In vitro comparative study of vibro-acoustography versus pulse-echo ultrasound in imaging permanent prostate brachytherapy seeds

Background

Permanent prostate brachytherapy (PPB) is a common treatment for early stage prostate cancer. While the modern approach using trans-rectal ultrasound guidance has demonstrated excellent outcome, the efficacy of PPB depends on achieving complete radiation dose coverage of the prostate by obtaining a proper radiation source (seed) distribution. Currently, brachytherapy seed placement is guided by trans-rectal ultrasound imaging and fluoroscopy. A significant percentage of seeds are not detected by trans-rectal ultrasound because certain seed orientations are invisible making accurate intra-operative feedback of radiation dosimetry very difficult, if not impossible. Therefore, intra-operative correction of suboptimal seed distributions cannot easily be done with current methods. Vibro-acoustography (VA) is an imaging modality that is capable of imaging solids at any orientation, and the resulting images are speckle free.

Objective and methods

The purpose of this study is to compare the capabilities of VA and pulse-echo ultrasound in imaging PPB seeds at various angles and show the sensitivity of detection to seed orientation. In the VA experiment, two intersecting ultrasound beams driven at f₁ = 3.00 MHz and f₂ = 3.020 MHz respectively were focused on the seeds attached to a latex membrane while the amplitude of the acoustic emission produced at the difference frequency 20 kHz was detected by a low frequency hydrophone.

Results

Finite element simulations and results of experiments conducted under well-controlled conditions in a water tank on a series of seeds indicate that the seeds can be detected at any orientation with VA, whereas pulse-echo ultrasound is very sensitive to the seed orientation.

Conclusion

It is concluded that vibro-acoustography is superior to pulse-echo ultrasound for detection of PPB seeds.     

A Simple Systematical Law of E2＋ Values for Heavy Nuclei in the NpNn Scheme and the Evolution of the Z=64 Shell Gap

A systematics of excitation energy of the first 2^＋ state E2＋ in even-even heavy nuclei （A ≥ 120） is studied in the NpNn scheme. It is found that a simple exponential function describes the dependence of E2＋ values on NpNn values very well. In addition, the Z = 64 shell gap is reexamined by investigating the systematics of the 52 ≤ Z ≤66 region. It is found that the Z = 64 shell gap is largest at N = 82 and becomes smMler with either increasing or decreasing of neutron numbers. The effects of this shell gap become negligible for counting the valence proton numbers when N ≥ 92 or N ≤ 72.     

A fractal model for heat transfer of nanofluids by convection in a pool

Based on the fractal distribution of nanoparticles, a fractal model for heat transfer of nanofluids is presented in the Letter. Considering heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids, the formula of calculating heat flux of nanofluids by convection is given. The proposed model is expressed as a function of the average size of nanoparticle, concentration of nanoparticle, fractal dimension of nanoparticle, temperature and properties of fluids. It is shown that the fractal model is effectual according to a good agreement between the model predictions and experimental data.     

On Debye temperature anomaly observed in Ge-Se-Ag glasses

Anomalous values of Debye temperature have been obtained from recoil free factor measurements Ge-Se-Ag glasses recently [B. Arcondo, M.A. Urena, A. Piarristeguy, A. Pradel, M. Fontana, Physica B 389 (2007) 77]. In the present paper we show that this anomaly may arise due to the presence of anharmonic potential at the high spin ferrous site. We use q Lamb Mossbauer factor and anharmonic Lamb Mossbauer factor to study this anharmonicity.     

Coupling of cavity modes and guiding modes in two-dimensional phononic crystals

Cavity modes for the single-cavity and the double-cavities in two-dimensional phononic crystal are studied by using a plane waves expansion supercell method. We show that the single-cavity behaves like an atom while the double-cavities behave like a molecule. Couplings of cavity modes with the waveguide modes are investigated for typical configurations. Suitably designed waveguides with introduced cavities might be used as acoustic filter in waveguide applications.     

Diffusive, super-diffusive and ballistic transport in the long-range correlated 1D Anderson model

In this paper, we study the 1D Anderson model with long-range correlated on-site energies. This diagonal-correlated disorder is considered in such a way that the random sequence of site energies ε_n has a 1/k^α power spectrum, where k is the wave-vector of the modulations on the random sequence landscape. Using the Runge-Kutta method to solve the time-dependent Schrödinger equation, we compute the participation number and the Shannon entropy for an initially localized wave packet. We observe that strong correlations can induce ballistic transport associated with the emergence of low-energy extended states, in agreement with previous works in this model. We further identify an intermediate regime with super-diffusive spreading of the wave-packet.     

A theoretical analysis of acoustic microscopy with converging acoustic beams

A theoretical analysis is carried out to synthesize acoustic material signatures (AMS) of solid plates immersed in water. The distinctive feature of this analysis is that it avoids three major simplifying assumptions of the presently available techniques, which are, paraxial approximation, assumption of perfect reflection and Gaussian summation of the incident field. Presently available techniques can avoid some but not all of these simplifying assumptions for computing the AMS. In this paper the analysis is carried out for lowfrequency acoustic waves generated by a cylindrical transducer without a lens rod. Reasons for these changes in the conventional acoustic microscope geometry is given. The AMS is synthesized for an aluminium plate in presence as well as in absence of water on its one side. As expected a significant difference is observed between the signatures generated under these two situations.     

Coupling of Acoustical Plane p-Wave to a Cased Borehole

Theoretical and numerical study on the coupling acoustic field of the plane p-wave to a cased borehole is carried out. The medium outside the cased borehole is modeled as the porous medium. The scattering field characteristics in the cased borehole are investigated when a plane fast p-wave is incident in tilt to the cased borehole from the porous medium. The scattering fields inside and outside the cased borehole are analyzed and deduced by Biot＇s theory under the boundary conditions on each interface, and they are numerically studied. It is found that the scattering field has strong resonant characteristics and there exists a series of resonant frequencies and peaks. The effects of the frequency, radii of each interface, incident angle, porosity, and other parameters on the resonant acoustic field have been investigated in detail in the fast and slow formations respectively. The resonant characteristics of the scattering field are also analyzed from the physical sense.     

Phononic band structure in a two-dimensional hybrid triangular graphite lattice

The propagation of acoustic wave in a two-dimensional phononic crystal of a hybrid triangular graphite array is investigated by the plane wave expansion (PWE) method. Our numerical results show that the location and width of the band gaps can be tuned by altering the radii of scatters at different positions.     

Determination of Thermal Conductivity of Liquids by a Multi-Point Laser Pump Method

As an advanced optical method, a multi-point pump method is presented for measurements of thermo-physical properties of liquids. Meanwhile, based on the laser-induced thermal grating method, a new theory model is presented and used to analyse the thermal effects caused by the multi-point laser pump, by which the thermal conductivity of liquids can be obtained. The results of some typical liquids, such as water, ethanol and acetone, are presented and are consistent with those of acknowledged values, demonstrating that the multi-point method is simple and useful for characterizing thermal properties of liquids.     

The effective thermal conductivity of porous media based on statistical self-similarity

A fractal model is presented based on the thermal-electrical analogy technique and statistical self-similarity of fractal saturated porous media. A dimensionless effective thermal conductivity of saturated fractal porous media is studied by the relationship between the dimensionless effective thermal conductivity and the geometrical parameters of porous media with no empirical constant. Through this study, it is shown that the dimensionless effective thermal conductivity decreases with the increase of porosity (?) and pore area fractal dimension (Df) when ks/kg>1. The opposite trends is observed when ks/kg<1. In addition, the dimensionless effective thermal conductivity decreases with increasing tortuous fractal dimension (Dt). The model predictions are compared with existing experimental data and the results show that they are in good agreement with existing experimental data.     

Sensitivity of Josephson junctions to high-pass filtered noise of black-body radiation

The influence of the nonwhite noise on the Josephson junction is considered by using the averaging principle. It is shown that in contrast to the case of white noise there is a non-zero critical current, but it has high sensitivity to the noise power. The dependence of noise power on the critical current can be used for the detection of cold black-body radiation.     

The vibration and rotation of piezoelectric particles in high frequency electric fields observed by a thermoacoustic method

We have observed, by a thermoacoustic method, the acoustic resonance vibration of small (diameter 115 m) piezoelectric particles in high frequency (15 MHz) electric fields. The frequency dependence of the thermoacoustic signal gives direct information about the size distribution of the particles.In very strong rf electric fields we also observed a rotation of the vibrating particles by large angles — as originally suggested by Melcher and Shiren [3] — orienting the initially random rf dipoles parallel to the rf electric fields.The observed strong forces acting on vibrating piezoelectric particles in rf fields can probably be used as a new method of selectively extracting particles of a given size from a broad distribution of very small particles.     

Ultrasonic resonator with electrical discharge cell for ozone generation

The effect of ultrasound waves in an ultrasonic resonator cell on ozone generation by a hollow needle to plate electrical discharge enhanced by the airflow through the needle is experimentally investigated. It was found that the application of ultrasound waves increases ozone generation for discharge when the needle is negatively biased, and has no effect on ozone generation for the discharge when the needle is biased positively. We try to explain the influence of ultrasound on the discharge mechanisms.     

Diffusion and correlation in a coherent representation

Using a Fock-space formalism for the Master equation and introducing the density operator we present an unified method to derive kinetic equations for hopping processes with and without exclusion on a lattice. The corresponding Liouvillians are written in terms of Fermi or Bose operators, respectively. Although the Liouvillians are different the averaged particle numbers obey the same diffusion equation. Differences appear in the correlation functions only. The Master equation can be transformed into a differential equation in a coherent state representation. Using the algebraic properties of Grassmann numbers we are able to find the exact statonary solution for diffusion with exclusion. The conductivity can be derived in the bosonic and the fermionic case. The results are in accordance with those obtained with different other methods.     

Water Surface Wave in a Trough with Periodical Topographical Bottom under Vertical Vibration

We investigate the water surface waves in a vertically vibrated long rectangular trough with several identical Plexiglas rectangles lined periodically on the bottom. The band structure is computed theoretically by the method of transfer matrix. Some interesting phenomena, such as the localized wave, especially the solitary-like wave inside the band gap . are observed in the experiments.     

The influence of the micro-topology on the phononic band gaps in 2D porous phononic crystals

The phononic band structures of two-dimensional metal porous phononic crystals consisting of different lattices (the lattice structures transformed from square to triangle), and pores of various shapes (circle, square, and triangle) and sizes are studied numerically by using Finite Difference Time Domain (FDTD) scheme. It is found that for x-y mode waves, the absolute phononic band gaps (PBGs) rely more on the pore shapes. For triangular pores, the PBG is opening in the whole process of the lattice transformation, and for circular ones, the PBG is closed after a certain lattice structure. No PBG forms in the crystals with square pores. The PBG can be varied by adjusting the size of the pores. But a critical porosity exists for the opening of the PBG.     

Vibro-acoustography imaging of permanent prostate brachytherapy seeds in an excised human prostate - Preliminary results and technical feasibility

Objective:

The objective in this work is to investigate the feasibility of using a new imaging tool called vibro-acoustography (VA) as a means of permanent prostate brachytherapy (PPB) seed localization to facilitate post-implant dosimetry (PID).

Methods and materials:

Twelve OncoSeed (standard) and eleven EchoSeed (echogenic) dummy seeds were implanted in a human cadaver prostate. Seventeen seeds remained after radical retropubic prostatectomy. VA imaging was conducted on the prostate that was cast in a gel phantom and placed in a tank of degassed water. 2-D magnitude and phase VA image slices were obtained at different depths within the prostate showing location and orientation of the seeds.

Results:

VA demonstrates that twelve of seventeen (71%) seeds implanted were visible in the VA image, and the remainder were obscured by intra-prostatic calcifications. Moreover, it is shown here that VA is capable of imaging and locating PPB seeds within the prostate independent of seed orientation, and the resulting images are speckle free.

Conclusion:

The results presented in this research show that VA allows seed detection within a human prostate regardless of their orientation, as well as imaging intra-prostatic calcifications.     

Are deformed modes still Raman active for single-wall carbon nanotubes?

Using group theory calculations combined with the force-constant model and molecular-dynamics simulations, whether the deformed modes are Raman active or not for (10,10) and (10,0) single-wall carbon nanotubes under hydrostatic pressure is discussed. With increasing pressure, the tube symmetry lowers from D_20h to D_2h then to C_2h point group. For D_20h, A_1g is changed to A_g, while E_1g and E_2g are split: E_1g→B_2g+B_3g→2B_g and E_2g→A_g+B_1g→2A_g. On the basis of the correlation between D_20h, D_2h, and C_2h point groups, the deformed modes should be still Raman active. The result can help us clarify the essence of the experimental observations.