Pediatric DXA: technique and interpretation

This article reviews dual X-ray absorptiometry (DXA) technique and interpretation with emphasis on the considerations unique to pediatrics. Specifically, the use of DXA in children requires the radiologist to be a “clinical pathologist” monitoring the technical aspects of the DXA acquisition, a “statistician” knowledgeable in the concepts of Z-scores and least significant changes, and a “bone specialist” providing the referring clinician a meaningful context for the numeric result generated by DXA. The patient factors that most significantly influence bone mineral density are discussed and are reviewed with respect to available normative databases. The effects the growing skeleton has on the DXA result are also presented. Most important, the need for the radiologist to be actively involved in the technical and interpretive aspects of DXA is stressed. Finally, the diagnosis of osteoporosis should not be made on DXA results alone but should take into account other patient factors

The complex role of bismuth as promoting element to inhibit deactivation of Pd-Bi/C catalysts in the selective oxidation of glucose to gluconic acid

Bismuth is a well-established promoter of Pd/C catalysts used for the partial oxidation of alcohols, aldehydes and, in particular, sugars. It inhibits deactivation due to overoxidation but, simultaneously, gets leached in the reacting solution, a fact that would suggest disappearance of its promoting effect and subsequent deactivation. The extent of leaching changes in a complex way. The present paper deals with complementary experiments carried out to understand how the soluble fraction of Bi could be involved in the overall mechanistic scheme of glucose oxidation into gluconate. Monometallic Pd/C and bimetallic Pd−Bi/C catalysts of various compositions were used. Whatever the initial catalyst composition, the XPS surface intensity ratio measured in used catalysts lies in the range 0.4–0.6, suggesting that the dynamic state of the catalyst involves the association of 1 Bi and 2 to 3 Pd atoms. The performances of a monometallic Pd/C catalyst are significantly improved in the presence of adequate amounts of soluble Bi. Considering that Bi-glucose and highly stable Bi-gluconate complexes can form, it is suggested that one of them, most likely the second one, can get very strongly bound to the surface of Pd or Pd−Bi alloys and that this association constitutes the active site. A too large amount of soluble Bi complex inhibits the reaction, probably by preventing access of glucose to the catalytic site. Long term deactivation can be due to either the action of oxygen or progressive loss of the surface complex

Prevalence of abnormal bone density of pediatric patients prior to blood or marrow transplant

Osteoporosis and osteopenia are long-term side effects of bone marrow transplant (BMT). The purpose of this study was to determine the prevalence of bone mineral density (BMD) abnormalities in pediatric patients prior to BMT. Forty-four pediatric patients were evaluated with DEXA scans. The average Z-score was -0.37. Thirty-six percent had abnormal BMD. Sixty-seven percent of ALL patients had abnormal BMD. Patients with non-malignant diseases were significantly more likely to have abnormal BMD. Patients with ALL had more defects than solid tumor patients. Females had more defects than males. These results demonstrate BMD defects are common in children prior to BMT, especially in patients with ALL