Towards validation of computational analyses of peri-implant displacements by means of experimentally obtained displacement maps.

Micro-finite element (µFE) analysis has recently been introduced for the detailed quantification of the mechanical interaction between bone and implant. The technique has been validated at an apparent level. The aim of this study was to address the accuracy of µFE analysis at the trabecular level. Experimental displacement fields were obtained by deformable image registration, also known as strain mapping (SM), of dynamic hip screws implanted in three human femoral heads. In addition, displacement fields were calculated using µFE analysis. On a voxel-by-voxel basis, the coefficients of determination (R(2)) between experimental and µFE-calculated displacements ranged from 0.67 to 0.92. Linear regression of the mean displacements over nine volumes of interest yielded R(2) between 0.81 and 0.84. The lowest R(2) values were found in regions of very small displacements. In conclusion, we found that peri-implant bone displacements calculated with µFE analysis correlated well with displacements obtained from experimental SM.

Structural evidence for ligand specificity in the binding domain of the human androgen receptor. Implications for pathogenic gene mutations.

The crystal structures of the human androgen receptor (hAR) and human progesterone receptor ligand-binding domains in complex with the same ligand metribolone (R1881) have been determined. Both three-dimensional structures show the typical nuclear receptor fold. The change of two residues in the ligand-binding pocket between the human progesterone receptor and hAR is most likely the source for the specificity of R1881 to the hAR. The structural implications of the 14 known mutations in the ligand-binding pocket of the hAR ligand-binding domains associated with either prostate cancer or the partial or complete androgen receptor insensitivity syndrome were analyzed. The effects of most of these mutants could be explained on the basis of the crystal structure.

[A Doppler ultrasound device for determining blood volume flow]. / Ein Doppler-Ultraschall-Gerät zur Bestimmung des Blut-Volumenflusses.

A novel ultrasonic quantitative Doppler procedure has been developed which allows for the measurement of real-time volume flow in large blood vessels. It makes use of a 2D array transducer, which enables parallel sampling of a measuring slice placed in normal position to the sound beam. With this arrangement, volume flow can be computed without measuring the angle of incidence. Moreover, the 2D velocity distribution can be assessed within intervals of 10 to 30 ms.

Ultrasonic phased-array scanner with digital echo synthesis for Doppler echocardiography.

For the purpose of the quantitative assessment of subtle disease processes in the cardiovascular system an electronically steered sector scanner that combines echographic imaging and Doppler blood velocity measurements has been developed. The integrated operation of a fast Fourier transform (FFT) Doppler signal processor for the simultaneous blood velocity evaluation of 64 individual gates is among the specific design goals. The instrument incorporates an unusually high degree of digital signal processing, which allows for high integration density, easy manufacturing and high reliability in future designs. The complex Doppler spectra are determined for each of the 64 Doppler gates in real time, and the subsequent computation of the first moment provides a reliable estimate of the mean blood flow velocities at the respective locations. The instantaneous velocity profile along the Doppler beam is displayed together with the calculated volume flow rate and a range-selected complete frequency spectrum. Results of both in vitro and in vivo tests indicate that in the future, a higher degree of digital signal processing could be implemented in complex ultrasonic systems.