Model-based magnetization retrieval from holographic phase images.

The phase shift of the electron wave is a useful measure for the projected magnetic flux density of magnetic objects at the nanometer scale. More important for materials science, however, is the knowledge about the magnetization in a magnetic nano-structure. As demonstrated here, a dominating presence of stray fields prohibits a direct interpretation of the phase in terms of magnetization modulus and direction. We therefore present a model-based approach for retrieving the magnetization by considering the projected shape of the nano-structure and assuming a homogeneous magnetization therein. We apply this method to FePt nano-islands epitaxially grown on a SrTiO3 substrate, which indicates an inclination of their magnetization direction relative to the structural easy magnetic [001] axis. By means of this real-world example, we discuss prospects and limits of this approach.

Imaging of nanoparticle-labeled stem cells using magnetomotive optical coherence tomography, laser speckle reflectometry, and light microscopy.

Cell transplantation and stem cell therapy are promising approaches for regenerative medicine and are of interest to researchers and clinicians worldwide. However, currently, no imaging technique that allows three-dimensional in vivo inspection of therapeutically administered cells in host tissues is available. Therefore, we investigate magnetomotive optical coherence tomography (MM-OCT) of cells labeled with magnetic particles as a potential noninvasive cell tracking method. We develop magnetomotive imaging of mesenchymal stem cells for future cell therapy monitoring. Cells were labeled with fluorescent iron oxide nanoparticles, embedded in tissue-mimicking agar scaffolds, and imaged using a microscope setup with an integrated MM-OCT probe. Magnetic particle-induced motion in response to a pulsed magnetic field of 0.2 T was successfully detected by OCT speckle variance analysis, and cross-sectional and volumetric OCT scans with highlighted labeled cells were obtained. In parallel, fluorescence microscopy and laser speckle reflectometry were applied as two-dimensional reference modalities to image particle distribution and magnetically induced motion inside the sample, respectively. All three optical imaging modalities were in good agreement with each other. Thus, magnetomotive imaging using iron oxide nanoparticles as cellular contrast agents is a potential technique for enhanced visualization of selected cells in OCT.

Single-port liver cyst fenestration combined with single-port laparoscopic cholecystectomy using completely reusable instruments.

We report a technique for umbilical single-port liver cyst fenestration combined with cholecystectomy using only standard and reusable laparoscopic instruments. The single-port technique seems to be a safe and simple technique for liver cyst fenestration with cholecystectomy and is cosmetically superior to standard laparoscopic procedures.