Gel Phantom Research Articles

Development of a shoulder-mounted robot for MRI-guided needle placement: phantom study.

This paper presents new quantitative data on a signal-to-noise ratio (SNR) study, distortion study, and targeting accuracy phantom study for our patient-mounted robot (called Arthrobot). Arthrobot was developed as an MRI-guided needle placement device for diagnostic and interventional procedures such as arthrography. We present the robot design and inverse kinematics. Quantitative assessment results for SNR and distortion study are also reported. A respiratory motion study was conducted to evaluate the shoulder mounting method. A phantom study was conducted to investigate end-to-end targeting accuracy. Combined error considering targeting accuracy, respiratory motion, and structure deformation is also reported. The SNR study showed that the SNR changes only 2% when the unpowered robot was placed on top of a standard water phantom. The distortion study showed that the maximum distortion from the ground truth was 2.57%. The average error associated with respiratory motion was 1.32mm with standard deviation of 1.38mm. Results of gel phantom targeting studies indicate average needle placement error of 1.64mm, with a standard deviation of 0.90mm. Noise and distortion of the MR images were not significant, and image quality in the presence of the robot was satisfactory for MRI-guided targeting. Combined average total error, adding mounting stability errors and structure deformation errors to targeting error, is estimated to be 3.4mm with a standard deviation of 1.65mm. In clinical practice, needle placement accuracy under 5mm is considered sufficient for successful joint injection during shoulder arthrography. Therefore, for the intended clinical procedure, these results indicate that Arthrobot has sufficient positioning accuracy.

P209] Determination of the relative dose distribution around an intrabeam electronic brachytherapy source using Fricke gel dosimetry

Purpose The INTRABEAM radiotherapy system is the most commonly used electronic brachytherapy (eBT) system in Europe for cancer treatment. To deliver the prescribed dose, medical physicists use the dose distribution data provided by the manufacturer (Zeiss). This work aims at verifying the correctness of these data for the specific case of breast cancer treatment by comparing the relative dose distribution predicted by Zeiss with that measured using gel dosimetry and that calculated using Monte Carlo simulation. Methods In this work, a Fricke gel dosimeter was used together with MRI readings. This method presents significant advantages as it enables relative dose distribution measurements in 3D, with millimetric spatial resolution. Firstly, the gel response was studied in terms of dose and energy dependence, using several dose levels in different X-ray reference beams. Meanwhile, these irradiation experiments were simulated using the Monte Carlo code Penelope for determining the relative absorbed dose distributions within the gel phantoms and the mean energies of the photon spectra at different depths. Once calibrated, the gel was poured into a dedicated phantom, surrounding the INTRABEAM source associated to a spherical 4 cm diameter applicator, irradiated under clinical conditions. Monte Carlo calculations were then used to convert the absorbed doses to gel into absorbed doses to water, and to obtain the relative absorbed dose to water distribution, required for the comparison. Results As no significant energy dependence was found within the uncertainty limits, the CCRI50b X-ray beam, whose energy spectrum is close to the one of the considered INTRABEAM source, was used to calibrate the gel response in absorbed dose. The polynomial relation obtained was then applied to the measurements with the INTRABEAM system to determine the relative absorbed dose distribution in gel, then converted into a relative dose distribution in water. The predicted, measured and calculated relative dose distributions are in excellent agreement, within the uncertainty limits. Conclusions The agreement obtained between the three methods validates both gel dosimetry as a powerful tool for measuring relative dose distributions delivered by low energy X-ray beams, and the relative dose distribution provided by Zeiss with the INTRABEAM system.

T2* Relaxation of Agar Gel With and Without The Presence of Tumor-Like Structure as Obtained from Resting State Fmri Sequence Protocol

The objective of this study was to determine the change in signal-to-noise ratio (SNR) as a function of TE of agar gel phantom with and without the presence of tumor-like structure, using a resting state fMRI sequence protocol. The phantoms were prepared using a conventional method. Citrus hystrix DC (kaffir lime) was used to mimick tumor and was submerged in the agar gel. The phantoms were scanned using a 3T-MRI system. An rsfMRI sequence protocol (TR = 2000 ms; TE = 51 ms - 115 ms) was used in obtaining the SNR at several TEs. In addition, a standard MRI phantom as control was also scanned using the same sequence protocol. For the prepared phantoms, the SNR was obtained from several 7-mm diameter ROIs at a distance 2, 4 and 6 cm from the centre of the image and was averaged. For the standard MRI phantom, similar ROI diameter was used for SNR determination but for three different slice thickneses; 3, 5 and 10 mm. The MRI, agar gel and agar gel with kaffir lime phantoms show T2* relaxation that fits the exponential equation S ∝ e-TE/T2*. The average T2* for the standard MRI phantom is 86.7 ± 0.1 ms. The average T2* for agar gel phantom is 70.1 ± 0.1 ms while T2* is shortened to an average of 54.8 ± 0.1 ms for agar gel phantom with kaffir lime. This indicate an increase in local magnetic field inhomogeneity in the vicinity of the tumor. The relaxation is thus faster causing a drop in the magnetic resonance signal intensity. The agar gel and agar gel with tumor mimicking phantom are suitable for a long TE rsfMRI scans.

MRI-Based Quantification of Magnetic Susceptibility in Gel Phantoms: Assessment of Measurement and Calculation Accuracy.

The local magnetic field inside and around an object in a magnetic resonance imaging unit depends on the magnetic susceptibility of the object being magnetized, in combination with its geometry/orientation. Magnetic susceptibility can thus be exploited as a source of tissue contrast, and susceptibility imaging may also become a useful tool in contrast agent quantification and for assessment of venous oxygen saturation levels. In this study, the accuracy of an established procedure for quantitative susceptibility mapping (QSM) was investigated. Three gel phantoms were constructed with cylinders of varying susceptibility and geometry. Experimental results were compared with simulated and analytically calculated data. An expected linear relationship between estimated susceptibility and concentration of contrast agent was observed. Less accurate QSM-based susceptibility values were observed for cylindrical objects at angles, relative to the main magnetic field, that were close to or larger than the magic angle. Results generally improved for large objects/high spatial resolution and large volume coverage. For simulated phase maps, accurate susceptibility quantification by QSM was achieved also for more challenging geometries. The investigated QSM algorithm was generally robust to changes in measurement and calculation parameters, but experimental phase data of sufficient quality may be difficult to obtain in certain geometries.

Histotripsy Using Fundamental and Second Harmonic Superposition Combined with Hundred-Microsecond Ultrasound Pulses

A novel histotripsy approach based on fundamental and second harmonic superposition and incorporating hundred-microsecond-long pulses and two-stage pulse protocol is proposed in this study to rapidly generate mechanically homogenized lesions. Two pulse stages were applied: stage 1, pulses with a pulse duration of 500–600 μs and pulse repetition frequency of 100 Hz, and stage 2, multiple periods, each composed of multiple pulses with the same pulse duration and pulse repetition frequency as those in stage 1, but with an off-time of 600 ms between periods. A custom-designed 1.1/2.2-MHz two-element confocal-annular array, with an f-number of 0.69, and lateral and axial full width at half-maximum pressure dimensions of approximately 1.0 and 6.0 mm, was used. The peak positive/negative pressures at the focus were +22/–7 MPa for 1.1 MHz and +56/–14 MPa with shock wave for 2.2 MHz. To investigate the feasibility of this approach, experiments were designed and performed in tissue-mimicking polyacrylamide gel phantoms with bovine serum albumin and in ex vivo porcine tissues. Cavitation and boiling activities were observed through high-speed photography, and the corresponding acoustic emissions were recorded through passive cavitation detection. Ex vivo experimental results revealed that complete tissue homogeneous regions with regular long tear shape and typical dimensions of 5.80 ± 0.19 mm in axial and 2.20 ± 0.26 mm in lateral were successfully generated in porcine kidney samples. The hematoxylin and eosin staining evidenced that the lesions were thoroughly homogenized and sharply demarcated from untreated regions. These results indicated that the histotripsy approach using fundamental and second harmonic superposition combined with hundred-microsecond pulses and two-stage pulse protocol can efficiently obtain a mechanical disruption of soft tissues with spatial precision, and this approach may have the potential to be developed as a useful tool for precise tumor treatment.

Toward invivo dosimetry in external beam radiotherapy using x-ray acoustic computed tomography: A soft-tissue phantom study validation.

To study, using phantoms made from biological tissues, the feasibility and practical challenges of monitoring the position of the radiation beam and the deposited dose by x-ray acoustic computed tomography (XACT) during external beam radiotherapy delivery. A prototype XACT system with a single immersion ultrasound transducer, which was positioned around the target sample driven by a motor-controlled rotation stage, was used to acquire the x-ray acoustic (XA) signals produced by a medical linear accelerator (Linac) to form an XACT image of the irradiated phantom. To investigate the feasibility of XACT in tracking the position of radiation dose, a large piece of veal liver with embedded fat tissue was imaged and beam misalignments were measured. Next, we explored the sensitivity of XACT in monitoring and quantifying the delivered dose, in which a block of porcine gel was embedded with equally spaced lard cylinders and imaged. The doses on the lard cylinders modulated by physical wedges were quantified from the XACT image and were verified by comparison to measurements from radiochromic films as the gold standard. Then, to simulate how XACT can perform in a targeted tissue in the human body, a porcine gel phantom with lard cylinders covered by different materials (bone, muscle, and air gap, respectively) was also imaged. The reconstructed XACT images of the phantoms show congruence with the boundaries of the beam field and the interfaces between the different tissue materials. The beam displacement from the target was tracked properly by the reconstructed XACT images. An intensity difference as small as 2.9% in delivered dose region can be measured from XACT images P=0.02. The intensities of XACT images were highly correlated to the film measurements with an R2 better than 0.986. The expected variances of dose delivered to different target regions as a result of the difference in attenuation were successfully captured by the XACT images. This study validated the feasibility of XACT in accurately obtaining relative dose maps of tissue-mimicking phantoms. XACT offers a practical method for verifying the beam position against the target and quantifying the relative dose delivered to the target during external beam radiotherapy.

Detection of gaps between high-intensity focused ultrasound (HIFU)-induced lesions using transient axial shear strain elastograms.

High-intensity focused ultrasound (HIFU) is becoming an effective and noninvasive treatment modality for cancer and solid tumors. In order to avoid the cancer relapse and guarantee the success of ablation, there should be no gaps left among all HIFU-generated lesions. However, there are few imaging approaches available for detecting the HIFU lesion gaps in real time during ablation. Transient axial shear strain elastograms (ASSEs) were proposed and evaluated both numerically and experimentally to detect the lesion gaps immediately after the cessation of therapeutic HIFU exposure. Acoustic intensity and subsequent acoustic radiation force were first calculated by solving the nonlinear Khokhlov-Zabolotskaya-Kuznetzov (KZK) equation. Motion of being- and already-treated lesions during and after HIFU exposure was simulated using the transient dynamic analysis module of finite element method (FEM). The corresponding B-mode sonography of tissue-mimicking phantom with two HIFU lesions inside was simulated by FIELD II, and then axial strain elastograms (ASEs) under static compression and transient ASSEs were reconstructed. An ultrasound imaging probe was integrated with the HIFU transducer and used to obtain radio frequency (RF) echo signals at high frame rate using plane wave imaging (PWI). The resulting strains were mapped using the correlation-based method and block search strategy. Acoustic radiation force from the therapeutic HIFU burst is sufficiently strong to produce significant displacement. As a result, large and highly localized axial shear strain appears in the gap zone between two HIFU-generated lesions and then disappears after sufficient HIFU ablation (no gap between them). Such capability of detecting the lesion gap is validated at the varied acoustic radiation force density, gap width, and the size of the lesion. In contrast, conventional ASEs using the static compression cannot distinguish whether a gap exists between lesions. Static ASEs and transient ASSEs reconstructed using both high-speed photography and sonography in the gel phantom show the same conclusion as that in the simulation. Ex vivo tissue experiments further confirmed that the presence of large axial shear strain in the gap zone. The ratios of axial shear strain in the porcine kidney and liver samples had statistical differences for two HIFU-generated lesions without and with a gap (P < 0.05). Large axial shear strain induced by the acoustic radiation force from therapeutic HIFU burst only appears between two HIFU-generated lesions with a gap between them. Transient ASSEs reconstructed immediately after the cession of HIFU exposure can easily, reliably, and sensitively detect the gap between produced lesions, which would provide real-time feedback to enhance the success of HIFU ablation.

Portable ultrasound imaging system with super-resolution capabilities

This paper discusses an ultrasound technique where the echo signals from the array of transducer elements are compressed to as few as two RF channels while still in analog domain, with a much simplified front-end electronics. The method can achieve resolutions well beyond the diffraction limit, which is set by the excitation signal wavelength and numerical aperture of the imaging system. The fundamental principle that underlies this model based imaging technique is the preservation of the spatial frequency information content of the recorded echo signals with the help of pseudo-random apodization function followed by summation. A Verasonics V1 ultrasonic scanner is used to conduct experiments using an anechoic cyst made from gel phantom, immersed in degassed water. The estimated images were compared to those obtained using traditional B-mode delay-and-sum imaging available with the Verasonics V1 ultrasound machine. The estimated images using the proposed imaging technique showed a contrast ratio of 0.96 and Full-Width-Half-Maximum (FWHM) of about half the wavelength at a depth of 9.1 cm and at 1.875 MHz center frequency while the traditional delay and sum images had a contrast ratio of 0.62 and FWHM of about 5.5 wavelengths.

Effect of adjuvant on cutaneous cryotherapy

The present study is carried out to quantify the effect of NaCl in 0.6% (w/v) agarose gel for cryosurgical applications. The concentration of NaCl is taken as 0%, 5%, 10% and 20% (w/v). In this study liquid nitrogen is sprayed using a 0.8 mm nozzle diameter. The distance from the nozzle to the agarose gel surface is 27 mm. The spray cooling is carried out for a single freeze-thaw cycle (freezing 120 s and thawing 130 s). The transient temperature history and ice front are measured experimentally. To validate the numerical study with the experimental study, energy equation with phase change is considered. The numerically calculated results show good confirmation with the experimentally measured results. The ablation volume, lethal front and gap (distance between lethal front and ice front) are calculated numerically as these parameters are difficult to determine experimentally. The lowest temperature, obtained at the end of 120 s of freezing, decreases with the increase in the NaCl concentration in the gel phantom. The ice front obtained in the radial and axial directions decreases with the addition of NaCl concentration in the gel. The ablation volume enclosed by − 25 °C isothermal surface in the case of 20% NaCl-gel is 111% larger than 0% NaCl-gel while it is 64% for − 50 °C isothermal surface. It is interestingly found that the calculated gap decreases with the addition of NaCl concentration.

High-intensity focused ultrasound (HIFU) ablation by frequency chirp excitation: reduction of the grating lobe in axial focus shifting

High-intensity focused ultrasound (HIFU) ablation has gained popularity in tumor treatment. However, the pre-focal heating due to the presence of the grating lobe may generate unintended heating in clinical applications and limit the steering abilities of the phased array design. In order to solve this problem, frequency chirp excitation was proposed and evaluated both numerically and experimentally. First, propagation of an HIFU burst through multi-layer media was simulated in a nonlinear acoustic model using the angular spectrum approach. Influences of axial focus shifting on the acoustic intensity at the both grating and main lobes at different excitation frequencies were investigated. It was found that different excitation frequencies result in variations in the position and magnitude of the grating lobe in the pre-focal region, but have little influence on the main lobe. Thus, the frequency chirp excitation can spread the acoustic energy in the pre-focal region, and subsequently reduce the temperature elevation. The performances of downward and upward frequency chirps in different sweeping times were compared to those of conventional excitation at the constant frequency. Then, HIFU plane ablation was evaluated. Even without the cooling time between treatment spots when using the frequency chirps, the pre-focal heating was still less than that at the constant frequency. Finally, the thermocouple measurement in the gel phantom showed an ~40% reduction in pre-focal temperature elevations produced by a single-element concave HIFU transducer using the frequency chirps. Altogether, the frequency chirp excitation could effectively reduce the pre-focal grating lobe at a large axial focus shifting distance, which may enhance both the efficacy and safety of clinical HIFU ablation.

Adjuvant-perfluorocarbon based approach for improving the effectiveness of cryosurgery in gel phantoms

The current study suggests novel methods to enhance freezing inside the tissue mimicking gel phantoms during the cryosurgery process. In this study, freezing of gel phantoms is carried out by a cryosurgery setup and the temperature is measured in real time using a data acquisition system. Alumina is used as an adjuvant and the variation of the alumina concentration in the gel phantoms results in a decrease of end temperature achieved after cryosurgery. However, the lowest end temperature is attained when the alumina concentration in the gel phantom is 1% (w/v) and for further studies this optimal concentration is utilised. It is observed that with the increase in insertion depth of the cryoprobe (from 1 to 1.5 cm), there is a decrease in end temperature at each thermocouple location in these alumina gel phantoms. The cooling of these alumina containing gel phantoms in presence of a perfluorohexane layer reveals that there is an inhibition of freezing due to this low thermal conductivity barrier (the axial ice ball depth is reduced from 2 cm to 1.5 cm). Furthermore, with the addition of glycine (i.e. 1% (w/v) alumina 5% (w/v) glycine gel phantom), a substantial end temperature decrease is observed at the thermocouples placed nearer to the cryoprobe, thus indicating the usefulness of this strategy in enhancing localised freezing. In conclusion, this study provides various new approaches that enhance the efficacy of cryosurgery immensely.

A study on improving the outcome of cryosurgery using low thermal conductivity emulsions

This study proposes a novel approach that utilises low thermal conductivity emulsions of perfluorodecalin as insulation around the tumour interface. The study reports the preparation of low thermal conductivity perfluorodecalin (PFD) emulsions (30%, 50%, 70% and 90% (w/v)) using probe sonication. The determination of thermal conductivity of these emulsions experimentally reveals a decrease in magnitude with the increase in the concentration of perfluorodecalin. The dynamic light scattering (DLS) and zeta potential studies indicate monodisperse and stable emulsions. Fourier transform infrared spectroscopy (FTIR) analysis confirms the presence of perfluorocarbon phase in the emulsion. The results of differential scanning calorimetry and theoretical estimation of thermal conductivity demonstrate that the increase of perfluorodecalin concentration lowers the specific heat and thermal conductivity of the emulsions. Experimental studies have been performed during cryosurgical freezing on an agarose gel phantom in the presence of a low thermal conductivity emulsion layer. The results suggest that in the presence of PFD 90 emulsion layer around the gel phantom the temperature at the 10 mm axial thermocouple the temperature is found to be 11 ∘C, whilst in the absence of this emulsion layer, the temperature is − 4 ∘C at the same thermocouple location, suggesting the insulating ability of perfluorocarbon emulsion layer. In conclusion, this study proposes a new approach that utilises low thermal conductivity emulsions for enhancing the cryosurgical freezing and minimising the damage to a defined region.

Knowledge of endoscopic ultrasound-delivered fiducial composition and dimension necessary when planning proton beam radiotherapy.

Background and study aims Little consideration has been given to selection of endoscopic ultrasound-guided fiducials for proton radiotherapy and the resulting perturbations in the therapy dose and pattern. Our aim was to assess the impact of perturbations caused by six fiducials of different composition and dimensions in a phantom gel model. Materials and methods The phantom was submerged in a water bath and irradiated with a uniform 10 cm × 10 cm field of 119.7 MeV monoenergetic spot scanning protons delivered through a 45 mm range shifter. The proton “Bragg Peak” was evaluated. Results Dose perturbations manifesting as dose reductions up to 30 % were observed. A carbon composite (1 × 5 mm) and gold (0.4 × 10 mm) fiducial with backload potential rather than dedicated EUS pre-loaded gold fiducial needles had the best performance in terms of minimizing the dose perturbation. Conclusions Our data demonstrate that a carbon composite fiducial has a less untoward effect on proton therapy dose distribution than dedicated EUS pre-loaded gold fiducial needles. Such information is important to consider when selecting fiducials specifically for proton therapy.

Deliberate practice using validated metrics improves skill acquisition in performance of ultrasound-guided peripheral nerve block in a simulated setting

Study objectivesThe aim of this study was to compare the effects of deliberate vs. self-guided practices (both using validated metrics) on the acquisition of needling skills by novice learners. DesignRandomized Controlled Study. SettingSimulation lab, Department of Anesthesia, St.Vincent's Hospital, Dublin. SubjectsEighteen medical students. InterventionsStudents were assigned to either (i) deliberate practice (n = 10) or (ii) self-guided practice (n = 8) groups. After completion of a ‘learning phase’, subjects attempted to perform a predefined task, which entailed advancing a needle towards a target on a phantom gel under ultrasound guidance. Subsequently, all subjects practiced this task using predefined metrics. Only subjects in the deliberate practice group had an expert anesthesiologist during practice. Immediately after completing ‘practice phase’, all subjects attempted to perform the same task, and, on the following day, made two further attempts in succession. Two trained consultant anesthesiologists assessed a video of each performance independently using the pre-defined metrics. MeasurementsNumber of procedural steps completed and number of errors made. Main resultsCompared with novices who self-guided their practice using metrics, those who undertook expert-supervised deliberate practice using metrics completed more steps (performance metrics) immediately after practice (median [range], 14.5 [12–15] vs. 3 [1–10], p < 0.0001) and 24 h later (15 [12–15] vs. 4.5 [1–11], p < 0.0001 and 15 [11–15] vs. 4 [2–14], p < 0.0001). They also made fewer errors immediately after practice (median [range], 0 [0–0] vs. 5 [3–8], p < 0.0001) and 24 h later, (0 [0–3] vs. 6.5 [3–8], p < 0.0001 and 0 [0–3] vs. 4 [2–7], p < 0.0001). ConclusionCombining deliberate practice with metrics improved acquisition of needling skills.

Design and characterization of tissue-mimicking gel phantoms for diffusion kurtosis imaging.

The aim of this work was to create tissue-mimicking gel phantoms appropriate for diffusion kurtosis imaging (DKI) for quality assurance, protocol optimization, and sequence development. A range of agar, agarose, and polyvinyl alcohol phantoms with concentrations ranging from 1.0% to 3.5%, 0.5% to 3.0%, and 10% to 20%, respectively, and up to 3g of glass microspheres per 100ml were created. Diffusion coefficients, excess kurtosis values, and relaxation rates were experimentally determined. The kurtosis values for the plain gels ranged from 0.05 with 95% confidence interval (CI) of (0.029,0.071) to 0.216(0.185,0.246), well below the kurtosis values reported in the literature for various tissues. The addition of glass microspheres increased the kurtosis of the gels with values up to 0.523(0.465,0.581) observed for gels with the highest concentration of microspheres. Repeat scans of some of the gels after more than 6 months of storage at room temperature indicate changes in the diffusion parameters of less than 10%. The addition of the glass microspheres reduces the apparent diffusion coefficients (ADCs) and increases the longitudinal and transverse relaxation rates, but the values remain comparable to those for plain gels and tissue, with ADCs observed ranging from 818(585,1053)×10-6 mm2 /s to 2257(2118,2296)×10-6 mm2 /s, R1 values ranging from 0.34(0.32,0.35) 1/s to 0.51(0.50,0.52) 1/s, and R2 values ranging from 9.69(9.34,10.04) 1/s to 33.07(27.10, 39.04) 1/s. Glass microspheres can be used to effectively modify diffusion properties of gel phantoms and achieve a range of kurtosis values comparable to those reported for a variety of tissues.

Conductivity Rise During Irreversible Electroporation: True Permeabilization or Heat?

PurposeIrreversible electroporation (IRE) induces apoptosis with high-voltage electric pulses. Although the working mechanism is non-thermal, development of secondary Joule heating occurs. This study investigated whether the observed conductivity rise during IRE is caused by increased cellular permeabilization or heat development.MethodsIRE was performed in a gelatin tissue phantom, in potato tubers, and in 30 patients with unresectable colorectal liver metastases (CRLM). Continuous versus sequential pulsing protocols (10-90 vs. 10-30-30-30) were assessed. Temperature was measured using fiber-optic probes. After temperature had returned to baseline, 100 additional pulses were delivered. The primary technique efficacy of the treated CRLM was compared to the periprocedural current rise. Seven patients received ten additional pulses after a 10-min cool-down period.ResultsTemperature and current rise was higher for the continuous pulsing protocol (medians, gel: 13.05 vs. 9.55 °C and 9 amperes (A) vs. 7A; potato: 12.70 vs. 10.53 °C and 6.0A vs. 6.5A). After cooling-down, current returned to baseline in the gel phantom and near baseline values (Δ2A with continuous- and Δ5A with sequential pulsing) in the potato tubers. The current declined after cooling-down in all seven patients with CRLM, although baseline values were not reached. There was a positive correlation between current rise and primary technique efficacy (p = 0.02); however, the previously reported current increase threshold of 12–15A was reached in 13%.ConclusionThe observed conductivity rise during IRE is caused by both cellular permeabilization and heat development. Although a correlation between current rise and efficacy exists, the current increase threshold seems unfeasible for CRLM.

Deduction of two-dimensional blood flow vector by dual angle diverging waves from a cardiac sector probe

Color Doppler method is widely used for noninvasive diagnosis of heart diseases. However, the method can measure one-dimensional (1D) blood flow velocity only along an ultrasonic beam. In this study, diverging waves with two different angles were irradiated from a cardiac sector probe to estimate a two-dimensional (2D) blood flow vector from each velocity measured with the angles. The feasibility of the proposed method was evaluated in experiments using flow poly(vinyl alcohol) (PVA) gel phantoms. The 2D velocity vectors obtained with the proposed method were compared with the flow vectors obtained with the particle image velocimetry (PIV) method. Root mean square errors of the axial and lateral components were 11.3 and 29.5 mm/s, respectively. The proposed method was also applied to echo data from the left ventricle of the heart. The inflow from the mitral valve in diastole and the ejection flow concentrating in the aorta in systole were visualized.

A multi-purpose electromagnetic actuator for magnetic resonance elastography

An electromagnetic actuator was designed for magnetic resonance elastography (MRE). The actuator is unique in that it is simple, portable, and capable of brain, abdomen, and phantom imagings. A custom-built control unit was used for controlling the vibration frequency and synchronizing the trigger signals. An actuation unit was built and mounted on the specifically designed clamp and holders for different imaging applications. MRE experiments with respect to gel phantoms, brain, and liver showed that the actuator could produce stable and consistent mechanical waves. Estimated shear modulus using local frequency estimate method demonstrated that the measurement results were in line with that from MRE studies using different actuation systems. The relatively easy setup procedure and simple design indicated that the actuator system had the potential to be applied in many different clinical studies.

Prediction of HIFU Propagation in a Dispersive Medium via Khokhlov–Zabolotskaya–Kuznetsov Model Combined with a Fractional Order Derivative

High intensity focused ultrasound (HIFU) has been proven to be promising in non-invasive therapies, in which precise prediction of the focused ultrasound field is crucial for its accurate and safe application. Although the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation has been widely used in the calculation of the nonlinear acoustic field of HIFU, some deviations still exist when it comes to dispersive medium. This problem also exists as an obstacle to the Westervelt model and the Spherical Beam Equation. Considering that the KZK equation is the most prevalent model in HIFU applications due to its accurate and simple simulation algorithms, there is an urgent need to improve its performance in dispersive medium. In this work, a modified KZK (mKZK) equation derived from a fractional order derivative is proposed to calculate the nonlinear acoustic field in a dispersive medium. By correcting the power index in the attenuation term, this model is capable of providing improved prediction accuracy, especially in the axial position of the focal area. Simulation results using the obtained model were further compared with the experimental results from a gel phantom. Good agreements were found, indicating the applicability of the proposed model. The findings of this work will be helpful in making more accurate treatment plans for HIFU therapies, as well as facilitating the application of ultrasound in acoustic hyperthermia therapy.

Repeatability, reproducibility, and accuracy of quantitative mri of the breast in the community radiology setting.

Quantitative diffusion-weighted MRI (DW-MRI) and dynamic contrast-enhanced MRI (DCE-MRI) have the potential to impact patient care by providing noninvasive biological information in breast cancer. To quantify the repeatability, reproducibility, and accuracy of apparent diffusion coefficient (ADC) and T1 -mapping of the breast in community radiology practices. Prospective. Ice-water DW-MRI and T1 gel phantoms were used to assess accuracy. Normal subjects (n = 3) and phantoms across three sites (one academic, two community) were used to assess reproducibility. Test-retest analysis at one site in normal subjects (n = 12) was used to assess repeatability. 3T Siemens Skyra MRI quantitative DW-MRI and T1 -mapping. Quantitative DW-MRI and T1 -mapping parametric maps of phantoms and fibroglandular and adipose tissue of the breast. Average values of breast tissue were quantified and Bland-Altman analysis was performed to assess the repeatability of the MRI techniques, while the Friedman test assessed reproducibility. ADC measurements were reproducible across sites, with an average difference of 1.6% in an ice-water phantom and 7.0% in breast fibroglandular tissue. T1 measurements in gel phantoms had an average difference of 2.8% across three sites, whereas breast fibroglandular and adipose tissue had 8.4% and 7.5% average differences, respectively. In the repeatability study, we found no bias between first and second scanning sessions (P = 0.1). The difference between repeated measurements was independent of the mean for each MRI metric (P = 0.156, P = 0.862, P = 0.197 for ADC, T1 of fibroglandular tissue, and T1 of adipose tissue, respectively). Community radiology practices can perform repeatable, reproducible, and accurate quantitative T1 -mapping and DW-MRI. This has the potential to dramatically expand the number of sites that can participate in multisite clinical trials and increase clinical translation of quantitative MRI techniques for cancer response assessment. 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.