The Concentration of P³²in Some Superficial Tissues of Living Patients

Abstract

The turnover of a radio-element in an organ can be followed either by assays on tissues taken from a large group of animals sacrificed or biopsied at different times, or by successive in vivo determinations of the concentration on a single group of animals which need be neither sacrificed nor biopsied. The latter alternative, so desirable in medical studies on man, is feasible because many radio-elements can be detected and measured at a distance, without disturbing the biochemical processes in which they are taking part. In its most general terms, the problem consists in measuring at points external to the human body the radiation emitted by a radioactive substance taken up by a definite region of the body. The success of measuring such radiation will depend on the penetrating properties of the radiation and on the degree to which the radioactive isotope is localized in the tissue in question. Gamma ray-emitting isotopes of elements which are localized to a high degree are obviously the most desirable. Thus radio-iodine, a gamma ray emitter which localizes mostly in the thyroid, has been used successfully by Hamilton (1, 2) and by Hertz (3) in their study of thyroid metabolism. The concentration of other gamma ray emitters, not localized to the same degree, cannot be readily determined because of the difficulty of preventing the detector (be it a Geiger-Muller counter, an ionization chamber, or a photographic film) from registering radiation originating in tissues surrounding the organ under investigation.3 The study of the in vivo concentration of beta ray-emitting isotopes is limited, on the one hand, to the most superficial layers of the body, on account of the small penetration of the radiation; it is facilitated, on the other hand, by the fact that localization of the region of interest is easily accomplished by light screening. Since most of the radio-elements available today are beta ray emitters, it seems likely that investigations of this nature will be useful in providing extensive information on the dynamics of skin metabolism. Before closing these general remarks, it is well to point out that, theoretically at least, there is a definite possibility of investigating beta ray concentrations in the interior of the body by means of their Bremsstrahlung, namely, by the process of converting the kinetic energy of electrons into x-rays. To be sure, these investigations may require sensitive apparatus, but no great difficulty is to be feared on this account if the patients are given therapeutic doses and the radio-elements are well localized. Such a favorable situation is to be expected, for instance, in the use of radio-strontium, because of its marked deposition in bone (6) and because of the abundance therein of elements of relatively high atomic number which favor the conversion of electronic energy into x-rays (7).