Abstract
Photoacoustic computed tomography (PACT) has been widely explored for non-ionizing functional and molecular imaging of humans and small animals. In order for light to penetrate deep inside tissue, a bulky and high-cost tunable laser is typically used. Light-emitting diodes (LEDs) have recently emerged as cost-effective and portable alternative illumination sources for photoacoustic imaging. In this study, we have developed a portable, low-cost, five-dimensional (x, y, z, t, PACT system using multi-wavelength LED excitation to enable similar functional and molecular imaging capabilities as standard tunable lasers. Four LED arrays and a linear ultrasound transducer detector array are housed in a hollow cylindrical geometry that rotates 360 degrees to allow multiple projections through the subject of interest placed inside the cylinder. The structural, functional, and molecular imaging capabilities of the LED–PACT system are validated using various tissue-mimicking phantom studies. The axial, lateral, and elevational resolutions of the system at 2.3 cm depth are estimated as 0.12 mm, 0.3 mm, and 2.1 mm, respectively. Spectrally unmixed photoacoustic contrasts from tubes filled with oxy- and deoxy-hemoglobin, indocyanine green, methylene blue, and melanin molecules demonstrate the multispectral molecular imaging capabilities of the system. Human-finger-mimicking phantoms made of a bone and blood tubes show structural and functional oxygen saturation imaging capabilities. Together, these results demonstrate the potential of the proposed LED-based, low-cost, portable PACT system for pre-clinical and clinical applications.
Highlights
Photoacoustic computed tomography (PACT) is a nonionizing and noninvasive hybrid imaging modality that provides three-dimensional (3-D) optical-absorption-based functional and molecular contrast images of living subjects with high spatial resolution using ultrasound detection [1,2,3,4]
In the sub-sections, we present experimental validation studies to test the structural, functional, and molecular imaging capabilities of our Light-emitting diodes (LEDs)–PACT system
Q(y) represents the optical source located at the boundary, either the LEDs or laser surrounding the region of interest; Φ(y) is the calculated fluence distribution due to the source q(y)
Summary
Photoacoustic computed tomography (PACT) is a nonionizing and noninvasive hybrid imaging modality that provides three-dimensional (3-D) optical-absorption-based functional and molecular contrast images of living subjects with high spatial resolution using ultrasound detection [1,2,3,4] It relies on the photoacoustic effect, which is the generation of broadband ultrasound waves by the tissue chromophores that absorb short light pulses and undergo thermoelastic expansion. Most PACT systems use Q-switched, Nd:YAG (neodymium-doped yttrium aluminum garnet)/OPO (optical parametric oscillator)-based, nanosecond pulsed tunable lasers and a multichannel ultrasound detector array with related data acquisition hardware [13,14,15,16,17] These lasers typically deliver hundreds of mJ pulse energy to allow a sufficient photoacoustic signal-to-noise (SNR) ratio from targets situated several centimeters deep inside the tissue, such as deep vasculature of human breast. The high pulse energy lasers usually operate at low pulse repetition frequency (1 KHz) when the targeted application requires
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