Ultrasound-modulated optical tomography at new depth

Abstract

Abstract. Ultrasound-modulated optical tomography (UOT) has the potential to reveal optical contrast deep inside soft biological tissues at an ultrasonically determined spatial resolution. The optical imaging depth reported so far has, however, been limited, which prevents this technique from broader applications. Our latest experimental exploration has pushed UOT to an unprecedented imaging depth. We developed and optimized a UOT system employing a photorefractive crystal-based interferometer. A large aperture optical fiber bundle was used to enhance the efficiencies for diffuse light collection and photorefractive two-wave-mixing. Within the safety limits for both laser illumination and ultrasound modulation, the system has attained the ability to image through a tissue-mimicking phantom of 9.4 cm in thickness, which has never been reached previously by UOT.

Dependence of optical scattering from Intralipid in gelatin-gel based tissue-mimicking phantoms on mixing temperature and time

“…In circumstances where a static matrix with limited water mobility or with complex sample structures is desired, hydrogels, such as gelatin gel, are preferred. [18][19][20][21][22][23] Fabrication of such hydrogel phantoms with Intralipid additive is nontrivial-the main variables being the mixing temperature and time. To mix Intralipid thoroughly with hydrogel in the liquid phase, e.g., a gelatin-water solution, the mixture has to be kept warm to prevent the hydrogel matrix from solidifying.…”

Deep tissue imaging with acousto-optical tomography and spectral hole burning with slow light effect: a theoretical study

“…They were capable of imaging 9.4 cm into a tissue phantom. 7 However, both systems operate with wavelengths outside the range for biological tissue (∼700 to 900 nm) and further development is needed for PRCs at relevant operating wavelengths. Yet, these are experimental results that show >9-cm optical imaging is possible.…”

“…However, the modulated light signal is very small compared with the background light, mainly due to the small volume of the US focus. [1][2][3][4] Despite this challenge, there have been multiple configurations of AOT systems designed to move toward in vivo imaging, such as speckle imaging, 5 heterodyne holography, 6 photorefractive crystal (PRC)-based detection, 7,8 and spectral hole burning (SHB). 9,10 Over the past 6 years, there have been mostly phantom imaging studies with very few in vivo imaging studies for AOT.…”

Lock-in camera based heterodyne holography for ultrasound-modulated optical tomography inside dynamic scattering media

“…The second type of method uses crystal based holography to convert the wavefront of a reference beam to the complex wavefront of the sample beam, so the two beams can interfere constructively on a large single-pixel detector. [16][17][18][19] This method, however, can be affected by speckle decorrelation due to scatterers' motion inside living biological tissue, since the response time of the crystal is usually much longer than the speckle correlation time ($0.1-1 ms) of living tissue. [20][21][22] Recently, Ramaz's group demonstrated the promise of Sn 2 P 2 S 6 :Te and Nd:YVO 4 crystals for UOT, because of their short response times.…”

“…These values are 1.6-1.9 times as large as the measured FWHM (¼150lm) of the 1D acoustic intensity profile, which is not uncommon and possibly due to the absorption of the tagged photons by the object when they are tagged in the vicinity of the object. 12,37 If the spans between 25% and 75% of the contrasts are used, 19 the lateral resolutions are 142lm, 163lm, and 153lm, when s c >50s,¼1ms, and¼26ls. The object width can be obtained by x 2 Àx 1 , which gives 1.51mm, 1.61mm, and 1.62mm when s c >50s,¼1ms, and¼26ls.…”