Multilevel testing of constraints induced by structural equation modeling in fMRI effective connectivity analysis: A proof of concept

In functional MRI (fMRI), effective connectivity analysis aims at inferring the causal influences that brain regions exert on one another. A common method for this type of analysis is structural equation modeling (SEM). We here propose a novel method to test the validity of a given model of structural equation. Given a structural model in the form of a directed graph, the method extracts the set of all constraints of conditional independence induced by the absence of links between pairs of regions in the model and tests for their validity in a Bayesian framework, either individually (constraint by constraint), jointly (e.g., by gathering all constraints associated with a given missing link), or globally (i.e., all constraints associated with the structural model). This approach has two main advantages. First, it only tests what is testable from observational data and does allow for false causal interpretation. Second, it makes it possible to test each constraint (or group of constraints) separately and, therefore, quantify in what measure each constraint (or, e..g., missing link) is respected in the data. We validate our approach using a simulation study and illustrate its potential benefits through the reanalysis of published data.

Four-dimensional flow cardiovascular magnetic resonance aortic cross-sectional pressure changes and their associations with flow patterns in health and ascending thoracic aortic aneurysm

BACKGROUND

Ascending thoracic aortic aneurysm (ATAA) is a silent and threatening dilation of the ascending aorta (AscAo). Maximal aortic diameter which is currently used for ATAA patients management and surgery planning has been shown to inadequately characterize risk of dissection in a large proportion of patients. Our aim was to propose a comprehensive quantitative evaluation of aortic morphology and pressure-flow-wall associations from four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) data in healthy aging and in patients with ATAA.

METHODS

We studied 17 ATAA patients (64.7 ± 14.3 years, 5 females) along with 17 age- and sex-matched healthy controls (59.7 ± 13.3 years, 5 females) and 13 younger healthy subjects (33.5 ± 11.1 years, 4 females). All subjects underwent a CMR exam, including 4D flow and three-dimensional anatomical images of the aorta. This latter dataset was used for aortic morphology measurements, including AscAo maximal diameter (iDMAX) and volume, indexed to body surface area. 4D flow MRI data were used to estimate 1) cross-sectional local AscAo spatial (∆PS) and temporal (∆PT) pressure changes as well as the distance (∆DPS) and time duration (∆TPT) between local pressure peaks, 2) AscAo maximal wall shear stress (WSSMAX) at peak systole, and 3) AscAo flow vorticity amplitude (VMAX), duration (VFWHM), and eccentricity (VECC).

RESULTS

Consistency of flow and pressure indices was demonstrated through their significant associations with AscAo iDMAX (WSSMAX:r = -0.49, p < 0.001; VECC:r = -0.29, p = 0.045; VFWHM:r = 0.48, p < 0.001; ∆DPS:r = 0.37, p = 0.010; ∆TPT:r = -0.52, p < 0.001) and indexed volume (WSSMAX:r = -0.63, VECC:r = -0.51, VFWHM:r = 0.53, ∆DPS:r = 0.54, ∆TPT:r = -0.63, p < 0.001 for all). Intra-AscAo cross-sectional pressure difference, ∆PS, was significantly and positively associated with both VMAX (r = 0.55, p = 0.002) and WSSMAX (r = 0.59, p < 0.001) in the 30 healthy subjects (48.3 ± 18.0 years). Associations remained significant after adjustment for iDMAX, age, and systolic blood pressure. Superimposition of ATAA patients to normal aging trends between ∆PS and WSSMAX as well as VMAX allowed identifying patients with substantially high pressure differences concomitant with AscAo dilation.

CONCLUSION

Local variations in pressures within ascending aortic cross-sections derived from 4D flow MRI were associated with flow changes, as quantified by vorticity, and with stress exerted by blood on the aortic wall, as quantified by wall shear stress. Such flow-wall and pressure interactions might help for the identification of at-risk patients.

Effect of sonification types in upper-limb movement: a quantitative and qualitative study in hemiparetic and healthy participants

BACKGROUND

Movement sonification, the use of real-time auditory feedback linked to movement parameters, have been proposed to support rehabilitation. Nevertheless, if promising results have been reported, the effect of the type of sound used has not been studied systematically. The aim of this study was to investigate in a single session the effect of different types of sonification both quantitatively and qualitatively on patients with acquired brain lesions and healthy participants.

METHODS

An experimental setup enabling arm sonification was developed using three different categories of sonification (direct sound modulation, musical interaction, and soundscape). Simple moving forward movements performed while sliding on a table with both arms were investigated with all participants. Quantitative analysis on the movement timing were performed considering various parameters (sound condition, affected arm and dominance, sonification categories). Qualitative analysis of semi-structured interviews were also conducted, as well as neuropsychological evaluation of music perception.

RESULTS

For both the patient and healthy groups (15 participants each), average duration for performing the arm movement is significantly longer with sonification compared to the no-sound condition (p < 0.001). Qualitative analysis of semi-structured interviews revealed different aspects of motivational and affective aspects of sonification. Most participants of both groups preferred to complete the task with sound (29 of 30 participants), and described the experience as playful (22 of 30 participants). More precisely, the soundscape (nature sounds) was the most constantly preferred (selected first by 14 of 30 participants).

CONCLUSION

Overall, our results confirm that the sonification has an effect on the temporal execution of the movement during a single-session. Globally, sonification is welcomed by the participants, and we found convergent and differentiated appreciations of the different sonification types.

Value of aortic volumes assessed by automated segmentation of 3D MRI data in patients with thoracic aortic dilatation: A case-control study

PURPOSE

The purpose of this study was to investigate the benefit of aortic volumes compared to diameters or cross-sectional areas on three-dimensional (3D) magnetic resonance imaging (MRI) in discriminating between patients with dilated aorta and matched controls.

MATERIALS AND METHODS

Sixty-two patients (47 men and 15 women; median age, 66 years; age range: 33-86 years) with tricuspid aortic valve and ascending thoracic aorta aneurysm (TAV-ATAA) and 43 patients (35 men and 8 women; median age, 51 years; age range: 17-76 years) with bicuspid aortic valve and dilated ascending aorta (BAV) were studied. One group of 54 controls matched for age and sex to patients with TAV-ATAA (39 men and 15 women; median age, 68 years; age range: 33-81 years) and one group of 42 controls matched for age and sex to patients with BAV (34 men and 8 women; median age, 50 years; age range: 17-77 years) were identified. All participants underwent 3D MRI, used for 3D-segmentation for measuring aortic length, maximal diameter, maximal cross-sectional area (CSA) and volume for the ascending aorta.

RESULTS

An increase in ascending aorta volume (TAV-ATAA: +107%; BAV: +171% vs. controls; P < 0.001) was found, which was three times greater than the increase in diameter (TAV-ATAA: +29%; BAV: +40% vs. controls; P < 0.001). In differentiating patients with TAV-ATAA from their controls, the indexed ascending aorta volume showed better performances (AUC, 0.935 [95% confidence interval (CI): 0.882-0.989]; accuracy, 88.7% [95% CI: 82.9-94.5]) than indexed ascending aorta length (P < 0.001), indexed ascending aorta maximal diameter (P = 0.003) and indexed ascending aorta maximal CSA (P = 0.03). In differentiating patients with BAV from matched controls, indexed ascending aorta volume showed significantly better performances performance (AUC, 0.908 [95% CI: 0.829-0.987]; accuracy, 88.0% [95% CI: 80.9-95.0]) than indexed ascending aorta length (P = 0.02) and not different from indexed ascending aorta maximal diameter (P = 0.07) or from indexed ascending aorta maximal CSA (P = 0.27) CONCLUSION: Aortic volume measured by 3D-MRI integrates both elongation and luminal dilatation, resulting in greater classification performance than maximal diameter and length in differentiating patients with dilated ascending aorta or aneurysm from controls.

Feasibility of a New Regional Myocardial Strain Parameter for the Detection of Wall Motion Abnormalities in Arrhythmogenic Right Ventricular Cardiomyopathy

Purpose

To evaluate a cardiac MRI feature tracking (FT)-derived parameter that combines right ventricular (RV) longitudinal and radial motions in detecting arrhythmogenic right ventricular cardiomyopathy (ARVC).

Materials and Methods

Patients with ARVC (n = 47; median age, 46 [IQR, 30-52] years; 31 men) were compared with controls (n = 39; median age, 46 [IQR, 33-53] years; 23 men) and separated into two groups based on fulfillment of major structural 2020 International criteria. Cine data from 1.5-T cardiac MRI examinations were analyzed using FT, resulting in conventional strain parameters and a novel composite index named the longitudinal-to-radial strain loop (LRSL). Receiver operating characteristic (ROC) analysis was used to assess diagnostic performance of RV parameters.

Results

Volumetric parameters differed significantly between patients in the major structural criteria group and controls but not between patients in the no major structural criteria group and controls. Patients in the major structural criteria group had significantly lower magnitudes of all FT parameters than controls, including RV basal longitudinal strain, radial motion fraction, circumferential strain, and LRSL (-15.6% ± 6.4 vs -26.7% ± 13.9; -9.6% ± 4.89 vs -13.8% ± 4.7; -6.9% ± 4.6 vs -10.1% ± 3.8; and 217.0 ± 128.9 versus 618.6 ± 356.3, respectively). Only LRSL differed between patients in the no major structural criteria group and controls (359.5 ± 195.8 vs 618.6 ± 356.3; P < .0001). Parameters with the highest area under the ROC curve values for discriminating patients in the no major structural criteria group from controls were LRSL, RV ejection fraction, and RV basal longitudinal strain (0.75, 0.70, and 0.61, respectively).

Conclusion

A new parameter combining RV longitudinal and radial motions showed good diagnostic performance in ARVC, even in patients without major structural abnormalities.Keywords: Arrhythmogenic Right Ventricular Dysplasia, Strain, Wall Motion Abnormalities, Right Ventricle, MRI, Inherited Cardiomyopathy Supplemental material is available for this article. © RSNA, 2023.

Brain Metabolic Alterations in Seropositive Autoimmune Encephalitis: An 18F-FDG PET Study

INTRODUCTION

Autoimmune encephalitis (AE) diagnosis and follow-up remain challenging. Brain ¹⁸F-fluoro-deoxy-glucose positron emission tomography (FDG PET) has shown promising results in AE. Our aim was to investigate FDG PET alterations in AE, according to antibody subtype.

METHODS

We retrospectively included patients with available FDG PET and seropositive AE diagnosed in our center between 2015 and 2020. Brain PET Z-score maps (relative to age matched controls) were analyzed, considering metabolic changes significant if |Z-score| ≥ 2.

RESULTS

Forty-six patients were included (49.4 yrs [18; 81]): 13 with GAD autoantibodies, 11 with anti-LGI1, 9 with NMDAR, 5 with CASPR2, and 8 with other antibodies. Brain PET was abnormal in 98% of patients versus 53% for MRI. The most frequent abnormalities were medial temporal lobe (MTL) and/or striatum hypermetabolism (52% and 43% respectively), cortical hypometabolism (78%), and cerebellum abnormalities (70%). LGI1 AE tended to have more frequent MTL hypermetabolism. NMDAR AE was prone to widespread cortical hypometabolism. Fewer abnormalities were observed in GAD AE. Striatum hypermetabolism was more frequent in patients treated for less than 1 month (p = 0.014), suggesting a relation to disease activity.

CONCLUSION

FDG PET could serve as an imaging biomarker for early diagnosis and follow-up in AE.

Myocardial fibrosis assessed by magnetic resonance imaging in asymptomatic heterozygous familial hypercholesterolemia: the cholcoeur study

BACKGROUND

Familial Hypercholesterolemia (FH) is an underdiagnosed condition with an increased cardiovascular risk. It is unknown whether lipid accumulation plays a role in structural myocardial changes. Cardiovascular Magnetic Resonance (CMR) is the reference technique for the morpho-functional evaluation of heart chambers through cine sequences and for myocardial tissue characterization through late gadolinium enhancement (LGE) and T1 mapping images. We aimed to assess the prevalence of myocardial fibrosis in FH patients.

METHODS

Seventy-two asymptomatic subjects with genetically confirmed FH (mean age 49·24, range 40 to 60 years) were prospectively recruited along with 31 controls without dyslipidaemia matched for age, sex, BMI, and other cardiovascular risk factors. All underwent CMR including cine, LGE, pre- and post-contrast T1 mapping. Extracellular volume (ECV) and enhancement rate of the myocardium (ERM = difference between pre- and post-contrast myocardial T1, normalized by pre-contrast myocardial T1) were calculated.

FINDINGS

Five FH patients and none of the controls had intramyocardial LGE (p= 0·188). While no changes in Native T1 and ECV were found, post-contrast T1 was significantly lower (430·6 ± 55ms vs. 476·1 ± 43ms, p<0·001) and ERM was higher (57·44± 5·99 % vs 53·04±4·88, p=0·005) in HeFH patients compared to controls. Moreover, low post-contrast T1 was independently associated with the presence of xanthoma (HR 5·221 [1·04-26·28], p= 0·045). A composite score combining the presence of LGE, high native T1 and high ERM (defined as ≥ mean ± 1·5 SD) was found in 20·8% of the HeFH patients vs. 0% in controls (p<0·000, after adjustment for main confounders).

INTERPRETATION

CMR revealed early changes in myocardial tissue characteristics in HeFH patients, that should foster further work to better understand and prevent the underlying pathophysiological processes.

Non-Invasive Ultrasonic Description of Tumor Evolution

Simple Summary

During tumor evolution, heterogeneous structural and functional changes occur in the tumor microenvironment. These complex changes have pro- or anti-tumorigenesis effects and have an impact on therapy efficiency. Therefore, the tumor microenvironment needs to be non-invasively characterized over time. The aim of this preclinical work is to compare the sensitivity of modifications occurring during tumor evolution of volume, immunohistochemistry and non-invasive quantitative ultrasound parameters (Shear Wave Elastography and dynamic Contrast-Enhanced Ultrasound) and to study the link between them. The complementary evaluation over time of multiple morphological and functional parameters during tumor growth underlines the need to integrate histological, morphological, functional, and, ultimately, genomic information into models that can consider the temporal and spatial variability of features to better understand tumor evolution.

Abstract

Purpose: There is a clinical need to better non-invasively characterize the tumor microenvironment in order to reveal evidence of early tumor response to therapy and to better understand therapeutic response. The goals of this work are first to compare the sensitivity to modifications occurring during tumor growth for measurements of tumor volume, immunohistochemistry parameters, and emerging ultrasound parameters (Shear Wave Elastography (SWE) and dynamic Contrast-Enhanced Ultrasound (CEUS)), and secondly, to study the link between the different parameters. Methods: Five different groups of 9 to 10 BALB/c female mice with subcutaneous CT26 tumors were imaged using B-mode morphological imaging, SWE, and CEUS at different dates. Whole-slice immunohistological data stained for the nuclei, T lymphocytes, apoptosis, and vascular endothelium from these tumors were analyzed. Results: Tumor volume and three CEUS parameters (Time to Peak, Wash-In Rate, and Wash-Out Rate) significantly changed over time. The immunohistological parameters, CEUS parameters, and SWE parameters showed intracorrelation. Four immunohistological parameters (the number of T lymphocytes per mm² and its standard deviation, the percentage area of apoptosis, and the colocalization of apoptosis and vascular endothelium) were correlated with the CEUS parameters (Time to Peak, Wash-In Rate, Wash-Out Rate, and Mean Transit Time). The SWE parameters were not correlated with the CEUS parameters nor with the immunohistological parameters. Conclusions: US imaging can provide additional information on tumoral changes. This could help to better explore the effect of therapies on tumor evolution, by studying the evolution of the parameters over time and by studying their correlations.

Quantitative and Qualitative Approach for Shear Wave Elastography in Superficial Lymph Nodes

The diagnostic contribution of 2-D shear-wave elastography (SWE) in management of superficial lymph nodes (LNs) of any origin was evaluated in 222 patients referred for needle core biopsy. Each patient underwent conventional B-mode/Doppler ultrasound examinations (conventional ultrasound) and SWE. Quantitative SWE parameters and qualitative SWE map features were extracted. Carcinomas were found to be significantly stiffer than benign LNs (29.5 ± 32.3 kPa vs. 6.7 ± 12.3 kPa). Lymphomas exhibited intermediate stiffness (11.4 ± 5.2 kPa). Qualitative SWE analysis provided color patterns specific to histopathology (stiff rim, nodular and undetermined patterns related to malignancy and blue pattern to benignity). Adding SWE to conventional ultrasound improved the sensitivity of LN diagnosis (from 81.1% to 92.0%) but decreased its specificity (from 73.2% to 67.6%) because of the high prevalence of lymphomas compared with carcinomas. Inter-observer agreement for quantitative SWE was good (intra-class correlation coefficient = 0.82) as was inter-observer diagnostic agreement for qualitative SWE (κ = 0.65). LN location and histology type were found to influence the reported diagnostic performance of SWE.

Automated Extraction of Mutual Independence Patterns Using Bayesian Comparison of Partition Models

Mutual independence is a key concept in statistics that characterizes the structural relationships between variables. Existing methods to investigate mutual independence rely on the definition of two competing models, one being nested into the other and used to generate a null distribution for a statistic of interest, usually under the asymptotic assumption of large sample size. As such, these methods have a very restricted scope of application. In this article, we propose to change the investigation of mutual independence from a hypothesis-driven task that can only be applied in very specific cases to a blind and automated search within patterns of mutual independence. To this end, we treat the issue as one of model comparison that we solve in a Bayesian framework. We show the relationship between such an approach and existing methods in the case of multivariate normal distributions as well as cross-classified multinomial distributions. We propose a general Markov chain Monte Carlo (MCMC) algorithm to numerically approximate the posterior distribution on the space of all patterns of mutual independence. The relevance of the method is demonstrated on synthetic data as well as two real datasets, showing the unique insight provided by this approach.

Ultrasound-triggered delivery of paclitaxel encapsulated in an emulsion at low acoustic pressures

We investigated the in vitro ultrasound-triggered delivery of paclitaxel, a well known anti-cancerous drug, encapsulated in an emulsion and in the presence of CT26 tumor cells. The emulsion was made of nanodroplets, whose volume comprised 95% perfluoro-octyl bromide and 5% tributyl O-acetylcitrate, in which paclitaxel was solubilized. These nanodroplets, prepared using a high-pressure microfluidizer, were stabilized by a tailor-made and recently patented biocompatible fluorinated surfactant. The delivery investigations were performed at 37 °C using a high intensity focused ultrasound transducer at a frequency of 1.1 MHz. The ultrasonic pulse was made of 275 sinusoidal periods and the pulse repetition frequency was 200 Hz with a duty cycle of 5%. The measured viabilities of CT26 cells showed that paclitaxel delivery was achievable for peak-to-peak pressures of 0.4 and 3.5 MPa, without having to vaporize the perfluorocarbon part of the droplet or to induce inertial cavitation.

T1 mapping-derived signature of myocardial involvement in idiopathic inflammatory myopathy compared to acute viral myocarditis: a texture-based analysis

Funding Acknowledgements

Type of funding sources: None.

Background. Recent studies revealed the ability of MRI T1 mapping to characterize myocardial involvement in both idiopathic inflammatory myopathy (IIM) and acute viral myocarditis (AVM), as compared to healthy controls. However, neither myocardial T1 nor T2 maps were able to discriminate between IIM and AVM patients, when considering conventional myocardial mean values and derived indices such as lambda and extracellular volume.

Purpose. To investigate the ability of T1 mapping-derived texture analysis to differentiate IIM from AVM.

Methods. Forty patients, 20 with IIM (51 ± 17 years, 9 men) and 20 with AVM (34 ± 13 years, 16 men) underwent 1.5T MRI T1 mapping using a modified Look-Locker inversion-recovery sequence before and 15 minutes after injection of a gadolinium contrast agent. After manual delineation of endocardial and epicardial borders and co-registration of all inversion time images, native and post-contrast T1 maps were estimated. Myocardial texture analysis was performed on native T1 maps. Textural features such as: autocorrelation, contrast, dissimilarity, energy and sum entropy were used to build a least squares-based linear regression model. Finally, receiver operating characteristic (ROC) analysis was used to investigate the ability of such texture features score to classify IIM vs. AVM patients, compared to the performance of mean myocardial T1. A Wilcoxon rank-sum test was also used to test difference significance between groups.

Results. Both native and post-contrast mean myocardial T1 values were comparable between IIM (native: 1022 ± 43 ms; post-contrast: 319 ± 44 ms) and AVM (1056 ± 59 ms, p = 0.07; 318 ± 35 ms, p = 0.90, respectively) groups. Results of ROC analyses are provided in the Table, indicating that a better discrimination between IIM and AVM patients was obtained when using texture features, with higher AUC and accuracy than mean T1 values (Figure).

Conclusion. Texture analysis derived from MRI T1 maps without contrast agent injection was able to discriminate between IIM and AVM with higher accuracy, sensitivity and specificity than conventional T1 indices. Such analysis could provide a useful myocardial signature to help diagnose and manage cardiac alterations associated with IIM in patients presenting with myocarditis and primarily suspected of AVM.

Table Area under curve (AUC) Accuracy Sensitivity Specificity Native T1 0.67 0.70 0.65 0.75 Post-contrast T1 0.49 0.60 0.25 0.95 Texture features score 0.85 0.82 0.90 0.75 ROC analyses for classification between IIM and AVM patients Abstract Figure

Capturing complex right ventricular wall motion abnormalities in arrhythmogenic right ventricular cardiomyopathy by combining longitudinal and radial myocardial dynamics in feature-tracking MRI

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): INSERM Liliane Bettencourt doctoral grant

Background

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) is ass­­ociated with complex spatial and temporal right ventricular (RV) wall motion abnormalities. While cardiac magnetic resonance (CMR) is the gold-standard imaging technique, its diagnosic performance remains suboptimal and additional CMR biomarkers reflecting ARVC pathophysiology are needed.

Purpose

To evaluate the performance of a CMR feature-tracking (FT)-derived parameter combining both longitudinal and radial RV deformation and motion for the characterization of RV wall motion abnormalities in ARVC.

Methods

Thirty-nine patients with definite or borderline ARVC (median age 45 years, interquartile range 31–51, 56% males) were compared to 20 healthy controls with comparable age, sex and weight distributions. All subjects had 1.5T CMR including short axis and 4-chamber views steady-state free precession acquisitions. A custom FT software adapted to RV wall segmentation and tracking was used to assess RV wall deformation and motion in the 3 space directions resulting in: 1) global longitudinal strain (GLS) estimated on the 4 chamber view from the RV free wall, 2) basal circumferential strain (BCS) and radial motion fraction (BRMF) estimated as an average of short-axis slices comprised in the RV third basal portion. To capture the complex RV motion in ARCV, a longitudinal to radial strain loop (LRSL) was displayed and its area was calculated.

Results

The ARVC group comprised 28 (72%) patients with definite and 11 (28%) with borderline diagnosis . As compared to controls, LVEF and RVEF were significantly lower in ARVC patients (61(interquartile range (IQR) 52-71) vs. 71%(IQR 55-88) , p = 0.03 and 47%(IQR 16-63) vs. 57%(IQR 49-63) , p = 0.02, respectively), LVEF remaining within normal range limits. While there was no significant difference in RV GLS between ARVC patients and controls (median -17.7%(IQR -24–15) vs. -17.5%(IQR -20.1–15.2), p = 0.67) , BCS and BRMF were significantly lower in ARVC patients vs. controls [-7.5%(IQR -12.3–8.4.) vs. -9.8%(IQR -13.8–8.6.), p = 0.004 and -12.2(IQR -14.4–8.7.) vs. -14.9%(IQR -16.6–13.2) p = 0.0007, respectively] . The LRSL area was significantly and markedly lower in ARVC patients vs. controls [70.6 (IQR 16.3-63.1) vs. 144.1 (IQR 110.4-251.3), p = 0.0002] . LRSL area outperformed RVEF, BCS and BRS in separating ARVC from controls (area under receiving operator characteristics curve 0.82 vs. 0.78, 0.73 and 0.78, respectively).

Conclusion

In ARVC, a FT-derived parameter combining longitudinal and radial RV wall deformation and motion provided better discrimination of ARVC patients from controls than conventional FT measurements. Its implementation in clinical practice may bolster CMR performance to characterize ARVC wall motion abnormalities.

Abstract Figure

Wave decomposition applied to LA phasic longitudinal strain evaluated from MRI feature tracking to estimate a true LA booster strain index

Funding Acknowledgements

Type of funding sources: None.

Background. Feature tracking (FT) is an emerging approach for the evaluation of both left atrium (LA) and left ventricular (LV) myocardial strain from the same cine MRI dataset. We hypothesized that the LA active contraction longitudinal strain, is a merge of an intrinsic LA booster contraction with the early diastolic LA emptying, especially when this latter is extended because of a poor LV relaxation (Figure 1, bottom). Such index can be estimated through LA phasic strain wave-decomposition as conventionally done for pressure curves to estimate forward and reflected components.

Purpose. To compare the newly proposed LA intrinsic or "true" booster index (Sla_fit) against the conventional index (Sla) in terms of associations with LV remodeling (LV mass/ LV volume), LV systolic longitudinal strain (LV_GLS), and transmitral LV filling indices in healthy controls and aortic valve stenosis (AVS) patients with preserved LV ejection fraction.

Methods. We studied 55 patients (34 AVS:71 ± 11years, 21 controls:66 ± 9years) who had an MRI exam with cine SSFP and phase contrast (PC) images. FT was applied to cine images to extract LV and LA phasic longitudinal strain and strain rates. Transmitral flow early (E, cm/s) and late (A, cm/s) filling peak velocities were calculated from PC data. To estimate intrinsic LA booster index, the LA longitudinal strain curve corresponding to the reservoir and conduit phases was fitted using two half cosine waves, to account for an eventual LA filling to LA early emptying asymmetry, while fitting the LA contraction with a full cosine wave (Figure 1). The peak of this latter wave was defined as the intrinsic LA booster strain index (Sla_fit), while the second peak of the measured LA strain was defined as the conventional LA booster strain (Sla).

Results. While conventional Sla was significantly higher than intrinsic LA booster Sla_fit in AVS patients (13.55 ± 4.26 vs. 8.09 ± 6.07, p = 0.0002), it was nearly equivalent in controls (14.34 ± 4.30 vs.13.43 ± 4.23, p =.49). But the newly proposed LA booster strain index was significantly related to LV_GLS (r=-48,p=.0004); to LV remodeling (r=-.44,p = 0.0012) as well as to transmitral flow A wave ( r=-.49, p=.0005) none of these associations were significant when considering conventional LA booster strain. Interestingly our intrinsic LA booster index Sla_fit was significantly associated with LV longitudinal strain in both controls (r=-.55,p = 0.009) and asymptomatic AVS (N = 10) (r=-.77,p = 0.0081) but not in symptomatic AVS (N = 24) (p&gt;.70). This may reveal a maintained LA-LV coupling in the asymptomatic phase and an uncoupling in the symptomatic phase, caused by elevated LV filling pressures.

Conclusions. A promising index for the quantitative evaluation of intrinsic LA booster function was proposed and its consistency was demonstrated through its significant associations with LV remodeling, LV longitudinal strain and transmitral late filling peak.

Abstract Figure.

Quantitative magnetic resonance imaging measures of three-dimensional aortic morphology in healthy aging and hypertension

Automated segmentation of three-dimensional (3D) aortic magnetic resonance imaging (MRI) renders a possible retrospective selection of any location to perform quantification of aortic caliber perpendicular to its centerline and provides regional and global 3D biomarkers such as length, diameter, or volume. However, normative age-related values of such measures are still lacking. The aim of this study was to provide normal values for 3D aortic morphological measures and investigate their changes in aging and hypertension. This was a retrospective study, in which 119 healthy controls (HC: 48 ± 14 years, 61 men) and 82 hypertensive patients (HT: 60 ± 14 years, 43 men) were enrolled. 1.5 and 3 T/3D steady state free precession or spoiled gradient echo were used. Automated 3D aortic segmentation provided aortic length, diameter, volume for the ascending (AAo), and descending aorta (DAo), along with cross-sectional diameters at three aortic landmarks. Age, sex, body surface area (BSA), smoking, and blood pressures were recorded. Both groups were divided into two subgroups (≤50 years, >50 years). Statistical tests performed were linear regression for age-related normal values and confidence intervals, Wilcoxon rank sum test for differences between groups (HC or HT), and multivariate analysis to identify main determinants of aortic morphological changes. In HC, linear regression revealed an increase in the AAo (respectively DAo) length by 2.84 mm (7.78 mm), maximal diameter by 1.36 mm (1.29 mm), and volume by 4.28 ml (8.71 ml) per decade. AAo morphological measures were higher in HT patients than in HC both ≤50 years but did not reach statistical significance (length: +2 mm, p = 0.531; diameter: +1.4 mm, p = 0.2936; volume:+6.8 ml, p = 0.1857). However, length (+6 mm, p = 0.003), maximal diameter (+4 mm, p < 0.001) and volume (+12 ml, p < 0.001) were significantly higher in HT patients than in HC, both >50 years. In a multivariate analysis, age, sex, and BSA were the major determinants of aortic morphology, irrespective of the presence of hypertension. Global and segmental aortic length, volume, and diameters at specific landmarks were automatically measured from 3D MRI to serve as normative measures of 3D aortic morphology. Such indices increased significantly with age and hypertension among the elderly subjects. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 3.

In vitro evaluation of polymeric nanoparticles with a fluorine core for drug delivery triggered by focused ultrasound

Polymeric nanoparticles are being intensively investigated as drug carriers. Their efficiency could be enhanced if the drug release can be triggered using an external stimulus such as ultrasound. This approach is possible using current commercial apparatus that combine focused ultrasound with MRI to perform ultrasonic surgery. In this approach, nanoparticles made of a perfluoro-octyl bromide core and a thick polymeric (PLGA-PEG) shell may represent suitable drug carriers. Indeed, their perfluorocarbon core are detectable by ¹⁹F MRI, while their polymeric shell can encapsulate drugs. However, their applicability in ultrasound-triggered drug delivery remains to be proven. To do so, we used Nile red as a model drug and we measured its release from the polymeric shell by spectrofluorometry. In the absence of ultrasound, only a small amount of Nile red release was measured (<5%). Insonations were performed in a controlled environment using a 1.1 MHz transducer emitting tone bursts for a few minutes, whereas a focused broadband hydrophone was used to detect the occurrence of cavitation. In the absence of detectable inertial cavitation, less than 5% of Nile red was released. In the presence of detectable inertial cavitation, Nile red release was ranging from 10% to 100%, depending of the duty cycle, acoustic pressure, and tank temperature (25 or 37 °C). Highest releases were obtained only for duty cycles of 25% at 37 °C and 50% at 25 °C and for a peak-to-peak acoustic pressure above 12.7 MPa. Electron microscopy and light scattering measurements showed a slight modification in the nanoparticle morphology only at high release contents. The occurrence of strong inertial cavitation is thus a prerequisite to induce drug release for these nanoparticles. Since strong inertial cavitation can lead to many unwanted biological effects, these nanoparticles may not be suitable for a therapeutic application using ultrasound-triggered drug delivery.

Are Gadolinium-Enhanced MR Sequences Needed in Simultaneous 18F-FDG-PET/MRI for Tumor Delineation in Head and Neck Cancer?

BACKGROUND AND PURPOSE

PET/MRI with ¹⁸F-FDG has demonstrated the advantages of simultaneous PET and MR imaging in head and neck cancer imaging, MRI allowing excellent soft-tissue contrast, while PET provides metabolic information. The aim of this study was to evaluate the added value of gadolinium contrast-enhanced sequences in the tumor delineation of head and neck cancers on ¹⁸F-FDG-PET/MR imaging.

MATERIALS AND METHODS

Consecutive patients who underwent simultaneous head and neck ¹⁸F-FDG-PET/MR imaging staging or restaging followed by surgery were retrospectively included. Local tumor invasion and lymph node extension were assessed in 45 head and neck anatomic regions using ¹⁸F-FDG-PET/MR imaging by 2 rater groups (each one including a radiologist and a nuclear medicine physician). Two reading sessions were performed, one without contrast-enhanced sequences (using only T1WI, T2WI, and PET images) and a second with additional T1WI postcontrast sequences. The results were compared with the detailed histopathologic analysis, used as reference standard. The κ concordance coefficient between the reading sessions and sensitivity and specificity for each region were calculated.

RESULTS

Thirty patients were included. There was excellent agreement between the contrast-free and postgadolinium reading sessions in delineating precise tumor extension in the 45 anatomic regions studied (Cohen κ = 0.96, 95% CI = [0.94-0.97], P < .001). The diagnostic accuracy did not differ between contrast-free and postgadolinium reading sessions, being 0.97 for both groups and both reading sessions. For the 2 rater groups, there was good sensitivity for both contrast-free (0.83 and 0.85) and postgadolinium reading sessions (0.88 and 0.90, respectively). Moreover, there was excellent specificity (0.98) for both groups and reading sessions.

CONCLUSIONS

Gadolinium chelate contrast administration showed no added value for accurate characterization of head and neck primary tumor extension and could possibly be avoided in the PET/MR imaging head and neck workflow.

Use of FDG-PET/CT for systemic assessment of suspected primary central nervous system lymphoma: a LOC study

INTRODUCTION

Primary Central Nervous System Lymphoma (PCNSL) is a rare disease with different therapeutic implications than systemic lymphoma. In this study, we evaluated whole-body ¹⁸FDG-PET/CT for pre-chemotherapy imaging of suspected PCNSL.

METHODS

One hundred and thirty consecutive immunocompetent patients were retrospectively included. The results of initial ¹⁸FDG-PET/CT, contrast-enhanced CT (CeCT) and bone marrow biopsy (BMB) when available were compared to a gold standard based on pathological diagnosis or follow-up.

RESULTS

CNS lesion pathology showed large B-cell lymphoma in 95% of patients, including 11 patients with primary vitro-retinal lymphoma. Ten patients (8%) where ultimately diagnosed with systemic lymphoma involvement, including five pathologically confirmed cases, all of which were detected by ¹⁸FDG-PET/CT. ¹⁸FDG-PET/CT showed incidental systemic findings unrelated to lymphoma in 14% of patients. An SUVmax threshold of nine enabled good discrimination between systemic lymphoma and other lesions (sensitivity 92% and specificity 89%). CeCT and BMB performed in 108 and 77 patients respectively revealed systemic lesions in only three patients.

CONCLUSION

¹⁸FDG-PET/CT detected concomitant occult systemic involvement in a non-negligible proportion of suspected PCNSL cases (8%). In this setting its sensitivity is higher than that of CeCT. All of our patients ultimately diagnosed with concomitant systemic involvement had positive ¹⁸FDG-PET/CT. We believe it constitutes a safe one-stop shop evaluation for the systemic pre-treatment imaging of suspected PCNSL.

Comparison of different methods for the estimation of aortic pulse wave velocity from 4D flow cardiovascular magnetic resonance

BACKGROUND

Arterial pulse wave velocity (PWV) is associated with increased mortality in aging and disease. Several studies have shown the accuracy of applanation tonometry carotid-femoral PWV (Cf-PWV) and the relevance of evaluating central aorta stiffness using 2D cardiovascular magnetic resonance (CMR) to estimate PWV, and aortic distensibility-derived PWV through the theoretical Bramwell-Hill model (BH-PWV). Our aim was to compare various methods of aortic PWV (aoPWV) estimation from 4D flow CMR, in terms of associations with age, Cf-PWV, BH-PWV and left ventricular (LV) mass-to-volume ratio while evaluating inter-observer reproducibility and robustness to temporal resolution.

METHODS

We studied 47 healthy subjects (49.5 ± 18 years) who underwent Cf-PWV and CMR including aortic 4D flow CMR as well as 2D cine SSFP for BH-PWV and LV mass-to-volume ratio estimation. The aorta was semi-automatically segmented from 4D flow data, and mean velocity waveforms were estimated in 25 planes perpendicular to the aortic centerline. 4D flow CMR aoPWV was calculated: using velocity curves at two locations, namely ascending aorta (AAo) and distal descending aorta (DAo) aorta (S1, 2D-like strategy), or using all velocity curves along the entire aortic centreline (3D-like strategies) with iterative transit time (TT) estimates (S2) or a plane fitting of velocity curves systolic upslope (S3). For S1 and S2, TT was calculated using three approaches: cross-correlation (TTc), wavelets (TTw) and Fourier transforms (TTf). Intra-class correlation coefficients (ICC) and Bland-Altman biases (BA) were used to evaluate inter-observer reproducibility and effect of lower temporal resolution.

RESULTS

4D flow CMR aoPWV estimates were significantly (p < 0.05) correlated to the CMR-independent Cf-PWV, BH-PWV, age and LV mass-to-volume ratio, with the strongest correlations for the 3D-like strategy using wavelets TT (S2-TTw) (R = 0.62, 0.65, 0.77 and 0.52, respectively, all p < 0.001). S2-TTw was also highly reproducible (ICC = 0.99, BA = 0.09 m/s) and robust to lower temporal resolution (ICC = 0.97, BA = 0.15 m/s).

CONCLUSIONS

Reproducible 4D flow CMR aoPWV estimates can be obtained using full 3D aortic coverage. Such 4D flow CMR stiffness measures were significantly associated with Cf-PWV, BH-PWV, age and LV mass-to-volume ratio, with a slight superiority of the 3D strategy using wavelets transit time (S2-TTw).

Contribution of endobronchial ultrasound elastography to the characterization of mediastinal lymphadenopathy: A single-center, prospective, observational study

BACKGROUND

Endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) is a reliable technique providing high diagnostic yield in mediastinal lymphadenopathy. However, mediastinoscopy is sometimes necessary to eliminate false-negative results. Elastography is a recent technique that can be combined with EBUS to evaluate the elasticity and consequently the nature of a tissue. The primary objective was to evaluate the diagnostic performance of EBUS-TBNA combined with elastography for the assessment of mediastinal lymph nodes.

METHODS

Single-center, prospective study in patients with mediastinal lymphadenopathy. EBUS-TBNA combined with elastography was performed in each patient. Several elastographic parameters were studied: colorimetric score, average elasticity, elasticity ratio, percentage of hard areas. The final diagnosis was that obtained by TBNA cytology, histology of a surgical biopsy, when performed, or follow-up CT and PET-CT at 6 months.

RESULTS

Overall, 110 lymph nodes were examined in 87 patients: 44 were malignant according to TBNA. These nodes had significantly higher elasticity ratio, percentage of hard areas and colorimetric score and significantly lower average elasticity compared to benign nodes (P<0.001). With a negative predictive value of 100%, the cut-offs defined by receiver operating characteristic curves were 1.4 for elasticity ratio, 84.8 for average elasticity, 32.6 for percentage of hard areas and 3 for colorimetric score. No adverse events were observed.

CONCLUSION

Endobronchial ultrasound elastography is a non-invasive technique that can contribute to prediction of the nature of lymph nodes by distinguishing malignant from benign nodes. Although EBUS cannot replace histological examination, elastography can provide reliable complementary information when combined with EBUS.

Closed-Loop Control of the Centre of Pressure in Post-Stroke Patients With Balance Impairments

When a lightly touched surface is moved according to a closed-loop control law, it has been shown in young adults that the centre of pressure (CoP) can be displaced in a controllable way without the conscious cooperation of participants. In this closed-loop paradigm, the surface velocity was continuously adjusted according to the CoP position. Since the closed-loop control of the CoP does not require the participant's voluntary cooperation, it could be of interest for the development of innovative biofeedback devices in balance rehabilitation. Before anticipating the implementation of this closed-loop control paradigm with patients, it is necessary to establish its effects on people suffering from balance impairments. The aim of this paper was to assess the effects of this CoP closed-loop control in post-stroke (PS) patients and aged-matched healthy controls. Efficacy of the closed-loop control for driving the patients' CoP was assessed using the saturation time and two scores computing the error between the predefined and the current CoP trajectories. 68% and 83% of the trials were considered as successful in patients and controls, respectively. The global tracking error of the closed-loop score was similar between the two groups. However, when examining the real CoP displacement from the starting position to the desired one, PS patients responded to the closed-loop control to a lesser extent than controls. These results, obtained in the same conditions for healthy and PS individuals could be improved by tuning the closed-loop parameters according to individual characteristics. This paper paves the road towards the development of involuntary/automatic biofeedback techniques in more ecological conditions.

Furosemide Unmasks Inhibitory Dysfunction after Spinal Cord Injury in Humans: Implications for Spasticity

Spasticity after spinal cord injury has considerable quality of life implications, impacts on rehabilitation efforts and necessitates long-term multi-disciplinary pharmacological and non-pharmacological management. The potassium chloride co-transporter (KCC2) plays a central role in intracellular chloride homeostasis and the inhibitory function of mature neurons. Animal studies consistently have demonstrated a downregulation of KCC2 activity after spinal cord transection, causing a shift from the inhibitory action of gamma-aminobutyric acid and glycine to an excitatory effect. Furosemide, a recognized KCC2 antagonist in animals, blocks the formation of inhibitory post-synaptic potentials in spinal motoneurons without affecting excitatory post-synaptic potentials. Based on observations in animals studies, we hypothesized that furosemide may be used to unmask KCC2 downregulation after spinal cord injury in humans, which contributes to reflex hyperexcitability. We have shown previously that furosemide reduces both pre-synaptic and post-synaptic inhibition in healthy subjects without altering monosynaptic excitatory transmission. These findings provide evidence that furosemide may be used in humans to evaluate inhibitory synapses in the spinal cord. In this present study, we show that furosemide fails to modulate both pre- and post-synaptic inhibitions relayed to soleus spinal motor neurons in persons with spinal cord injury. The lack of furosemide effect after spinal cord injury suggests KCC2 dysfunction in humans, resulting in reduced inhibitory synaptic transmission in spinal neurons. Our findings suggest that KCC2 dysfunction may be an important etiological factor in hyperreflexia after spinal cord injury. These observations may pave the way to novel therapeutic strategies against spasticity centered on chloride homeostasis.

Abnormal cortical brain integration of somatosensory afferents in ALS

OBJECTIVES

Infraclinical sensory alterations have been reported at early stages of amyotrophic lateral sclerosis (ALS). While previous studies mainly focused on early somatosensory evoked potentials (SEPs), late SEPs, which reflect on cortical pathways involved in cognitive-motor functions, are relatively underinvestigated. Early and late SEPs were compared to assess their alterations in ALS.

METHODS

Median and ulnar nerves were electrically stimulated at the wrist, at 9 times the perceptual threshold, in 21 ALS patients without clinical evidence of sensory deficits, and 21 age- and gender-matched controls. SEPs were recorded at the Erb point using surface electrodes and using a needle inserted in the scalp, in front of the primary somatosensory area (with reference electrode on the ear lobe).

RESULTS

Compared to controls, ALS patients showed comparable peripheral (N9) and early cortical component (N20, P25, N30) reductions, while the late cortical components (N60, P100) were more depressed than the early ones.

CONCLUSIONS

The peripheral sensory alteration likely contributed to late SEP depression to a lesser extent than that of early SEPs.

SIGNIFICANCE

Late SEPs may provide new insights on abnormal cortical excitability affecting brain areas involved in cognitive-motor functions.

Patient emergency assessment following deliberate self-poisoning with benzodiazepines: Can cognitive markers predict recall of the psychiatric interview? A pilot study

STUDY HYPOTHESIS

In cases of deliberate self-poisoning (DSP), patients often ingest benzodiazepines (BZDs), known to alter memory. Experts recommend recovery of the patient's cognitive capacity before psychiatric assessment. Unfortunately, there is no validated tool in common practice to assess whether sufficient cognitive recovery has occurred after DSP with BZDs to ensure patient memory of the assessment.

OBJECTIVE

The aim of the study was to identify cognitive functions and markers which predict preserved memory of the mental health care plan proposed at the emergency department after DSP.

METHODS

We recruited patients admitted for DSP with BZDs and control patients. At the time of the psychiatric assessment, we performed cognitive tests and we studied the relationship between these tests and the scores of a memory test performed 24 h after.

RESULTS

In comparison with the control group, we found memory impairment in the BZD group. We found significant impairment on the Trail Making Test A (TMT A) in the BZD group in comparison with the control group, while TMT A and Wechsler Adult Intelligence Scale (WAIS) Coding test scores were significantly correlated with memory scores.

CONCLUSIONS

Attentional functions tested by WAIS Coding test and TMT A were correlated with memory score. It could be profitable to assess it in clinical practice prior to a psychiatric interview.

Functional Connectivity's Degenerate View of Brain Computation

Brain computation relies on effective interactions between ensembles of neurons. In neuroimaging, measures of functional connectivity (FC) aim at statistically quantifying such interactions, often to study normal or pathological cognition. Their capacity to reflect a meaningful variety of patterns as expected from neural computation in relation to cognitive processes remains debated. The relative weights of time-varying local neurophysiological dynamics versus static structural connectivity (SC) in the generation of FC as measured remains unsettled. Empirical evidence features mixed results: from little to significant FC variability and correlation with cognitive functions, within and between participants. We used a unified approach combining multivariate analysis, bootstrap and computational modeling to characterize the potential variety of patterns of FC and SC both qualitatively and quantitatively. Empirical data and simulations from generative models with different dynamical behaviors demonstrated, largely irrespective of FC metrics, that a linear subspace with dimension one or two could explain much of the variability across patterns of FC. On the contrary, the variability across BOLD time-courses could not be reduced to such a small subspace. FC appeared to strongly reflect SC and to be partly governed by a Gaussian process. The main differences between simulated and empirical data related to limitations of DWI-based SC estimation (and SC itself could then be estimated from FC). Above and beyond the limited dynamical range of the BOLD signal itself, measures of FC may offer a degenerate representation of brain interactions, with limited access to the underlying complexity. They feature an invariant common core, reflecting the channel capacity of the network as conditioned by SC, with a limited, though perhaps meaningful residual variability.

Left atrial aging: a cardiac magnetic resonance feature-tracking study

Importance of left atrial (LA) phasic function evaluation is increasingly recognized for its incremental value in terms of prognosis and risk stratification. LA phasic deformation in the pathway of normal aging has been characterized using echocardiographic speckle tracking. However, no data are available regarding age-related variations using feature-racking (FT) techniques from standard cine magnetic resonance imaging (MRI). We studied 94 healthy adults (41 ± 14 yr, 47 women), who underwent MRI and Doppler echocardiography on the same day for left ventricular (LV) diastolic function evaluation. From cine MRI, longitudinal strain and strain rate, radial motion fraction, and radial relative velocity, respectively, corresponding to the reservoir, conduit, and LA contraction phases, were measured using dedicated FT software. Longitudinal strain and radial motion fraction decreased gradually and significantly with aging for both reservoir (r > 0.31, P < 0.003) and conduit (r > 0.54, P < 0.001) phases, whereas they remained unchanged during the LA contraction phase. Subsequently, the LA contraction-to-reservoir ratio increased significantly with age (r > 0.44, P < 0.001). Longitudinal strain rate and radial relative velocity significantly decreased with age (reservoir: r = 0.39, P < 0.001, conduit: r > 0.54, P < 0.001), and these associations tended to be stronger in women than in men. Finally, associations of LA functional indexes with age were stronger in individuals with lower transmitral early-to-atrial maximal velocity ratio and mitral annulus maximal longitudinal velocity, as well as higher transmitral early maximal-to-mitral annulus maximal longitudinal velocity ratio, highlighting the LV-LA interplay. Age-related changes in LA phasic function indexes were quantified by cine MRI images using a FT technique and were significantly related to age and LV diastolic function.

Predicting functional connectivity from structural connectivity via computational models using MRI: an extensive comparison study

The relationship between structural connectivity (SC) and functional connectivity (FC) in the human brain can be studied using magnetic resonance imaging (MRI). However many of the underlying physiological mechanisms and parameters cannot be directly observed with MRI. This limitation has motivated the recent use of various computational models meant to bridge the gap. However their absolute and relative explanatory power and the properties that actually drive that power remain insufficiently characterized. We performed an extensive comparison of seven mainstream computational models predicting FC from SC. We investigated the extent to which simulated FC could predict empirical FC. We also applied graph theory to the entire set of simulated and empirical FCs in order to further characterize the relationships between the models and the MRI data. The comparison was performed at three different spatial scales. We found that (i) there were significant effects of scale and model on predictive power; (ii) among all models, the simplest model, the simultaneous autoregressive (SAR) model, was found to consistently perform better than the other models; (iii) the SAR also appeared more 'central' from a graph theory perspective; and (iv) empirical FC only appeared weakly correlated with simulated FCs, and was featured as 'peripheral' in the graph analysis. We conclude that the substantial differences existing between these computational models have little impact on their predictive power for FC and that their capacity to predict FC from SC appears to be both moderate and essentially underlined by a simple core linear process embodied by the SAR model.

Geometry is a major determinant of flow reversal in proximal aorta

The aim of this study is to quantify aortic backward flow (BF) using phase-contrast cardiovascular magnetic resonance (PC-CMR) and to study its associations with age, indexes of arterial stiffness, and geometry. Although PC-CMR blood flow studies showed a simultaneous presence of BF and forward flow (FF) in the ascending aorta (AA), the relationship between aortic flows and aging as well as arterial stiffness and geometry in healthy volunteers has never been reported. We studied 96 healthy subjects [47 women, 39 ± 15 yr old (19–79 yr)]. Aortic stiffness [arch pulse wave velocity (PWVAO), AA distensibility], geometry (AA diameter and arch length), and parameters related to AA BF and FF (volumes, peaks, and onset times) were estimated from CMR. Applanation tonometry carotid-femoral pulse-wave velocity (PWVCF), carotid augmentation index, and time to return of the reflected pressure wave were assessed. Whereas FF parameters remained unchanged, BF onset time shortened significantly ( R2 = 0.18, P < 0.0001) and BF volume and BF-to-FF peaks ratio increased significantly ( R2 = 0.38 and R2 = 0.44, respectively, P < 0.0001) with aging. These two latter BF indexes were also related to stiffness indexes (PWVCF, R2 > 0.30; PWVAO, R2 > 0.24; and distensibility, R2 > 0.20, P < 0.001), augmentation index ( R2 > 0.20, P < 0.001), and aortic geometry (AA diameter, R2 > 0.58; and arch length, R2 > 0.31, P < 0.001). In multivariate analysis, aortic diameter was the strongest independent correlate of BF beyond age effect. In conclusion, AA BF estimated using PC-CMR increased significantly in terms of magnitude and volume and appeared earlier with aging and was mostly determined by aortic geometry. Thus BF indexes could be relevant markers of subclinical arterial wall alterations.

MR and applanation tonometry derived aortic impedance: association with aging and left ventricular remodeling

PURPOSE

We sought to noninvasively estimate aortic impedance indices from MR and tonometric data.

MATERIALS AND METHODS

MR aortic velocity-encoded and carotid applanation tonometry pressure data of 70 healthy subjects (19-79 years) were used to calculate the following indices from impedance spectrum: (i) characteristic impedance (Zc) reflecting pulsatile component of left ventricular (LV) afterload, (ii) frequency of the minimal impedance magnitude related to arterial compliance (FMIN ), (iii) total peripheral resistance (TPR) related to steady LV load, (iv) impedance oscillatory index (ZINDEX ) related to proximal reflections, and (v) reflection magnitude (RM). Associations with age and LV remodeling (LV mass/end-diastolic volume) were investigated using multivariate analysis.

RESULTS

All indices except Zc were associated with age independent of subjects characteristics and systolic blood pressures. They were all significantly associated with the well-established carotid-femoral pulse wave velocity (r ≥ 0.29; P < 0.01). However, such associations were not independent of age. Pulsatile index Zc was independently associated with carotid pulse pressure (r = 0.53, P < 0.001). Moreover, conversely to conventional stiffness indices, Zc and TPR were independently associated with LV remodeling (r = 0.30, r = 0.43, respectively, P < 0.01).

CONCLUSION

We estimated aortic impedance from velocity-encoded MR and tonometry data resulting in reliable impedance and reflection indices as confirmed by their significant and independent associations with age and LV remodeling.

Influence of the AGTR1 A1166C genotype on the progression of arterial stiffness: A 16-year longitudinal study

BACKGROUND

We examined the influence of the AGTR1 A1166C genotype on the 16-year evolution of pulse wave velocity (PWV) in a middle-aged population. In a cross-sectional study, we reported that the presence of the AGTR1 1166C allele was associated with higher aortic stiffness compared with the AGTR1 1166AA genotype.

METHODS

The study was conducted in 259 subjects who underwent 3 health check-ups over 16 years at the Centre IPC-Paris: an initial visit in 1992-1993, an intermediate visit in 1998-1999, and a final visit in 2007-2008. Aortic stiffness was assessed during the 3 visits by measuring carotid-femoral PWV. AGTR1 A1166C polymorphism was assayed by allele-specific oligonucleotide hybridization.

RESULTS

AGTR1 1166C allele carriers (AC + CC genotypes) had a 35% more pronounced increase in PWV over this 16-year period when compared with the AGTR1 1166AA subjects (3.01 ± 0.32 vs. 1.92 ± 0.23 m/s; P < 0.001). This increase remained significant after adjustment for age, sex, initial PWV values, and changes in blood pressure (+37%; P < 0.05). The genotype-related differences in PWV were only observed at the last visit (i.e., later in life, after the age of 55 years). The effects of this genotype on PWV were not related to the presence of antihypertensive treatment.

CONCLUSIONS

This is the first long-term longitudinal study indicating that AT1 1166C carriers are at increased risk of pronounced arterial stiffening during aging especially after the age of 55.

Assessment of routine malaria diagnosis in the Venezuelan Amazon

The quality of routine malaria diagnosis is a crucial topic of malaria control. The aim of this assessment was to monitor and evaluate the quality of routine malaria diagnosis in Amazonas (Venezuela) and to improve the quality control system. The traditional non-blinded quality control system was found to be overburdened with diagnostic samples. A modified sampling system with fewer samples to be tested was proposed. Expert microscopists blindly double-checked 1000 slides and 550 rapid diagnostic tests (RDT) (OptiMAL-IT) from health posts (HP). For Plasmodium vivax, HP microscopy and OptiMAL-IT showed sensitivies of 86% and 63%, respectively. For P. falciparum, HP microscopy and OptiMAL-IT showed sensitivities of 68% and 89%, respectively. Both methods lost accuracy when fewer parasites occurred in the sample. HP microscopists from different municipalities displayed significant differences in diagnostic quality. Overall, quality of routine malaria diagnosis in the Venezuelan Amazon is good but not optimal. The change from the traditional non-blinded quality control system to blinded cross-checking of a minimal selection of samples is - comparatively - a low cost intervention with possibly high impact on the quality of routine malaria diagnosis. The introduction of RDTs should be discussed carefully in order not to displace an existing network of HP microscopists.

Differential automatic diagnosis between Alzheimer's disease and frontotemporal dementia based on perfusion SPECT images

OBJECTIVE

Alzheimer's disease (AD) and frontotemporal dementia (FTD) are among the most frequent neurodegenerative cognitive disorders, but their differential diagnosis is difficult. The aim of this study was to evaluate an automatic method returning the probability that a patient suffers from AD or FTD from the analysis of brain perfusion single photon emission computed tomography images.

METHODS AND MATERIALS

A set of 116 descriptors corresponding to the average activity in regions of interest was calculated from the images of 82 AD and 91 FTD patients. A set of linear (logistic regression and linear discriminant analysis) and non-linear (support vector machines, k-nearest neighbours, multilayer perceptron and kernel logistic PLS) classification methods was subsequently used to ascertain diagnoses. Validation was carried out by means of the leave-one-out protocol. Diagnoses by the classifier and by four physicians (visual assessment) were compared. Since images were acquired in different hospitals, the impact of the medical centre on the diagnosis of both the classifier and the physicians was investigated.

RESULTS

Best results were obtained with support vector machine and partial least squares regression coupled with k-nearest neighbours methods (PLS+K-NN), with an overall accuracy of 88%. PLS+K-NN was however considered as the best method since performances obtained with leave-one-out cross-validation were closer to whole-database learning. The performances of the classifier were higher than those of experts (accuracy ranged from 65 to 72%). Physicians found it more difficult to diagnose the images from centres other than their own, and it affected their performances.

CONCLUSIONS

The performances obtained by the classifier for the differential diagnosis of AD and FTD were found convincing. It could help physicians in daily practice, particularly when visual assessment is inconclusive, or when dealing with multicentre data.

Influence of facial skin attributes on the perceived age of Caucasian women

BACKGROUND AND OBJECTIVE

The facial appearance of a person does not always reflect the chronological age; some people look younger or older than they really are. Many studies have described the changes in skin properties (colour, wrinkles, sagging, micro relief, etc.) with age, but few of them have analysed their influence on the perceived age. The primary objective of this study was to assess the contribution of individual skin attributes of the face on the perceived age of Caucasian women. Secondary objectives were to assess the influence of age and gender of graders with regard to the age perception.

SUBJECTS AND METHOD

A random sample of 173 subjects of 20 to 74 years of age was taken from a database of more than 5000 healthy Caucasian women. A trained grader performed visual assessment of facial skin attributes (using a visual analogue scale), and a front face photograph was taken from each subject. Photographs were shown to 48 graders (20 men and 28 women, aged 22-64 years) who were asked to estimate the age of the subjects. Graders were classified as young (less than 35 years), middle age (35-50 years) and seniors (older than 50 years). Partial Least Square regression models were built to predict the chronological and the perceived age from the measured facial individual attributes. The contribution of each attribute within the regression model enabled to measure the relevance of this attribute with regards to age prediction.

RESULTS

The eye area and the skin colour uniformity were the main attributes related to perceived age. For age prediction, older graders' estimations were more driven by lips border definition shape and eyes opening, whereas younger graders' (older than 50 years) estimations were more driven by dark circles, nasolabial fold and brown spots. There were statistically significant differences in graders' age perception between gender and among age ranges. Our findings suggest that female graders are more accurate than male, and younger graders (under 35 years) are more accurate than older (over 50 years) to predict Caucasian women age from facial photographs.

CONCLUSIONS

Different skin attributes influence the estimation of age. These attributes have a different weight in the evaluation of the perceived age, depending on the age and of the observer. The most important attributes to estimate age are eyes, lips and skin colour uniformity.

DD-HDS: A method for visualization and exploration of high-dimensional data

Mapping high-dimensional data in a low-dimensional space, for example, for visualization, is a problem of increasingly major concern in data analysis. This paper presents data-driven high-dimensional scaling (DD-HDS), a nonlinear mapping method that follows the line of multidimensional scaling (MDS) approach, based on the preservation of distances between pairs of data. It improves the performance of existing competitors with respect to the representation of high-dimensional data, in two ways. It introduces (1) a specific weighting of distances between data taking into account the concentration of measure phenomenon and (2) a symmetric handling of short distances in the original and output spaces, avoiding false neighbor representations while still allowing some necessary tears in the original distribution. More precisely, the weighting is set according to the effective distribution of distances in the data set, with the exception of a single user-defined parameter setting the tradeoff between local neighborhood preservation and global mapping. The optimization of the stress criterion designed for the mapping is realized by "force-directed placement" (FDP). The mappings of low- and high-dimensional data sets are presented as illustrations of the features and advantages of the proposed algorithm. The weighting function specific to high-dimensional data and the symmetric handling of short distances can be easily incorporated in most distance preservation-based nonlinear dimensionality reduction methods.