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Fast optical-resolution photoacoustic microscopy using a 2-axis water-proofing MEMS scanner.

Kim JY, Lee C, Park K, Lim G, Kim C - Sci Rep (2015)

Bottom Line: We have successfully monitored the flow of carbon particles in vitro with a volumetric display frame rate of 0.14 Hz.Finally, we have successfully obtained in vivo PA images of microvasculatures in a mouse ear.It is expected that our compact and fast OR-PAM system can be significantly useful in both preclinical and clinical applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Republic of Korea.

ABSTRACT
Optical-resolution photoacoustic microscopy (OR-PAM) is a novel label-free microscopic imaging tool to provide in vivo optical absorbing contrasts. Specially, it is crucial to equip a real-time imaging capability without sacrificing high signal-to-noise ratios (SNRs) for identifying and tracking specific diseases in OR-PAM. Herein we demonstrate a 2-axis water-proofing MEMS scanner made of flexible PDMS. This flexible scanner results in a wide scanning range (9 × 4 mm(2) in a transverse plane) and a fast imaging speed (5 B-scan images per second). Further, the MEMS scanner is fabricated in a compact footprint with a size of 15 × 15 × 15 mm(3). More importantly, the scanning ability in water makes the MEMS scanner possible to confocally and simultaneously reflect both ultrasound and laser, and consequently we can maintain high SNRs. The lateral and axial resolutions of the OR-PAM system are 3.6 and 27.7 μm, respectively. We have successfully monitored the flow of carbon particles in vitro with a volumetric display frame rate of 0.14 Hz. Finally, we have successfully obtained in vivo PA images of microvasculatures in a mouse ear. It is expected that our compact and fast OR-PAM system can be significantly useful in both preclinical and clinical applications.

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Lateral and axial spatial resolutions of the 2A-WP-MEMS-OR-PAM system.(a) PA MAP image of the edge of a sharp blade. (b) ESF fitting from the experimental data across the a-a′ line in (a) and fitted LSF by the first derivative of the ESF. (c) Cross-sectional PA B-scan image of a carbon fiber. (d) LSF fitting from experimental data across the b-b′ line in (c). FWHM, full width at half maximum; MAP, maximum amplitude projection; ESF, edge spread function; and LSF, line spread function.
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f2: Lateral and axial spatial resolutions of the 2A-WP-MEMS-OR-PAM system.(a) PA MAP image of the edge of a sharp blade. (b) ESF fitting from the experimental data across the a-a′ line in (a) and fitted LSF by the first derivative of the ESF. (c) Cross-sectional PA B-scan image of a carbon fiber. (d) LSF fitting from experimental data across the b-b′ line in (c). FWHM, full width at half maximum; MAP, maximum amplitude projection; ESF, edge spread function; and LSF, line spread function.

Mentions: To test the performance of the developed 2A-WP-MEMS-OR-PAM system, the lateral and axial resolutions were measured by imaging the edge of a sharp blade and a carbon fiber with a step size of 0.5 μm as shown in Fig. 2. The edge spread function (ESF) was fitted using the maximum amplitude projection (MAP) data across the a-a′ line (Fig. 2(a)). The first derivative of the ESF creates a line spread function (LSF), and the full width at half maximum (FWHM) of the LSF was considered as the lateral resolution. The measured lateral resolution was 3.6 μm as shown in Fig. 2(b). The theoretical laser spot size is calculated as follows: , where 2W0 is the spot size, f is the focal length, λ is 532 nm, and d is the collimated beam diameter (e.g., 12 mm). Additionally, a carbon fiber with a diameter of ~6 μm was photoacoustically imaged to quantify the axial resolution as shown in Fig. 2(c). The LSF of the carbon fiber was fitted by a Gaussian function, and then the FWHM was utilized as the axial resolution. The quantified axial resolution was 27.7 μm, and the theoretical value based on the ultrasound transducer's bandwidth was 26 μm. These spatial resolutions indicate that the developed 2A-WP-MEMS-OR-PAM system is sufficient to resolve capillaries.


Fast optical-resolution photoacoustic microscopy using a 2-axis water-proofing MEMS scanner.

Kim JY, Lee C, Park K, Lim G, Kim C - Sci Rep (2015)

Lateral and axial spatial resolutions of the 2A-WP-MEMS-OR-PAM system.(a) PA MAP image of the edge of a sharp blade. (b) ESF fitting from the experimental data across the a-a′ line in (a) and fitted LSF by the first derivative of the ESF. (c) Cross-sectional PA B-scan image of a carbon fiber. (d) LSF fitting from experimental data across the b-b′ line in (c). FWHM, full width at half maximum; MAP, maximum amplitude projection; ESF, edge spread function; and LSF, line spread function.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4300456&req=5

f2: Lateral and axial spatial resolutions of the 2A-WP-MEMS-OR-PAM system.(a) PA MAP image of the edge of a sharp blade. (b) ESF fitting from the experimental data across the a-a′ line in (a) and fitted LSF by the first derivative of the ESF. (c) Cross-sectional PA B-scan image of a carbon fiber. (d) LSF fitting from experimental data across the b-b′ line in (c). FWHM, full width at half maximum; MAP, maximum amplitude projection; ESF, edge spread function; and LSF, line spread function.
Mentions: To test the performance of the developed 2A-WP-MEMS-OR-PAM system, the lateral and axial resolutions were measured by imaging the edge of a sharp blade and a carbon fiber with a step size of 0.5 μm as shown in Fig. 2. The edge spread function (ESF) was fitted using the maximum amplitude projection (MAP) data across the a-a′ line (Fig. 2(a)). The first derivative of the ESF creates a line spread function (LSF), and the full width at half maximum (FWHM) of the LSF was considered as the lateral resolution. The measured lateral resolution was 3.6 μm as shown in Fig. 2(b). The theoretical laser spot size is calculated as follows: , where 2W0 is the spot size, f is the focal length, λ is 532 nm, and d is the collimated beam diameter (e.g., 12 mm). Additionally, a carbon fiber with a diameter of ~6 μm was photoacoustically imaged to quantify the axial resolution as shown in Fig. 2(c). The LSF of the carbon fiber was fitted by a Gaussian function, and then the FWHM was utilized as the axial resolution. The quantified axial resolution was 27.7 μm, and the theoretical value based on the ultrasound transducer's bandwidth was 26 μm. These spatial resolutions indicate that the developed 2A-WP-MEMS-OR-PAM system is sufficient to resolve capillaries.

Bottom Line: We have successfully monitored the flow of carbon particles in vitro with a volumetric display frame rate of 0.14 Hz.Finally, we have successfully obtained in vivo PA images of microvasculatures in a mouse ear.It is expected that our compact and fast OR-PAM system can be significantly useful in both preclinical and clinical applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Republic of Korea.

ABSTRACT
Optical-resolution photoacoustic microscopy (OR-PAM) is a novel label-free microscopic imaging tool to provide in vivo optical absorbing contrasts. Specially, it is crucial to equip a real-time imaging capability without sacrificing high signal-to-noise ratios (SNRs) for identifying and tracking specific diseases in OR-PAM. Herein we demonstrate a 2-axis water-proofing MEMS scanner made of flexible PDMS. This flexible scanner results in a wide scanning range (9 × 4 mm(2) in a transverse plane) and a fast imaging speed (5 B-scan images per second). Further, the MEMS scanner is fabricated in a compact footprint with a size of 15 × 15 × 15 mm(3). More importantly, the scanning ability in water makes the MEMS scanner possible to confocally and simultaneously reflect both ultrasound and laser, and consequently we can maintain high SNRs. The lateral and axial resolutions of the OR-PAM system are 3.6 and 27.7 μm, respectively. We have successfully monitored the flow of carbon particles in vitro with a volumetric display frame rate of 0.14 Hz. Finally, we have successfully obtained in vivo PA images of microvasculatures in a mouse ear. It is expected that our compact and fast OR-PAM system can be significantly useful in both preclinical and clinical applications.

Show MeSH