Showing papers on "Imaging phantom published in 1977"

Radionuclide emission computed tomography of the head with 99mCc and a scintillation camera.

Abstract: To investigate the potential application of radionuclide computed tomography (RCT) to nuclear medicine imaging using 99mTc, a tomographic system using a lightweight scintillation camera for brain imaging was constructed, and lesion contrast with RCT and conventional scintigraphy were compared. The detector revolves once around the patient's head at constant angular velocity, requiring approximately 20 min. Nine sections are reconstructed from the data, using either a Fourier transform or a filtered back-projection algorithm. In a phantom simulating the radionuclide distribution observed during brain imaging, quantitative lesion contrast was far superior in the RCT images. In a series of 25 patients with intracranial lesions, the average RCT lesion contrast was superior to that of standard scintigraphy by a factor of more than 2. An RCT image of an experimentally infarcted dog's heart, taken after the injection of 99mTc-MAA into the left atrium, also showed excellent correspondence to the gross anatomic defect. Although problems of photon absorption may occur in imaging larger body areas, RCT imaging in this feasibility study produced surprisingly good results that warrant further investigation of the technique.

The Humongotron--a scintillation-camera transaxial tomograph

Abstract: An emission transaxial tomographic system using a scintillation camera as the detector is described. The unit allows accurate positioning of a scintillation camera's detector at any angle around a patient in order to obtain the multiple projection images needed for transaxial tomography, and it is capable of imaging any area of the body. The camera can also be used for all types of conventional imaging procedures. Image processing is performed by a small on-line computer. A convolution algorithm and a mathematical technique for approximate absorption correction are used to obtain high-resolution and high-contrast images with good quantitative accuracy. The operation of the system is described and representative phantom and patient studies are presented to illustrate the capabilities of the system.

Compton scatter imaging of transverse sections: corrections for multiple scatter and attenuations

Abstract: The electron density (e cm-3) of a tissue sample can be determined by measuring the fluence of photons which it Compton scatters from a narrow incident beam of X- or gamma-radiation. This technique has been applied successfully to diagnostic denistometry (bone, lung), and less successfully to whole body tomography. In this work, the physics of Compton scatter tomography is examined with emphasis on transverse section scanning. The two major limitations of the scatter technique, attenuation of the single scatter photon fluence (of interest), and contamination of this fluence by multiply-scattered photons, are studied and corrective procedures are proposed. The methods described are applied to a simple test phantom; it is concluded that transverse images with an electron density precision of approximately 5% are possible.

Three-Dimensional Imaging in the Positron Camera Using Fourier Techniques

Abstract: A mathematical algorithm for three-dimensional reconstructions in the positron camera is described. Fourier techniques have been adapted for use in analysing the data from cameras with limited detector configuration. Noise instabilities from random fluctuations in the data are discussed and treated. The technique is tested on a computer-generated phantom and the results are presented. Ways of incorporating the effects of Compton scattering and detector response into the algorithm are discussed. It is concluded that the method is feasible and practical for obtaining accurate reconstructions.

Imaging soft tissue through bone with ultrasound transmission tomography by reconstruction.

Abstract: A phantom consisting of a 2.5‐cm‐diameter aluminum rod, a balloon filled with castor oil, and a balloon filled with a phenylated silicone fluid was imaged in water with ultrasound transmission tomography by reconstruction (UTTR). This phantom was chosen for investigation of the feasibility of detecting small changes in the ultrasound velocity and ultrasound attenuation coefficient of soft tissues in planes containing bones. Attenuationimages of a transverse section of a leg of lamb were obtained as well. Opposed transmitting and receiving transducers were scannned on either side of the imaged object, just as an x‐ray tube and detector are scanned in the pencil beam geometry employed with the first x‐ray computerized axial tomographic system. More than adequate signal was transmitted through the aluminum rod and the bone to obtain reconstructions; but, in these crude images, there were numerous artifacts which maintain the uncertainty regarding the future utility of this promising technique. Although velocityimaging should not be as sensitive to reflection and refraction as attenuationimaging, a very narrow ultrasound beam must be employed to obtain reasonable resolution in velocityimaging.

Implications of computed tomography for inhomogeneity corrections in photon beam dose calculations.

Abstract: Patient inhomogeneity information is investigated for use in radiotherapy planning. Absorbed doses measured in a phantom are compared to doses calculated for photon beams using various treatment planning inhomogeneity correction methods. Delineation of inhomogeneities with a spatial resolution of 5 mm and with an electron density accuracy of 2% in usually sufficient to allow doses to be calculated with a mean accuracy of better than 2% for 60Co and 3% for 25-MV x rays if the authors' Equivalent Tissue-Air Ratio Method is used.

Relative properties of tomography, K‐edge imaging, and K‐edge tomography

Abstract: The properties of tomography,K‐edge imaging, and K‐edge tomography are discussed in relation to the imaging of small concentrations of elements such as iodine and xenon and are compared by means of phantom images. It is demonstrated that the complementary selectivities provided by depth and energy subtraction are combined in K‐edge tomography. Using a three‐spectrum subtraction technique, the iodine difference signal predicted by computer calculations is on the order of 8000 times that of an equal concentration of bone. The corresponding ratio in tomography without energy subtraction is 20:1. It is argued that K‐edge tomography can successfully eliminate artifacts due to tissue inhomogeneities which presently enable 0.6% variations in tissue attenuation to mimic minimum detectable iodine signals in conventional computed tomography. Various instrumentation possibilities and energy subtraction techniques are discussed.

X-ray phantom

Abstract: An X-ray phantom having a radiolucent sealed case contains sea water, a floatation chamber sealed against the sea water and having an exterior opening, and various X-ray calibration targets for illustration of a variety of densities and shapes for radiographic study.

Imaging 123I with a scintillation camera. A study of detection performance and quality factor concepts

Abstract: Image quality, resolution and sensitivity of a scintillation camera equipped with various collimators have been investigated using high purity 123I. Pulse height distributions of 123I from a thyroid phantom partly in air and partly immersed in water demonstrated the substantial septa penetration of the 440 and 529 keV gamma rays of 123I with high resolution collimators. Line spread functions were recorded and the modulation transfer function was evaluated from them. The two concepts of 'figure of merit' also used were QB=Sa mod MTF mod 2, where Sa is the plane sensitivity and QC=S2/(S+2B), where S is the true signal from the object and B is the total background or noise due to septa penetration and scatter.

Slice geometry in computer assisted tomography.

Abstract: In computer assisted tomography, the slice being imaged is not a uniform slab because (1) the X-rays are not parallel, (2) the source and detector may not have equal dimensions, (3) the source collimator may produce a penumbra region on the detector, and (4) in some machines two slices are scanned simultaneously from a common focal spot. One method of measuring slice thickness, uniformity, and overlap is with a phantom containing an aluminum strip at a 45 degree angle. This provides a direct display, in the viewing plane, of the slice profile. Measurements have been made on seven new tomographic scanners, and photographs and plots of slice geometry are presented. It is suggested that slice thickness be defined as the full width at half maximum sensitivity, but that this measure should not necessarily be used as the desirable increment between scans.

Development of a Phantom for Evaluation and Assurance Of Image Quality in CT Scanning

Abstract: The development and use of a phantom for evaluation, comparison, and quality assurance of CT scanners will be discussed. Examples of measurements on seven CT scanners using early prototypes of the phantom will be presented along with measurements on several scanners using the final phantom configuration. The phantom contains four modular sections which are removable to allow for future fabrication and replacement of individual sections for specialized applications. Section I is used to measure contrast sensitivity and scan slice geometry of the system. Section II is used to measure the sensitometric response of the system. Section III is used to determine the spatial resolution of the system at various contrast levels. Section IV is used to determine the noise, spatial uniformity, alignment, and MTF of the system. In addition, it contains a part with fittings where items may be placed such as in vitro samples, dosimeters, or a motion phantom.

Physical aspects of electron-beam arc therapy

Abstract: The effect of different parameters on dose distribution in electron-beam arc therapy was studied in order to develop a technique for routine clinical use. A special diaphragm was designed to facilitate telecentric rotation. Dosimetry was performed with an ion chamber, film, and LiF powder in cylindrical polystyrene phantoms and an Alderson Rando phantom. Dose distributions were evaluated with regard to dose homogeneity, and a method of sharpening the dose fall-off near the ends of the arc was proposed. Criteria for selection of isocenter depth and field size were developed. Methods of dose calculation, calibration, and treatment planning are discussed.

Measurement of photon dose fraction in a neutron radiotherapy beam.

Abstract: Photondose fractions (PDFs) have been measured in and around a neutronradiotherapy beam with a tissue‐equivalent proportional counter (TEPC) and with paired ion chambers. The PDFs were found to increase linearly with increasing field size and width depth in phantom. PDFs were shown to decrease with decreasing phantom size and to be larger in the shielded region of the phantom than in the direct beam. Uncertainties in the PDF values were estimated to be 10%–15% for the TEPC measurements but about 50% for the measurement made with ion chambers.

Proton penetration and control in nonhomogeneous phantoms

Abstract: Accurate bolus is needed for extension of Bragg-peak therapy. Proton beam-stopping profiles in a lucite-styrofoam-tissue phantom and in a Rando phantom were recorded photographically. Air volumes caused the largest distortions. Lucite bolus was cut to achieve desired beam-stopping profiles. Verification of bolus effect in situ will be important to control beam penetration within 5 mm.

Estimation of organ depth by gamma ray spectral comparison.

Abstract: In order to measure the amount of radioactive tracker taken up by an organ in the human body, it is necessary to determine the depth of the organ in the body. A procedure is presented which is similar to the valley-to-peak method of Mohindra and McNeill (1965) but involves analysis of the entire pulse-height spectrum. Measurements are made on 131I with a water phantom and a single collimated detector in a fixed position. A set of calibration spectra are taken for a source at depths ranging from 2 to 15 cm in 1 cm increments. Then test spectra are taken for fixed times with sources placed at various depths. By comparing a test spectrum with the calibration spectra, it is possible to calculate the source depth. The method is checked for dependence of calculated depth on source thickness and on background concentration.

Computerized Tomograpy Using Video Techniques

Abstract: A review of a series of qualitative and quantitative investigations of the capabilities of fluoroscopic systems to produce images having a sufficiently high quality to be used as the input for producing computerized transaxial tomograms is given. Examples of tomographic sections obtained from fluoroscopic image inputs are presented. In addition a quantitative comparison of computerized tomograms of a specially constructed phantom was made between reconstructions made with the EMI head scanner and those made from images provided by a large screen low light level TV camera fluoroscopic system. A phantom made from Lucite containing rods of various materials and sizes was used. The computer printout of each was analyzed and a high degree of correlation (r = 0.98) was noted between the results of both systems. The differential attenuation detectability of the fluoroscopic system was found to be comparable to or better than the EMI unit. As expected from a consideration of the quantum statistics for each system, the noise in the obtained reconstructions was also comparable. It is concluded that such a fluoroscopic system performs favorably when compared to the presently available commercial systems.

Validity of computer simulation of blood vessel imaging in angiography.

Abstract: The computer-simulation technique for imaging of vessels in angiography is being recognized as a useful tool for the study of the effect of physical parameters on the vessel image. We have examined the validity of this technique by comparing the computed image distribution directly with experimental results. The input x-ray pattern of a blood vessel phantom, the line spread function (LSF) of the focal spot, and the LSF of a screen-film system were measured. From the data obtained, the final image distributions of the phantom were computed and compared with the experimentally determined distributions. A high-precision device for the alignment and positioning of the vessel phantom was employed in the experiments. Results indicate that computer simulation can correctly predict the image distribution of the blood vessel phantom.

Biophysical studies with high-energy argon ions 1. Depth dose measurements in tissue-equivalent liquid and in water.

Abstract: The beam of high-energy argon ions available at the Lawrence Berkeley Laboratory BEVALAC was employed for biophysical experimentation. In preparation for radiobiological studies, depth doses were measured with a homogeneous tissue-equivalent ionization chamber which traversed the central axis of a tissue-equivalent liquid phantom irradiated by a large, uniform beam of ions. Ancillary measurements showed that for this beam: (1) the depth dose profiles measured in a water phantom and in a tissue-equivalent liquid phantom are essentially the same, provided that the difference in the electron densities of the liquids is taken into account; (2) the depth dose profile measured behind a water absorber is essentially the same as that measured within a water phantom; and (3) reliable dosimetry for tissue can be performed using air instead of tissue-equivalent gas in the cavity of a tissue-equivalent plastic ionization chamber. Biological results are reported in succeeding papers.

Computed Tomography Using a Cs137 Source

Abstract: The purpose of this work was to explore the use of a monenergetic gamma ray source and pulse counting techniques for use In a CT device. The ideal source for CT scanning is one with a 100-keV gamma ray, long lifetime and low-cost availabiltly in high specific activity. However, since the attenuation coefficient of tissue-like materials varies slowly with energy a Cs-137 source was used without significant disadvantage. Phantoms consisting of brass, aluminum and low-Z, organic polymers were scanned with 2.0 mm ray spacing and up to 60 angular orientations. The results from 0.1% statistical accuracy data obtained with the prototype scanner have demonstrated that a 2.5% density gradient can be detected. One of the advantages of a Cs-137 source is that the calculated attenuation coefficients are directly proportional to physical densities of the materials scanned.

Radiographic apparatus with correction for radiation hardness variations

Abstract: In a radiographic apparatus employing a fan-shaped spread of penetrating radiation the nature of the source can cause the energy spectrum of the radiation to be variable with position in the fan. Means are provided to modify output signals from the apparatus to correct for errors caused by such variations. The modifying factors required can be calculated or can be determined using a phantom body by a method which is described.

A phantom for simulating fast dynamic studies on a gamma camera

Abstract: There is a requirement for a simple, easily standardized, dynamic phantom which will enable calibration studies to be made on parameters such as time resolution, display intensity and photographic exposure settings. The use of a source, suspended over the camera collimator, as a simple pendulum, has been found to provide a useful dynamic phantom. The period of the oscillation, the amplitude and the source strength can all be easily altered and various physiological studies can be simulated. Its use to simulate left ventricular ejection fraction curves, and an extension to provide a technique for testing physiological triggering systems, are described briefly.