Probe Calibration Research Articles

A Novel Ultrasound Probe Spatial Calibration Method Using a Combined Phantom and Stylus

Intra-operative ultrasound (US) is a popular imaging modality for its non-radiative and real-time advantages. However, it is still challenging to perform an interventional procedure under two-dimensional (2-D) US image guidance. Accordingly, the trend has been to perform three-dimensional (3-D) US image guidance by equipping the US probe with a spatial position tracking device, which requires accurate probe calibration for determining the spatial position between the B-scan image and the tracked probe. In this report, we propose a novel probe spatial calibration method by developing a calibration phantom combined with the tracking stylus. The calibration phantom is custom-designed to simplify the alignment between the stylus tip and the B-scan image plane. The spatial position of the stylus tip is tracked in real time, and its 2-D image pixel location is extracted and collected simultaneously. Gaussian distribution is used to model the spatial position of the stylus tip and the iterative closest point-based optimization algorithm is used to estimate the spatial transformation that matches these two point sets. Once the probe is calibrated, its trajectory and the B-scan image are collected and used for the volume reconstruction in our freehand 3-D US imaging system. Experimental results demonstrate that the probe calibration approach results in less than 1-mm mean point reconstruction accuracy. It requires less than 5 min for an inexperienced user to complete the probe calibration procedure with minimal training. The mockup test shows that the 3-D images are geometrically correct with 0.28°-angle accuracy and 0.40-mm distance accuracy.

Neural-Network-Based Sensor Data Fusion for Multi-Hole Fluid Velocity Probes

For measuring three components of velocity in unknown flow fields, multi-hole pressure probes possess a significant advantage. Unlike methods such as hot-wire anemometry, laser-Doppler velocimetry and particle-image velocimetry, multi-hole pressure probes can provide not only the three components of local velocity, but also static and stagnation pressures. However, multi-hole probes do require exhaustive calibration. The traditional technique for calibrating these probes is based on either look-up tables or polynomial curve fitting, but with the low cost and easy availability of powerful computing resources, neural networks are increasingly being used. Here, we explore the possibility to further reduce measurement uncertainty by implementing neural-network-based methods that have not been previously used for probe calibration, including supervised and unsupervised learning neural networks, regression models and elastic-map methods. We demonstrate that calibrating probes in this way can reduce the uncertainty in flow angularity by as much as 50% compared to conventional techniques.

A novel approach based on artificial neural network for calibration of multi-hole pressure probes

Imperfections in the manufacturing process of flow measuring probes affect their measuring behavior. Nevertheless, in order to provide the highest possible accuracy, each individual multi-hole pressure probe has to be calibrated before using them in turbomachinery. This paper presents a novel method based on artificial neural networks (ANN) to predict the flow parameters of multi-hole pressure probes. A two-stage ANN approach using multilayer perceptron (MLP) is proposed in this study. The two-stage prediction approach involves two MLP networks, which represent the calibration data and the prediction error. For a given set of inputs, outputs from both networks are combined to estimate the measured value. The calibration data of a 5-hole probe at RWTH Aachen was used to develop and validate the proposed ANN models and two-stage prediction approach. The results showed that the ANN can predict the flow parameters with high accuracy. Using the two-stage approach, the prediction accuracy was further improved compared to polynomial functions, i.e. a commonly used method in probe calibration. Furthermore, the proposed approach offers high interpolation capabilities while preventing overfitting (i.e. failure to fit new data). Unlike polynomials, it is shown that the ANN based method can provide accurate predictions at intermediate points without large oscillations.

Feasibility of spectral pH measurement during the low-pH virus inactivation step of continuous therapeutic antibody production.

Acidic virus inactivation is commonly used during production of biotherapeutic products to provide virus safety in case of undetected virus contamination. Accurate pH measurement is required to ensure the product pH reaches a virus-inactivating level (typically 3.5-3.7), and a level post-inactivation that is appropriate for later purification steps (typically 5.5-7.5). During batch low-pH inactivation in discrete tanks, potentiometric glass probes are appropriate for measuring pH. During continuous inactivation for 2-3 weeks in an enclosed product stream, probe calibration drift and lag may lead to poor accuracy, and operational difficulties when compensating for drift. Monitoring the spectral response of compounds (indicators) in the product stream whose spectra are pH-sensitive offers a possible alternative way to measure pH without these drawbacks. Such indicators can already exist in the stream (intrinsic) or can be added (extrinsic). Herein are reported studies evaluating the feasibility of both.Promising ultraviolet screening results with the two extrinsics studied, thiamine and ascorbic acid, led to the addition of both to product stream samples titrated to different potentiometric pH values in the 3.3-4.5 range (a representative range encountered during continuous inactivation), and attempts to model pH using sample ultraviolet spectra. One model, based on variability in six spectral attributes, was able to predict pH of an independent sample set within ±0.07 units at the 95% confidence level. Since a typical inactivating pH tolerance is ±0.1 units, the results show that extrinsic indicators potentially can measure inactivation pH with sufficient accuracy. Suggested future steps and an alternative approach are presented.

The laboratory calibration of a soil moisture capacitance probe in sandy soils

Determining and mitigating landslide risk is a technical-scientific objective, particularly for the protection and proper territorial management and planning. The slope stability depends on the pore pressure distribution, which is influenced by the saturation front propagation through the unsaturated zone, whose monitoring is useful to understand any possible instabilities. Such monitoring may be undertaken by sensors based on the measurement of the relative dielectric permittivity. Reliable relationships between the measurement and the soil moisture are necessary. The main objective of this study is to assess a laboratory calibration protocol for a specific capacitance sensor (Drill & Drop, Sentek Sensor Technologies). Two monogranular sands have been selected for the calibration purpose. The laboratory tests were performed under three relative density values (D<sub>R</sub> equal to 40%, 60% and 80%) for seven volumetric water content values (θ<sub>v</sub> ranging from 0.00% to 36.26%). Based on the experimental measurements, the soil-specific calibration curves were determined at an assigned relative density value; in particular, a simple power law is adopted to describe the probe’s reading as a function of the volumetric water content. The results point out that the relative density values slightly affect the tests, thus, the soil-specific calibration curves are derived based on a simple regression analysis fitting the whole set of the laboratory tests validated for each sand. The calculated coefficient of determination (R<sup>2</sup> = 0.96÷0.99) and root mean square error (RMSE = 1.4%÷2.8%) values confirm the goodness of fit. In order to propose more general fitting curves, suitable for both the investigated sands, multiple linear regressions are performed by considering θ<sub>v</sub> and the mean grain size, D<sub>50</sub> as independent variables; again, the R<sup>2</sup> and RMSE values equal to 0.97 and 2.41%, respectively, confirm the suitability of the calibration curve. Finally, the laboratory calibration curves are compared with the manufacturer-supplied curves, thus, enhancing the need for the soil-specific calibration.

Lunar Near Surface Plasma Environment from Chandrayaan-2 Lander Platform:RAMBHA-LP payload

The near surface lunar plasma environment is modulated by important components like the photoelectron sheath, solar wind, lunar surface potential, etc. In situ measurements of lunar near surface plasma are not available as of now. Previous lunar missions which explored the near surface environment have arrived at estimates of lunar photo electron densities mainly from lunar sample returns. The Chandrayaan-2 lunar mission affords a unique opportunity to explore the near surface lunar plasma environment from the lunar lander platform. A Langmuir probe is developed indigenously for probing the tenuous lunar near surface plasma environment from the top deck of the lunar lander. The probe is designed to cater to a wide dynamic range of 10/cc to 10,000/cc. The probe behaviour is characterized in the ambient room conditions using a current source. The sensitivity of the probe to incoming ionized species is also characterized in a vacuum chamber. The Langmuir probe response is characterized such that the input current to the probe is correctly deciphered during the mission duration. The calibration of the present Langmuir probe is carried out using a standard calibrated Langmuir probe. The details of the theoretical simulations of the expected currents, the characterization and calibration activities are presented and discussed.

Verification of needle guidance accuracy in pelvic phantom using registered ultrasound and MRI images for intracavitary/interstitial gynecologic brachytherapy

PurposeIn combined intracavitary/interstitial (IC/IS) gynecologic brachytherapy, trackers attached to interstitial needles of localize real-time needle trajectories, and intraoperative ultrasound (US) images provide updated anatomy information during needle insertions. To achieve an effective visualization and image guidance, real-time needle trajectories and US images can be unified in preoperative magnetic resonance imaging (MRI) image space together. This study evaluates the rigid registration accuracy between US images and MRI images as well as the registration accuracy between US images and real-time needle trajectories in a pelvic phantom.Material and methodsA method for US probe calibration and accomplished rigid registration between MRI images and US images was proposed. An IC/IS applicator was designed. Micro electromagnetic sensor to track and localize real-time needle trajectories in 3D MRI image space was used. Marker validation to test the accuracy of US probe calibration and pelvic phantom validation to test the registration accuracy between US images and MRI images was conducted as well as and pelvic phantom study to verify the registration accuracy between real-time needle trajectories and needle trajectories in registered US images.ResultsUS probe calibration accuracy was 0.80 ±0.23 mm (n = 60). Registration accuracy between US images and MRI images were 1.01 ±0.22 mm in the axial plane (n = 60) and 1.14 ±0.20 mm in the sagittal plane (n = 24). Registration accuracy between real-time needle trajectories and needle trajectories in registered US images were 1.25 ±0.31 mm (n = 40) and 1.61 ±0.28 degrees (n = 5), respectively.ConclusionsIn this study, we showed that under ideal conditions, rigid registration between MRI images and US images obtained high accuracy for real-time image guidance. Additionally, registered US images provided accurate image guidance during visual needle insertion in IC/IS gynecologic brachytherapy to achieve a combination of effective visualization and image guidance.

On-Chip Metal Tiling for Improving Grounded mm-Wave Antenna-on-Chip Performance in Standard Low-Cost Packaging

Gluing an antenna-on-chip (AoC) directly on a ground plane or heat sink in the lead frame is a standard process for commercial applications. To reduce the effect of losses in the silicon substrate and improve the antenna’s radiation efficiency, the wafer thickness is often drastically reduced. However, the close proximity of the antenna and ground plane can cause an impedance mismatch. Metal tiles, which are embedded in silicon dioxide layers, are designed as an artificial magnetic conductor (AMC) to increase the radiation efficiency and tune the antenna impedance. A double-layer AMC is applied instead of a single-layer AMC to reduce the silicon dielectric loss. Additionally, the double-layer AMC has more capacitance to tune the impedance when integrating with a monopole on-chip antenna. The resulting −10 dB impedance bandwidth is increased to 5.8 GHz around the 60 GHz band, the simulated realized gain increases by 3.3 dB, and the simulated antenna radiation efficiency is increased from 11% to 21%. The measured input impedance of the AoC shows good agreement with the simulation results after probe calibration.

3D printing of fillable individual thyroid replicas based on nuclear medicine DICOM data used as phantoms for gamma probe calibration.

To proof the feasibility of manufacturing patient-indivdual (anthropomorphic) thyroid replicas from I-124 PET DICOM datasets by means of 3D printing. A possible field of application is the use of those phantoms for the calibration of gamma probes. After editing of the DICOM datasets using several software types and transferring into a dedicated stereolithography format, 10 fillable thyroid replicas (35-200 mL) made of polylactide acid were manufactured via 3D printing. All replicas were filled with a water-solution containing 3.5 MBq I-131 and applied to a standard neck phantom. Calibration factor measurements were carried out using a clinical gamma probe. Measurements were performed with three different tilts: + 15°, 0° and -15°. The influence of the replicas' volume and the tilt was investigated. Manufacturing of the replicas was successful in all cases. The time required for data processing was 13 ± 2 (median: 12, range: 9-25) min and 4-11 h for 3D printing (size-dependent). The printing process could be done overnight. Measured mean calibration factor for straight gamma probe positioning (0° tilt) was 31 965 ± 3360 (33 893, 25 470-34 253) cpm/MBq. A tilt of -15° resulted in lower calibration factors (-7.7 %), whereas a tilt of + 15° led to higher values (+ 9.5 %); p = 0.001. The calibration factors were highly inversely proportional correlated to the volume of the replicas (r = -0.91, p < 0.001). 3D printing of patient-individual (anthropomorphic) fillable thyroid replicas was feasable for a large range of volumes. The study demonstrates the influence of the volume as well as the tilt of the measured object for calibration factor measurements with gamma probes.

Deep learning approach for automatic out-of-plane needle localisation for semi-automatic ultrasound probe calibration.

The authors present a deep learning algorithm for the automatic centroid localisation of out-of-plane US needle reflections to produce a semi-automatic ultrasound (US) probe calibration algorithm. A convolutional neural network was trained on a dataset of 3825 images at a 6 cm imaging depth to predict the position of the centroid of a needle reflection. Applying the automatic centroid localisation algorithm to a test set of 614 annotated images produced a root mean squared error of 0.62 and 0.74 mm (6.08 and 7.62 pixels) in the axial and lateral directions, respectively. The mean absolute errors associated with the test set were 0.50 ± 0.40 mm and 0.51 ± 0.54 mm (4.9 ± 3.96 pixels and 5.24 ± 5.52 pixels) for the axial and lateral directions, respectively. The trained model was able to produce visually validated US probe calibrations at imaging depths on the range of 4–8 cm, despite being solely trained at 6 cm. This work has automated the pixel localisation required for the guided-US calibration algorithm producing a semi-automatic implementation available open-source through 3D Slicer. The automatic needle centroid localisation improves the usability of the algorithm and has the potential to decrease the fiducial localisation and target registration errors associated with the guided-US calibration method.

A Four-Probe Method Using Different Probe Spacings for Measurement and Exact Reconstruction of Parallel Profiles

To realize the measurement and exact reconstruction of a pair of parallel profiles, a new scanning method using four displacement sensors as probes and different probe spacings has been invented with the advantage of preventing data processing error. The measuring device is placed between the measured objects and moved by a scanning stage to collect measurement data of both measured profiles. Considering many existing methods, the high lateral resolution of the reconstruction result and the rejection of the data processing error cannot always be achieved at the same time. When the measured profiles are in the short wavelength range, data processing errors are often on the same order of magnitude as the height difference of the measured profiles. The new method can eliminate both the straightness error of the measurement reference and the data processing error. The exact reconstruction retaining the high lateral resolution and without data processing error can be realized by rational position arrangement of sensors and corresponding processing method of the measurement data. The new method possesses the following advantages: (i) achievement of the exact reconstruction without data processing error; (ii) high lateral resolution not limited by probe spacing; (iii) concise operation without zero calibration of probes; and (iv) suitability for on-machine measurement. The feasibility and advantages of the new method were demonstrated by theoretical analyses, simulations, and experimental results.

A General Workflow for Characterization of Nernstian Dyes and Their Effects on Bacterial Physiology

The electrical membrane potential (Vm) is one of the components of the electrochemical potential of protons across the biological membrane (proton motive force), which powers many vital cellular processes. Because Vm also plays a role in signal transduction, measuring it is of great interest. Over the years, a variety of techniques have been developed for the purpose. In bacteria, given their small size, Nernstian membrane voltage probes are arguably the favorite strategy, and their cytoplasmic accumulation depends on Vm according to the Nernst equation. However, a careful calibration of Nernstian probes that takes into account the tradeoffs between the ease with which the signal from the dye is observed and the dyes’ interactions with cellular physiology is rarely performed. Here, we use a mathematical model to understand such tradeoffs and apply the results to assess the applicability of the Thioflavin T dye as a Vm sensor in Escherichia coli. We identify the conditions in which the dye turns from a Vm probe into an actuator and, based on the model and experimental results, propose a general workflow for the characterization of Nernstian dye candidates.

Hot-film/hot-wire anemometer calibration for low velocities using image processing

Calibration of hot-wire and hot-film probes at low velocities is a difficult task because the dynamic pressure at these velocities is very low and may not be measured easily. To overcome this problem, substituent techniques have been presented in the literature that rely on other phenomena and utilize different hardware. This paper describes a simple and low-cost method which proposes to move the anemometer probe in quiescent air (here by means of a swinging arm) and track this motion with a camera. After processing of the images, velocity time history of the probe is found by numerical calculations. Calibration curve is then obtained without any predetermined relationship. Using a medium-speed video camera that is often found in laboratories would avoid the need to a position sensor and a complicated arm on which this sensor is mounted. This technique can be used not only for pendulums but also for other means of moving probes in quiescent medium.

Calibration of thermocouple-based scanning thermal microscope in active mode (2ω method).

We present a procedure dedicated to the calibration of a scanning thermal microscopy probe operated in an active mode and a modulated regime especially for the measurement of solid material thermal conductivities. The probe used is a microthermocouple wire mounted on a quartz tuning fork. Measurements on reference samples are performed successively in vacuum and ambient air conditions revealing a clear difference in the dependence of the thermal interaction between the probe and the sample on the sample properties. Analytical modeling based on the resolution of the heat equation in the wire probe and a description of the thermal interaction using a network of thermal conductances are used to fit experimental data and analyze this difference. We have experimentally verified that the effective thermal contact radius of the probe tip depends on the sample thermal conductivity in ambient conditions, whereas it remains constant in vacuum. We have defined the measurement range of the technique based on the decrease in the probe sensitivity at high thermal conductivities. Considering the experimental noise of our electrical device, it is shown that the maximum measurable value of thermal conductivity is near 23 W m-1 K-1 in vacuum and 37 W m-1 K-1 in ambient air conditions. Moreover, the lowest uncertainties are obtained for thermal conductivities below 5 W m-1 K-1 typically.

Sub-rf period electrical characterization of a pulsed capacitively coupled argon plasma

Transient plasmas (such as pulsed power plasmas) can be of interest to both industry, where they allow for new processing windows, and basic science, where their dynamics are of interest. However, their study requires time resolved diagnostic techniques. One powerful diagnostic is current and voltage (IV) measurements, which along with the power and impedance calculated from them, can be used to characterize a plasma. This is especially true as it is an outside the chamber, noninvasive technique and can be used in systems where a probe or fiber optic bundle/window will affect processing results or fail due to deposition. To obtain accurate IV values, frequency dependent probe calibrations must be performed and frequency dependent parasitic impedances in the system and propagation delay between the forward traveling fundamental frequency and backward traveling harmonic frequencies must be taken into account. To separate the fundamental and harmonic frequencies, a fast Fourier transform (FFT) is traditionally performed in continuous wave plasmas. In transient plasmas, a time resolved FFT is necessary. This article presents a method to perform each of these steps while demonstrating their importance and giving some measurements of a pulsed power, 75 mTorr, capacitively coupled argon plasma.

Electronic Stark Effect in Isolated Ion Pairs.

Stark spectral shifts of a molecular probe are commonly used to estimate the local electric field in condensed media. The very large fields reported, typically in the 0.1-10 GV m-1 range, are, however, difficult to reproduce in a controlled manner, limiting the calibration of these molecular probes to ranges below 0.1 GV m-1. In this context, we investigated gas-phase, isolated, molecular ion pairs, where a phenyl ring is immersed in the electric field produced by the nearby ionic groups. The intensity of the electric field is chemically tuned in the 1 GV m-1 range by changing the nature of the cations, and the phenyl ring response is monitored by UV spectroscopy. A quadratic Stark effect is observed, demonstrating the possibility to characterize molecular probes in a solvent-free environment and in the very large field range they typically meet in condensed media such as biological environments.

An open-ended probe with an antenna for the measurement of the water content in the soil

Knowledge of water content (WC) in soil is especially necessary in agriculture to assess the individual irrigation state of the plant. Therefore, there is a need to develop sensors able to measure WC in large volumes and in possibly wide frequency range, e.g. by modifications of the classical open-ended (OE) probes which are characterized by low penetration depth of electromagnetic waves. The objective of the research presented in this paper was to test the performance of an open-ended dielectric probe with an antenna (OE-A) in the frequency range 1 MHz–6 GHz for three mineral soils using vector network analyzer (VNA) one port (reflective) measurements. Firstly, numerical simulations of the probe using Ansys HFSS software were performed, followed by the probe calibration on reference materials and measurements of the soil samples to determine soil moisture. The simulation and measurement results of the real part of dielectric permittivity (ε') were in good agreement with literature data up to 350 MHz. ε'obtained for the tested soils was connected with their moisture and the relation between ε'and volumetric water content (θv) was determined and compared with the Topp’s equation. The obtained results proved that our probe can be used for the measurement of the WC in soils in the frequency range from 50 MHz to 350 MHz.

Traceable atomic force microscope based on monochromatic light interference

Atomic force microscope (AFM) is widely applied to the measurement of the micro-nano structures due to its three-dimensional spatial resolution of sub-nanometer. However, the height measurement traceability in the z-axis is complex to be implemented in conventional AFMs. In this paper, a traceable AFM is developed based on the monochromatic light interference (MLI) principle without probe calibration. The height change of the AFM's probe is directly detected by extracting the phase change of the MLI fringes on the probe tip with the Hilbert transform based phase extraction algorithm, and the three-dimensional surface topography is reconstructed with a surface recovery algorithm. The configuration of tracing to the wavelength of the monochromatic light in real-time further improves the measurement accuracy of the MLI-AFM. A prototype MLI-AFM is established to demonstrate its measurement accuracy enhancement.

Comparison of cardiac output using invasive (Pulmonary Artery catheter Continuous cardiac Output), less invasive (FloTrac) and non invasive (Pulse Wave Transit Time) methods in patients undergoing off pump coronary artery bypass grafting

Aim and Objective: This study was undertaken in patients undergoing off-pump coronary artery bypass grafting (OPCABG) with aim of comparing cardiac output using invasive pulmonary artery catheter continuous cardiac output (PAC CCO), less invasive (FloTrac pulse contour based) and non invasive pulse wave transit time (PWTT) methods. Materials and Methods: Longitudinal observational study carried out in the department of Anesthesiology (CVTS OT) of super speciality hospital tertiary care hospital run by state Government with total 995 data sets taken from 25 subjects undergoing off pump coronary artery bypass grafting. Swan Ganz pulmonary artery catheter was inserted through the right internal jugular vein through introducer sheath and attached to the Edward vigilance II continuous cardiac output monitor for continuous monitoring of cardiac output invasively. Similarly cardiac output was measured with less invasive (FloTrac) monitor attached to a dedicated left femoral artery line. Non invasive (Estimated Continuous cardiac output (esCCO) based on pulse wave transit time) monitor attached to ECG and Spo2 probe sensor & calibration done with non –invasive blood pressure (NIBP) and the required demographic characteristics entered. Results: Mean cardiac output assessed by invasive, less invasive and non invasive method was 3.91+/-0.87, 5.71+/-0.87 and 6.03 +/- 0.99 L/min respectively. There was poor correlation between less invasive and the invasive with r=0.25 and also poor correlation between non-invasive and invasive with correlation coefficient of r=0.27. Both less invasive (FloTrac) and non invasive methods (PWTT) showed higher estimation when compared to the invasive (PAC CCO). The Bland Altman analysis showed poor agreement between less invasive (FloTtrac) and the invasive (PAC CCO) method, whereas the non invasive (PWTT based esCCO) showed good agreement. Percentage error were 68% and 126% for non-invasive (PWTT based es CCO) and less invasive (FloTrac) respe

Probe Calibration in Lossy Liquid Using Small Dipole Antennas for Megahertz-Band Specific Absorption Rate Measurements

The transmit antenna factor of a dipole antenna in a tissue-equivalent liquid phantom is derived from the power transmission formula and used in the calibration of an electric field probe for specific-absorption-rate (SAR) measurements of wireless power transfer systems operating in the megahertz band. First, we determine the length of the reference dipole antenna to be used in the calibration by the method of moments. Then, we construct a calibration system, including in-house fabricated dipole antennas and a phantom liquid with a concentration of 0.074 mol/L. The transmit antenna factor is then determined from the measured S-parameters and the conversion factor (CF) of the probe immersed inside the liquid phantom is derived by using our proposed calibration procedure. The CF is compared with that provided by a manufacturer to confirm the validity of our calibration method. An uncertainty budget is provided and the difference between the manufacturer’s value and our result is indicated to be within 2.6%, less than the expanded uncertainty, indicating the validity.