Bassem Hiba

Cardiac and respiratory double self-gated cine MRI in the mouse at 7 T.

ECG‐gated cardiac MRI in the mouse is hindered by many technical difficulties in ECG signal recording inside static and variable high magnetic scanner fields. The present study proposes an alternative robust method of acquiring auto‐gated cardiac and respiratory cine images in mouse heart. In our approach, a motion synchronization signal is extracted from the echo peak MR signal of a non‐triggered radial acquisition. This signal is then used for both cardiac and respiratory retrospective gating before cine image reconstruction. Highly asymmetric echoes were acquired to achieve the radial k‐space sampling in order to avoid radial acquisition related artifacts and to increase auto‐gating robustness. In vivo experiments demonstrated the feasibility and robustness of self‐gated cine‐MRI in the mouse heart at 7T. The signal‐to‐noise and contrast‐to‐noise ratios of the self‐gated and ECG‐gated images were comparable, all parameters being equal. Magn Reson Med, 2006.

Evolution of renal oxygen content measured by BOLD MRI downstream a chronic renal artery stenosis

BACKGROUND A decrease in renal oxygen content can be measured non-invasively by the increase of the R2* value derived from blood oxygen level-dependent magnetic resonance imaging (BOLD MRI). The aim of this study was to test if renal hypoxia occurs in kidneys downstream a chronic and unilateral renal artery stenosis. METHODS Chronic renal ischaemia was induced in rats using a calibrated clip inserted on the right renal artery. R2* was determined, using a multiple recalled gradient-echo sequence, before and once a week after a clip insertion over 4 weeks, in a group of clipped (n = 8) and sham-operated (n = 7) rats. RESULTS At baseline, in stenotic kidneys, R2* was higher in the outer stripe of outer medulla (105 ± 4.6) and the outer medulla (99 ± 2.5) than in the cortex (84 ± 2.5; P < 0.002 for comparison with both areas). R2* was unchanged in the cortex, the outer stripe of outer medulla and the outer medulla in stenotic kidneys, sham-operated kidneys and contralateral kidneys during the 4 weeks. Mean blood pressure was higher in rats with clipped kidney than in sham-operated rats from Day 11 and remained increased thereafter. The renal volume increased progressively in sham-operated kidneys and contralateral kidneys, whereas it slightly decreased in stenotic kidneys. CONCLUSIONS Our study shows that after 4 weeks, no renal hypoxia can be detected in the kidney downstream to a renal artery stenosis, suggesting that atrophy could be induced by other factors.

Cardiac and respiratory self-gated cine MRI in the mouse: comparison between radial and rectilinear techniques at 7T.

ECG‐gated cardiac MRI in the mouse is hindered by many technical difficulties in ECG signal recording inside high magnetic field scanners. The present study proposes a robust rectilinear method of acquiring cardiac and respiratory self‐gated cine images in mouse hearts. In this approach, a motion‐synchronization MR signal is collected in the center of k‐space simultaneously with imaging data in each readout of a nontriggered rectilinear acquisition. This signal is then used for both cardiac and respiratory retrospective gating before cine image reconstruction. The value of this approach for overcoming ECG‐gating failure was demonstrated by performing cardiac imaging in eight mice with myocardial infarction. Comparison with an auto‐gated radial k‐space sampling technique, previously reported for cardiac applications in the mouse, found the rectilinear strategy more robust, thanks to a more reliable self‐gating signal, while the radial strategy was less sensitive to motion and flow artifacts. Magn Reson Med 58:745–753, 2007.

Quantitative assessment of skeletal muscle degeneration in patients with myotonic dystrophy type 1 using MRI.

To identify MRI biomarkers that could be used to follow disease progression and therapeutic efficacy in one individual muscle in patients with myotonic dystrophy type 1 (DM1).

MRI of Tibialis Anterior Skeletal Muscle in Myotonic Dystrophy Type 1

OBJECTIVE The aim of this study was to evaluate whether magnetic resonance imaging (MRI) can be used as a noninvasive approach to assessment of disease severity and muscle damage in Myotonic Dystrophy type 1 (DM1). METHODS The MRI findings in legs of 41 patients with DM1 were evaluated with respect to the tibialis anterior (TA) skeletal muscle impairment. Magnetic resonance imaging findings were compared with TA strength measurements obtained by quantitative manual testing, duration of the disease and with the length of the CTG repeats. RESULTS Muscle MRI abnormalities were observed in 80% of DM1 patients, ranging from edema-like abnormalities alone to severe atrophy/fatty replacement. Edema-like abnormalities seem to be an earlier MRI marker of the disease. Fatty infiltration/atrophy correlated with the TA muscle force (r = 0.95), the severity (P = 0.00001) of the disease but not with the duration of the disease (P = 0.3) or the length of the CTG repeats (P > 0.10), measured in peripheral leukocytes. Evaluation of other muscles of the legs revealed that the medial gastrocnemius and soleus muscles were the most frequently and severely affected muscles, while tibialis posterior muscles were relatively spared. Edema-like abnormalities are most frequently observed in the skeletal muscles of the anterior compartment. CONCLUSION Muscle MRI is helpful to depict muscle abnormalities but does not seem to be a reliable indicator of skeletal muscle involvement in DM1 since the decrease in TAmuscle force is not correlated with MRI abnormalities in some patients.

Age-Related Modifications of Diffusion Tensor Imaging Parameters and White Matter Hyperintensities as Inter-Dependent Processes

Microstructural changes of White Matter (WM) associated with aging have been widely described through Diffusion Tensor Imaging (DTI) parameters. In parallel, White Matter Hyperintensities (WMH) as observed on a T2-weighted MRI are extremely common in older individuals. However, few studies have investigated both phenomena conjointly. The present study investigates aging effects on DTI parameters in absence and in presence of WMH. Diffusion maps were constructed based on 21 directions DTI scans of young adults (n = 19, mean age = 33 SD = 7.4) and two age-matched groups of older adults, one presenting low-level-WMH (n = 20, mean age = 78, SD = 3.2) and one presenting high-level-WMH (n = 20, mean age = 79, SD = 5.4). Older subjects with low-level-WMH presented modifications of DTI parameters in comparison to younger subjects, fitting with the DTI pattern classically described in aging, i.e., Fractional Anisotropy (FA) decrease/Radial Diffusivity (RD) increase. Furthermore, older subjects with high-level-WMH showed higher DTI modifications in Normal Appearing White Matter (NAWM) in comparison to those with low-level-WMH. Finally, in older subjects with high-level-WMH, FA, and RD values of NAWM were associated with to WMH burden. Therefore, our findings suggest that DTI modifications and the presence of WMH would be two inter-dependent processes but occurring within different temporal windows. DTI changes would reflect the early phase of white matter changes and WMH would appear as a consequence of those changes.

Structural hippocampal network alterations during healthy aging: a multi-modal MRI study.

While hippocampal atrophy has been described during healthy aging, few studies have examined its relationship with the integrity of White Matter (WM) connecting tracts of the limbic system. This investigation examined WM structural damage specifically related to hippocampal atrophy in healthy aging subjects (n = 129), using morphological MRI to assess hippocampal volume and Diffusion Tensor Imaging (DTI) to assess WM integrity. Subjects with Mild Cognitive Impairment (MCI) or dementia were excluded from the analysis. In our sample, increasing age was significantly associated with reduced hippocampal volume and reduced Fractional Anisotropy (FA) at the level of the fornix and the cingulum bundle. The findings also demonstrate that hippocampal atrophy was specifically associated with reduced FA of the fornix bundle, but it was not related to alteration of the cingulum bundle. Our results indicate that the relationship between hippocampal atrophy and fornix FA values is not due to an independent effect of age on both structures. A recursive regression procedure was applied to evaluate sequential relationships between the alterations of these two brain structures. When both hippocampal atrophy and fornix FA values were included in the same model to predict age, fornix FA values remained significant whereas hippocampal atrophy was no longer significantly associated with age. According to this latter finding, hippocampal atrophy in healthy aging could be mediated by a loss of fornix connections. Structural alterations of this part of the limbic system, which have been associated with neurodegeneration in Alzheimers disease, result at least in part from the aging process.

In vivo assessment of mouse hindleg intramyocellular lipids by 1H-MR spectroscopy

RATIONALE AND OBJECTIVES (1)H-magnetic resonance spectroscopy ((1)H-MRS) has proved to be the sole in vivo technique able to measure intramyocellular lipids (IMCL) in both humans and animals. Mouse models are now widely used for physiologic studies and drug discovery. However, IMCL assessment using (1)H-MRS is hindered in this animal model by the small muscle size and strong contamination from the extramyocellular lipid (EMCL) signal. The objective of this study was to the use of (1)H-MRS for IMCL quantification in mice at different ages. MATERIALS AND METHODS Noninvasive IMCL quantification was performed at 7 T in tibialis anterior (TA) muscles of healthy male C57/BL6 mice (n = 9; age, 13.6 +/- 1 months), db/db mice (n = 4), and their C57BL/KSJ control littermates (n = 4) at 7 and 17 weeks of age. RESULTS The IMCL content of diabetic mice TA was significantly higher than their littermates (2.41 +/- 0.5 vs. 1.21 +/- 0.35, P < .01). An age effect was observed, with TA IMCL levels being lower in older than younger control mice, but increasing between 7 and 17 weeks in the db/db mice. CONCLUSIONS The feasibility of (1)H-MRS spectroscopy was demonstrated in mice muscle, despite its small size, and used to assess IMCL content in db/db mice.

Gender and strain variations in left ventricular cardiac function and mass determined with magnetic resonance imaging at 7 tesla in adult mice.

Objectives: We sought to assess with magnetic resonance imaging (MRI) the influence of strain type and gender on left ventricular (LV) global function and mass in 3 inbred mouse strains with a normal cardiac phenotype. Materials and Methods: A total of 30 mice from 3 inbred strains (C57BL/6, 29S2/SvPasCrl, and C3HFeJ) were studied on a 7.05-T MR scanner using ECG-triggered cine sequences. LV mass and volumes were calculated with inclusion and exclusion of papillary muscles (PMs) in the LV wall. Results: Significant differences were found with strain and gender (P < 0.001), with strain–effect but no gender–effect for ejection fraction (EF), end-diastolic volume (EDV), and end-systolic volume (ESV). There were no differences in LV mass between strains but lower values in female mice except in the C3H strain. The exclusion of PMs led to the relative underestimation of EF (−6.1%) and of LV mass (−6.4 mg) and the relative overestimation of EDV (6.3 &mgr;L) and ESV (5.3 &mgr;L). Inter- and intraobserver reproducibility was better when PMs were included. Conclusion: The use of MRI demonstrates cardiac interstrain and gender-related phenotypic diversities that are essential factors to consider when building genomic databases and designing studies.

Simultaneous segmentation of the left and right heart ventricles in 3D cine MR images of small animals

New high resolution image techniques allow to capture the anatomy and movement of the heart of small animals. The availability of these in vivo images can be very useful for medical research, however the amount of generated data for large animal studies makes manual analysis a very tedious task. To cope with the problem of automatic analysis of these images, we propose the use of the deformable elastic template method to perform automatic segmentation of the ventricles. To adapt the method to the specificities of high-resolution MRI, several improvements are presented, including an image-context dependent scheme for more robust segmentation. Qualitative results show that our method is able to correctly retrieve the hearts contours in 3D