[Study on optical system of medical fiberscope].
The optical imaging principles of medical fiberscoptic endoscopes and their design featuies are described with GIS-105 Fibreoptic Endoscope as an example in this paper.
Endoscopes↗
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Biexponential diffusion attenuation in the rat spinal cord: computer simulations based on anatomic images of axonal architecture.
Water diffusion in neurological tissues is known to possess multicomponent diffusion behavior. The fractions of fast and slow apparent diffusion components have often been attributed to the volume fractions of extracellular space (ECS) and intracellular space (ICS) although diffusion fractions are at variance with the tissue compartment volume ratios. In this article this puzzle was examined with a finite difference diffusion simulation model on the basis of optical images from sectioned rat spinal cord. Here the results show that assignment of fractions obtained from biexponential fits of fast and slow diffusion attenuation to ECS and ICS volume ratios is not correct. Rather, the observed multicomponent diffusion behavior is caused by motional restriction and limited intercompartmental water exchange in that at long diffusion times diffusion attenuation is shown to become monoexponential. Although the measured apparent diffusion fractions also depend on T2 relaxation time of water protons in the various compartments, the sensitivity to T2 is small and thus T2 differences are unlikely to explain the mismatch between apparent diffusion fractions and cellular volume fractions.
Animals↗
In vivo imaging of gene and cell therapies.
Molecular imaging can be broadly defined as the in vivo characterization and measurement of biological processes at the cellular and molecular level. In contrast to commonly used clinical imaging, it sets forth to probe the molecular abnormalities that are the basis of disease, rather than imaging the end effects of these molecular alterations. Development of new imaging technologies requires a multidisciplinary collaboration between biologists, chemists, physicists, and imaging scientists to create novel agents, signal amplification strategies, and imaging techniques that successfully address these questions. In this article we attempt to present some of the recent developments and show how molecular imaging can be used, at least experimentally, to assess specific molecular targets for gene- and cell-based therapies. In particular, we place emphasis on the development and use of experimental small-animal models, which are particularly inclined toward this approach, primarily in combination with magnetic resonance (MR), radionuclide, and optical imaging. In the future, specific imaging of disease targets will allow earlier detection and characterization of disease, as well as earlier and direct molecular assessment of treatment efficacy.
Animals↗
Intrinsic optical signals from rat primary auditory cortex in response to sound stimuli presented to contralateral, ipsilateral and bilateral ears.
In the auditory cortex, primitive features of acoustic stimuli are represented for auditory scene analysis. A typical example of a feature representation is the tonotopic map, in which sound frequencies are spatially arranged in an orderly manner. Some neurons in the auditory cortex are sensitive to sound source location, which is another important feature for auditory scene analysis. In the present study, using the intrinsic optical imaging technique, we attempted to visualize the two-dimensional pattern of neuronal population responses in the primary auditory cortex of rats to pure tones presented at various frequencies and sound intensities. The observed arrangements of sound frequencies were consistent with those obtained by electrophysiological mapping, which indicates that our intrinsic optical recording can visualize populational responses of neurons. We also found different temporal patterns of intrinsic signals elicited in response to contralateral, ipsilateral, and bilateral ear stimulations. Finally we try to explain the observed differential time courses of intrinsic signal responses from the theoretical point of view on the conduction of neural activities, based on the so far anatomically identified neural pathways in the rodent auditory system.
Acoustic Stimulation↗
Optical intrinsic signal imaging responses are modulated in rodent somatosensory cortex during simultaneous whisker and forelimb stimulation.
Optical intrinsic signal imaging (OIS) was used to investigate physiologic interactions between spatially and functionally distinct cortical somatosensory systems. The OIS response magnitude was evaluated after simultaneous stimulation of single whiskers and forelimb digits. Whisker C1 was deflected at a frequency of 10 Hz for 2 seconds while low- or high-intensity vibratory stimuli were applied to forelimb digits. The OIS responses to simultaneous whisker and forelimb stimulation were compared with lone whisker stimulated controls. Overall, addition of a second stimulus caused decreases in barrel cortex response magnitude. Three different response patterns were detected within individual trial sets. Modulation of barrel cortex evoked potentials provided evidence that changes in OIS responses observed here may be partially influenced by vascular responses to changes in neuronal activity. However, OIS responses in the barrel region during lone forelimb stimulation that were unaccompanied by evoked potentials suggested the possibility of independent vascular dynamic influences on response modulation. This study demonstrates that cortical responses at the level of primary sensory processing may be significantly influenced by activity in adjacent regions. Furthermore, it reveals that vascular and neuronal characteristics of interregional modulation do not co-localize and may produce responses in which one component increases while the other decreases.
Animals↗
Olfactory input to the parahippocampal region of the isolated guinea pig brain reveals weak entorhinal-to-perirhinal interactions.
The processing of olfactory inputs by the parahippocampal region has a central role in the organization of memory in mammals. The olfactory input is relayed to the hippocampus via interposed synapses located in the piriform and entorhinal cortices. Whether olfactory afferents directly or indirectly project to other areas of the parahippocampal region beside the entorhinal cortex (EC) is uncertain. We performed an electrophysiological and imaging study of the propagation pattern of the olfactory input carried by the fibres that form the lateral olfactory tract (LOT) into the parahippocampal region of the in vitro isolated guinea pig preparation. Laminar analysis was performed on field potential depth profiles recorded with 16-channel silicon probes at different sites of the insular-parahippocampal cortex. The LOT input induced a large amplitude polysynaptic response in the lateral EC. Following appropriate LOT stimulation, a late response generated by the interposed activation of the hippocampus was observed in the medial EC. LOT stimulation did not induce any local response in area 36 of the perirhinal cortex (PRC), while a small amplitude potential with a delay similar to the lateral EC response was inconsistently observed in PRC area 35. No PRC potentials were observed following the responses evoked by LOT stimulation in either the lateral or the medial EC. These findings were substantiated by current source density analysis of PRC laminar profiles. To further verify the absence of EC-to-PRC field interactions after LOT stimulation, high-resolution optical imaging of neuronal activity was performed after perfusion of the isolated brain with the voltage-sensitive dye RH-795. The optical recordings confirmed that olfactory-induced activity in the EC does not induce massive PRC activation. The present findings suggest that the olfactory input into the parahippocampal region is confined to the entorhinal cortex. The results also imply that, as demonstrated for the PRC-to-EC pathway, the propagation of neuronal activity from the EC to the PRC is hindered, possibly by a powerful inhibitory control generated within the EC.
Animals↗
Selective imaging of biofilms in porous media by NMR relaxation.
Nuclear magnetic resonance imaging (NMRI) techniques were employed to identify and selectively image biological films (biofilm) growing in aqueous systems. Biofilms are shown to affect both the longitudinal (T1) and transverse (T2) NMR relaxation time values of proximal water hydrogens. Results are shown for biofilm growth experiments performed in a transparent parallel-plate reactor. A comparison of biofilm distributions by both NMR and optical imaging yielded general agreement for both an open-flow system and an idealized porous system (the reactor without and with packed glass beads, respectively). The selective imaging of biofilm by relaxation NMRI is dependent upon the resolution of relaxation times for the fluid phases, dynamic range, and signal-to-noise ratio. For open-flow systems, the use of a rapid and quantitative T2-sorted NMRI technique was preferred. For porous systems where T2 values are generally more similar, a T1-weighted technique was preferred.
Biofilms↗
Noninvasive of adenovirus tumor retargeting in living subjects by a soluble adenovirus receptor-epidermal growth factor (sCAR-EGF) fusion protein.
PURPOSE: To demonstrate that non-invasive bioluminescent imaging can monitor restricted expression from a nonreplicating adenovirus in which the cyclooxygenase-2 (COX-2) promoter drives firefly luciferase. PROCEDURES: Adenovirus in which the COX-2 promoter drives the firefly luciferase imaging gene was injected intratumorally into xenografts that express relatively low and relatively high levels of COX-2. Adenovirus that expresses Renilla Luciferase from the cytomegalovirus early promoter was co-injected, to normalize for injection, leakage, vascularization, etc. COX-2 restricted firefly luciferase and global Renilla Luciferase activities were measured by optical imaging techniques both in vivo and in isolated tissues. RESULTS: Dramatic reduction in hepatic luciferase expression after intravenous viral injection can be imaged non-invasively in living animals. Following intratumoral injection, luciferase levels in tumor xenografts that express differing endogenous COX-2 levels reflect the luciferase levels observed when these cells are infected in cell culture. Essentially no luciferase expression is observed in liver following intratumoral injection. CONCLUSION: Both tissue restricted expression and transcriptional redirection to tumors expressing COX-2 can be imaged non-invasively following injection of Adenovirus expressing firefly luciferase from the COX-2 promoter.
Adenoviridae↗
Image restoration with the Viterbi algorithm.
The Viterbi algorithm (VA) is known to given an optimal solution to the problem of estimating one-dimensional sequences of discrete-valued pixels corrupted by finite-support blur and memoryless noise. A row-by-row estimation along with decision feedback and vector quantization is used to reduce the computational complexity of the VA and allow the estimation of two-dimensional images. This reduced-complexity VA (RCVA) is shown to produce near-optimal estimation of random binary images. In addition, simulated restorations of gray-scale images show the RCVA estimates to be an improvement over the estimates obtained by the conventional Wiener filter (WF). Unlike the WF, the RCVA is capable of superresolution and is adaptable for use in restoring data from signal-dependent Poisson noise corruption. Experimental restorations of random binary data gathered from an optical imaging system support the simulations and show that the RCVA estimate has fewer than one third of the errors of the WF estimate.
Algorithms↗
Visualizing gene expression by whole-body fluorescence imaging.
Transgene expression in intact animals now can be visualized by noninvasive techniques. However, the instruments and protocols developed so far have been formidable and expensive. We describe here a system for rapidly visualizing transgene expression in major organs of intact live mice that is simple, rapid, and eminently affordable. Green fluorescent protein (GFP) is expressed in the cells of brain, liver, pancreas, prostate, and bone, and its fluorescence is encoded in whole-body optical images. For low-magnification images, animals are illuminated atop a fluorescence light box and directly viewed with a thermoelectrically cooled color charge-coupled device camera. Higher-magnification images are made with the camera focused through an epi-fluorescence dissecting microscope. Both nude and normal mice were labeled by directly injecting 8 x 10(10) plaque-forming units/ml of adenoviral GFP in 20-100 microl PBS and 10% glycerol into either the brain, liver, pancreas, prostate, or bone marrow. Within 5-8 h after adenoviral GFP injection, the fluorescence of the expressed GFP in brain and liver became visible, and whole-body images were recorded at video rates. The GFP fluorescence continued to increase for at least 12 h and remained detectable in liver for up to 4 months. The system's rapidity of image acquisition makes it capable of real-time recording. It requires neither exogenous contrast agents, radioactive substrates, nor long processing times. The method requires only that the expressed gene or promoter be fused or operatively linked to GFP. A comparatively modest investment allows the study of the therapeutic and diagnostic potential of suitably tagged genes in relatively opaque organisms.
Adenoviridae↗
Intralamellar relationships within the collagenous architecture of the annulus fibrosus imaged in its fully hydrated state.
The anisotropic, inhomogeneous, multiply collagenous architecture of the annulus reflects the complex pattern of mainly tensile stresses developed in this region of the disc during normal function. Structural and mechanical responses of fully hydrated in-plane sections taken from within single lamellae of the outer annulus of healthy bovine caudal discs have been investigated using a micromechanical technique in combination with simultaneous high-resolution differential interference contrast optical imaging. Responses both along and across (i.e. transverse to) the primary direction of the mono-array of collagen fibres were studied. Stretching along the alignment direction revealed a biomechanical response consistent with the behaviour of an array whose overall strength is governed primarily by the strength of embedding of the fibres in the vertebral endplates, rather than from interfibre cohesion along their length. The mono-aligned array, even when lacerated, is highly resistant to any further tearing across the alignment direction. Although not visible in the relaxed mono-arrays, transverse stretching revealed a highly complex set of interconnecting structures embodying hierarchical relationships not previously revealed. It is suggested that these structures might play an important role in the containment under pressure of the nuclear contents. The dramatic differences in rupture behaviour observed along vs. across the primary fibre direction are consistent with the known clinical consequences arising from varying degrees of annular wall damage, and might also explain various types of disc herniation. The lamellar architecture of the healthy disc revealed by this investigation provides an important reference framework for exploring structural changes associated with disc trauma and degeneration.
Animals↗
CFD simulation of aggregation and breakage processes in laminar Taylor-Couette flow.
An experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of approximately 10 microm latex spheres suspended in an aqueous solution undergoing laminar Taylor-Couette flow was carried out according to the following program. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry experiments. Subsequently, the quadrature method of moments (QMOM) was implemented into the CFD code to obtain predictions for mean particle size that account for the effects of local shear rate on the aggregation and breakage. These predictions were then compared with experimental data for latex sphere aggregates (using an in situ optical imaging method) and with predictions using spatial average shear rates. The mean particle size evolution predicted by CFD and QMOM using appropriate kinetic expressions that incorporate information concerning the particle morphology (fractal dimension) and the local fluid viscous effects on aggregation collision efficiency match well with the experimental data.
Biophysics↗
CFD simulation of shear-induced aggregation and breakage in turbulent Taylor-Couette flow.
An experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of approximately 10 microm latex spheres suspended in an aqueous solution undergoing turbulent Taylor-Couette flow was carried out. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry experiments. Subsequently, the quadrature method of moments (QMOM) was implemented into the CFD code to obtain predictions for mean particle size that account for the effects of local shear rate on the aggregation and breakage. These predictions were then compared with experimental data for latex sphere aggregates (using an in situ optical imaging method). Excellent agreement between the CFD-QMOM and experimental results was observed for two Reynolds numbers in the turbulent-flow regime.
Journal Article↗
High-resolution imaging of bone precursor cells within the intact bone marrow cavity of living mice.
Bone precursor cells (BPCs) play a critical role in bone maintenance and regeneration. Currently, no tool exists to study BPCs or other bone marrow cell types directly within their complex microenvironment. Here, we describe in vivo magnetic resonance imaging (MRI) of anatomical structures inside the medullary cavity of the mouse femur. We demonstrate that BPCs passively labeled with iron oxide-containing particles can be monitored by MRI within the intact bone marrow at an in-plane resolution of 43x25 microm. Anatomical detail provided by MRI is complemented by functional optical imaging of reporter gene expression. Single-cell dual iron oxide-reporter gene labeling has potential for combined cell tracking and cell biology studies. In summary, we describe a versatile platform suitable for studying the biology of many bone marrow cell types in living bone.
Animals↗
Converting to an optical disk system.
Optical disk technology is a move to the future. It is an exciting time to brave the new frontiers and change from a manual to an optical disk system. Since the technology is so new in health care environments and because each facility is unique, there is no "right" way to do optical imaging. Opportunities flourish to "do it your way." The process is challenging and time consuming, but the rewards of providing health information users with a quality record system make the investment worthwhile. Complete, thorough planning and education will ease the transition to tomorrow's system. Stop dreaming, make a commitment, and move forward--optical disk systems in health care are achievable successes!
Capital Expenditures↗
Functional imaging with cellular resolution reveals precise micro-architecture in visual cortex.
Neurons in the cerebral cortex are organized into anatomical columns, with ensembles of cells arranged from the surface to the white matter. Within a column, neurons often share functional properties, such as selectivity for stimulus orientation; columns with distinct properties, such as different preferred orientations, tile the cortical surface in orderly patterns. This functional architecture was discovered with the relatively sparse sampling of microelectrode recordings. Optical imaging of membrane voltage or metabolic activity elucidated the overall geometry of functional maps, but is averaged over many cells (resolution >100 microm). Consequently, the purity of functional domains and the precision of the borders between them could not be resolved. Here, we labelled thousands of neurons of the visual cortex with a calcium-sensitive indicator in vivo. We then imaged the activity of neuronal populations at single-cell resolution with two-photon microscopy up to a depth of 400 microm. In rat primary visual cortex, neurons had robust orientation selectivity but there was no discernible local structure; neighbouring neurons often responded to different orientations. In area 18 of cat visual cortex, functional maps were organized at a fine scale. Neurons with opposite preferences for stimulus direction were segregated with extraordinary spatial precision in three dimensions, with columnar borders one to two cells wide. These results indicate that cortical maps can be built with single-cell precision.
Analysis of Variance↗
Optical recording of spontaneous respiratory neuron activity in the rat brain stem.
We report on the optical imaging of spontaneous respiratory neuron bursts in the ventrolateral medulla (VLM) of medullary slices or brain stem-spinal cord preparations. A medullary slice with a thickness of 1.0-1.4 mm or brain stem-spinal cord from 0- to 4-d-old rats was stained with fluorescent voltage-sensitive dye, RH795. Optical signals were recorded as a fluorescence change by using an optical recording apparatus with a 128 x 128 photodiode array and a maximum time resolution of 0.6 ms. Motoneuronal activity was simultaneously recorded at the hypoglossal nerve roots or fourth cervical ventral roots. Fluorescence changes corresponding to the spontaneous inspiratory burst activity were detected in the hypoglossal nucleus and VLM in slice preparations, and in a limited area extending rostrocaudally in the VLM of the brain stem-spinal cord preparation. These measurements did not require signal averaging by multiple trials. Results suggest that inspiratory neurons are localized in more compact form at the level of the nucleus ambiguous than at the more rostral VLM, and that peak activity during the inspiratory phase propagates from the caudal to the rostral VLM. In 60% of brain stem-spinal cord preparations, weak and scattered fluorescence changes preceding the inspiratory burst activity were detected more predominantly in the rostral part of the VLM. The present findings show the feasibility of optical recordings for the in vitro analysis of spontaneous respiratory neuron activity in the medulla.
Animals↗
A far-field-viewing sensor for making analytical measurements in remote locations.
We demonstrate a far-field-viewing GRINscope sensor for making analytical measurements in remote locations. The GRINscope was fabricated by permanently affixing a micro-Gradient index (GRIN) lens on the distal face of a 350-micron-diameter optical imaging fiber. The GRINscope can obtain both chemical and visual information. In one application, a thin, pH-sensitive polymer layer was immobilized on the distal end of the GRINscope. The ability of the GRINscope to visually image its far-field surroundings and concurrently detect pH changes in a flowing stream was demonstrated. In a different application, the GRINscope was used to image pH- and O2-sensitive particles on a remote substrate and simultaneously measure their fluorescence intensity in response to pH or pO2 changes.
Chemistry Techniques, Analytical↗