First-pass and delayed magnetic resonance imaging studies of reperfused myocardial infarction with iron oxide particles.
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Animals↗
Biomedical subjects
M Amiel
Publications and source records attributed to M Amiel.
Carboxymethyl-dextran-gadolinium-DTPA as a blood-pool contrast agent for magnetic resonance angiography. Experimental study in rabbits.
RATIONALE AND OBJECTIVES: The authors evaluate the efficiency of various doses of a paramagnetic macromolecular contrast agent, a gadolinium (Gd)-DTPA-dextran conjugate, as a blood-pool contrast media, in a transverse three-dimensional time-of-flight (TOF) magnetic resonance (MR) angiography sequence of the abdominal aorta in rabbits. METHODS: Imaging experiments were performed on a 1.5-T magnet, using a transverse three-dimensional TOF tilted optimized nonsaturating excitation (TONE) sequence. The macromolecular contrast media used was a carboxymethyl-dextran-Gd-DTPA (CMD-Gd-DTPA). Different concentrations of CMD-Gd-DTPA (0.005, 0.01, 0.03, 0.05 mmol Gd/kg) were evaluated. A comparative study using Gd-DOTA (0.01 and 0.1 mmol/kg) was performed. A visual analysis based on the gain in the visualized length of small arteries (renal arteries), and a quantitative analysis based on the percent contrast enhancement of the aorta plotted against distance in the slab from the top edge of the acquisition volume were obtained. RESULTS: A signal-to-noise ratio enhancement of the distal part of the aorta and an improvement in the visualized length of the renal arteries were noted for concentrations of CMD-Gd-DTPA ranging form 0.01 to 0.05 mmol Gd/kg. Venous enhancement was noted for concentrations greater than 0.01 mmol Gd/kg when using CMD-Gd-DTPA or Gd-DOTA. CONCLUSION: Carboxymethyl-dextran-Gd-DTPA reduced, in part, the saturation effect in a three-dimensional transverse TOF TONE MR angiography in rabbits. To prevent venous enhancement, observed with the higher concentrations used in this study, a decrease in the polydispersity of the polymer should be a goal in the future. Rapid extravasation of the low-molecular weight fraction of the polymer could explain the venous enhancement.
Animals↗
Can we optimize our angiographic views every time? Qualitative and quantitative evaluation of a new functionality.
RATIONALE AND OBJECTIVES: For determining the optimum angulations of the x-ray beam with respect to the vascular morphology of a given patient, the authors present a solution combining a single-plane angiographic system and a dedicated procedure. METHODS: The clinical evaluation of the vessel profiling acquisitions focuses on qualitative appraisal and quantitative analysis of conventional and optimum projections. RESULTS: The qualitative evaluation demonstrates the pitfall for an operator to discern optimum from conventional projections. The 70% of preferences for vessel profiling bear witness to the constraints imposed occasionally by the optimum angulations, which may be impracticable for various reasons. However, vessel profiling yields lesions inspection at an optimum view, free of geometric foreshortening. Moreover, there is less risk of superimposition with other branches. From a quantitative standpoint, vessel profiling unveils the lesion with a length significantly longer than in conventional view. CONCLUSIONS: Vessel profiling offers a qualitative optimization of angiographic images and more exact quantitative analysis.
Angiocardiography↗
[The "melting pot" of so-called interventional radiology. Plea for a new semantic approach and another strategic vision].
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France↗
[Optimization of coronary angiographic views. Qualitative and quantitative evaluation of a new system].
A coronary angiographic view is said to be "optimal" when the directing radius of the X-ray beam is perpendicular to the long axis of a stenosis. The object was to fulfill two criteria: 1) the accurate calculation of the spatial orientation of the stenosis to obtain the optimal position, 2) rapid and optimal positioning of the angiographic material with easy rotation around the axis of the stenosis. Two combined solutions were proposed:the Advantx L/C (GE Medical systems) angiocardiographic system with three motorised axes of rotation and a specific software. This software takes into account two longitudinal axes of the stenosis traced by the operator in two conventional incidences and then determines the angles of optimal positioning (accuracy +/-5 degrees). During 97 consecutive coronary angiograms, the software was used in 23 cases (24%) and judged to be useful in 16 cases (70%). In 2 of the 23 cases (8%) the mechanical angles calculated could not be used, the incidences being incompatible with the patient's position. During the angiograms, the best two images of stenosis (one conventional, one optimal) were retained to form a pair of images. Eight observers analysed 37 pairs of images shown side by side. 65% of the images selected from each pair as being the best descriptive appearance of the stenosis came from the optimised system. During quantitative analysis, only the length of stenosis differed statistically between the two modes of acquisition (1.26 +/- 0.36 mm; p = 0.0014). This system is useful during coronary angiography for providing optimal views of stenosis free from any geometric distorsion and without superimposition of adjacent branches.
Coronary Angiography↗
Noninvasive assessment of no-reflow phenomenon in a canine model of reperfused infarction by contrast-enhanced magnetic resonance imaging.
The aim of this study was to test whether contrast-enhanced magnetic resonance (MR) imaging may assess in vivo the severity of the no-reflow phenomenon in a dog model of infarction with 2-hour coronary occlusion followed by reperfusion (6 hours). Subsecond MR imaging combined with intravenous bolus administration of superparamagnetic iron oxide particles (SPIO) was performed at the fifth hour of reperfusion. An MR index was calculated using the difference of signal-intensity enhancement between ischemic and nonischemic zones during the SPIO first pass. Dogs were separated into two groups according to the severity of ischemia: collateral blood flow in the central ischemic zone at 120 minutes of occlusion (radioactive microsphere technique) < 22.5% of the flow in the nonischemic zone (group I) or > 22.5% (group II). Mean collateral blood flow during occlusion was lower in group I (11.3% +/- 2.9%, n = 7) than in group II (66.8% +/- 19.8%, n = 6, p < 0.05). Mean infarct size was significantly larger in group I (58.6% +/- 4.9% of the area-at-risk, n = 7) than in group II (16.5% +/- 6.5%, n = 6, p < 0.05). For the entire population (n = 13), the infarct size was inversely correlated to the collateral blood flow (r = -0.64, p = 0.02, standard error of estimate = 0.24). The relative rate of enhancement in ischemic myocardium (MR index) was significantly lower in group I (38.1% +/- 10.9%) than in group II (142.8% +/- 32%; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Fast MR angiography of the aortoiliac arteries and arteries of the lower extremity: value of bolus-enhanced, whole-volume subtraction technique.
OBJECTIVE: MR angiography of the abdominal aorta and lower limb arteries has been hampered by the need to depict long segments of the arteries in short imaging times. To overcome these limitations, we combined fast acquisition of coronal sections with bolus-enhancement technique, subtraction, and whole-volume projection display. The purpose of this preliminary study was to determine the value of using this technique in patients with abdominal aortic lesions and atherosclerotic occlusive disease of the lower limbs. SUBJECTS AND METHODS: Ten healthy volunteers and 20 patients with abdominal aortic aneurysms (n = 15), vascular graft (n = 3), arteriovenous fistula (n = 1), and abdominal aortic dissection (n = 1) were examined by segmented K-space ultrafast gradient-echo sequences. Sequential 50-cm coronal sections were acquired before and after an IV bolus injection of gadolinium (0.1 mmol/kg). Subtraction images were created by subtracting precontrast from postcontrast images. In all MR images, signal intensity was measured in the aorta, the inferior vena cava, and the background tissues. The final MR angiogram was a summation image of each subtracted image and was compared with a preoperative conventional arteriogram. Data from each study were collected prospectively and analyzed in a blinded manner. The radiologist evaluated depiction of the following specific areas: the abdominal aorta, common iliac arteries on both sides, superficial femoral arteries and above-knee popliteal arteries, below-knee popliteal arteries, superior mesenteric artery, and renal arteries. The aneurysms were categorized as infrarenal or suprarenal and as involving or not involving the iliac arteries. The graft was considered patent if depicted at both its origin and its periphery. RESULTS: In the healthy volunteers, bolus-enhanced subtraction MR angiography depicted without in-plane saturation the aorta, iliac arteries, and arteries of the lower extremity in less than 2 min. Gadolinium significantly increased the aortic signal-to-noise ratio from 25 +/- 3 to 232 +/- 8 (p < .0001), whereas the signal intensity of the inferior vena cava, muscles, and fat remained relatively stable. Examinations were thought to be interpretable in all but two patients. Clear delineation of aneurysms, intimal flap and arteriovenous fistula, and graft patency (n = 3) or occlusion (n = 2) were similarly diagnosed by conventional and MR angiography. Superior mesenteric artery was depicted in all cases on postcontrast images before subtraction. The number of renal arteries (n = 29) was correctly identified in all 15 patients who had renal areas included in their aortograms on postcontrast images before subtraction. However, renal arteries throughout their full length were usually obscured by renal veins and bowel contrast enhancement on the final MR angiogram. Furthermore, bolus-enhanced subtraction MR angiography was able to depict all lower limb arteries. CONCLUSION: Although further evaluation and technical improvements are required, our preliminary results indicate that bolus-enhanced subtraction MR angiography is a promising new method for fast abdominal and peripheral vascular imaging.
Adult↗
[Exploration of the thoracic aorta. Excluding the aortic valve].
MRI has become the reference technique for the diagnosis and assessment of thoracic aortic aneurysms and subacute or chronic aortic dissections, and in the postoperative surveillance of the thoracic aorta. Several MRI techniques can now be used to investigate the thoracic aorta. The technique most widely used at the present time is Spin Echo imaging, which allows a multi-plane morphological approach to the thoracic aorta. It is often completed by a dynamic gradient echo sequence (cine-MRI) and, more recently, by ultra-rapid sequences (Turbo-Flash) following the injection of contrast agent. Phase-coding has also been proposed for the various intraluminal velocities. In the emergency situation, the examination of choice is less clearly defined due to the development of new techniques (transoesophageal ultrasonography, spiral computed tomography, MRI). The diagnostic strategy depends on the patient's clinical state, the respective advantages and limitations of each technique and the human and material resources available.
Aortic Dissection↗
[Exploration of the thoracic aorta, excluding the aortic valve].
MRI has become the reference technique for the diagnosis and assessment of thoracic aortic aneurysms and subacute or chronic aortic dissections, and in the postoperative surveillance of the thoracic aorta. Several MRI techniques can now be used to investigate the thoracic aorta. The technique most widely used at the present time is Spin Echo imaging, which allows a multi-plane morphological approach to the thoracic aorta. It is often completed by a dynamic gradient echo sequence (cine-MRI) and, more recently, by ultra-rapid sequences (Turbo-Flash) following the injection of contrast agent. Phase-coding has also been proposed for the various intraluminal velocities. In the emergency situation, the examination of choice is less clearly defined due to the development of new techniques (transoesophageal ultrasonography, spiral computed tomography, MRI). The diagnostic strategy depends on the patient's clinical state, the respective advantages and limitations of each technique and the human and material resources available.
Aortic Dissection↗
Three-dimensional coronary arteriography.
In this paper we present a new imaging technique for three-dimensional (3-D) X-ray coronary arteriography. The goal is to provide in near to real-time a 3-D representation of the coronary arterial tree, helpful to better understand its topology and locate the possible lesions. The 3-D reconstruction of the coronary arteries is obtained from a set of X-ray conic projections acquired during a rotation of the imaging chain around the patient. Images are taken before and after injection of contrast agent. A subset of mask and opacified images is selected, corresponding to the same phase in the cardiac cycle. These images are subtracted and corrected for geometric distortion. The reconstruction is performed by using a two-step non-parametric detection/estimation method. Due to heart motion and propagation of the contrast agent, the number of available projections is very small. Typically 4 or 6 projections are available if the opacification is stable during 2 or 3 cardiac cycles and when using a biplane acquisition system. High resolution 512(3) reconstructions of the coronary arteries from a cadaver heart are presented, with a voxel size of 0.4 mm. The 3-D reconstruction provides a good 3-D representation of the global structure, even with a number of projections as small as 4.
Computer Graphics↗
Automated myocardial edge detection from breath-hold cine-MR images: evaluation of left ventricular volumes and mass.
This paper describes an automated edge detection method for the delineation of the endo- and epicardial borders of the left ventricle from magnetic resonance (MR) images. The feasibility of this technique was demonstrated by processing temporal series of cardiac MR images obtained in 12 healthy subjects and acquired from the apex to the base of the heart in multiple anatomic short axis planes with a breath-hold cine-MR acquisition sequence. This procedure allows the entire heart to be imaged in less than 5 min. The automatic program correctly identified the edges in most cases. In poor contrasted images, a fast and user-friendly interactive procedure was used to correct the border delineation. The proposed method for the contour tracing requires a limited degree of control by the user and thus considerably reduces the tedious and long operator time inherent in the usual manual contour tracing tool. The left ventricular volumes were directly measured from these sets of contours by using the Simpson rule, allowing the end-diastolic volumes (EDV), the end-systolic volumes (ESV), the ejection fraction (EF) and the myocardial mass to be determined. The values measured in this study with the dedicated software were similar to the literature values (EDV = 78.3 ml/m2; ESV = 21.1 ml/m2; EF = 73%). Associated with the ultrafast breath-hold cine-MR imaging, the described edge detection method provides an efficient clinical tool for the direct assessment of cardiac function.
Adult↗
Coronary arteries: new design for three-dimensional arterial phantoms.
Few three-dimensional (3D) anthropomorphic phantoms are available for testing 3D reconstruction and quantitation of vessels. The authors built a new realistic model of arteries with use of stereolithography, a computer-aided design and computer-aided manufacturing technique. Each phantom is composed of the physical object and its digital "twin." The entire coronary artery tree and complex stenoses were manufactured with a precision below 0.1 mm.
Arteries↗
Screening patients for renal artery stenosis: value of three-dimensional time-of-flight MR angiography.
OBJECTIVE: The purpose of this study was to determine the value of three-dimensional time-of-flight MR angiography in screening patients for the presence of renal artery stenoses. SUBJECTS AND METHODS: Fifty-three patients who were thought to have renovascular hypertension on clinical grounds were prospectively examined with three-dimensional time-of-flight MR angiography. IV digital subtraction angiograms and duplex sonograms were available for all patients. For 21 patients in whom IV angiograms were of high quality and showed the renal arteries to be normal, as confirmed with duplex sonograms, intraarterial digital subtraction angiograms were not obtained for MR correlation. In the other 32 patients, intraarterial angiograms of the abdominal aorta were obtained. MR angiograms were interpreted independently by two radiologists who were unaware of the findings on angiography and duplex sonography. Our preliminary clinical experience suggested that a signal loss in the renal arteries on maximum-intensity-projection MR angiograms indicated a potential stenosis and that the degree of stenosis could not be measured accurately with MR angiography. The search for stenoses was focused on the proximal and middle parts of the vessel, as far as 3 cm from the origin of the vessel. We used intraarterial angiography to measure and grade renal artery stenoses. On intraarterial angiograms, stenoses that involved more than 50% of the vessel's section were considered significant (n = 24) and stenoses that involved 50% or less of the section were considered insignificant (n = 7). These 31 stenoses were found in 26 of the 32 patients who had intraarterial digital subtraction angiography. RESULTS: All 24 significant stenoses appeared as a cutoff of signal intensity on MR angiograms. Results were false-positive in 20 cases: in eight cases, arteries were of small diameter; in seven cases, the stenoses were insignificant; in two cases, the acquisition volume was incorrectly positioned; in two cases, there was a sharp angle in the proximal part of the renal artery; and in one case, no explanation was found. MR angiography had a sensitivity of 100% for detecting stenoses in the proximal 3 cm of the renal artery; stenoses more than 3 cm from the origin of the arteries could not be detected reliably. CONCLUSION: Our results suggest that three-dimensional time-of-flight MR angiography is a simple method for detecting stenoses of the proximal portion of the main renal arteries. However, more work is needed before widespread clinical use of such a technique is feasible.
Angiography, Digital Subtraction↗
Dynamic contrast-enhanced MR angiography of pulmonary embolism: comparison with pulmonary angiography.
OBJECTIVE: Subsecond contrast-enhanced MR angiography, which is not a flow-based technique and does not require cardiac gating or breath-holding, provides multiplanar, rapid, dynamic visualization of the pulmonary arteries. Accordingly, we evaluated the use of this technique in the diagnosis of thrombi in both the proximal and peripheral portions of the pulmonary arteries. Digital subtraction angiography was used as the gold standard for the diagnosis. SUBJECTS AND METHODS: Twenty-three consecutive patients with suspected pulmonary embolism were included in the study. All patients had intraarterial digital subtraction angiography, which showed emboli in 12 patients (13 proximal and six peripheral emboli). MR angiography was done within 24 hr of digital subtraction angiography. Subsecond contrast-enhanced MR angiograms were obtained in the long axis of each pulmonary artery after a unique injection of contrast medium (0.1 mmol/kg) in an antecubital vein. Fifteen dynamic frames of each pulmonary artery were alternately obtained in less than 1 min. MR angiograms were interpreted by two observers who had no knowledge of the findings on digital subtraction angiography. A diagnosis of pulmonary emboli was made when MR angiograms showed a constant intraluminal filling defect or an abrupt vascular cutoff. RESULTS: All thrombi in the proximal branches of the pulmonary arteries were visualized on MR angiograms (n = 13), whereas none of the thrombi in the distal part of the pulmonary arteries were seen (n = 6). In the 11 patients in whom no pulmonary emboli were shown by digital subtraction angiography, findings on MR angiograms were normal (sensitivity, 0.7; specificity, 1.0). CONCLUSION: Our results suggest that dynamic contrast-enhanced MR angiography is an accurate method for detecting emboli in the proximal portions of the pulmonary arteries but is of no value in detecting peripheral emboli.
Angiography, Digital Subtraction↗
Diagnosis of bronchial carcinoid tumor by ultrafast contrast-enhanced MR imaging.
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Bronchi↗
3D display of high resolution vertebral structure images.
In this paper we present a methodology for three-dimensional representation of vertebral structures. A set of X-ray CT images is obtained on a specific high resolution acquisition system. The images are then segmented in order to separate trabecular and cortical structures. Finally, the complex 3D surfaces are visualized using a volume rendering technique.
Humans↗
[Artefacts and intravascular ultrasonography. Analysis and implications for a better reliability in the interpretation of images and measurements].
Intravascular ultrasound catheters provide cross-sectional images of vessel walls and surrounding tissues with rotating transducers, and the behavior of ultrasound in heterogeneous media both cause degradation of image quality. Qualitative and quantitative analyses of in vivo studies are operator-dependent and limited by artifacts. We investigated these limitations by an in vitro study on plexiglass phantoms and segments of fresh arteries. We observed, analyzed and interpreted the most specific reasons for image artifacts: geometric distortions, the point spread function of the imaging system and the near field effects. Various practical implications have resulted from this study. Knowledge of the most obvious pitfalls will enable the user to obtain maximum benefits from intravascular ultrasound imaging, and to appreciate its limitations.
Arterial Occlusive Diseases↗
Artifacts in intravascular ultrasound imaging: analyses and implications.
The ability of an intravascular ultrasound catheter to give cross-sectional images of vessel walls and surrounding tissues, and the behavior of ultrasound in heterogeneous media, are at the origin of degradation of image quality. Qualitative and quantitative analyses of in vivo studies are then operator-dependent and are limited by artifacts. We investigated these limitations by an in vitro study on plexiglass phantoms and segments of fresh arteries. We used a 20 MHz transducer mounted on the tip of a 4.8 F catheter and an interventional ultrasound system. The ultrasound beam is reflected onto the rotating transducer at 600 rotations per minute (RPM), creating 360 degrees real-time images (10 images/second). We then observed, analyzed and interpreted the most specific reasons for image artifacts: geometric distortions, multiple echoes, the point spread function (PSF) of the imaging system, near-field effects, "petal-shaped" effect, and ultrasound speckle. Various practical implications have resulted from this study. Only a thorough knowledge of how to avoid some of the most obvious pitfalls will enable the user to obtain maximum benefits from intravascular ultrasound imaging, and to appreciate its limitations.
Arteries↗