The impact of signal-to-noise ratio, diffusion-weighted directions and image resolution in cardiac diffusion tensor imaging - insights from the ex-vivo rat heart

Background: Cardiac diffusion tensor imaging (DTI) is limited by scan time and signal-to-noise (SNR) restrictions. This invariably leads to a trade-off between the number of averages, diffusion-weighted directions (ND), and image resolution. Systematic evaluation of these parameters is therefore important for adoption of cardiac DTI in clinical routine where time is a key constraint. Methods: High quality reference DTI data were acquired in five ex-vivo rat hearts. We then retrospectively set 2 ≤ SNR ≤ 97, 7 ≤ ND ≤ 61, varied the voxel volume by up to 192-fold and investigated the impact on the accuracy and precision of commonly derived parameters. Results: For maximal scan efficiency, the accuracy and precision of the mean diffusivity is optimised when SNR is maximised at the expense of ND. With typical parameter settings used clinically, we estimate that fractional anisotropy may be overestimated by up to 13% with an uncertainty of ±30%, while the precision of the sheetlet angles may be as poor as ±31°. Although the helix angle has better precision of ±14°, the transmural range of helix angles may be under-estimated by up to 30° in apical and basal slices, due to partial volume and tapering myocardial geometry. Conclusions: These findings inform a baseline of understanding upon which further issues inherent to in-vivo cardiac DTI, such as motion, strain and perfusion, can be considered. Furthermore, the reported bias and reproducibility provides a context in which to assess cardiac DTI biomarkers

Comparison of diffusion tensor imaging by cardiovascular magnetic resonance and gadolinium enhanced 3D image intensity approaches to investigation of structural anisotropy in explanted rat hearts

Background: Cardiovascular magnetic resonance (CMR) can through the two methods 3D FLASH and diffusion tensor imaging (DTI) give complementary information on the local orientations of cardiomyocytes and their laminar arrays. Methods: Eight explanted rat hearts were perfused with Gd-DTPA contrast agent and fixative and imaged in a 9.4T magnet by two types of acquisition: 3D fast low angle shot (FLASH) imaging, voxels 50 × 50 × 50 μm, and 3D spin echo DTI with monopolar diffusion gradients of 3.6 ms duration at 11.5 ms separation, voxels 200 × 200 × 200 μm. The sensitivity of each approach to imaging parameters was explored. Results:The FLASH data showed laminar alignments of voxels with high signal, in keeping with the presumed predominance of contrast in the interstices between sheetlets. It was analysed, using structure-tensor (ST) analysis, to determine the most (v 1 ST ), intermediate (v 2 ST ) and least (v 3 ST ) extended orthogonal directions of signal continuity. The DTI data was analysed to determine the most (e 1 DTI ), intermediate (e 2 DTI ) and least (e 3 DTI ) orthogonal eigenvectors of extent of diffusion. The correspondence between the FLASH and DTI methods was measured and appraised. The most extended direction of FLASH signal (v 1 ST ) agreed well with that of diffusion (e 1 DTI ) throughout the left ventricle (representative discrepancy in the septum of 13.3 ± 6.7°: median ± absolute deviation) and both were in keeping with the expected local orientations of the long-axis of cardiomyocytes. However, the orientation of the least directions of FLASH signal continuity (v 3 ST ) and diffusion (e 3 ST ) showed greater discrepancies of up to 27.9 ± 17.4°. Both FLASH (v 3 ST ) and DTI (e 3 DTI ) where compared to directly measured laminar arrays in the FLASH images. For FLASH the discrepancy between the structure-tensor calculated v 3 ST and the directly measured FLASH laminar array normal was of 9 ± 7° for the lateral wall and 7 ± 9° for the septum (median ± inter quartile range), and for DTI the discrepancy between the calculated v 3 DTI and the directly measured FLASH laminar array normal was 22 ± 14° and 61 ± 53.4°. DTI was relatively insensitive to the number of diffusion directions and to time up to 72 hours post fixation, but was moderately affected by b-value (which was scaled by modifying diffusion gradient pulse strength with fixed gradient pulse separation). Optimal DTI parameters were b = 1000 mm/s2 and 12 diffusion directions. FLASH acquisitions were relatively insensitive to the image processing parameters explored. Conclusions: We show that ST analysis of FLASH is a useful and accurate tool in the measurement of cardiac microstructure. While both FLASH and the DTI approaches appear promising for mapping of the alignments of myocytes throughout myocardium, marked discrepancies between the cross myocyte anisotropies deduced from each method call for consideration of their respective limitations

Physical activity and risk of Metabolic Syndrome in an urban Mexican cohort

Abstract Background In the Mexican population metabolic syndrome (MS) is highly prevalent. It is well documented that regular physical activity (PA) prevents coronary diseases, type 2 diabetes and MS. Most studies of PA have focused on moderate-vigorous leisure-time activity, because it involves higher energy expenditures, increase physical fitness, and decrease the risk of MS. However, for most people it is difficult to get a significant amount of PA from only moderately-vigorous leisure activity, so workplace activity may be an option for working populations, because, although may not be as vigorous in terms of cardio-respiratory efforts, it comprises a considerable proportion of the total daily activity with important energy expenditure. Since studies have also documented that different types and intensity of daily PA, including low-intensity, seem to confer important health benefits such as prevent MS, we sought to assess the impact of different amounts of leisure-time and workplace activities, including low-intensity level on MS prevention, in a sample of urban Mexican adults. Methods The study population consisted of 5118 employees and their relatives, aged 20 to 70 years, who were enrolled in the baseline evaluation of a cohort study. MS was assessed according to the criteria of the National Cholesterol Education Program, ATP III and physical activity with a validated self-administered questionnaire. Associations between physical activity and MS risk were assessed with multivariate logistic regression models. Results The prevalence of the components of MS in the study population were: high glucose levels 14.2%, high triglycerides 40.9%, high blood pressure 20.4%, greater than healthful waist circumference 43.2% and low-high density lipoprotein 76.9%. The prevalence of MS was 24.4%; 25.3% in men and 21.8% in women. MS risk was reduced among men (OR 0.72; 95%CI 0.57–0.95) and women (OR 0.78; 95%CI 0.64–0.94) who reported an amount of ≥30 minutes/day of leisure-time activity, and among women who reported an amount of ≥3 hours/day of workplace activity (OR 0.75; 95%CI 0.59–0.96). Conclusion Our results indicate that both leisure-time and workplace activity at different intensity levels, including low-intensity significantly reduce the risk of MS. This finding highlights the need for more recommendations regarding the specific amount and intensity of leisure-time and workplace activity needed to prevent MS

Sparse hand-held probe for optoacoustic ultrasound volumetric imaging: An experimental proof-of-concept study

We present an experimental proof-of-concept study on the performance of a sparse segmented annular array for optoacoustic imaging. A capacitive micromachined ultrasonic transducer was equipped with a negatively focused acoustic lens and scanned in an annular fashion to exploit the performance of the sparse array geometry proposed in our recent numerical studies [Biomed. Opt. Express 10, 1545 (2019); J. Biomed. Opt. 23, 025004 (2018)]. A dedicated water tank was made using a 3D printer for light delivery and mounting the sample. A phantom experiment was carried out to showcase the possibility of full-field optoacoustic ultrasound (OPUS) imaging and confirm the earlier numerical results. This proof of concept opens the door towards a prototype of OPUS imaging for (pre-) clinical studies

Imagerie photoacoustique multispectrale au moyen d'une sonde ultrasonore CMUT: résultats préliminaires

Présentation oraleNational audienceL'effet photoacoustique (PA) est la génération d'ondes acoustiques par un objet illuminé à l'aide d'une onde lumineuse pulsée. L'imagerie photoacoustique, basée sur cet effet, présente ainsi les avantages des deux modalités dont elle est issue, notamment le contraste optique et la résolution des ultrasons. Cette nouvelle modalité, très prometteuse, s'applique parfaitement à l'imagerie de tissus biologiques et en particulier du système vasculaire. Dans ce contexte, nous avons réalisé un système expérimental d'imagerie PA dont nous présentons les caractéristiques ainsi que les résultats préliminaires obtenus sur des fantômes bi-modalités. La partie optique est constituée d'un laser pulsé réglable en longueur d'onde et délivrant des impulsions lumineuses de l'ordre de la nanoseconde. La seconde partie de ce banc concerne la réception des ondes ultrasonores, réalisée grâce à un échographe clinique de recherche couplé à un module d'acquisition. Nous présentons les méthodes d'acquisition et de formation des images PA acquises sur ce système expérimental à l'aide d'une sonde CMUT (capacitive micromachined ultrasonic transducer). Nous montrons que la bande passante théoriquement infinie en réception est particulièrement adaptée aux signaux PA large bande. Plusieurs fantômes bi-modalités, dont nous maitrisons les propriétés optiques et acoustiques ont été imagés. Nous décrivons la sensibilité du système en fonction de la nature des absorbeurs optiques choisis et de l'excitation multispectrale fournie par le laser

Imagerie photoacoustique : plateforme expérimentale et résultats préliminaires

International audienceL’effet photoacoustique (PA) permet de générer des ondes acoustiques à partir d’un objet éclairé par une ´ onde lumineuse pulsée. L’imagerie photoacoustique, basée sur cet effet, présente ainsi les avantages des deux modalités dont elle est issue, notamment le contraste optique et la résolution des ultrasons. Cette nouvelle modalité, très prometteuse, s’applique parfaitement à l’imagerie de tissus biologiques et en particulier du système vasculaire. Dans ce contexte, nous avons realisé un système expérimental d’imagerie PA dont nous présentons les caractéristiques ainsi que les résultats préliminaires obtenus sur des fantômes bi-modalités. Nous présentons les méthodes d’acquisition et de formation des images PA acquises sur ce système expérimental à l’aide d’une sonde cMUT (capacitive micromachined ultrasonic transducer). Nous montrons que la bande passante théoriquement infinie en réception est particulièrement adaptée aux signaux PA large bande. Plusieurs fantômes bi-modalités, dont nous maitrisons les propriétés optiques et acoustiques ont ´ été imagés. Nous décrivons la sensibilité du système en fonction de la nature des absorbeurs optiques choisis et de l’excitation laser multispectrale

Imagerie photoacoustique : plateforme expérimentale et résultats préliminaires

International audienceL’effet photoacoustique (PA) permet de générer des ondes acoustiques à partir d’un objet éclairé par une ´ onde lumineuse pulsée. L’imagerie photoacoustique, basée sur cet effet, présente ainsi les avantages des deux modalités dont elle est issue, notamment le contraste optique et la résolution des ultrasons. Cette nouvelle modalité, très prometteuse, s’applique parfaitement à l’imagerie de tissus biologiques et en particulier du système vasculaire. Dans ce contexte, nous avons realisé un système expérimental d’imagerie PA dont nous présentons les caractéristiques ainsi que les résultats préliminaires obtenus sur des fantômes bi-modalités. Nous présentons les méthodes d’acquisition et de formation des images PA acquises sur ce système expérimental à l’aide d’une sonde cMUT (capacitive micromachined ultrasonic transducer). Nous montrons que la bande passante théoriquement infinie en réception est particulièrement adaptée aux signaux PA large bande. Plusieurs fantômes bi-modalités, dont nous maitrisons les propriétés optiques et acoustiques ont ´ été imagés. Nous décrivons la sensibilité du système en fonction de la nature des absorbeurs optiques choisis et de l’excitation laser multispectrale