Filtering and segmentation of 3D angiographic data: Advances based on mathematical morphology.

In the last 20 years, 3D angiographic imaging has proven its usefulness in the context of various clinical applications. However, angiographic images are generally difficult to analyse due to their size and the complexity of the data that they represent, as well as the fact that useful information is easily corrupted by noise and artifacts. Therefore, there is an ongoing necessity to provide tools facilitating their visualisation and analysis, while vessel segmentation from such images remains a challenging task. This article presents new vessel segmentation and filtering techniques, relying on recent advances in mathematical morphology. In particular, methodological results related to spatially variant mathematical morphology and connected filtering are stated, and included in an angiographic data processing framework. These filtering and segmentation methods are evaluated on real and synthetic 3D angiographic data.

3D segmentation of coronary arteries based on advanced mathematical morphology techniques.

In this article, we propose an automatic algorithm for coronary artery segmentation from 3D X-ray data sequences of a cardiac cycle (3D-CT scan, 64 detectors, 10 phases). This method is based on recent mathematical morphology techniques (some of them being extended in this article). It is also guided by anatomical knowledge, using discrete geometric tools to fit on the artery shape independently from any perturbation of the data. The application of the method on a validation dataset (60 images: 20 patients in 3 phases) led to 90% correct (and automatically obtained) segmentations, the 10% remaining cases corresponding to images where the SNR was very low.

Magnetic resonance angiography: from anatomical knowledge modeling to vessel segmentation.

Magnetic resonance angiography (MRA) has become a common way to study cerebral vascular structures. Indeed, it enables to obtain information on flowing blood in a totally non-invasive and non-irradiant fashion. MRA exams are generally performed for three main applications: detection of vascular pathologies, neurosurgery planning, and vascular landmark detection for brain functional analysis. This large field of applications justifies the necessity to provide efficient vessel segmentation tools. Several methods have been proposed during the last fifteen years. However, the obtained results are still not fully satisfying. A solution to improve brain vessel segmentation from MRA data could consist in integrating high-level a priori knowledge in the segmentation process. A preliminary attempt to integrate such knowledge is proposed here. It is composed of two methods devoted to phase contrast MRA (PC MRA) data. The first method is a cerebral vascular atlas creation process, composed of three steps: knowledge extraction, registration, and data fusion. Knowledge extraction is performed using a vessel size determination algorithm based on skeletonization, while a topology preserving non-rigid registration method is used to fuse the information into the atlas. The second method is a segmentation process involving adaptive sets of gray-level hit-or-miss operators. It uses anatomical knowledge modeled by the cerebral vascular atlas to adapt the parameters of these operators (number, size, and orientation) to the searched vascular structures. These two methods have been tested by creating an atlas from a 18 MRA database, and by using it to segment 30 MRA images, comparing the results to those obtained from a region-growing segmentation method.

Determination of vessel cross section for flow rate quantification.

This study was motivated by the interest of measuring different cardiac parameters for which changes in the flow rate during a cardiac cycle needs to be determined at different positions along a vessel segment. These measurements result in a great number of images for which automatic contour detection is very helpful. A model-based algorithm for intraluminal contour detection has been developed in order to allow an accurate quantitative image analysis. The algorithm permits to select contours automatically on all the frames and slices of an imaging study. Images obtained on a flow phantom simulating the effects of blood circulation in large arteries have been used to validate the method. They were acquired with a specially designed interleaved multi slice and phase sequence, using a standard whole-body 2 Tesla NMR scanner. A potential in vivo application of the algorithm has been demonstrated on abdominal aorta images.

In vitro validation of MR measurements of arterial pulse-wave velocity in the presence of reflected waves.

A magnetic resonance imaging projective velocity encoding sequence was used to determine the pulse-wave velocity in an artery model. To this end, a well-defined flow phantom simulating flow propagation in large arteries was used. In order to validate the measurement method in the presence of large reflected waves, these were deliberately created in the phantom. The projective sequence was applied to two measurement sites and the wave velocity was determined from the spatial and temporal separations of the foot of the velocity waveform. A theoretical model describing reflection and attenuation phenomena was compared with experimental velocity waveforms. The model showed that reflections and attenuation can explain the important changes in velocity waveforms. The model also confirmed that in the presence of reflecting waves, the foot of the waveform can be used as a characteristic point for measurements through changes in the waveform.

Myocardial flow reserve parametric map, assessed by first-pass MRI compartmental analysis at the chronic stage of infarction.

Regional myocardial flow and flow reserve (MFR) were assessed by compartmental analysis of Gd-enhanced MRI first-pass data in 7 patients with atypical chest pain, and in 15 patients with previous transmural myocardial infarction. The FE product (Flow x Extraction coefficient), derived from the modified Kety equation, was measured in regions corresponding to the Tetrofosmine-SPECT fixed defect and in remote normal regions. The FE product at rest and hyperemic FE product were similar in healed revascularized tissues (70.5 +/- 15.6 and 112.5 +/- 19.5 ml/mn/100 g, respectively) and in normal myocardium (76.2 +/- 18.3 and 142.2 +/- 33.0, respectively). In contrast, the FE index (48.8 +/- 15.2 and 60.7 +/- 18.0, respectively, P < 0.01 versus the two previous groups) and the MFR (1.27 +/- 0.20 vs. 1.91 +/- 0.29 in normal regions) were reduced in healed fibrotic tissues when the infarct-related artery remained occluded. Myocardial flow reserve maps allowed correct identification of regions corresponding to an occluded infarct-related artery.

Fabrication of elastomer arterial models with specified compliance.

A simple way of making elastic tubes using a mechanical lathe for precise control of the wall thickness is proposed in this study. These tubes are particularly useful for modeling properties of large arteries. Tubes with different geometric parameters and hence different elastic behavior have been made with a silicon elastomer (Rhodorsil RTV 1556). They have been created to be used for compliance measurements in hemodynamics research. Within a limited range of pressures, depending on the wall thickness, such tubes can be used to study models in which the compliance value is assumed to be constant.

Comparison between abnormalities in segmental endocardial motion and abnormalities in segmental wall thickening after anterior myocardial infarction. A cine-magnetic resonance study.

In this study, two patterns of regional contract on of the left ventricle have been studied: endocardial motion and wall thickening, in order to check which of these was the most affected after myocardial infarction. The clinical relevance of this comparison was to assess which parameter of the regional contraction abnormality would best depict the severity of the infarction. Long axis cine-magnetic resonance slices were used to assess segmental systolic left ventricular endocardial motion and segmental systolic wall thickening in 39 normal subjects and in 30 patients at the chronic stage of an anterior myocardial infarction. In the group of normal subjects, endocardial motion and wall thickening showed significant regional heterogeneity. Overall endocardial motion was greater than overall wall thickening: 9.5 +/- 2.0 mm vs 7.1 +/- 1.8 mm. P = 4 x 10(-12) (3.1 +/- 1.2 mm vs 2.0 +/- 0.7 mm, P = 9 x 10(-5) after infarction). A significant linear correlation was found between these two parameters. In the infarction group, abnormality scores for endocardial motion and for wall thickening were calculated. These scores were defined as the average values exceeding the mean minus two standard deviations of the normal range for segments corresponding to the antero-septal-apical walls. The abnormality score for endocardial motion greater than the abnormality score for wall thickening: 0.31 +/- 0.12 vs 0.20 +/- 0.07, P = 9 x 10(-4). We conclude that, in clinical practice, endocardial motion is affected to a greater degree by myocardial infarction than is wall thickening and therefore constitutes a more discriminant index in the assessment of post-infarction patients.

[Dynamic cartography of flow patterns by cine-MRI. Presentation of the technique and preliminary results for major vessels]. / Cartographie dynamique des flux par ciné-IRM. Présentation de la technique et résultats préliminaires sur les gros vaisseaux.

The authors report the principles, experimental evaluation and clinical approach of a method for dynamic imaging of flow patterns by NMRI, based upon the phase modulation technique. The imaging method is based upon gradient echo, functioning in "cine" and "flow compensated" mode. Modifications in this sequence enable attribution to the moving spins phase of a value which is considered to be proportional to the flow rate. A map of rates is then obtained from the phase image. Calibration of this sequence in vitro has shown excellent correlations between flow rate and the phase information thus obtained: r always > 0.98 for rates up to m/s. The first results obtained in vivo for the thoracic and abdominal aorta, in 11 control subjects, show that the technique is suitable for the study of pulsatile blood flow, providing very detailed information concerning the spatial distribution of flow rates. Mean flow in the suprarenal abdominal aorta (4.6 +/- 1.6 l/min) is 32% greater than that in the inferior vena cava (3.1 +/- 1 l/min), corresponding to an estimation of portal vein flow of 1.5 l/min. Practical limitations related to the use of a resistive magnet are nevertheless stressed and the authors list the technical aspects necessary for the better clinical utilisation of this non-invasive flowmetric technique. A review of the current literature forms the basis for an assessment of the potential importance of dynamic and quantitative NMRI of flow patterns in the cardiovascular area.

[Acute myocardial infarction: immediate coronary angioplasty for failure or contra-indications of thrombolytic therapy. Apropos of a series of 100 cases]. / Infarctus myocardique aigu: angioplastie coronaire immédiate en cas d'échec ou de contre-indication la thrombolyse. A propos d'une série de 100 cas.

One hundred patients admitted to a centre of interventional cardiology with acute myocardial infarction of less than 6 hours, underwent coronary angioplasty of first intention because of contra-indications to thrombolytic therapy (n = 20) or after thrombolytic therapy with streptokinase (n = 54), acylenzymes (n = 12) or tissue type plasminogen activator (n = 14). The indication of angioplasty were those of the TIMI (Thrombolysis in Myocardial Infarction) classification (occluded artery, TIMI grade 0) (n = 60) (suboccluded artery, TIMI grade 1) (n = 40). The criterion of success of angioplasty was an increase greater than 1 of TIMI grade. Reperfusion of the coronary artery was obtained by angioplasty in 95% of failures of thrombolysis and in 90% of patients with contra-indications to thrombolytic therapy. The early reocclusion rate at D1 was 2%. Repeat angioplasty at D1 was successful in both these cases and the arteries were still patent at D21. The reocclusion rate at the third week in 75 patients who underwent control coronary angiography was 5.3%. In patients with arterial occlusion, immediate angioplasty attained two objectives in the same procedure: a high rate of emergency myocardial reperfusion and a low rate of reocclusion. The average left ventricular ejection fraction (all arteries) significantly improved (+9.2% in absolute values) when the artery remained patent (p less than 0.001), especially when the initial ejection fraction was low. In the patients who had occluded arteries at control angiography at 3 weeks, the ejection fraction decreased (-4% in absolute values) (NS). The following complications were observed: 4 coronary artery dissections and haematomas at the site of femoral puncture in patients who had received thrombolytic therapy (10 drained surgically). The hospital mortality was 3% and global mortality after an average follow-up period of 19.6 months was 5%. Coronary angioplasty in acute myocardial infarction carries a low risk and seems to be beneficial in patients with contra-indications to or failure of thrombolysis.

[Value of cine magnetic resonance imaging in the diagnosis and quantification of valvular regurgitation. Comparison with angiography and Doppler echocardiography]. / Valeur du ciné-IRM dans le diagnostic et la quantification des fuites valvulaires. Comparaison avec l'angiographie et l'échocardiographie doppler.

Thirty-three patients presenting with regurgitation of the mitral valve (19 cases), tricuspid valve (14 cases) or aortic valve (11 cases) documented by angiography (n = 20) and/or doppler-echocardiography (n = 28) were examined by cine-MRI in order to test this method in valvular regurgitation. Sixteen ECG-synchronized cine-MRI images were acquired by the GRASS technique every 40 ms on appropriate projections, with a resistive 0.28 Tesla Bruker magnet. The semiology of normal and pathological blood flow images at cine-MRI is described. Valvular regurgitations present as "signal void" jets the chronology and spatial extension of which depend on the severity of the lesion. The differential diagnosis with physiological flows is discussed. The diagnostic sensitivity of the method was 29/29 when compared with angiography and 29/33 when compared with doppler-echocardiography (2 cases of 1/4 mitral regurgitation and 2 cases 1/4 tricuspid regurgitation were not visible at cine-MRI). The specificity of this method, as can be judged from 104 patients explored, also seems to be satisfactory. The severity of regurgitation was graded from 1 to 4 with the three methods, on the basis of strict criteria. The differences in grade evaluation exceeded +/- 1 point in only one case of mitral regurgitation which was greatly underestimated by the doppler method as compared with angiography and cine-MRI. Thus, cine-MRI is a reliable method to evaluate valvular regurgitations and their severity. It solves the practical problem raised by non-echogenic patients when catheterization is to be postponed or avoided.

[Comparison of the left ventricular stroke volume and fraction measured with MRI and contrast ventriculography]. / Comparaison des volumes et des fractions d'éjection ventriculaires gauches mesures en IRM et par ventriculographie de contraste.

27 patients who underwent a contrast ventriculography in right anterior oblique at 30 degrees (for various cardiopathies) were studied by MRI with a mean delay of 5.7 +/- 6.2 days. After location of the medio-ventricular area, a diastolic horizontal section (apex of the R wave) and a systolic section (descending portion of the T wave) are carried out using the spin ultrasound technique. The same calculations are used for MRI au X-Ray contours (modified area-length method) by two strictly independent operators. With MRI, the LVSF is under estimated (40.4 +/- 19%) as compared angiography (46.1 +/- 18%). The linear correlation is 0.79 and in half of the patients (13 in 27) the deviation of the LVSF exceeds 10 p. cent. The volumes also tend to be underestimated with MRI (97 +/- 50 and 64 +/- 51 ml for the diastole and systole respectively) compared with angiography (123 +/- 66 and 73 +/- 62 ml), but the difference is only significant for the diastole and the linear correlation coefficients are improved at 0.82 and 0.90. Underestimation of the parameters measured with MRI is the consequence of multiple factors including the imprecise determination of the true telesystole, the marked effect of the partial volume related to the thickness of the section, and especially the obliquity of the plane studied on MRI, compared with the long axis of the heart. The error made by using a calculation algorithm, conceived for projective methods showing the long axis of the modeled ellipsoid, also explains the underestimation of volumes obtained with MRI, tomographic method. The simple technique used here seems especially interesting in the analysis of segmental contraction. Finally, the development of cine-MRI will undoubtedly be extremely beneficial in the study of ventricular contraction and relaxation.

[Value of nuclear magnetic resonance in dilated cardiomyopathy. Approach to intraventricular hemodynamics]. / Intérêt de l'IRM dans les myocardiopathies dilatées. Approche de l'hémodynamique intraventriculaire.

The value of magnetic resonance imaging (MRI) with multiechoes spin-echo sequences was investigated in 22 patients with dilated cardiomyopathy (group I) and 25 normal subjects serving as controls (group II). The results of MRI in group I were compared with those of echocardiography and radionuclide ventriculography. Measurements of left ventricular dimensions at echography and MRI showed a tendency, with MRI, to overestimate wall thickness and underestimate ventricular diameter. Thus, for diastolic LV we had 63.8 +/- 10.5 mm with MRI vs 70.6 +/- 7.6 mm with echography, the corresponding figures for posterior wall thickness being 112 +/- 1.4 mm vs 9.9 +/- 1.1 mm respectively. These differences seem to be due to MRI introducing a partial volume effect dependent on the thickness of slices and of their orientation in relation to the cardiac axis. MRI evaluation of left ventricular function by calculation of myocardial fibre shortening fractions correlated poorly with the echocardiographic value of the same parameter and with the radionuclide ejection fraction (r = 0.58 and 0.575 respectively; p less than 0.05). For better quantification of the cardiac pump function, planimetry of the endocardial contour during diastole and systole is required. It would seem that the value of MRI resides in the possibility it offers to explore left intraventricular haemodynamics by studying the "flow signal" obtainable from multiechoes sequences at different moments of the cardiac cycle. During systole, we found a left intraventricular signal that was reinforced on even echoes and much more intense in cardiomyopathy patients (scores = 1.61 +/- 1.06) than in controls (score = 0.77 +/- 0.7; p less than 0.01). The intensity score for this signal correlated with the ejection fraction in group I subjects (r = 0.82).

[Treatment of fractures of the clavicle by closed pinning inside-out without back-and-forth]. / Traitement des fractures de la clavicule par embrochage à foyer fermé de dedans en dehors sans va-et-vient.

Pinning of fractures of the clavicle is easily and safely done by introducing the pin through the medial fragment. The pointed tip is embedded into the cortex of the lateral fragment and the inner end of the pin is bent at a right angle to fix it to the bone. Insertion is made with image intensification to avoid vascular damage and to guide the passage of the pin through the medial fragment without danger. Of 25 fractures treated in this way, only two, treated at the beginning of the series, required open reduction. No other immobilisation was necessary. All the fractures united uneventfully.

[The contribution of magnetic resonance imaging in congenital heart diseases]. / Apport de l'imagerie par résonance magnétique dans les cardiopathies congénitales.

The diagnostic value of magnetic resonance imaging (MRI) was assessed in 30 patients with congenital heart disease, including 7 patients with postoperative sequellae. The images obtained by synchronizing the MRI spectrometer with the electrocardiogramme were recorded in 2 or 3 different planes (sagittal, frontal and transverse) and compared to clinical, angiographic and/or echocardiographic data. The MRI provided high resolution tomographic images enabling spatial reconstitution of the heart by the use of different planes. These images were particularly useful for showing the position and dimensions of the ventricles (both chamber size and wall thickness) and their relationship to the atria and great vessels. These results confirm the value of this new non-invasive imaging technique in the diagnosis of congenital heart disease, not counting the additional information on blood flow and tissue characterisation that will soon become available.

[Importance of magnetic resonance imaging in myocardial infarct]. / Apport de l'imagerie par résonance magnétique dans l'infarctus du myocarde.

Imagery by magnetic resonance (IMR) represents a new modality of medical imagery based on the interaction between the magnetic fields produced by radio-frequency waves and living substance. IMR finds an interesting application in the study of different stages of myocardial infarction. In 30 cases of myocardial infarction IMR was compared with thallium tomoscintigraphy and echocardiography. In the acute stage, myomalacia appears in IMR as a superbrilliant zone, and in the chronic stage parietal thinning and dyskinesias are apparent. Intraventricular thromboses, but also hemostasis in aneurysmatic or akinetic sites are visualised as a high-intensity signal within these areas. IMR represents therefore a new means of evaluation of size and evolution of the necrosis. This procedure provides also functional informations about the contraction and flow anomalies.

[Diagnostic elements of a right papyraceous ventricle. The value of nuclear magnetic resonance]. / Eléments diagnostiques du ventricule droit papyracé. Intérêt de la résonance magnétique nucléaire.

We are reporting the case of a young man presenting repeated syncopes linked to episodes of ventricular tachycardia. The rhythm disorders were due to the existence of a papyraceous right ventricle with concomitant involvement of the left ventricle disclosed during the etiological work-up. We are reporting, at this time, the usual diagnostic elements of this disease, but mostly original data provided by the nuclear magnetic resonance, as the clinical examination and the EKG are often less revealing except for late potentials always found in the arrhythmic form. The right, ventricular dysplasia and the papyraceous right ventricle represent two very close entities. Particular characteristics enable to differentiate them and also the differential diagnosis with other diseases are discussed by stressing the advantage of magnetic resonance imaging, a new method, non invasive, which lends itself well to the analysis of cardiac morphology.

[Nuclear magnetic resonance in the diagnosis of aortic diseases]. / Apport de la résonance magnétique nucléaire dans le diagnostic des affections aortiques.

The diagnostic value of nuclear magnetic resonance imaging was assessed in a number of aortic pathologies: aneurysms of the thoracic and abdominal aorta, sinus of Valsalva aneurysms and dissection of the aorta. The imager was equipped with a resistor magnet providing a field of 0.15 Tesla. An electrocardiographic gating system was perfected. The images obtained were very satisfactory as they provided three dimensional morphological information and a qualitative assessment of blood flow. Further studies are now required with comparison with other invasive and non-invasive diagnostic methods to determine the clinical role of NMR imaging and to evaluate the diagnostic sensitivity and specificity of this new technique.

[Spatial ventricular gradient studied by computerized vectorcardiography. Normal and pathological values. Interpretation and clinical evaluation]. / Le gradient ventriculaire spatial étudié par vectocardiographie informatisée. Valeurs normales et pathologiques. Essai d'interprétation et d'évaluation clinique.

The ventricular gradient is a reflection of uneven ventricular repolarisation. Until recently is was only appreciated in the frontal plane of the classical electrocardiogramme and expressed as the sum of the vectors representing the surfaces under the QRS complex and T wave. We used computerised vectorcardiography to obtain a more exact evaluation of the size and spatial orientation of the vector gradient. The spatial vector gradient was calculated in a control group and in a number of pathological conditions. The reference values were established in 70 normal subjects with a mean age of 36 +/- 21 years: 0.092 +/- 0.016 m V.s for amplitude: 38.4 degrees +/- 6.1 for thesite and 21.6 degrees +/- 8.7 for the azimuth. The size and spatial orientation of the ventricular gradient can be used to define normal limits and to distinguish subgroups by using the values of the site and azimuth. The spatial ventricular gradient is a new approach to defining the limits of normality in poorly understood abnormalities of ventricular repolarisation. It may also be useful in the comprehension of certain forms of cardiac arrhythmia related to desynchronisation of ventricular repolarisation.