Hadatomo™ Z Photoacoustic Microscope WEL5200

The photoacoustic effect was discovered by Graham Bell in the 19th century.
In the 20th century, its applications included gas analysis instruments. With the technical innovation on laser, ultrasonic wave and PC, its applications for in-vivo imaging is being developed in the 21st century.

When pulses of light with a certain wavelength are irradiated into tissue, material with absorption characteristics to the wavelength (hemoglobin) selectively absorbs their energy and causes adiabatic expansion.
It generates thermoelastic waves, propagating within the tissue as ultrasonic waves, so they can be captured as signals, by sensors installed on the surface of the body.
The propagation time of the ultrasonic waves give accurate depth information, and they can visualize images of material distribution. Also, by using the absorbing characteristics of light, high contrast images can be obtained.

Tissue has high-scattering characteristics against light. Therefore, the optical imaging has limitations on penetration depth, because the light radiated to the tissue, and the light reflected in the tissue, are both affected by the scattering characteristics.
In contrast, on the ultrasound imaging, the irradiated light for the tissue are affected with the scattering characteristics, but the generated ultrasonic waves keep high-propagation characteristics within the tissue, achieving better penetration depth compared to the optical imaging.

Ultrasonography visualizes structure of tissue noninvasively, utilizing the hardness difference of the living tissues.
However, it is difficult to visualize blood vessels within the dermis, because hardness differences are hardly found in shallow area of tissues.
In contrast, optical imaging, such as microscopy can obtain high-resolution images, but their immersion depth is less than 1 mm. This means in the shallow area of tissues, in the range of mm to cm, there are areas where existing technology could not visualize.

Photoacoustic imaging is a novel imaging method to visualize the area of mm to cm.

Advantest has been researching and developing the photoacoustic imaging technique. In 2016, we launched Photoacoustic microscope Hadatomo™ and in 2019, we launched high-resolution version of Photoacoustic microscope, Hadatomo™ Z.
Hadatomo™ Z can use two-wavelength photoacoustic imaging and ultrasound imaging. Using the two-wavelengths (532/556 nm) photoacoustic imaging, calculation such as oxygen saturation becomes possible, and superimposing the ultrasound images and the photoacoustic images can clearly display blood vessels running within the dermis. In 2020, we developed new 2-wavelengths lasers (575/650 nm) for Hadatomo™ Z. The image obtained with the 650 nm wavelength can visualize melanin, while the image obtained with the 575 nm wavelength can visualize vascular network, so the melanin and the vascular network can be displayed separately.
The system is a valuable new research tool for dermatology researchers.

Absorption coefficient of the oxy-hemoglobin and the deoxy-hemoglobin are different in each wavelength. By utilizing the 532 + 556 nm Laser Unit, we can calculate the oxygen saturations from the measured photoacoustic signals. In contrast, absorption coefficient of melanin is as high as hemoglobin, so it is difficult to distinguish the melanin and the blood vessels.

In the wavelength of 650 nm, absorption coefficient of the hemoglobin is lower, so that selective visualization of melanin is possible. In the image obtained with the 575 nm wavelength, both melanin and blood vessels are similarly visualized. However, by calculating the difference between the signals obtained with the 650 nm and 575 nm wavelengths, blood vessels can be extracted. By superimposing both images, 3D images of the melanin and the blood vessels can be created.