Reliability of stabilised commercial dynamometers for measuring hip abduction strength: a pilot study.

BACKGROUND: Reliable quantification of hip abductor strength in a clinical setting is challenging. OBJECTIVES: To examine the intrarater and interrater reliability of three commonly used commercial dynamometers in the measurement of hip abduction. METHODS: Supine gravity minimised measures of unilateral hip abduction strength were recorded in 10 women (mean (SD) age 23.5 (1.9) years) using three different commercially available dynameters. Measurements were repeated over a three day period with a different device used on each day. RESULTS: Intrarater reliability ranged from 0.880 to 0.958 across the three devices, and measures of interrater reliability ranged from 0.899 to 0.948. CONCLUSION: Commercially available dynamometers can be used to quantify hip abduction strength with good to excellent reliability. A previously undescribed method of quantifying hip abduction strength in a clinical setting using readily available instrumentation is presented.

Optical phase contrast measurement of ultrasonic fields.

This report describes an optical phase contrast imaging technique for the measurement of wide bandwidth ultrasound fields in water. In this method, a collimated optical wavefront (lambda(l) = 810 nm) impinges on a wide bandwidth ultrasound pulse. The method requires that refractive index perturbations induced by the ultrasound field be sufficiently small. Specifically, on exit from the acoustic field, the phase of the optical wavefront must be proportional to the ray sum of local density taken in the direction of propagation of the incident optical wave. A similar restriction is placed on the dimensions of the ultrasound pulse. Repeated measurement of this phase as the ultrasound field is rotated through 180 degrees about an axis normal to the direction of propagation of the incident optical wave generates the Radon transform of the ultrasonically induced refractive index perturbation. Standard tomographic reconstruction techniques are used to reconstruct the full three-dimensional refractive index perturbation. A simple two-lens imaging system and an optical signal processing element from phase contrast microscopy provide a method of directly measuring an affine function of the desired optical phase for small optical phase shifts. The piezo- and elasto-optic coefficients (the first partial derivatives of refractive index with respect to density and pressure) relate refractive index to density and pressure via a linear model. The optical measurement method described in this paper provides a direct, quantitative measurement of the piezo- and elasto-optic coefficients (from the density or pressure fields).

Three-dimensional optical measurement of instantaneous pressure.

Local perturbations in material density induced in a material by a compressional wave give rise to local perturbations in refractive index. Accurate, high-resolution, three-dimensional, optical measurements of an instantaneous refractive index perturbation in a homogeneous, optically transparent medium may be obtained from measurements of scattered optical intensity alone. The method of generalized projections allows incorporation of optical intensity measurements into an iterative algorithm for computing the phase of the interrogating optical pulse as the solution of a fixed point equation. The complex optical field amplitude, computed in this manner, is unique up to a constant unit magnitude complex coefficient. The three-dimensional refractive index distribution may be computed via the Fourier slice reconstruction algorithm from the optical phase data under the assumption of weak optical scattering. The refractive index perturbation is related to local instantaneous pressure under a linear, small-displacement model for the mechanical wave. A numerical simulation of the measurement experiment, phase recovery, and reconstruction process for a plane piston ultrasound transducer with a semicircular aperture and center frequency of 1.5 MHz is described and corresponds very well with experiment. Experimental data obtained using an 810-nm laser source are used to reconstruct the three-dimensional pressure field from two elements of a 2.5-MHz linear array. Comparison with a measurement obtained via a 500-microm needle hydrophone shows excellent agreement.