The Effects of Fatty Desposits on the Accuracy of the Fibroscan Liver Transient Elastography Ultrasound System

A new generation of ultrasound transient elastography (TE) systems have emerged which exploit the well-known correlation between the liver’s pathological and mechanical properties through measurements of the Young’s elastic modulus; however, little work has been carried out to examine the effect that fatty deposits may have on the TE measurement accuracy. An investigation was carried out on the effects on the measurement accuracy of a transient elastography ultrasound system, the Fibroscan®, caused by overlaying fat layers of varying thickness on healthy liver-mimicking phantoms, simulating in vivo conditions for obese patients. Furthermore, a steatosis effect similar to that in non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) was simulated to investigate its effect on the TE system. A range of novel elastography fat-mimicking materials were developed using 6-10wt% poly(vinyl alcohol) cryogel capable of achieving a range of acoustic velocities (1482-1530m/s) and attenuation coefficients (0.4-1dB/MHz/cm) for simulating different liver states. Laboratory-based acoustic velocities and attenuation coefficients were measured while the Young’s modulus was established through a gold standard compression testing method. A significant variation of the Young’s elastic modulus was measured in healthy phantoms with overlaying fat layers of thicknesses exceeding 45mm, impinging on the scanners region of interest, overestimating the compression tested values by up to 11kPa in some cases. Furthermore, Fibroscan® measurements of the steatosis phantoms showed a consistent overestimation (~54%), which strongly suggests that the speed of sound mismatch between that of liver tissue and that assumed by the scanner is responsible for the high clinical cut-offs established in the case of ALD and NAFLD

Evaluation of CIRS String Doppler Phantom as a Test Tool for Use in a Doppler Ultrasound Quality Assurance Program

Ultrasound Doppler systems are routinely used to perform blood flow velocity measurements which assist in the clinical assessment and diagnosis of vascular. Doppler measurements of peak velocities for vascular applications provide an indication of the degree of the stenosis which will ultimately assist in deciding how a patient is managed. It is imperative that Doppler systems are capable of accurately measuring blood flow velocities to ensure correct diagnosis and appropriate patient treatment; therefore such systems should be evaluated regularly as part of a Quality Assurance program. Although a range of Doppler test phantoms have been developed for quality control (QC) purposes to establish the measurement accuracy and stability of Doppler systems only a limited number of such test phantoms are commercially available, the easiest of these devices to operate is the String Phantom. Currently, only one string Doppler phantom is commercially available, namely the CIRS Model 043. In this study an evaluation of the performance of this test device was carried out as a number of problems currently exist with it such as the filament type, the fact that the filament passes through a water–air interface and vibrations from the motor. This study has established that the braided-silk filament, provided with the phantom, should not be used as it introduces errors of as much as 24% for the mean velocity accuracy and 20% for the intrinsic spectral broadening (ISB) depending on the soak time of the filament. Rather, to avoid such errors it is advised that the phantom be retrofitted with a filament made from an O-ring rubber. While this eliminates the temporal changes in backscatter seen with the braided-silk filament, further discrepancies were observed, even with an O-ring filament, when the filament velocity was set in the range 26–44 cm/s, where a resonance effect significantly increased the variability of the maximum velocity accuracy and ISB measurements. This was most likely as a result of the imposed vibrations from the motor, which is mounted directly onto the tank wall; hence, it would prove practical to avoid taking measurements in this velocity range where resonance effects are observed

Review of Ultrasound Elastography Quality Control and Training Test Phantoms

While the rapid development of ultrasound elastography techniques in recent decades has sparked its prompt implementation in the clinical setting adding new diagnostic information to conventional imaging techniques, questions still remain as to its full potential and efficacy in the hospital environment. A limited number of technical studies have objectively assessed the full capabilities of the different elastography approaches, perhaps due, in part, to the scarcity of suitable tissue-mimicking materials and appropriately designed phantoms available. Few commercially-available elastography phantoms possess the necessary test target characteristics or mechanical properties observed clinically, or indeed reflect the lesion-to-background elasticity ratio encountered during clinical scanning. Thus, while some phantoms may prove useful, they may not fully challenge the capabilities of the different elastography technniques, proving limited when it comes to quality control (QC) and/or training purposes. Although a variety of elastography tissue-mimicking materials, such as agar and gelatine dispersions, co-polymer in oil and poly(vinyl) alcohol cryogel, have been developed for specific research purposes, such work has yet to produce appropriately designed phantoms to adequately challenge the variety of current commercially-available elastography applications. Accordingly, there is a clear need for the further development of elastography TMMs and phantoms to keep pace with the rapid developments in elastography technology, to ensure the performance of these new diagnostic approaches are validated, and for clinical training purposes

Regenerative agriculture in Aotearoa New Zealand - research pathways to build science-based evidence and national narratives.

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

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

An Audit of a Hospital-Based Doppler Ultrasound Quality Control Protocol Using a Commercial String Doppler Phantom

Results from a four-year audit of a Doppler quality assurance (QA) program using a commercially available Doppler string phantom are presented. The suitability of the phantom was firstly determined and modifications were made to improve the reliability and quality of the measurements. QA of Doppler ultrasound equipment is very important as data obtained from these systems is used in patient management. It was found that if the braided-silk filament of the Doppler phantom was exchanged with an O-ring rubber filament and the velocity range below 50cm/s was avoided for Doppler quality control (QC) measurements, then the Maximum Velocity Accuracy (MVA) error and Intrinsic Spectral Broadening (ISB) results obtained using this device had a repeatability of 18 ± 3.3% and 19 ± 3.5%, respectively. A consistent overestimation of the MVA of between 12% and 56% was found for each of the tested ultrasound systems. Of more concern was the variation of the overestimation within each respective transducer category: MVA errors of the linear, curvilinear and phased array probes were in the range 12.3 – 20.8%, 32.3 – 53.8% and 27 – 40.7%, respectively. There is a dearth of QA data for Doppler Ultrasound; it would be beneficial if a multicentre longitudinal study was carried out using the same Doppler ultrasound test object to evaluate sensitivity to deterioration in performance measurement

Social deprivation and the rate of emergency medical admission for older persons

Background: Deprivation Status increases the annual admission incidence of emergency medical admissions; the extent to which deprivation influences the admission of older persons is less well known. Aim: To examine whether deprivation within a hospital catchment area influences emergency medical admissions for the elderly population. Design: The relationship between Deprivation Status, Dependency Ratio (population proportion of non-working age (<15 or ≥65 years) and age for all emergency admissions (82 368 episodes of 44 628 patients), over a 13-year period, were examined and ranked by quintile. Methods: Univariate and multi-variable risk estimates (incidence rate ratios) were calculated, using truncated Poisson regression. Results: The Dependency Ratio and the Deprivation index independently predicted the annual incidence rate of medical emergencies; however, when calculated for older persons, the corresponding incidence rate ratios showed a falling trend with increasing Deprivation Status—Q2 0.51 (95% confidence interval [CI]: 0.50, 0.52), Q3 0.59 (95% CI: 0.58, 0.60), Q4 0.51 (95% CI: 0.50, 0.52) and Q5 0.37 (95% CI: 0.36, 0.38). Thus, with increasing Deprivation Status, the proportion of total admission from the ≥65-year cohort fell substantially. Conclusion: The admission incidence rate for emergency medical patients is strongly influenced by the catchment area Deprivation Status. However, because of its greater impact on the younger population, increasing deprivation alters the ratio of younger to older persons as a proportion of total emergency admissions