Photoacoustic imaging capabilities of light emitting diodes (LED) and laser sources: A comparison study

Photoacoustic imaging (PAI) maps functional and molecular optical contrasts of tissue at ultrasonic spatial resolution and imaging depth. To generate detectable PA signals from deeper regions, expensive, bulky and high-energy class IV lasers are conventionally employed. Light emitting diodes (LED) have recently emerged as an alternative excitation source for PA imaging offering many advantages including portability, affordability, speed, multi-wavelength excitation, and eye/skin safety. Although the output energy of LED's is far lower than lasers, high pulse repetition rate offers possibility to average more frames and thus improve the SNR. In this work, we performed controlled experiments on tissue-mimicking phantoms to compare the PAI performance of laser and LED light sources comprehensively. Our studies demonstrate that the LED based PA systems are ideal for low resource and point-of-care settings where the required depth of penetration is within 2-3 cms., whereas a high-energy laser is found to be more effective for higher penetration depths (<3 cm). In addition, it is clear from our results that LED-based PA imaging offers higher frame rate with similar spatial resolution and decent signal to noise ratio, which is comparable to conventional laser-based photoacoustic imaging.