Analysis of the potential for non-invasive imaging of oxygenation at heart depth, using ultrasound optical tomography (UOT) or photo-acoustic tomography (PAT)

Abstract

Despite the important medical implications, it is currently an open task to find optical non-invasive techniques that can image deep organs in humans. Addressing this, photo-acoustic tomography (PAT) has received a great deal of attention in the past decade, owing to favorable properties like high contrast and high spatial resolution. However, even with optimal components PAT cannot penetrate beyond a few centimeters, which still presents an important limitation of the technique. Here, we calculate the absorption contrast levels for PAT and for ultrasound optical tomography (UOT) and compare them to their relevant noise sources as a function of imaging depth. The results indicate that a new development in optical filters, based on rare-earth-ion crystals, can push the UOT technique significantly ahead of PAT. Such filters allow the contrastto-noise ratio for UOT to be up to three orders of magnitude better than for PAT at depths of a few cm into the tissue. It also translates into a significant increase of the image depth of UOT compared to PAT, enabling deep organs to be imaged in humans in real time. Furthermore, such spectral holeburning filters are not sensitive to speckle decorrelation from the tissue and can operate at nearly any angle of incident light, allowing good light collection. We theoretically demonstrate the improved performance in the medically important case of non-invasive optical imaging of the oxygenation level of the frontal part of the human myocardial tissue. Our results indicate that further studies on UOT are of interest and that the technique may have large impact on future directions of biomedical optics.

Efficient optical pumping using hyperfine levels in 145Nd3+:Y2SiO5 and its application to optical storage

“…spectral hole burning) as a necessary preparation step in various applications, such as optical quantum memories [1][2][3][4], spectrum radio-frequency analysers [5,6], and narrow spectral filters for biological imaging [7,8]. For the latter application, there is a special interest in materials such as YSO doped with neodymium and thulium [9]. Common to all these techniques is the need for creating narrow and deep spectral holes in the inhomogeneously broadened optical transition.…”

“…Such background absorptions would not allow very efficient (50% or above) quantum memories based on cavity enhancement [23,24], as demonstrated in praseodymium and europium doped materials [25,26]. Also, there is an interest in using the 883 nm resonance in Nd 3+ :Y 2 SiO 5 crystal for biological imaging [9], but spectral filtering with high dynamic range requires a lower residual absorption. Hence, further application of Nd 3+ -doped materials in these research areas would greatly benefit from longer spectral hole lifetimes.…”

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

“…In reflectance geometries, our results are very similar to the CNR values calculated using the DA. 14 We first compare our model with our previous study 14 to note any differences between the two models. First, there is a slight difference at shallow depths (<2 cm).…”

“…This study follows the work of Walther et al, 14 in which simulations are setup to determine if AOT can be used to image the heart through muscle tissue. However, the DA was substituted for fluence maps from MC simulations.…”

Ultrasound-modulated optical tomography in scattering media: flux filtering based on persistent spectral hole burning in the optical diagnosis window

“…This results in the creation of ultrasonically tagged photons shifted from the carrier frequency fL by ±fUS [3] [see Figure 1(a)]. By filtering these tagged photons, we retrieve a signal proportional to the local optical irradiance along the US path, with the spatial resolution of the US [4]. The ratio of tagged photons to the total number of photons lies between 10 -3 and 10 -4 with short bursts [5].Two parameters are critical for imaging applications.…”