The Alestle - Vol. 54 No. 42 - 02/21/2002

Vol. 54 No. 4

Civil Procedure--In Personam Actions and the Nonresident Motorist Statutes

International audienc

Methodological developments for myocardial tissue characterization using MRI : applications to the evaluation of hypertrabeculation and to multi-slice acceleration of dynamic MRI and T1 mapping

L’altération du tissu myocardique est la conséquence de nombreuses cardiomyopathies. L’imagerie par résonance magnétique (IRM) est un outil de choix pour la caractérisation tissulaire in vivo du myocarde, à laquelle s’ajoute l’évaluation fonctionnelle du cœur. La non-compaction du ventricule gauche (NCVG) est un phénomène découvert récemment, caractérisé par la présence d’une couche myocardique hypertrabéculée pouvant résulter en une fonction cardiaque anormale. Mais la distinction entre une couche de trabéculation normale ou pathologique reste un sujet de débat, et son évaluation présente donc un intérêt majeur pour l’aide au diagnostic de la NCVG. En outre, la cartographie du temps de relaxation T1 offre un outil pertinent à la caractérisation tissulaire avancée en IRM, puisqu’elle constitue un marqueur de la fibrose myocardique avec l’utilisation d’un agent de contraste. Un des défis de l’imagerie cardiovasculaire est le mouvement respiratoire, conduisant à la nécessité un nombre important d’apnées répétées pour explorer l’intégralité du myocarde avec différents contrastes et modalités. Or, pour des patients présentant des maladies cardiovasculaires, ces apnées sont souvent difficiles à maintenir durant un examen. Les récentes techniques d’accélération multi-bandes (MB ou SMS : Simultaneous multi-slice) permettent d’acquérir plusieurs coupes simultanément et ainsi de réduire le nombre d’apnées par examen. Ce travail de thèse a permis d’établir de nouvelles techniques pour la caractérisation tissulaire du myocarde, d’une part dans l’évaluation de l’hypertrabéculation et d’autre part en intégrant les techniques SMS à l’IRM cardiaque.Myocardial tissue alteration is the consequence of several cardiomyopathies. Magnetic resonance imaging (MRI) is a tool of choice for in vivo tissue characterization of the myocardium, coupled with functional evaluation of the heart. Left ventricular non-compaction (LVNC) is a recently discovered phenomenon characterized by the presence of a prominent hypertrabeculated myocardial layer that can result in abnormal heart function. However, the discrimination between normal and pathological trabecular layer remains a matter of debate, and its assessment is therefore of major interest in the diagnosis of LVNC. In addition, T1 mapping offers a relevant tool for advanced tissue characterization in MRI, as it is a marker of myocardial fibrosis with the use of a contrast agent. One of the challenges of cardiovascular imaging is respiratory movement, leading to the need for numerous repeated breath-holds to explore the entire myocardium with different contrasts and modalities. However, for patients with cardiovascular diseases, these breath-holds are a heavy burden during an MRI examination. Simultaneous multi-slice techniques (SMS) are an interesting solution to acquire several slices simultaneously and thus reduce the number of breath-holds per examination. The work of this thesis has enabled the establishment of novel techniques for myocardial tissue characterization, on one hand, in the evaluation of excess of trabeculation, and on the other hand, by incorporating SMS techniques into cardiac MRI

Simultaneous multi‐slice cardiac cine with Fourier‐encoded self‐calibration at 7 Tesla

International audiencePurposeTo accelerate cardiac cine at 7 tesla using simultaneous multi‐slice (SMS) acquisition with self‐calibration to resolve misalignment between calibration and imaging data due to breathing motion.MethodsA spoiled‐gradient echo cine sequence was modified with radiofrequency phase‐cycled SMS excitations. A Fourier encoding strategy was applied along the cardiac phase dimension to allow for slice untangling and split‐slice GRAPPA calibration. Split‐slice GRAPPA was coupled with regular GRAPPA (SMS‐GRAPPA) and L1‐SPIRiT (SMS‐L1SPIRiT) for image reconstruction. 3‐slice SMS cine MRI was evaluated in ten subjects against single‐slice cine MRI in terms of SNR and contrast‐to‐noise ratio and slice leakage.ResultsSNR decreased significantly from 10.1 ± 7.1 for single‐slice cine to 7.4 ± 2.8 for SMS‐GRAPPA (P = 0.02) and was recovered to 9.0 ± 4.5 with SMS‐L1SPIRiT (P = 0.02). Contrast to noise ratio decreased significantly from 14.5 ± 8.1 for single‐slice cine to 5.6 ± 3.6 for SMS‐GRAPPA (P < 0.0001) and increased slightly but significantly back to 6.7 ± 4.4 for SMS‐L1SPIRiT (P = 0.03). Specific absorption rate restrictions imposed a reduced nominal flip angle (−37 ± 7%, P = 0.02) for 3‐slice SMS excitations compared to single‐slice acquisitions. SMS slice leakage increased significantly from apex (8.6 ± 6.5 %) to base (13.1 ± 4.1 %, P = 0.03) in the left ventricle.ConclusionThree‐fold acceleration of cine at 7T was achieved using the proposed SMS technique. Fourier encoding self‐calibration and regularized image reconstruction enabled simultaneous acquisition of three slices without significant SNR decrease but significant CNR decrease linked to the reduced nominal excitation flip angle

Simultaneous multi-slice T1 mapping using MOLLI with blipped CAIPIRINHA bSSFP

International audienceThis study evaluates the possibility for replacing conventional 3slices,3breath-holds MOLLI cardiac T1 mapping with singlebreath-hold 3 simultaneous multi-slice (SMS3) T1 mapping using blipped-CAIPIRINHASMS-bSSFP MOLLI sequence. As a major drawback, SMS-bSSFP presents unique artefacts arising from side-lobe slice excitations that are explained by imperfect RF modulation and bSSFP low flip angle enhancement. Amplitude-only RF modulation (AM) is proposed to reduce these artefacts in SMS-MOLLIcompared to conventional Wong multi-band RF modulation (WM)

Deep Learning–based Automated Segmentation of the Left Ventricular Trabeculations and Myocardium on Cardiac MR Images: A Feasibility Study

International audienc

Exercise stress CMR reveals reduced aortic distensibility and impaired right-ventricular adaptation to exercise in patients with repaired tetralogy of Fallot.

BackgroundThe aim of our study was to evaluate the feasibility of exercise cardiac magnetic resonance (CMR) in patients with repaired tetralogy of Fallot (RTOF) and to assess right and left ventricular adaptation and aortic wall response to exercise in comparison with volunteers.Methods11 RTOF and 11 volunteers underwent prospective CMR at rest and during exercise. A supine bicycle ergometer was employed to reach twice the resting heart rate during continuous exercise, blood pressure and heart rate were recorded. Bi-ventricular parameters and aortic stiffness were assessed using accelerated cine sequences and flow-encoding CMR. A t-test was used to compare values between groups. A Mann Whitney test was used to compare values within groups.ResultsIn RTOF both ventricles showed an impaired contractile reserve (RVEF rest 36.2±8.3%, +1.3±3.9% increase after exercise; LVEF rest 53.8±6.1%, +5.7±6.4% increase after exercise) compared to volunteers (RVEF rest 50.5±5.0%, +10.4±7.1% increase after exercise, p = 0.039; LVEF rest 61.9±3.1%, +12.2±4.7% increase after exercise, p = 0.014). RTOF showed a reduced distensibility of the ascending aorta during exercise compared to volunteers (RTOF: 3.4±1.9 10-3.mmHg-1 vs volunteers: 5.1±1.4 10-3.mmHg-1; p = 0.027). Ascending aorta distensibility was correlated to cardiac work in the volunteers but not in RTOF.ConclusionRTOF showed an impaired contractile reserve for both ventricles. The exercise unmasked a reduced distensibility of the ascending aorta in RTOF, which may be an early sign of increased aortic rigidity

Semi-automatic detection of myocardial trabeculation using cardiovascular magnetic resonance: correlation with histology and reproducibility in a mouse model of non-compaction

International audienceBackground: The definition of left ventricular (LV) non-compaction is controversial, and discriminating between normal and excessive LV trabeculation remains challenging. Our goal was to quantify LV trabeculation on cardiovascular magnetic resonance (CMR) images in a genetic mouse model of non-compaction using a dedicated semi-automatic software package and to compare our results to the histology used as a gold standard.MethodsAdult mice with ventricular non-compaction were generated by conditional trabecular deletion of Nkx2–5. Thirteen mice (5 controls, 8 Nkx2–5 mutants) were included in the study. Cine CMR series were acquired in the mid LV short axis plane (resolution 0.086 × 0.086x1mm3) (11.75 T). In a sub set of 6 mice, 5 to 7 cine CMR were acquired in LV short axis to cover the whole LV with a lower resolution (0.172 × 0.172x1mm3). We used semi-automatic software to quantify the compacted mass (Mc), the trabeculated mass (Mt) and the percentage of trabeculation (Mt/Mc) on all cine acquisitions. After CMR all hearts were sliced along the short axis and stained with eosin, and histological LV contouring was performed manually, blinded from the CMR results, and Mt, Mc and Mt/Mc were quantified. Intra and interobserver reproducibility was evaluated by computing the intra class correlation coefficient (ICC).Results: Whole heart acquisition showed no statistical significant difference between trabeculation measured at the basal, midventricular and apical parts of the LV. On the mid-LV cine CMR slice, the median Mt was 0.92 mg (range 0.07–2.56 mg), Mc was 12.24 mg (9.58–17.51 mg), Mt/Mc was 6.74% (0.66–17.33%). There was a strong correlation between CMR and the histology for Mt, Mc and Mt/ Mc with respectively: r2 = 0.94 (p < 0.001), r2 = 0.91 (p < 0.001), r2 = 0.83 (p < 0.001). Intra- and interobserver reproducibility was 0.97 and 0.8 for Mt; 0.98 and 0.97 for Mc; 0.96 and 0.72 for Mt/Mc, respectively and significantly more trabeculation was observed in the Mc Mutant mice than the controls.Conclusion: The proposed semi-automatic quantification software is accurate in comparison to the histology and reproducible in evaluating Mc, Mt and Mt/ Mc on cine CMR

Prognostic value of cardiovascular magnetic resonance T1 mapping and extracellular volume fraction in nonischemic dilated cardiomyopathy

International audienceAbstract Background Heart failure- (HF) and arrhythmia-related complications are the main causes of morbidity and mortality in patients with nonischemic dilated cardiomyopathy (NIDCM). Cardiovascular magnetic resonance (CMR) imaging is a noninvasive tool for risk stratification based on fibrosis assessment. Diffuse interstitial fibrosis in NIDCM may be a limitation for fibrosis assessment through late gadolinium enhancement (LGE), which might be overcome through quantitative T1 and extracellular volume (ECV) assessment. T1 and ECV prognostic value for arrhythmia-related events remain poorly investigated. We asked whether T1 and ECV have a prognostic value in NIDCM patients. Methods This prospective multicenter study analyzed 225 patients with NIDCM confirmed by CMR who were followed up for 2 years. CMR evaluation included LGE, native T1 mapping and ECV values. The primary endpoint was the occurrence of a major adverse cardiovascular event (MACE) which was divided in two groups: HF-related events and arrhythmia-related events. Optimal cutoffs for prediction of MACE occurrence were calculated for all CMR quantitative values. Results Fifty-eight patients (26%) developed a MACE during follow-up, 42 patients (19%) with HF-related events and 16 patients (7%) arrhythmia-related events. T1 Z-score (p = 0.008) and global ECV (p = 0.001) were associated with HF-related events occurrence, in addition to left ventricular ejection fraction (p  32.1% (optimal cutoff) remained the only CMR independent predictor of HF-related events occurrence (HR 2.15 [1.14–4.07], p = 0.018). In the arrhythmia-related events group, patients had increased native T1 Z-score and ECV values, with both T1 Z-score > 4.2 and ECV > 30.5% (optimal cutoffs) being independent predictors of arrhythmia-related events occurrence (respectively, HR 2.86 [1.06–7.68], p = 0.037 and HR 2.72 [1.01–7.36], p = 0.049). Conclusions ECV was the sole independent predictive factor for both HF- and arrhythmia-related events in NIDCM patients. Native T1 was also an independent predictor in arrhythmia-related events occurrence. The addition of ECV and more importantly native T1 in the decision-making algorithm may improve arrhythmia risk stratification in NIDCM patients. Trial registration NCT02352129. Registered 2nd February 2015—Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT0235212