The counterbend phenomenon in flagellar axonemes and cross-linked filament bundles

Recent observations of flagellar counterbend in sea urchin sperm show that the mechanical induction of curvature in one part of a passive flagellum induces a compensatory countercurvature elsewhere. This apparent paradoxical effect cannot be explained using the standard elastic rod theory of Euler and Bernoulli, or even the more general Cosserat theory of rods. Here, we develop a geometrically exact mechanical model to describe the statics of microtubule bundles that is capable of predicting the curvature reversal events observed in eukaryotic flagella. This is achieved by allowing the interaction of deformations in different material directions, by accounting not only for structural bending, but also for the elastic forces originating from the internal cross-linking mechanics. Large-amplitude static configurations can be described analytically, and an excellent match between the model and the observed counterbend deformation was found. This allowed a simultaneous estimation of multiple sperm flagellum material parameters, namely the cross-linking sliding resistance, the bending stiffness, and the sperm head junction compliance ratio. We further show that small variations on the empirical conditions may induce discrepancies for the evaluation of the flagellar material quantities, so that caution is required when interpreting experiments. Finally, our analysis demonstrates that the counterbend emerges as a fundamental property of sliding resistance in cross-linked filamentous polymer bundles, which also suggests that cross-linking proteins may contribute to the regulation of the flagellar waveform in swimming sperm via counterbend mechanics.     

Sclerosed liver hemangioma mimicking malignant tumor at MR imaging: Pathologic correlation

This case report illustrates atypical magnetic resonance (MR) imaging findings in a liver hemangioma mimicking a malignant lesion—lower signal intensity than cerebrospinal fluid on T2-weighted spin-echo images and lack of early enhancement on dynamic contrast material—enhanced gradient-echo images. Pathologic analysis demonstrated nearly total replacement of the vascular cavities by dense fibrous tissue. In this rare, sclerosed form, this lesion could not be defined as a hemangioma with MR imaging.     

In Vivo Evaluation of a Retrievable Vena Cava Filter—The Dibie-Musset Filter: Experimental Results

Purpose: To evaluate, in an animal model, the efficacy and safety of a 7 Fr percutaneous vena cava filter for temporary or permanent use. Methods: The Dibie-Musset (DM) filter is a wire preformed into a double-spiral shape with a spring effect. The experiment was performed in 15 adult sheep and consisted of the insertion of 45 filters, clot trapping tests, and filter retrieval. Follow-up in all sheep consisted of radiologic (abdominal radiograph, inferior vena cavogram, abdominal computed tomography), macroscopic, and microscopic examinations between days 8 and 386 after filter placement. Results: Of the 45 filters implanted in 15 sheep, 29 were retrieved between day 0 and day 15. Filtration efficiency was 100% for clots 4 × 4 × 20 mm. No long-term (1 year) side-effects were detectable. Microscopic examination of the vein wall showed only a dense intimal fibrosis without signs of acute inflammation at 1 year. Conclusion: These results support the efficiency and safety of the DM filter in an animal model.     

Cine-MR Fourier phase imaging for quantification of regional wall asynergy in patients with anterior myocardial infarction

PURPOSE: The aim of this study was to evaluate whether Fourier analysis of cine-MR could detect wall motion abnormalities in patients with myocardial infarction. METHODS: Ten patients with anterior myocardial infarction (seven men and three women; mean age, 58 +/- 16 years) were compared with six control subjects (four men and two women; mean age, 49 +/- 24 years). Gradient echo cardiac cine-MR slices were transformed using a commercially available Fourier algorithm to obtain phase angles of endocardial segments. Mean phase angle and phase dispersion (i.e., SD around the mean) were calculated. Segmental wall motion was evaluated using a 16-segment model and correlated to Fourier phase analysis. RESULTS: Mean phase angle and phase dispersion were increased in patients compared with control subjects (respectively, 191 degrees +/- 23 degrees vs. 161 degrees +/- 25 degrees, P < 0.0001 and 21 degrees +/- 10 degrees vs. 11 degrees +/- 8 degrees, P = 0.0007). Analysis of variance showed a significant increased dispersion on basal slices (P = 0.002) mostly due to flow-void and entry slice phenomenon. CONCLUSIONS: Fourier phase analysis of cardiac cine-MR is feasible and allows the evaluation of ventricular asynergy on the basis of endocardial wall motion.     

High-resolution three-dimensional micro-computed tomography detects bone loss and changes in trabecular architecture early: comparison with DEXA and bone histomorphometry in a rat model of disuse osteoporosis.

RATIONALE AND OBJECTIVES: The ability of three-dimensional micro-computed tomography (3D-microCT) to detect changes in a rat model of disuse osteoporosis was evaluated and compared with two reference techniques: dual x-ray absorptiometry (DEXA) for bone mass, and bone histomorphometry (BHM) for bone mass and trabecular micro-architecture. METHODS: Forty-two rats were divided into controls or were hindlimb unloaded for 7, 13, and 23 days. DEXA bone mineral density measurements were performed on right tibiae. Then, after plastic embedding, bone volume (BV/TV) and trabecular (Tb)-derived parameters of trabecular bone architecture (Tb Th, thickness; Tb N, number) were measured with BHM. 3D-microCT measurements of BV/TV, Tb Th, and Tb N were carried out on left tibiae. RESULTS: Unloaded rats lost bone in a time-dependent manner. DEXA and 3D-microCT detected bone loss earlier than BHM. The decreases in Tb Th and Tb N were observed at day 13 only with 3D-microCT (P < 0.05 and P < 0.01, respectively). All bone mass and architectural parameters measured with the three techniques correlated significantly (0.59, 0.89, P < 0.001), except Tb Th. CONCLUSIONS: 3D-microCT is a valid technique for bone mass and micro-architecture measurements in this rat model of disuse osteoporosis.     

Dy-DTPA derivatives as relaxation agents for very high field MRI: the beneficial effect of slow water exchange on the transverse relaxivities.

Proton longitudinal and transverse relaxivities of Dy(DTPA)(2-) and Dy-DTPA bisamide derivatives (Dy(DTPA-BA): Dy-DTPA bisamide, Dy(DTPA-BEA): Dy-DTPA bisethylamide, Dy(DTPA-BnBA): Dy-DTPA bis-n-butylamide, and Dy(DTPA-BBMA): Dy-DTPA bisbismethylamide) were analyzed between 0.47 T and 18.8 T. Curie longitudinal relaxation was clearly observed at magnetic fields larger than 2.4 T, but the longitudinal relaxivities are limited by the fast rotation of the complexes. Rotational correlation times were separately assessed by deuterium relaxometry of the diamagnetic deuterated lanthanum analogs. Transverse relaxivity, which depends on the square of the magnetic field and on the residence time of the coordinated water molecule (tau(M)), was more than 7.5 times larger at 18.8 T and 310 K for Dy(DTPA-BA) and Dy(DTPA-BEA) as compared to Dy(DTPA)(2-). This difference is mainly related to the slower water exchange of the bisamide complexes, as confirmed by the values of tau(M) measured by oxygen-17 relaxometry. Such Dy-complexes, characterized by relatively long tau(M) values (tauM310 larger than 100 ns but smaller than 1 micros), thus appear to be useful as negative T(2) (or transverse) contrast agents for high-field imaging. This was demonstrated by the spin-echo images of phantoms obtained at 4.7 T on samples containing Dy(DTPA)(2-) and Dy(DTPA-BEA).     

Staging puberty in slipped capital femoral epiphysis: importance of the triradiate cartilage

In 83 children with slipped capital femoral epiphysis, puberty was staged at the time of diagnosis using bone age, closure of triradiate cartilage, Risser index, and the pubertal diagram of Dimeglio. In boys 95% and in girls 83% of slips occurred during the accelerating phase of puberty (stage 1 and 2), in which mainly the limbs grow. In boys (54%) and in girls (66%), most slips occurred in stage 1. The triradiate cartilage was still open at the time of diagnosis in 65% of boys and 64% of girls. Staging puberty is useful to differentiate the risk for slipped capital femoral epiphysis and to evaluate the risk for a contralateral slip. Closure of the triradiate cartilage is a simple measure to identify this risk. Once the triradiate cartilage is closed, there is a 4% chance of a contralateral slip.