Kinetics of cell spreading.

Cell spreading is a fundamental event where the contact area with a solid substrate increases because of actin polymerization. We propose in this Letter a physical model to study the growth of the contact area with time. This analysis is compared with experimental data using the ameoba Dictyostelium discoideum. Our model couples the stress, which builds up at the margin of the contact area when the cell spreads, to the biochemical processes of actin polymerization. This leads to a scaling analysis of experimental data with a characteristic time whose order of magnitude compares well with our experimental results.

Magnetic resonance imaging of aneurysms of the abdominal aorta.

Experience with magnetic resonance imaging (MRI) of 10 normal control patients and 13 patients with known abdominal aortic aneurysms is presented. The aorta, renal artery origins, and iliac arteries were clearly identified in all control patients. Ten out of 13 aneurysms were optimally visualized. Three cases early in the experience were poorly seen and permitted less confident measurements. Renal artery origins were identified in 12 cases and judged to be uninvolved by the aneurysm in 11. Iliac arteries were identified in 11 cases and judged to be definitely aneurysmal in three. Sonography clearly depicted all 13 aneurysms. Correlation of the actual anteroposterior (AP) and transverse diameter aneurysm measurements with both techniques was excellent. Sonography failed to identify the renal artery origins in all cases, but could infer noninvolvement in two cases. Iliac arteries were seen in eight cases and judged definitely aneurysmal in three. According to these preliminary results, both MRI and sonography provide accurate AP and transverse outer wall measurements. MRI is superior in determining the presence of renal and/or iliac involvement. The authors recommend, however, that sonography continue to be the preliminary screening method.