Biomedical subjects

P Palanchon

Publications and source records attributed to P Palanchon.

4 recordsLinked to original sources

PubMed2004

Emboli detection using a new transducer design.

We have presented, in a previous study, a new approach to detect, characterize and estimate the size of gaseous emboli, based on the nonlinear behavior of gaseous bubbles. In this study, a specific transducer design has been developed to be used for such a purpose. It is composed of two separate transmitting and receiving capabilities. The transmit part, consisting of a lead zirconate-titanate (PZT) material, emits at a frequency of 500 kHz and could generate pressures up to 410 kPa. On the top of the transmit surface, a thin polyvinylidene difluoride (PVDF) layer is glued and used for receiving frequencies from 250 kHz (f0/2) up to 2.5 MHz (5 f0). To evaluate this new design, ultrasonic measurements were carried out with gas bubbles with diameters ranging from 10 microm up to 90 microm and solid particles between 350 microm and 550 microm. The experimental results confirmed our previous findings: gaseous emboli with a diameter close to the resonance size scatter significantly at higher harmonic components (from the second harmonic up to the fifth), and bubbles with a diameter around twice the resonance size produce a subharmonic and/or an ultraharmonic component. Meanwhile, solid particles and other bubble sizes behave only linearly and their scattered spectrum appeared without any harmonics. The study demonstrates the utility of this approach in using a single transducer to detect and characterize selective gaseous emboli from other particles using their nonlinear behavior.

Acoustics↗

PubMed2004

Bladder volume measurements with a limited number of fixed ultrasound beams.

Over the past 30 years, various ultrasonic methods have been suggested to measure bladder volume. Ultrasound (US) represents a noninvasive and simple way to assess such volumes. Bladder volumes are usually estimated from cross-sectional planes obtained with instruments using full imaging capabilities, but their accuracy remains limited. This study presents a simple ultrasonic technique that allows the assessment of bladder volume, using only five US beams distributed in a single sagittal plane at predetermined angles. Depending on the number of beams intercepting the bladder, the depth and the height of the bladder could be estimated, and the volume of urine then computed from an empirical formula. To check the validity of the approach, 110 different bladder volume measurements were performed using a 2-D scanning instrument. A total of 33 measurements were used to deduce the empirical formula, which was then used to estimate the volume for the other 77 scans. The computed volumes were compared with calibrated volume data available through voiding or catheterization. A mean error of 9.64% was found, with a relatively constant accuracy for the different volume ranges investigated. Based on this method, a prototype composed of five single-element transducers was developed and tested in clinical situations with 30 patients. The measurements led to a mean error of 70 mL +/- 60 mL with respect to the reference volume. Overall, this study demonstrated the reliability of the proposed method for bladder volume measurements.

Adult↗

PubMed2003

Subharmonic and ultraharmonic emissions for emboli detection and characterization.

Emboli detection and characterization is of importance for different patients, such as those undergoing carotid or cardiac surgery. The emboli occur as particulate or gaseous matters. To select the appropriate treatment and reduce the risk of embolism, it is essential to first detect and then classify and, ultimately, size the emboli. We propose, in this study, an approach to characterize and size the emboli based on the nonlinear properties of the emboli. Gaseous emboli were produced by generating single and uniform air bubbles. These bubbles had diameters ranging from 40 microm to 120 microm. Acoustic measurements were carried out and special attention was devoted to the generation of subharmonic and first ultraharmonic components for gas bubbles of different sizes and at different acoustic pressures. For the scanning frequency and the applied acoustic pressures used in this study, only bubbles ranging from 58 microm up to 110 microm are capable of generating a subharmonic and an ultraharmonic frequency component. However, gas emboli outside this range behave differently. In conclusion, such an approach can be used to provide information needed to classify and size emboli.

Acoustics↗

PubMed2001

New technique for emboli detection and discrimination based on nonlinear characteristics of gas bubbles.

Detection and characterization of emboli in the blood stream is of high clinical importance for making decisions after surgery. In this study, a new technique based on the nonlinear oscillations of gas bubbles was applied to gaseous emboli detection, characterization and sizing. To simulate gaseous emboli, an experimental system was developed to produce air bubbles of uniform diameters ranging from 19 microm up to 200 microm. The ultrasonic setup consisted of low-frequency transducers operating at 130 kHz and 250 kHz and using low acoustic pressures (30 kPa and 55 kPa). The experimental and theoretical results show that, depending on the transmitted frequency and the bubble sizes, higher harmonic components were produced in the frequency spectrum of the backscattered echo. Nonresonating bubbles scatter either linearly when their sizes are far away from the resonance size or nonlinearly at the second or third harmonic frequency when their sizes are getting close to the resonance size. Only resonant bubbles or bubbles very close to the resonance size are able to scatter at higher harmonic frequencies (fourth and fifth). This property is used to discriminate resonating bubbles from other bubble sizes. The appearance of harmonic component in the frequency spectrum seems to be an unambiguous tool to differentiate gaseous emboli from solid emboli that scatter linearly.

Acoustics↗