Showing papers on "Imaging phantom published in 1970"

Dose Rates in a Slab Phantom from Monoenergetic Gamma Rays

Abstract: Gamma-ray flux-to-dose-rate conversion factors obtained with a philosophy consistent with that used for neutrons have not been generally available. To eliminate this inconsistency and develop more ...

Quantitative assessment of scanning-system parameters.

Abstract: There is a recognized need to investigate radio nuclide scanning on a system basis beginning with the radiopharmaceutical and the clinical problem and encompassing the instrumentation and observer performance To be effective such investigations must be based upon quantitative measurement of sys tem performance over a range of system-design pa rameters and over a range of medical problems Although many investigators have measured the performance of discrete components, there has been no systematic investigation of the entire scanning system This has been due largely to the difficulties associated with varying realistic phantom organs and real detector systems and the time consumed in repeating tests to compensate for statistical flue tuations Similarly, the limited availability of appro priate data-storage and data-processing equipment has prevented effective exploration of the effects of data processing on performance Techniques and instrumentation have now been developed to overcome these limitations based on a combination of scanning hardware components and digital simulation to form a system for quantitatively investigating all parameters of the scanning tech nique The system provides the capability for study ing the effects on image interpretation due to physical characteristics of the radionuclide, charac tenistics of the clinical problem, characteristics of the detector and effects of various data-processing operations In this system the input data are pro vided by either a digital simulation of a scanning system viewing an organ or alternatively by a scan ner at the Johns Hopkins Medical Institutions scan fling a phantom or a patient The digital simulation of a particular organ and detector provides the detector-output data in a form representing a normalized scan without statistical fluctuation noise Stored data from these scans are then operated on by a general-purpose computer which is programmed to introduce the parameters associated with activity levels, lesion size and loca tion, detector efficiency and scanning time, among others After being transformed to include quantum fluctuation noise, these data represent a complete simulation of a scan These simulation data are processed in an on-line digital computer and pre sented on a digitally-controlled, TV-like display The effect of the combined parameters of the system are studied by measuring the performance of ob servers in detecting and characterizing lesions The value of computed quantities such as area counts in assisting the visual evaluation of a scan can be assessed Many different parameterscan be rapidly varied, and large numbers of tests can be run so that quantitative results may be obtained consistent with the statistical nature of the problem The system has been used to study the effects of the density of counts, or counts per unit area, on the detectability of lesions of graded sizes in the scan image of a kidney This density of counts in the scan image is a direct function of the activity of the radiopharmaceutical or equivalently of the total time devoted to the scan Hence, the resultant curves of the probability of lesion detection as a function of peak counting rate provide for the first time a quantitative value on the quantity of radioactivity

A phantom method to evaluate the clinical effectiveness of a tomographic device.

Abstract: The physical properties of a tomographic device which affect the clinical tomogram can be readily examined and evaluated with phantom techniques consisting of a lead diaphragm with a 3 mm. pin hole and a compound phantom containing 5 test objects.The technique for using these phantoms and their effectiveness are described.

A projection chest phantom for in vivo dosimetry.

Abstract: A unique projection chest phantom has been constructed of very inexpensive materials. This phantom provides for complete variability of chest thickness and incorporates bone structures of a bone-equivalent substance. The phantom contains lung cavities in which doped artificial lungs can simulate any possible lung deposition. The phantom is designed to be especially useful for calibration of in vivo lung counters when measuring low-energy x-rays and gamma rays (10 to 100 keV). Construction details and a comparison of results with those obtained using a commercial phantom show a reasonable relationship and demonstrate the usefulness of the projection concept.