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Quantitative assessment of Thiel soft-embalmed human cadavers using shear wave elastography.

INTRODUCTION Thiel soft-embalmed human cadavers are increasingly being used as a model to train surgeons and anesthetists because they look and feel like patients. However, there is a need to validate quantitatively the tissue properties of this model. Thus, the main objective of this study was to measure the elasticity of tissue in the Thiel soft-embalmed cadaver, using results in the literature for human volunteers for comparison. MATERIALS AND METHODS Two independent ultrasound-trained operators measured the elasticity (Youngs modulus), E, of the thyroid, parotid and submandibular glands, the gastrocnemius and masseter muscles and the supraspinatus tendon in six Thiel soft-embalmed human cadavers using quantitative shear wave elastography. Each measurement was repeated 10 times. The elasticity values of Thiel soft-embalmed human cadavers were compared with human values reported in the literature. The relationship between elasticity and gender, age at death and number of days after embalming was also investigated. RESULTS Elasticity data for the cadavers displayed similar patterns as in the literature for human volunteers. The results show a positive correlation between Youngs modulus (YM) and time after embalming, but no correlation with cadaver age at death or gender. CONCLUSIONS The stiffness of the Thiel embalmed soft cadaver was validated against historical human data, confirming the life-like quality of the cadavers. Our results indicate that shear wave elastography is a promising tool to evaluate the stiffness of Thiel embalmed soft cadavers.

A randomised, single-blind technical study comparing the ultrasonic visibility of smooth-surfaced and textured needles in a soft embalmed cadaver model

Visibility of the needle tip and shaft is important during ultrasound‐guided regional anaesthesia in order to prevent nerve trauma. Tip and shaft visibility is reduced when needles are inserted in‐plane at wide angles and out‐of‐plane at narrow angles to the ultrasound probe. Although textured needles are more reflective than smooth needles, we hypothesised that poor visibility of the tip and shaft still remained using the above angle‐probe combinations. In a single‐blind study, we compared the visibility of a textured Tuohy needle, a textured single‐shot needle and a conventional smooth‐surfaced Tuohy needle when inserted into the biceps and deltoid muscles of a soft embalmed cadaver. One hundred and forty‐four needles were block‐randomised to in‐plane and out‐of‐plane insertions at 30°, 45°, 60° and 75° to the ultrasound beam. Two blinded raters assessed needle tip visibility on video recordings of the insertions using a binary scale (0 = not visible, 1 = visible) and shaft visibility using a 5‐point Likert scale. The median (IQR [range]) proportions of visible needle tips were 83% (67–83 [50–100]%) for the textured Tuohy, 75% (67–83 [33–83]%) for the textured single‐shot needle and 33% (33–46 [0–50]%) for the smooth‐surfaced Tuohy (p = 0.0007). Median (IQR [range]) needle shaft visibility was rated as 4.0 (3.5–4.7 [3.0–4.9]) for the textured Tuohy, 4.0 (3.8–4.5 [2.7–4.9]) for the textured single‐shot needle and 3.0 (2.4–3.3 [2.3–3.5]) for the smooth‐surfaced Tuohy (p = 0.015). Nevertheless, visibility was reduced at wide angles in‐plane and narrow angles out‐of‐plane both for needle tips (p = 0.004) and shafts (p = 0.005).

A feasibility study of soft embalmed human breast tissue for preclinical trials of HIFU- preliminary results

Breast cancer is the commonest cancer in women in the UK, accounting for 30% of all new cancers in women, with an estimated 49,500 new cases in 20101. With the widespread negative publicity around over-diagnosis and over-treatment of low risk breast cancers, interest in the application of non-invasive treatments such as magnetic resonance imaging (MRI) guided high intensity focused ultrasound (HIFU) has increased. Development has begun of novel US transducers and platforms specifically designed for use with breast lesions, so as to improve the range of breast lesions that can be safely treated. However, before such transducers can be evaluated in patients in clinical trials, there is a need to establish their efficacy. A particular issue is the accuracy of temperature monitoring of FUS with MRI in the breast, since the presence of large amounts of surrounding fat can hinder temperature measurement. An appropriate anatomical model that imposes similar physical constraints to the breast and that responds to...

Acoustic characterization of Thiel liver for magnetic resonance-guided focused ultrasound treatment

Abstract Background: The purpose of this work was to measure the essential acoustic parameters, i.e., acoustic impedance, reflection coefficient, attenuation coefficient, of Thiel embalmed human and animal liver. The Thiel embalmed tissue can be a promising, pre-clinical model to study liver treatment with Magnetic Resonance-guided Focused Ultrasound (MRgFUS). Material and methods: Using a single-element transducer and the contact pulse-echo method, the acoustic parameters, i.e., acoustic impedance, reflection coefficient and attenuation coefficient of Thiel embalmed human and animal liver were measured. Results: The Thiel embalmed livers had higher impedance, similar reflection and lower attenuation compared to the fresh tissue. Conclusions: Embalming liver with Thiel fluid affects its acoustic properties. During MRgFUS sonication of a Thiel organ, more focused ultrasound (FUS) will be backscattered by the organ, and higher acoustic powers are required to reach coagulation levels (temperatures >56 °C).

Mapping tissue shear modulus on Thiel soft-embalmed mouse skin with shear wave optical coherence elastography

A quantitative measurement of the mechanical properties of biological tissue is a useful assessment of its physiologic conditions, which may aid medical diagnosis and treatment of, e.g., scleroderma and skin cancer. Traditional elastography techniques such as magnetic resonance elastography and ultrasound elastography have limited scope of application on skin due to insufficient spatial resolution. Recently, dynamic / transient elastography are attracting more applications with the advantage of non-destructive measurements, and revealing the absolute moduli values of tissue mechanical properties. Shear wave optical coherence elastography (SW-OCE) is a novel transient elastography method, which lays emphasis on the propagation of dynamic mechanical waves. In this study, high speed shear wave imaging technique was applied to a range of soft-embalmed mouse skin, where 3 kHz shear waves were launched with a piezoelectric actuator as an external excitation. The shear wave velocity was estimated from the shear wave images, and used to recover a shear modulus map in the same OCT imaging range. Results revealed significant difference in shear modulus and structure in compliance with gender, and images on fresh mouse skin are also compared. Thiel embalming technique is also proven to present the ability to furthest preserve the mechanical property of biological tissue. The experiment results suggest that SW-OCE is an effective technique for quantitative estimation of skin tissue biomechanical status.

Soft-embalmed human breast tissue as a model for pre-clinical trials of HIFU - preliminary results

Around 52,000 people are diagnosed with breast cancer each year in the UK. With the controversy around over diagnosis arising from the breast screening programme there is intense interest in the possibility of safe effective non-invasive treatment of cancers. As a non-invasive method of lumpectomy, focused ultrasound surgery (FUS) may offers reduced risk of infection, fewer complications and a shorter recovery time. It also allows more precise treatment as a result of real-time guidance by magnetic resonance (MR) or ultrasound. Even though specially designed FUS transducers for breast cancer treatment are now becoming available, transducer efficacy needs to be tested with a suitable preclinical model. A specific issue is the accuracy of temperature monitoring of FUS with MRI in the breast, since the presence of large amounts of surrounding fat can impair temperature measurement with the proton resonant frequency. An appropriate anatomical model that enforces comparable physical constraints to the breast and that responds to FUS in the same way would be extremely advantageous. The aim of this feasibility study is to explore the use of soft embalmed cadaveric breast tissue for these purposes. We report here the early results of MRI-guided FUS experiments sonicating dissected breast samples from a soft-embalmed human cadaver with a high body mass index (BMI).

Automated performance assessment of ultrasound systems using a dynamic phantom

Quality assurance of medical ultrasound imaging systems is limited by repeatability, difficulty in quantifying results, and the time involved. A particularly interesting approach is demonstrated in the Edinburgh pipe phantom which, with an accompanying mathematical transformation, produces a single figure of merit for image quality from individual measurements of resolution over a range of depths. However, the Edinburgh pipe phantom still requires time-consuming manual scanning, mitigating against its routine use. This paper presents a means to overcome this limitation with a new device, termed the Dundee dynamic phantom, allowing rapid set-up and automated operation. The Dundee dynamic phantom is based on imaging two filamentary targets, positioned by computer control at different depths in a tank of 9.4% ethanol–water solution. The images are analysed in real time to assess if the targets are resolved, with individual measurements at different depths again used to calculate a single figure of merit, in this case for lateral resolution only. Test results are presented for a total of 18 scanners in clinical use for different applications. As a qualitative indication of viability, the figure of merit produced by the Dundee dynamic phantom is shown to differentiate between scanners operating at different frequencies and between a relatively new, higher quality system and an older, lower quality system.

Automated transducer testing and calibration with a dynamic phantom

Variation in transducer array performance for biomedical imaging and non-destructive testing (NDT) is inherent in manufacturing, and performance degradation also occurs when the devices are in service. It is already straightforward to determine basic device functionality through transmit and receive sensitivity measurements and from electrical impedance. However, this requires special equipment and procedures likely to be inaccessible to end users. Nevertheless, validation of transducer performance is of increasing importance as the use of array systems grows for NDT and for medical diagnosis and treatment management by non-specialist users. Our objective here was to produce an automated system for array validation through calculation of the resolution integral (RI). The dynamic phantom that has been developed is based on imaging two filamentary targets positioned in a tank of liquid tissue-mimicking material under computer control. The mechanism for this is reliable and inexpensive, with the filaments coupled magnetically through the tank wall. Images are captured and analysed to assess targets resolution in an automated feedback loop. The new phantom has been tested on a total of 18 imaging systems in clinical use. Results were repeatable and consistent when compared with those produced with more conventional techniques. Furthermore, RI calculation successfully differentiated recent, high quality scanners from others and also differentiated linear flat and convex probes and phased arrays. The dynamic phantom thus offers assessment of ultrasound imaging systems quantitatively for purchasing decisions, delivery acceptance and on-going quality assessment. With further work, it will be developed to test systems rigorously and to benchmark them for comparison and prior to introduction to service.

Validation of an automated dynamic phantom to assess the performance of ultrasound system

There are many different approaches to evaluate image quality of ultrasound systems. Usually these tests are carried out manually, they are very time consuming, the results are subjective and repeatability can be poor. As one proposed improvement, the resolution integral produces one single figure of merit for image quality. The work reported here is based on a novel approach for grey-scale testing, based on the resolution integral, which can produce non-subjective and repeatable results for each combination of imaging system and transducer array. A total of 21 systems have been tested with three different depth settings to demonstrate its capabilities.