Max Langer | INSA Lyon (original) (raw)

Papers by Max Langer

2010 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2010

In zoom-in tomography, the aim is to image a region of interest lying partially or fully within t... more In zoom-in tomography, the aim is to image a region of interest lying partially or fully within the imaged object, using a high resolution tomographic scan covering only the ROI, and a low resolution scan covering the whole object. We analyze the problem from a multiresolution point of view and propose an algorithm for combining the two data sets using the discrete wavelet transform and the Haar wavelet. We compare the proposed algorithm to a previously reported method that involves padding of the high resolution data with a supersampled version of the low resolution data, to zero padding and edge extension, using synthetic data sets. We show that the proposed algorithm is insensitive to offsets between the two data sets, but that it is slightly more sensitive to noise.

ABSTRACT PURPOSE MRI coupled with the injection of Ultrasmall particles of iron oxide (USPIO) has... more ABSTRACT PURPOSE MRI coupled with the injection of Ultrasmall particles of iron oxide (USPIO) has been successfully applied for pre-clinical and clinical studies of cerebral inflammation following stroke. Current limitations of this approach are represented by the difficulty of interpreting MR signal changes in terms of exact localization and quantification of USPIO. To overcome this limitation, Synchrotron Radiation phase micro computerized tomography (SR-PCT) was proposed as a new method to visualize USPIO distribution into the whole brains of mice. METHOD AND MATERIALS The following samples were imaged : i) USPIO phantoms with concentrations in the range 0,15 nM – 1500 µM ii) 16 post-mortem brains with intracerebral injections of iron concentrations [15-1,500] µmol Fe/l and iii) 8 post-mortem brains of mice having received intravenous injection of USPIO after induction of experimental stroke. The X-ray beam transmitted through the specimen was acquired on a detector using a LuAg scintillator screen, visible light optics and a 2048x2048 CCD detector. The pixel size was set to 8µm, which provides a field of view of 16 mm3. For each scan, 1999 radiographs were taken at different angles evenly distributed between 0 and 360 degrees. Finally, the Fil-tered Back Projection algorithm was applied to obtain a reconstructed 3D volume, i.e. a stack of 2048 slices of 2048x2048. RESULTS In vitro, the relationship between iron concentrations and absorption coefficients was linear for concentrations superior to 10 µM. In stereotaxicallly injected brains, SR-PCT was able to detect hyperintense signals in all mice, while allowing an accurate localization in the brain compared to T2-weighted MRI. In stroke animals, SR-PCT provided exquisite anatomical details compared to immunohistologic slices, allowing to identify both healthy and pathological brain structures. Visualization of bright spots in the ischemic lesions co-localized with hypointense signals detected by MRI . CONCLUSION Microtomography with SR-PCT showed a good sensitivity to USPIO detection, while allowing an accurate localization. Further analysis are warranted to investigate quantitative performances of the approach. CLINICAL RELEVANCE/APPLICATION Microtomography with SR-PCT represents a promising tool for brain imaging

2011 18th IEEE International Conference on Image Processing, 2011

Biological microscopic imaging is receiving increasing interest with the development of new modal... more Biological microscopic imaging is receiving increasing interest with the development of new modalities. In this context Synchrotron Radiation (SR) Nano-CT demonstrates a high potential in opening new horizons. We recall the principle of SR micro-CT and its advantages over standard X-ray micro-CT in terms of accuracy and signal to noise ratio. We briefly present data acquisition and reconstruction in absorption and phase CT. While in the first case image reconstruction is based simply on the standard filtered back projection algorithm, in the later case it involves a preliminary step of phase retrieval. Applications of this technique in bone research in conjunction with specific image analysis developments are shown. At the micrometer scale, trabecular and cortical bone have been analyzed in human samples and mice. At the nanometer scale, we present recent data on the osteocyte network which has never before been investigated in 3D. Open problems for the segmentation and quantification of the complex canalicular network are highlighted.

Current osteoporosis reports, 2014

Micro-computed tomography (micro-CT)-a version of X-ray CT operating at high spatial resolution-h... more Micro-computed tomography (micro-CT)-a version of X-ray CT operating at high spatial resolution-has had a considerable success for the investigation of trabecular bone micro-architecture. Currently, there is a lot of interest in exploiting CT techniques at even higher spatial resolutions to assess bone tissue at the cellular scale. After recalling the basic principles of micro-CT, we review the different existing system, based on either standard X-ray tubes or synchrotron sources. Then, we present recent applications of micro- and nano-CT for the analysis of osteocyte lacunae and the lacunar-canalicular network. We also address the question of the quantification of bone ultrastructure to go beyond the sole visualization.

Optics Express, 2013

The study analyzes noise in X-ray in-line phase tomography in a biomedical context. The impact of... more The study analyzes noise in X-ray in-line phase tomography in a biomedical context. The impact of noise on detection of iron oxide nanoparticles in mouse brain is assessed. The part of the noise due to the imaging system and the part due to biology are quantitatively expressed in a Neyman Pearson detection strategy with two models of noise. This represents a practical extension of previous work on noise in phase-contrast X-ray imaging which focused on the theoretical expression of the signal-tonoise ratio in mono-dimensional phantoms, taking account of the statistical noise of the imaging system only. We also report the impact of the phase retrieval step on detection performance. Taken together, this constitutes a general methodology of practical interest for quantitative extraction of information from X-ray in-line phase tomography, and is also relevant to assessment of contrast agents with a blob-like signature in high resolution imaging.

Physics in medicine and biology, Jan 24, 2014

In this article, a set of three computer vision tools, including scale invariant feature transfor... more In this article, a set of three computer vision tools, including scale invariant feature transform (SIFT), a measure of focus, and a measure based on tractography are demonstrated to be useful in replacing the eye of the expert in the optimization of the reconstruction parameters in x-ray in-line phase tomography. We demonstrate how these computer vision tools can be used to inject priors on the shape and scale of the object to be reconstructed. This is illustrated with the Paganin single intensity image phase retrieval algorithm in heterogeneous soft tissues of biomedical interest, where the selection of the reconstruction parameters was previously made from visual inspection or physical assumptions on the composition of the sample.

Molecular Imaging and Biology, 2013

Purpose: The purpose of this study was to introduce synchrotron radiation X-ray phase computed to... more Purpose: The purpose of this study was to introduce synchrotron radiation X-ray phase computed tomography (SR-PCT) as a new method of visualizing ultrasmall superparamagnetic particles of iron oxide (USPIO) distribution into the brains of mice with neuroinflammation. Procedures: The sensitivity of the technique was assessed by performing back-to-back SR-PCT and magnetic resonance imaging (MRI) in mice stereotaxically injected with a range of USPIO concentrations. Eight mice with cerebral ischemia were then intravenously injected with USPIOs and imaged back-to-back with MRI and SR-PCT. Results: SR-PCT proved sensitive enough to detect iron in nanomolar quantities. In strokeinduced animals, SR-PCT showed hyperintense areas in the regions of MR signal loss and immunostaining for macrophages. SR-PCT, moreover, identified brain anatomy as clearly as histology, without the need for sectioning or staining, with an examination time of 44 min per brain at an isotropic spatial resolution of 8 μm. Conclusion: SR-PCT has potential for cellular imaging in intact brain, with unequaled neuroanatomy.

Journal of Biomechanics, 2012

The mechanical properties of cortical bone are determined by a combination bone tissue compositio... more The mechanical properties of cortical bone are determined by a combination bone tissue composition, and structure at several hierarchical length scales. In this study the spatial distribution of tissue level properties within a human femoral shaft has been investigated. Cylindrically shaped samples (diameter: 4.4 mm, N ¼56) were prepared from cortical regions along the entire length (20-85% of the total femur length), and around the periphery (anterior, medial, posterior and lateral quadrants). The samples were analyzed using scanning acoustic microscopy (SAM) at 50 MHz and synchrotron radiation micro computed tomography (SRmCT). For all samples the average cortical porosity (Ct.Po), tissue elastic coefficients (c ij ) and the average tissue degree of mineralization (DMB) were determined. The smallest coefficient of variation was observed for DMB (1.8%), followed by BV/TV (5.4%), c ij (8.2-45.5%), and Ct.Po (47.5%). Different variations with respect to the anatomical position were found for DMB, Ct.Po and c ij . These data address the anatomical variations in anisotropic elastic properties and link them to tissue mineralization and porosity, which are important input parameters for numerical multi-scale bone models.

Applied Physics Letters, 2013

X-ray phase-contrast imaging techniques are used at synchrotron facilities to visualize tiny dens... more X-ray phase-contrast imaging techniques are used at synchrotron facilities to visualize tiny density variations in bulk samples. They overcome the limitations of other non-destructive methods, which often provide insufficient spatial and/or density resolution. Holotomography (HT) and X-ray grating interferometry (XGI) are among the most powerful phase-contrast techniques. Here, we show a direct comparison of HT versus XGI. We find that XGI excels in fidelity of the density measurements and is more robust against low-frequency artifacts, while HT is superior in spatial resolution. This study gives indications for applications and developments of phase-contrast imaging. V C 2013 AIP Publishing LLC. [http://dx.

Journal of Applied Physics, 2014

Model-based CT performance assessment and optimization for iodinated and noniodinated imaging tas... more Model-based CT performance assessment and optimization for iodinated and noniodinated imaging tasks as a function of kVp and body size Med.