The most recent statistics on cancer reported by NIH Publication NO.89- 2789 stated that breast cancer has the highest incidence rate and mortality rate in the US. X-ray mammography is the most common medical diagnostic tool to quantitatively diagnose breast problems. Due to the possibility of danger from ionized x-ray radiation, the difficulty to detect small growths on one mm size in the early stages of cancer; and the inablity to determine whether the growth is benign or malignant, a safe non-ionized visible and/or near infrared optical imaging system for optical mammography with mm spatial resolution is needed. Picosecond Optical Kerr gate is a well-known ultrafst time gated imaging technique. Based on our results of ultrashort laser pulse imaging and ballistic photon migration process, we propose to ectend our preliminary research of 3-D picosecond Kerr imaging to design and test the multi-stage picosecond Kerr imaging technique with improved sensitivity and sub- millimeter spatial resolution for the future optical mammography. Based on the earliest time-of-flight arrival of photons, the gated ballistic image part (a fraction of incident photone with the shortest travel times through a turbid medium) can be used to construct an undistorted image. However, in the ballistic imaging of a turbid medium such as the breast, the delayed diffusive component may be 10(6) times greater than the ballistic component. A multi-stage Kerr gate will be needed to remove the diffusive delayed noise. The transmitted signal through a single Kerr gate is about 10% of its leakage noise is about 10-4. A four-stage Kerr gate has the potential to remove a factor of 10(16) of the diffusive noise or delayed noise with an overall transmitted siganl to noise ratio up to 10(12) for imaging. Furthermore, beside the advantage of removing the long tail pulse component, the temporal resolution can be improved through the adjustment ofthe time delay between gated pulses. This approach greatly improves the conventional transillumination method. In this project, multi-stage Kerr gates will be designed and tested and the signal to noise will be measured. Spatial and temporal resolutions of these gates will be compared and image reconstruction program will be initiated. The outcome of this research will show the direction, feasibility and limitation of multi-stage time-gated imaging for the future in-vivo breast cancer diagnosis.
