The present paper applies an optoacoustic method for generation of the first and second sound waves in superfluid helium4. Two wave equations related to pressure and temperature vibrations in time unit are concluded using linear hydrodynamic equations and conducting numeral calculations, and two thermal and electrostriction mechanism are observed. Analyses incurred in this paper are related to crystal parts of superfluid helium. Absorption coefficient of these crystal parts is nearly zero, and the only dominant mechanism is electrostriction one. Two sound waves are studied including first sound wave that is propagation of pressure vibrations and second sound wave that is propagation of temperature vibration in superfluid helium4. We shine laser light in the form of a continuous wave on superfluid helium4 after generating wave equations, and observe generation normal first and second sound waves and fast and slow sound waves in superfluid helium4.We Also observed that reducing of the laser beam radius amplitude (w), increases the pressure and temperature vibrations amplitude in superfluid helium4.

Background: Nowadays cancer detection in preliminary stages is one of the most important problems for physicians. One of the new imaging techniques, which have special capability in the detection of small size lesions, is optoacoustic imaging. In this paper have introduced this technique and have simulated optoacoustic wave generation in spherical tumors of breast.Material and Methods: In this research for the generation of acoustic pressure as a result of laser energy reception in an absorbing sphere, a transfer functions in backward mode has been introduced. Then using this model effect of changes in laser pulse width, dimensions and depth of tumor and absorption coefficient of tumor and media on properties of generated ultrasound have been surveyed. All of simulations have been accomplished in MATLAB7 software platform.Results: investigation of pulse width effect on generated optoacoustic wave illustrated that increase of laser pulse duration causes to increase in ultrasound amplitude. Investigation of tumor absorption coefficient as a function of tumor type showed that Increase of absorption coefficient of tumor causes to increase in ultrasound amplitude, but more increase in absorption coefficient causes to saturation in ultrasound amplitude and in high absorption coefficient relation between generated ultrasound amplitude and absorption coefficient because of order two.Conclusion: For designing a laser- ultrasound system with maximum efficiency, we can choose optimum system using this model and simulation results with testing of various parameters of available laser systems. In addition, we can use obtained results for tumor specification in clinical applications of this technique.

Introduction: Photo-acoustic that idiomatically is called optoacoustic or laser-ultrasound is a technique that uses optical energy for the generation of ultrasound waves in various media. The waveform of the generated ultrasound contains useful information about the optical properties of the absorbing media and is influenced by laser pulse specifications. The obtained pressure signal undergoes changes prior to reaching the transducer due to the propagation in the media. In this research, the effect of laser parameters, the properties of the absorbent media and acoustic diffraction in generated ultrasound wave, have been investigated.Materials and Methods: In this research, a frequency domain has been introduced for the generation of acoustic pressure as a result of laser energy reception transfer functions in two modes of forward and backward. By the use of this model, the effect of the pulse duration, the profile and wavelength of laser and also the absorption coefficient of the sample in the generated ultrasound properties have been investigated. A transfer function for the acoustic diffraction has been introduced and the effect of diffraction in ultrasound waveform has been simulated. Also the effect of the longitudinal and the radial distance of ultrasound transducer from the irradiated surface and also the ultrasonic source dimension that is influenced by laser beam diameter in ultrasound waveform, have been surveyed. All the simulations have been accomplished in MATLAB7 software platform. Results: Increasing laser pulse duration causes an increase in the amplitude of ultrasound and a decrease in its frequency content. The increase in the amplitude causes an increase in the absorption coefficient of the sample. The generated optoacoustic waves in response to lasers with Gaussian and asymmetric Gaussian profile are not significantly different, consequently Gaussian pulse can be used in modeling with good approximation. As a result of acoustic diffraction while propagating in media, a backward single pole wave changes to a bipolar one. An increase in ultrasonic source dimension (laser beam diameter) causes an increase in the amplitude and the width of the optoacoustic waves.Discussion and Conclusion: To design a laser-ultrasound system with maximum efficiency, one has to choose a laser wavelength in which tissue has a high absorption coefficient. The pulse duration and the beam diameter of the laser should be chosen correctly with respect to the ultrasonic transducer properties.

Introduction: Tinnitus is the phantom auditory perception of sound in the absence of an external or internal acoustic stimulus. The treatment is difficult due to multiple etiologies and great psychological influence. The purpose of this study was to determine alterations in auditory physiological and electrophysiological responses associated with temporary suppression of tinnitus induced by low-level laser (LLL) irradiation.Methods: This study was conducted on 20 subjects with subjective tinnitus. All subjects signed the informed consent form and satisfied all the study eligibility criteria. Visual analog scale (VAS) for loudness, loudness matching of tinnitus (LMT), pitch matching of tinnitus (PMT), Persian-tinnitus questionnaire (P-TQ) and Persian-tinnitus handicap inventory (P-THI) were conducted pre- and post-low level laser therapy (LLLT) for all the subjects. Electrocochleography (ECochG) and distortion product otoacoustic emissions (DPOAEs) were recorded in 11 subjects. Continuous wave diode lasers, including red (630 nm) and infra-red (808 nm) were applied, and were both designed by the Canadian Optic and Laser (COL) Center. Twelve sessions of laser therapy were performed, 2 sessions per week for each subject. Total dose was 120 Joule/ ear/ session.Results: LLL irradiation could cause a significant decrease in subjective tests scores consisting of VAS for loudness, PMT, P-TQ, P-THI, but did not result in a significant improvement of objective evaluating parameters except for compound action potential (CAP) amplitude.Conclusion: LLLT might be a subjectively effective treatment for short-term improvement of tinnitus. Defining a new protocol for optimizing LLLT parameters may be an option to improve parameters of objective tests.

In this paper sound generation by laser pulse irradiated on a solid block is investigated. After an introduction to known mechanisms and main equation of laser acoustics, the laser pulse profile of NdYAG laser by straight radiation on a photo-resistor was recorded and the profile was substituted as an optoacoustic source in related equation of sound evolution. Finally the solution of numerically solved equation and measured generated sound were compared. Results show that there exists direct relationship between generated sound pulse width and laser pulse width. Furthermore there exists reverse relationship between generated sound pulse width and solid block thickness. In addition, results of simulation and experimental data measured by laser microphone with photo-resistor detector are compared by obtained sound spectrum from Spectrogram which confirm previous theoretical and experimental data. Finally general rule of the similarity of sound pulse profile and sound generator laser pulse profile are observed in this experiment.

Background: Hybrid imaging modalities which simultaneously benefit from capabilities of combined modalities provides an opportunity to modify quality of the images which can be obtained by each of the combined imaging systems. One of the imaging modalities, emerged in medical research area as a hybrid of ultrasound imaging and optical imaging, is photoacoustic imaging which apply ultrasound wave generated by tissue, after receiving laser pulse, to produce medical images.Materials and Methods: In this review, using keywords such as photoacoustic, optoacoustic, laser-ultrasound, thermoacoustic at databases such as PubMed and ISI, studies performed in the field of photoacoustic and related findings were evaluated.Results: Photoacoustic imaging, acquiring images with high contrast and desired resolution, provides an opportunity to perform physiologic and anatomic studies. Because this technique does not use ionizing radiation, it is not restricted by the limitation of the ionizing-based imaging systems therefore it can be used noninvasively to make images from cell, vessels, whole body imaging of the animal and distinguish tumor from normal tissue.Conclusion: Photoacoustic imaging is a new method in preclinical researches which can be used in various physiologic and anatomic studies. This method, because of application of non-ionizing radiation, may resolve limitation of radiation based method in diagnostic assessments.