[Dual-photon densitometry of the lumbar spine. Basic experience and results].

The principle of assessment of absorption of gamma radiation (single photon radiation, i.e. with one radiation energy) was first applied to assess the content of mineral substances in peripheral bones. Earlier and more marked affection of the spine in osteoporosis led to the development of dual-photon densitometry, i.e. differential assessment of the absorption of gamma radiation with two energies, which makes it possible to eliminate the ratio of soft tissues in absorption of the radiation (the source of radiation is gadolinium 153Gd). The equipment is more complicated and more expensive, the operation more time consuming and more pretentious. Various circumstances - most frequently changes of the spine with foci of increased density - make it difficult or impossible to evaluate and use the results in one third of patients with disorders of the bones (most frequently osteoporosis), incl. 1/2 of the patients above 60 years of age. Short-term reproducibility of the estimations is satisfactory - variation coefficients of repeated measurements in g.cm-1 and in g.cm-2 are less than 2%. Examination of 183 controls (83 men, 100 women) indicates a drop of the mineral content in L2 to L4 with age in women from 25 to 30 years to old age with a slight acceleration during the menopause, in men a decline only after the age of 60 years. In younger age groups the scatter of our normal values in men is greater than in women. The bone density in g, g.cm-1 as well as in 9.cm-2 rises significantly in the order L2 less than L3 less than L4. Except for the limited applicability of results the basic experience is on the whole favourable. From the clinical aspects the evaluation of pathological findings, to which a separate paper will be devoted, is of decisive importance.