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

Abstract

Ultrasound-modulated optical tomography (UOT) images optical contrast deep inside scattering media. Heterodyne holography based UOT is a promising technique that uses a camera for parallel speckle detection. In previous works, the speed of data acquisition was limited by the low frame rates of conventional cameras. In addition, when the signal-to-background ratio was low, these cameras wasted most of their bits representing an informationless background, resulting in extremely low efficiencies in the use of bits. Here, using a lock-in camera, we increase the bit efficiency and reduce the data transfer load by digitizing only the signal after rejecting the background. Moreover, compared with the conventional four-frame based amplitude measurement method, our single-frame method is more immune to speckle decorrelation. Using lock-in camera based UOT with an integration time of 286 ls, we imaged an absorptive object buried inside a dynamic scattering medium exhibiting a speckle correlation time (s c ) as short as 26 ls. Since our method can tolerate speckle decorrelation faster than that found in living biological tissue

Focusing light inside dynamic scattering media with millisecond digital optical phase conjugation

“…Then, we calculated the correlation coefficients between the first and each of the ensuing frames of the recorded speckle patterns. By fitting the correlation coefficient R I versus time, using $R_{\mathrm{normalI}}(t)=exp(-2t^2/{\tau }_{\mathrm{normalc}}^2)$ [15,54,56], we obtained the speckle correlation time τ c , defined as the time during which the correlation coefficient decreases to 1/e 2 (= 13.5%) at a given tissue movement speed. As an example, Fig.…”

“…edge 4.2, we can reduce the exposure time to 0.1 ms while roughly maintaining the frame rate. This change can reduce the system runtime by ~0.4 ms. For TRUE focusing, since the signal is often buried in a large background, it is ideal to use a lock-in camera to digitize only the signal after rejecting the background [24,54,57]. We have used a commercial lock-in camera to measure the wavefront in TRUE focusing within 0.3 ms, but the data transfer of this camera takes longer than 10 ms, limited by the low data transfer speed of USB 2.0 [24].…”

“…Since the speckle correlation time is inversely proportional to the tissue movement speed [15,54], in our experiments, we moved the tissue at different speeds to control the speckle correlation time observed on the phase conjugate mirror. This moving sample strategy has been used in previous works [14,15,23,36,38,53–55]; however, it cannot be excluded that the decorrelation caused by a moving scattering medium is subtly different from the decorrelation caused by living biological tissue or other dynamic scattering media such as fog and turbid water.…”

Acousto optic imaging beyond the acoustic diffraction limit using speckle decorrelation

“…Thus the current acquisition time, composed of 24 phase-shifting images per measurement, was 2 seconds per realization, excluding diffuser rotation and data processing. The acquisition time can be shortened by orders of magnitude using faster detection approaches, such as lock-in camera detection [27], and fast cameras [28]. Another approach for improved acquisition time is using an ultra-fast plane-wave AOT approach [25], based on nonlinear crystals.…”

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

“…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.…”