3D MRI heart segmentation of mouse embryos.

MRI has become an effective tool for anatomical mice studies. Currently, embryologists study the development of mouse embryos in order to understand the mechanisms of human development. The aim of the research presented in this paper, is to develop a semi-automatic image segmentation framework based 3D deformable models to identify cardiac malformations which are a major cause of death in children. The segmentation systems have been used to segment 3D mouse embryos heart structures. Results on the ventricles and on the heart muscle are presented and compared with manually segmented models.

Measurement of knee cartilage thickness using MRI: a reproducibility study in a meniscectomized guinea pig model of osteoarthritis.

The in vivo precision (reproducibility) of quantitative MRI is of particular importance in osteoarthritis (OA) progression of small magnitude and response to therapy. In this study, three-dimensional high-resolution MRI performed at 7 T was used to assess the short-term reproducibility of measurements of mean tibial cartilage thickness in a meniscectomized guinea pig model of OA. MR image acquisition was repeated five times in nine controls (SHAM) and 10 osteoarthritic animals 3 months after meniscectomy (MNX), in vivo. The animals were then killed for histomorphometric assessment and correlation with the MRI-based measurements. Medial tibial cartilage thickness was measured on MR images using semi-automatic dedicated 3D software developed in-house. The reproducibility of measurements of cartilage thickness was assessed by five repeated MRI examinations with a short recovery delay between examinations (48 h). The computed coefficients of variation were 8.9% for the SHAM group and 8.2% for the MNX group. The coefficients of variation were compatible with expected thickness variations between normal and pathological animals. A positive agreement and significant partial correlation (Spearman r' = 0.74; P < 0.01) between the MRI and histomorphometric data was established. Three-dimensional high-resolution MRI is a promising non-invasive research tool for in vivo follow-up. This modality could be used for staging and monitoring therapy response in small-animal models of OA.

Knee cartilage thickness measurements using MRI: a 4(1/2)-month longitudinal study in the meniscectomized guinea pig model of OA.

OBJECTIVE: The aim of this study was to follow, over a 4(1/2)-month period, the medial tibia cartilage thickness on a meniscectomy (MNX) guinea pig osteoarthritis (OA) model and to compare with control animals, using three-dimensional high-resolution magnetic resonance imaging (3D HR-MRI). METHODS: MRI experimentations were performed in vivo at 7 T on guinea pig knee joints. 3D HR-MR images were acquired in 60 controls (SHAM) and 45 osteoarthritic animals (MNX) at four time-points (15, 45, 90 and 135 days) after surgery. Medial tibial cartilage thickness was measured from MRI images using in-house dedicated 3D software followed by a statistical analysis. At each time-point 15 SHAM and 15 MNX animals were sacrificed for histomorphometric assessments. RESULTS: No significant difference of mean cartilage thickness between the groups was found at early stage (D45) using MRI; however, significant differences were found between the groups at D90 (P<0.001) and D135 (P<0.001). Histomorphometry data confirmed the pathological status of the animals and was well correlated with MRI at D15 (r=0.79, P<0.01), D45 (r=0.67, P<0.01), and D135 (r=0.39, P<0.05) for SHAM, and at D45 (r=0.63, P<0.01), and D135 (r=0.81, P<0.01) for MNX. CONCLUSION: Medial tibial cartilage measurement based on HR-MR images enables the monitoring of longitudinal cartilage thickness changes. This technique showed significant differences between SHAM and MNX as from D90 after surgery. It could be used as a noninvasive and reproducible tool to monitor therapeutic response in this OA model.

The SIMRI project: a versatile and interactive MRI simulator.

This paper gives an overview of SIMRI, a new 3D MRI simulator based on the Bloch equation. This simulator proposes an efficient management of the T2* effect, and in a unique simulator integrates most of the simulation features that are offered in different simulators. It takes into account the main static field value and enables realistic simulations of the chemical shift artifact, including off-resonance phenomena. It also simulates the artifacts linked to the static field inhomogeneity like those induced by susceptibility variation within an object. It is implemented in the C language and the MRI sequence programming is done using high level C functions with a simple programming interface. To manage large simulations, the magnetization kernel is implemented in a parallelized way that enables simulation on PC grid architecture. Furthermore, this simulator includes a 1D interactive interface for pedagogic purpose illustrating the magnetization vector motion as well as the MRI contrasts.

Two-dimensional spatial and temporal displacement and deformation field fitting from cardiac magnetic resonance tagging.

Tagged magnetic resonance imaging is a specially developed technique to noninvasively assess contractile function of the heart. Several methods have been developed to estimate myocardial deformation from tagged image data. Most of these methods do not explicitly impose a continuity constraint through time although myocardial motion is a continuous physical phenomenon. In this paper, we propose to model the spatio-temporal myocardial displacement field by a cosine series model fitted to the entire tagged dataset. The method has been implemented in two dimensions (2D)+time. Its accuracy was successively evaluated on actual tagged data and on a simulated two-dimensional (2D) moving heart model. The simulations show that an overall theoretical mean accuracy of 0.1 mm can be attained with adequate model orders. The influence of the tagging pattern was evaluated and computing time is provided as a function of the model complexity and data size. This method provides an analytical and hierarchical model of the 2D+time deformation inside the myocardium. It was applied to actual tagged data from a healthy subject and from a patient with ischemia. The results demonstrate the adequacy of the proposed model for this evaluation.

A synchrotron radiation microtomography system for the analysis of trabecular bone samples.

X-ray computed microtomography is particularly well suited for studying trabecular bone architecture, which requires three-dimensional (3-D) images with high spatial resolution. For this purpose, we describe a three-dimensional computed microtomography (microCT) system using synchrotron radiation, developed at ESRF. Since synchrotron radiation provides a monochromatic and high photon flux x-ray beam, it allows high resolution and a high signal-to-noise ratio imaging. The principle of the system is based on truly three-dimensional parallel tomographic acquisition. It uses a two-dimensional (2-D) CCD-based detector to record 2-D radiographs of the transmitted beam through the sample under different angles of view. The 3-D tomographic reconstruction, performed by an exact 3-D filtered backprojection algorithm, yields 3-D images with cubic voxels. The spatial resolution of the detector was experimentally measured. For the application to bone investigation, the voxel size was set to 6.65 microm, and the experimental spatial resolution was found to be 11 microm. The reconstructed linear attenuation coefficient was calibrated from hydroxyapatite phantoms. Image processing tools are being developed to extract structural parameters quantifying trabecular bone architecture from the 3-D microCT images. First results on human trabecular bone samples are presented.

On the influence of the phase of conjugate quadrature filters in subband image coding.

The influence of the phase of conjugate quadrature filters (CQFs) on the performances of a subband coding scheme is analyzed. When the filter length is short, the phase characteristic has virtually no influence on the peak signal-to-noise ratio (PSNR)/bit rate results and on the performance of postprocessing algorithms such as edge detection.