Bowel opacification for abdominal computed tomography in children: a clinical trial of oral Telebrix 38

Computed tomography (CT) of the abdomen is an important diagnostic tool for detecting abnormalities of the solid organs and, to a lesser extent, the gastrointestinal tract. For an optimal CT study, the gastrointestinal and urinary tracts should be opacified with oral and intravenous radiopaque contrast agents. The authors tested the effectiveness of dilute oral meglumine and sodium ioxithalamate (Telebrix 38, Mallinckrodt Canada Inc., Pointe-Claire, Que.) as a bowel marker in 50 CT examinations of the abdomen and pelvis. The study objective was assessment of patient acceptance, safety of the product, degree of bowel opacification and image quality. Of children who were capable of answering the question, 93% said they would be willing to take the 2% oral solution of Telebrix again if required. No adverse effect attributable to the contrast medium was noted. Opacification of the gastrointestinal tract was excellent in the majority of cases, and the diagnostic quality of the CT images was good. The authors concluded that 2% Telebrix is an effective and safe bowel opacification agent for abdominal and pelvic CT scanning.     

Dynamic spike threshold reveals a mechanism for synaptic coincidence detection in cortical neurons in vivo

Cortical neurons are sensitive to the timing of their synaptic inputs. They can synchronize their firing on a millisecond time scale and follow rapid stimulus fluctuations with high temporal precision. These findings suggest that cortical neurons have an enhanced sensitivity to synchronous synaptic inputs that lead to rapid rates of depolarization. The voltage-gated currents underlying action potential generation may provide one mechanism to amplify rapid depolarizations. We have tested this hypothesis by analyzing the relations between membrane potential fluctuations and spike threshold in cat visual cortical neurons recorded intracellularly in vivo. We find that visual stimuli evoke broad variations in spike threshold that are caused in large part by an inverse relation between spike threshold and the rate of membrane depolarization preceding a spike. We also find that spike threshold is inversely related to the rate of rise of the action potential upstroke, suggesting that increases in spike threshold result from a decrease in the availability of Na(+) channels. By using a simple neuronal model, we show that voltage-gated Na(+) and K(+) conductances endow cortical neurons with an enhanced sensitivity to rapid depolarizations that arise from synchronous excitatory synaptic inputs. Thus, the basic mechanism responsible for action potential generation also enhances the sensitivity of cortical neurons to coincident synaptic inputs.     

Magnetic resonance imaging of benign bone lesions: cysts and tumors

A benign bone lesion may have a typical appearance on plain radiographs. This is the case with benign cortical defects and osteochondroma. With most other lesions, cross-sectional imaging is needed to complete the study of the tumor. The nidus of osteoid osteoma is well demonstrated on computed tomography, but magnetic resonance imaging also will show the nidus in most cases. Magnetic resonance imaging is considered the modality of choice for evaluation of other benign musculoskeletal lesions because it is highly sensitive to changes in the signal intensity of bone marrow and adjacent soft tissues. It provides useful information for diagnosis of the lesion as in primary or secondary aneurysmal bone cyst, chondroblastoma, osteoblastoma, fibrous dysplasia, and osteofibrous dysplasia, and it helps differentiate these lesions from osteomyelitis, Langerhans' cell histiocytosis, and stress fracture. Bone scanning is most useful for depicting multiple silent lesions as may be seen in multiple osteochondromatosis, nonossifying fibromas, and polyostotic fibrous dysplasia.