Sel-Brian B. Colak

Clinical optical tomography and NIR spectroscopy for breast cancer detection

The results of the first set of clinical trials with the Philips optical mammography prototype system are summarized. This optical mammo prototype is designed to image the interior of the female breast with the help of near-infrared (NIR) laser light transmission measurements. This study is expected to lead to optical tomography systems for breast cancer detection. This paper presents information on the design of the optical mammo system, the clinical measurements and the imaging results from an initial group of ten patients, and discussions about ongoing research on optical tomography.

Tomographic image reconstruction from optical projections in light-diffusing media

The recent developments in light generation and detection techniques have opened new possibilities for optical medical imaging, tomography, and diagnosis at tissue penetration depths of ~10 cm. However, because light scattering and diffusion in biological tissue are rather strong, the reconstruction of object images from optical projections needs special attention. We describe a simple reconstruction method for diffuse optical imaging, based on a modified backprojection approach for medical tomography. Specifically, we have modified the standard backprojection method commonly used in x-ray tomographic imaging to include the effects of both the diffusion and the scattering of light and the associated nonlinearities in projection image formation. These modifications are based primarily on the deconvolution of the broadened image by a spatially variant point-spread function that is dependent on the scattering of light in tissue. The spatial dependence of the deconvolution and nonlinearity corrections for the curved propagating ray paths in heterogeneous tissue are handled semiempirically by coordinate transformations. We have applied this method to both theoretical and experimental projections taken by parallel- and fan-beam tomography geometries. The experimental objects were biomedical phantoms with multiple objects, including in vitro animal tissue. The overall results presented demonstrate that image-resolution improvements by nearly an order of magnitude can be obtained. We believe that the tomographic method presented here can provide a basis for rapid, real-time medical monitoring by the use of optical projections. It is expected that such optical tomography techniques can be combined with the optical tissue diagnosis methods based on spectroscopic molecular signatures to result in a versatile optical diagnosis and imaging technology.

First results from the Philips optical mammoscope

The Philips Optical Mammoscope Prototype is a versatile CW optical mammography apparatus with which fully 3D images of breast tissue can be obtained at several wavelengths. We present the properties of the machine, and show the first images obtained with it. We elaborate on the tissue parameter that can be quantitatively reconstructed from the measurements, and show some preliminary research into the natural variation of this parameter.

DETECTION LIMIT IN LOCALIZING OBJECTS HIDDEN IN A TURBID MEDIUM USING AN OPTICALLY SCANNED PHASED ARRAY

In this paper the sensitivity of a phased array and a continuous wave measurement setup are compared. Both techniques are used to image inhomogeneities hidden inside a tissuelike turbid medium. We have found that despite the higher technical complexity of the phased array measurement, its sensitivity in detecting inhomogeneities is virtually the same as the sensitivity of the continuous wave measurement.

Optical image reconstruction with deconvolution in light diffusing media

We describe a simple reconstruction method for diffuse optical imaging based on modified back-projection approach for medical tomography. These modifications are based primarily on the deconvolution of the broadened image by a point spread function which is dependent on the scattering of light in tissue. The nonlinearities in the image formation are handled empirically by coordinate transformations. Although our method is an approximate image reconstruction technique, it may provide a basis for rapid, real time medical monitoring by using optical projections. We have applied this method to experimental projections taken by parallel and fan beam tomography geometries on biomedical phantoms with multiple objects. The results presented in this report indicate considerable improvement in image resolution.

Breast imaging using optical tomography

Due to its nonionizing nature, optical mammography could be a very attractive alternative to X-ray screening. The authors have developed a cw optical tomography apparatus with which three-dimensional images of breasts can be obtained in vivo, and it is now being used for clinical research in the Academic Hospital in Maastricht. It measures the attenuation coefficient of breast tissue. The magnitude of the reduced scattering coefficient in breast tissue is approximately 1 mm/sup -1/ and varies less than the absorption coefficient. The subject has to lie down on the machine and let one of her breasts hang freely in a cup containing a fluid. The fluid matches the mean optical properties of the breast, and is kept at approximately 31 /spl deg/C for comfort. The cup has a conical shape with a maximum diameter of 130 mm. On the boundary of the cup 255 optical fibers are mounted that lead to one detector each. Interleaved, 255 fibers are mounted that can be selected sequentially to receive the light of one of three diode lasers that are operating at different wavelengths, namely 658 nm, 786 nm, and 919 nm. All detectors measure simultaneously.

Resolution and sensitivity limits of optical imaging in highly scattering media

Using photon-density-waves (PDW), (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 650 MHz. 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 PDW shows a much stronger attenuation as compared to the cw light intensity. The implications of the lower signal-to-noise 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 PDW as compared to cw light. Therefore, we find no clear advantage of PDW over cw light for obtaining sharper tomographic images of the diffuse media, regardless of the inverse scattering method used.

Spectral space-time coding for multimode fiber communications

We describe how the data carrying capacity of a multimode fiber can be increased by spectrally modulated space-time encoding of its spatial mode structure. The operation of such an optical communication system is demonstrated by experiments and simulations.