Frequency domain photoacoustic correlation (radar) imaging: a novel methodology for non-invasive imaging of biological tissues

Photoacoustic radar phase-filtered spatial resolution and co-registered ultrasound image enhancement for tumor detection

“…Unlike the US image, the PA image is less sensitive to the presence of the surrounding body parts, but is highly sensitive to the presence of increased blood flow in the tumor, thereby providing much clearer information regarding the tumor, manifested as better contrast and sensitivity than its pure US counterpart. Figures 4(a), 4(b), 4(c) show the amplitude (see [18] for methodology), phase only and phase-filtered images, respectively, obtained by the PAR system. The phase image (Fig.…”

“…The FD modality also possesses depth-selective imaging capabilities [17] and can generate high peak power cross-correlation response through matched filtering. Energy compression, typically, ms-long frequency chirps compacted into a narrow correlation peak, significantly increases SNR [18]. The reconstructed image is the spatial cross-correlation function between the PA response and the reference signal used for laser source modulation (the radar principle).…”

Frequency-domain differential photoacoustic radar: theory and validation for ultrasensitive atherosclerotic plaque imaging

“…[5][6][7][8] While high-power pulsed lasers have been the main optical sources for conventional PA imaging, [5][6][7][8] a PA imaging modality has also been under intense development based on frequency-modulated (chirped) optical excitation with lowpower continuous-wave (CW) lasers and frequency-domain (FD) signal processing to obtain depth-resolved images of tissue chromophores. [14][15][16] The technology is called the photoacoustic radar (PAR) and provides several unique imaging features including (1) efficient noise filtering and high signal-to-noise ratio (SNR) with low power irradiation; (2) micrometer axial resolution; (3) depth information, mapped into the PA spectrum; (4) physiological information based on the target's optical properties; and (5) reliable measurements based on two complementary channels of amplitude and phase. [14][15][16][17] Furthermore, the use of CW optical sources in PAR allows flexible waveform engineering on the modulating optical signals that can lead to several unique or enhanced imaging features.…”

“…[14][15][16] The technology is called the photoacoustic radar (PAR) and provides several unique imaging features including (1) efficient noise filtering and high signal-to-noise ratio (SNR) with low power irradiation; (2) micrometer axial resolution; (3) depth information, mapped into the PA spectrum; (4) physiological information based on the target's optical properties; and (5) reliable measurements based on two complementary channels of amplitude and phase. [14][15][16][17] Furthermore, the use of CW optical sources in PAR allows flexible waveform engineering on the modulating optical signals that can lead to several unique or enhanced imaging features. From this perspective, our earlier introduction of single-frequency wavelength-modulated differential spectroscopy [18][19][20] leads to the present multifrequency intravascular differential PA radar (IV-DPAR) system as an excellent example of the many waveform engineering possibilities for further advances in atherosclerosis imaging, beyond the physical limitations of the conventional PAR and pulsebased PA counterparts.…”

Interference-free Detection of Lipid-laden Atherosclerotic Plaques by 3D Co-registration of Frequency-Domain Differential Photoacoustic and Ultrasound Radar Imaging

“…In the Center for Advanced Diffusion-wave and Photoacoustic Technologies (CADIPT), University of Toronto, a PA imaging method has been under intense development based on frequency-modulated (chirped) optical excitation with low power continuous wave (CW) lasers and frequency-domain (FD) signal processing. This modality is called the Photoacoustic Radar (PAR) and has been shown to be competitive with conventional pulsed-based PA systems, providing high signal-to-noise ratio (SNR), sub-mm axial resolution and depth-resolved/molecularly specific optical contrast of the subsurface tissue chromophores, while utilizing low power irradiation and a narrowband detector 13,14 . Furthermore, use of CW optical sources in PAR allows flexible waveform engineering on the modulating optical signals that can lead to several unique or enhanced imaging features 20 .…”