<title>Resolution and sensitivity limits of optical imaging in highly scattering media</title>

Abstract

Using Photon-Density-Waves (PWD), (multiple) objects embedded in a highly scattering medium with optical properties similar to tissue are detected. The measurements were performed with near-infra-red laser light at 675 nm which was either kept continuous-wave (CW) or amplitude modulated (AM) at 219 MHz or 650MHz. We find that the spatial resolution of the projection image shows only slight improvements as the frequency is increased. This improvement comes at the expense of signal strength in the modulated part of the light. That is, the PWD shows a much stronger attenuation as compared to the CW light intensity. The implications of the lower signal-tonoise ratio at high modulation frequencies is that the modulated light projections are less suitable for further data processing. For a given data acquisition system, this fact cancels the advantages of the higher raw resolution of PWD as compared to CW light. Therefore, we find no clear advantage of PWD over CW light for obtaining sharper tomographic images of the diffuse media, regardless of the inverse scattering method used.

Optical imaging in medicine: I. Experimental techniques

“…However, the specifications of the system and the results of clinical trials have not been widely published at this time. Investigators at Philips Research Laboratories in The Netherlands are also known to be interested in the commercial possibilities of frequency domain systems, and have published results of preliminary experiments (Papaioannou et al 1995).…”

Tomographic image reconstruction from optical projections in light-diffusing media

“…32 These improvements are primarily due to the attenuation of these waves in diffuse media, which is stronger than the attenuation coefficient of the cw wave at the same fundamental optical wavelength. 33 Obviously similar enhancements in sharpness can also be achieved with an optical wavelength located at a stronger attenuation region for the diffuse media. Both of these latter methods, however, come at the expense of a low transmitted signal-tonoise ratio because of the high attenuation coefficient.…”

“…Both of these latter methods, however, come at the expense of a low transmitted signal-tonoise ratio because of the high attenuation coefficient. 33 All the experimental techniques for improving the projection image described above come at the expense of low transmitted signals. Therefore, after a limit, the sharpness of the images is compromised by the noise in the image.…”

“…F͓PSF͑s, ͔͒ ͮ d, (33) where PSF͑s, ͒ is the projection of the PSF. For the present example, it always has the same shape, regardless of the angle of the projection.…”

Development of a time‐resolved optical tomography system for neonatal brain imaging

“…The company reports a significant improvement as compared to conventional continuous intensity laser transillumination mammography systems, and evaluation of the system is continued by Dr. E. Gratton's research group at the University of Illinois (Urbana-Champaign) [Fantini 1996]. In the meantime in Holland, Philips (Eindhoven) have developed and evaluated frequency-domain [Papaioannou 1995] and continuous intensity [Colak 1997] mammography systems. The latter consists of a large number of sources and detectors arranged in a cone shape.…”