Walter Mauderli

Cadmium Telluride Gamma Camera

A small 4 cm X 4 cm prototype CdTe gamma camera has been constructed which demonstrates sensitivity and spacial resolution superior to the standard Anger camera. The camera is based on an array of linear solid state detectors contained within a laminar collimator which confines the field of view to one dimension. The array is rotated stepwise through 180° and data from each position recorded and computer processed. This technique leads to a major enhancement in sensitivity relative to the multihole collimator. Clinical images have been obtained and a larger CdTe camera is planned.

Rotating laminar emission camera with Ge-detector: further developments

A germanium (Ge) camera with laminar collimator-detector geometry, ROLEC, simulating a 195 X 195 mm2 detection area, has been constructed and tested. The detector consists of five separate Ge blocks grooved into distinct electrical channels. Results show that ROLEC measuring times have to be about 3 X greater than Anger camera measuring times to achieve a 5% signal-to-noise ratio with each device. Both spatial and energy resolution of the ROLEC exceed that of the Anger camera but sensitivity variations along the detector strips pose a significant problem in development of a clinically useful device.

A Germanium Laminar Emission Camera

A 30 elenent laminar Collimator with a segmented high purity Ge detector gave spatial resolutions to 1.5 mm for 2 dimensional Tc99m imaging. Detector, collimator and imaging aspects are discussed.

Rotating laminar emission camera with GE‐Detector: An analysis

Design criteria for a germanium detector emission camera with laminar collimator-detector geometry are reported. In this design, parallel plates above a grooved germanium slab form detector channels which accumulate data in multiple projections through 180 degrees. Activity distribution is determined through mathematical reconstruction from the projections. The laminar design has greater efficiency than a hole-collimated device due to a favorable open area ratio and due to collimation in only one dimension. The relative sensitivity at the center of the detector strip increases with detector length and distance from collimator face. Spatial resolution depends upon the design geometry (septal penetration and scatter within the crystal are of such small magnitude that degradation of the point spread function is minimal). A 30 channel protype device (ROLEC) shows good correlation with theoretically determined PSF and signal-to-noise ratio (SNR). Measuring times projected for a clinical sized device (300 mm diam) are about 4.6 times that of the Anger camera (with same SNR) and high resolution collimator.

Rotating laminar emission camera with GE-detector: experimental results.

Experimental results of a prototype rotating laminar emission camera (ROLEC) for nuclear medicine imaging are reported. A 11.5 mm thick, 45 x 45 mm high-purity germanium detector is segmented into 30 1.47 mm wide parallel channels and collimated with 39 mm high parallel plates. Projection data acquired at multiple angular orientations as the detector-collimator assembly is rotated about its center are mathematically reconstructed to image the activity distribution. The spatial resolution of the ROLEC is at least twice as good, at all distances, as that of gamma cameras with high resolution collimators. The better energy resolution of the germanium enhances the detection and resolution of the ROLEC in comparison to gamma cameras with NaI(T1) crystals, the relative superiority increasing with greater volumes and with greater depths. Adequate sensitivity is maintained while achieving these improvements in spatial resolution and in practice; ROLEC images are acquired in less time than pinhole collimator images with gamma cameras.

Analysis of errors in three-dimensional reconstruction of radium implants from stereo radiographs.

The present method of steroe shift for three-dimensional (3-D) reconstruction of radium implants has been found to produce displacement errors. Analysis shows that the maximum displacement error decreases as the shift (S) increases with fixed focal spot-film distance (H), while conversely for a fixed shift distance the maximum displacement error with increased focal spot-film distance. The authors suggest that sufficiently accurate 3-D reconstruction may be achieved when H greater than or equal to 100 cm and H/S less than 2.

Plastic scintillation filament detector system for 14CO2 breath-analysis tests.

A 14CO2-measuring system for breath-analysis tests is described which utilizes plastic-scintillator filaments as radiation-detector elements. The 14C radioactivity in expired breath is measured directly, thus eliminating the need for trapping and counting of liquid scintillation-counting solutions. Total CO2 concentration in expired breath is measured by an infrared detector, making no assumption of endogenous CO2 output and enabling results to be expressed as either a concentration (percentage of administered dose per unit of CO2) or total expired 14CO2. Advantages of this system over an ionization chamber are: significantly lower background variation and shorter breathing time to fill completely the detecting chamber with expired air. The system is easy to operate, transportable on a small cart to the patients bed if necessary, and applicable for continuous monitoring of 14CO2 in experimental animal studies.

A coded aperture device for on-line imaging with megavoltage photon beams

A prototype coded aperture device based upon a liquid-filled strip ion chamber has been investigated as an on-line imaging unit for portal imaging of megavoltage photon beams. The strip ion chamber was used to collect integrated data for a series of pixels along a line across the field of view. By translating the detector, in equal steps in a direction perpendicular to its length, the data for a complete projection of the image were collected. Multiple-projection data, corresponding to different angular views, were collected by sequentially rotating the detector in equal angular steps and then translating through the field. The portal image was reconstructed from the multiple-projection data by a convolution-filtered back-projection algorithm. The phantom images taken with a cobalt-60 radiation source were found to be of similar contrast to film images. The signal-to-noise ratio, including the noise propagation of the reconstruction process for an image of 101 ? 101 pixels, was 207:1. For a translational step of 2 mm the spatial resolution of the system was found to be 4.2 mm, as determined from the full width at half maximum of the point spread function.

COORDINATE MEASURING DEVICE FOR RADIUM APPLICATIONS.

Abstract A device for the automatic measurement and recording of x–y coordinates is described. Voltage measurements, proportional to the distance from a point in question to two fixed points, are recorded on IBM punch cards which are then ready for submission to a computer for processing. The calculated x–y coordinates have been found to deviate less than 0.1% from the true values.

60Co Dosimetry with a Desk-Top Computer

Polynomial central-axis depth-dose approximations for 60Co have been developed and used with a small desk-top computer to determine treatment time and 5-mm given dose for a variety of treatment conditions. Deviation of the polynomial approximations from manually calculated values is less than 1%. This method provides a quick and easy means of obtaining the treatment time and 5-mm given dose corresponding to a chosen tumor dose and eliminates the need for manual calculations and the use of tables, thereby reducing the chance of human error.