Imaging Of Small Objects Research Articles

A compact gamma camera with scintillation array and parallel-hole collimator

A new compact gamma camera for small object imaging has been developed. It consists of a pixelized Nal(T1) scintillator array coupled to a position sensitive photomultiplier tube (Hamamatsu R2486) with a parallel-hole lead collimator. The compact camera has better spatial resolution than Anger camera. The average value of intrinsic spatial resolutions is 2.3 mm (FWHM). The overall spatial resolution (FWHM) is 3, 5 and 6 mm at 0, 2.5 and 3 mm SCD (source-to-collimator distance), respectively. The phantom studies with the compact camera have demonstrated that parallel-hole collimator gamma camera is a practical technique for nuclear medicine application.

Performance Evaluation of Macro Lens for Digital Close Range Photogrammetry

Recently, documentation and visualization of various cultural heritages have been receiving attention, and small Buddha such as less than 10 cm tall which was stored in the womb of Buddha is also included in cultural heritages. In order to document these small objects in conservation of cultural heritage, zoom lenses are generally used. However, there are still issues for digital documentation of these small objects using zoom lenses. These problems include sharp imaging and distortions which occur with changes in focal length setting. On the other hand, macro lenses have ability in sharp imaging of small objects from the view point of working distance.With this motive, zoom and macro lens was mounted on digital single lens reflect camera, and accuracy and performance evaluations of the both lenses were investigated in this paper.

Multi-pinhole collimator design for small-object imaging with SiliSPECT: a high-resolution SPECT

We have designed a multi-pinhole collimator for a dual-headed, stationary SPECT system that incorporates high-resolution silicon double-sided strip detectors. The compact camera design of our system enables imaging at source–collimator distances between 20 and 30 mm. Our analytical calculations show that using knife-edge pinholes with small-opening angles or cylindrically shaped pinholes in a focused, multi-pinhole configuration in combination with this camera geometry can generate narrow sensitivity profiles across the field of view that can be useful for imaging small objects at high sensitivity and resolution. The current prototype system uses two collimators each containing 127 cylindrically shaped pinholes that are focused toward a target volume. Our goal is imaging objects such as a mouse brain, which could find potential applications in molecular imaging.

Plasma focus based repetitive source of fusion neutrons and hard x-rays

A plasma focus device capable of operating at 0.2 pulses per second during several minutes is used as a source of hard x-rays and fast neutrons. An experimental demonstration of the use of the neutrons emissions for radiation probing of hydrogenated substances is presented, showing a particular application in detecting water concentrations differences in the proximity of the device by elastic scattering. Moreover, the device produces ultrashort hard x-rays pulses useful for introspective images of small objects, static or in fast motion, suitable for the identification of internal submillimetric defects. Clear images of metallic objects shielded by several millimeters iron walls are shown.PACS Codes: 29.25.Dz,52.59.Px

A compact CT/SPECT system for small-object imaging

We report herein on a low-cost, high-performance dual imaging modality CT/SPECT system for small objects or animals. The system is realized from a commercial micro-focus X-ray tube, a Gd2O2S:Tb phosphor screen and a CCD camera. SPECT/planar imaging is obtained using a pinhole collimator with the same camera module as for X-ray/CT. Fusion of anatomic and functional images from the two modalities is easily accomplished by adjusting the magnification of the two modalities. Using an X-ray tube of 15 μm focal spot size, an image magnification of 1:1500, a field of view of 110 mm×110 mm, and adopting variable gamma detection geometry, the system may serve for numerous imaging applications and can be expanded into high-sensitivity (300 cpm/μCi), sub-millimeter (0.86 mm) SPECT resolution over a field of view of 20 mm in diameter.

Subpixel edge location based on orthogonal Fourier–Mellin moments

In order to satisfy the stringent requirements for edge location accuracies in such fields as medical image analysis and satellite remote sensing, an approach based on orthogonal Fourier–Mellin moments is proposed to use the lower radial orders and the rotation invariance of these moments to describe small objects in images, and edge location is accomplished by setting the edge in the vertical direction and analyzing the interrelationships among the orthogonal Fourier–Mellin moments with different orders and degrees, and consequently the specific characteristics of the edge can be fully extracted. Experimental results show that the proposed method can be used to achieve an edge location accuracy of 0.16 pixel for straight lines with noise and 0.23 pixel for curves with noise. It can therefore be concluded that the proposed method is an efficient approach to satisfy the stringent requirements for higher edge location accuracies in such fields as medical image analysis and satellite remote sensing.

Kinetic Models for Imaging in Random Media

We derive kinetic models for the correlations and the energy densities of wave fields propagating in random media. These models take the form of radiative transfer and diffusion equations. We use these macroscopic models to address the detection and imaging of small objects buried in highly heterogeneous media. More specifically, we quantify the influence of small objects on (i) the energy density measured at an array of detectors and (ii) the correlation between the wave field measured in the absence of the object and the wave field measured in the presence of the object. We analyze the advantages and disadvantages of such measurements as a function of the level of disorder in the random media. Numerical simulations verify the theoretical predictions.

TH‐C‐330A‐04: Novel Learning‐Based Approach to Optimal EPID Image Deblurring and Enhancement

Purpose: Finite focal spot size in X‐ray imaging equipment has a blurring effect on acquired images. For practical reasons, it is neither possible nor desirable to reduce the spot size of medical linacs below a certain diameter. This affects task performance in IGRT, where the blurring of the edges of structures reduces positioning accuracy. Since the focal spot size and shape of linacs vary, the filter must be customized to a particular linac. We have developed an algorithm that learns to deblur portal images by comparing actual images to their Monte Carlo (MC) generated ideal counterparts. Method and Materials: A training object containing sharp edges of all orientations is imaged to capture the blurring and noise characteristics of the system. MC simulations in which a point source irradiates a digital version of the training object are used to generate ideal images. These are used as training data to optimize the convolution kernel that effects deblurring. Owing to the nature of the training data, the kernel will deblur the image as well as enhance edges. We assume since the object is 1m from the source, blurring is uniform for all transverse object planes. Results: Large samples of phantom and patient images were used to evaluate filter performance. A marked improvement in image quality is apparent. Evaluation of spatial resolution (MTF) and contrast‐to‐noise ratio (CNR) reveals a dramatic improvement in MTF but reduction in CNR. However, since the CNR remains above 70 at doses of 1MU, the increase in noise will not effect IGRT task performance. Conclusion: This work indicates the utility of this novel image enhancement technique in clinical images. In particular, visibility of small objects in images, such as prostate seeds, is remarkably enhanced.Conflict of Interest: Sponsored by Siemens.

Evaluating performance of a pixel array semiconductor SPECT system for small animal imaging

Small animal imaging has recently been focused on basic nuclear medicine. We have designed and built a small animal SPECT imaging system using a semiconductor camera and a newly designed collimator. We assess the performance of this system for small object imaging. We employed an MGC 1500 (Acrorad Co.) camera including a CdTe semiconductor. The pixel size was 1.4 mm/pixel. We designed and produced a parallel-hole collimator with 20-mm hole length. Our SPECT system consisted of a semiconductor camera with the subject holder set on an electric rotating stage controlled by a computer. We compared this system with a conventional small animal SPECT system comprising a SPECT-2000H scanner with four Anger type cameras and pinhole collimators. The count rate linearity for estimation of the scatter was evaluated for a pie-chart phantom containing different concentrations of 99mTc. We measured the FWHM of the 99mTc SPECT line source along with scatter. The system volume sensitivity was examined using a flood source phantom which was 35 mm long with a 32-mm inside diameter. Additionally, an in vivo myocardial perfusion SPECT study was performed with a rat. With regards to energy resolution, the semiconductor camera (5.6%) was superior to the conventional Anger type camera (9.8%). In the count rate linearity evaluation, the regression lines of the SPECT values were y = 0.019x + 0.031 (r2 = 0.999) for our system and y = 0.018x + 0.060 (r2 = 0.997) for the conventional system. Thus, the scatter count using the semiconductor camera was less than that using the conventional camera. FWHMs of our system and the conventional system were 2.9 +/- 0.1 and 2.0 +/- 0.1 mm, respectively. Moreover, the system volume sensitivity of our system [0.51 kcps/(MBq/ ml)/cm] was superior to that of the conventional system [0.44 kcps/(MBq/ml)/cm]. Our system provided clear images of the rat myocardium, sufficient for practical use in small animal imaging. Our SPECT system, utilizing a semiconductor camera, permits high quantitative analysis by virtue of its low scatter radiation and high sensitivity. Therefore, this system may contribute to molecular imaging of small animals and basic medical research.

Evaluation of an efficient compensation method for quantitative fan-beam brain SPECT reconstruction

Fan-beam collimators are designed to improve the system sensitivity and resolution for imaging small objects such as the human brain and breasts in single photon emission computed tomography (SPECT). Many reconstruction algorithms have been studied and applied to this geometry to deal with every kind of degradation factor. This paper presents a new reconstruction approach for SPECT with circular orbit, which demonstrated good performance in terms of both accuracy and efficiency. The new approach compensates for degradation factors including noise, scatter, attenuation, and spatially variant detector response. Its uniform attenuation approximation strategy avoids the additional transmission scan for the brain attenuation map, hence reducing the patient radiation dose and furthermore simplifying the imaging procedure. We evaluate and compare this new approach with the well-established ordered-subset expectation-maximization iterative method, using Monte Carlo simulations. We perform quantitative analysis with regional bias-variance, receiver operating characteristics, and Hotelling trace studies for both methods. The results demonstrate that our reconstruction strategy has comparable performance with a significant reduction of computing time.

Large area x-ray and neutron imaging using three-dimensional arrays of microlenses

Linear arrays of biconcave microlenses have been shown to be capable of imaging small objects using either x rays or neutrons. Because these lenses have small apertures and finite lengths, they are limited in their field of view (FOV). To increase the FOV, we propose that two sets of three-dimensional arrays of these microlenses be used. The spacing of the microlenses is calculated to achieve a complete image with uniform brightness. General design criteria are discussed in situations where either a one-to-one image or a magnified image is required.

X-ray imaging using a single plastic scintillating fiber

In this work, we demonstrated that the data acquisition for either computerized tomography (CT) or digital radiography (DR) could be achieved by using a single plastic scintillation fiber coupled with a photomultiplier. The method is simple and particularly useful for imaging small objects. We describe the experimental set-up and procedure used in obtaining images. We show that the results obtained by using this method are impressive and the method can be implemented in many laboratories to demonstrate the concept of radiation imaging.

On the 2003 Nobel Prize in medicine or physiology awarded to Paul C. Lauterbur and Sir Peter Mansfield.

On the 2003 Nobel Prize in medicine or physiology awarded to Paul C. Lauterbur and Sir Peter Mansfield.

Three-dimensional optical tomography: resolution in small-object imaging.

Near-infrared (NIR) optical tomography provide estimates of the internal distribution of optical absorption and transport scattering from boundary measurement of light propagation within biological tissue. Although this is a truly three-dimensional (3D) imaging problem, most research to date has concentrated on two-dimensional modeling and image reconstruction. More recently, 3D imaging algorithms are demonstrating better estimation of the light propagation within the imaging region and are providing the basis of more accurate image construction algorithms. As 3D methods emerge, it will become increasingly important to evaluate their resolution, contrast, and localization of optical property heterogeneity. We present a concise study of 3D reconstructed resolution of a small, low-contrast, absorbing and scattering anomaly as it is placed in different locations within a cylindrical phantom. The object is an 8-mm-diameter cylinder, which represents a typical small target that needs to be resolved in NIR mammographic imaging. The best resolution and contrast is observed when the object is located near the periphery of the imaging region (12-22 mm from the edge) and is also positioned within the multiple measurement planes, with the most accurate results seen for the scatter image when the anomaly is at 17 mm from the edge. Furthermore, the accuracy of quantitative imaging is increased to almost 100% of the target values when a priori information regarding the internal structure of imaging domain is utilized.

Monte Carlo simulations of pinhole imaging accelerated by kernel-based forced detection

Pinhole collimation can provide both higher sensitivity and resolution than parallel hole collimation when used to image small objects. When objects are placed close to the pinhole, small pinhole diameters combined with high-magnification pinhole geometries yield ultra high resolution images. With Monte Carlo (MC) calculations it is possible to simulate accurately a wide range of features of pinhole imaging. The aim of the present work is to accelerate MC simulations of pinhole SPECT projections. To achieve speed-up, forced detection (FD), a commonly used acceleration technique, is replaced by a kernel-based forced detection (KFD) step. In KFD, instead of tracing individual photons from the source or last scatter position to the detector, a position dependent kernel (point spread function (PSF)) is projected on the detector. The PSFs for channel and knife edge pinhole apertures model the penetration effects through the aperture material. For simulations, the PSFs are pre-calculated and stored in tables. The speed-up and accuracy achieved by using KFD were validated by means of digital phantoms. MC simulations with FD and with KFD converge to almost identical images. However, KFD converges to an equal image noise level one to four orders of magnitude faster than FD, depending on the number of photons simulated. A simulator accelerated by KFD could serve as a practical tool to improve iterative image reconstruction.

Computer microtomography using a laboratory x‐ray fluorescence microbeam spectrometer—A feasibility study

AbstractAbsorption tomography imaging of small objects was performed using parallel beam geometry and a laboratory microbeam x‐ray fluorescence (µ‐XRF) spectrometer. Two x‐ray tubes, with Mo and Cr anodes, were used to perform tomographic imaging with different energies, namely 5.411 and 17.5 keV. The primary beam was collimated–focused using a tapered single glass capillary with an exit diameter of about 12 µm. The spatial resolution of the collimated x‐ray beam was about 25 µm (FWHM). The attenuated primary beam was measured using a standard Si(Li) energy‐dispersive detector. Depending on the beam intensity, two measuring modes were utilized: direct measurement of the transmitted beam and measurement of the secondary radiation excited by the transmitted beam in the yttrium target. The tomographic images of several small objects were obtained, namely a glass capillary, the tip of a match, a burned wooden stick and the head of a fly. The limitations of computer microtomography imaging using laboratory µ‐XRF are discussed and the solutions to the approached problems are presented. Copyright © 2001 John Wiley & Sons, Ltd.

Radiographic films as a detection system for a CT-scanner

A new, low cost, device based on a first generation CT-scanner has been developed. The instrument exploits the high performance of radiographic films in terms of spatial resolution and image definition and is able to produce tomographic images of small objects (10×10 cm). It can be used at different energies and it is a useful instrument for examining a large amount of different samples. The entire system is composed of an X-ray tube, a rotating table, a scanner, a simple system for radiographic film translation and software based on a Filtered Back Projection algorithm for the image reconstruction.

Computed tomography with image intensifier: potential use for nondestructive testing and imaging of small objects

An image intensifier based computed tomography scanner and a tube source of X-rays are used for nondestructive evaluation, imaging of small objects for archaeological studies and conservation of works of art and micro analysis of soft materials. It consists of a charge coupled device (CCD) camera and an acquisition board. The CCD camera and the acquisition board allow image processing, filtration and restoration. The object is irradiated by an X-ray tube with a conical collimator and rotated on 180°. Projections are obtained at various angles as cross sectional image slices. A reconstruction program written in pascal is able to give the reconstruction matrix of the linear attenuation coefficients, simulates the matrix and related tomography. The flux emitted by the tube is filtered using the appropriate filters at the chosen optimum energy and reasonable monochromacy is achieved for all the images. Although X-ray imaging is a potential tool for strongly attenuating materials, the images of weakly attenuating materials provide new information to know about their structure and also the foreign body for the image reconstruction at an optimum value. The image of the plastic material which contains the internal defect is studied thoroughly at the optimum value in order to image the small objects for nondestructive testing, archaeological studies and conservation of works of art. The images are analysed using the profile data showing the internal defect of the object to obtain information at the optimum value. At the optimum value and with the aid of the tomographic image, the size and location of the defect could be ascertained.

Imaging of small birefringent objects by polarised light conventional and confocal microscopes

In this work a theory for describing small birefringent objects imaged in polarised light conventional and confocal microscopes is developed. Due to the polarisation dependent nature of the problem a full electromagnetic theory is used. The solution permits the analysis of a polarised light optical microscope imaging small birefringent objects of arbitrary type, including form birefringence, as long as it can be characterised by a third-rank dielectric tensor. The optical microscope is equipped with two Babinet–Soleil compensators on the illumination side that can be freely adjusted to set the polarisation state of the illumination from linear through elliptical to circular. Numerical examples are presented for the most important practical cases of images of small birefringent objects.

Using a flatbed scanner as a stereoscopic near-field camera

It is shown that flatbed scanners are inherently high quality 3D scanners. Currently developed first prototypes have many applications in industry and multimedia. Because of their big depth of focus, they can be used not only for scanning printed paper, but also for scanning small objects. The nonparallel optics also make it possible to create stereoscopic images of small objects with flatbed scanners, as first described elsewhere (R. Schubert, 1998). The author describes the method for doing this. He also shows examples of stereoscopic images made in this way so that you can judge for yourself their quality and particular properties. Finally, he describes possible accessories that will let you use flatbed scanners routinely in a lot of areas, including hobbies and professional applications. Combining dedicated 3D imaging and evaluation software as well as 3D output devices results in a high quality, low cost 3D scanner. Currently work is under way to specify, design, and build the first prototypes.