Nosil J, Sethi V, Bland J, Kloiber R
Department of Radiological Sciences and Diagnostic Imaging, Foothills Hospital, Calgary, AB, Canada.
Phys Med Biol. 1987 Nov;32(11):1407-16. doi: 10.1088/0031-9155/32/11/003.
Radioactive sources of finite volume containing 133Xe, 67Ga, 99Tcm and 111In were used to measure the attenuation coefficient, mu, in water at six different energies in the range 80-296 keV using an Anger camera. The experimental accuracy was about 7% for the volume range from 40-225 ml when corrections were made for background. The same radioactive sources were used to measure zero attenuation count rates per unit of activity. The theoretical basis was also derived, which confirms our experimental findings, i.e. the measurement of the thickness of the attenuator using a dual energy method. The determination of the linear attenuation coefficient in the broad-beam geometry situation is possible by accounting for cross-talk, scatter and out-of-target activity. By correcting for the broad-beam geometry, agreement with the narrow-beam geometry linear attenuation coefficient was obtained. We also demonstrate the use of the technique to accurately determine the depth of the organ using two separate energies. This methodology is independent of the organ volume for determination of the depth. It is hoped that our findings will provide a better understanding of the photon interactions when extended sources are used. Such a knowledge can also be applied to organ volume measurements.
