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The magnetic resonance absorption spectrum, T1 and T2 relaxation time distributions, and magnetization transfer properties of ex vivo breast tissue have been characterized at 1.5 T and 37 degrees C. The fraction of fibroglandular tissue within individual tissue samples (n = 31) was inferred from the tissue volumetric water content obtained by integration of resolvable broad-line fat and water resonances. The spectroscopically estimated water content was strongly correlated with that extracted enzymatically (Pearson correlation coefficient 0.98, P < < 0.01), which enabled the assignment of principal relaxation components for fibroglandular tissue (T2=0.04+/-0.01, T1=1.33+/-0.24 s), and for adipose tissue (T2=0.13+/-0.01, T1=0.23+/-0.01 s, and T2=0.38+/-0.03, T1=0.62+/-0.16 s). Th e relaxation components for fibroglandular tissue exhibited strong magnetization transfer, whereas those for adipose tissue showed little magnetization transfer effect. These results ultimately have applicability to the optimization of clinical magnetic resonance imaging and research investigations of the breast.

Photonics Research Ontario (PRO) is an Ontario Provincial Center of Excellence supporting a broad range of laserprocessing activities within its photonics program. These activities are centered at the University of Toronto, and split between an industrial-user facility and the individual research programs of principal investigators. The combined effort furnishes forefront laser systems and advanced optical tools to explore novel processing applications in photonic, biomedical, and microelectronic areas. Facilities include laser micromachining stations, excimer-based mask-projection stations, extremely short wavelength lasers such as the molecular fluorine laser (157 nm), and ultrafast laser systems (100 fs -1 ps). The latter two advanced lasers offer interesting advantages and contrasts in processing 'difficult' materials through linear and nonlinear absorption processes, respectively. These laser systems provide fine precision and strong interaction with a wide range of materials, including 'transparent' glasses, and also ceramics and metals. Applications fall broadly into several areas: wafer-level circuit trimming (electronics), high-resolution ultrasonic transducers (biomedical devices), and the shaping of optical waveguides and Bragg-gratings for photonic components (telecommunications). This paper summarizes the laserprocessing infrastructure and research activities at PRO.

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