Showing papers in "IEEE Transactions on Medical Imaging in 1986"
TL;DR: The problem which is solved is the inversion of this linear functional transformation, that is the following questions are answered: can every line function satisfying suitable regularity conditions be regarded as constructed in this way?
Abstract: When one integrates a function of two variables x,y - a point function f(P) in the plane - subject to suitable regularity conditions along an arbitrary straight line g then one obtains in the integral values F(g), a line function. In Part A of the present paper the problem which is solved is the inversion of this linear functional transformation, that is the following questions are answered: can every line function satisfying suitable regularity conditions be regarded as constructed in this way? If so, is f uniquely known from F and how can f be calculated? In Part B a solution of the dual problem of calculating a line function F(g) from its point mean values f(P) is solved in a certain sense. Finally, in Part C certain generalizations are discussed, prompted by consideration of non-Euclidean manifolds as well as higher dimensional spaces. The treatment of these problems, themselves of interest, gains enhanced importance through the numerous relationships that exist between this topic and the theory of logarithmic and Newtonian potentials. These are mentioned at appropriate places in the text.
726 citations
TL;DR: An improved echo planar high-speed imaging technique using spiral scan is presented and experimental advantages are discussed, and some preliminary experimental results will be presented and further possible improvements suggested.
Abstract: An improved echo planar high-speed imaging technique using spiral scan is presented and experimental advantages are discussed. This proposed spiral-scan echo planar imaging (SEPI) technique employs two linearly increasing sinusoidal gradient fields, which results in a spiral trajectory in the spatial frequency domain (k-domain) that covers the entire frequency domain uniformly. The advantages of the method are: 1) circularly symmetric T2 weighting, resulting in a circularly symmetric point spread function in the image domain; 2) elimination of discontinuities in gradient waveforms which in turn will reduce initial transient as well as steady-state distortions; and 3) effective rapid spiral-scan from dc to high frequency in a continuous fashion, which ensures multiple pulsing with interlacing for further resolution improvement without T2 decay image degradation. Some preliminary experimental results will be presented and further possible improvements suggested.
505 citations
TL;DR: Criteria for the distinguishability of two different conductivity distributions inside a body by electric current computed tomography (ECCT) systems with a specified precision are given.
Abstract: We give criteria for the distinguishability of two different conductivity distributions inside a body by electric current computed tomography (ECCT) systems with a specified precision. It is shown in a special case how these criteria can be used to determine the measurement precision needed to distinguish between two different conductivity distributions. It is also shown how to select the patterns of current to apply to the body in order to best distinguish given conductivity distributions with an ECCT system of finite precision.
443 citations
TL;DR: The basic theory of fractional Brownian motion is extended to the discrete case and it is shown that the power spectral density of such a discrete process is only approximately proportional to |f|a instead of in direct proportion as in the continuous case.
Abstract: Fractals have been shown to be useful in characterizing texture in a variety of contexts. Use of this methodology normally involves measurement of a parameter H, which is directly related to fractal dimension. In this work the basic theory of fractional Brownian motion is extended to the discrete case. It is shown that the power spectral density of such a discrete process is only approximately proportional to |f|a instead of in direct proportion as in the continuous case. An asymptotic Cramer-Rao bound is derived for the variance of an estimate of H. Subsequently, a maximum likelihood estimator (MLE) is developed to estimate H. It is shown that the variance of this estimator nearly achieves the minimum bound. A generation algorithm for discrete fractional motion is presented and used to demonstrate the capabilities of the MLE when the discrete fractional Brownian process is contaminated with additive Gaussian noise. The results show that even at signal-to-noise ratios of 30 dB, significant errors in estimation of H can result when noise is present. The MLE is then applied to X-ray images of the human calcaneus to demonstrate how the line-to-line formulation can be applied to the two-dimensional case. These results indicate that it has strong potential for quantifying texture.
363 citations
IBM1
TL;DR: For the 3D-reconstruction of organ surfaces from tomograms, a shading method based on the partial volume effect is presented and it is shown, that at least for bone and soft tissue surfaces, the results are superior to conventional shading.
Abstract: For the 3D-reconstruction of organ surfaces from tomograms, a shading method based on the partial volume effect is presented. In contrast to methods based on the depth and/or the angle of the voxel surface, here the gray-level gradient along the surface is used for shading. It is shown, that at least for bone and soft tissue surfaces, the results are superior to conventional shading. This is due to the high dynamic range of the gray levels within a small spatial neighborhood.
278 citations
TL;DR: This paper demonstrates the existence of a selective pulse, and provides a sound mathematical and computational basis for pulse design, and shows that the pulses are optimal in the class of piecewise continuous functions of duration T.
Abstract: Most magnetic resonance imaging sequences employ field gradients and amplitude modulated RF pulses to excite only those spins lying in a specific plane. The fidelity of the resulting magnetization distribution is crucial to overall image resolution. Conventional RF-pulse design techniques rely on the small tip-angle approximation to Bloch's equation, which is inadequate for the design of 90° and 180° pulses. This paper demonstrates the existence of a selective pulse, and provides a sound mathematical and computational basis for pulse design. It is shown that the pulses are optimal in the class of piecewise continuous functions of duration T. An optimal pulse is defined as the pulse on the interval that achieves a magnetization profile "closest" to the desired distribution. Optimal control theory provides the mathematical basis for the new pulse design technique. Computer simulations have verified the efficacy of the 90° and the 180° inversion and "pancake-flip" optimal pulses.
266 citations
TL;DR: The method, the iterative image space reconstruction algorithm (ISRA), is able to reconstruct data from a scanner with a spatially variant point spread function in less time than other proposed algorithms.
Abstract: The trend in the design of scanners for positron emission computed tomography has traditionally been to improve the transverse spatial resolution to several millimeters while maintaining relatively coarse axial resolution (1-2 cm). Several scanners are being built with fine sampling in the axial as well as transverse directions, leading to the possibility of the true volume imaging. The number of possible coincidence pairs in these scanners is quite large. The usual methods of image reconstruction cannot handle these data without making approximations. It is computationally most efficient to reduce the size of this large, sparsely populated array by back-projecting the coincidence data prior to reconstruction. While analytic reconstruction techniques exist for back-projected data, an iterative algorithm may be necessary for those cases where the point spread function is spatially variant. A modification of the maximum likelihood algorithm is proposed to reconstruct these back-projected data. The method, the iterative image space reconstruction algorithm (ISRA), is able to reconstruct data from a scanner with a spatially variant point spread function in less time than other proposed algorithms. Results are presented for single-slice data, simulated and actual, from the PENN-PET scanner.
241 citations
TL;DR: This procedure brings out the features in the image with little or no enhancement of the noise, and finds that adaptive Neighborhoods with surrounds whose width is a constant difference from the center yield improved enhancement over adaptive neighborhoods with a constant ratio of surround to center neighborhood widths.
Abstract: X-ray mammography is the only breast cancer detection technique presently available with proven efficacy. Mammographic detection of early breast cancer requires optimal radiological or image processing techniques. We present an image processing approach based on adaptive neighborhood processing with a new set of contrast enhancement functions to enhance mammographic features. This procedure brings out the features in the image with little or no enhancement of the noise. We also find that adaptive neighborhoods with surrounds whose width is a constant difference from the center yield improved enhancement over adaptive neighborhoods with a constant ratio of surround to center neighborhood widths.
225 citations
TL;DR: In this paper, an accelerated form of the EM algorithm for PET is presented, in which the changes to the image, as calculated by the standard algorithm, are multiplied at each iteration by an overrelaxation parameter.
Abstract: The EM method that was originally developed for maximum likelihood estimation in the context of mathematical statistics may be applied to a stochastic model of positron emission tomography (PET). The result is an iterative algorithm for image reconstruction that is finding increasing use in PET, due to its attractive theoretical and practical properties. Its major disadvantage is the large amount of computation that is often required, due to the algorithm's slow rate of convergence. This paper presents an accelerated form of the EM algorithm for PET in which the changes to the image, as calculated by the standard algorithm, are multiplied at each iteration by an overrelaxation parameter. The accelerated algorithm retains two of the important practical properties of the standard algorithm, namely the selfnormalization and nonnegativity of the reconstructed images. Experimental results are presented using measured data obtained from a hexagonal detector system for PET. The likelihood function and the norm of the data residual were monitored during the iterative process. According to both of these measures, the images reconstructed at iterations 7 and 11 of the accelerated algorithm are similar to those at iterations 15 and 30 of the standard algorithm, for two different sets of data. Important theoretical properties remain to be investigated, namely the convergence of the accelerated algorithm and its performance as a maximum likelihood estimator.
153 citations
TL;DR: Several methods for magnetic resonance angiography that create projection images based solely on flowing blood are described, including variations of thick-slice 2-D spin-wrap imaging, line-scan imaging, and volumetric imaging with time-varying gradients.
Abstract: This paper describes several methods for magnetic resonance angiography that create projection images based solely on flowing blood. To both remove static tissue from the image and generate signals from blood, two classes of methods considered are temporal subtraction and cancelling excitation. Temporal subtraction, analogous to digital subtraction angiography with live and mask images, is performed via phase or magnitude differences in blood signals, while cancelling excitation is characterized by its removal of static structures by selectively exciting only flowing material. Means of projection imaging which incorporate these flow-sensitive methods include variations of thick-slice 2-D spin-wrap imaging, line-scan imaging, and volumetric imaging with time-varying gradients.
123 citations
TL;DR: It is demonstrated that using the filter coefficients to reconstruct the image removes the truncation artifacts and improves the resolution, but determining the autoregressive (AR) portion of the ARMA filter by algorithms that minimize the forward and backward prediction errors leads to significant image degradation.
Abstract: The modeling of data is an alternative to conventional use of the fast Fourier transform (FFT) algorithm in the reconstruction of magnetic resonance (MR) images. The application of the FFT leads to artifacts and resolution loss in the image associated with the effective window on the experimentally-truncated phase encoded MR data. The transient error modeling method treats the MR data as a subset of the transient response of an infinite impulse filter (H(z) = B(z)IA(z)). Thus, the data are approximated by a deterministic autoregressive moving average (ARMA) model. The algorithm for calculating the filter coefficients is described. It is demonstrated that using the filter coefficients to reconstruct the image removes the truncation artifacts and improves the resolution. However, determining the autoregressive (AR) portion of the ARMA filter by algorithms that minimize the forward and backward prediction errors (e.g., Burg) leads to significant image degradation. The moving average (MA) portion is determined by a computationally efficient method of solving a finite difference equation with initial values. Special features of the MR data are incorporated into the transient error model. The sensitivity to noise and the choice of the best model order are discussed. MR images formed using versions of the transient error reconstruction (TERE) method and the conventional FFT algorithm are compared using data from a phantom and a human subject. Finally, the computational requirements of the algorithm are addressed.
TL;DR: A convolutional backprojection algorithm is derived for a fan beam geometry that has its center-of-rotation displaced from the midline of the fan beam, showing how the news algorithm corrects for this misalignment.
Abstract: A convolutional backprojection algorithm is derived for a fan beam geometry that has its center-of-rotation displaced from the midline of the fan beam. In single photon emission computed tomography (SPECT), where a transaxial converging collimator is used with a rotating gamma camera, it is difficult to precisely align the collimator so that the mechanical center-of-rotation is colinear with the midline of the fan beam. A displacement of the center-of-rotation can also occur in X-ray CT when the X-ray source is mispositioned. Standard reconstruction algorithms which directly filter and backproject the fan beam data without rebinning into parallel beam geometry have been derived for a geometry having its center-of-rotation at the midline of the fan beam. However, in the case of a misalignment of the center-of-rotation, if these conventional reconstruction algorithms are used to reconstruct the fan beam projections, structured artifacts and a loss of resolution will result. We illustrate these artifacts with simulations and demonstrate how the news algorithm corrects for this misalignment. We also show a method to estimate the parameters of the fan beam geometry including the shift in the center-of-rotation.
TL;DR: The implementation of a method for improving the quality (by reducing artifacts) of images reconstructed from small numbers of projections is described, based on an algorithm originally proposed by McKinnon and Bates and includes enhancements suggested by Heffernan and Robb.
Abstract: The implementation of a method for improving the quality (by reducing artifacts) of images reconstructed from small numbers of projections is described. The technique is based on an algorithm originally proposed by McKinnon and Bates [1] and includes enhancements suggested by Heffernan and Robb [2]. Emphasis is placed on practical aspects of algorithm implementation, including important noise-suppressing refinements not previously incorporated into the algorithm. The efficacy of the method is demonstrated using actual X-ray projection data of the intact beating heart recorded with the Mayo Clinic's dynamic spatial reconstructor. The implications of improved "stop-action" reconstruction of the heart are considered in the context of additional objectives, including automatic object recognition and definition, and improved four-dimensional reconstruction of the beating heart.
TL;DR: A new data space is proposed, to be called the uniform-ladder space, in which the sampling space is the same as the display space, and sampled points are uniformly distributed in each horizontal line as well as in each radial ray so that the data are displayed as they are acquired without any interpolation process required.
Abstract: In a conventional digital ultrasound sector scanner, the sampling space is in polar coordinates while the display space is in Cartesian coordinates, which necessitates a coordinate transformation process. As a result, a number of artifacts appear in the displayed image. In this paper, we propose a new data space, to be called the uniform-ladder space, in which the sampling space is the same as the display space. In this new approach, sampled points are uniformly distributed in each horizontal line as well as in each radial ray so that the data are displayed as they are acquired without any interpolation process required. To implement the new real-time sector scanner, two frequency synthesizers with very high-speed switching time and a low-pass filter are required. The former determines the precise location of the data points in the new data space, and the latter fills the gap between pixels in the horizontal direction. Mathematical models of various interpolation schemes are devised to compare their performance.
TL;DR: The display system facilitates operator interactivity, e.g., the user can point at structures within the volume image, remove selected image regions to more clearly visualize underlying structure, and control the orientation of brightened oblique planes through the volume.
Abstract: Described is a system for the multidimensional display and analysis of tomographic images utilizing the principle of variable focal (varifocal) length optics. The display system uses a vibrating mirror in the form of an aluminized membrane stretched over a loudspeaker, coupled with a cathode ray tube (CRT) display monitor suspended face down over the mirror, plus the associated digital hardware to generate a space filling display. The mirror is made to vibrate back and forth, as a spherical cap, by exciting the loudspeaker with a 30 Hz sine wave. "Stacks" of 2-D tomographic images are displayed, one image at a time, on the CRT in synchrony with the mirror motion. Because of the changing focal length of the mirror and the integrating nature of the human eye-brain combination, the time sequence of 2-D images, displayed on the CRT face, appears as a 3-D image in the mirror. The system simplifies procedures such as: reviewing large amounts of 3-D image information, exploring volume images in three dimensions, and gaining an appreciation or understanding of three-dimensional shapes and spatial relationships. The display system facilitates operator interactivity, e.g., the user can point at structures within the volume image, remove selected image regions to more clearly visualize underlying structure, and control the orientation of brightened oblique planes through the volume.
TL;DR: A novel progressive quantization scheme is developed for optimal progressive transmission of transformed diagnostic images that delivers intermediately reconstructed images of comparable quality twice as fast as the more usual zig-zag sampled approach.
Abstract: In radiology, as a result of the increased utilization of digital imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), over a third of the images produced in a typical radiology department are currently in digital form, and this percentage is steadily increasing. Image compression provides a means for the economical storage and efficient transmission of these diagnostic pictures. The level of coding distortion that can be accepted for clinical diagnosis purposes is not yet well-defined. In this paper we introduce some constraints on the design of existing transform codes in order to achieve progressive image transmission efficiently. The design constraints allow the image quality to be asymptotically improved such that the proper clinical diagnoses are always possible. The modified transform code outperforms simple spatial-domain codes by providing higher quality of the intermediately reconstructed images. The improvement is 10 dB for a compression factor of 256:1, and it is as high as 17.5 dB for a factor of 8:1. A novel progressive quantization scheme is developed for optimal progressive transmission of transformed diagnostic images. Combined with a discrete cosine transform, the new approach delivers intermediately reconstructed images of comparable quality twice as fast as the more usual zig-zag sampled approach. The quantization procedure is suitable for hardware implementation.
TL;DR: How a two-dimensional (gradient, density) feature space can be used for the segmentation of such discrete scenes into three classes in a meaningful way is described and illustrated using examples from medical imaging.
Abstract: Consider a three-dimensional "scene" in which a density f(x, y, z) is assigned to every point (x, y, z). In a discretized version of the scene the density D(i, j, k) assigned to the (i, j, k) th volume element (voxel) is the average value of f(x, y, z) over the voxel. Suppose that the points in the original scene can be meaningfully segmented into classes 1, 2, and 3 separated by two threshold values l and u. Partial volume artifact is the phenomenon that a voxel (i, j, k) which is at the interface of class 1 and class 3 (and thus contains only points with low and high densities) usually has a density D(i, j, k) between l and u, and so cannot be distinguished by density alone from a voxel which contains only points in class 2. We describe how a two-dimensional (gradient, density) feature space can be used for the segmentation of such discrete scenes into three classes in a meaningful way. We illustrate the method using examples from medical imaging.
TL;DR: Modifications to an older PET system to improve its dead time, scatter fraction, and spatial resolution in high count rate, short duration studies are documents, a new dual-tapered collimator reduces scatter by 33 percent while providing excellent resolution uniformity in all slices.
Abstract: This paper documents modifications to an older PET system to improve its dead time, scatter fraction, and spatial resolution in high count rate, short duration studies. A new dual-tapered collimator reduces scatter by 33 percent while providing excellent resolution uniformity in all slices. A data encoding scheme produces uniformly sampled parallel projections from the coincidence data in real time while the detector array executes an orbital motion. The image uniformity, scatter compensation and high count-rate performance have been validated up to 40 kBq/cc in a 20 cm flood source. The errors in image quantification due to counting statistics, live time, and random counts are estimated from repeated measurements on a contrast phantom at high count-rates. The effects of two methods of scatter compensation on image contrast are shown in contrast phantoms and a typical glucose utilization study. Blood flow measurements using 0-15 labeled water bolus method, made under different physiological conditions, reflected the changes expected. The true count efficiency of 75 kcps/(uCi/cc) permits these studies to be done with only 500-900 MBq (13-25 mCi) injected activity.
TL;DR: An algebraic reconstruction method for NMR imaging from data acquired with imaging gradients having essentially arbitrary time dependence is presented and an overdetermined linear system is obtained.
Abstract: An algebraic reconstruction method for NMR imaging from data acquired with imaging gradients having essentially arbitrary time dependence is presented. With reasonable discretization, an overdetermined linear system is obtained for which there exist simple factorized 1-inverses of the coefficient matrices; a computationally efficient reconstruction scheme then follows. Some numerical simulations are also described.
TL;DR: The properties of singular value decomposition are used to implement an SVD spatial domain pseudoinverse restoration filter that is attractive for poor imaging conditions and has potential for improving lesion detection in nuclear medicine images.
Abstract: The properties of singular value decomposition (SVD) are used to implement an SVD spatial domain pseudoinverse restoration filter. This type of filter is attractive for poor imaging conditions (low spatial resolution, high image noise) and is thus appealing for nuclear medicine images. The method might offer some advantages over more traditional frequency domain filter techniques since the restoration is performed on a local rather than global basis. High-contrast thyroid phantom images collected at different count densities and low-contrast liver phantom images were processed with the SVD filter. Restored images yielded improved spatial resolution, lesion contrast, and signal-to-noise ratio. The SVD pseudoinverse restoration filter implemented as an interactive process permits the operator to terminate filtering at a stage where the visually "best" image is obtained compared to the original data. Processed images suggest that the technique may have potential for improving lesion detection in nuclear medicine.
TL;DR: Introduction a la mesure d'entropie comme moyen de caracterisation des images, Clarification de l'utilisation of the mesure de l’entropies.
Abstract: Introduction a la mesure d'entropie comme moyen de caracterisation des images. Clarification de l'utilisation de la mesure de l'entropie
TL;DR: A novel magnetic resonance imaging system is explored which uses data collected in the presence of quadrature phase sinusoidal gradients along an excited plane and it is shown that the resulting magnetization signal (FID) is a sum of the Hankel transforms of the radial modulators of the imaged plane.
Abstract: A novel magnetic resonance imaging system is explored which uses data collected in the presence of quadrature phase sinusoidal gradients along an excited plane. It is shown that the resulting magnetization signal (FID) is a sum of the Hankel transforms of the radial modulators of the imaged plane. An efficient processing system is suggested which extracts the different Hankel transforms from the received signal. These transforms are used to directly reconstruct the two-dimensional (2-D) image using either 1-D inverse Hankel transforms or a 2-D inverse Fourier transform. A "snapshot" data acquisition procedure is described which enables the collection of all the required data from a signal FID. The main advantages of the proposed system are rapid acquisition time, the ability to trade-off acquisition time, and SNR and resonant gradient circuits.
TL;DR: A software system, CTIP, written in Fortran is discussed which remaps the computerized tomography image gray level so that both the lung and heart regions are clearly visible with a "natural anatomical appearance".
Abstract: A software system, CTIP, written in Fortran is discussed which remaps the computerized tomography (CT) image gray level so that both the lung and heart regions are clearly visible with a "natural anatomical appearance." The system is adaptive to image statistics derived from the gray-level histogram of the entire image. Unprocessed, conventional remap, and processed images were compared by 22 radiologists, with 82 percent preferring the processed images. All of the respondents agreed that the processed images possessed a "more anatomical" appearance than the conventional remapping approach.
TL;DR: To enable full utilization of detector resolution, a "bank array" of detectors is proposed and an EM algorithm is adopted for image reconstruction and some modifications for reducing the quantity of computation, improving the convergence speed, and suppressing statistical noise are used.
Abstract: Feasibility of stationary positron emission tomography (PET) using discrete detectors has been investigated by simulation studies. To enable full utilization of detector resolution, a "bank array" of detectors is proposed and an EM algorithm is adopted for image reconstruction. The bank array consists of an odd number of detector banks arranged on a circular ring with a gap equal to one half the detector width. The EM algorithm [11] is used with some modifications for reducing the quantity of computation, improving the convergence speed, and suppressing statistical noise, so as to meet the present purpose. Simulation studies involving several phantoms show that the stationary PET with the new detector array provides image quality which is good enough for clinical applications. For fast dynamic studies with low spatial resolution, the convolution-backprojection method is efficient, but for high-resolution static imaging, resolution enhancement by an iterative method is required. Problems arising in the corrections for attenuation of photons and detector sensitivity, etc., are also discussed. A totally stationary PET avoids the mechanical problems associated with accurate movement of heavy assemblies and is particularly advantageous in gated cardiac imaging or in fast dynamic studies. Elimination of a scan along the detector plane allows a quick scan in the axial direction to achieve three-dimensional imaging with a small number of detector rings.
TL;DR: A system to analyze the chemical properties of a region of tissue located deep inside the human body without having to access it is proposed using a high precision detection of X-rays or ¿-rays from an external source Compton scattered from the tissue under inspection.
Abstract: A system to analyze the chemical properties of a region of tissue located deep inside the human body without having to access it is proposed. The method is based on a high precision detection of X-rays or ?-rays (photons) from an external source Compton scattered from the tissue under inspection. The method provides chemical information of plane regions lying not too deep inside the body (<6 cm). The amount of radiation absorbed by the body is about the same as needed for a standard X-ray tomography. The exposure time is estimated to be shorter than 10 min.
TL;DR: A cylindrical sector image grid with equal area pixels for representing tomographic images is described which offers computational advantages for some algebraic and stochastic reconstruction strategies.
Abstract: A cylindrical sector image grid with equal area pixels for representing tomographic images is described which offers computational advantages for some algebraic and stochastic reconstruction strategies. An evaluation of techniques for resampling from the cylindrical representation to the standard square pixel representation is included. The resampling techniques of nearest-neighbors, bilinear, cubic B spline, two high resolution cubic spline, and overlap weighting are evaluated by their noise propagation, resolution recovery, noise power spectra, and visual appearance.
TL;DR: A brief biographical review of the life and works of Johann Radon is presented in this paper, with a focus on the work of Radon's son, John Radon.
Abstract: A brief biographical review of the life and works of Johann Radon is presented.
TL;DR: Experimental measurements demonstrated that the SPECT resolution for volume sources was sufficient for quantitation, although some limitations exist with respect to source sizes smaller than the detector resolution.
Abstract: The response characteristics of two tomographic systems were compared for imaging of positron emitters: a) a SPECT system with a 3/8 in crystal and 511 keV detector shielding, equipped with a specially designed 511 keV collimator, and b) a PET V system using coincidence detection. SPECT transverse plane resolution was 19 mm FWHM and 35 mm FWTM for a radius of rotation of 16 cm. Corresponding resolution for PET was 14 mm FWHM and 28 mm FWTM. Transverse images through a phantom containing cylindrical sources of various cross sections and uniform activity were obtained for each detector. The measured count density or recovery coefficient was found to decrease with source size, the dependence being similar for both systems. The theoretical values for recovery coefficients were calculated by convolution of a Gaussian fit to the SPECT resolution (FWHM, FWTM) values with the uniform cross section of each source. This simple mathematical model confirmed that the recovery coefficient dependence on source size was primarily related to the limited resolution of the detector. Experimental measurements demonstrated that the SPECT resolution for volume sources was sufficient for quantitation, although some limitations exist with respect to source sizes smaller than the detector resolution.
TL;DR: It is concluded that the clinical potentiality of the device is good and the quality of the reconstructions is high, and the reconstruction can be carried out in less than 11 min on a standard 16 bit minicomputer (HP1000).
Abstract: In this paper, we discuss the applicability of a time-coded aperture system?especially designed for thyroid tomography?on the basis of phantom experiments. Our studies show that 1) the quality of the reconstructions is high (e.g., a cold spot of 6 mm diameter in a thyroid phantom can easily be detected), and 2) the reconstruction can be carried out in less than 11 min on a standard 16 bit minicomputer (HP1000). It is therefore concluded that the clinical potentiality of the device is good.