RESUMEN
In the 'thermo-acoustic sensing technique' (TAST), a burst of sound, called the 'thermometer' beam is passed through tissue and its transit time is measured. A focused sound field, called the heating field, then warms a small volume in the path of the therometer beam, in proportion to the absorption. Finally, the therometer beam burst is repeated and its transit time subtracted from that of the initial thermometer burst. This difference measures the velocity perturbation in the tissue produced by the heating field. The transit time difference is td = K integral of infinity-infinity IP dchi where K is the instrument constant, I the heating field intensity, and P a perturbation factor which characterizes the tissues. The integration is carried out along the path of the thermometer beam. The perturbation factor is P = (formula: see text) where C is the specific heat, rho the denisty, V the velocity of sound, (formula: see text) the temperature coefficient of velocity and alpha the heating field absorption coefficient which is apparently sensitive to tissue structure and condition. Experiments on a fixed human brain showed an ability to distinguish between various tissue types combined with a spatial resolution of better than 3 mm. Should predictions based on the data and theory prove correct, TAST may become a non-invasive alternative to biopsy.
Asunto(s)
Termografía , Ultrasonido , Encéfalo/diagnóstico por imagen , Neoplasias Encefálicas/diagnóstico por imagen , Diagnóstico Diferencial , Relación Dosis-Respuesta en la Radiación , Meningioma/diagnóstico por imagen , Modelos Biológicos , Movimiento (Física) , Radiografía , Sonido , Temperatura , Termómetros , Ultrasonido/instrumentación , UltrasonografíaRESUMEN
Calcium absorption and endogenous loss of calcium were measured in a group of patients with Crohn's disease, using a simultaneous metabolic balance and calcium isotope regimen. Calcium malabsorption resulting in negative calcium balance was found in only 4 of 31 patients with Crohn's disease. No elevation of endogenous fecal calcium or total secreted intestinal calcium was observed in 10 patients studied, regardless of the level of net or true calcium absorption. Correlation between calcium balance and serum protein loss was observed, but no association was noted with intestinal fat excretion, d-xylose absorption, bacterial colonization of the jejunum, or glucocorticosteroid therapy. The results indicate that in this group of patients with Crohn's disease involving different areas of the intestine, calcium malabsorption occurred infrequently and that the levels of calcium excretion correlated best with enteric protein loss.