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.

Introduction: After caries, periodontal tissue inflammation (periodontitis) is the most common oral health problem. Photoacoustic imaging (PAI) is a new technique that uses simple components such as a diode laser and a condenser microphone. This study aimed to evaluate the performance of a simple PAI system in periodontal disease imaging by using an animal model. Methods: Normal periodontal and periodontitis tissues were obtained from Sprague–, Dawley rats categorized as the control group, treatment group 1 (7 days of periodontitis induction), treatment group 2 (11 days of periodontitis induction), and treatment group 3 (14 days of periodontitis induction). The PAI system was controlled by LabVIEW and Arduino IDE software from a personal computer. Results: Results revealed that the optimal frequency of laser modulation for periodontal tissue imaging was 19 kHz with a duty cycle of 50%. The photoacoustic (PA) intensity of periodontal tissues was −, 68. 71 dB for treatment group 3, −, 70. 34 dB for treatment group 2, −, 71. 69 dB for treatment group 1, and −, 73. 07 dB for the control group. PA image analysis showed that the PA intensity from periodontal disease groups was higher than the control group. Conclusion: This study indicates the feasibility of using a simple PAI system to differentiate normal periodontal tissues from periodontitis tissues.

Purpose: A Photoacoustic Imaging (PAI) as a non-invasive hybrid imaging modality has the potential to be used in a wide range of pre-clinical and clinical applications. There are different optical excitation sources that affect the performance of PAI systems. Our goal is proving the capability of the Light-Emitting Diode (LED) based PAI system for imaging of objects in different depths. Materials and Methods: In this study the Full Width of Half Maximum (FWHM) and Contrast to Noise Ratio (CNR) of LED-based PAI system is evaluated using agar, and Poly-Vinyl Alcohol Cryogel (PVA-C) phantoms. Results: The results show that axial and lateral FWHM of the photoacoustic image in agar phantom 1%, are 0. 59 and 1. 16 mm, respectively. It is capable of distinguishing objects about 250 μ m. Furthermore, one of the main improvements of photoacoustic images is achieved by proposed LED-based system that is a 26% higher CNR versus the ultrasound images. Conclusion: Therefore, the provided technical characteristics in this study have made designed LED-based PAI system as a suitable tool for preclinical and clinical imaging.

Introduction: Pulsed photoacoustic imaging with wideband medical application is a technique in which the absorption of optieal pulse in chromophores produces ultrasonic thermoelastic waves. The waves are detected by an ultrasonic transducer at the surface of the tissue. The transducer with adequate resolution and acoustic sensitivity provides molecular imaging of superficial tissue structures such as the microvessels and skin. In this article, the sensitivity of the optical detection systems were measured in comparison with that of the calibrated hydrophone under the same experimental conditions. Material and Methods: A continuous Nd: YAG laser, a pulsed Nd: YAG laser, an optical stress detection system, a Fabry Perot detection system, a needle hydrophone, a fast-photodiode and a 500 MHz digital oscilloscope were used. Laser pulses (energy = 10 mJ, pulsewidth = 6 ns) were delivered via an optical fiber (600 mm) into an aqueous solution of Indocyanine Green (ICG). The pulses absorbed in the solution, and then acoustic waves produced and received by ultrasonic transducer at the surface of the tissue. The other side of the transducer was illuminated by the continuous laser at the wavelength of 532 nm .The modulated optical beam was detected by the photodiode and the digital oscilloscope. Therefore, a photoacoustic signal was observed as a bipolar signal on the oscilloscope monitor.The sensitivity of the of the optical stress transducer was measured in comparison with a Fabry Perot detection system and a needle hydrophone by measuring a signal to noise ratio (SNR) and a noise equivalent pressures (NEP).Results: The SNR of hydrophone, optical stress transducer and Fabry Perot were 56dB, 45 dB and 26 dB respectively. NEP of hydrophone, Fabry Perot detection system and optical stress detection system were 11 kPa, 13 kPa and 15 kPa, respectively. So NEP of Fabry Perot was 2 kPa higher than that of the Optical stress detection system.Discussion: NEP of Fabry Perot is higher that of the optical stress detection system. Because the bandwidth of the Fabry Perot was 8 MHz higher than that of the optical stresses detection system. Conclusion: The combination of high sensitivity and the small active area makes the optical stress system particularly suitable for photoacoustic imaging applications.