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Variations in attentuation coefficients for Tc-99m photons with source depth and region-of-interest size

Conference · · J. Nucl. Med.; (United States)
OSTI ID:6653616
; ; ; ;
A theoretical attenuation coefficient (..mu.. =0.15 cm/sup -1/) and an empirically determined coefficient (..mu..') have been used in count-based determinations of ventricular volumes. The value ..mu..' is influenced by scatter conditions. The authors have investigated the effect of source depth and region-of-interest (ROI) size on ..mu..' using a water phantom. A Tc-99m point source positioned in the phantom at depths from 4 to 25 cm and in air at 2.5 cm was imaged with a gamma camera with a 20% window. The empirical ..mu..' was equal to 1n(A/B)/C, where A= background corrected count rate of source in air and B= background corrected count rate at source depth C. A 96 cc Tc-99m-filled sphere was imaged in a water phantom at a depth of 9 cm and 1 cc of this sample was imaged in air. Fourteen ROTs ranging from 180 to 1600 pixels (1 pixel = 0.174 cm/sup 2/) were drawn around the image of the sphere. The value of ..mu..' was equal to 1n(96D/E)/F, where D= background corrected count rate for 1 cc source and E= background corrected count rate for the sphere ROI at depth F (9 cm). For the point source at increasing depths the value of ..mu..' increased from 0.086 to 0.13 cm/sup -1/ approximately linearly. With increasing ROI size the value of ..mu..' decreased nonlinearly from 0.113 to 0.087 cm/sup -1/ with the decrements becoming smaller with larger ROIs. The empirically determined attenuation coefficient ..mu..' is influenced by source depth and ROI size. Use of such a coefficient should include consideration of these factors.
Research Organization:
Duke Univ. Medical Center, Durham, NC
OSTI ID:
6653616
Report Number(s):
CONF-840619-
Conference Information:
Journal Name: J. Nucl. Med.; (United States) Journal Volume: 25:5
Country of Publication:
United States
Language:
English

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Related Subjects

550601 -- Medicine-- Unsealed Radionuclides in Diagnostics
61 RADIATION PROTECTION AND DOSIMETRY
62 RADIOLOGY AND NUCLEAR MEDICINE
655003* -- Medical Physics-- Dosimetry
ATTENUATION
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOMEDICAL RADIOGRAPHY
COMPUTERIZED TOMOGRAPHY
COUNTING TECHNIQUES
DEPTH DOSE DISTRIBUTIONS
DIAGNOSTIC TECHNIQUES
DOSIMETRY
ELEMENTARY PARTICLES
EMISSION COMPUTED TOMOGRAPHY
GAMMA DOSIMETRY
HOURS LIVING RADIOISOTOPES
IMAGE PROCESSING
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LIGHT SCATTERING
LIGHT TRANSMISSION
MASSLESS PARTICLES
MATERIALS
MEDICINE
NUCLEAR MEDICINE
NUCLEI
ODD-EVEN NUCLEI
PHOTON COMPUTED TOMOGRAPHY
PHOTONS
POINT SOURCES
PROCESSING
RADIATION DOSE DISTRIBUTIONS
RADIATION SOURCES
RADIATION TRANSPORT
RADIOISOTOPE SCANNING
RADIOISOTOPES
RADIOLOGY
SCATTERING
SCINTISCANNING
SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY
SPATIAL DOSE DISTRIBUTIONS
TECHNETIUM 99
TECHNETIUM ISOTOPES
TISSUE-EQUIVALENT MATERIALS
TOMOGRAPHY
VARIATIONS
YEARS LIVING RADIOISOTOPES