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Breaking the spatial resolution barrier via iterative sound-light interaction in deep tissue microscopy.

Si K, Fiolka R, Cui M - Sci Rep (2012)

Bottom Line: Random scattering causes the ballistic focus, which is conventionally used for image formation, to decay exponentially with depth.Optical imaging beyond the ballistic regime has been demonstrated by hybrid techniques that combine light with the deeper penetration capability of sound waves.This development opens up practical high resolution fluorescence imaging in deep tissues.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Janelia Farm Research Campus, 19700 Helix Drive, Ashburn, Virginia 20147, USA.

ABSTRACT
Optical microscopy has so far been restricted to superficial layers, leaving many important biological questions unanswered. Random scattering causes the ballistic focus, which is conventionally used for image formation, to decay exponentially with depth. Optical imaging beyond the ballistic regime has been demonstrated by hybrid techniques that combine light with the deeper penetration capability of sound waves. Deep inside highly scattering media, the sound focus dimensions restrict the imaging resolutions. Here we show that by iteratively focusing light into an ultrasound focus via phase conjugation, we can fundamentally overcome this resolution barrier in deep tissues and at the same time increase the focus to background ratio. We demonstrate fluorescence microscopy beyond the ballistic regime of light with a threefold improved resolution and a fivefold increase in contrast. This development opens up practical high resolution fluorescence imaging in deep tissues.

No MeSH data available.


Related in: MedlinePlus

(a–d) Schematic illustration of the iterative focus improvement.(a) The initial incident light field (purple) propagates to the ultrasound focus (yellow circle). A simulated speckle pattern at the sound focus (location marked with the white arrows) is shown in the right inset. A small portion of the input light is frequency shifted (green). (b) In the first DOPC iteration, the green light field is time-reversed and is re-focused into the ultrasound focus, resulting in a more confined sound light interaction (right inset). A portion of the light is frequency shifted (purple). (c) The purple light field is time reversed and is re-focused into the ultrasound zone, further shrinking the sound-light interaction zone. (d) After nine iterations, the time-reversed purple light field results in a much improved focus. (e) Experimental setup; PO, Pockels cell; I, Isolator; BS, beam splitter; AOM, acousto-optical modulator; ND, neutral density filter, BB, beam block; DL, delay line; BE, beam expander; P, polarizer; BP, bandpass filter; L1, f = 35 mm lens; L2, f = 50 mm lens; D, fluorescence detector. Scalebar: 10 microns.
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f1: (a–d) Schematic illustration of the iterative focus improvement.(a) The initial incident light field (purple) propagates to the ultrasound focus (yellow circle). A simulated speckle pattern at the sound focus (location marked with the white arrows) is shown in the right inset. A small portion of the input light is frequency shifted (green). (b) In the first DOPC iteration, the green light field is time-reversed and is re-focused into the ultrasound focus, resulting in a more confined sound light interaction (right inset). A portion of the light is frequency shifted (purple). (c) The purple light field is time reversed and is re-focused into the ultrasound zone, further shrinking the sound-light interaction zone. (d) After nine iterations, the time-reversed purple light field results in a much improved focus. (e) Experimental setup; PO, Pockels cell; I, Isolator; BS, beam splitter; AOM, acousto-optical modulator; ND, neutral density filter, BB, beam block; DL, delay line; BE, beam expander; P, polarizer; BP, bandpass filter; L1, f = 35 mm lens; L2, f = 50 mm lens; D, fluorescence detector. Scalebar: 10 microns.

Mentions: Let us assume that the transverse profile of the sound modulation zone and hence the phase conjugation beam at the sound focus is defined as and that we employ two digital optical phase conjugation (DOPC) systems28, DOPC1 and DOPC2. DOPC1 first illuminates the sample and the sound modulated light is recorded by DOPC2, which is schematically shown in Fig. 1 a. DOPC2 then generates a phase conjugation beam that focuses back to the sound focus (Fig. 1 b). Different from the first illumination, the DOPC2 beam has a focused light distribution at the sound focus. Therefore the emerging sound modulated light has a new spatial profile . If we let the two DOPC systems take turns to illuminate the sample and to record the sound modulated light, we can achieve a focus profile , where N is the iteration number (Fig. 1 c–d ).


Breaking the spatial resolution barrier via iterative sound-light interaction in deep tissue microscopy.

Si K, Fiolka R, Cui M - Sci Rep (2012)

(a–d) Schematic illustration of the iterative focus improvement.(a) The initial incident light field (purple) propagates to the ultrasound focus (yellow circle). A simulated speckle pattern at the sound focus (location marked with the white arrows) is shown in the right inset. A small portion of the input light is frequency shifted (green). (b) In the first DOPC iteration, the green light field is time-reversed and is re-focused into the ultrasound focus, resulting in a more confined sound light interaction (right inset). A portion of the light is frequency shifted (purple). (c) The purple light field is time reversed and is re-focused into the ultrasound zone, further shrinking the sound-light interaction zone. (d) After nine iterations, the time-reversed purple light field results in a much improved focus. (e) Experimental setup; PO, Pockels cell; I, Isolator; BS, beam splitter; AOM, acousto-optical modulator; ND, neutral density filter, BB, beam block; DL, delay line; BE, beam expander; P, polarizer; BP, bandpass filter; L1, f = 35 mm lens; L2, f = 50 mm lens; D, fluorescence detector. Scalebar: 10 microns.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3475990&req=5

f1: (a–d) Schematic illustration of the iterative focus improvement.(a) The initial incident light field (purple) propagates to the ultrasound focus (yellow circle). A simulated speckle pattern at the sound focus (location marked with the white arrows) is shown in the right inset. A small portion of the input light is frequency shifted (green). (b) In the first DOPC iteration, the green light field is time-reversed and is re-focused into the ultrasound focus, resulting in a more confined sound light interaction (right inset). A portion of the light is frequency shifted (purple). (c) The purple light field is time reversed and is re-focused into the ultrasound zone, further shrinking the sound-light interaction zone. (d) After nine iterations, the time-reversed purple light field results in a much improved focus. (e) Experimental setup; PO, Pockels cell; I, Isolator; BS, beam splitter; AOM, acousto-optical modulator; ND, neutral density filter, BB, beam block; DL, delay line; BE, beam expander; P, polarizer; BP, bandpass filter; L1, f = 35 mm lens; L2, f = 50 mm lens; D, fluorescence detector. Scalebar: 10 microns.
Mentions: Let us assume that the transverse profile of the sound modulation zone and hence the phase conjugation beam at the sound focus is defined as and that we employ two digital optical phase conjugation (DOPC) systems28, DOPC1 and DOPC2. DOPC1 first illuminates the sample and the sound modulated light is recorded by DOPC2, which is schematically shown in Fig. 1 a. DOPC2 then generates a phase conjugation beam that focuses back to the sound focus (Fig. 1 b). Different from the first illumination, the DOPC2 beam has a focused light distribution at the sound focus. Therefore the emerging sound modulated light has a new spatial profile . If we let the two DOPC systems take turns to illuminate the sample and to record the sound modulated light, we can achieve a focus profile , where N is the iteration number (Fig. 1 c–d ).

Bottom Line: Random scattering causes the ballistic focus, which is conventionally used for image formation, to decay exponentially with depth.Optical imaging beyond the ballistic regime has been demonstrated by hybrid techniques that combine light with the deeper penetration capability of sound waves.This development opens up practical high resolution fluorescence imaging in deep tissues.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Janelia Farm Research Campus, 19700 Helix Drive, Ashburn, Virginia 20147, USA.

ABSTRACT
Optical microscopy has so far been restricted to superficial layers, leaving many important biological questions unanswered. Random scattering causes the ballistic focus, which is conventionally used for image formation, to decay exponentially with depth. Optical imaging beyond the ballistic regime has been demonstrated by hybrid techniques that combine light with the deeper penetration capability of sound waves. Deep inside highly scattering media, the sound focus dimensions restrict the imaging resolutions. Here we show that by iteratively focusing light into an ultrasound focus via phase conjugation, we can fundamentally overcome this resolution barrier in deep tissues and at the same time increase the focus to background ratio. We demonstrate fluorescence microscopy beyond the ballistic regime of light with a threefold improved resolution and a fivefold increase in contrast. This development opens up practical high resolution fluorescence imaging in deep tissues.

No MeSH data available.


Related in: MedlinePlus