Photoacoustic Device Probes Tissue with Low-Cost Laser Diodes

Photoacoustic (PA) technologies offer a noninvasive approach to probing biological tissues, but have seen limited use in clinical applications, partially due to bulky, expensive laser sources. A compact PA sensing instrument for biomedical tissue diagnosis, powered by laser diodes, could provide clinicians with a practical, effective tool for evaluating breast disease.

By providing a cost-effective path to tissue diagnosis, the compact PA sensing instrument could bridge the gap between PA research and its practical application. The instrument is the work of a research team from the Indian Institute of Technology Indore.

The researchers integrated multiple laser diodes for PA excitation within a compact casing and developed a pulsed current supply unit that induces the laser diodes to generate a 25 ns current pulse at a frequency of 20 kHz. They characterized the optical laser diode casing and power supply unit in terms of pulse width, laser intensity, and repeatability with multiple laser diodes.

The photoacoustic spectral response (PASR) sensing instrument is based on low-cost laser diodes, which enable a more compact, lower cost system. The advance could allow greater implementation and access to the imaging modality. Courtesy of Khan et al., doi 10.1117/1.JBO.29.1.017002.

To boost signal strength, the team focused the laser diodes in the casing on one spot. This enhanced the PA signal amplitude, improving signal-to-noise ratio (SNR). Time-domain PA signal amplitude revealed that optical energy increased when the number of laser diodes was increased.

The researchers compared the laser diode-based PA system with a traditional Nd:YAG laser-based PA system and found that the systems demonstrated similar PA responses. Acoustic spectral magnitude showed that the new PA sensing instrument was efficacious with a conventional PA setup.

The team used the compact PA sensing system to study fibrocystic changes in the breast in vitro. The researchers analyzed the frequency spectra of the PA signals to quantitatively assess tissue properties.

The system differentiated tissue types based on quantitative spectral parameters, including peak frequency, mean frequency, and spectral energy. The PA spectral response revealed distinct spectral patterns corresponding to different tissue types. The fibrocystic breast disease tissue exhibited a higher dominant frequency peak and energy compared to the normal breast tissue.

The fibrocystic breast disease sample demonstrated a dominant frequency peak around 1.60 MHz, indicative of increased tissue density due to heightened glandular and stromal elements. In contrast, normal breast tissue showed a lower peak frequency of 0.26 MHz, reflecting its fibrofatty composition. A histopathological examination validated these findings, affirming the correlation between spectral responses and tissue characteristics. The researchers also used the system to correlate the PA spectral parameter with the elastic properties of fibrocystic breast disease tissue compared to normal breast parenchyma tissue samples.

Ultrasound and mammogram are currently the most common diagnostic modalities used for clinical diagnosis of breast diseases, followed by fine needle aspiration cytological examination. Due to problems with the accuracy of these imaging modalities, there is a need for an alternative screening technique that provides clinicians with greater insight into the disease diagnosis than traditional approaches.

The experimental results suggest that the PA sensing instrument could provide a rapid, reliable, noninvasive method to assess tissue density and identify pathological changes in breast tissue, which could enable more timely interventions and therefore improve outcomes.

The use of advanced signal processing techniques and high-frequency transducers could enhance the system’s capabilities for real-time and in vivo studies, which could expand its clinical utility. In the future, laser diodes with different wavelengths could be incorporated into the same optical casing to investigate biological tissues across a wide range of wavelengths.

The research was published in the Journal of Biomedical Optics (www.doi.org/10.1117/1.JBO.29.1.017002).