Showing papers in "IEEE Transactions on Medical Imaging in 1984"
TL;DR: It is concluded that this system allows the measurement of coronary arterial dimensions in an objective and highly reproducible way.
Abstract: To evaluate the efficacy of modern therapeutic procedures in the catheterization laboratory, the effects of vasoactive drugs, as well as the effects of short and long term interventions on the regression or progression of coronary artery disease, an objective and reproducible technique for the assessment of coronary artery dimensions was developed. This paper describes the methodology of such a computer-assisted analysis system, as well as the results from a validation study on the accuracy and precision. A region in a 35 mm cineframe encompassing a selected arterial segment is optically magnified and converted into video format by means of a specially constructed cinevideo converter and digitized for subsequent analysis by computer. Contours of the arterial segment are detected automatically on the basis of first and second derivative functions. Contour data are corrected for pincushion distortion; arterial dimensions are presented in mm, where the calibration factor is derived from a computer-processed segment of the contrast catheter. The accuracy and precision of the edge detection procedure as assessed from cinefilms of perspex models (%-D stenosis ⩽70 percent) filled with contrast agent were -30 and 90 μm, respectively. The variablity of the analysis procedure by itself in terms of absolute arterial dimensions was less than 0.12 mm, and in terms of percentage arterial narrowing for coronary obstructions less than 2.74 percent. It is concluded that this system allows the measurement of coronary arterial dimensions in an objective and highly reproducible way.
269 citations
TL;DR: An algorithm is designed and applied which interpolates/extrapolates the missing Fourier domain information by POCS and reconstructs an image by DFM and a simulated human thorax cross section is restored and reconstructed.
Abstract: We consider the problem of reconstructing CAT imagery by the direct Fourier method (DFM) when not all view data are available. To restore the missing information we use the method of projections onto convex sets (POCS). POCS is a recursive image restoration technique that finds a solution consistent with the measured data and a priori known constraints in both the space and Fourier domain. Because DFM reconstruction is a frequency-domain technique it is ideally matched to POCS restoration when, for one reason or another, we are forced to generate an image from a less than complete set of view data. We design and apply an algorithm (PRDF) which interpolates/extrapolates the missing Fourier domain information by POCS and reconstructs an image by DFM. A simulated human thorax cross section is restored and reconstructed. The restorations using POCS are compared with the Gerchberg-Papoulis extrapolation method and shown to be superior. Applications of PRDF to other types of medical imaging modalities are discussed.
135 citations
TL;DR: Computer simulations show that the implementation of the pseudoinverse transformation in this algorithm yields excellent results for thin cylinders irradiated by transverse magnetic waves, even in the presence of realistic uncertainties in the scattered field measurements.
Abstract: A new reconstruction algorithm as applied to electromagnetic imaging is proposed. It is aimed at reconstructing constitutive parameter distributions of infinitely long dielectric cylinders with arbitrary cross section, from the scattered fields they produce. Computer simulations show that the implementation of the pseudoinverse transformation in this algorithm yields excellent results for thin cylinders irradiated by transverse magnetic (TM) waves, even in the presence of realistic uncertainties in the scattered field measurements.
127 citations
TL;DR: An automated method for the simultaneous correction of patient motion and gray values prior to subtraction in digitized angiography that is proved to be very efficient to correct for patient motion artifacts and is computationally cheap.
Abstract: This paper deals with an automated method for the simultaneous correction of patient motion and gray values prior to subtraction in digitized angiography. The algorithm consists of maximizing the deterministic sign change (DSC) criterion with respect to three registration parameters (two translational shifts and one constant value added to the pixel values of the image with contrast medium). This method is proved to be very efficient to correct for patient motion artifacts and is computationally cheap. Its main advantage is to permit the use of regions of interest which include vascular structures for the registration procedure. This method can be proposed for a routine use on every commercial digitized angiographic system.
100 citations
TL;DR: Although in practice the restoration process must be left incomplete because of inescapable noise and quantization artifacts, the experimental results demonstrate that for reasons of stability the convergence conditions derived for the noise-free, unconstrained case should be satisfied.
Abstract: Tomosynthetic reconstructions suffer from the disadvantage that blurred images of object detail lying outside the plane of interest are superimposed over the desired image of structures in the tomosynthetic plane. It is proposed to selectively reduce these undesired superimpositions by a constrained iterative restoration method, suitably generalized to permit simultaneous deconvolution of multiple planes. Sufficient conditions are derived ensuring the convergence of the iterations to the exact solution in the absence of noise and constraints. Although in practice the restoration process must be left incomplete because of inescapable noise and quantization artifacts, the experimental results demonstrate that for reasons of stability the convergence conditions derived for the noise-free, unconstrained case should be satisfied. In order to establish a basis for a formal stopping criterion of the iteration procedure, the buildup of noise in the sequence of iterative restorations arising from white noise in the original radiographs is investigated theoretically and experimentally. This results in the derivation of an approximation to the limiting noise variance in the reconstructions which is verified experimentally.
98 citations
TL;DR: A new tomographic reconstruction method is proposed which permits the reconstruction of a region of interest within a slice from partially truncated scanning data, and a reconstructed image after iterative processes exhibits good quality.
Abstract: A new tomographic reconstruction method is proposed which permits the reconstruction of a region of interest within a slice from partially truncated scanning data. This method utilizes two types of source data, namely a series of truncated projections and the outline of the object's cross section. The principle of this algorithm is to estimate the outside area of truncation in one projection from the projection data of the other viewing angles and the outline data of the object. The above estimation is accomplished by following two repeated procedures: 1) the modification of the calculated projection data compared each time with the already measured projection data of the truncated area, and 2) the modification of the reconstructed image compared also each time with the shape of the object. Computer simulation shows the convergence of the results obtained by this algorithm thus verifying its validity, and a reconstructed image after iterative processes exhibits good quality.
62 citations
TL;DR: The process of imaging by detection of the annihilation gamma rays generated from positron emitters which have been injected into a patient by a particle accelerator has been studied in detail.
Abstract: The process of imaging by detection of the annihilation gamma rays generated from positron emitters which have been injected into a patient by a particle accelerator has been studied in detail. The relationships between patient dose and injected activity have been calculated for C-11, N-13, C-15, F-17, and Ne-19 and measured for C-11 and Ne-19 with good agreement with the calculations. The requirements for imaging of the small amounts of activity that can be injected safely have been analyzed in terms of one specific application of the radioactive beam injection technique, that of Bragg peak localization in support of radiotherapy by heavy ions. The characteristics of an existing camera with sufficient sensitivity and spatial accuracy for that task are described. Results of the calculations of radioactive beam flux requirements are shown.
39 citations
TL;DR: The method, which does not require additional knowledge with respect to any of the NMR parameters involved, is shown to be effective when at least four inversion recovery images with different inversion times of a particular object slice are available.
Abstract: A method is described which enables unambiguous retrieval of sign information in a set of magnetic resonance magnitude images of the inversion recovery type. The proposed method starts from the observation that the inversion recovery curve S is a monotonically increasing function of the inversion time TI, and comes down to finding the zero-crossing time TI0 of this curve for each pixel within the image. ?S? and S are then related by S(TI) = -?S(TI)? for TI ? TI0 and S(TI) = + ?S(TI)? for TI ? TI0. The method, which does not require additional knowledge with respect to any of the NMR parameters involved, is shown to be effective when at least four inversion recovery images with different inversion times of a particular object slice are available. The efficacy of sign retrieval is demonstrated by imaging experiments on phantoms and human subjects. The validity of the polarity restoration method is established by viewing its results against the results of conventional methods, i.e., NMR spectroscopy.
38 citations
TL;DR: Two basic forms of the multislice encoded imaging methods using LPR are investigated, i.e., Fourier and Hadamard-like encoding matrices and applications of the methods to the experimented NMR imaging show good agreement with predicted behavior.
Abstract: Line-integral projection reconstruction (LPR) in NMR imaging was found to be useful and has several advantages such as the imaging capability of objects having short T2 and compensation of phase fluctuations arising from the system instability. Although single slice LPR is found to be inefficient and poor in signal-to-noise ratio (SNR), the multislice encoded LPR method is of interest since it has a high SNR and also the capability of selected regional volume or multislice imaging. The latter, i.e., regional volume imaging capability, is a unique property of NMR imaging and offers a variety of imaging capabilities such as simultaneous multislice imaging of sagittal, transaxial, or coronal views. In this paper, we have investigated two basic forms of the multislice encoded imaging methods using LPR, i.e., Fourier and Hadamard-like encoding matrices. Applications of the methods to the experimented NMR imaging show good agreement with predicted behavior.
36 citations
TL;DR: In this article, the thickness of a malignant nevus was measured in situ using fiber optics directed into the surrounding skin, and transilluminations were performed to check all the nevi on a patient.
Abstract: The thickness of a malignant nevus has been found to be an important prognostic factor for patients with melanoma. We have designed a new method of imaging nevi that permits their thickness to be measured in situ. Using fiber optics directed into the surrounding skin, we transilluminate the nevus. Three images are picked up by a digitizing TV camera: the vertical image (90°), a glancing image (180°), and one at 45°, obtained by using two front-silvered mirrors held next to the nevus in a "nevoscope." The digitized images are used in a computed tomography algorithm to calculate approximate vertical cross sections of the nevus. The algorithm is one we recently developed to permit reconstruction from a very few projections. Our method is completely noninvasive. It may be used to check all the nevi on a patient. Without excisions, we could establish a baseline three-dimensional shape for each nevus, follow any changes in time, and obtain an early warning of increase in thickness and possible malignancy.
34 citations
TL;DR: A set of algorithms are developed to reconstruct a functional three-dimensional surface model of the cardiac left ventricle from a set of two-dimensional cross-sectional image slices generated by PET.
Abstract: Positron emission tomography (PET) allows the in vivo assessment of biochemical activity in humans. The newer PET cameras can create several imaging planes, or slices, through an organ inside the body. The interpretation of two-dimensional (2-D) slices of an organ is often difficult for the clinician since he or she has to form a three-dimensional (3-D) mental composite of the structure of interest. We have developed a set of algorithms to reconstruct a functional three-dimensional surface model of the cardiac left ventricle from a set of two-dimensional cross-sectional image slices generated by PET. The theoretical techniques for this reconstruction method are applicable to most organs provided that the appropriate models for the organs are considered. An automatic boundary detection algorithm outlines the surface of the left ventricle from the 2-D images and assigns intensity values to the surface points whose level is proportional to the local activity. A 3-D surface of the intensity levels, with pseudocolor enhancement, is then displayed with the long axis of the heart in a vertical position. Such a display allows the 3-D myocardial tracer uptake to be clearly visualized by the clinician for better diagnosis.
TL;DR: Simulations which demonstrate the effectiveness of this technique are presented along with results obtained by processing a radiographic temporal image sequence.
Abstract: A method is presented for the processing of temporal image sequences to enhance a desired process and suppress an undesired (interfering) process and random noise. Furthermore, the processed information is contained in a single frame which is easily interpreted. The method consists of collecting information about the desired and interfering processes from the frames of the given image sequence. The information is in the form of vectors that characterize the temporal properties of the processes. Matrices are formed by performing outer product expansions on these vectors and an eigenvector matrix is found which will simultaneously diagonalize these matrices. By calculating the inner product of a selected eigenvector from this matrix with the image sequence, an enhanced image of the desired process is obtained. A parameter can be adjusted which will increase the amount of suppression for either random noise or the interfering process. At one limit setting of this parameter, a matched filter for the desired process results, while at the other extreme, very high attenuation of the interfering process will occur. Simulations which demonstrate the effectiveness of this technique are presented along with results obtained by processing a radiographic temporal image sequence.
TL;DR: PCR-I has been designed and built to demonstrate the concept of analog coding to provide high resolution positron tomographic images without interpolative motion and Parameters related to dead time and random and prompt scatter coincidences have been studied.
Abstract: PCR-I has been designed and built to demonstrate the concept of analog coding to provide high resolution positron tomographic images without interpolative motion. The instrument uses 360 bismuth germanate (BGO) detectors coupled through a lucite light pipe to 90 phototubes. The measured resolution at the center is 4.8 mm. A straightforward extension of the concept will lead to a tomograph capable of obtaining resolution below 3 mm for low energy positron emitters. The sensitivity of PCR-I is 46 000/s for a 20 cm diameter phantom uniformly filled with 1 μCi/cc of a positron emitter. Parameters related to dead time and random and prompt scatter coincidences have been studied. Phantom measurements demonstrate the resolution and uniformity of PCR-I. Animal studies carried out to date include 18F in rat skeleton, 11C-palmitate and 11C-labeled red cells in dog heart and blood flow, and blood volume in monkey brain using C15O2 and C15O.
TL;DR: An analytical model is presented, extended from a previous model, which considers accidental coincidences and shows that for a certain radioactivity distribution a gain in image signal-to-noise ratio of about 5 dB is achieved by the time-of-flight method over the conventional method.
Abstract: An accidental coincidence is defined as the erroneous registration of two photons, originating from separate positron annihilations, as having originated from the same positron annihilation. Previous analyses which did not consider accidental coincidences indicated that for a certain radioactivity distribution a gain in image signal-to-noise ratio of about 5 dB is achieved by the time-of-flight method over the conventional method. Subsequent experiments have validated this prediction in low counting rate situations. For higher, typical counting rates these experiments showed a significantly larger gain of about 9 dB, which was attributed to the way in which the time-of-flight method suppresses the degrading effects of accidental coincidences. We present an analytical model, extended from a previous model, which considers accidental coincidences. Calculations of signal-to-noise ratio, using this model, compare well with the experiments and show that the additional gain is indeed due to the treatment of accidental coincidences. An understanding of the model leads to an intuitive explanation of the gain mechanism and a determination of an effective coincidence-timing window that is achieved by the time-of-flight method.
TL;DR: The paper analyzes the behavior of the macroscopic magnetization and compares the FR method with other methods and proposes "figure of merit" expressions for relative signal-to-noise (S/N) ratios, scan time reduction ratios, and image contrast and presents experimental results.
Abstract: This paper describes the "fast recovery" (FR) method for fast NMR imaging. The FR method combines a sequence of four RF pulses-alternating selective 90° nutation pulses and nonselective 180° pulses-with a gradient field pulse sequence which includes "spoiler" pulses to destroy the coherence between successive sequence cycles. We use the 2-D backprojection method of image reconstruction, but other imaging methods could be applied. The paper analyzes the behavior of the macroscopic magnetization-compares the FR method with other methods and proposes "figure of merit" expressions for relative signal-to-noise (S/N) ratios, scan time reduction ratios, and image contrast-and presents experimental results, including backprojection image reconstruction 2-D images and computed T1 and T2 images. For the FR method, in theory and practice, we find that, after each scan sequence cycle, magnetization is restored to equilibrium quickly and exactly; scan time can consequently be less than a tenth that for the saturation recovery method without any penalty in signal-to-noise ratio. Image contrast is even higher than that of the SR method, and compromise "optimum" sequence (interpulse timing) parameters give high image contrast for a wide range of tissue T1 and T2 (spin-lattice and spin-spin relaxation time) values.
TL;DR: The speed of convergence of the hybrid algorithms compared to traditional iterative techniques, and their accuracy in reconstructing photon activity, even with 180° data, makes them attractive for use in quantitative analysis of SPECT reconstructions.
Abstract: Most methods that have been proposed for attenuation compensation in single-photon emission computed tomography (SPECT) either rely on simplifying assumptions, or use slow iteration to achieve accuracy. Recently, hybrid methods which combine iteration with simple multiplicative correction have been proposed by Chang and by Moore et al. In this study we evaluated these methods using both simulated and real phantom data from a rotating gamma camera. Of special concern were the effects of assuming constant attenuation distributions for correction and of using only 180° of projection data in the reconstructions. Results were compared by means of image contrast, %RMS error, and a ?2 error statistic. Simulations showed the hybrid methods to converge after 1-2 iterations when 360° data were used, less rapidly for 180° data. The Moore method was more accurate than our modified Chang method for 180° data. Phantom data indicated the importance of using an accurate attenuation map for both methods. The speed of convergence of the hybrid algorithms compared to traditional iterative techniques, and their accuracy in reconstructing photon activity, even with 180° data, makes them attractive for use in quantitative analysis of SPECT reconstructions.
TL;DR: This paper presents some techniques which are performed in the frequency domain after the application of the Fourier transform and shows that the storage of the angiographic image sequence as Fourier coefficients leads to data compression and convenient data access in an image database.
Abstract: Digital angiography is widely considered simply as a method in which images taken at different times are subtracted from each other. This paper presents some techniques which are performed in the frequency domain after the application of the Fourier transform. Nonselective bypass angiograms and intravenous ventriculograms are taken as examples to show that simple procedures utilizing these techniques exhibit the advantages of improved signal-to-noise ratio in the subtraction images, reduction of motion artifacts, easy application of phase-synchronous subtraction, integration, and quantitative visualization of blood propagation. It is furthermore shown that the storage of the angiographic image sequence as Fourier coefficients leads to data compression and convenient data access in an image database.
TL;DR: The effect of energy discrimination and shielding on positron imaging data quality was investigated using a detector pair to simulate a ring positron emission tomograph to show that for NaI(T1) detectors, the lowest possible energy threshold level is optimal, with the corresponding optimal shielding depth determined by the level of activity to be imaged.
Abstract: The effect of energy discrimination and shielding on positron imaging data quality was investigated using a detector pair to simulate a ring positron emission tomograph. Formulas are presented relating the sensitivity, random fraction, and scatter fraction for a detector pair to the same parameters for a ring system. Data were fitted to detector pair expressions for the variation of the above parameters with shielding depth in order to obtain information on the effect of energy threshold level. These fitted curves were used to determine the sensitivity, random fraction, and scatter fraction, as well as an overall data quality factor as a function of energy threshold level and shielding depth. Data were obtained for both NaI(T1) and BGO detector types using activity levels in the range of 1.5 ?Ci/cm3. Results show that for NaI(T1) detectors, the lowest possible energy threshold level is optimal, with the corresponding optimal shielding depth determined by the level of activity to be imaged. For BGO detectors, a tradeoff exists between energy thresholds of 100-400 keV and shielding depths of 15-30 cm with smaller shielding depths requiring higher energy thresholds.
TL;DR: An arbitrary integer picture matrix can be exactly and uniquely encoded as a tree structured discrete contour map which requires only closed contour lines composed of chain coded vertical or horizontal unit length directed line segments.
Abstract: An arbitrary integer picture matrix can be exactly and uniquely encoded as a tree structured discrete contour map. This new discrete contour map model requires only closed contour lines composed of chain coded vertical or horizontal unit length directed line segments. An example is given of an X-ray computed tomogram showing a brain tumor and hydrocephalus which is analyzed by this contour map image processing.
TL;DR: Success was achieved at algorithmic identification of normal anatomy and tumor in X-ray computed tomography of the brain by the computer selected contour lines correspond exactly to the sketch that a physician would draw to depict the image.
Abstract: The topology of a discrete contour map exactly representing a digital image provides a simple structural organization for image recognition Success was achieved at algorithmic identification of normal anatomy and tumor in X-ray computed tomography of the brain Image analysis using contour map topology identifies only those image brightness thresholds having significance for object segmentation The computer selected contour lines correspond exactly to the sketch that a physician would draw to depict the image
TL;DR: A position sensitive detector of novel design has been developed to permit CT information to be obtained using a radiotherapy simulator for assisting radiation treatment planning including inhomogeneity corrections.
Abstract: A position sensitive detector of novel design has been developed to permit CT information to be obtained using a radiotherapy simulator. The scanner has been engineered to obtain the outline of high contrast internal anatomy such as lung tissue and external body contour for the purpose of assisting radiation treatment planning including inhomogeneity corrections. The mode of operation of the scanner is described and the novel reconstruction problem presented by this scanner is discussed. Clinical images are shown which illustrate the usefulness of this scanner in assisting in the conservative management of patients receiving postoperative radiotherapy for breast cancer.
TL;DR: In this paper, a multi-tracer digital film autoradiography (DFA) and a single tracer multiwire proportional chamber autorecoder (MWPCA) have been developed for the simultaneous study of regional myocardial blood flow and metabolism in the canine heart.
Abstract: A multitracer digital film autoradiography (DFA) and a single-tracer multiwire proportional chamber autoradiography (MWPCA) have been developed for the simultaneous study of regional myocardial blood flow and metabolism in the canine heart. Radioactive indicators of flow (plastic microspheres), metabolism (deoxy-2-D-glucose labeled either with 14C or 3H), and flow and metabolism (201T1), were used in the same experiment. Multiple tracers were discriminated by film autoradiography on the basis of their properties (particulate or nonparticulate, short or long half-life), and by multiple film exposure. A multiwire chamber was used for 3H detection. Perfusional and metabolic maps were obtained in transverse microslices of the heart (40 ?m thick) by digital image processing. The operation, the advantages and limits of the single techniques as well as their combined use are described. The two techniques are complementary: DFA, although time consuming and proportionality limited, allows the use of multiple tracers and it is mandatory for particulate tracer detection due to its high spatial resolution; MWPCA, in spite of a lower resolution provides a very fast and proportional detection as compared to DFA, but limited to only one tracer at the time.
TL;DR: Three-dimensional simulation studies lead to the conclusion that both questions can be answered affirmatively and time-coded emission tomography is a potentially useful imaging technique for diagnostic clinical practice.
Abstract: In this paper we discuss the potentialities of a time-coded single photon emissive imaging system for thyroid tomography. We have performed three-dimensional simulation studies in order to answer two questions: 1) does this coded aperture device produce good quality reconstructions, and 2) can the reconstruction be carried out sufficiently fast on a microcomputer. Our study leads to the conclusion that both questions can be answered affirmatively. Hence, time-coded emission tomography is a potentially useful imaging technique for diagnostic clinical practice.
TL;DR: It is shown that spatial resolution not only aids in identifying small structures, but improves the detectability of larger features by preserving their object contrast.
Abstract: NMR imaging is used as an example of how spatial resolution can be improved in a signal-to-noise (S/N) limited situation The NMR imaging process consists of two components-generating the NMR signal and localizing it in space This paper will show that spatial resolution not only aids in identifying small structures, but improves the detectability of larger features by preserving their object contrast
TL;DR: An automatic gain control detection system was developed for the purpose of amplifying the signal to the right level for the computer correlation and to compensate for the attenuation of the ultrasound in the tissue.
Abstract: Various types of malignant and benign breast tumors are associated with clusters of calcifications with grain sizes 01 to a few mm spread out over volumes of a few cc A series of phantoms containing calcium carbonate grains embedded in a gelatin mixture were made and the ultrasound scattering patterns were measured with 225 MHz transducers Scatterings from the calcifications were distinguished from the larger reflections from tissue interfaces by computer correlation of the signals obtained from transducers placed at three different angles An automatic gain control detection system was developed for the purpose of amplifying the signal to the right level for the computer correlation and to compensate for the attenuation of the ultrasound in the tissue
TL;DR: This paper proposes some advanced data acquisition methods for quantitative single photon emission CT, one example of which is the odd number angular sampling method over 360° for a widely distributed object and the other is fine angular sampling of 180° for an nonsymmetrically localized small object in an attenuation cross section.
Abstract: This paper proposes some advanced data acquisition methods for quantitative single photon emission CT. One example of such methods is the odd number angular sampling method over 360° for a widely distributed object, and the other is fine angular sampling of 180° for a nonsymmetrically localized small object in an attenuation cross section. The image quality, such as the spatial resolution and the signal-to-noise ratio, becomes better than that reconstructed from conventional conjugate projection data. The reconstruction technique used in computer simulation is the iterative correction matrix method, but other techniques are also applicable. Comparison between the weighted back projection method and the correction matrix method is also presented.