Showing papers on "Imaging phantom published in 1975"

A positron-emission transaxial tomograph for nuclear imaging (PETT).

Abstract: An apparatus was developed for obtaining emission transaxial images of sections of organs containing positron-emitting radiopharmaceuticals. The detection system is a hexagonal array of 24 NaI (Tl) detectors connected to coincidence circuits to achieve the “electronic” collimation of annihilation photons. The image is formed by a computer-applied algorithm which provides quantitative reconstruction of the distribution of activity. Computer simulations, phantom and animal studies show that this approach is capable of providing images of better contrast and resolution than are obtained with scintillation cameras. Advantages of positron vs. single photon reconstruction tomography are discussed.

Ripple suppression during reconstruction in transverse tomography

Abstract: In many transverse tomographic reconstruction techniques using filtered projections, ringing or overshoot is found in regions where the attenuation suddenly changes. Such artifacts are obtained with iterative techniques as well. A modification of the filter often used in corrected tomography which produces very small ringing in such regions is described. A transmission device such as the EMI Scanner was computer simulated. Projections were calculated through a phantom and the phantom then reconstructed using different filters. The phantom consisted of a disc with diameter 32 arbitrary units centred at the origin of the plane.

1975 Memorial Award Paper. Image generation and display techniques for CT scan data. Thin transverse and reconstructed coronal and sagittal planes.

Abstract: The various limitations to computerized axial tomographic (CT) interpretation are due in part to the 8-13 mm standard tissue plane thickness and in part to the absence of alternative planes of view, such as coronal or sagittal images. This paper describes a method for gathering multiple overlapped 8 mm transverse sections, subjecting these data to a deconvolution process, and then displaying thin (1 mm) transverse as well as reconstructed coronal and sagittal CT images. Verification of the deconvolution technique with phantom experiments is described. Application of the phantom results to human post mortem CT scan data illustrates this method's faithful reconstruction of coronal and sagittal tissue densities when correlated with actual specimen photographs of a sectioned brain. A special CT procedure, limited basal overlap scanning, is proposed for use on current first generation CT scanners without hardware modification.

Digital tomographic imaging with time-modulated pseudorandom coded aperture and Anger camera

Abstract: The properties of a time-modulated pseudorandom coded aperture with digital reconstruction are compared with those of conventional collimators used in gamma-ray imaging. The theory of this coded aperture is given and the signal-to-noise ratio in an element of the reconstructed image is shown to depend on the entire source distribution. Experimental results with a preliminary 4 × 4-cm pseudorandom coded aperture and an Anger camera are presented. These results include phantom and human thyroid images and tomographic images of a rat bone scan. The experimental realization of the theoretical advantages of the time-modulated coded aperture gives reason for continuing the clinical implementation and further development of the method.

A Comparative Study of 3-D Image Reconstruction Algorithms with Reference to Number of Projections and Noise Filtering

Abstract: A comparative study of four popular 3-D image reconstruction algorithms has been made. Particular attention was given to artifacts generated and noise sensitivity. The methods considered include two spatial domain convolution algorithms, the Linear Superposition with Compensation (LSC) and a Fourier Convolution Method (FCM), a direct Fast Fourier Transform method (FFT), and an algebraic technique, the Simultaneous Iterative Reconstruction Technique (SIRT). The methods were compared by computing reconstructed images for an identical input phantom image. The phantom image contains several edges and a 2% contrast object. Variations, artifacts and noise sensitivity are easily visualized by perspective plots of the reconstructed images. Considerations as to the optimum algorithm for a particular application are discussed.

Test apparatus for nuclear imaging devices

Abstract: A single test phantom for evaluating the scan of a nuclear imaging device is provided which comprises a container having a sealed cavity therein, the outer walls simulating the outline of a human organ or a portion of the body which can be scanned. A means to allow injection of a suitable radioisotope into the cavity is provided, as are a plurality of radioisotope-collecting areas of various sizes and depths which simulate the various conditions that would be seen in a typical scan. By comparing the scan of the test phantom to the test phantom itself, the physician via the single scan can determine whether the nuclear imaging device being tested is properly calibrated and is in satisfactory operating order in an environment simulating an actual scan of a patient.

X-ray scatter background signals in transmission radiography.

Abstract: With monoenergetic x‐ray beams incident on polystyrene phantoms, the spectra of the transmitted x rays were measured with a scintillation spectrometer. The scattered and unscattered components of the transmitted x‐ray fluence at a point on the beam axis were determined as a function of (i) the incident x‐ray energy (18, 22, 32, 49, 58, 69, and 660 keV), (ii) the phantom thickness (5.3, 10, and 21 cm), (iii) the scatter solid angle determined by the exposed area of the phantom and the separation distance of the image plane (0.090, 0.31, 0.66, 1.8, 3.5, 4.3, 4.8, and 5.1 sr), and (iv) the beam diameter at the image plane (25, 17, and 10 cm). The results indicate that, as the incident x‐ray energy d e c r e a s e s from 660 to 30 keV, the contribution of the scattered component to the transmitted fluence i n c r e a s e s from approximately 50% to 90% for the 21‐cm phantom and from 21% to 50% for the 5.3‐cm phantom. For typical cases, the data show the effect of the scatter component on the ratio of the image to the background signals. In addition, the examples show that optimum conditions for maximizing this signal ratio may be obtained by a careful selection of the incident x‐ray energy for low‐, medium‐, and high‐contrast objects.

Contrast of dose distributionin phantom heads due to aperture and plane wave sources

Abstract: Current microwave biologic effects research uses both aperture and plane wave sources. In this theoretic investigation, the dose rate (time rate of energy absorption per unit mass) patterns are compared between phantom heads irradiated by both microwave sources. Two brain tissue-equivalent spheres with radii of 3.3 and 7 cm are used to simulate monkey and human heads, respectively. In addition, a five-layered tissue-equivalent sphere is employed to simulate more closely the various tissues in a monkey head. Theoretic formulations of dose rate patterns in multi-layered tissue-equivalent spheres due to separate plane wave and aperture source treatments are derived from the summation of spherical harmonics technique. Calculations are made for the dose rate patterns along two cross-sectional planes and three rectangular axes in the spheres. The results of these calculations indicate variations in dose rate patterns for different sources and phantom head sizes. For aperture irradiation, microwave energy penetration into the phantom heads appears weak compared to the "hot spots" prominent in the plane wave exposure situation. It is concluded that for different radiation sources, direct comparison of biologic results by external field measurements as the only common denominator may not be dosimetrically valid. The results also indicate that for the same measured exposure rate (power density), the microwave energy absorption pattern in a human head may vary according to the type of radiation source.

Effect of film graininess and geometric unsharpness on image quality in fine-detail skeletal radiography.

Abstract: Three direct x-ray films and three geometric conditions were used to study the effect of noise and sharpness on high resolution radiography of the hand. The Wiener spectrum of film graininess and the MTF of geometric unsharpness were measured. Radiographs of a wire mesh and a hand phantom, together with the Wiener spectra and MTFs, led to the following conclusions regarding fine-detail skeletal radiography, as currently employed: 1) bone structure detectable in vivo does not show minute structural detail; 2) the technique is primarily noise-limited; 3) the use of better geometry or finer grain film for improving resolution or noise is of limited practical value, whereas the use of poorer geometry or more noisy film results in appreciable degradation of skeletal images; and 4) the present standard technique for in vivo radiography of the hand, therefore, may be very nearly optimal for clinical applications.

The Effect of Improving Energy Resolution on Gamma Camera Performance: A Quantitative Analysis

Abstract: The Modulation Transfer Functions (MTF) of two commercial cameras and of a single element germanium camera fitted with different collimator configurations have been studied theoretically and experimentally in order to separate the different elements which contribute to the imaging capabilities of a gamma camera. Effects due to size and shape of collimator holes, and to positron range at 511 keV have been treated as filtering functions, predicting the behavior of a camera quite accurately. The effect of energy resolution has then been studied by noting the changes in MTF and the corresponding changes in the computer generated image of a low contrast circularly symmetric phantom as a function of energy resolution. The possibility of excellent imaging under low contrast situations with high-energy resolution detectors is demonstrated, and the required penalty in camera speed is documented.

[Reduction in radiation scatter during radiographic magnification techniques (author's transl)].

Abstract: The reduction in scatter during magnification techniques is compared with the effect of grids. The results of extensive measurements concerning scatter and distance in a water phantom are shown in 24 diagrams. The various factors were altered as follows: distance 0-1.5 m., phantom thickness 0-27.5 cm., area 5 cm. x 5 cm. - 30 cm. x 30 cm. and kilovoltage 50-150 kv. The amount of scatter immediately behind the phantom is compared with that through a grid by observing image quality for given amounts of scatter. This "grid-equivalent" image quality can be used to determine the circumstances under which a magnification technique can be employed without using a grid.

Imaging Efficiency of Ge and NaI(Tl) Gamma-Ray Detectors

Abstract: A figure of merit is derived for the efficiency with which a detector images a ?-ray emitting object using the signal-to-noise ratio as the criterion. Photons scattered in the detector that ultimately culminate in photoelectric absorption produce an undesirable background when imaging with position-sensitive detectors as in cameras. When imaging with detectors that are not position sensitive as in scanners, these photons contribute to the image of the object. In comparison with NaI(Tl), Ge detectors have lower photoelectric efficiency and higher detector scatter. However, these are offset by much higher energy resolution and the consequent near complete tissue-scatter rejection. As a result, the imaging efficiency for a brain phantom at 150 keV is shown to be comparable for Ge and NaI(Tl) cameras. In the case of scanners, the imaging efficiency of Ge was calculated to be 40-75% higher for a brain phantom with a one ?-ray emitting radionuclide such as 99mTc, and effectively 2-2.5 times higher for a three ?-ray emitting radionuclide such as 67Ga. The imaging efficiency, which depends on absorption characteristics and energy resolution, is a measure of the total performance of the detector. It is shown that in addition to being useful for comparing different types of detectors, this figure of merit also provides means for optimizing imaging parameters such as detector thickness.

The influence of air cavities on the dose distribution of high-energy electron beams.

Abstract: A Lucite phantom containing cylindrical air cavities was irradiated with high-energy electrons from a betatron. By measuring depth-dose curves, the relative enhancement in electron fluence adjacent to the cavity on the side opposite to the beam entrance was determined as a function of the initial electron energy, the dimensions of the cavity and its depth in the phantom. The enhancement factor was found to be critically dependent on energy, the height of the cavity and its depth in the phantom, but to a lesser extent on its diameter. The experimental results have been compared with calculations based on multiple scattering theory.

Standard Phantom Object for Measurements of Gray Scale and Dynamic Range of Ultrasonic Equipment

Abstract: The present study was undertaken to design a Standard Phantom Object for measurements of gray scale and dynamic range of Ultrasonic Imaging equipments in accordance with the test procedures contained in the National Science foundation Experimental R&D Incentives Program, Experiement No. 5, NSF 73-34 (Revised May 17, 1974)- Three Phantom Object geometries are studied and the required specifications are discussed in reference to high-resolution pulse-echo imaging techniques. The test objects are experimentally evaluated based on their performance with variations in the numerical aperture and pulse-spectrum of an imaging system as well as the surface finish and temperature of the Phantom Object. Performance at other frequencies and imaging modalities is discussed. Data is also included on the velocity and reflectance (including temperature effects) of various engineering materials of which the test Phantom Objects were fabricated during evaluation.

Measurement of absorbed fractions for photon sources distributed uniformly in various organs of a heterogeneous phantom.

Abstract: A physical representation of the Snyder -- Fisher heterogeneous mathematical phantom has been designed and constructed. The phantom is suitable for studies involving radiation dose distributions in Reference Man from both internally and externaily applied radiation fields. The physical phantom contains skeletal components, lungs, and soft-tissue regions similar to the mathematical Snyder -- Fisher phantom. A complete description of the phantom and its composition is given. The phantom was used to determine dose distributions within the phantom resulting from photon emitters distributed uniformly in selected organs. These dose distributions were used to determine absorbed fractions for ihe mathematically defined phantom organs. The absorbed fractions are given and are compared with the absorbed fraction estimates by Snyder, et al. In general, estimates of the absorbed fractions, obtained experimentally, full within the range predicted by twice the coefficient of variation of the calculated value. (auth)

Experimental investigations into dissolution of size of detail and contrast in the angiotomograms

Abstract: A comparative investigation on the resolution of angio-tomography and cut-film changer technique, standard views and direct geometrical radiographic magnification were carried out, using a phantom. Catheters of varying calibre and contrast were tested. The most significant result was the finding that lower concentrations of contrast were necessary to demonstrate small vessels or catheters when using angio-tomography or magnification, than with conventional techniques. It was also shown that angio-tomography and a magnification technique are able to show smaller and less contrasty vessels.

Depth-dose measurements of d-T neutrons for radiotherapy applications.

Abstract: In connection with clinical applications of fast neutrons, depth-dose measurements have been carried out for collimated 15 MeV neutron beams at various source-to-skin distances, using different phantoms of the upper part of the human body. The distribution of fast, thermal and intermediate neutron dose or kerma and gamma dose over the phantoms was determined with tissue-equivalent ionization chambers, gold foils with and without cadmium covers and a shielded Geiger-Muller counter, respectively. In order to determine the tumour dose and the exit dose for the irradiation of patients with pulmonary metastases, depth-dose measurements have been performed for an inhomogeneous phantom containing lung-equivalent material. The measurements indicate a considerable difference in depth dose with respect to the dose distribution in a homogeneous phantom. Measurements with sulphur activation detectors to monitor the exit dose are discussed and compared with the results obtained in the actual patient irradiations.

Letter: Electron back-scattering from lead in a perspex phantom.

Abstract: Recently, some investigations were published in your journal concerning the back-scattering of high-energy electrons in the region up to 10 MeV (Saunders and Peters, 1974; Weatherburn et al., 1975). Let me supplement these findings with results obtained with our 42 MeV Betatron. The measurements were carried out in a Perspex phantom The measurements were carried out in a Perspex phantom at electron energies between 10 MeV and 40 MeV using the PTW soft radiation chamber.

Dielectric Measurements for the Design of a Phantom Eye

Abstract: Measurements at microwave frequencies of the complex permittivity of four partitions of the rabbit eye are reported. The small quantity of some of these tissues required the design of a special sample holder and appropriate techniques for its use.

More data on the energy change of x-rays in a mouse phantom.

Abstract: Results published by Puite and Crebolder (see abstr. A58615 of 1974) for a mouse phantom in the range 1.4-2.75 mm Cu HVL were obtained by taking advantage of the difference in energy dependence of two well known TL phosphors: LiF and CaF2. These data are compared with the results of some recent experiments which used sintered undoped BeO (Thermalox 995) as TL detector.

A tomographic test object.

Abstract: Testing of the tomographic and photographic system is a prerequisite for successful reproduction of minor details particularly in tomography of the temporal bone. A test phantom has been developed, consisting of a single layer of small metal balls which can be adjusted to varying inclinations to the tomographic plane. It involves a simple procedure for examining the homogeneity and stability of the tomographic layer at wide movement angles and may also be used for calculating the layer thickness.

Avoiding phantom light effects in traffic signals - using liquid crystals producing colour change from magnetic field effects

Abstract: Installation in a light signal system to avoid phantom lighting effects. This is suitable for traffic or other signal installations where light-rays from the setting sun or other traffic users can create phantom lighting effects. The light signal installation has a light source, a collecting lens and a signal closing pane. A light transparent hollow element is fitted filled with liquid crystals and located within the effective area of a magnetic or electric field which can be switched on. In the liquid crystals a colour is dissolved which when the electric or magnetic field is switched which when the electric or magnetic filed is into a neutral colour.

An Inexpensive Laboratory X-Ray Tomographic Scanner

Abstract: A computerized transverse-axial x-ray scanning tomography system has been constructed and operated using inexpensive and readily available components. The system is used only for the scanning of phantoms and the image reconstruction is carried out on an IBM 360/75. Images reconstructed from data taken by the device are able to resolve radiographic density variations of about 1/2% over distances of 0.5 cm.