Retrospective gating on animal studies with microCT has gained popularity in recent years. Previously, we use ECG signals for cardiac gating and breathing airflow or video signals of abdominal motion for respiratory gating. This method is adequate and works well for most applications. However, through the years, researchers have noticed some pitfalls in the method. For example, the additional signal acquisition step may increase failure rate in practice. X-Ray image-based gating, on the other hand, does not require any extra step in the scanning. Therefore we investigate imagebased gating techniques. This paper presents a comparison study of the image-based versus signal-based approach to retrospective gating. The two application areas we have studied are respiratory and cardiac imaging for both rats and mice. Image-based respiratory gating on microCT is relatively straightforward and has been done by several other researchers and groups. This method retrieves an intensity curve of a region of interest (ROI) placed in the lung area on all projections. From scans on our systems based on step-and-shoot scanning mode, we confirm that this method is very effective. A detailed comparison between image-based and signal-based gating methods is given. For cardiac gating, breathing motion is not negligible and has to be dealt with. Another difficulty in cardiac gating is the relatively smaller amplitude of cardiac movements comparing to the respirational movements, and the higher heart rate. Higher heart rate requires high speed image acquisition. We have been working on our systems to improve the acquisition speed. A dual gating technique has been developed to achieve adequate cardiac imaging.
The grating based approach to phase contrast imaging is rather inefficient in the use of the available x-ray flux
due to the presence of two absorption gratings and it requires longer scan times compared to conventional CT
because multiple images are needed at each projection angle. To avoid these drawbacks, a proof-of-principle
experiment was developed to obtain absorption, phase contrast (DPC) and dark field images (DCI) in a single
exposure using only a non-absorbing phase grating, a micro-focus source in cone-beam geometry and a highresolution
Image registration is a powerful tool in various tomographic applications. Our main focus is on microCT
applications in which samples/animals can be scanned multiple times under different conditions or at different
time points. For this purpose, a registration tool capable of handling fairly large volumes has been developed,
using a novel pseudo-3D method to achieve fast and interactive registration with simultaneous 3D visualization.
To reduce computation complexity in 3D registration, we decompose it into several 2D registrations, which are
applied to the orthogonal views (transaxial, sagittal and coronal) sequentially and iteratively. After registration
in each view, the next view is retrieved with the new transformation matrix for registration. This reduces the
computation complexity significantly. For rigid transform, we only need to search for 3 parameters (2 shifts, 1
rotation) in each of the 3 orthogonal views instead of 6 (3 shifts, 3 rotations) for full 3D volume. In addition, the
amount of voxels involved is also significantly reduced.
For the proposed pseudo-3D method, image-based registration is employed, with Sum of Square Difference
(SSD) as the similarity measure. The searching engine is Powell's conjugate direction method. In this paper,
only rigid transform is used. However, it can be extended to affine transform by adding scaling and possibly
shearing to the transform model. We have noticed that more information can be used in the 2D registration if
Maximum Intensity Projections (MIP) or Parallel Projections (PP) is used instead of the orthogonal views. Also,
other similarity measures, such as covariance or mutual information, can be easily incorporated.
The initial evaluation on microCT data shows very promising results. Two application examples are shown:
dental samples before and after treatment and structural changes in materials before and after compression.
Evaluation on registration accuracy between pseudo-3D method and true 3D method has been performed.
We have developed a compact grating-based in-vivo phase-contrast micro-CT system with a rotating gantry. The 50 W microfocus x-ray source operates with 20 to 50 kV peak energy. The length of the rotating interferometer is around 47 cm. Pixel size in the object is 30 micron; the field of view is approx. 35 mm in diameter, suited to image a mouse. The interferometer consists of three gratings: an absorption grating close to the x-ray source, a phase grating to introduce a π/2 phase shift and an absorption analyzer grating positioned at the first fractional Talbot distance. Numerous drives and actuators are used to provide angular and linear grating alignment, phase stepping and object/gantry precision positioning. Phantom studies were conducted to investigate performance, accuracy and stability of the scanner. In particular, the influences of gantry rotation and of temperature fluctuations on the interferometric image acquisition were characterized. Also dose measurements were performed. The first imaging results obtained with the system show the complementary nature of phase-contrast micro-CT images with respect to absorption-based micro-CT. Future improvements, necessary to optimize the scanner for in-vivo small-animal CT scanning on a regular and easy-to-use basis, are also discussed.
In our dual-modality microCT/microXRF system, the two sub-systems are combined in one machine, sharing a
travelling sample holder. The microXRF, based on a pin-hole collimator and a photon-counting energysensitive 2D-detector, obtains 3D chemical composition maps of a sample. These images often lack structural information. With the built-in microCT, 3D structural information of the sample can be obtained. The two subsystems need to be properly calibrated and aligned. This calibration and alignment procedure needs to be done for all pin-hole collimators, but only need to be performed once after the system is assembled. The two modalities are calibrated separately, by analyzing projection images of a 3-ball phantom. The phantom is made of a very thin plastic cylinder, on which 3 copper balls are attached at well-chosen locations. The same phantom is used for both sub-systems and is scanned sequentially. We have evaluated this calibration method on various CT scanners and it has proven to be very effective. But it is more challenging for the XRF subsystem due to the strong absorptions. The two imaging spaces are calibrated relative to their own coordinate systems. To align the two sub-systems, the centers of the balls in reconstructed volumes are determined and then aligned using a rigid transformation. Repeated tests have shown that the mechanical movements are stable and the reconstructed image volumes can
be well co-registered.
In synchrotron set-ups with a parallel x-ray beam, the spatial resolution is fully defined by the x-ray camera performance.
This is also true in some laboratory x-ray imaging and CT instruments with an object position close to the detector. Fiber
optic coupling does not allow camera resolutions reaching micron and submicron range, while cameras with lens
coupling demonstrate resolutions close to diffraction limit, i.e. around 0.5 microns.
Considering the conversion of x-rays to light in scintillator materials as a type of fluorescence under certain excitation, it
should be possible to implement a method similar to Stochastic Optical Reconstruction Microscopy (STORM) in
fluorescent microscopy to overcome diffraction limit in detector resolution. Our idea to overcome diffraction limit in
such detectors is as follows. Every x-ray photon produces a significant amount of optical photons emitted from one
particular point inside the scintillator. A fraction of the emitted optical photons is collected by a lens and hits the detector
with a spread defined by the diffraction limit. Comparing the signal spread from every individual x-ray photon with the
expected pre-calculated spread function, one can find the exact positions of primary x-ray photon. Using such exact
positions to create images instead of collecting all incoming optical photons allows tracking exact positions of all
original emitting points of x-ray photons without influence of optical diffraction limit. It can create images with a spatial
resolution significantly better than what can be achieved in conventional diffraction limited optical acquisition.
Proper selection of modern key components allows eliminating most artifacts in micro-CT and nano-CT systems already
during data acquisition. X-ray cameras with direct photon detection allow avoiding ring artifacts. Newly developed fully
depleted CCD sensors show an energy response similar to traditional cameras with a thin scintillator, but without any
geometrical distortions and flashes from x-ray photons penetrating through the fiber optics. Air-bearing rotation stages
and piezo-positioning minimizes mechanical inaccuracies in acquiring angular projections. Beam hardening can be
eliminated by energy-selective photon counting imaging.
X-ray fluorescence (XRF) allows imaging of the chemical composition of a specimen. We developed a 2<sup>nd</sup> generation
prototype laboratory system that can produce 3D chemical maps using microXRF as well as volumetric microCT
images. The latter can be used to overlay morphological information on top of the XRF image for co-registration. It is
also employed for attenuation correction during the tomographic reconstruction of the XRF images. The new system has
various hardware and software changes to improve the performance, stability and flexibility. A deep depleted CCD was
employed to improve the detection efficiency for high-energy fluorescence X rays. The use of a deep depleted CCD
requires signal-clustering techniques to correct for charge diffusion in the CCD to obtain the correct energy of the
fluorescence x rays. Furthermore, energy drift correction techniques were put in place to ensure stability of energy
measurement during very long scan times. To minimize the contribution of the long CCD readout times to the total scan
time, the exposure frames are dynamically adjust during the scan to the maximum time allowed for operation under
photon counting mode. The XRF component has a spatial resolution of 70 μm and an energy resolution of 180 eV at 6.4
An integrated microCT/microXRF system has been designed and built at SkyScan. The two sub-systems are aligned. The
microCT provides 3D morphological information of the sample, which can be also used for attenuation correction during
microXRF reconstruction. The microXRF, based on a pin-hole collimator and a photon-counting energy-sensitive 2Ddetector,
obtains 2D projections of 3D chemical composition inside the sample with 50-70 microns spatial resolution.
The reconstruction of 3D microXRF scans is challenging because of very low photon counting statistics due to limited
power of laboratory x-ray sources and the strong self-absorption of the low-energy fluorescence photons. We have
developed a maximum-likelihood expectation-maximization (ML-EM) algorithm based on Poisson model. This
algorithm has proven to be rather robust and good reconstructions have been obtained with sample scans. Regularization
is necessary to achieve stable reconstruction. One method is to apply smoothing between iterations. Two different
smoothing kernels have been evaluated: 3D symmetric Gaussian kernel and minimization of total variation. For further
improvement, a multi-ray resolution recovery technique has been evaluated.
The self-absorption is currently compensated by a simplified method: the correction coefficients are pre-calculated and
obtained by forward-projecting the attenuation map for both the primary X-rays and the fluorescence photons. The
attenuation maps at the energy of fluorescence photons are approximated from the CT image.
Most X-ray systems are limited in spatial resolution by the x-ray source performance. In laboratory sources, x-rays are
generated by the interaction of an electron beam with a metal target. Bulk target sources produce a spot size in the
micron range. Thin layer targets allow a spot size improvement down to hundreds of nanometers, but with a significant
flux reduction. Until now a spatial resolution under 100 nm could only be achieved by imaging with Fresnel zone plates
with limited depth of focus, typically - several microns. This is acceptable for imaging of flat objects, but it creates a
problem for tomography, which requires all parts of a bulk object to be in focus.
To overcome the limitations, we invented an x-ray source with a new type of target. Because x-ray cameras can only
collect photons from a small angle, the new emitter is physically shaped in such way that the camera can see it as a small
dot, but it has a big length along the direction perpendicular to the camera creating a significant flux without
compromising the resolution. Evaluation shows that structures down to 50 nm can be distinguished while maintaining a
significant x-ray flux and infinite depth of focus required for nano-tomographical reconstruction.
We have developed an x-ray computer tomography (CT) add-on to perform X-ray micro- and nanotomography in any
scanning electron microscope (SEM). The electron beam inside the SEM is focused on a metal target to generate x-rays.
Part of the X-rays pass through the object that is installed on a rotation stage. Shadow X-ray images are collected by a
CCD camera with direct photon detection mounted on the external wall of the SEM specimen chamber. An extensive
description on the working principles of this micro/nano-CT add-on together with some examples of CT-scans will be
given in this paper. The resolution that can be obtained with this set-up and the influence of the shape of the electron
beam are discussed. Furthermore, possible improvements on this SEM-CT set-up will be discussed: replacing the backilluminated
CCD with a fully depleted CCD with improved quantum efficiency (QE) for higher energies, reduces the
exposure time by 6 when using metal targets with x-ray characteristic lines around 10 keV.
Reconstruction theory requires that an object should be fully inside the field of view (FOV) of the scanning geometry. This implies that the number of pixels in the detector determines the smallest resolvable details for a given FOV size. Many commercially available micro-CT scanners use a 1-megapixel cameras with 1K pixels in horizontal direction, which can resolve features of 1/1000 of the FOV size. Using a large format detector and a few offset positions will
increase imaging resolution, but will also dramatically reduces
number of X-ray photons collected per pixel. To improve acquisition efficiency without compromising scanning time, we developed and implemented in commercially produced SkyScan-1172 scanners an adaptive geometry approach. To achieve a chosen magnification, the distances between x-ray source, detector and object are adjusted automatically to most compact geometry with maximum use of X-ray. This
adaptive geometry improves significantly the acquisition speed for a large range of magnifications and allows using 10+ megapixels detectors instead of detectors with 1-2 megapixels. Flexible acquisition geometry also opens possibility to use phase-contrast enhancement for improvement in spatial resolution.
Many detection systems for acquiring two-dimensional projections in emission tomography (like SPECT, micro-SPECT, micro-XRF) are based on pinhole optics and a photon counting array detector. Practically all such detection systems use a standard round pinhole with cone-shaped openings on both sides to improve efficiency for inclined beams. Theoretical analysis shows that a square pinhole with pyramidal openings can improve sensitivity and efficiency of photon detection
of such detectors. Replacing a round/cone pinhole by a square/pyramidal one increases the number of counted photons in
the central part of the image by 25% and even more in the sides and in the corners of the imaging area. In the case of multi-pinhole optics, square pinhole shape allows better filling of used detector area without overlaps of partial images. Experimental comparison between round and square pinholes has been done on a micro-XRF setup. The imaging geometry parameters are identical in both cases. Performance is evaluated on efficiency and spatial resolution. The tests show significant efficiency improvement in the case of using a camera with a square pinhole shape.
Micro-CT and especially nano-CT scanning requires very high mechanical precision and stability of object manipulator, which is difficult to reach. Several other problems, such as drift of emission point inside an X-ray source, thermal expansion in different parts of the scanner, mechanical vibrations, and object movement or shrinkage during long scans, can also contribute to geometrical inaccuracies. All these inaccuracies result in artifacts which reduce achievable spatial resolution. Linear distortions can be partially compensated by rigid X/Y shifts in projection images. More complicated object movement and shrinkage will require non-linear transforms. This paper investigates techniques to compensate geometrical inaccuracies by linear transformation only. We have developed two methods to estimate individual X/Y shifts in each measured projection. The first method aligns measured projections with forward-projected projections
iteratively to reach an optimal X/Y shift estimation. It is more suitable for mechanical inaccuracies caused by random and jittery movement. The second method uses a very short reference scan acquired immediately after a main scan to obtain estimates of X/Y shifts. This method is rather effective for mechanical inaccuracies caused by slow and coherent mechanical drifts. Both methods have been implemented and evaluated on multiple scanners. Significant improvements
in image quality have been observed.
High resolution micro-CT scanners are becoming widely used for <i>in vivo</i> imaging of small laboratory animals. However, imaging of chest area remains a challenging task due to periodic respiratory and cardiac motion, where respiratory motion dominates. To reduce motion artifacts and to allow dynamic imaging, we propose a retrospective
synchronization method for scans of chest area in our <i>in vivo</i> micro-CT scanners. In this synchronization method, we acquire projection images in a step-and-shoot mode, where multiple images are acquired covering more than one motion cycle at each step with exact time marks of every acquisition. In the meanwhile motion signals are recorded. An offline sorting program has been developed to sort images into corresponding motion phases. We have evaluated our method on respiratory motion. Compared to prospective synchronization methods, our method has several advantages: 1. flexible in
sorting; 2. continuous imaging: maximum utilization of radiation dose applied to the animal; 3. possibility for 4D dynamic imaging; 4. can be used during irregular breathing cycle. This method has been applied to two of SkyScan <i>in-vivo</i> scanners. Initial results indicate that the proposed method is adequate.
We have developed a compact laboratory scanner, which combines X-ray microtomography (microCT) with X-ray microfluorescence tomography (3D microXRF). This dual-modality scanner opens possibility for nondestructive threedimensional volumetric analysis of local chemical composition, enhanced by morphological information provided by the
built-in microCT. Unlike known microXRF methods based on collimated beam and detector, our microXRF scanner includes a full-field acquisition system based on an energy-sensitive detector with 512x512 pixels operating in photon counting mode. It allows detection of two-dimensional photon energy distribution in the range of 3...20keV. Up to 8 sets of energy windows can be selected for independent and simultaneous collection of microXRF images. By object rotation
the scanner acquires projections in transmission and fluorescence mode for subsequent 3D reconstruction. The system acquires data in such a way that the CT scans and XRF scans match each other in magnification and angular position. This makes image registration much easier and more accurate. MicroCT data is reconstructed with a FBP algorithm. All microXRF datasets are reconstructed by a maximum likelihood iterative algorithm, which uses corresponding CT images
for absorption correction.
A new, ultra-fast microCT instrument with scanning+reconstruction cycle under 50 seconds for full 3D-volume has been created. The scanner based on the scanning geometry with static object and rotation of source-camera pair(s), which allows using it for industrial applications as well as for low-dose in-vivo imaging of small laboratory animals where rotation of the object is not acceptable. Acquisition part contains two pairs of x-ray sources and cameras for data collection from complementary directions simultaneously. Reconstruction engine (cone-beam reconstruction by modified Feldkamp algotithm) includes 1, 2 or 4 dual Intel-Xeon computers working in parallel under control of the host PC through local network. The instrument specifications are following: voxel size is 48 or 96 um for corresponding 1024x1024x1024 or 512x512x512 reconstruction array; scanning time with parallel reconstruction is 50 seconds for 96um resolution. X-ray sources peak energy can be adjusted in the range of 20-65kV. Typical scanning dose is 0.4Gy. The scanner itself is a compact desktop instrument, which contains all x-ray parts and necessary shielding for safe operations in the normal laboratory environments.
A compact laboratory x-ray "nano-CT" scanner has been created for 3D non-invasive imaging with 150-200 nanometers 3D spatial resolution, using advanced x-ray technologies and specific physical phenomena for signal detection. This spatial resolution in volume terms is 3 orders better than can be achieved in synchrotron tomography, 5 orders better then in existing laboratory micro-CT instruments and 10-12 orders better in comparison to clinical CT. The instrument employs an x-ray source with a 300-400nm x-ray spot size and uses small-angle scattering to attain a detail detectability of 150-200nm. An object manipulator allows positioning and rotation with an accuracy of 150nm. The x-ray detector is based on an intensified CCD with single-photon sensitivity. A typical acquisition cycle for 3D reconstruction of the full object volume takes from 10 to 60 minutes, with the collection of several hundred angular views. Subsequent volumetric reconstruction produces results as a set of cross sections with isotropic voxel size down to 140 x 140 x 140nm, or as a 3D-model, which can be virtually manipulated and measured. This unique spatial resolution in non-invasive investigations gives previously unattainable 3D images in several application areas, such as composite materials, paper and wood microstructure, biomedical applications and others.
This is the first report where desktop x-ray microtomography was implemented for quantitative analysis of the level of calcification in different organic material from early stage embryos to bones. A technique for the definition of local calcium density was developed. Differences in local calcium density from 0.7*10<SUP>9</SUP> to 11.7*10<SUP>9</SUP> (atoms per micrometers <SUP>3</SUP>) were detected.
Small laboratory animals (mice and rats) are widely used in development of drugs and treatments. To recognize the internal changes in the very early stage inside the body of alive animal, high-resolution micro-CT scanner has been developed. Initial changes in the bone structure can be found as features in the size range of 10 microns. By this reason a voxel size for reconstructed cross sections has been chosen as small as 10 microns. Full animal body may be up to 80 mm in diameter and up to 200 mm in length. By this reason the reconstructed cross section format selected as 8000 x 8000 pixels (float-point). A new 2D detection system with multibeam geometry produces dataset for reconstruction of hundreds of cross sections after one scan. Object illuminated by microfocus sealed x-ray source with 5 microns spot size. Continuously variable energy in the range of 20- 100 kV and energy filters allows estimate material composition like in DEXA systems. Direct streaming of the projection data to the disk reduce irradiation dose to the animal under scanning. Software package can create realistic 3D images from the set of reconstructed cross sections and calculate internal morphological parameters.
An x-ray microtomograph (or micro-CT) is an instrument for nondestructive 3-dimensional reconstruction of the object's internal microstructure without physical cut or time consuming specimen preparation. By using modern technology in x-ray sources and detectors several micro-CT systems were created as a simply usable desktop instrument. First micro- CT system is a laboratory instrument, giving true spatial resolution over ten million times more detailed (in the term of volume parts) than the medical CT-scanners. The instrument contains a sealed microfocus x-ray source, a cooled x-ray digital CCD-camera and a Dual Pentium computer for system control and 3D reconstructions running under Windows 2000. The instrument includes possibilities for image analysis in the nondestructively reconstructed internal microstructure and realistic 3D visualization. During scanning, objects are displaced in normal environment conditions, without vacuum or preparation. Another micro-CT scanner is a low-cost portable instrument, which can be connected to any external Pentium-based PC. Third instrument - microlaminograph - can create nondestructive slicing in any place of big planar objects (electronic assemblies, PCBs, etc.). This system uses principles of tomosynthesis from incomplete dataset for slicing in internal object's layers. The main application areas for micro-CT and microlaminography systems are biomedical research, material sciences, electronic components, etc.
Nondestructive information from the internal structure of plastic and composites in natural or adjustable environmental conditions can be obtained by transmission x- ray microscopy. Combination of x-ray microscopy technique with tomographical reconstruction allows getting three- dimensional information about the internal microstructure. A desktop x-ray microscopy-microtomograph SkyScan-1072 has been used in different application areas including plastic, epoxy and metal composite materials and products. The x-ray magnification ranges between 15 and 180. Reconstruction time is near 10 sec per cross section. One of most important application area is composite material where one wants to investigate the 3D structure and reaction to external influences. The system allows obtaining transmission image through the object's materials and to reconstruct nondestructively any cross section or complete internal 3D structure. The sample can be loaded in situ to investigate the reaction of matrix and enforcing structures to external strain. Liquid's absorption and transport through porous materials can be shown directly in three-dimensions. Small details up to 2-3 micrometer in size can be visualized inside the specimen. Software included powerful image processing package to calculate the numerical characteristics of the object's internal microstructure and to create realistic 3D visualization with possibilities of rotation and cutting of reconstructed object into the screen as well as flight simulator for fly through the object microstructure. Microscopical 3D visualization without vacuum and coatings allows displaying the natural specimen structure as well as examine its behavior under external influences (loading, chemical reactions, interaction with other solids, liquids, gases, etc.).
Laboratory instruments for high-resolution microtomography (micro-CT) are based on the object irradiation by the x-ray sources with spot size in the micron range. The microfocus laboratory x-ray sources produce x-ray radiation by interaction of electron beam with a metal target. Spot size in this case is defined by focusing of electron beam and limited by melting point of the metal target. That means the improvement in spot size and spatial resolution can be done only against power of the x-ray sources. For most effective collection of x-ray flux from the low-power sources two- dimensional detectors should be used for images acquisition. By this reason the x-ray geometry in the high-resolution micro-CT instruments corresponding to cone-beam acquisition with relatively big divergent angle. In such geometry all conventional fan-beam CT-reconstruction algorithms may produce significant geometrical distortions. We developed and tested reconstruction software packages for different algorithms: fan-beam, cone-beam (Feldkamp) and spiral (helical) scans using two-dimensional detectors. All algorithms were applied to different simulations as well as to the real datasets from the commercial micro-CT instruments. From the results of testing a number of strong and weak points at different approaches have been found.
We developed and tested reconstruction software packages for different algorithms: fan-beam, cone-beam (Feldkamp) and spiral (helical) scans. All algorithms were applied to different simulations as well as to the real datasets from the commercial micro-CT instruments. From the results of testing a number of strong and weak points at different approaches was found. Several examples from the different application areas (bone microstructure, industrial applications) show typical reconstruction artifacts with different algorithms.
Small laboratory animals (mice and rats) are widely used in development of drags and treatments. To recognize the internal changes in the very early stage inside the animal body, Skyscan starts development on high-resolution micro-CT scanner for in-vivo 3D-imaging. Initial changes in the bone structure can be found as features in the size range of 10 microns. By this reason a voxel size for reconstructed cross sections has been chosen as < 10 microns. Because of full animal may be up to 8 cm in diameter the reconstructed cross section format selected as 8000 X 8000-pixels (float- point). A 2D detection system with new multi-beam geometry produce dataset for reconstruction of hundreds cross- sections after one scan. Object illuminated by microfocus sealed X-ray source with 5 microns spot size. Continuously variable energy in the range of 20 - 100 kV and energy filters allows estimate material composition like in DEXA systems. Direct streaming of the projection data to the disk reduce irradiation dose to the animal under scanning. Software package can create realistic 3D-images from the set of reconstructed cross sections and calculate internal morphological parameters.
An X-ray microtomography (or micro-CT) is an instrument for high-resolution 3D reconstruction of objects internal microstructure without destruction or time consuming specimen preparation. By using modern technology in x-ray sources and detectors several micro-CT systems were created as a simply usable desktop instrument. First micro-CT system is a laboratory instrument, giving true spatial resolution over a ten million times more detailed (in the term of volume parts) than the medical CT-scanners. The instrument contains a sealed microfocus X-ray source, a cooled X-ray digital CCD-camera and a Dual Pentium computer for system control and 3D-reconstructions running under Windows NT.
The combination of x-ray microscopy with tomographical reconstruction allows getting 3D information about the internal microstructure by a non-destructive way. A desktop high- resolution X-ray micro-CT (microtomograph) has been developed for 3D reconstruction and realistic visualization of the internal microstructure with spatial resolution in the micron range. The instrument was successfully tested for inspection, defectoscopy and back engineering in MEMS and integrated multichip sensors.
X-ray laminography is a method that allows getting local depth information from big flat objects like PCBs and electronic assemblies. The few X-ray laminography systems recently introduced on the market cannot reach the spatial resolution that is necessary for inspection of modern electronic assemblies. According to the needs in high-resolution inspections for electronic industry a digital X-ray microlaminography system has been developed on the base of multilayer tomosynthesis approach. This instrument is based on the new x-ray geometry with minimum moving parts. It can reach a spatial resolution of several microns in plane and in depth and visualize layer-by-layer area of 5 X 5 mm at any place in an object up to several hundreds mm in size. Typical scanning time is 20 seconds for 20 layers and 90 seconds for 100 layers. The software package includes the system control and multilayer tomosynthesys (layer-by-layer separation) during acquisition, as well as a three-dimensional rendering program for realistic visualization of the object's microstructure. The main application areas are BGA inspection, Flip-Chips, multilayer PCBs, micromechanics (watch, etc.).
Microtomography systems usually are laboratory devices designed for defectoscopy and three- dimensional nondestructive testing. Initial data acquisition for X-ray and optical microtomography takes a relatively long time because of the low radiation intensity of fine- focus sources. It is therefore impracticable to employ expensive specialized processors for data input and image reconstruction. A more practical approach involves the use of image processing systems based on personal computers. It is shown that such equipment can handle the tasks of data acquisition and 3-D image reconstruction and visualization very effectively. The efficiency of a microtomograph system depends on the capabilities of software and of the system of data input into the computer. To speed up image reconstruction, use is sometimes made of a specialized coprocessor to carry out convolution with back projection. The software package usually contains programs to perform the operations of image reconstruction and 3-D visualization.