significant modification in diffusion over time in the control group. CONCLUSIONS:This preliminary experience in rats shows that dynamic diffusion-weighted MRI can be used to study noninvasively the in vivo renal hemodynamic response after injection of iodinated contrast.

The results of MR angiography at 1.0 T with digital intraarterial angiography in the screening of patients with suspected renal hypertension were compared. In this first phase of the study, 10 volunteers underwent examination with both two-dimensional (2D) with traveling saturation time-of-flight (TOF) magnetic resonance angiography (MRA) with various parameters to develop a protocol for evaluation of the renal arteries. In the second phase, 36 patients with suspected renovascular hypertension underwent both 2D TOF MRA and intraarterial digital angiography to evaluate the clinical value of MRA. The degree of stenosis was graded with a two-point scale. In volunteers, using 2D acquisitions C/N ratios indicated the best flip angle as being 55 degrees (p = .02). MRA showed 100% (70/70) of all main arteries and 86% (6/7) of all accessory renal arteries seen on angiography. MRA had a sensitivity of 94% (15/16) and a specificity of 98% (60/61) for detection of stenoses of greater than 50% present in 14 patients. 2D-TOF MRA at 1.0 T shows promise in the noninvasive diagnosis of patients with suspected renovascular hypertension.

The purpose of this study was to compare the performance of 2D vs. 3D time-of-flight (TOF) methods in imaging the normal pulmonary arteries with commercially available 1.0 T equipment. The study was conducted in 20 volunteers and 7 patients with suspected pulmonary embolism (PE). To reduce artifacts caused by cardiac and respiratory motion, MR images were acquired in volunteers using two-dimensional (2D), gradient-recalled echo (GRE), breath-hold techniques, and three-dimensional (3D) acquisitions. Sagittal thin (6-MM) segmented k-space 2D sections obtained with cardiac gating during systole (turboFLASH, TR/TE9/6 ms, 14 segments of 9 lines) and incremented flip-angles (TONE), and 50-mm 3D volume TONE acquisitions with 32 partitions (FISP, TR/TE34/10ms) were successively performed. In the second phase of the study, patients were examined only with the 3D technique. Images of volunteers were qualitatively and quantitatively analyzed. S/N ratios were statistically compared by means of the paired-sample Wilcoxon ranked-signed test, a value of p < .05 being significant. In volunteers, 3D acquisitions displayed significantly more segment-order pulmonary arteries on average than did 2d acquisitions displayed significantly more segment-order pulmonary arteries on average than did 2D acquisitions (2.95 +/- 0.64 vs. 2.2 +/- 0.85, respectively; p < .01). Moreover, the signal intensity of arteries within the lungs was less homogeneous in the 2D than in the 3D technique, with a signal intensity ratio between peripheral and proximal arteries of 63% +/- 7% and 73% +/- 2%, respectively (p < .05). In patients, no erroneous diagnoses were obtained using the 3D technique. 3D images of normal lungs provide MR angiograms of better quality than do 2D images, and require less contribution from subjects because they are performed in free breathing. Ongoing improvements in MR sequences and further studies are now necessary to assess the value of 3D TONE MRA in the diagnosis of PE.

Purpose: To evaluate the combined performance of two time-of-flight methods in imaging the pulmonary arteries. Materials and methods: This study was prospectively conducted in 28 patients suspected for pulmonary embolism (PE). Sixteen patients were free of pulmonary vascular disease, and 12 had pulmonary vascular disease as demonstrated by pulmonary angiography. To reduce artifacts caused by cardiac and respiratory motion, MR images were acquired in all subjects using bi-dimensional (2D), gradient-recalled echo (GRE), breath-hold techniques. Sagittal thin (6-mm) sections obtained with ECG gating, k-space segmentation and incremented flip-angles (TONE), and coronal thick (15-mm) sections obtained after a unique injection of Gadolinium chelate were used. Results: High quality images were obtained in all 16 (100%) subjects free of pulmonary disease with both techniques, and in 10 and 12 (87% and 100%) patients suspected for pulmonary artery disease with sagittal and coronal Gd-enhanced MRA, respectively, In patients free of pulmonary disease, TONE images exhibited distal pulmonary arteries with 2.1 subsegmental divisions on average, whereas Gd-enhanced TurboFLASH images were the most accurate to identify proximal pulmonary arteries within the mediastinum, even if only 0.8 subsegmental divisions were seen on average. A correct diagnosis of pulmonary embolism was obtained in all cases but one, with use of both MRA techniques, with an overall accuracy of 86%. Conclusion: The association of segmented sagittal GRE images and coronal first-pass Gd-enhanced GRE images can provide information upon normal and diseased pulmonary arteries within the mediastinum until subsegmental pulmonary branches, even in patients with short-breathing. Further studies of patients with various pulmonary artery diseases will confirm whether this technique makes pulmonary MRA feasible in clinical routine situations.