Articles

Assessment of the Accuracy of an Ultrasound Elastography Liver Scanning System using a PVA-Cryogel Phantom with Optimal Acoustic and Mechanical Properties

S. Cournane et al. — Wed, 26 Jan 2011 03:18:19 PST

The accuracy of a transient elastography liver-scanning ultrasound system was assessed using a novel application of PVA-cryogel as a tissue-mimicking material with acoustic and shear elasticity properties optimized to best represent those of liver tissue. Although the liver scanning system has been shown to offer a safer alternative for diagnosing liver cirrhosis through stiffness measurement, as compared to the liver needle biopsy exam, the scanner’s accuracy has not been fully established. The Young’s elastic modulus values of 5-6wt% PVA cryogel phantoms, also containing glycerol and 0.3μm Al2O3 and 3μm Al2O3, were measured using a ‘gold standard’ mechanical testing technique and transient elastography. The mechanically measured values and acoustic velocities of the phantoms ranged between 1.6 16.1kPa and 1540 1570m/s, respectively, mimicking those observed in liver tissue. The values reported by the transient elastography system overestimated the Young’s elastic modulus values representative of the progressive stages of liver fibrosis by up to 32%. These results were attributed to the relative rather than absolute nature of the measurement arising from the single-point acoustic velocity calibration of the system, rendering the measurements critically dependent on the speed of sound of the sample under investigation. Given the wide range of acoustic velocities which exist in the liver, spanning healthy tissue to cirrhotic pathology, coupled with the system’s assumption that the liver is approximately elastic when it is rather highly viscoelastic, care should be exercised when interpreting the results from this system in patient groups.

A Review of the Different Methods for Assessing Standing Balance

Jacinta Browne et al. — Wed, 16 Jun 2010 08:33:14 PDT

This paper is a review of the balance assessment methods currently used to evaluate standing balance. Most of the presently available instrumentation appears to be more suited to research laboratories than to routine clinical situations. Functional assessments of balance appear to be the quickest test to administer and do not require expensive equipment however only gross changes in balance can be detected making them suitable as a screening tool for identifying subject’s needing more thorough evaluation. Force platforms appear to be most suited balance assessment instrumentation to the clinical situation since it produces a real time display and can detect small changes in subject’s ability to maintain their balance making them suitable for thorough evaluations of balance and for monitoring patient’s progress.

Clinical Assessment of the Quantitative Posturography System (QPS)

Jacinta Browne et al. — Wed, 16 Jun 2010 08:33:13 PDT

The objectives of this study were to evaluate a novel design dynamic force platform the Quantitative Posturography System (QPS). The evaluation consisted of identifying the effects due to ageing and disease of the postural control system and also to examine the relationship between functional performance and postural sway. An AOVA design and Pearson-Product correlation design were used. Seventy healthy subjects, seven subjects with Parkinson’s disease and eight subjects with a history of falls took part in the study. It was found that the QPS was able to identify changes due to both the ageing process and disease on the postural control system. Also a moderate correlation coefficient was found between the sway parameters of the QPS and the two functional balance assessment tests, the Single Leg Stance Test (SLST) and the Functional Reach Test (FR test). In conclusion, the QPS was able to detect the change in the postural control system due to both the ageing process and disease. It was also found that there is a moderately strong relationship between functional performance and postural sway.

Development of a Novel Method for Assessing Balance: the Quantitative Posturography System

Jacinta Browne et al. — Wed, 16 Jun 2010 08:33:13 PDT

Balance is the ability to maintain equilibrium while sitting or standing. There are a number of different methods, which are used to assess balance: technical methods such as Sway Magnetometry, Ataxia Meter and Force Platforms and clinical methods such as Functional Reach Test, Berg Balance Test and Fall Risk Index. The most frequently used technical method is the force platform. There are two types of Force Platform a static and a dynamic Force Platform of which the dynamic Force Platform has been found to be more sensitive at detecting impaired balance. The Quantitative Posturography System (QPS) described in this paper is a type of dynamic Force Platform, however it has a simpler design to the currently available dynamic Force Platforms and can match the subjects sway exactly for tilting in the Anterio-Posterior and Medio-Lateral directions with its novel design. This paper describes the novel design of the QPS and its calibration.

Development of a Quality Control Procedure for Force Platforms

Jacinta Browne et al. — Wed, 16 Jun 2010 08:33:12 PDT

A force platform is a technical method of quantitatively assessing balance indirectly. The use of force platforms in physiotherapy departments has become more prominent over the last few years. However, the main drawback in the use of force platforms is the lack of comprehensive calibration procedures, which casts doubt on the results obtained with these systems. Existing calibration tests are limited to testing the spatial accuracy of the force platform. This paper describes a comprehensive quality control test procedure which was developed. It is proposed that the developed quality control test procedure could be used to test all types of force platform and it includes a description of how the tests should be carried out, the frequency with which they should be carried out and the expected performance for each of the tests as recommended for the most part by the Association Francaise de Posturologie.