Μm Pixel Resolution Research Articles

Computational study on the effect of loading alteration caused by disc degeneration on the trabecular architecture in human lumbar spine

A thorough understanding of age-related phenomena on the trabecular architecture in the human lumbar spine can help the diagnosis and prognosis of age-related architectural changes, and provide an insight into the corresponding clinical assessments. In this paper we considered the different loading conditions of the young and old lumbar spines mainly caused by disc degeneration and studied the effect of loading alteration on trabecular architecture in lumbar spines. A two-dimensional μFE models with a 40 μm pixel resolution were built to represent the full trabecular architecture in the human lumbar spine, and a topology optimization with the aid of finite element method was conducted to numerically investigate the trabecular morphological changes. Topology optimization iteratively distributes material in a design domain producing optimal layout or configuration, and it has been widely and successfully used for the study of bone remodeling. As a result of adaptive response of bone remodeling due to different loading conditions, we obtained two distinctively different trabecular architectures for the young and old lumbar spines, and we observed a strong correlation between our numerical results and the actual trabecular architecture in the literature. The proposed numerical framework and results demonstrated the potential use of the topology optimization-based numerical tool for putative treatments in advance of actual clinical procedures for the patients.

Fourier-transform infrared anisotropy in cross and parallel sections of tendon and articular cartilage

BackgroundFourier Transform Infrared Imaging (FTIRI) is used to investigate the amide anisotropies at different surfaces of a three-dimensional cartilage or tendon block. With the change in the polarization state of the incident infrared light, the resulting anisotropic behavior of the tissue structure is described here.MethodsThin sections (6 μm thick) were obtained from three different surfaces of the canine tissue blocks and imaged at 6.25 μm pixel resolution. For each section, infrared imaging experiments were repeated thirteen times with the identical parameters except a 15° increment of the analyzer's angle in the 0° – 180° angular space. The anisotropies of amide I and amide II components were studied in order to probe the orientation of the collagen fibrils at different tissue surfaces.ResultsFor tendon, the anisotropy of amide I and amide II components in parallel sections is comparable to that of regular sections; and tendon's cross sections show distinct, but weak anisotropic behavior for both the amide components. For articular cartilage, parallel sections in the superficial zone have the expected infrared anisotropy that is consistent with that of regular sections. The parallel sections in the radial zone, however, have a nearly isotropic amide II absorption and a distinct amide I anisotropy.ConclusionFrom the inconsistency in amide anisotropy between superficial to radial zone in parallel section results, a schematic model is used to explain the origins of these amide anisotropies in cartilage and tendon.

Computational study of Wolff's law with trabecular architecture in the human proximal femur using topology optimization

In the field of bone adaptation, it is believed that the morphology of bone is affected by its mechanical loads, and bone has self-optimizing capability; this phenomenon is well known as Wolff's law of the transformation of bone. In this paper, we simulated trabecular bone adaptation in the human proximal femur using topology optimization and quantitatively investigated the validity of Wolff's law. Topology optimization iteratively distributes material in a design domain producing optimal layout or configuration, and it has been widely and successfully used in many engineering fields. We used a two-dimensional micro-FE model with 50 μm pixel resolution to represent the full trabecular architecture in the proximal femur, and performed topology optimization to study the trabecular morphological changes under three loading cases in daily activities. The simulation results were compared to the actual trabecular architecture in previous experimental studies. We discovered that there are strong similarities in trabecular patterns between the computational results and observed data in the literature. The results showed that the strain energy distribution of the trabecular architecture became more uniform during the optimization; from the viewpoint of structural topology optimization, this bone morphology may be considered as an optimal structure. We also showed that the non-orthogonal intersections were constructed to support daily activity loadings in the sense of optimization, as opposed to Wolff's drawing.

Back-illuminated CCD for coherent soft X-ray imaging

Direct-illumination CCDs find increasing use in coherent X-ray imaging due to their good spatial resolution and signal-to-noise ratio. These CCDs offer a high quantum efficiency for soft X-rays near the 3d transition metal L edges. We compare front- and back-illuminated CCDs and describe a method to obtain images with a large dynamic range (five orders of magnitude) and high spatial resolution. Back-illuminated CCDs are resistant to radiation damage at the soft X-ray energies and provide a true 13.5 μm pixel resolution. High quality diffraction images are obtained in magnetic studies from metallic multilayer structures in reflection geometry.

Direct evidence of lipid translocation between adipocytes and prostate cancer cells with imaging FTIR microspectroscopy

Various epidemiological studies show a positive correlation between high intake of dietary FAs and metastatic prostate cancer (CaP). Moreover, CaP metastasizes to the bone marrow, which harbors a rich source of lipids stored within adipocytes. Here, we use Fourier transform infrared (FTIR) microspectroscopy to study adipocyte biochemistry and to demonstrate that PC-3 cells uptake isotopically labeled FA [deuterated palmitic acid (D(31)-PA)] from an adipocyte. Using this vibrational spectroscopic technique, we detected subcellular locations in a single adipocyte enriched with D(31)-PA using the upsilon(as+s)(C-D)(2+3) (D(31)-PA): upsilon(as+s)(C-H)(2+3) (lipid hydrocarbon) signal. In addition, larger adipocytes were found to consist of a higher percentage of D(31)-PA of the total lipid found within the adipocyte. Following background subtraction, the upsilon(as)(C-D)(2+3) signal illuminated starved PC-3 cells cocultured with D(31)-PA-loaded adipocytes, indicating translocation of the labeled FA. This study demonstrates lipid-specific translocation between adipocytes and tumor cells and the use of FTIR microspectroscopy to characterize various biomolecular features of a single adipocyte without the requirement for cell isolation and lipid extraction.

Polarized IR microscopic imaging of articular cartilage

The objective of this spectroscopic imaging study is to understand the anisotropic behavior of articular cartilage under polarized infrared radiation at 6.25 µm pixel resolution. Paraffin embedded canine humeral cartilage-bone blocks were used to obtain 6 µm thick tissue sections. Two wire grid polarizers were used to manipulate the polarization states of IR radiation by setting them for various polarizer/analyzer angles. The characteristics of the major chemical components (amide I, amide II, amide III and sugar) of articular cartilage were investigated using (a) a polarizer and (b) a combination of a polarizer and an analyzer. These results were compared to those obtained using only an analyzer. The infrared anisotropy (variation in infrared absorption as a function of polarization angles) of amide I, amide II and amide III bands correlates with the orientation of collagen fibrils along the tissue depth in different histological zones. An ‘anisotropic flipping’ region of amide profiles indicates the possibility of using Fourier transform infrared imaging (FTIRI) to determine the histological zones in cartilage. Cross-polarization experiment indicates the resolution of overlapping peaks of collagen triple helix and/or proteoglycan in articular cartilage.

Silicon Image Sensor Technology for in vivo Detection of Surfactant-Induced Corneocyte Swelling and Drying

Background: Several instrumental methods can indirectly assess some specific aspects of cutaneous irritation at the level of the stratum corneum (SC). Objective: There is a need for developing more sensitive approaches in this field. Methods: We assessed a recently introduced innovative tool (SkinChip^®) based on capacitive pixel-sensing technology in its potential to detect early discrete manifestations of skin irritation. The sensor generates a detailed non-optical picture corresponding to a capacitance map of the skin surface reaching 50 µm pixel resolution. Some topographical details can be easily disclosed and the SC hydration as well. Two surfactant solutions were tested on volunteers. These solutions were applied under test patches for 2 days on the volar forearms. Clinical and SkinChip assessments were performed 3 h after removing the patch. Results: The generated images allowed a precise observation of skin irritation which appeared as a two-step process. Early changes consisted of darker pixels corresponding to overhydrated swollen corneocytes at the irritated sites. Two days later, the same area appeared as white pixels, indicating the loss of corneocyte hydration. Conclusion: The SkinChip device appears to be a very sensitive tool for detecting the early steps of surfactant-induced skin irritation affecting the SC.

Development and application of a neutron sensor for single event effects analysis

The development and application of a charge-coupled device (CCD) sensor for neutron detection is described. The sensor provides images of neutron-induced single-event effects (SEEs) at 9 μm pixel resolution and a charge/pixel resolution of typically 36.6 electronic charges. Example results are presented, showing the charge profiles resulting from single events observed during tests in a representative neutron spectrum. The sensor enables aspects of SEE phenomena to be studied directly in more detail than hitherto.

High resolution MR based polymer dosimetry versus film densitometry: a systematic study based on the modulation transfer function approach

Precise methods of modern radiation therapy such as intensity modulated radiotherapy (IMRT), brachytherapy (BT) and high LET irradiation allow for high dose localization in volumes of a few mm3. However, most dosimetry methods—ionization chambers, TLD arrangements or silicon detectors, for example—are not capable of detecting sub-mm dose variations or do not allow for simple dose imaging. Magnetic resonance based polymer dosimetry (MRPD) appears to be well suited to three-dimensional high resolution relative dosimetry but the spatial resolution based on a systematic modulation transfer function (MTF) approach has not yet been investigated. We offer a theoretical construct for addressing the spatial resolution in different dose imaging systems, i.e. the dose modulation transfer function (DMTF) approach, an experimental realization of this concept with a phantom and quantitative comparisons between two dosimetric systems: polymer gel and film dosimetry. Polymer gel samples were irradiated by Co-60 photons through an absorber grid which is characterized by periodic structures of different spatial period (a), the smallest one at width of a/2 = 280 µm. The modulation in dose under the grid is visualized via calibrated, high resolution, parameter-selective (T2) and dose images based on multi-echo MR imaging. The DMTF is obtained from the modulation depth of the spin–spin relaxation time (T2) after calibration. Voxel sizes below 0.04 mm3 could be achieved, which are significantly smaller than those reported in MR based dose imaging on polymer gels elsewhere, using a powerful gradient system and a highly sensitive small birdcage resonator on a whole-body 3T MR scanner. Dose modulations at 22% of maximum dose amplitude could be observed at about 2 line pairs per mm. The polymer DMTF results are compared to those of a typical clinical film-scanner system. This study demonstrates that MR based gel dosimetry at 200 µm pixel resolution might even be superior, with reference to relative spatial resolution, to the results of a standard film-scanner system offering a nominal scan resolution of 200 µm.

Imaging the internal structure of the rat cochlea using optical coherence tomography at 0.827 μm and 1.3 μm

Objective The purpose of this study was to use high-speed optical coherence tomography (OCT) to obtain cross-sectional images of the rat cochlea. Study design and methods The cochleae of Sprague- Dawley rats were imaged within 2 to 4 hours after death. Specimens were prepared by removing the bulla to expose the mesotympanum; some images were obtained in intact temporal bones removed from the cranium. The central element of an OCT imaging device is a Michelson interferometer combined with a low-coherence light source. This study used 2 OCT systems with different light sources: 1) a semiconductor optical amplifier operating and 2) a superluminescent diode with peak emissions wavelengths of 1.3 μm and 827 nm, respectively. Images (1.87 × 2.00 mm or 1.87 × 1.00 mm, 10 × 10 μm pixel resolution) were acquired at a frame rate of 1 Hz. Cross-sectional images at 100-μm increments were obtained from a medial-to-lateral direction. Results The scala vestibuli, scala media, scala tympani, modiolus, spiral ligament, and several turns of the cochlea were identified. Conclusion These images reflect the ability of OCT to provide images of the internal cochlea structure with micron scale resolution and at near-real time frame rates.

Microfabrication by ion milling: The lathe technique

Several novel and unusual microstructures were made by focused ion beam milling. These microstructures include needles, hooks, forks, and similar shapes resulting from 360° access afforded to the ion beam by a rotation mounting device. The lengths of the microstructures are in the 10 μm range, and the thicknesses all in the 1–2 μm range. Similar procedures were used to make prototype stylus geometries for scanning probe microscopy applications. Resolution limits to the fabrication process come mainly from the grain structure of the material being sputtered. The ion beam is 0.3 μm in diameter, and 0.08 μm pixel resolution for ion beam location was used to generate the objects. Start-to-finish fabrication time for most of the objects made was ∼2 h without any effort to streamline the process.