Showing papers on "Imaging phantom published in 1974"

Three-dimensional reconstruction in nuclear medicine by iterative least-squares and fourier transform techniques

Abstract: Quantitative three-dimensional distribution of radioisotopes in patients is determined by digital reconstruction of data from many views taken by rotating the subject at 10 deg intervals before the gamma camera. The superiority of these techniques over conventional tomography is demonstrated by comparisons between reconstruction algorithms such as back-projection, simultaneous iterative reconstruction, iterative least-squares, and back-projection of filtered projection. The filtered back-projection technique (convolution method) is superior in speed; however, for quantitative results that take into account both noise and attenuation, the iterative least-squares method gives the best approximation to the real source distributions. Resolution is 1.25 cm for detection of holes in 20-cm-diamieter objects. Mathematical basis and FOR-TRAN listings applicable to transmission and emission imaging are given, as well as results of phantom and patient studies. (60 references) (auth)

Gamma camera collimator considerations for imaging 123I.

Abstract: Line-spread functions and energy spectra for commercially produced 123I were obtained on an Anger scintillation camera using three different collimators. Images of a thyroid phantom were also obtained using the same collimators. Although the 529-keV gamma ray of 123I has a relative intensity of only about 1%, it and other high-energy but low-abundance gamma rays seriously degrade images by virtue of septum penetration through thin-wall collimators. Use of the pinhole collimator minimizes this problem.

Quantitation of Tumor Volumes and Response to Therapy with Ultrasound B-Scans

Abstract: A technique employing serial ultrasonic B-scans and a computer for measuring volumes of internal anatomical structures is described. Phantom studies indicate that this method is accurate to within 5% for phantom volumes in the 200–2000 cm3 range. The technique was applied to monitor the spleen-tumor volume in a patient with chronic lymphocytic leukemia and the liver-tumor volume in a patient with retroperitoneal rhabdomyosarcoma. The data suggest that the method is clinically useful for determining normal organ and tumor volumes and for evaluating response to therapy.

Electronic device corrects for motion in gamma camera images.

Abstract: Previous efforts to remove motion artifacts from gamma camera images have required access to a computer, mechanical linkage to the patient, or a high counting rate. An instrument which does not have these limitations has been built and tested. The device operates by using the Angner camera's x- and y- coordinate signals to hold the cathode-ray tube display stationary regardless of any motion of the source in front of the crystal. As the connting rate is decreased to zero, the device automatically ceases to stabilize the image and it appears as normal. The instrument is straightforward to operate. No external counting rate dependent adjustments are required. Preliminary phantom studies have shown that the instrument effectively tracks and corrects for motion. Corrected views of a moving phantom appear almost identical to normal views of a stationary phantom. The instrument has been evaluated in two medical centers, and both have found it useful for sharpening liver scintigrams. (auth)

Absorption Edge Fluoroscopy

Abstract: The technique presented is an approach to absorp tion edge transmission imaging which eliminates the need for monoenergetic x-ray sources, detector scanning, and energy analysis of transmitted x-rays Subtraction of images formed with heavily filtered x-ray beams peaked at energies above and below the K absorption edge is accomplished with image-intensified fluoroscopy equipment coupled to a pair of storage tubes Images of iodine and xenon concentrations of 1 mg/cm2 have been imaged in 15 cm phantoms in a few seconds When automated, the system will provide similar sensitivity in 20 cm phantoms, with imaging times of 1 second or less with resolution on the order of 1 mm Several preliminary images are presented which relate to possible future clinical studies

Calculation of the effects caused by bone present in phantoms irradiated by negatively charged pions.

Abstract: The effects caused by bone present in phantoms irradiated by negatively charged pions on absorbed dose, cell survival, oxygen enhancement ratio, and relative biological effectiveness have been estimated using Monte Carlo methods. The influence of bone along the pion path and also the influence of a bone–tissue interface parallel to the direction of motion of the pions have been considered. Calculated results, as a function of spatial coordinates in a 30‐g/cm2‐thick tissue phantom with bone both included and excluded, are presented. All of the biological data reported here are for T‐1 human kidney cells. The extent to which the effects of bone in the path of the pion beam can be approximated by using results for tissue and measuring depth in the phantom in g/cm2 is considered and discussed.

Measured and calculated dose distributions from neutrons incident on a tissue-equivalent phantom.

Abstract: Doses from recoil ions and from neutron-produced gamma rays were measured separately as functions of depth in a tissue-equivalent phantom having a diameter of 30 cm and a height of 60 cm. Sources of fast neutrons were the Health Physics Research Reactor (a bare unmoderated reactor) and D-T neutrons produced by a small accelerator. Effects of scattered neutrons and gamma rays and of gamma rays incident from the core of the reactor were subtracted from measured distributions by using simultaneous measurements in an identical phantom shielded by a shadow shield, and by blank runs with the phantom tanks empty. The shadow shield was filled with borax and paraffin, and the ends were covered by lead. The system used to measure recoil ion doses was insensitive to gamma rays and consisted of a small Hurst-type polyethylene wall, cyclopropane-filled proportional counter coupled to a Radsan dose integrator. Gamma ray doses were measured by a small Philips GM counter practically insensitive to neutrons. Both systems of detection were calibrated frequently with standardized radiation sources. Results compared well on an absolute basis with Monte Carlo calculations for a broad beam of neutrons having a similar spectral distribution unilaterally incident on a cylindrical tissue-equivalent phantom of the same dimensions.

Another method of calibration for low energy X-ray beams

Abstract: Describes a method using the PTW soft radiation chamber, the measuring volume of which is a cylinder 5.2 mm in diameter and of 1 mm depth and this volume is embedded in a perspex carrier. Using a phantom constructed to perspex plates into which this chamber fits, it is possible to measure depth dose distribution tissue half value depth, etc. in steps of 1 mm. The chamber and phantom can also be used to measure the build up effect of high energy photons and electrons.

Efficiency of phantom impact test in safety glass testing

Abstract: For investigating the safety of passengers impacting windshields, above all the test series in the development of new glass constructions, the phantom thest is practically indespensable. But since the evaluation values for internal safety--head acceleration and lacerations-- can only be properly measured when the movement carried out at impact is realistic, the tests must be carried out at the impact angles occurring in motor vehicles. The results of the phantom test depend largely on the construction of the phantom head. Due to the use of phantom heads of varying construction (because of lack of test regulations), the results of the individual testing installations frequently deviate from one another. In a test series with HPR safety glass (2.0/2.8/0.76 mm flat panes of 24 x 36 in), the effect of several parameters (head mass and head spring suspension, head freely movable or head guided on evaluation values for resultant head acceleration, Severity Index. Head Impact Criterion, tolerance value, and Laceration index) was investigated. The test series were carried out at impact angles of a = 45, 60, and 90 deg at rates of 20-50 km/h. The results, supplemented by motion analysis of the impact process, were compared to the results of sled tests with test dummies previously used by other testing installations on similar glass constructions and under comparable test conditions.

Temperature Distributions Induced by 2450 MHz Microwave Radiation in a Trilayered Spherical Phantom

Abstract: The properties of phantom modeling materials used in the fabrication of a trilayered spherical phantom and the characteristics of heating patterns induced in the phantom by 2450 MHz microwave radiation are discussed. The techniques used in the preparation of the simulated fat, muscle and brain materials resulted in material mixtures with homogeneous, reproducible and stable dielectric properties. The dielectric properties of these simulated materials exhibited no temperature dependence from 20° to 50°C. The heating patterns in the trilayered spherical phantom were obtained using an inexpensive liquid crystal photographic technique. The characteristics of these heating patterns are shown to be in good qualitative agreement with heating patterns obtained by thermographic techniques and theoretical calculations in homogeneous spherical phantoms. Heating patterns recorded in a bilayered spherical phantom by liquid crystal techniques have a shape and location similar to heating patterns observed in the...

A theoretical evaluation of plastic dosimetry phantoms

Abstract: An analytical model has been developed for the calculation of rad R along the central axis of circular fields. The input data required by the model are photon fluence, phantom density, mass attenuation and mass energy absorption coefficients and differential Compton scattering cross-sections. The accuracy of the model was assessed by comparing (a) calculated and experimental central axis depth dose for 137Cs and 60Co gamma -ray beams and (b) f-factors calculated by the model with those published in Handbook 85 for 0.66, 1.25, 5.0 and 10 MeV. The principal source of error is attributed to an approximation in the calculation of dose from tertiary scatter. The model has been used to compare plastic and water dosimetry phantoms for the calibration of high energy X- and gamma -ray beams according to the recommendations of the AAPM. The results indicate that the use of lucite or polystyrene dosimetry phantoms will result in an overestimation in the determination of dose to water by less than 1% for most photon energies.