RESUMEN
Dual-energy X-ray absorptiometry (DXA) of the lumbar spine provides an estimation of the bone mineral content (BMC) corrected by the projected area of the spine and expressed in g/cm2. This two-dimensional estimate of the bone mineral density (BMD) is influenced by the skeletal size, assessed by the subject's height. In order to obtain an estimate of the volumetric BMD, we measured BMC with a new DXA device (Sophos L-XRA) equipped with 24 detectors and a rotating arm, thus allowing scanning of the lumbar spine in both an anteroposterior (AP) projection and a lateral (LAT) projection with the patient in a supine position. Comparison between the results obtained on the third (L3) and fourth (L4) lumbar vertebrae with automatic or manual analysis showed that the best precision was obtained with the lateral measurement of L3 alone with an automatic soft tissue baseline determination. Results were expressed in g/cm2 and in g/cm3 (by dividing the g/cm2 value by the width (AP area divided by the height of the vertebra) of L3), and were compared with those obtained by conventional AP scanning of L2-4 (g/cm2). The in vivo precision error evaluated by triplicate measurements on 10 controls was 17 mg/cm2 (1.96%) and 5.2 mg/cm3 (2.31%) for LAT L3 as compared with 13 mg/cm2 (1.15%) for AP L2-4. Volumetric BMD (g/cm3) measurement, assessed in vitro on a calibrated hydroxyapatite phantom, and the absolute values obtained in normal women were similar to those obtained by quantitative computed tomography (QCT).(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Absorciometría de Fotón/métodos , Densidad Ósea/fisiología , Vértebras Lumbares/fisiología , Absorciometría de Fotón/instrumentación , Adulto , Anciano , Estatura , Estudios de Cohortes , Femenino , Humanos , Masculino , Persona de Mediana Edad , Osteoporosis Posmenopáusica/fisiopatología , Reproducibilidad de los ResultadosRESUMEN
Radioactive gases are very useful in the study of pulmonary disorders because they allow an assessment of regional lung function. The most widely used radioactive gases are Xe-133 and, more recently, Kr-81m. This paper is a review of the physical characteristics of Kr-81m, its production from the parent Rb-81, the different methods to produce Rb-81, the different types of generators which can be used in hospitals, and the clinical applications of pulmonary ventilation imaging. The paper suggests that Kr-81m offers several advantages over previous methods that used Xe-133 due to its improved spatial resolution, its capacity to provide superimposable ventilation and perfusion images in multiple projections, and its total lung dose which is ten times lower than that of Xe-133.