The Investigation of the Absorption of ^99mTc γ-rays by Bone and Soft Tissue

Abstract

Recently, the scintigram with ^99mTc-labeled compounds has been routine procedure, because of it's ideal physical characteristics. The short physical half life of six hours, the absence of beta emission, and the gamma rays of 140 keV permit the administration of large amount of radioactivity.
For scintigram of deep or large organ, the absorption of ^99mTcγ-rays by bone and soft tissue should not be negligible. For example, bone scintigram with ^99mTc-phospho-rous compounds shows different pictures depending upon the anterior and the posterior views, because of it's rather lower energy.
Therefore, the linear attenuation coefficient and the half value layer of bone and soft tissue were measured with ^99mTc γ-rays and others (¹⁹⁷Hg, ²⁰³Hg, ¹³¹I, ¹⁹⁸Au, ⁸⁵Sr) .
Results:
1) The linear attenuation coefficient of ^99mTcγ-rays was : bone -0.240 cm^-1, acrylite -0.173 cm^-1, Mix D -0.155 cm^-1.
2) The half value layer of ^99mTcγ-rays was: bone -2.89 cm, acrylite -3.98 cm, Mix D -4.47 cm.
It was concluded that the lower photon energy of ^99mTc was influenced by bone and soft tissue, but it appeared to be most suitable for the present imaging devices. Therefore, pictures of multiple views are necessary in case of the scintigram with ^99mTc-la-beled compounds.