Biomedical subjects

J M Bonny

Publications and source records attributed to J M Bonny.

8 recordsLinked to original sources

PubMed2006

MRI virtual biopsies: analysis of an explanted endovascular device and perspectives for the future.

Information that can be obtained by magnetic resonance imaging (MRI) of explanted endovascular devices must be validated as this method is non-destructive. Histology of such a device together with its encroached tissues can be elegantly performed after polymethymethacrylate (PMMA) embedding, but this approach requires destruction of the specimen. The issue is therefore to determine if the MRI is sufficient to fully validate an explanted device based upon the characterization of an explanted specimen. An AneuRx device deployed percutaneously 25 months earlier in a 75-year-old patient was removed en bloc at autopsy together with the surrounding aneurysmal sac and segments of the upstream and downstream arteries. Macroscopic pictures were taken and a slice of the cross-section was processed for histology after polymethylmethacrylate (PMMA) embedding. For the magnetic resonance imaging investigation, the device was inserted in a Biospec 4.7 T MRI system with a 20 mm diameter birdcage resonator used for both emission and reception. A Spin-Echo (SE) was used to acquire both T1 proton density (PD) and T2 weighted images. A gradient-echo (GE) sampling of a free induction decay (GESFID) was used to generate multiple GE images using a single excitation pulse so that four images at different TE were obtained in the same acquisition. The selected explanted device was outstandingly well-healed compared to most devices harvested from humans. No inflammatory process was observed in contact or at distance of the materials. In MRI T1 images display no specific contrast and were homogeneous in the different tissues. The contrast was improved on proton density weighed images. On the T2 weighed images, the different areas were well identified. The diffusion images displayed in the surrounding B region had the greatest diffusion coefficient and the greatest anisotropy. The MRI analysis of the explanted AneuRx device illustrates the possibilities of this technique to characterize the interaction of the endovascular graft with the surrounding tissues. MRI is a breakthrough to investigate explanted medical devices but it also can be advantageously used in vivo to obtain virtual biopsies, because real biopsies to determine the 3 Bs (biocompatibility, biofunctionality and bioresilience) cannot be carried out as they could obviously initiate infection and degradation of the foreign materials.

Aged↗

PubMed2000

Imaging of water and fat fractions in high-field MRI with multiple slice chemical shift-selective inversion recovery.

Fat and water fractions were quantified at high field using a chemical shift-selective inversion recovery (CSS-IR) sequence to address the major difficulties encountered at high field by phase-sensitive techniques used for fat/water discrimination. Water- and fat-suppressed images were perfectly registered, which is a prerequisite for quantification. Immunity of the inversion pulse to B(1) field modulations and off-resonance effects was tested for two adiabatic inversion pulses, with hyperbolic secant and asymmetric hyper-pulse waveforms. Taking into account adiabaticity, immunity to off-resonance, radiofrequency power requirements, and specific absorption rate, the former was chosen. A close correlation was found between fat content measured by CSS-IR at 4.7 T (R(2)= 0.97, P < 0.001) and 9.4 T (R(2)= 0.99, P < 0.05) and that measured by Soxhlet extraction. Different sources of bias (low signal-to-noise ratio, magnetization transfer effect) are discussed. J. Magn. Reson. Imaging 2000;12:488-496.

Adipose Tissue↗

PubMed2000

Benefit of endurance training in elderly people over a short period is reversible.

The present study assessed daily activity, physical capacity and body composition in 11 initially sedentary healthy subjects [5 men and 6 women, mean age 62.8 (SD 2.7) years] before training (T(o)), after completion of 7 (T(7w)) and 14 (T(14w)) weeks of training, and again 6 (T(6m)) and 12 (T(12m)) months after training. The mean daily activity index decreased from T(7w) to T(12m) reaching a lower level than at T(o) [T(12m) - T(o) = -1.5 (SD 4.6) units, P = 0.18]. Mean maximal oxygen uptake (VO(2max)) and its corresponding mean power output (Wdot(max)) were increased by 12.5 (SD 6.6)% (P = 0. 003) and 22.8 (SD 12.8)% (P = 0.003), respectively, at T(14w), and returned to their T(o) levels within 1 year. Mean body mass (m(b)) remained stable until T(6m) but increased significantly by 2.6 (SD 3. 7)% from T(6m) to T(12m) (P < 0.05). Mean fat mass (m(f), from bioelectrical impedance analysis measurements) tended to decrease [-2.0 (SD 4.2)%, P = 0.10] during the training period but increased by 7.8 (SD 10.9)% between T(6m) and T(12m) (P < 0.05). The mean fat free mass did not vary during the study period (P = 0.81) but magnetic resonance imaging (MRI) showed that mean thigh muscle volume decreased between T(7w) and T(12m) to less than at T(o) [T(12m) - T(o) = -2.3 (SD 3.6)%, P = 0.05]. Therefore, this study confirmed the favourable effects of endurance training on the physical capacity and body composition of elderly people, but demonstrated that the training programme would have to be continued to maintain the training-related benefits (i.e. increased VO(2max) and Wdot(max)) which would otherwise be lost within 1 year. After training, m(b) and m(f) were found to be increased. Furthermore, a fast and reproducible MRI protocol was validated for study of small intra-individual variations in tissue volumes in longitudinal studies.

Adipose Tissue↗

PubMed2000

Detection of susceptibility effects using simultaneous T(2)* and magnetic field mapping.

Tracking susceptibility effects is a convenient way to detect small inclusions in a bulk tissue matrix by MRI. We propose a quantitative assessment of these susceptibility effects by simultaneously mapping T(2)* and magnetic field from the time course of magnitude and phase using a multiple GE sequence at 4.7 T. A high-pass scheme is also introduced to highlight the mesoscopic magnetic field variations due to local susceptibility differences specifically in the magnetic field map. Applying this method to muscle tissue, we demonstrate that connective tissue generates detectable susceptibility effects through concomitant local magnetic field variation and T(2)* shortening.

Adipose Tissue↗

PubMed1998

Characterization in vivo of muscle fiber types by magnetic resonance imaging.

Magnetic resonance imaging has been used to characterize muscle fiber types. Here, T1 and T2 values were determined in pure slow-twitch and fast-twitch rabbit muscles and in rabbit muscles with mixed fiber types. The muscles with high proportions of oxidative slow-twitch fibers had higher T2 values than the others. Echo time, orientation of muscle fibers in B0, and moving spins had no effect on relaxation parameters. The results are discussed in terms of slow myosin isoform content and oxidative metabolism.

Adenosine Triphosphatases↗

PubMed1996

T2 maximum likelihood estimation from multiple spin-echo magnitude images.

An optimal maximum likelihood (ML) method is described for an unbiased estimation of monoexponential T2 from magnitude spin-echo images. The algorithm is based on a Gaussian assumption of noise distribution. The validity of this assumption was checked by a statistical chi 2 test on spin-echo and fast low-angle shot surface coil images. Monte-Carlo simulations of magnitude data showed that the ML estimate standard deviation is lower than that produced by a weighted least-squares fitting on signal logarithm. Correction schemes are proposed to reduce bias deriving from magnitude reconstruction. The variance of the ML estimate converged rapidly toward the theoretical algebraic expression of the Cramér-Rao lower bound.

Likelihood Functions↗

PubMed1992

Automatic detection of the left ventricular myocardium long axis and center in thallium-201 single photon emission computed tomography.

A new method for centering and reorienting automatically the left ventricle in thallium-201 myocardial single photon emission computed tomography (SPET) is proposed. The processing involves the following steps: (a) the transverse sections of the left ventricle are segmented, (b) the three-dimensional skeleton of the left ventricle is extracted using tools of mathematical morphology, (c) the skeleton is fitted to a quadratic surface by the least-squares method, (d) the left ventricle is reoriented and centered using the long axis and the coordinates of the centre of the quadratic surface. A series of 30 consecutive exercise and redistribution 201Tl SPET studies were centered and reoriented by two operators twice with this method, and twice manually. There was no significant difference in the mean realignment performed by the automatic and the manual methods while centering differed moderately in some instances. In all cases and for all parameters, the reproducibility of the automatic method was 1.00, while it ranged between 0.74 and 0.98 with the manual centering and reorientation. This automatic approach provides a fast and highly reproducible method for the reconstruction of short- and long-axis sections of the left ventricle in 201Tl SPET.

Adult↗

PubMedDate not supplied

3D modeling in myocardial 201TL SPECT.

A method to model the left ventricular myocardium in thallium-201 Single Photon Emission Computed Tomography (SPECT) is presented. This method is based on the fitting of the morphological skeleton of the left ventricle to a truncated bullet. This automatic approach would provide a more reproducible visualization of the organ for clinical applications.

Computer Graphics↗