Int J Thermophys (2013) 34:1481–1488 DOI 10.1007/s10765-013-1399-x Ultra-Deep Bone Diagnostics with Fat–Skin Overlayers Using New Pulsed Photothermal Radar K. Sreekumar · A. Mandelis Received: 31 January 2012 / Accepted: 15 January 2013 / Published online: 31 January 2013 © Springer Science+Business Media New York 2013 Abstract The constraints imposed by the laser safety (maximum permissible expo- sure) ceiling on pump laser energy and the strong attenuation of thermal-wave signals in tissues significantly limit the photothermally active depth in most biological spec- imens to a level which is normally insufficient for practical applications (a few mm below the skin surface). A theoretical approach for improvement of the signal-to-noise ratio (SNR), minimizing the static (dc) component of the photothermal (PT) signal and making use of the PT radiometric nonlinearity has been introduced. At low fre- quencies fixed-pulse-width chirps of large peak power were found to be superior to all other equal energy modalities, with an SNR improvement by up to two orders of mag- nitude. Compared to radar peak delay and amplitude, the long-delayed radar output amplitude is found to be more sensitive to subsurface conditions. Two-dimensional spatial plots of this parameter depicting the back-surface conditions of bones with and without fat tissue overlayers are presented. Pulsed-chirp radar thermography has been demonstrated to monitor the degree of demineralization in goat rib bone with a substantial SNR and spatial resolution that is not practicable with harmonic radars of the same energy density. Keywords Bone demineralization · Bone diagnostics · Osteoporosis · Photothermal radar · Photothermal radiometry K. Sreekumar (B ) · A. Mandelis Centre for Advanced Diffusion-Wave Technologies, Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, ON M5S 3G8, Canada e-mail: sreekumarkaiplavil@yahoo.co.in A. Mandelis e-mail: mandelis@mie.utoronto.ca 123