Quality assessment of confocal microscopy slide-based systems: Instability

Quality assessment in light microscopy for routine use through simple tools and robust metrics

Although there is a need to demonstrate reproducibility in light microscopy acquisitions, the lack of standardized guidelines monitoring microscope health status over time has so far impaired the widespread use of quality control (QC) measurements. As scientists from 10 imaging core facilities who encounter various types of projects, we provide affordable hardware and open source software tools, rigorous protocols, and define reference values to assess QC metrics for the most common fluorescence light microscopy modalities. Seven protocols specify metrics on the microscope resolution, field illumination flatness, chromatic aberrations, illumination power stability, stage drift, positioning repeatability, and spatial-temporal noise of camera sensors. We designed the MetroloJ_QC ImageJ/Fiji Java plugin to incorporate the metrics and automate analysis. Measurements allow us to propose an extensive characterization of the QC procedures that can be used by any seasoned microscope user, from research biologists with a specialized interest in fluorescence light microscopy through to core facility staff, to ensure reproducible and quantifiable microscopy results.

Confocal Laser Scanning Microscopy of Morphology and Apoptosis in Organogenesis-Stage Mouse Embryos

BACKGROUND

After fluorochromes are incorporated into cells, tissues, and organisms, confocal microscopy can be used to observe three-dimensional structures. LysoTracker Red (LT) is a paraformaldehyde-fixable probe that concentrates into acidic compartments of cells and indicates regions of high lysosomal activity and phagocytosis, both of which correlate to apoptotic activity. Thus, LT is a good indicator of apoptosis visualized by confocal microscopy. Results of LT staining of apoptotic cell death correlate well with other whole mount apoptosis vital dyes such as Nile blue sulfate and neutral red, with the added benefit of being fixable in situ. Nile blue sulfate can also be used as a non-vital, nonspecific dye to visualize general morphology. Stains such as acridine orange can be used for surface staining of fixed embryos to yield confocal images that are similar to scanning electron micrographs.

METHODS

Mouse embryos were stained with LT, fixed with paraformaldehyde/glutaraldehyde, dehydrated with methanol (MEOH), and cleared with benzyl alcohol/benzyl benzoate (BABB). Following this treatment, the tissues were nearly transparent. Embryos are mounted on depression slides, and serial sections are imaged by confocal microscopy, followed by 3-D reconstruction.

RESULTS

Embryos or tissues as thick as 500 microns (μm) can be visualized after clearing with BABB. LysoTracker staining reveals apoptotic regions in organogenesis-stage mouse embryos. Morphological observation of tissue was facilitated by combining autofluorescence with Nile blue sulfate staining of fixed embryos or opaque surface staining with acridine orange staining.

CONCLUSIONS

The use of BABB for clearing LT vital-stained and fixed embryos matches the refractive index of the tissue to the suspending medium, allowing increased penetration of laser light in a confocal microscope. Nile blue sulfate used as a non-vital dye provides a nonspecific staining of fixed embryos that can then be cleared with methyl salicylate for confocal observation. Sample preparation and staining procedures described here, with optimization of confocal laser scanning microscopy, allow for the detection and visualization of morphological structure and apoptosis in embryos up to 500 μm thick, and stained specimens can be fixed and mounted on depression slides.

IntensityCheck - The light measuring app for microscope performance checks and consistent fluorescence imaging

Quantitative fluorescence imaging is an essential tool in biomedical research. It requires consistent and repeatable conditions such as constant sample illumination. Even on a confocal microscope this can usually only be achieved by using an external laser power meter. By combining low-cost wireless Arduino based light sensors with an easy to use Android smartphone app we provide microscope users with a simple but powerful tool to maintain sample illumination for quantitative imaging, for tracking the intensity, stability and alignment of the light sources and for comparing microscope performance.

Which Elements to Build Co-localization Workflows? From Metrology to Analysis

Co-localization analysis is one of the main interests of users entering a facility with slides in hands and nice analysis perspectives in mind. While being available through most, if not all, analysis software, co-localization tools are mainly perceived as black boxes, fed with images, that will, hopefully, return (the expected) numbers.In this chapter, we will aim at deconstructing existing generic co-localization workflows, extracting elementary tools that may be reused and recombined to generate new workflows. By differentiating work cases, identifying co-localization reporters and the metrics others have been using, we aim at providing the audience with the elementary bricks and methods to build their really own co-localization workflows. A special emphasis is given on the preparatory phase where the acquisition system is assessed, using basic metrological tests.

Fidelity test for through-focus or volumetric type of optical imaging methods

Rapid increase in interest and applications of through-focus (TF) or volumetric type of optical imaging in biology and other areas has resulted in the development of several TF image collection methods. Achieving quantitative results from images requires standardization and optimization of image acquisition protocols. Several standardization protocols are available for conventional optical microscopy where a best-focus image is used, but to date, rigorous testing protocols do not exist for TF optical imaging. In this paper, we present a method to determine the fidelity of the TF optical data using the TF scanning optical microscopy images.

Enhancing optical microscopy illumination to enable quantitative imaging

There has been an increasing push to derive quantitative measurements using optical microscopes. While several aspects of microscopy have been identified to enhance quantitative imaging, non-uniform angular illumination asymmetry (ANILAS) across the field-of-view is an important factor that has been largely overlooked. Non-uniform ANILAS results in loss of imaging precision and can lead to, for example, less reliability in medical diagnoses. We use ANILAS maps to demonstrate that objective lens design, illumination wavelength and location of the aperture diaphragm are significant factors that contribute to illumination aberrations. To extract the best performance from an optical microscope, the combination of all these factors must be optimized for each objective lens. This requires the capability to optimally align the aperture diaphragm in the axial direction. Such optimization enhances the quantitative imaging accuracy of optical microscopes and can benefit applications in important areas such as biotechnology, optical metrology, and nanotechnology.

Step beyond Kohler illumination analysis for far-field quantitative imaging: angular illumination asymmetry (ANILAS) maps

For far-field optical imaging of three-dimensional objects and such critical applications as quantitative optical imaging, optical metrology, and optical lithography, it is necessary not only to meet the Kohler illumination condition (i.e. uniform spatial intensity) but also to minimize angular illumination asymmetry (ANILAS) at the sample plane. The presence of ANILAS results in distorted optical images, and most likely in erroneous quantitative measurements. ANILAS results from optical and illumination aberrations, optical misalignment and other problems. We present a detailed procedure to measure and create maps of ANILAS across the field-of-view (FOV). ANILAS maps enable visualization of the state of illumination at the sample plane. Since the presence of ANILAS is detrimental to quantitative measurements, it is important to know the magnitude and type of ANILAS across the FOV before making any attempt to correct it. Here we intentionally create different types of illumination distortions and generate corresponding ANILAS maps, which help us evaluate the state of illumination beyond the Kohler illumination criterion. We expect that the ANILAS maps will be helpful for a wide range of far-field imaging applications.

Intravital Imaging of Neutrophil Priming Using IL-1β Promoter-driven DsRed Reporter Mice

Neutrophils are the most abundant leukocytes in human blood circulation and are quickly recruited to inflammatory sites. Priming is a critical event that enhances the phagocytic functionality of neutrophils. Although extensive studies have unveiled the existence and importance of neutrophil priming during infection and injury, means of visualizing this process in vivo have been unavailable. The protocol provided enables monitoring of the dynamic process of neutrophil priming in living animals by combining three methodologies: 1) DsRed reporter signal - used as a measure of priming 2) in vivo neutrophil labeling - achieved by injection of fluorescence-conjugated anti-lymphocyte antigen 6G (Ly6G) monoclonal antibody (mAb) and 3) intravital confocal imaging. Several critical steps are involved in this protocol: oxazolone-induced mouse ear skin inflammation, appropriate sedation of animals, repeated injections of anti-Ly6G mAb, and prevention of focus drift during imaging. Although a few limitations have been observed, such as the limit of continuous imaging time (~ 8 hr) in one mouse and the leakage of fluorescein isothiocyanate-dextran from blood vessels in the inflammatory state, this protocol provides a fundamental framework for intravital imaging of primed neutrophil behavior and function, which can easily be expanded to examination of other immune cells in mouse inflammation models.

Confocal microscopy for high-resolution and high-content analysis of the cell cycle

Optical fluorescence microscopy offers a wide range of technological solutions to address many questions in biomedical research. Spatial resolution has been greatly improved by the use of confocal microscopes, providing a 3-D analysis of the intracellular space. Automation has contributed to make confocal analysis available for high-content image cytometry studies. However, the storage, browsing, and analysis of the amount of data generated can challenge the feasibility of such studies. Presented in this chapter is a multistep acquisition and analysis protocol that can bypass such difficulties by an analysis-driven data collection. Cell-cycle analysis of low-resolution data can be employed to select cell populations of interest that can then be imaged at extremely high resolution and subjected to high-content analysis.

Evaluating confocal microscopy system performance

A confocal microscope was evaluated with a series of tests that measure field illumination, lens clarity, laser power, laser stability, dichroic functionality, spectral registration, axial resolution, scanning stability, PMT quality, overall machine stability, and system noise. These tests will help investigators measure various parameters on their confocal microscopes to insure that they are working correctly with the necessary resolution, sensitivity, and precision. Utilization of this proposed testing approach will help eliminate some of the subjectivity currently employed in assessing the CLSM performance.

ConfocalCheck--a software tool for the automated monitoring of confocal microscope performance

Laser scanning confocal microscopy has become an invaluable tool in biomedical research but regular quality testing is vital to maintain the system's performance for diagnostic and research purposes. Although many methods have been devised over the years to characterise specific aspects of a confocal microscope like measuring the optical point spread function or the field illumination, only very few analysis tools are available. Our aim was to develop a comprehensive quality assurance framework ranging from image acquisition to automated analysis and documentation. We created standardised test data to assess the performance of the lasers, the objective lenses and other key components required for optimum confocal operation. The ConfocalCheck software presented here analyses the data fully automatically. It creates numerous visual outputs indicating potential issues requiring further investigation. By storing results in a web browser compatible file format the software greatly simplifies record keeping allowing the operator to quickly compare old and new data and to spot developing trends. We demonstrate that the systematic monitoring of confocal performance is essential in a core facility environment and how the quantitative measurements obtained can be used for the detailed characterisation of system components as well as for comparisons across multiple instruments.

A computational platform for robotized fluorescence microscopy (I): high-content image-based cell-cycle analysis

Hardware automation and software development have allowed a dramatic increase of throughput in both acquisition and analysis of images by associating an optimized statistical significance with fluorescence microscopy. Despite the numerous common points between fluorescence microscopy and flow cytometry (FCM), the enormous amount of applications developed for the latter have found relatively low space among the modern high-resolution imaging techniques. With the aim to fulfill this gap, we developed a novel computational platform named A.M.I.CO. (Automated Microscopy for Image-Cytometry) for the quantitative analysis of images from widefield and confocal robotized microscopes. Thanks to the setting up of both staining protocols and analysis procedures, we were able to recapitulate many FCM assays. In particular, we focused on the measurement of DNA content and the reconstruction of cell-cycle profiles with optimal parameters. Standard automated microscopes were employed at the highest optical resolution (200 nm), and white-light sources made it possible to perform an efficient multiparameter analysis. DNA- and protein-content measurements were complemented with image-derived information on their intracellular spatial distribution. Notably, the developed tools create a direct link between image-analysis and acquisition. It is therefore possible to isolate target populations according to a definite quantitative profile, and to relocate physically them for diffraction-limited data acquisition. Thanks to its flexibility and analysis-driven acquisition, A.M.I.CO. can integrate flow, image-stream and laser-scanning cytometry analysis, providing high-resolution intracellular analysis with a previously unreached statistical relevance.

Quality control protocol for confocal systems

Quantitative analysis of confocal imaging experiments require more stringent quality control of instrument function than qualitative imaging. Unfortunately, there are no standard procedures for quality control that are uniformly implemented, and, in multi user facilities experimenters rarely have access to the QC information. This paper proposes an easy and very efficient protocol that could be performed at the beginning of each day, experiment or even slide. It takes only a few minutes to assess laser stability, stage stability, channel registration in 3 dimensions and flatness of field. The information may be used either to calibrate data or, in more severe cases to request servicing the instrument.

Quality assurance testing for modern optical imaging systems

The days of being able to ascertain instrument performance by simply peering through the eye pieces at a specimen are gone. However, users and granting agencies need to be confident that data collected on these instruments is uniform and quantifiable both over time and between instruments. Ideally, a LASER should not fluctuate, illumination should be completely uniform, and colors should be perfectly aligned. To check the current performance of imaging equipment, we conducted a worldwide research study utilizing three image-based tests: long-/short-term illumination stability, co-registration of signals across various wavelengths, and field illumination uniformity. To differentiate between "acceptable" and "unacceptable" performance, the deviation in illumination power could not exceed 10% (long term) or 3% (short term), the difference in the center-of-mass of imaged multicolored beads could not exceed >1 pixel between different wavelengths, and field illumination values could not exceed 10% (horizontal) or 20% (diagonal) deviation. This study established the current state of microscope performance through simple, efficient, and robust tests, while defining relative standards to assist cores in maintaining their instruments in optimal operating conditions. We developed cross-platform performance standards that will improve the validity of quantitative measurements made using various light microscopes.

Method of calibration of a fluorescence microscope for quantitative studies

Confocal microscopy is based on measurement of intensity of fluorescence originating from a limited volume in the imaged specimen. The intensity is quantized in absolute (albeit arbitrary) units, producing a digital 3D micrograph. Thus, one may obtain quantitative information on local concentration of biomolecules in cells and tissues. This approach requires estimation of precision of light measurement (limited by noise) and conversion of the digital intensity units to absolute values of concentration (or number) of molecules of interest. To meet the first prerequisite we propose a technique for measurement of signal and noise. This method involves registration of a time series of images of any stationary microscope specimen. The analysis is a multistep process, which separates monotonic, periodic and random components of pixel intensity change. This approach permits simultaneous determination of dark and photonic components of noise. Consequently, confidence interval (total noise estimation) is obtained for every level of signal. The algorithm can also be applied to detect mechanical instability of a microscope and instability of illumination source. The presented technique is combined with a simple intensity standard to provide conversion of relative intensity units into their absolute counterparts (the second prerequisite of quantitative imaging). Moreover, photobleaching kinetics of the standard is used to estimate the power of light delivered to a microscope specimen. Thus, the proposed method provides in one step an absolute intensity calibration, estimate of precision and sensitivity of a microscope system.

Evaluation and purchase of confocal microscopes: numerous factors to consider

The purchase of a confocal microscope is a difficult decision. Many factors need to be considered, which include hardware, software, company, support, service, and price. These issues are discussed to help guide the purchasing process.

Darkfield-confocal microscopy detection of nanoscale particle internalization by human lung cells

Background

Concerns over the health effects of nanomaterials in the environment have created a need for microscopy methods capable of examining the biological interactions of nanoparticles (NP). Unfortunately, NP are beyond the diffraction limit of resolution for conventional light microscopy (~200 nm). Fluorescence and electron microscopy techniques commonly used to examine NP interactions with biological substrates have drawbacks that limit their usefulness in toxicological investigation of NP. EM is labor intensive and slow, while fluorescence carries the risk of photobleaching the sample and has size resolution limits. In addition, many relevant particles lack intrinsic fluorescence and therefore can not be detected in this manner. To surmount these limitations, we evaluated the potential of a novel combination of darkfield and confocal laser scanning microscopy (DF-CLSM) for the efficient 3D detection of NP in human lung cells. The DF-CLSM approach utilizes the contrast enhancements of darkfield microscopy to detect objects below the diffraction limit of 200 nm based on their light scattering properties and interfaces it with the power of confocal microscopy to resolve objects in the z-plane.

Results

Validation of the DF-CLSM method using fluorescent polystyrene beads demonstrated spatial colocalization of particle fluorescence (Confocal) and scattered transmitted light (Darkfield) along the X, Y, and Z axes. DF-CLSM imaging was able to detect and provide reasonable spatial locations of 27 nm TiO₂ particles in relation to the stained nuclei of exposed BEAS 2B cells. Statistical analysis of particle proximity to cellular nuclei determined a significant difference between 5 min and 2 hr particle exposures suggesting a time-dependant internalization process.

Conclusions

DF-CLSM microscopy is an alternative to current conventional light and electron microscopy methods that does not rely on particle fluorescence or contrast in electron density. DF-CLSM is especially well suited to the task of establishing the spatial localization of nanoparticles within cells, a critical topic in nanotoxicology. This technique has advantages to 2D darkfield microscopy as it visualizes nanoparticles in 3D using confocal microscopy. Use of this technique should aid toxicological studies related to observation of NP interactions with biological endpoints at cellular and subcellular levels.

An integrated imaging approach to the study of oxidative stress generation by mitochondrial dysfunction in living cells

BACKGROUND

The mechanisms of action of many environmental agents commonly involve oxidative stress resulting from mitochondrial dysfunction. Zinc is a common environmental metallic contaminant that has been implicated in a variety of oxidant-dependent toxicological responses. Unlike ions of other transition metals such as iron, copper, and vanadium, Zn(2+) does not generate reactive oxygen species (ROS) through redox cycling.

OBJECTIVE

To characterize the role of oxidative stress in zinc-induced toxicity.

METHODS

We used an integrated imaging approach that employs the hydrogen peroxide (H2O2)-specific fluorophore Peroxy Green 1 (PG1), the mitochondrial potential sensor 5,5 ,6,6 -tetrachloro-1,1 ,3,3 -tetraethylbenzimidazolylcarbocyanine iodide (JC-1), and the mitochondria-targeted form of the redox-sensitive genetically encoded fluorophore MTroGFP1 in living cells.

RESULTS

Zinc treatment in the presence of the Zn(2+) ionophore pyrithione of A431 skin carcinoma cells preloaded with the H(2)O(2)-specific indicator PG1 resulted in a significant increase in H(2)O(2) production that could be significantly inhibited with the mitochondrial inhibitor carbonyl cyanide 3-chlorophenylhydrazone. Mitochondria were further implicated as the source of zinc-induced H(2)O(2) formation by the observation that exposure to zinc caused a loss of mitochondrial membrane potential. Using MTroGFP1, we showed that zinc exposure of A431 cells induces a rapid loss of reducing redox potential in mitochondria. We also demonstrated that zinc exposure results in rapid swelling of mitochondria isolated from mouse hearts.

CONCLUSION

Taken together, these findings show a disruption of mitochondrial integrity, H(2)O(2) formation, and a shift toward positive redox potential in cells exposed to zinc. These data demonstrate the utility of real-time, live-cell imaging to study the role of oxidative stress in toxicological responses.

A versatile platform for comprehensive chip-based explorative cytometry

Analysis of the immense complexity of the immune system is increasingly hampered by technical limitations of current methodologies, especially for multiparameter- and functional analysis of samples containing small numbers of cells. We here present a method, which is based on the stepwise functional manipulation and analysis of living immune cells that are self-immobilized within microfluidic chips using automated epifluorescence microscopy overcoming current limitations for comprehensive immunophenotyping. Crossvalidation with flow cytometry revealed a 10-fold increased sensitivity and a comparable specificity. By using small sample volumes and cell numbers (2-10 microl, down to 20,000 cells), we were able to analyze a virtually unlimited number of intracellular and surface markers even on living immune cells. We exemplify the scientific and diagnostic potential of this method by (1) identification and phenotyping of rare cells, (2) comprehensive analysis of very limited sample volume, and (3) deep immunophenotyping of human B-cells after in vitro differentiation. Finally, we propose an informatic model for annotation and comparison of cytometric data by using an ontology-based approach. The chip-based cytometry introduced here turned out to be a very useful tool to enable a stepwise exploration of precious, small cell-containing samples with an virtually unlimited number of surface- and intracellular markers.

A phosphatidylcholine-BODIPY 581/591 conjugate allows mapping of oxidative stress in P. falciparum-infected erythrocytes

The chromophore, BODIPY 581/591, has an extended conjugated system that reacts with oxygen centered-radicals leading to changes in its spectral characteristics. Fatty acid-conjugated BODIPY 581/591 transfers readily between membrane bilayers and can be used as a sensor of oxidative stress in cell populations. We report here the use of a phosphatidylcholine (PC) derivative of BODIPY 581/591, which transfers much less rapidly between membranes. This allows the analysis of oxidative stress in individual cells and in different compartments within cells. Quantitative imaging and flow cytometry were used to measure the ratio of fully conjugated to oxidized probe in model systems and in Plasmodium falciparum-infected erythrocytes. We observed an increase in the oxidation of the parasite-associated BODIPY 581/591-PC as the intraerythrocytic parasite matures. By contrast, BODIPY 581/591-PC associated with the erythrocyte membrane experiences a low level of oxidation even in the later stages of parasite development. Treatment with a pro-oxidant compound caused increased oxidation of the probe in the parasite compartment, but less so in the host cell membrane. Conversely, treatment with ferricyanide increases oxidation of the probe in the erythrocyte cell membrane but does not inhibit parasite growth. Chromatographic analysis of the lipids in infected erythrocytes shows no evidence for loss of alpha-tocopherol or the accumulation of lipid hydroperoxides indicating that, despite the increased oxidative stress, the parasite membranes remain protected from substantial lipid oxidation. We have established BODIPY 581/591-PC as a useful probe of the spatial distribution of oxidative stress in P. falciparum-infected erythrocytes; however, the probe appears to be more sensitive to oxidative damage than endogenous lipids.

Comparative study of human erythrocytes by digital holographic microscopy, confocal microscopy, and impedance volume analyzer

Red blood cell (RBC) parameters such as morphology, volume, refractive index, and hemoglobin content are of great importance for diagnostic purposes. Existing approaches require complicated calibration procedures and robust cell perturbation. As a result, reference values for normal RBC differ depending on the method used. We present a way for measuring parameters of intact individual RBCs by using digital holographic microscopy (DHM), a new interferometric and label-free technique with nanometric axial sensitivity. The results are compared with values achieved by conventional techniques for RBC of the same donor and previously published figures. A DHM equipped with a laser diode (lambda = 663 nm) was used to record holograms in an off-axis geometry. Measurements of both RBC refractive indices and volumes were achieved via monitoring the quantitative phase map of RBC by means of a sequential perfusion of two isotonic solutions with different refractive indices obtained by the use of Nycodenz (decoupling procedure). Volume of RBCs labeled by membrane dye Dil was analyzed by confocal microscopy. The mean cell volume (MCV), red blood cell distribution width (RDW), and mean cell hemoglobin concentration (MCHC) were also measured with an impedance volume analyzer. DHM yielded RBC refractive index n = 1.418 +/- 0.012, volume 83 +/- 14 fl, MCH = 29.9 pg, and MCHC 362 +/- 40 g/l. Erythrocyte MCV, MCH, and MCHC achieved by an impedance volume analyzer were 82 fl, 28.6 pg, and 349 g/l, respectively. Confocal microscopy yielded 91 +/- 17 fl for RBC volume. In conclusion, DHM in combination with a decoupling procedure allows measuring noninvasively volume, refractive index, and hemoglobin content of single-living RBCs with a high accuracy.

Proposal of a set of model polymer additives designed for confocal FRAP diffusion experiments

The migration of additives from food packaging to food stuffs is kinetically governed by the diffusion coefficient (D) of the additive within the polymer. Food safety authorities have recently allowed the use of mathematical models to predict D, with the additive molecular weight as a single entry parameter. Such models require experimental values to feed the databases, but these values are often scattered. To deal with this issue, a fluorescent chemically homologous series of model additives was synthesized with molecular weights (MW) ranging from 236 g.mol (-1) to 1120 g.mol (-1). This set was then used to collect diffusion coefficients D through confocal fluorescence recovery after photobleaching (FRAP). This microscopic technique allows in situ packaging micro migration tests. The FRAP method was tested against results from the literature before being applied to two different model polystyrenes in a preliminary study to investigate the relationship D = f(MW). Our intermediate objective was to compare various experimental D = f(MW) from our method with predictions from other mathematical or semiempirical models.

Precision of light intensity measurement in biological optical microscopy

Standardization and calibration of optical microscopy systems have become an important issue owing to the increasing role of biological imaging in high-content screening technology. The proper interpretation of data from high-content screening imaging experiments requires detailed information about the capabilities of the systems, including their available dynamic range, sensitivity and noise. Currently available techniques for calibration and standardization of digital microscopes commonly used in cell biology laboratories provide an estimation of stability and measurement precision (noise) of an imaging system at a single level of signal intensity. In addition, only the total noise level, not its characteristics (spectrum), is measured. We propose a novel technique for estimation of temporal variability of signal and noise in microscopic imaging. The method requires registration of a time series of images of any stationary biological specimen. The subsequent analysis involves a multi-step process, which separates monotonic, periodic and random components of every pixel intensity change in time. The technique allows simultaneous determination of dark, photonic and multiplicative components of noise present in biological measurements. Consequently, a respective confidence interval (noise level) is obtained for each level of signal. The technique is validated using test sets of biological images with known signal and noise characteristics. The method is also applied to assess uncertainty of measurement obtained with two CCD cameras in a wide-field microscope.

Reliability of confocal microscopy spectral imaging systems: Use of multispectral beads

BACKGROUND

There is a need for a standardized, impartial calibration, and validation protocol on confocal spectral imaging (CSI) microscope systems. To achieve this goal, it is necessary to have testing tools to provide a reproducible way to evaluate instrument performance.

METHODS

We evaluated fluorescent spectral beads (FocalCheck) from Molecular Probes/Invitrogen that consist of four pairs with emissions between 500 and 725 nm and a europium macrocycle quantum dye bead. These bead tools compliment our previously published protocol for testing spectral imaging systems that used an inexpensive multi-ion discharge lamp (MIDL) that contains Hg(+), Ar(+), and inorganic fluorophores that emits distinct, stable spectral features.

RESULTS

We acquired the spectra of the FocalCheck beads on a Zeiss 510 Meta, a Leica TCS-SP1, a Leica SP2 AOBS, an Olympus FV 1000, and a Nikon C1Si confocal systems and a PARISS microscopic spectral system and of the europium beads on the Leica TCS-SP1 and PARISS spectral imaging systems. A lack of performance with some equipment between 650 and 750 nm was identified using the far red pair of the FocalCheck beads. The position of the slider in front of PMT 2 that reflects light into PMT 1 and PMT 3 affected the measurement of all bead intensities. Unmixing algorithms were used to separate beads with different fluorochromes and separate two fluorochromes on the same bead.

CONCLUSIONS

The FocalCheck multi-spectral beads yielded similar profiles on four CSI systems and a PARISS spectral system. The utilization of the spectral FocalCheck beads is helpful to evaluate proper spectral performance, especially in the far red region. Europium beads provide a very narrow spectrum that can help to identify machines that have spectral problems. The dyes located on individual beads or mixed together in ring-core configuration can be used as test particles to demonstrate spectral unmixing with various algorithms.

Confocal laser scanning microscopy of whole mouse ovaries: excellent morphology, apoptosis detection, and spectroscopy

BACKGROUND

Ovaries consist of numerous follicles, oocytes, and granulosa cells in different stages of development. Many of these follicles will undergo an apoptotic process during the lifetime of the animal. By using proper tissue preparation methods, the events within the whole ovary can be observed by using 3D confocal microscopy.

METHODS

Whole ovaries were stained with LysoTracker Red (LT), fixed with 4% paraformaldehyde (PF) and 1% glutaraldehyde (Glut), dehydrated with methanol (MEOH), and cleared with benzyl alcohol and benzyl benzoate (BABB). Using this tissue preparation technique, the ovary becomes relatively transparent, allowing its morphology to be observed with confocal microscopes. A spectral imaging system (PARISS) located on a conventional microscope was used to interpret the LT dye spectra and fixation products in the tissues with different excitation wavelengths.

RESULTS

Apoptosis in the follicle was detected as clusters of intensely stained granulosa cells located in close proximity to the oocytes. The fixation with Glut and PF preserved morphological details, increased tissue fluorescence, thus increased the signal to noise of the background image.

CONCLUSIONS

Thick tissues can be imaged after they are properly stained, aldehyde fixed, and BABB cleared. LT intensely stained single cells or clusters of apoptotic cells in the follicles and the nucleolus. Spectral differences between LT as an indicator of apoptosis and Glut-PF fixation was used to visualize ovarian morphology and apoptosis. The PARISS spectrophotometer revealed spectral peaks for LT at 609.6 nm and for Glut-PF at 471.3 nm. The proper use of the spectra from these fluorescence molecules is the foundation for high quality morphological images of apoptosis. By sequentially imaging the two probes with a 488 nm laser and a 543/568 nm laser, there was a reduction in fluorescent cross talk and an increase in image quality.