Biomedical subjects

K L Greer

Publications and source records attributed to K L Greer.

40 records · Page 3Linked to original sources

PubMedDate not supplied

An overview of a camera-based SPECT system.

Camera-based single photon emission computed tomography (SPECT) provides increased information about the organ scanned by eliminating superpositioned radionuclidic activity in the reconstructed images. Current literature contains little detail regarding the potential of and the technical aspects involved in using this emerging imaging modality. A description of the instrumentation supplements a general, but practical, background for nuclear medicine personnel. Some of the considerations for successfully utilizing a SPECT system are described, along with a discussion of the basis for these procedures. Pitfalls are mentioned and clinical images from our SPECT imaging system are included.

Calibration↗

PubMedDate not supplied

Tc-99m attenuation coefficients in water-filled phantoms determined with gamma cameras.

Quantitative imaging with gamma cameras requires compensation for attenuation of source photons. Some methods of compensation make use of a constant or average estimated attenuation coefficient mu. A value for mu of 0.15 cm-1 for 140.5-keV photons in water or tissue is commonly used. This value, however, neglects scattered photons which are detected within the energy window in gamma camera imaging. Values for mu of 0.12 cm-1 used in attenuation compensation of Tc-99m single-photon emission computed tomography scans of uniform cylindrical sources have been shown to give improved results compared with use of mu = 0.15 cm-1. In this study, gamma cameras and a multichannel pulse-height analyzer were used to determine effective values of mu for photons in water as a function of energy window. Two cylindrical water-filled phantoms, circular and elliptical, were used with a point source of Tc-99m at depths up to 18 cm. Energy data were integrated over the top half of the photopeak, and over 10%, 20%, and 30% windows centered on the photopeak. Attenuation curves were exponential for all photopeak windows with values of mu of 0.12 +/- 0.014 cm-1 for all windows up to 20% and 0.1 cm-1 for a 30% window. This study suggests that a value of mu of 0.11-0.12 cm-1 is, in fact, appropriate for use in attenuation compensations where an average is required.

Models, Structural↗

PubMedDate not supplied

Monte Carlo evaluation of Compton scatter subtraction in single photon emission computed tomography.

In single photon emission computed tomography (SPECT), Compton scattering produces a background that degrades the image quality and contributes erroneously to quantitative measurements. A clinically implementable compensation algorithm has previously been reported that subtracts a Compton scatter image, acquired in an energy window set below the energy of the photopeak, from the primary image acquired in the photopeak window. We present an evaluation and justification of the assumptions made in the previous empirical development of the subtraction algorithm. A Monte Carlo model of the SPECT system in which the Compton scattered vents may be followed independently of the nonscattered events was used to evaluate this subtraction technique. Simulation shows that the assumptions made in the experimental application of this algorithm were valid. Specifically (1) the "scatter" energy window used in the experiment (91-125 keV for imaging Tc-99m) contains only scattered events, (2) the shape of the line spread function (LSF) for the events in the scatter window is a reasonable approximation to the shape of the scatter in the photopeak window, and (3) the ratio of the number of scattered events in the photopeak window to the number of events in the scatter window is 0.57, close to the value of 0.5 derived heuristically. Thus, Monte Carlo simulation validates the basic assumptions underlying the empirical implementation of the scatter subtraction algorithm.

Humans↗

PubMedDate not supplied

Cone beam collimation for single photon emission computed tomography: analysis, simulation, and image reconstruction using filtered backprojection.

This paper presents an analysis of two cone beam configurations (having focal lengths of 40 and 60 cm) for the acquisition of single photon emission computed tomography (SPECT) projection data. A three-dimensional filtered backprojection algorithm is used to reconstruct SPECT images of cone beam projection data obtained using Monte Carlo simulations. The mathematical analysis resulted in on-axis point source sensitivities (calculated for a distance of 15 cm from the collimator surface) for cone beam configurations that were 1.4-3 times the sensitivities of parallel-hole and fan beam geometries having similar geometric resolutions. Cone beam collimation offers the potential for improved sensitivity for SPECT devices using large-field-of-view scintillation cameras.

Humans↗