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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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(a) Fabricated 2-axis water-proofing MEMS scanner. (b) Scheme of torsional motions along the X and Y axes, respectively. Red color indicates the electromagnetically stimulated NMs while the resting NMs are indicated by yellow color. (c) Schematic of the 2A-WP-MEMS-OR-PAM system. NM, neodymium magnet; AM, aluminum mirror; COM, computer; PD, photodiode; BS, beam splitter; AMP, amplifier; UT, ultrasound transducer; CL, condenser lens; PH, pin hole; OL, objective lens; BC, beam combiner; AL, acoustic lens; MS, MEMS scanner; and SM, sample. Author J.Y.K created the figure.
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f1: (a) Fabricated 2-axis water-proofing MEMS scanner. (b) Scheme of torsional motions along the X and Y axes, respectively. Red color indicates the electromagnetically stimulated NMs while the resting NMs are indicated by yellow color. (c) Schematic of the 2A-WP-MEMS-OR-PAM system. NM, neodymium magnet; AM, aluminum mirror; COM, computer; PD, photodiode; BS, beam splitter; AMP, amplifier; UT, ultrasound transducer; CL, condenser lens; PH, pin hole; OL, objective lens; BC, beam combiner; AL, acoustic lens; MS, MEMS scanner; and SM, sample. Author J.Y.K created the figure.

Mentions: Fig. 1(a) shows the photograph of the 2-axis water-proofing MEMS scanner. A 2-axis MEMS scanner consists of a movable layer of PDMS and fixed housing of electromagnets. An aluminum coated mirror, which significantly reflects both light and ultrasound, is torsionally actuated by controlled electromagnetic forces. This electromagnetic force is induced by four pairs of Neodymium permanent magnets and homemade electromagnets. The resonance frequencies of the fabricated 2-axis MEMS scanner in water were measured 50 and 30 Hz along the X and Y axes, respectively. The scanning property of the MEMS scanner is mainly characterized by a frequency and amplitude of a driving voltage. Due to the low stiffness of PDMS, the required driving voltage can be reduced. The strong resistance and hydrophobicity of PDMS itself provides a water-proofing property to prevent electrical short by water leaking20. In addition, the gimbaled structure of the only one PDMS layer could avoid mechanical coupling between two axes as shown in Fig. 1(b), and thus help to improve the scanning accuracy and linearity. The size of the fabricated 2-axis MEMS scanner is 15 × 15 × 15 mm3 along the X, Y and Z axes, respectively. Fig. 1(c) shows a schematic diagram of the 2A-WP-MEMS-OR-PAM system. The collimated laser beam is confocally aligned with the ultrasound focus through the opto-ultrasound beam combiner in front of an ultrasonic transducer to maximize the SNRs. When two AC driving signals are applied to the 2-axis MEMS scanner, coaxially-aligned light beam and photoacoustic (PA) waves scan the sample surface along the X-Y plane. The generated PA signals are amplified with a 50 dB gain and finally converted into PA images via Hilbert transformation.


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)

(a) Fabricated 2-axis water-proofing MEMS scanner. (b) Scheme of torsional motions along the X and Y axes, respectively. Red color indicates the electromagnetically stimulated NMs while the resting NMs are indicated by yellow color. (c) Schematic of the 2A-WP-MEMS-OR-PAM system. NM, neodymium magnet; AM, aluminum mirror; COM, computer; PD, photodiode; BS, beam splitter; AMP, amplifier; UT, ultrasound transducer; CL, condenser lens; PH, pin hole; OL, objective lens; BC, beam combiner; AL, acoustic lens; MS, MEMS scanner; and SM, sample. Author J.Y.K created the figure.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: (a) Fabricated 2-axis water-proofing MEMS scanner. (b) Scheme of torsional motions along the X and Y axes, respectively. Red color indicates the electromagnetically stimulated NMs while the resting NMs are indicated by yellow color. (c) Schematic of the 2A-WP-MEMS-OR-PAM system. NM, neodymium magnet; AM, aluminum mirror; COM, computer; PD, photodiode; BS, beam splitter; AMP, amplifier; UT, ultrasound transducer; CL, condenser lens; PH, pin hole; OL, objective lens; BC, beam combiner; AL, acoustic lens; MS, MEMS scanner; and SM, sample. Author J.Y.K created the figure.
Mentions: Fig. 1(a) shows the photograph of the 2-axis water-proofing MEMS scanner. A 2-axis MEMS scanner consists of a movable layer of PDMS and fixed housing of electromagnets. An aluminum coated mirror, which significantly reflects both light and ultrasound, is torsionally actuated by controlled electromagnetic forces. This electromagnetic force is induced by four pairs of Neodymium permanent magnets and homemade electromagnets. The resonance frequencies of the fabricated 2-axis MEMS scanner in water were measured 50 and 30 Hz along the X and Y axes, respectively. The scanning property of the MEMS scanner is mainly characterized by a frequency and amplitude of a driving voltage. Due to the low stiffness of PDMS, the required driving voltage can be reduced. The strong resistance and hydrophobicity of PDMS itself provides a water-proofing property to prevent electrical short by water leaking20. In addition, the gimbaled structure of the only one PDMS layer could avoid mechanical coupling between two axes as shown in Fig. 1(b), and thus help to improve the scanning accuracy and linearity. The size of the fabricated 2-axis MEMS scanner is 15 × 15 × 15 mm3 along the X, Y and Z axes, respectively. Fig. 1(c) shows a schematic diagram of the 2A-WP-MEMS-OR-PAM system. The collimated laser beam is confocally aligned with the ultrasound focus through the opto-ultrasound beam combiner in front of an ultrasonic transducer to maximize the SNRs. When two AC driving signals are applied to the 2-axis MEMS scanner, coaxially-aligned light beam and photoacoustic (PA) waves scan the sample surface along the X-Y plane. The generated PA signals are amplified with a 50 dB gain and finally converted into PA images via Hilbert transformation.

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