Precision Scientific Imaging: An Overview


When Imaging Gets Difficult, PixCellent has the answer

Imaging has a central role to play in an ever increasing range of scientific disciplines and applications. For all applications, whether they be leading-edge research work or quality control procedures in a production environment, being "the best" is vitally important. Having the best equipment can give you a real lead in your chosen field. For imaging applications, this means having a camera system that can deliver the best possible image, whatever the operating conditions. Any image can only be of use if it reveals the desired detail, whether for general inspection purposes or for measurement. Conventional camera systems are often simply not good enough when imaging conditions get difficult. Typical examples could include imaging at very low light levels, or resolving fine details with very low contrast, or applications that require very long exposure times - or combinations of all these! Any situation where difficult imaging conditions apply can usually benefit from the use of cooled CCD (Charge Coupled Device) cameras. Specifically designed to cope with a wide variety of imaging problems, cooled CCD cameras have found applications in fields as varied as astronomy, spectroscopy, the life sciences, physical sciences, manufacturing and quality control. Just a importantly, PixCellent has become a world leader in the manufacture, supply, installation and support of these cameras and offer a wealth of experience and applications advice.

Our Imaging System Selection Guide helps you to choose exactly the right imaging system for your application. Alternately please send details of your application to PixCellent Imaging Ltd (sales@pixcellent.com)so that our engineers can understand better the details of your application and so make some suggestions as to the optimal configuration of a precision imaging system for your application.

For a general introduction to the characteristics of CCD detectors and the electronics systems used to control them please look at our on-line tutorial entitled Guide to the Role of CCDs in Imaging.


Going for "the best"

A number of factors are particularly important when trying to optimise image quality, and cooled CCD cameras address each of these in a particular way. The major parameters of interest are:

Each of the major components of our cooled CCD camera systems, including the CCD detector, cooling head, digital signal processor and camera control electronics have been designed to bring major benefits for the user in each of these areas.


A guide to good imaging

Exceptional sensitivity is required for any application where the light levels to be detected are very low. The cooled CCD system solves this through its inherent high sensitivity combined with the possibility of using extended exposure times. The excellent sensitivity has other benefits in allowing lower illumination conditions to be used to protect light-sensitive samples.
Outstanding low-contrast capabilities are important when images have features of interest that are of similar brightness with very low contrast. This is vitally important in the detection of very weak features in the presence of a large background signal.
The use of special high resolution CCD detectors to generate the image scan reveal finer detail of smaller features than can be seen with most conventional camera systems.
many applications require image data to be quantified. More precise quantitative measurements can be made digitally than from analogue data. All PixCellent cooled CCD cameras generate digital data directly.


Cooled CCD Camera Systems


Make the most of your image

Cooled CCD cameras offer the perfect solution for dealing with imaging problems faced by scientists and researchers across an enormous range of disciplines, where conventional cameras may simply be inadequate. The signals may be weak, the contrast may be low or there may be a weak signal masked by a much stronger one.
But why is the cooled CCD system so much better?
The CCD detector itself consists of a large number of individual active image elements called pixels. CCDs are available in a variety of overall sizes, with different numbers of pixels and different individual pixels sizes. For any given CCD size, the larger the number of pixels, the finer the detail that can be resolved in the image.
Cooling the CCD is a particularly important factor. It brings great sensitivity by reducing the inherent electronic noise in the camera. This sensitivity is important for low light level applications such as chemi-luminescent and bio-luminescent imaging microscopy, X-ray imaging methods in medicine, non-destructive testing and diffraction studies and in astronomy, imaging polarimetry and spectroscopy.
Cooling the CCD also allows the image to be digitised to much finer greyscale resolution, enabling very low contrast features to be distinguished and displayed. It also offers the potential for weak signals to be detected even in the presence of much stronger signals that would otherwise "swamp" the image of interest.
Flexible camera control allows PixCellent cooled CCD camera to be operated with variable exposure times and with variable camera readout rates and formats. This enables the same system to be used both in dynamic imaging applications and those in which the signal does not vary significantly with time, but may be inherently weak.


Better Low-Contrast Capability

The intensity of an image ranges from dark to bright. Camera systems divide this range into a number of discrete levels, known as grey levels. The smallest contrast level that can be distinguished is one of these steps. In order to get good contrast separation, the camera system must be capable of dividing up the brightness range into as many steps or grey levels as possible. The more grey levels there are the smaller each step is an so lower contrast features can be seen in the image. As an illustration of this , a typical TV rate camera system would have, at best, 256 grey levels, whilst some PixCellent camera systems can have as many as one million grey levels.
This dramatic difference in grey scale resolution means that the cooled CCD system can allow many more low-contrast features to be distinguished.
In addition, if there are weak features of low contrast in an image in the presence f an overall high background signal level, the cooled CD can be "tuned in" to the particular grey level region for these weak features only, excluding the large background.
Grey scale resolution is also known as dynamic range. The more grey levels, the greater the dynamic range of the camera system.

 


Applications for Cooled CCD Cameras in the Life Sciences


Biological Sciences

Cooled CCD cameras have an important role to play in a host of biological sciences. Such areas include electrophoresis, fluorescence imaging and a wide range of microscope techniques, including optical and electron microscopy. Many areas of microscopy, such as fluorescence, chemiluminescence and violuminescence benefit greatly from the sensitivity and dynamic range of PixCellent imaging systems.


Cell dynamics

Studies of the dynamics of living organisms using fluorescence microscopy are greatly enhanced by cooled CCD imaging systems. Applications are as diverse as calcium ratio imaging, dynamic studies of neurons and muscle cells, and other cell mechanisms.
For these applications fast readout systems are used to allow images to be displayed at near standard video rate, so that cell dynamics may be monitored in real time. These applications frequently give low contrast images and the exceptional grey scale resolution of the cooled CCD systems from PixCellent becomes extremely important.
Fluorescence signals are frequently weak and are often viewed against strong background emission from the sample itself, the microscope slide, the coverslip glass and sometimes even from the microscope optics. The normal procedure for obtaining satisfactory images would be to increase the intensity of the excitation source, but this can lead to photobleaching (damage of the Fluorophore) and, of course, damage to the living cells under study.
The use of cooled CCD cameras allows the excitation intensity to be significantly reduced, while still maintaining excellent image quality and preserving sample viability.
Fast readout system have allowed studies of voltage sensitive dyes to be made for neurological applications so that changes resulting from electrical activity in brain tissue can be monitored.
The special dyes used for these applications alter their absorbance characteristics as a function of applied voltage. These changes can be quite small and need to be detected in the presence of a large background signal. Electrical activity in the tissue under study is a dynamic phenomenon, causing rapid changes in the resulting image form the dye. The introduction of sub-array read-out techniques by PixCellent has greatly increased the image readout rates for these cameras allowing faster events to be followed. this technique can provide an order of magnitude improvement in readout rates for some applications.


Chemi- and bio- luminescence

The phenomena of generating light through a chemical reaction (chemiluminescence) or where the light is emitted from living organisms (bioluminescence) is a rapidly growing area of scientific imaging. For bioluminescence, only live cells can produce light. The dependence of the emissions on cellular viability, enables the technique to be used to evaluate bacterial injury and recovery, and to monitor the activity of antibacterial agents.
Bioluminescence can be use din a range of assays. These include the measurement of antibiotic levels, toxicity and genotoxicity and the detection of oxygen. The technique can also be used to detect genetically altered bacteria following release into the environment. Probably the most common use of bacterial bioluminescence is in the area of microbiology, as a reporter gene for the study of gene expression in both prokaryotic and eukaryotic systems.
For these ultra-low light level applications the ultimate in sensitivity is required. Extremely low noise levels can be achieved in the camera using liquid nitrogen cooling. In addition, the rapid readout capabilities of PixCellent cooled CCD cameras can be used to monitor changes in emission patterns allowing information on the kinetics of change to be deduced.


Electrophoresis

Electrophoresis is an important tool in the detection and analysis of samples of DNA, proteins and carbohydrates. Conventional staining methods give reasonable sensitivity, whilst radio labelling techniques can allow the detection of very small amounts of material. Recent advances in the fluorescent labelling of biologically important molecules before electrophoresis, however, have given a great improvement in sensitivity and ease of use when used in conjunction with an PixCellent electrophoresis imaging system. The samples may be viewed in the gel without unpacking or post-electrophoresis staining and drying, leading to much simpler operating procedures. Digital imaging offers precise quantitation of signals, which allows the accurate measurement of components within a complex sample.
These improvements in the quantitative analysis of proteins can be brought about by the addition of a few simple steps to the processing of a protein sample prior to electrophoresis which allows the proteins to be fluorescently labelled. The sensitivity, speed and resolution of the method allows fast, easy gel running and a sensitivity superior to silver staining. In addition, preparation procedures are far less complicated. The resulting fluorescence intensity from a protein spot is highly linear with concentration. leading to precise quantitation.


Applications for Cooled CCD Cameras in the Physical Sciences


High Energy Imaging

High energy radiation sources, such as X-rays, electron beams and neutron beams are important in the evaluation of the structural details of semi-opaque materials. With X-ray imaging techniques used in areas as varied as industrial quality control, non-destructive testing, crystallography and medicine, the need to optimise image quality has never been more important. Cooled CCD cameras offer outstanding capabilities for the recording of X-ray images, where contrast is often weak, and the variation of X-ray absorption by different materials can lead to saturation in conventional film images. The field of electron microscopy is well established in both materials and life sciences and full use can be made of the excellent sensitivity offered by cooled CCD cameras. Specialist techniques such as neutron beam irradiation are finding applications in the aerospace industry and, like X-ray systems, benefit from the wide dynamic range offered by PixCellent camera systems.


X-ray Imaging

Many samples inspected with X-rays feature areas of interest that have either relatively low absorbence, or a very wide range of absorbence. For example, hollow or less dense areas of the samples will allow much greater transmission of X-rays than solid, dense areas. In either case, the wide dynamic range of PixCellent imaging systems readily accommodates this wide range of intensities and still allows low contrast features to be inspected. these precision X-ray camera systems are able to detect features that would otherwise be lost in the background noise. Fast read out controller are available which are well suited to the demands of the latest production line volumes, by enabling X-ray images to be viewed in real time on a display monitor. this allows an instant decision to be made as to whether a component should be rejected or go onto the next stage of production. All PixCellent imaging systems are fully digital, so automatic analysis can be used to make product quality control easier, faster and more reliable.
PixCellent offers a range of seem-custom X-ray imaging configurations and can advise on phosphor, optical coupling and X-ray shielding issues.
The quality of the images obtained with PixCellent imaging systems is dramatically better than those obtained with film or conventional video cameras operating at TV rates. Applications using tomographic reconstruction methods benefit greatly from the excellent signal to noise ratio of data obtained from an PixCellent cooled CCD camera. The superb image quality is also invaluable in increasing customer and regulatory authority confidence when traceability is critical in, for example, the aerospace and defence industries. These industries frequently have requirements to store component information and images to up to 10 years following the end of production. Here, the use of electronic archiving methods, enabling images to be saved on disk, tape or optical disk can be of great benefit. Storing images in this way significantly reduces the amount of physical storage space required for the QC function.


Neutron Radiography

The recent development of a relatively compact superconducting cyclotron has made it possible for neutron radiography to be available at manufacturing sites.
Neutrons are strongly attenuated by hydrogenous materials, but less so by metallic elements. thus this radiographic technique can be used to image materials such as fluids, rubber, plastic or adhesive within a metallic assembly. These methods have recently been applied to engine development in the aerospace industry, where, for example, the flow of oil can be observed as the engine is operating. Other applications include identification of the presence and position of internal seals and gaskets, flows in hydraulic components and leakages. The use of cooled CCD cameras as part of the sophisticated imaging system for this technique, allows the rapid acquisition of high resolution images, displayed in a large screen format. Once again the wide dynamic range of the PixCellent cameras allows fine detail to be observed readily in the image. The digital images acquired can be transferred to a workstation for processing and analysis and for classification and storage of the data.


Applications for Cooled CCD Cameras in Spectroscopy and Astronomy

PixCellent has a long history in the development of cooled CCD cameras for applications in spectroscopy and astronomy. Imaging and spectroscopy in astronomy generally require long exposures. Such exposures often necessitate the use of liquid nitrogen coolers and thinned, large area CCDs. In contrast, for guiding and wavefront sensing, the need is for fast readout with the lowest possible read noise. Many other spectroscopic techniques, outside the field of astronomy, can benefit from the use of cooled CCDs to provide an extremely sensitive and versatile detection system.


Spectroscopy

Spectroscopy is used to analyse the composition of samples of many different types. An enormous variety of spectroscopic techniques produce very low light levels and require detectors with extremely wide dynamic range. These include Raman, inductively coupled plasma (ICP), fluorescence and absorbance spectroscopy. All benefit from the use of a cooled CCD imaging system for detection. PixCellent CCD systems offer speed of acquisition combined with excellent sensitivity and good contrast resolution. For some applications, a special parallel clock accelerator allows over a thousand spectra to be acquired at a rate of one million per second. In these systems, the CCD is operated in a different mode to standard imaging, with only a few rows of the CCD device illuminated by light emerging from the spectrograph. After each chosen exposure, the parallel clocks operate the device in frame transfer mode and the image acquired in the exposed rows undergoes a fast transfer to the next set of rows hidden under a mask. Repetition of this process moves the images acquired from each exposure under the masked part of the CCD until the store is full. The CCD can then be read out in the normal way.

PixCellent has experience with a variety of spectroscopic methods. Systems are available with extended UV response (out to 70 nm) or enhanced near IP response (out to beyond 1.0 microns). All PixCellent camera system are 2-dimensional imaging systems. These are ideally suited to the next generation of imaging spectroscopy applications, where 3-dimensional data sets (x, y and wavelength) are acquired.


Astronomy

Research in astronomy is highly competitive business and world-class astronomers simply cannot afford to compromise on the quality and performance of their detector systems. For many years PixCellent has been the acknowledged leader in supplying the highest performance CCD camera systems to the world's observatories. Whether the requirement is for imaging or spectroscopic detectors, for acquisition and guiding systems or for wavefront detection in active and adaptive optics applications, PixCellent has a suitable system for the job. Systems may be selected to give a read our noise of only a few electrons, with very high detector quantum efficiency or with frame rates in excess of 1000 Hz, depending on the application. PixCellent can also supply systems customised to individual requirements.
The sensitivity and dynamic range of the best cooled, high resolution CCD detector systems allow the study of galaxies that are billions of light years away. With sensitivity in the far red, to beyond 1 micron, new regions of the spectra of stars, galaxies and quasars can be investigated. Some of the faintest images and spectra ever taken have been obtained with PixCellent CCD detector systems for astronomy.
Atmospheric fluctuations seriously limit the performance of ground-based optical telescopes. The increasing importance of adaptive optical systems for wavefront correction applications has emphasised the need for sensitive low-noise camera systems able to operate at several hundred frames per second.
PixCellent systems are already in use at many observatories for acquisition, guiding, tip-tilt and Shack-Hartmann type wavefront sensing applications.


Acquisition and Guiding of Optical Telescopes

When a telescope is pointed at a particular object, the observer needs to verify that the field of view is as expected. this is achieved by imaging the field for, say, 0.1 to 10 seconds. A relatively rapid read-out and display capability is then needed and the cycle repeated until the field is centred. This is known as the acquisition phase. The next phase is to keep the field precisely aligned for the duration of the exposure which could be as long as one or two hours. Telescope guiding is achieved by selecting a star away from the main science field as a reference. A small area centred on the reference guide star is then read out at 0.1 to 10 Hz to allow any drift from the starting position of the reference object to be compensated for. this compensation can either be done manually or by an image processing system linked to the telescope automatically. A range of other sophisticated techniques are available to further improve the performance of astronomy systems. These include tip-tilt guiding, fast wavefront detection and wavefront error measurement systems. PixCellent can provide complete hardware and software solutions for these requirements, but is equally happy to co-operate in the development and supply of components to interface to existing hardware and software.


System Selection Made Easy

Choosing a camera system from PixCellent for your application couldn't be simpler. With system selection guides and expert advice available from PixCellent the optimum configuration can be chosen for both now and the future. Some practical examples are given here to show how the application determines the best choice of CCD detector, cooling head, controller etc. In addition, a comprehensive range of options and accessories ensures that the PixCellent system can be interfaced to almost any imaging device. Remember that we do not expect you to make the best selection without our help, and this we are always very happy to give.


Example 1: Application: Bioluminescence

A research worker studying gene replacement techniques in plants used the lux gene as a marker of the success or otherwise of her methods. She needed very high sensitivity to the luminescence and expected to need long integration times. PixCellent recommended a large area detector to allow the minimum demagnification onto the detector to maximise sensitivity. A thinned (back-illuminated) CCD gave over 80 percent detection efficiency at the wavelength of interest. To allow very long integration times and the possibility of on-chip binning to further increase sensitivity we advised a liquid nitrogen cooled system for ultimate low noise performance.


Example 2: Application: X-ray imaging

A manufacturer in the aerospace industries needed to check critical parts for internal stress cracks caused during the manufacturing process. Relatively high energy X-rays were used for this and the resolution of the X-ray source and the cracks to be detected called for a fairly high resolution (1280x1024) CCD to be read-out in a fraction of one second for inspection, storage, and archiving. PixCellent suggested its patented X-ray imaging technology, using a thermoelectrically cooled head with the CCD lens coupled to a custom phosphor screen matched to the X-ray energies to be used. The customer was particularly concerned about the detection of low contrast features and the cooled systems from PixCellent greatly exceeded the low-contrast capabilities of the film methods used previously. In addition, the digital data produced and archived by a system made by PixCellent greatly helped to convince regulatory authorities that components inspection and traceability requirements were being met.


Example 3: Application: Calcium Ratio Imaging

Calcium transport in cells happens on timescales of fractions of a second or less. In order to study this, pairs of images must be taken in different colours in rapid succession. A customer working with this application selected a fast-read cameras from PixCellent with a high resolution CCD detector of 80 by 80 pixels of 24 microns. By PixCellent's standards this was a relatively high light level application so short exposures (as short as 2 msec or 500 Hz frame rate at full resolution) could be used with a thermoelectrically cooled CCD head. Of particular value was the ability of the PixCellent fast controller to read out small sub-arrays on the CCD to further reduce the time interval between the frames in each pair. The camera was integrated onto the microscope with a fast filter wheel to give minimum time between consecutive frames within the pair or group, and for this application an interface to a specialist software package gave the customer a complete solution to their requirements.


Example 4: Application: Astronomy

A group of astronomers wishing to measure the local observing conditions on a site in the Canary Islands needed a camera capable of very fast read out over a small field of view. They wanted to use an array of small lenses to generate images of a star from each segment of the aperture of the telescope. The array of 8x8 lenses generated 64 star images onto a custom fast 64x64 pixel frame transfer detector. They were able to take up to 20,000 frames in one sequence at over 865 frames per second. This allowed accurate measurements of the image motions on a 4-metre telescope due to atmospheric fluctuations.


Full Software Control

All PixCellent camera systems are controlled by software. Using custom designed, Windows based packages running on PCs, workstations or a network environment, comprehensive facilities are provided for hardware control and image acquisition, display, archiving, processing and analysis. High quality images and control menus can be viewed in a single, high-resolution monitor or a multi-screen display. A host of facilities is provided to allow the system to be used in the manner most appropriate to the application. Our software is designed to be easy to use by non-experts as well as offering comprehensive facilities for the more experienced user wishing to customise the imaging system.


Camera control

Fingertip control of all important camera parameters is offered through PixCellent's sophisticated, yet simple to use software packages. Three key camera functions under user control are exposure time, readout rate and sensitivity. Adjusting the camera exposure time allows the system to be optimised for the type of signal available. Thus low level signals that change little over time will benefit from longer exposures, whilst dynamic events need shorter exposures. Motion in dynamic events can also be frozen by the choice of the appropriate exposure time. Programmable camera readout rate allows the optimum balance between signal to noise ratio and readout speed to be determined, depending on the particular application. The software can also control the camera sensitivity. In this way, the adjustments can be made to low light level response and grey level resolution. In addition, the software can be used to run the camera in special ways for certain applications, giving the user added flexibility. One very useful facility is that of sub-array readout. This allows readout speed to be increased whilst maintaining spatial resolution by using the software to select a specific sub-area of the image to be read out. The area of interest can be of any size and at any position on the detector chip. In this way, unwanted pixels are not read out, saving time.


Image manipulation

Since cooled CCD cameras are used to improve image quality, image capture, storage and display are important considerations. Simple software control allows images to be frozen (or captured) on the display screen and saved to disk if required. Images can be saved in standard formats for export to, for example, DTP packages. For image display, the control software allows multiple screens and image windows to be active. A high resolution colour monitor is used to display excellent quality pseudo-colour or greyscale images. A special dual monitor display facility is also available which allows two monitors to be used side by side as if they were a single monitor with twice the horizontal pixel resolution. The mouse moves smoothly from one screen to the other.


Customer Support

A software support service is offered through regular upgrades of all PixCellent software packages, All upgrades of relevant packages are supplied free of charge during the warranty period.


Windows 95/98 Software


Intuitive and easy to use

By providing software control of all the important camera parameters as well as image acquisition and manipulation, PixCellent imaging systems are extremely easy to use. The adoption of Windows user interfaces for control provides a flexible platform for future developments, yet is accepted as being a standard in the field of scientific instrumentation. It is also an ideal platform for the processing and analysis of images and comprehensive facilities are provided within the software for these purposes. A user interface based on the Windows environment is very versatile. It allows users to build their own operational routines to be initiated by a single command. Further evidence of the flexibility of PixCellent software is the availability of extension modules to allow software to be used in more specialist applications as well as developed for custom turn-key applications.


Image Processing and Analysis

An extensive range of image processing facilities are optionally provided, with algorithms for edge detection, convolution and geometric structure analysis as well as many morphological operations from binary erosion to grey scale segmentation techniques. Quantitative measurements can play an important role in numerous imaging applications. PixCellent systems are available with software which is designed to allow measurements from images or objects within images to be made. Such measurements include areas, moments of inertia and feret diameters, Measured values can be displayed graphically, or exported to other packages for further processing if required.


Customised System Development

PixCellent has made a substantial commitment to working with customers to develop customised systems. This collaboration works equally well with end users or OEM customers. The key to partnership success has been the ability to develop hardware and software systems that are targeted to specific requirements in order to provide cost-effective solutions. PixCellent has in-house expertise in the fields of analogue and digital electronics, computer hardware, software and systems, physics, optics, imaging, biochemistry and astronomy as well as design, manufacturing and production technologies. All of this will assure potential customers that working with PixCellent will yield the most cost-effective solutions without compromising quality.


Hardware development

PixCellent has the capability to develop either specialist sub-systems or complete instruments, depending on the particular need. Not only does the company have extensive experience in the development of electronic systems and sub-systems, but it also has expertise in areas of mechanical automation such as motorised platforms for cameras, filters and microscopes. In all developments, instrument integrity and operator safety and convenience are of paramount importance.


Software Development

PixCellent's software expertise extends well beyond camera control and image acquisition and manipulation. Software has been written for complete instrument operation and for customised image analysis, together with the design of user-friendly user interfaces.


Prototyping

PixCellent has the capability to take the design of instruments through to prototype stage and beyond into fill production for OEM customers. Using both in-house skills and local access to almost any technology that might be required, PixCellent can help to develop a continuing and evolving product line that provides outstanding performance at every stage of its evolution.


Documentation

A standard part of PixCellent's contribution to OEM agreements is the provision of high quality documentation, from technical drawings and parts lists to user manuals.


Further Information

PixCellent has produced a comprehensive set of supplementary information, which is updated regularly.


Customer Support Services


The Customer

A vital part of the PixCellent approach to business is the level of support services it offers to end-user and OEM customers alike. Support starts from help with the initial choice of system, through interfacing to existing equipment where appropriate, and finally to a telephone, fax and e-mail "Hotline" Support service.


The Company

PixCellent is a company with a world-wide reputation for supplying scientific imaging systems of the highest specifications and quality both to end users and to OEM customers.

 

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Site last updated: 12 April, 1999.