Biomedical subjects

Graham M Treece

Publications and source records attributed to Graham M Treece.

11 recordsLinked to original sources

PubMed2006

3D elastography using freehand ultrasound.

We present an elastography system using freehand 3D ultrasound. A review is provided of the standard elastography methods that have been adapted for this purpose. The scanning protocol is simple and promising results are presented of 3D strain images from freehand scans. Robustness is a problem, however, and the main sources of error are explained. Measures have been developed to improve the quality of the freehand images by means of drop-out correction and frame filtering. Results from the application of these techniques provide an indication of development strands which should lead to a system that is both easy-to-use and produces reliable, high quality images.

Elasticity↗

PubMed2006

Rapid, easy and reliable calibration for freehand 3D ultrasound.

This paper presents improvements to the plane-based technique for calibrating freehand 3D ultrasound systems. The improvements are designed to make it easier for inexperienced users to perform plane-based calibration and to know that they have got a reliable result. In particular, we enable the calibration to be performed using water at room temperature while producing a result that is valid for average soft tissue and we show how it is possible to provide feedback on the reliability of the calibration using a metric based on the curvature of the calibration criterion function. We present comprehensive results showing that these innovations improve the precision of the calibration and offer useful feedback to the user.

Acoustics↗

PubMed2006

Subsample interpolation strategies for sensorless freehand 3D ultrasound.

Freehand 3D ultrasound can be acquired without a position sensor by deducing the elevational probe motion from the interframe speckle decorrelation. However, a freehand scan involves lateral and axial, as well as elevational, probe motion. The lateral sampling is determined by the A-line separation and is relatively sparse: lateral motion tracking therefore requires subsample interpolation. In this paper, we investigate the resilience of lateral interpolation techniques to simultaneous lateral and elevational probe motion. We propose a novel interpolation strategy and, through a series of in vitro experiments, compare its performance with that of established alternatives. The new technique is shown to be superior, limiting interpolation errors to around 5% of the length of the freehand reconstruction.

Algorithms↗

PubMed2005

Sensorless freehand 3D ultrasound in real tissue: speckle decorrelation without fully developed speckle.

It has previously been demonstrated that freehand 3D ultrasound can be acquired without a position sensor by measuring the elevational speckle decorrelation from frame to frame. However, this requires that the B-scans contain significant amounts of fully developed speckle. In this paper, we show that this condition is rarely satisfied in scans of real tissue, which instead exhibit fairly ubiquitous coherent scattering. By examining the axial and lateral correlation functions, we propose an heuristic technique to quantify the amount of coherency at each point in the B-scans. This leads to an adapted elevational decorrelation scheme which allows for the coherent scattering. Using the adapted scheme, we demonstrate markedly improved reconstructions of animal tissue in vitro.

Algorithms↗

PubMed2005

RF and amplitude-based probe pressure correction for 3D ultrasound.

Anatomical deformation caused by variable probe contact pressure is a significant problem in freehand 3D ultrasound, particularly for high resolution musculoskeletal and breast scans. We have previously published an amplitude-based algorithm for correcting such errors. In this paper, we compare this approach with a novel, elastography-inspired algorithm which works with the higher resolution radio-frequency (RF) signal. The results show that, although the RF-based algorithm is more precise in certain circumstances, both algorithms are able to compensate for probe pressure in 3D ultrasound data. Consequently, freehand 3D ultrasound users who do not have access to the RF signal are still in a position to perform effective probe pressure correction using the readily available video output, as long as this signal is not affected by significant amounts of frame averaging (persistence).

Algorithms↗

PubMed2005

A mechanical instrument for 3D ultrasound probe calibration.

We present a novel technique for 3D ultrasound probe calibration. The principle of operation is that the beam is aligned with a set of coplanar wires strung across a rigid frame. The probe and frame are mounted on a precision-manufactured mechanical instrument which allows adjustment and measurement of their relative pose. Semi-automatic image processing facilitates alignment of the beam and wires to within a tolerance of around 0.2 mm, despite the considerable beam thickness. The calibration process requires just a single view and relatively little user expertise. In a series of experiments with different ultrasound probes, we demonstrate the technique's high accuracy and precision. The latter is partly due to the elimination of the position sensor, a significant source of measurement noise, from the end-user calibration process.

Calibration↗

PubMed2005

Speckle classification for sensorless freehand 3-D ultrasound.

Despite being a valuable tool for volume measurement and the analysis of complex geometry, the need for an external position sensor is holding up the clinical exploitation of freehand 3-D ultrasound. Some sensorless systems have been developed, using speckle decorrelation for out-of-plane distance estimation, but their accuracy is still not as good as that of sensor-based systems. Here, we examine the widely held belief that accuracy can be improved by limiting the distance measurements to patches of ultrasound data containing fully developed speckle. Without speckle detection, we observe that scan separation is systematically underestimated by 33.1% in biological tissue. We describe a number of speckle detectors and show that they reduce the underestimate to about 25%. We conclude that speckle classification can improve the quality of distance estimation, but not sufficiently to achieve accurate, metric reconstruction of the insonified volume.

Humans↗

PubMed2003

Sensorless freehand 3-D ultrasound using regression of the echo intensity.

In freehand 3-D ultrasound (US), a position sensor is attached to the probe of a 2-D US machine. The resulting 3-D data permit flexible visualisation and more accurate volume measurement than can be achieved using 2-D B-scans alone; however, the use of the position sensor can be inconvenient for the clinician. The objective is, thus, to replace the sensor with a technique for estimating the probe trajectory based on the B-scan images, themselves. One such technique exists, based on decorrelation algorithms. This paper presents an alternative approach based on linear regression of the echo-envelope intensity signal. A probabilistic analysis of the speckle characteristics of the US signal leads to a linear model, on which the regression algorithm is based. The gradient parameter of this model is shown to be directly related to probe motion. The viability of the new approach is demonstrated through simulations and in vitro and in vivo experiments.

Algorithms↗

PubMed2003

High-definition freehand 3-D ultrasound.

This paper describes a high-definition freehand 3-D ultrasound (US) system, with accuracy surpassing that of previously documented systems. 3-D point location accuracy within a US data set can be achieved to within 0.5 mm. Such accuracy is possible through a series of novel system-design and calibration techniques. The accuracy is quantified using a purpose-built tissue-mimicking phantom, designed to create realistic clinical conditions without compromising the accuracy of the measurement procedure. The paper includes a thorough discussion of the various ways of measuring system accuracy and their relative merits; and compares, in this context, all recently documented freehand 3-D US systems.

Calibration↗

PubMed2003

Rapid registration for wide field of view freehand three-dimensional ultrasound.

A freehand scanning protocol is the only way to acquire arbitrary large volumes of three-dimensional ultrasound (US) data. For some applications, multiple freehand sweeps are required to cover the area of interest. Aligning these multiple sweeps is difficult, typically requiring nonrigid image-based registration as well as the readings from the spatial locator attached to the US probe. Conventionally, nonrigid warps are achieved through general elastic spline deformations, which are expensive to compute and difficult to constrain. This paper presents an alternative registration technique, where the warp's degrees of freedom are carefully linked to the mechanics of the freehand scanning process. The technique is assessed through an extensive series of in vivo experiments, which reveal a registration precision of a few pixels with comparatively little computational load.

Algorithms↗

PubMed2002

Analysis of speckle in ultrasound images using fractional order statistics and the homodyned k-distribution.

It is necessary to identify speckled regions in ultrasound images to control adaptive speckle suppression algorithms, for tissue characterisation, and to estimate the elevational separation of B-scans by speckle decorrelation. Previous authors have proposed classification techniques based on second order powers of the homodyned k-distribution, or lower order powers of the more limited k-distribution. In this paper we explore the speckle discrimination properties of statistics based on arbitrary powers of the ultrasound echo envelope signal using a combination of simulations and theoretical results from the homodyned k-distribution. We conclude that statistics based on powers less than one are surprisingly less effective than some higher powers. A simple discriminant function for speckle is evaluated quantitatively in simulation and qualitatively on sample B-scan images.

Algorithms↗