New techniques are developing all the time, as scientists push the boundaries in science ever forward, solutions to imaging problems are solved with newly developed techniques. Here is a look at some of the techniques known to us presently.

Optical Microscopy

There are many ‘terms’ involved in microscopy, so we have selected just a few of the main key features which currently affect the majority of labs involved in image analysis, whatever your application area: (Descriptions supplied by Andor Technology.)

Detection Limit
The Detection Limit is a measure of the smallest signal that can be detected in a single readout. The smallest signal is defined as the signal whose level is equal to the noise accompanying that signal, i.e. a signal to noise ratio (S/N) of unity. Sources of noise are: Shot noise of the signal itself, Shot noise of any dark signal, Readout noise.

Image Intensifier
An Image Intensifier is a device that amplifies the intensity of an image, not the size of the image. The device is small, typically 1 to 2 inches in diameter by about 1 inch thick. An image is projected on to the input window of the device and an intensified image appears on its exit window (usually a fiber optic plate). As well as amplifying, an image intensifier can rapidly be switched on and off, allowing it to be used as a very fast shutter.

Readout
Readout is the process by which data are taken from the pixels of the CCD and stored in computer memory. The pixels, which are arranged in a single row, are read out individually in sequence. Readout involves amplifying the charge on each pixel into a voltage, performing an A/D conversion, and storing the data in computer memory. The time taken to perform this operation is known as the "read time".

Resolution
A measure of how fine a detail can be detected, in terms of either space (spatial resolution), time (temporal resolution), or intensity. The greater the resolution of the image, the more information can be determined. In fluorescence applications using low light and/or thicker specimens, confocal imaging can greatly improve resolution.

Scanning
The CCD is continually being ‘scanned’ to prevent its becoming saturated. In an acquired scan the displayed charge undergoes A/D conversion and is acquired into computer memory so that it can be used for subsequent processing and display, i.e. it is readout.

Signal-to-Noise Ratio (SNR)
The Signal to Noise Ratio (S/N) is the ratio between a given signal and the noise associated with that signal. Noise has a fixed component and a variable component (shot noise) which is the square root of the signal. Thus, the Signal to Noise Ratio usually increases (improves) as the signal increases. The maximum Signal to Noise Ratio is the ratio between the maximum signal (i.e. the saturation level) and the noise associated with that signal. At near saturation levels the dominant source of noise is the shot noise of the signal.

Super-resolution
The term super-resolution refers to methods that surpass the so-called diffraction limit. Applications are wide ranging – from dynamic vesicle movements in the sub-100 nm range to fluorescence images of sub-cellular structures, enabling researchers to see details only previously possible with electron microscopy.

As microscopy has progressed, scientists have used combinations of the above techniques to further develop this field. Confocal microscopy for example, is an optical imaging technique enabling 3D imaging of structures from obtained images. It can increase optical resolution and contrast of an image by using point illumination and a spatial pinhole to eliminate out-of-focus light in certain specimens that are thicker than the focal plane. The signal-to-noise ratio is improved in comparison to widefield techniques, and it can be used with both live and fixed specimens.

Fluorescence confocal imaging is used for live cell images. Spinning disk and Sweptfield confocal systems are ideal for the imaging of high-speed intracellular events such as calcium ion dynamics. Confocal imaging is fundamental to advanced imaging techniques such as FLIM, FRET, FRAP and FLIP and can be used in association with TIRF imaging.

TIRF is a highly sensitive technique to perform functional investigations in living cells. The high signal to noise ratio and a resolution allows the visualization and to analysis of vesicles in transport and signaling events, as well as kinetic studies and single molecules detection.

CARS microscopy for example can be used in biological, pharmaceutical, and dermatological research, biomedical imaging, food processing, and materials science. Its potential has been demonstrated for various biomedical applications, such as the imaging of lipid transport, protein concentrations, DNA, RNA, tissue in a living organism, and order in liquid crystals. By integrating CARS technology into modern optical scanning microscope systems, the researcher has the latest technology in hand combined with an easy-to-use confocal system.

The use of fluorescence in microscopy allows the more specific analysis of a specimen. Permanent coupling of fluorescence molecules with biological substances, e.g. antibodies, mean that the diagnosis of illness is becoming much more exact. Fluorescence imaging is now combined with confocal and optical methods to enhance techniques for image analysis.

Consider Your Applications:

This list is not exhaustive but gives an indication of how diverse and widespread microscopy is. Consider whether your lab uses a combination of these topic areas. A microscope system that can interface with a number of these techniques may be preferable.

Manufacturers are creating systems with the ability to customize requirements. Various image analysis systems can be coupled with microscopes for specific applications. For example for live cell imaging, the primary considerations are signal-to-noise, image acquisition speed and specimen viability. Fluorescence microscopy such as TIRF, FLIM, FRAP and laser scanning, as an example, would be combined with a CCD or EMCCD for image acquisition. Researchers would look at the individual requirements of the live-cell imaging application and determine the best equipment to use following discussion with key manufacturers. Each application area is unique, however equipment can be used in different permutations to achieve individual results.

Acquisition of an image is obtained via either analogue methods (SLR camera, Microscope cameras) or more recently digital – CCD, sCMOS, color imaging, black and white cameras, and digital cameras. The benefit of digital cameras over the analogue counterpart is that a progressive scan output is produced which can be connected directly to a computer. The entire image is acquired during the exposure time and read out is line by line from the top of the image to the bottom. Consider the dynamic range you require in your digital solution. Manufacturers have developed solutions to enable diversity with this depending on application. No single detector will meet all the requirements of fluorescence microscopy, however consider your priorities such as exposure time, signal-to-noise. Consider your applications such as live cell imaging, single-molecule fluorescence imaging, and also consider whether you are using traditional brightfield or fluorescence microscopy to prepare the image.

Developments in this field are being made all the time. Microscopy is in the news regularly as scientists seek to push the boundaries and develop new techniques. Recently scientists at the University of Warwick, UK, in collaboration with a team at IBM Research, Zurich, have announced the success of imaging a molecule called ‘Pentacene’. This five linked, hexagonal ring of carbon structure was imaged with the use of scanning tunneling microscopy in conjunction with non contact atomic force microscopy to offer highly specific resolution.

Another UK based team from Imperial College, London, have combined two methods to investigate cell substrate interactions in biomedical research. A new technique developed – Light-Ion Microscopy (CLIM), combines ion and fluorescence microscopy to obtain topographical and biochemical information for the same area of a sample. Scanning ion microscopy (SIM) was developed in preference to SEM to avoid interference with the fluorescent signal.

News items such as this are regular, and our advice is to investigate the limitations and possibilities of individual equipment. Learn how to combine equipment, and how you can customize it to suit your requirements. Manufacturers produce equipment which can be upgraded, developed, and enabled to accept additional components. Think about choosing equipment which is best suited to your core requirements and develop it further from there.