Photorefractive detection of tissue optical and mechanical properties by ultrasound modulated optical tomography

Abstract

optical tomography is a developing hybrid imaging modality that combines high optical contrast and good ultrasonic resolution for imaging soft biological tissue. We developed a photorefractive-crystal-based, time-resolved detection scheme with the use of a millisecond long ultrasound burst to image both the optical and the mechanical properties of biological tissues, with improved detection efficiency of ultrasound-tagged photons.

Ultrasound-modulated optical tomography at new depth

“…3(a), the modulatedlight power from the same phantom as in Fig. 2(a) reached a slightly enhanced highest level during the ultrasound burst duration, and reached a second peak around 1 ms after the onset of the ultrasound burst due to the additional acoustic radiation force and shear wave effects 20,21 even though the transducer had been turned off. Within 5 to 6 ms, the second peak faded away as the shear waves propagated out of the ultrasound focus.…”

“…To image through thicker turbid media, we enlarged the ultrasonic modulation zone along the Z axis by using longer ultrasound bursts, which enhances the signal strength. 20 However, when the number of ultrasound cycles (N) was greater than 100, as shown in Fig. 3(a), the modulatedlight power from the same phantom as in Fig.…”

“…Within 5 to 6 ms, the second peak faded away as the shear waves propagated out of the ultrasound focus. This effect has been demonstrated 20,21 to be useful for sensing mechanical contrasts in additional to optical changes in turbid media. However, since the present work only focused on optical contrast detection and the shear wave propagation that was perpendicular to the ultrasound axis led to a compromised lateral spatial resolution, N ≤ 100 was preferred.…”

“…18 These detection schemes have been employed for conventional optical contrast imaging, multi-wavelength imaging, 19 mechanical contrast imaging, 20,21 quantitative measurement of optical properties, 15,22 real-time monitoring of thermal necrosis, 23 as well as assisting optical near-infrared spectroscopy 24 and diffuse optical tomography. 25 However, it remains an open question as to which detection technique is best suited for in vivo biomedical studies in terms of the SNR and the response time of the detection scheme-e.g., the time for the PRC to build up a saturated space charge field following the formation of an index grating by the signal beam and the reference beam.…”

Slow light for deep tissue imaging with ultrasound modulation

“…2 Compared to conventional ultrasound imaging, UOT images can have both optical and mechanical contrast in addition to being free of ultrasound speckle artifacts. 8 Likewise, the optical generation of ultrasound has led to powerful applications like photoacoustic spectroscopy for trace chemical detection which has multiple commercial and military uses. 9 When applied to biological imaging, this is known as photoacoustic tomography (PAT) and has shown great promise for imaging inside highly scattering tissue.…”