Showing papers on "Imaging phantom published in 1978"
TL;DR: The ECAT was designed and developed as a positron imaging system capable of providing high contrast, high resolution, quantitative images in two-dimensional (2-D) and tomographic formats and significantly reduces errors caused by motion and detector instability.
Abstract: The ECAT was designed and developed as a positron imaging system capable of providing high contrast, high resolution, quantitative images in two-dimensional (2-D) and tomographic formats. The flexibility in its variety of imaging problems. High (HR), medium (MR), and low (LR) tomographic resolutions are 0.95 +/- 0.1, 1.3 +/- 0.1, and 1.7 +/- 0.1 cm FWHM; high, medium, and low resolutions in 2-D images are 0.85 +/- 0.1, 1.3 +/- 0.1 and 1.7 +/- 0.1, depending on resolution mode employed. ECT system efficiency is 30,100, 15,900, and 9,200 c/sec/muCi/cc with a 20-cm diameter phantom at LR, MR, and HR. Because of the geometric, detector, electronic and shielding design of the system, count-rate capability and linearity are high, with minimum detection of scattered radiation and random coincidence. Measured error agrees well with theoretical statistical predictions down to a level of 1.4% standard deviation. The redundant sampling scheme of this system significantly reduces errors caused by motion and detector instability. Scan times are variable from 10 sec to several min/slice and multiple levels are automatically performed by computer control of patient bed. A variety of human studies illustrate image quality, resolution, and efficiency of both ECT and 2-D imaging mode. Examples of the noninvasive study method have been made possible through development of ECT.
280 citations
TL;DR: Stump pain occurred in 43 percent of soldiers who had traumatic amputations and was associated with phantom pain in 54 percent of these, suggesting phantom pain probably results from peripheral or spinal cord mechanisms, rather than from more rostra1 mechanisms.
Abstract: Seventy-three soldiers who had traumatic amputations were examined from 1 to 6 months after limb loss. All experienced phantom limb sensations and 67 percent experienced phantom limb pains, usually transient. Stump pain occurred in 43 percent and was associated with phantom pain in 54 percent of these. Of the 23 percent of the entire group who had evident stump pathology, 33 percent had phantom pains only, 20 percent had stump pains only, 40 percent had both, and 7 percent were pain-free. All stump ends exhibited an area of hyperpathia with hypoesthesia. Phantom pain probably results from peripheral or spinal cord mechanisms, or both, rather than from more rostra1 mechanisms.
251 citations
TL;DR: A multislice positron emission tomograph (PETT V) for imaging the human brain and the whole body of small experimental animals and the overall sensitivity of PETT V is 350,000 counts/sec/mCi.
Abstract: Imaging of the brain by positron emission tomography can be optimized for sensitivity by dedicating the design of the tomograph to this application. We have designed a multislice positron emission tomograph (PETT V) for imaging the human brain and the whole body of small experimental animals. The detector system of PETT V consists of a circular array of 48 NaI(Tl) scintillation detectors, each fitted with two photomultiplier tubes, with one dimensional positioning capability. Suitable sampling is achieved by rotation of the circular array of detectors and by a wobbling motion of the detector circle. The proposed system is capable of providing seven slices simultaneously, with a spatial resolution in the plane of the slice from 7 to 15 mm and with slice thicknesses of 7 and 14 mm. The minimum scanning time is 1 sec. The estimated overall sensitivity of PETT V is 350,000 counts/sec/mCi in a 20 cm diameter phantom for a resolution of approximately 1.5 x 1.5 cm. The system is under construction.
111 citations
TL;DR: The ratio of scattered-to-primary radiation has been measured for a range of x-ray tube voltages, field sizes and phantom thicknesses that typify clinical mammographic situations indicating that only from about 54 to 71% of the primary beam contrast is imaged in mammography.
Abstract: The ratio of scattered-to-primary radiation has been measured for a range of x-ray tube voltages, field sizes and phantom thicknesses that typify clinical mammographic situations. The relative intensity of scattered radiation measured was essentially independent of kVp but increased as the phantom thickness and radiation field size increased. For the range of field sizes and phantom thicknesses that typify clinical situations the intensity of scattered radiation varied from about 40 to 85% of the primary beam intensity indicating that only from about 54 to 71% of the primary beam contrast is imaged in mammography.
90 citations
TL;DR: An interesting feature of this method is that no detailed knowledge of the beam distribution or slice thickness is necessary in order to measure the radiation output level, to compare the performance of CT systems or the estimate patient's exposure for a particular combination of CT operation parameters.
Abstract: A simple method of comparing and/or monitoring the radiation output level of a Computed Tomography (CT) system, using a specially developed pencil-shaped ionization chamber, is presented. When the measurement is made with a phantom for the period of one tomographic scan, the result can be interpreted as the average exposure along the chamber axis resulting from the entire series of scans to be performed by the CT system. An interesting feature of this method is that no detailed knowledge of the beam distribution or slice thickness is necessary in order to measure the radiation output level, to compare the performance of CT systems or the estimate patient's exposure for a particular combination of CT operation parameters.
63 citations
TL;DR: A material-selective beam hardening correction procedure has been developed that allows the reconstruction of good approximations of linear attenuation coefficients with respect to a reference energy and its insensitivity with regard to energy settings and other machine parameters.
Abstract: Polychromaticity of the X-rays used in computed tomography (CT) has made it difficult to establish an absolute scale for CT values and has made quantitative comparisons between patients unreliable. The spectral shift of the X-rays depends on the material distribution within the structure measured and is significant if substantial amounts of bone, fat, or injected contrast material are present. A material-selective beam hardening correction procedure has been developed that allows the reconstruction of good approximations of linear attenuation coefficients with respect to a reference energy. With the aid of mathematical simulations and measurements on a physical phantom, the feasibility of the procedure and its insensitivity with regard to energy settings and other machine parameters are documented.
61 citations
03 Apr 1978
TL;DR: A tissue-equivalent human-torso phantom has been constructed for calibration of the counting systems used for in-vivo measurement of transuranic nuclides and will allow participating laboratories to prepare sets of transmission curves that can be used to predict the performance of their counting systems for a wide range of subject buildsmore and organ depositions.
Abstract: A tissue-equivalent human-torso phantom has been constructed for calibration of the counting systems used for in-vivo measurement of transuranic nuclides The phantom contains a human male rib cage, removable model organs, and includes tissue-equivalent chest plates that can be placed over the torso to simulate people with a wide range of statures The organs included are lungs, heart, liver, kidneys, spleen, and tracheo-bronchial lymph nodes Polyurethane with different concentrations of calcium carbonate was used to simulate the linear photon-attenuation properties of various human tissues--lean muscle, adipose-muscle mixtures, and cartilage Foamed polyurethane with calcium carbonate simulates lung tissue Transuranic isotopes can be incorporated uniformly in the phantom's lungs and other polyurethane-based organs by dissolution of the nitrate form in acetone with lanthanum nitrate carrier Organs have now been labelled with highly pure /sup 238/Pu, /sup 239/Pu, and /sup 241/Am for calibration measurements This phantom is the first of three that will be used in a US Department of Energy program of intercomparisons involving more than ten laboratories The results of the intercomparison will allow participating laboratories to prepare sets of transmission curves that can be used to predict the performance of their counting systems for a wide range of subject buildsmore » and organ depositions The intercomparison will also provide valuable information on the relative performance of a variety of detector systems and counting techniques« less
60 citations
TL;DR: Surface and internal radiation doses for abdominal computed tomography of children were determined using child-sized phantoms and seven models of CT body scanners and resolving power of each scanner was determined simultaneously with the radiation dose determination.
Abstract: Surface and internal radiation doses for abdominal computed tomography (CT) of children were determined using child-sized phantoms and seven models of CT body scanners. Resolving power of each scanner was determined simultaneously with the radiation dose determination. The average surface skin dose for a complete CT body examination ranged from 0.39 to 5.60 rad, varying with patient size and model of CT scanner employed. A high contrast (12%) resolving power phantom of water-filled holes in acrylic showed a range of 1.75--2.25 mm.
53 citations
TL;DR: In this article, the results of a research project on the heating of simulated human tissue in the induction field of portable radios at VHF were summarized, where measurements made with commercially available field probes indicated that, in some cases, apparent power levels higher than 10 mW/cm2are incident on the operator.
Abstract: The results of a research project on the heating of simulated human tissue in the induction field of portable radios at VHF are summarized. The investigation was initiated because measurements made with commercially available field probes indicated that, in some cases, apparent power levels higher than 10 mW/cm2are incident on the operator. Two phantom models have been built for RF heating tests. The first is a parallelepiped of simulated muscle material 26 in long, 9 in wide, and 6.5 in high, topped by a 0.5 in layer of fat and bone composition. The other phantom is a human-size head and shoulders. This "dummy" is a 1/3-in thick shell of bone composition containing simulated brain material. The measurements of temperature increment due to radiation were performed with a digital thermometer having a sensitivity of 0.01°C. Temperature measurements on the parallelepipedal phantom have shown that the penetrating power densities in the simulated tissue are substantially lower than what could be expected from an incident plane wave with the same E-field intensity. The physical reason for this apparent discrepancy is that the strong fields of static nature emanating from a VHF helical antenna (commonly used with portable radios) are normally rather than tangentially directed to the surface of the phantom. These fields practically collapse at the air-body interface because of the high complex dielectric constant of human flesh. The results of the measurements performed on the head phantom have shown that a 6-W portable radio with a helical antenna held at 0.2 in from the operator's mouth causes very little heating of the simulated biological tissue (less than 0.1°C is highest temperature increase for one minute exposure). The maximum power density penetrating the dummy is less than 1 mW/cm2in the middle forehead. No detectable temperature increase is present in the immediate eye area. This is because in normal use, the eyes of the operator are exposed to the relatively low fields at the base of the antenna. A health hazard is present if the user places the tip of the antenna in the immediate vicinity of the eye (less than a 0.2-in distance) and then operates the transmitter. In this case, the possibility of damage is greatly reduced by a thick insulating cap at the tip of the antenna.
45 citations
TL;DR: A Fourier deconvolution technique is described for obtaining three-dimensional medical images that uses a generalized matrix inversion by singular value decomposition to modify the low frequency Fourier components.
Abstract: A positron camera consisting of two high density proportional chambers is described. It provides a spatial resolution of 2.4 mm FWHM, a maximum data rate of 3000 c.p.s. and a sensitivity of 25 c.p.s. per ?Ci. Results of its application to angular correlation studies of condensed matter and to phantom and in vivo medical imaging are presented. A Fourier deconvolution technique is described for obtaining three-dimensional medical images. It uses a generalized matrix inversion by singular value decomposition to modify the low frequency Fourier components.
45 citations
TL;DR: Comparison with TLD measurements for a variety of CT scanners indicates that an accuracy of +/-15% can be achieved using this film dosimetry system, easier to use than thermoluminescent dosimetric (TLD) and provides a detailed map of the dose distribution.
Abstract: The authors describe a film dosimetry system for use in calculating the surface dose delivered by a CT scanner. Kodak XV-2 film is wrapped around a cylindrical water-filled phantom and the dose distribution is recorded. This system is easier to use than thermoluminescent dosimetry (TLD) and provides a detailed map of the dose distribution. Comparison with TLD measurements for a variety of CT scanners indicates that an accuracy of ± 15% can be achieved using this system. Dose distributions obtained with several scanners are shown.
TL;DR: In this paper, a linear relationship between the measured CT numbers and corresponding attenuation coefficients of known materials at the effective energy of the x-ray beam was determined by searching all energies for the best linear correlation between the CT number and the attenuation coefficient.
Abstract: The effective energy of a polychromatic beam for a Computed Tomography (CT) scanner can be measured directly only with difficulty. However, a linear relationship exists between the measured CT numbers and corresponding attenuation coefficients of known materials at the effective energy of the x-ray beam. The effective energy can then be determined by searching all energies for the best linear correlation between the CT numbers and the attenuation coefficients. This can be performed by two methods: graphically, by means of choosing visually the straightest of the fitted lines or, mathematically, by maximizing the correlation coefficient. The energy corresponding to the optimal fit is therefore selected as the effective energy. The latter method was implemented by computer and demonstrated by scanning the AAPM phantom, which contained known materials, and determining the effective energies and the relationship between the linear attenuation coefficients and CT numbers for three commercial units.
TL;DR: The design of a split high-pressure xenon detector array for tomochemistry in computed tomography (CT) is described and it was found that electron density and atomic number can be determined to an accuracy of better than 4%.
Abstract: The design of a split high-pressure xenon detector array for tomochemistry in computed tomography (CT) is described. Each detector produces a signal from the front primarily due to low energy photons and a signal from the back primarily due to high energy photons. Two methods are described whereby these signals are used to determine the photoelectric and Compton coefficients. From these, the electron density and average atomic number can be determined for each pixel in the image. These methods were tested by computer simulations of scans of a simple phantom, and the resulting Compton and photoelectric images are presented and compared with a conventional CT image. It was found that electron density and atomic number can be determined to an accuracy of better than 4%. The sensitivity to noise was studied, and it was found that the standard deviation of the mean of a 5 X 5 pixel region in the conventional image is about a factor of 3 lower than in the same region in the Compton image and about a factor of 40 lower than in the photoelectric image.
TL;DR: An X-ray imaging detector with good energy resolution, good spatial accuracy and high counting rate has been built for medical application as discussed by the authors, which requires, on the contrary to proportional counters, a high degree of gas purity but produces a significant improvement in energy resolution.
TL;DR: A technique is described for obtaining tomographic images of hydrogen distribution in animals using nuclear magnetic resonance (NMR), where spatial resolution is achieved by frequency selection and magnetic field shaping.
Abstract: A technique is described for obtaining tomographic images of hydrogen distribution in animals using nuclear magnetic resonance (NMR). Resonant frequency is proportional to magnetic field strength, so that spatial resolution is achieved by frequency selection and magnetic field shaping. The results of scanning a phantom and two rats are presented.
TL;DR: A detectability phantom is described which will provide a means of investigation of the effect on human detection capability of the peculiar correlations present in the noise present in CT scanner images.
Abstract: The EMI 5005 scanner produces images with noise characteristics similar to those in simulated CT reconstructions. A detectability phantom is described which will provide a means of investigation of the effect on human detection capability of the peculiar correlations present in the noise present in CT scanner images.
TL;DR: Imaging of a phantom--which stimulated tumors of low density contrast in a body part--by conventional radiography, computed tomographic scanning and theheavy-ion technique indicated superior density resolution for heavy-ion imaging at radiation dose.
Abstract: Heavy-ion radiography is performed by the passage of a beam of nuclei accelerated to energies of several hundred MeV/nucleon through an object. The technique of recording transmitted nuclei in a downstream stack of plastic sheets affords excellent resolution of density by recording the nuclei only at their stopping points. Imaging of a phantom - which simulated tumors of low density contrast in a body part - by conventional radiography, computed tomographic scanning and the heavy-ion technique indicated superior density resolution for heavy-ion imaging at low radiation dose. Superior imaging of tumors in pathologic specimens was demonstrated for heavy-ion imaging compared to conventional radiography. Values of stopping power for various tumors and normal tissues were determined by a computer-aided technique. Heavy-ion radiography shows promise for superior imaging of low contrast tumors at relatively low radiation dose levels.
TL;DR: Quantitative relationships were found concerning the spatial resolution for objects of varying sizes, concerning the partial volume effect and the thickness of the section for object of varying size, and concerning the relationship between resolution and partialVolume effect for small objects.
Abstract: The present work deals with the problem of demonstrating tissue changes of small volume by computer tomography. Measurements were carried out with the Somatom computer tomograph and evaluated by the Evaluscope (both Siemens); fourteen test situations were devised, using plexiglass rods of varying diameter and different penetration into the level being sectioned. Quantitative relationships were found concerning the spatial resolution for objects of varying sizes, concerning the partial volume effect and the thickness of the section for objects of varying size, and concerning the relationship between resolution and partial volume effect for small objects.
TL;DR: The authors found that CT localization of internal and external contours is accurate within +/- 1 mm and variation between predicted and measured dosage was less than 3% in all patients and in most RANDO phantom measurements.
Abstract: Accurate dose prediction for megavoltage photon therapy of carcinoma of the esophagus requires information on tumor depth, lung thickness, and lung density. The authors found that CT localization of internal and external contours is accurate within ± 1 mm. Lung density can be measured with an error of less than 0.02 g/cm3 in the range 0.25-1.00 g/cm3. Variance between predicted and measured dosage was less than 3 % in all patients and in most RANDO phantom measurements. Accurate radiation therapy planning is possible with CT information from a commercial scanner.
TL;DR: Melzack who introduced the "gate control" concept of pain some dozen years ago now has added important new insights toward a better understanding of chronic pain mechanisms and develops a hypothesis that explains puzzling observations about phantom body pain below the level of transection in paraplegic persons.
Abstract: Melzack who, with Wall, 1 introduced the "gate control" concept of pain some dozen years ago now has added important new insights toward a better understanding of chronic pain mechanisms. Together with Loeser, 2 he develops a hypothesis that explains puzzling observations about phantom body pain below the level of transection in paraplegic persons. Clearly, when all neural traffic between a body area and the brain is interrupted mechanically, impulse conduction along classic spinal pain tracts is halted. Yet, from 5% to 10% of paraplegics suffer severe discomfort from phantom body pain. Even more baffling, phantom body pain is experienced following cordectomy—the complete removal of one or more spinal cord segments. These are observations for which the segmental dorsal horn gate-control system theory provides less than satisfactory answers. 3 The severity of pain in paraplegic patients often leads to several attempts at deafferentation of the phantom body site with methods
TL;DR: In this paper, it was shown that the fast digital convolution technique used for parallel x-ray beams can be used also to reconstruct a density function for diverging xray beams, which when combined with what was called previously a generalized???-filter yields good accuracy, a flexibility to cope with noise and a substantial reduction in the xray dosage.
Abstract: It is shown here that the fast digital convolution technique used for parallel x-ray beams can be used also to reconstruct a density function for diverging x-ray beams. This technique when combined with what was called previously a generalized ???-filter yields good accuracy, a flexibility to cope with noise and a substantial reduction in the x-ray dosage. Finite field transforms and zero-order interpolation can be used also to improve the speed of the x-ray reconstruction process. Tests based on these methods are performed on an ideal phantom. A detailed comparison is made between a system using diverging beams, and a system using parallel beams with simulated data.
Journal Article•
TL;DR: In this paper, the performance characteristics of four wide field scintillation gamma cameras were evaluated for 140-keV gamma imaging, including intrinsic spatial resolution, energy resolution, uniformity and linearity distortion, and count-rate capability.
Abstract: Performance characteristics of four recent wide field scintillation gamma cameras were evaluated for 140-keV gamma imaging. Parameters measured included intrinsic spatial resolution, energy resolution, uniformity and linearity distortion, and count-rate capability and its influence on the spatial resolution. The system performance of the cameras was compared with representative parallel-channel collimators in terms of spatial resolution and relative sensitivity. Visual imaging comparisons of each camera system were performed by taking images of Rollo phantom containing four different lesion sizes, with four different contrast ratios, for equal imaging time.
TL;DR: A new breast phantom has been designed for use in evaluating mammographic system performance, and results demonstrate the usefulness of the basic phantom design, and suggest possible improvements.
Abstract: A new breast phantom has been designed for use in evaluating mammographic system performance. This phantom incorporates simulated calcifications and fibrillar objects in fat, of graded size, to permit measurements of detail visibility. A special methodology has been developed for measuring visible object size to achieve reproducible and clinically relevant results. Materials and construction of the phantom also permit carrying out dosimetry with an appropriate ionization chamber. Dosage and detail visibility measurements are reported for the Xerox 125, Min-R and Xonics systems. In addition to providing information regarding technique and image receptors, these results demonstrate the usefulness of the basic phantom design, and suggest possible improvements.
TL;DR: The major factor in image quality as seen in the two scanners seemed to be in the production of artifacts, which was apparent in artifacts from motion, high contrast discontinuities, beam hardening, and edge enhancement.
Abstract: Image quality in cranial computed tomography (CT) was evaluated with phantom and patient studies on both a first (single beam) and a second (multiple beam) generation scanner. When comparable radiation doses were used, there were only minor differences in resolution, low contrast detectability, and noise level. The pattern of noise relative to the size of the area in which it was measured was somewhat different. On patient studies, no differences were found when contrast-material-filled vessel visibility and gray--white matter distinction were analyzed. A lesion was obscured by streak artifacts in one scanner in one of 22 patients scanned on both machines. The major factor in image quality as seen in the two scanners seemed to be in the production of artifacts. This was apparent in artifacts from motion, high contrast discontinuities, beam hardening, and edge enhancement. Multiple factors must be considered in assessing CT image quality. In particular, further studies to quantitatively evaluate noise quality and artifact production are needed.
TL;DR: Before modulation transfer functions can be given credence, the authors need to know more about the frequency and amplitude patterns that show the difference between normal and disease and foster those techniques that are tailored to show best the most meaningful patterns.
Abstract: The success an observer has in distinguishing items in the radiographic image of a phantom varies in relation to the density, size and shape of those items. These three parameters of density, size and shape are inter-related (Rossman, 1966). Thus there is a danger that the ingredients of a phantom may be selected so as to give a false bias towards one technique rather than another if these ingredients do not bear close resemblance to the features of the pathological structures to be diagnosed. Before modulation transfer functions can be given credence, we need to know more about the frequency and amplitude patterns that show the difference between normal and disease. We should then only foster those techniques that are tailored to show best the most meaningful patterns.
TL;DR: Two techniques for localized 2450-MHz hyperthermia of experimental mouse cancers are described, which feature microwave bolusing for improved coupling and tumor heating uniformity.
Abstract: Two techniques for localized 2450-MHz hyperthermia of experimental mouse cancers are described. In the far-field approach superficial tumors are encapsulated in 5-cm mold-formed spheres of semi-solid phantom material, then placed in an anechoic chamber on an equipower surface. In the applicator approach, tissues are immersed in a temperature-controlled tissue-equivalent liquid bolus, and are irradiated by time-multiplexed parallel-opposed beams. Both techniques feature microwave bolusing for improved coupling and tumor heating uniformity.
TL;DR: In this article, the half back projection technique was investigated by imaging an acrylic phantom, consisting of several wells containing aqueous 99mTc solution using a parallel-hole collimator on a Searle camera connected to a computer and display system.
Abstract: The half back-projection technique was investigated by imaging an acrylic phantom, consisting of several wells containing aqueous 99mTc solution using a parallel-hole collimator on a Searle camera connected to a computer and display system.
Journal Article•
TL;DR: The pinhole collimator could resolve an infarct as small as 7 g, and use of the pinhole yielded a diagnostic accuracy of over 90%, compared with 75-80% for the high-resolution collimation, which was found to be satisfactory in most clinical imagings.
Abstract: Three collimators—high-resolution, converging, und pinhole—were eval uated for Tl-201 myocardial imaging. Line spread function, sensitivity meas urements, and phantom and animal studies were used. Features common to all the collimators were: a) better resolution at a closer distance with higher count density, and b) higher infarcA¬ detection rate in the tangential projection than in the en face view relative to the lesion. Furthermore, an infarcA¬ in the epicardial location was better visualized than one in the endocardial location. In terms of resolution and sensitivity, the high-resolution collimator was found to be satisfactory in most clinical imagings, but for visualization of an infarcA¬,its size by weight must be over 10—12g. The pinhole collimator could resolve an infarcA¬ as small as 7 g, and use of the pinhole yielded a diagnostic accuracy of over 90%, compared wilh 75—80% for the high-resolution collimator. Although the low sensitivity of the pinhole collimator precludes its routine clinical use, the selected view would increase diagnostic accuracy. The converging collimator performed poorly in terms of lesion detectability, and its routine clinical use is not encouraged. The conclusion drawn here is valid in the system ice have sludied, but the variety of converging collimators must be evaluated further for their specific purposes. J NucA Med 19: 1067-1073, 1978