A new system for studying electrical properties of cell suspension is presented, which is based on the piezoelectric pressure wave propagation (Piezo-PWP) method. Because of the introduction of ...ultrasound to the system, the biological effects of ultrasound must be considered. In the experiment, the most important impact of the ultrasound is the steady-state cavitation. Under the exposure to the ultrasound, diffuse double layers of tiny gas microbubbles and cells are deformed, and the tiny change of potential can be detected by the electrode. The changing procession of diffuse double layers and the interaction of microbubbles and cells are studied. The system includes three parts, the ultrasonic wave generator, the PWP experiment cavity and the signal receiver. The center frequency of the piezoelectric transducer is 1.7MHz. A low power intensity ultrasound is used in the experiment, so as not to injury cells. In the experiment, the absolute ethanol, the distilled water, the saline, the chicken blood serum, the chicken blood cell suspension, the chicken blood plasma and the fish egg suspension are used as samples. In the study, the model of the ultrasound propagation in the sample, is built up and analyzed, through which the procession of the ultrasound affecting the electrical properties of cell suspension is clear. According to experimental results of different samples, there are two reasons which result in changes of electrical properties of the cell suspension. One is that the mechanical wave makes the diffuse double layer of microbubble deformation. The other one is the deformation of the diffuse double layer of cells, caused by compression and stretching of the microbubble. The experimental results and the ultrasonic wave propagation model of the cell suspension, show that the system may be helpful to the research of the electrical properties of cell and mechanism of ultrasonic biological effect.
Heat deposition by interstitial routes, especially with ultrasound-based instruments, is becoming a valuable therapeutic option for the treatments of sites, which are difficult to access from outside ...of the body. The active part of most interstitial ultrasound applicators described in the literature is logically tubular to induce cylindrical volumes of coagulation necrosis. Because the pressure generated by such tubular transducers falls off rapidly with radial distance, we previously proposed using a rotating plane transducer. For a plane wave, the pressure fall-off is only due to attenuation, which makes deeper lesions and shorter treatment times possible. This work represents an advance in the development of ultrasound applicators designed for interstitial applications. This new applicator used a rotating slightly focused transducer. A brief theoretical analysis resulted in the choice of a long focal distance of 22 mm to obtain a nearly constant pressure all along the therapeutic depth. To experimentally validate this focal distance, pressure measurements were made in a tissue mimicking liquid phantom and the results were compared with those obtained with a plane transducer. In vitro experiments showed that necrosis could be induced at a depth of 15 mm. In the same conditions, the greatest depth attained with a plane transducer was only 10 mm. Because each individual lesion is narrower, more lesions and more time are required to necrose a cylindrical volume. The main advantage of this new type of applicator is that it can be used to induce necrosis at a greater depth without varying either the frequency, the intensity or the transducer cooling efficiency.
Microwave-induced thermoacoustic tomography was explored to image biological tissues. Short microwave pulses irradiated tissues to generate acoustic waves by thermoelastic expansion. The ...microwave-induced thermoacoustic waves were detected with a focused ultrasonic transducer to obtain two-dimensional tomographic images of biological tissues. The dependence of the axial and the lateral resolutions on the spectra of the signals was studied. A reshaping filter was applied to the temporal piezoelectric signals from the transducer to increase the weight of the high-frequency components, which improved the lateral resolution, and to broaden the spectrum of the signal, which enhanced the axial resolution. A numerical simulation validated our signal-processing approach.
We present a detailed experimental study to evaluate our finite element based nonlinear reconstruction algorithm for recovery of acoustic properties in heterogeneous scattering media. Using a ...circularly scanning ultrasound system at
500
KHz
, tissue phantom experiments were performed to study spatial resolution and contrast issues in model-based ultrasound tomography. Our results show that both acoustic attenuation and speed images can be quantitatively reconstructed in terms of the location, size, shape, and acoustic property value of the target when different contrast levels between the target and background were used. We also demonstrate that a high contrast target as small as
3
mm
in diameter can be quantitatively resolved with our acoustic speed and attenuation images.
This paper examines the distributions of the SAR (specific absorption rate) ratio and temperature elevation when an ultrasound beam propagates through the interface of muscle and bone. This interface ...is regarded as a flat boundary to partition the energy of the ultrasound beam, and the analytical solution of temperature distribution is based on the steady-state bio-heat transfer equation. The parameters considered are the incident angle of ultrasound beam, the ultrasound frequency, the acoustic attenuation coefficients of refracted longitudinal and shear waves in bone, and the blood perfusion in muscle. The results show that the peak of the SAR ratio is always at the interface of muscle and bone, while the peak of temperature is located in the bone region beyond the interface. A muscle with lower perfusion or a bone with higher acoustic attenuation results in the shifting of the temperature peak closer to the interface. It is more difficult to heat a higher perfused muscle in front of a bone using a lower frequency ultrasound since the temperature elevation for bone relative to muscle is greater.
External ultrasound hyperthermia is a very flexible modality for heating deep-seated tumors due to its deep penetration and focusing ability. However, under the constraints of the available acoustic ...aperture size for the ultrasonic beam, ultrasonic attenuation, as well as other anatomic properties, it may not be able to deliver sufficient ultrasonic energy to heat a large tumor located in a deep region without overheating the normal tissue between the tumor and the aperture. In this work, we employ a simulation program based on the steady-state bioheat transfer equation and an ideal ultrasound power deposition (a cone with convergent/divergent shape) to examine the relationship between the minimal diameter of the acoustic aperture and the tumor conditions. Tissue temperatures are used to determine the appropriate aperture diameter and the input power level for a given set of tumor conditions. Due to the assumed central axis symmetry of the power intensity deposition and anatomic properties, a two-dimensional
(r−z)
simulation program is utilized. Factors determining the acoustic aperture diameter and the input power level considered here are the tumor size, tumor depth, ultrasonic attenuation in tissue, blood perfusion, and temperature of the surface cooling water. Simulation results demonstrate that tumor size, tumor depth, and ultrasonic attenuation are major factors affecting the aperture diameter of the ultrasonic beam to obtain an appropriate temperature distribution, while blood perfusion and the temperature of the surface cooling water are the minor factors. Plots of the effects of these factors can be used as the guideline for designing an optimal ultrasound heating system, arranging the transducers, and planning further treatments.
Our purpose in this study is to describe an algorithm for the automatic detection of linear artifacts in medical images. Linear artifacts arise as a result of many different forms of tissues and ...tissue boundaries within the imaging volume. Additionally, linear artifacts can arise for artificial structures such as radioactive seeds and radioactive linear sources. It is the purpose of the described algorithm to automatically detect linear artifacts of a certain length and diameter. The algorithm was written and compiled on a Pentium-4 based computer in the Microsoft Visual C/C++ language. Inert coils supplied by Radiomed Inc. were implanted into a standard prostate ultrasound phantom. Transaxial ultrasound images of the implanted phantom were obtained at 2 mm increments. The coded algorithm was then applied to the ultrasound imaging volume to automatically segment out the implanted coils. Thirteen coils were implanted in the prostate phantom. Thirteen coils were automatically identified in the imaging volume. An algorithm was developed to automatically determine the position and orientation of radioactive coils within an imaging volume. The algorithm successfully identified thirteen coils implanted in an ultrasound prostate phantom.
Our purpose in this work was to assess the reliability of the calibration coefficient for magnetic resonance water proton chemical shift temperature mapping. Over a six month period, the calibration ...coefficient was measured 15 times in several different phantoms. A highly linear relationship between water proton chemical shift and temperature change was found. The average temperature calibration coefficient determined from all studies was
0.009±0.001
ppm
/°
C
.
Four of the 15 studies were conducted on the same day using the same phantom. The average temperature calibration coefficient of these four studies was
0.0096±0.0001
ppm
/°
C
.
A novel ultrasound applicator for superficial simultaneous thermoradiotherapy consisting of two parallel-opposed linear arrays and a double-sided scanning reflector was constructed and tested for ...penetration depth control. In this design the arrays operate at different frequencies (1 and 5 MHz, in this study) and the input power to each array element (five
2×2
cm
2
elements per array) is computer adjustable. The ultrasonic beams from the arrays are aimed at the scanning reflector which in turn deflects them simultaneously and in parallel toward the treatment volume. Relative intensity distributions generated by the prototype were measured in a degassed water phantom using a thermal technique for a selected reflector position; these showed that the ultrasonic intensity distribution can be controlled in the lateral dimensions by varying the input power level to individual array elements. A fixed-perfused canine kidney phantom was employed to demonstrate experimentally that real time penetration depth control is possible by varying the excitation magnitude of one array (frequency) relative to that of the other. It is concluded that the dual-frequency scanned-reflected ultrasound applicator offers a degree of dynamic three-dimensional control of the power deposition pattern of clinical significance.
The purpose of this paper is to develop and evaluate a self-tuning fuzzy logic controller for a scanned focused ultrasound hyperthermia system with the reference temperature
(T
r
)
determined from ...objective functions. This work employs simulation programs to develop the power deposition for the scanned focused ultrasound system and to solve the responses of temperature profiles based on the transient bioheat transfer equation. A fuzzy logic control algorithm is employed to determine the output power level for the heating system and an observer for blood perfusion variation is used to enhance the capability of the controller to adjust the required output power level for the treatment due to the drastic change of the blood perfusion. The reference temperature
(T
r
)
for the controller is based on objective functions to tune its value during the heating process, while a control temperature
(T
c
)
from the thermosensors located in the tumor region is used as the input for the controller. The objective function based on the entire temperature profile is used to evaluate the appropriateness of the heating temperature distribution for a time-variational blood perfusion. Simulation results demonstrate that the tumor region can be rapidly heated to the desired temperature level and maintained at that level despite blood perfusion variation. The resulting temperature profile, the objective function, and the output power level are related to the magnitude of blood perfusion, but are almost independent of the
T
c
location and the initial setting value of
T
r
.
The fuzzy logic control algorithm with
T
r
determined from objective functions can be used for controlling the entire temperature distribution through a single control temperature, and the combination of control and optimization allows appropriate temperature fields to be created during the entire heating process. The control algorithm does not require the accurate prior knowledge of the locations of the thermosensors and the appropriate setting value for
T
r
.
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