Vineyard and winery indicators of 'Shiraz' must fermentation behaviour

Nitrogen supply and rootstock have important consequences for the composition and quantity of nitrogenous compounds in the must, both of which impact on fermentation rate and wine quality. In the Sunraysia district (SE Australia), musts prepared from 'Shiraz' grapes from vines grafted onto three rootstocks and supplied with five different nitrogen (N) regimes were fermented to dryness. Leaf N at flowering and veraison, and berry and juice total N at harvest was influenced by N supply, but the juice total assimilable amino N pool was less sensitive. Consumption rate of soluble solids during fermentation was strongly and positively linearly related to %N in the petioles at veraison. The relationship described could be the basis of a tool to provide oenologists with timely data before harvest and receival on likely fermentation behaviour of specific parcels of grapes, and provide viticulturalists with another recognisable developmental stage to assess the efficacy of vineyard N management strategies within a season.

On the Adjoint Operator in Photoacoustic Tomography

Photoacoustic Tomography (PAT) is an emerging biomedical "imaging from coupled physics" technique, in which the image contrast is due to optical absorption, but the information is carried to the surface of the tissue as ultrasound pulses. Many algorithms and formulae for PAT image reconstruction have been proposed for the case when a complete data set is available. In many practical imaging scenarios, however, it is not possible to obtain the full data, or the data may be sub-sampled for faster data acquisition. In such cases, image reconstruction algorithms that can incorporate prior knowledge to ameliorate the loss of data are required. Hence, recently there has been an increased interest in using variational image reconstruction. A crucial ingredient for the application of these techniques is the adjoint of the PAT forward operator, which is described in this article from physical, theoretical and numerical perspectives. First, a simple mathematical derivation of the adjoint of the PAT forward operator in the continuous framework is presented. Then, an efficient numerical implementation of the adjoint using a k-space time domain wave propagation model is described and illustrated in the context of variational PAT image reconstruction, on both 2D and 3D examples including inhomogeneous sound speed. The principal advantage of this analytical adjoint over an algebraic adjoint (obtained by taking the direct adjoint of the particular numerical forward scheme used) is that it can be implemented using currently available fast wave propagation solvers.Comment: submitted to "Inverse Problems

Test materials for characterising heating from HIFU devices using photoacoustic thermometry

High intensity focused ultrasound (HIFU) is a non-invasive thermal therapy during which a focused ultrasound beam is used to destroy cells within a confined volume of tissue. Due to its increased use and advancements in treatment delivery, various numerical models are being developed for use in treatment planning software. In order to validate these models, as well as to perform routine quality checks and transducer characterisation, a temperature monitoring technique capable of accurately mapping the temperature rise induced is necessary. Photoacoustic thermometry is a rapidly emerging technique for non-invasive temperature monitoring, where the temperature dependence of the Gruneisen parameter leads to changes in the recorded photoacoustic signal amplitude with temperature. In order to use this technique to assess heating induced by HIFU in a metrology setting, a suitable test material must first be selected that exhibits an increase in the generated photoacoustic signal with temperature. In this study, the temperature dependence of the photoacoustic conversion efficiency (μaΓ) of several tissue-mimicking materials was measured for temperatures between 22 °C and 50 °C. Materials included were agar-based phantoms, copolymer-in-oil, gel wax, PVA cryogels, PVCP and silicone. This information provided a basis for the development of a volumetric phantom, which was sonicated in a proof-of-concept integrated photoacoustic thermometry system for monitoring of HIFU-induced heating. The results show the suitability of agar-based phantoms and photoacoustic thermometry to image the 3D heat distribution generated by a HIFU transducer

Estimation of Execution Parameters for k-Wave Simulations

Estimation of execution parameters takes centre stage in automatic offloading of complex biomedical workflows to cloud and high performance facilities. Since ordinary users have no or very limited knowledge of the performance characteristics of particular tasks in the workflow, the scheduling system has to have the capabilities to select appropriate amount of compute resources, e.g., compute nodes, GPUs, or processor cores and estimate the execution time and cost. The presented approach considers a fixed set of executables that can be used to create custom workflows, and collects performance data of successfully computed tasks. Since the workflows may differ in the structure and size of the input data, the execution parameters can only be obtained by searching the performance database and interpolating between similar tasks. This paper shows it is possible to predict the execution time and cost with a high confidence. If the task parameters are found in the performance database, the mean interpolation error stays below 2.29%. If only similar tasks are found, the mean interpolation error may grow up to 15%. Nevertheless, this is still an acceptable error since the cluster performance may vary on order of percent as well

The effect of curing temperature and time on the acoustic and optical properties of PVCP

Polyvinyl chloride plastisol (PVCP) has been increasingly used as a phantom material for photoacoustic and ultrasound imaging. As one of the most useful polymeric materials for industrial applications, its mechanical properties and behaviour are well-known. Although the acoustic and optical properties of several formulations have previously been investigated, it is still unknown how these are affected by varying the fabrication method. Here, an improved and straightforward fabrication method is presented and the effect of curing temperature and curing time on PVCP acoustic and optical properties, as well as their stability over time, is investigated. Speed of sound and attenuation were determined over a frequency range from 2 to 15 MHz, while the optical attenuation spectra of samples was measured over a wavelength range from 500 to 2200 nm. Results indicate that the optimum properties are achieved at curing temperatures between 160 °C and 180 °C, while the required curing time decreases with increasing temperature. The properties of the fabricated phantoms were highly repeatable, meaning the phantoms are not sensitive to the manufacturing conditions provided the curing temperature and time are within the range of complete gelation-fusion (samples are optically clear) and below the limit of thermal degradation (indicated by the yellowish appearance of the sample). The samples’ long term stability was assessed over 16 weeks and no significant change was observed in the measured acoustic and optical properties

Measurement of the temperature-dependent speed of sound and change in Gruneisen parameter of tissue-mimicking materials

Knowledge of the temperature dependence of the material properties of tissue-mimicking materials is useful or essential for many applications. This includes photoacoustic thermometry where the temperature dependence of the Grüneisen parameter of tissues leads to changes in the recorded photoacoustic signal amplitude with temperature. Here, a setup is described that can measure the temperature dependence of the speed of sound and photoacoustic conversion efficiency (μ a Γ) of tissue-mimicking materials. Agar-based phantoms, copolymer-in-oil, gel wax, PVCP, silicone and water were characterised in the newly developed setup for temperatures between 22°C and 50°C. This information provides a valuable resource for material characterisation and future development of tissue-mimicking materials

Measurement of the ultrasound attenuation and dispersion in 3D-printed photopolymer materials from 1 to 3.5 MHz

Over the past decade, the range of applications in biomedical ultrasound exploiting 3D printing has rapidly expanded. For wavefront shaping specifically, 3D printing has enabled a diverse range of new, low-cost approaches for controlling acoustic fields. These methods rely on accurate knowledge of the bulk acoustic properties of the materials; however, to date, robust knowledge of these parameters is lacking for many materials that are commonly used. In this work, the acoustic properties of eight 3D-printed photopolymer materials were characterised over a frequency range from 1 to 3.5 MHz. The properties measured were the frequency-dependent phase velocity and attenuation, group velocity, signal velocity, and mass density. The materials were fabricated using two separate techniques [PolyJet and stereolithograph (SLA)], and included Agilus30, FLXA9960, FLXA9995, Formlabs Clear, RGDA8625, RGDA8630, VeroClear, and VeroWhite. The range of measured density values across all eight materials was 1120–1180 kg · m−3, while the sound speed values were between 2020 to 2630 m · s−1, and attenuation values typically in the range 3–9 dB · MHz−1· cm−1

Time domain reconstruction of sound speed and attenuation in ultrasound computed tomography using full wave inversion

Ultrasound computed tomography (USCT) is a non-invasive imaging technique that provides information about the acoustic properties of soft tissues in the body, such as the speed of sound (SS) and acoustic attenuation (AA). Knowledge of these properties can improve the discrimination between benign and malignant masses, especially in breast cancer studies. Full wave inversion (FWI) methods for image reconstruction in USCT provide the best image quality compared to more approximate methods. Using FWI, the SS is usually recovered in the time domain, and the AA is usually recovered in the frequency domain. Nevertheless, as both properties can be obtained from the same data, it is desirable to have a common framework to reconstruct both distributions. In this work, an algorithm is proposed to reconstruct both the SS and AA distributions using a time domain FWI methodology based on the fractional Laplacian wave equation, an adjoint field formulation, and a gradient-descent method. The optimization code employs a Compute Unified Device Architecture version of the software k-Wave, which provides high computational efficiency. The performance of the method was evaluated using simulated noisy data from numerical breast phantoms. Errors were less than 0.5% in the recovered SS and 10% in the AA. V

Experimental study of beam distortion due to fiducial markers during salvage HIFU in the prostate

BACKGROUND: Prostate cancer is frequently treated using external beam radiation therapy (EBRT). Prior to therapy, the prostate is commonly implanted with a small number of permanent fiducial markers used to monitor the position of the prostate during therapy. In the case of local cancer recurrence, high-intensity focused ultrasound (HIFU) provides a non-invasive salvage treatment option. However, the impact of the fiducial markers on HIFU treatment has not been thoroughly studied to date. The objective of this study was to experimentally investigate the effect of a single EBRT fiducial marker on the efficacy of HIFU treatment delivery using a tissue-mimicking material (TMM). METHODS: A TMM with the acoustic properties of the prostate was developed based on a polyacrylamide hydrogel containing bovine serum albumin. Each phantom was implanted with a cylindrical fiducial marker and then sonicated using a 3.3 MHz focused bowl HIFU transducer. Two sets of experiments were performed. In the first, a single lesion was created at different positions along either the anteroposterior or left-right axes relative to the marker. In the second, a larger ablation volume was created by raster scanning. The size and position of the ablated volume were assessed using a millimetre grid overlaid on the phantom. RESULTS: The impact of the marker on the position and size of the HIFU lesion was significant when the transducer focus was positioned within 7 mm anteriorly, 18 mm posteriorly or within 3 mm laterally of the marker. Beyond this, the generated lesion was not affected. When the focus was anterior to the marker, the lesion increased in size due to reflections. When the focus was posterior, the lesion decreased in size or was not present due to shadowing. CONCLUSIONS: The presence of an EBRT fiducial marker may result in an undertreated region beyond the marker due to reduced energy arriving at the focus, and an overtreated region in front of the marker due to reflections. Depending on the position of the targeted regions and the distribution of the markers, both effects may be undesirable and reduce treatment efficacy. Further work is necessary to investigate whether these results indicate the necessity to reconsider patient selection and treatment planning for prostate salvage HIFU after failed EBRT

Measurement of the temperature-dependent output of lead zirconate titanate transducers

The effect of temperature and electrical drive conditions on the output of lead zirconate titanate (PZT) transducers is of particular interest in ultrasound metrology and medical ultrasound applications. In this work, the temperature-dependent output of two single-element PZT transducers was measured between 22 °C and 46 °C. Two independent measurement methods were used, namely radiation force balance measurements and laser vibrometry. When driven at constant voltage using a 50 matched signal generator and amplifier using continuous wave (CW) or quasi-CW excitation, the output of the two transducers increased on average by 0.6% per degree, largely due to an increase in transducer efficiency with temperature. The two measurement methods showed close agreement. Similar trends were observed when using single cycle excitation with the same signal chain. However, when driven using a pulser (which is not electrically matched), the two transducers exhibited different behaviour depending on their electrical impedance. Accounting for the temperature-dependent output of PZT transducers could have implications for many areas of ultrasound metrology, for example, in therapeutic ultrasound where a coupling fluid at an increased or decreased temperature is often used