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Pulsed laser diode based desktop photoacoustic tomography system for high-speed imaging

26 Feb | By Biophotonics.World
Pulsed laser diode based desktop photoacoustic tomography system for high-speed imaging
By: Manojit Pramanik

Traditional Nd:YAG/OPO lasers are expensive, heavy and bulky, limiting the translation of photoacoustic tomography system into clinics. For the past few years, small-size, low-cost pulsed laser diodes are replacing these Nd:YAG lasers for photoacoustic imaging. Researchers at Nanyang Technological University, Singapore have developed a compact, desktop low-cost pulsed laser diode based photoacoustic tomography system for high-speed imaging. Dynamic high-speed imaging ability of this system was demonstrated in small animal model, in article published in Optics Letters in 2019.

Photoacoustic (PA) imaging is a non-invasive emerging biomedical imaging modality combining optical imaging contrast with ultrasonic resolution. Pulsed laser beam illumination causes thermoelastic expansion of the biological tissue resulting in the emission of pressure waves known as photoacoustic waves. These waves can be collected around the tissue boundary using ultrasound transducers there by obtaining the optical absorption map of the tissue. 

“We have developed a pulsed laser diode (PLD) based photoacoustic tomography (PAT) system using multiple acoustic-reflector-augmented single-element ultrasound transducers for high-speed imaging applications” said Sandeep Kumar Kalva, a researcher working with Dr. Manojit Pramanik, assistant professor at Nanyang Technological University, School of Chemical and Biomedical Engineering, Singapore.

Quantel’s pulsed laser diode of 2 KHz pulse repetition rate was used along with commercially available cheap single-element ultrasound transducers augmented with 450acoustic reflector (SUTRs) to integrate this imaging system. Eight similar transducers were used enabling 450scanning. Dr. Pramanik said, “Mounting the laser inside the PAT scanner and by using the acoustic reflector, the PAT scanner volume can easily be minimized by placing the SUTRs in vertical position instead of conventional horizontal position. Moreover by using multiple SUTRs, the imaging speed is further reduced to 0.5 sec scan time instead of several minutes taken with low-repetition rate conventional Nd:YAG/OPO lasers.” 

The performance of this PLD-PAT system was characterized in terms of resolution and imaging depth using phantom-based studies. “A high spatial resolution of 165 μm was obtained with 5 MHz transducer and anin vitro imaging depth of 3 cm can be achieved using this system,” said Dr. Paul Kumar Upputuri, a research fellow working in Dr. Pramanik’s lab.

The high-speed dynamic imaging ability of this PLD-PAT system was demonstrated by monitoring the fast uptake and clearance process of indocyanine green (ICG) dye (injected into the tail vein of the small animal) in rat cortical vasculature. Continuous PA data was acquired using this system at 0.5 second scan speed. By using much more robust stepper motors or by using more number of transducers, the imaging speed can further be improved. Overall cost of this PLD-PAT system is ~10% of the full-ring array-based Nd:YAG/OPO PAT systems. This compact, low-cost, high-speed PLD-PAT system can be used for applications in characterization of pharmacokinetic and bio distribution profiles in drugs or any other contrast agents development process, neurofunctional activities in small animal studies.


Original article:

S. K. Kalva, P. K. Upputuri, and M. Pramanik, “High-speed, low-cost, pulsed-laser-diode-based second-generation desktop photoacoustic tomography system,” Optics Letters 44(1), 81-84 (2019). https://doi.org/10.1364/OL.44.000081 


Author: Manojit Pramanik

Methods and Techniques: Photoacoustic imaging (PAI, MSOT)

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