Images of diffraction of sound2/10/2024 ![]() ![]() Therefore, higher frequencies achieve higher imaging resolution, albeit at reduced penetration depths. A 50-MHz wave will undergo the same attenuation through a depth of 1 cm. For example, a 5-MHz acoustic wave propagating through a depth of 10 cm will undergo attenuation of ~25 dB. Therefore, deeper imaging involves narrower bandwidths and lower frequencies than more superficial imaging. The desired frequency response depends on the intended application, because ultrasound waves propagating in tissue undergo frequency-dependent attenuation on the order of ~0.5 dB per MHz per cm 8. For example, optoacoustic tomography of absorbers between 10 and 300 µm in size requires a detector with frequency responses from a few MHz to >150 MHz 7. To detect optoacoustic signals from absorbers ranging widely in size down to the micron scale, sensors must have central frequencies as well as bandwidths on the order of hundreds of MHz 6. ![]() These two parameters are critical for the resolution and size range of structures that can be detected in optoacoustic imaging. Four key performance parameters of ultrasound detectors are given below. In addition, optoacoustic imaging utilizes tomographic principles that generally require collection of data over wide acceptance angles (projections), which improves image quality and resolution as well as minimizes image artifacts. Optoacoustic signals collected in vivo can be up to three orders of magnitude weaker than the signals detected in medical ultrasound imaging because contrary to ultrasonography, optoacoustic signal generation occurs within the interrogated medium and is limited by the maximum light dose legally permissible for tissue illumination. While ultrasound image formation operates over a relatively narrow frequency band (typically 50% of the central frequency), optoacoustic signal generation based on ultra-short laser pulses is broadband and can span frequencies from sub-MHz to hundreds of MHz. Optoacoustic imaging defines new challenges for ultrasound detection compared to ultrasonography 1, 2, 3, 4, 5. We also review application areas that are enabled by all-optical sound detectors, including interventional imaging, non-contact measurements, magnetoacoustics, and non-destructive testing. In this review, we categorize different methods of optical ultrasound detection and discuss key technology trends geared towards the development of all-optical optoacoustic systems. Additionally, optical sensing of sound is less sensitive to electromagnetic noise, making it appropriate for a greater spectrum of environments. All-optical sound detectors yield a higher signal-to-noise ratio per unit area than piezoelectric detectors and feature wide detection bandwidths that may be more appropriate for optoacoustic applications, enabling several biomedical or industrial applications. Consequently, interest has shifted to utilizing entirely optical methods for measuring optoacoustic waves. However, the detection requirements of optoacoustic sensing and imaging differ from those of conventional ultrasonography and lead to specifications not sufficiently addressed by piezoelectric detectors. Originally developed for diagnostic ultrasound imaging, piezoelectric transducers are the most widespread technology employed in optoacoustic (photoacoustic) signal detection. ![]()
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |