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PubMed2003

Single-camera method to determine the optical axis position of ellipsoidal drops.

The sizing of droplets by optical imaging typically requires a small depth of field so that variations in the magnification ratio are minimized. However, if the location of the drop along the optical axis can be determined, a variable magnification ratio can be imposed on each imaged drop, and the depth of field can be increased. Previous research suggested that droplet location can be determined with a characteristic of droplet images that is obtained when the droplet is illuminated from behind. In this prior research, the method was demonstrated with spherical glass objects to simulate raindrops. Raindrop are known to deviate significantly from a spherical shape, especially when the drop size is large. We demonstrate the ability to locate the position of objects that deviate from sphericity. Deformed water drops and glass ellipsoids are tested, along with glass spheres. The role of refractive index is also discussed.

Journal Article↗
PubMed2002

In vivo molecular-genetic imaging.

Noninvasive in vivo molecular-genetic imaging has developed over the past decade and involves nuclear (PET, gamma camera), magnetic resonance, and in vivo optical imaging systems. Although three different imaging strategies - "direct," "indirect" and "surrogate" - are being used, most current in vivo molecular imaging strategies are "indirect" and involve the coupling of a "reporter gene" with a complimentary "reporter probe." Imaging the level of probe accumulation provides indirect information related to the level of reporter gene expression. Reporter gene constructs are driven by upstream promoter/enhancer elements; reporter gene expression can be "constitutive" leading to continuous transcription and used to identify the site of transduction and to monitor the level and duration of gene (vector) activity. Alternatively, reporter gene expression can be "inducible" leading to controlled gene expression. Controlled gene expression can be tissue-specific and/or responsive to the level of endogenous promoters and transcription factors. Several examples of imaging endogenous biological processes in animals using reporter constructs, radiolabeled probes and PET imaging are reviewed, including: 1) imaging transcriptional regulation (e.g., p53-dependent gene expression), 2) imaging weak promoters (cis- vs. trans-reporter configurations), 3) imaging post-transcriptional regulation of gene expression, 4) imaging protein-protein interactions. The development of versatile and sensitive assays that do not require tissue sampling will be of considerable value for monitoring molecular-genetic and cellular processes in animal models of human disease, as well as for studies in human subjects in the future. Non-invasive imaging of molecular-genetic and cellular processes will compliment established ex vivo molecular-biological assays that require tissue sampling, and will provide a spatial as well as a temporal dimension to our understanding of various diseases.

Animals↗
PubMed2004

Different effect of dioptric defocus vs. light scatter on the pattern electroretinogram (PERG).

To assess the quantitative effect of optical deficiencies on the Pattern Electroretinogram (PERG), we degraded the optical imaging onto the retina by dioptric defocus (+1.75-5 D), and by scatter transparencies. With optimal and degraded optics we measured the visual acuity and the steady-state PERG, evoked by checkerboards (check size 0.2-16 degrees), and flash stimuli. When the two optical degradation methods were equated for acuity, scatter transparencies reduced the PERG amplitude more than defocus. For scatter transparencies, there was a significant (p < 0.001) effect at 16 degrees, escalating for smaller checks. For defocus, significant effects were only observed for check sizes of 1.6 degrees and smaller. We explain the differences between the two blur techniques by their differing angular scattering functions. Dioptrical defocus leads to an underestimation of the effect of media opacities on the PERG. For the clinically relevant check size of 0.8 degrees, halving acuity reduces the amplitude by 15% with defocus and by 30% with scatter. With an acuity of 0.8 or higher, no clinically relevant effect of suboptimal refraction is seen.

Electroretinography↗
PubMed1998

Filter matrix estimation in automated DNA sequencing.

In four-color fluourescence-based automated DNA sequencing, a 4 x 4 filter matrix parameterizes the relationship between the dye-intensity signals of interest and the data collected by an optical imaging system. The filter matrix is important because the estimated DNA sequence is based on the dye intensities that can only be recovered via inversion of the matrix. In this paper, we present a calibration method for the estimation of the columns of this matrix, using data generated through a special experiment in which DNA samples are labeled with only one fluorescent dye at a time. Simulations and applications of the method to real data are provided, with promising results.

Algorithms↗
PubMed2004

Imaging in Oncology--SMi's Inaugural Conference. 17-18 March 2004, London, UK.

This was the first SMi meeting on the subject of imaging in oncology trials, and attracted an enthusiastic audience of approximately 40 delegates from industry and academia, including speakers who are highly respected in their fields. The meeting covered the use of magnetic resonance imaging and spectroscopy, positron emission tomography, ultrasound, computed tomography, single photon emission computed tomography, gamma-camera and optical imaging in clinical oncology trials. While these modalities have been used clinically for decades, their use in oncology trials has not been recognized as potential measures of surrogate endpoints, biomarkers and pharmacodynamic endpoints. A number of key issues were discussed during the meeting, including the necessity to standardize, validate and evaluate these imaging techniques before they can be recognized and widely used. Also discussed at some length were the difficulties and problems associated with not following imaging protocols in multicenter trials, which can lead to unusable data and wasted time and resources.

Animals↗
PubMed2002

Comparative optical coherence tomography imaging of human esophagus: how accurate is localization of the muscularis mucosae?

BACKGROUND: Early diagnosis of esophageal cancer limited to the mucosa allows local endoscopic treatment and thereby improves prognosis. Optical coherence tomography images of normal human esophageal tissue obtained with 2 systems with light sources that provide different wavelengths (800 nm and 1275 nm) were compared with histology to determine which wavelength is best suited for detailed optical coherence tomography imaging of the esophageal wall, and to precisely localize the muscularis mucosae. METHODS: Within 1 hour of surgical resection, an esophageal specimen was cleaned of excess blood with saline solution and soaked in formalin for a minimum of 48 hours. After optical coherence tomography imaging, the specimen was prepared for routine histologic assessment. To precisely localize the different layers of the esophageal wall on an optical coherence tomography image, well-defined structures within the esophageal wall were sought. RESULTS: The 1275 nm system with 12 mm resolution was superior in terms of imaging depth. As compared with histology, the 4 microm resolution of the 800 nm system made fine detail more visible. With minimal experience, the muscularis mucosae could be recognized with either system as a hyporeflective layer with a diameter of around 180 microm. CONCLUSIONS: Based on appearance and location of morphologic landmarks, layers of normal esophageal wall, specifically, the location and extent of the muscularis mucosae, could be recognized by using both the 800 nm and 1275 nm optical coherence tomography system. Although different conditions may be operative in vivo, the present ex vivo study further verifies by precise interpretation that optical coherence tomography provides precise images of the esophageal wall.

Esophagus↗
PubMed1999

Further evaluation of the initial negative response in functional magnetic resonance imaging.

The initial negative response (i.e., the dip) in the functional MR signal at stimulus onset has aroused much interest. Such a response is consistent with optical imaging data and can be potentially mapped to generate spatially more specific maps. However, there are still controversies regarding the exact origin of the initial response. In particular, experimental reports of its echo-time dependence have been inconsistent. Furthermore, several investigators have suggested the possibility of an apparent dip that may arise artifactually when the interstimulus interval (ISI) is not sufficiently long. The present study investigates the echo-time dependence of the initial response and the effect of the ISI on the initial response. Experimental results obtained at TEs of 21, 30, and 45 msec demonstrate that the initial dip has a TE dependence that is in agreement with a T2* contrast, and thereby consistent with a blood oxygenation level-dependent origin. At an ISI of 90 sec, a statistically significant initial negative response was detected and shown to be indistinguishable from that observed at an ISI of 45 sec, which was used in our previous studies, indicating that the initial negative response observed at 4 T is not a consequence of short ISI.

Echo-Planar Imaging↗
PubMed2001

Imaging of neuronal activity in the gut.

Over the past few years, several groups have used voltage-sensitive dyes or calcium-indicator dyes to optically monitor the activity of several enteric neurons simultaneously. Some of the initial practical problems have been solved and these studies have successfully shown the spread of electrical activation within the enteric neuronal circuitry in cultures and in ex vivo specimens. The basic mechanisms underlying voltage-sensitive dye or calcium-indicator signals and their relation to changes in membrane potential need further investigation. Application of these techniques will provide more insight into neuronal interaction and spread of activation. The ability to simultaneously record activity in other cells in the same focal plane offers the potential to investigate how the integrated neuronal circuits are linked to effector cells in their close neighbourhood. Progress in optical imaging of enteric neuronal activity should ultimately lead to a better knowledge of gastrointestinal physiology and pathophysiology.

Animals↗
PubMed2004

Comparison of the GDx VCC scanning laser polarimeter, HRT II confocal scanning laser ophthalmoscope, and stratus OCT optical coherence tomograph for the detection of glaucoma.

OBJECTIVE: To compare the abilities of current commercially available versions of 3 optical imaging techniques: scanning laser polarimetry with variable corneal compensation (GDx VCC), confocal scanning laser ophthalmoscopy (HRT II [Heidelberg Retina Tomograph]), and optical coherence tomography (Stratus OCT) to discriminate between healthy eyes and eyes with glaucomatous visual field loss. METHODS: We included 107 patients with glaucomatous visual field loss and 76 healthy subjects of a similar age. All individuals underwent imaging with a GDx VCC, HRT II, and fast retinal nerve fiber layer scan with the Stratus OCT as well as visual field testing within a 6-month period. Receiver operating characteristic curves and sensitivities at fixed specificities (80% and 95%) were calculated for parameters reported as continuous variables. Diagnostic categorization (outside normal limits, borderline, or within normal limits) provided by each instrument after comparison with its respective normative database was also evaluated, and likelihood ratios were reported. Agreement on categorization between methods (weighted kappa) was assessed. RESULTS: After the exclusion of subjects with unacceptable images, the final study sample included 141 eyes of 141 subjects (75 with glaucoma and 66 healthy control subjects). Mean +/- SD mean deviation of the visual field test result for patients with glaucoma was -4.87 +/- 3.9 dB, and 70% of these patients had early glaucomatous visual field damage. No statistically significant difference was found between the areas under the receiver operating characteristic curves (AUCs) for the best parameters from the GDx VCC (nerve fiber indicator, AUC = 0.91), Stratus OCT (retinal nerve fiber layer inferior thickness, AUC = 0.92), and HRT II (linear discriminant function, AUC = 0.86). Abnormal results for each of the instruments, after comparison with their normative databases, were associated with strong positive likelihood ratios. Chance-corrected agreement (weighted kappa) among the 3 instruments ranged from moderate to substantial (0.50-0.72). CONCLUSIONS: The AUCs and the sensitivities at high specificities were similar among the best parameters from each instrument. Abnormal results (as compared with each instrument's normative database) were associated with high likelihood ratios and large effects on posttest probabilities of having glaucomatous visual field loss. Calculation of likelihood ratios may provide additional information to assist the clinician in diagnosing glaucoma with these instruments.

Aged↗
PubMed2006

A light-emitting diode light source for imaging of neural activities with voltage-sensitive dyes.

We tested the possibility of using a high-power monochromatic InGaN light-emitting diode (LED) as an excitation light source for real-time optical imaging using the voltage-sensitive dye RH-795. Driven with a custom-designed, non-feedback-controlled constant-current circuit, the LED generated stable light with rapid on/off. The LED was comparable with commonly used halogen lamps in exciting RH-795. Acoustically evoked responses in the auditory cortex recorded with the two light sources were highly similar. Our results thus suggest that a high-power LED can be successfully used as an excitation light source for voltage-sensitive dyes, without the need of optical filters and shutters.

Animals↗
PubMed2004

Association of magnetic resonance imaging of anterior optic pathway with glaucomatous visual field damage and optic disc cupping.

PURPOSE: To investigate the association of magnetic resonance imaging (MRI) of anterior optic pathway with glaucomatous visual field damage and optic disc cupping. SUBJECTS AND METHODS: Twenty-three healthy volunteers (controls) and 31 glaucoma patients (14 with primary open angle glaucoma and 17 with normal tension glaucoma) were enrolled. All the participants showed no abnormal signs in their intracranial space and optic tract causing optic nerve atrophy and visual field defect, as confirmed by MRI. Multislice T1-weighted spin-echo imaging was performed in the sagittal plane followed by the coronal plane. MRI enabled the evaluation of the diameter of the optic nerve located in the retro-bulb space and the height of the optic chiasm in an observer-masked fashion. The MRI data were compared with the mean deviation (MD) score of the full threshold static visual field test and the optic cup-disc ratio (C/D ratio). RESULTS: The optic nerve diameter was significantly smaller in glaucoma patients (2.25 +/- 0.33 mm) than in controls (2.47 +/- 0.24 mm) and the height of the optic chiasm was significantly shorter in glaucoma patients (2.12 +/- 0.37 mm) than in controls (2.77 +/- 0.36 mm). The optic nerve diameter showed significant correlation with MD score (r = 0.547, P = 0.001) and C/D ratio (r = 0.407, P = 0.009). These correlations are similar to that between MD score and C/D ratio (r = 0.490, P = 0.001). The height of the optic chiasm showed significant correlation with MD score (r = 0.503, P = 0.01) and low correlation with C/D ratio (r = 0.339, P = 0.113). CONCLUSION: Glaucoma affects the anterior visual pathway anterogradely at least up to the optic chiasm, and these morphologic changes in the anterior visual pathway are correlated with glaucomatous optic nerve damage. MRI of the anterior visual pathway may be a good tool for evaluating glaucomatous damage objectively.

Adult↗
PubMed2004

Dynamic light scattering microscopy. A novel optical technique to image submicroscopic motions. I: theory.

The theoretical basis of an optical microscope technique to image dynamically scattered light fluctuation decay rates (dynamic light scattering microscopy) is developed. It is shown that relative motions between scattering centers even smaller than the optical resolution of the microscope are sufficient to produce significant phase variations resulting in interference intensity fluctuations in the image plane. The timescale and time dependence for the temporal autocorrelation function of these intensity fluctuations is derived. The spatial correlation distance, which reports the average distance between constructive and destructive interference in the image plane, is calculated and compared with the pixel size, and the distance dependence of the spatial correlation function is derived. The accompanying article in this issue describes an experimental implementation of dynamic light scattering microscopy.

Cell Movement↗
PubMedDate not supplied

Three-dimensional optical tomographic brain imaging in small animals, part 2: unilateral carotid occlusion.

This is the second part of a two-part study that explores the feasibility of 3-D, volumetric brain imaging in small animals by optical tomographic techniques. In part 1, we demonstrated the ability to visualize global hemodynamic changes in the rat head in response to elevated levels of CO(2) using a continuous-wave instrument and model-based iterative image reconstruction (MOBIIR) algorithm. Now we focus on lateralized, monohemispherically localized hemodynamic effects generated by unilateral common carotid artery (CCA) occlusion. This illustrates the capability of our optical tomographic system to localize and distinguish hemodynamic responses in different parts of the brain. Unilateral carotid occlusions are performed in ten rodents under two experimental conditions. In the first set of experiments the normal systemic blood pressure is lowered to 50 mmHg, and on unilateral carotid occlusion, we observe an ipsilateral monohemispheric global decrease in blood volume and oxygenation. This finding is consistent with the known physiologic response to cerebral ischemia. In a second set of experiments designed to observe the spatial-temporal dynamics of CCA occlusion at normotensive blood pressure, more complex phenomena are observed. We find three different types of responses, which can be categorized as compensation, overcompensation, and noncompensation.

Algorithms↗
PubMed2002

Imaging gene expression and endogenous molecular processes: molecular imaging.

Noninvasive molecular imaging has developed over the past decade and involves nuclear (positron emission tomography [PET], gamma camera), magnetic resonance, and optical imaging systems. Most current molecular imaging strategies are "indirect" and involve the coupling of a "reporter gene" with a complementary "reporter probe." Imaging the level of probe accumulation provides indirect information related to the level of reporter gene expression. Reporter gene constructs are driven by upstream promoter/enhancer elements; reporter gene expression can be leading to continuous transcription and used to identify the site of transduction and to monitor the level and duration of gene (vector) activity. Alternatively, reporter gene expression can be leading to controlled gene expression, or reporter genes can function as a "sensor" to monitor the level of endogenous promoters and transcription factors. The development of versatile and sensitive assays that do require tissue sampling will be of considerable value for monitoring molecular-genetic and cellular processes in animal models of human disease, as well as for studies in human subjects in the future. Noninvasive imaging of molecular-genetic and cellular processes will complement established molecular-biologic assays that require tissue sampling, and will provide a spatial as well as a temporal dimension to our understanding of various diseases. Several examples of imaging endogenous biologic processes in animals using reporter constructs, radiolabeled probes, and PET imaging are reviewed (e.g., p53-dependent gene expression, T-cell receptor-dependent activation of T-lymphocytes, and preliminary studies of endogenous HIF-1alpha expression). Issues related to the translation of noninvasive molecular imaging technology into the clinic are also discussed.

Animals↗
PubMed2001

Examination of in vitro chemosensitivity test using collagen gel droplet culture method with colorimetric endpoint quantification.

To develop a simpler method of performing the collagen gel droplet-embedded culture drug sensitivity test (CD-DST), we examined the introduction of colorimetric quantitative determination of images for evaluation of anticancer effect against cancer cells alone in the presence of fibroblasts, based on differences in proliferative morphology and stainability with neutral red of cells within collagen gel drops determined using a video-microscope and NIH Image software. In examinations using a human cancer cell line and a fibroblast cell line, a high degree of linearity between number of cancer cells and image-optical density was found within the range of 10(2) - 10( 6) cells / droplet (r (2) = 0.933). Using NIH Image, fibroblast cells could be eliminated at a cut-off value of 128, and an immunocytochemical method demonstrated that the cells eliminated from the image were indeed fibroblasts, and those remaining were cancer cells. CD-DST was carried out with mixtures of cancer cells with fibroblasts at various ratios, and the feasibility of evaluating anticancer activity in cancer cells alone with no effect of fibroblasts at any mixing ratio was confirmed. In addition, for CD-DST of primary cell cultures of human lung cancers collected at the time of surgery, a high correlation between results obtained with the volume supplementation method, a current cell quantification method, and those with the imaging colorimetric quantification method was obtained (r = 0.933). These results indicate that introduction of imaging colorimetric quantification utilizing NIH Image makes CD-DST a quick and simple method that should be highly useful for clinical chemosensitivity testing using primary cell cultures of human cancers.

Antineoplastic Agents↗
PubMed2003

Micromechanics-based digitally controlled tunable optical beam shaper.

A digitally controlled programmable optical beam shaper that uses a two-dimensional (2-D) small-tilt micromirror device is introduced. The optical intensity profile at any spatial position can be independently modified by use of a macropixel, incorporated with binary pulse-width modulation. An experimental proof-of-concept optical beam shaper with a commercial 2-D digital micromirror device has shown that the spatial profile of a He-Ne laser beam can be digitally manipulated. Investigation of the analog intensity control showed 256-level nonlinear degamma behavior with a measured 24.5-dB optical contrast ratio and a 10-bit spatial resolution. The performance of this tunable optical beam shaper is limited by the dimensions of the micromirror, the intermirror distance, the size of the optical beam, the number of bits used to control the micromirror, the diffraction effect, and the quality of the imaging optical system.

Journal Article↗
PubMed2006

Atherosclerosis neovascularization and imaging.

Neovascularization in atherosclerotic plaques is particularly prominent in complicated lesions, and has been recently identified as a marker of plaque vulnerability. This observation has led to a growing interest in the development of imaging techniques with the ability to visualize and quantify the extent of plaque neovascularization. Such feature may play an important role in identifying those lesions more prone to destabilization and rupture, and in the guidance and monitoring of therapeutic interventions. Several modalities have emerged as potential candidates for imaging neovessels in atherosclerotic lesions. They include magnetic resonance imaging, x-ray computed tomography, positron emission tomography, single photon emission computed tomography, ultrasound, or near-infrared optical imaging. These techniques differ in their achievable spatial and temporal resolution, availability, cost, reproducibility, degree of intrusiveness, capability to image atherosclerotic plaques in various vascular territories and ability to discern different plaque components, specifically the presence of neovessels. Molecular imaging, a rapidly evolving multidisciplinary field devoted to the visualization of specific physiopathologic processes at the cellular or molecular level, appears particularly well suited for this purpose because of its ability to target and visualize individual molecules specific to neoangiogenesis. In this manuscript we will review current evidence on the potential application of the various modalities, with a particular emphasis in molecular imaging.

Animals↗