Deeply penetrating in vivo photoacoustic imaging using a clinical ultrasound array system

Abstract

Using a hand-held photoacoustic probe integrated with a clinical ultrasound array system, we successfully imaged objects deeply positioned in biological tissues. The optical contrasts were enhanced by methylene blue with a concentration of ~30 mM. The penetration depth reached ~5.2 cm in chicken breast tissue by using 650-nm wavelength, which is ~4.7 times the 1/e optical penetration depth. This imaging depth was achieved using a laser fluence on the tissue surface of only 3 mJ/cm2, which is 1/7 of the American National Standards Institute (ANSI) safety limit (20 mJ/cm2). The noise equivalent sensitivity at this depth was ~11 mM. Further, after intradermal injection of methylene blue in a rat, a sentinel lymph node was easily detected in vivo, beneath a 2-cm thick layer of chicken breast. Also, blood located 3.5 cm deep in the rat was clearly imaged with intrinsic contrast. We have photoacoustically guided insertion of a needle into a rat sentinel lymph node with accumulated methylene blue. These results highlight the clinical potential of photoacoustic image-guided identification and needle biopsy of sentinel lymph nodes for axillary staging in breast cancer patients.

Nonionizing photoacoustic cystography in vivo

“…Recently, PAT has been extensively explored in preclinical and clinical studies, including primary cancer detection, lymph node staging and lymphangiography, brain activation, ophthalmology, and image-guided therapy [4][5][6][7][8]. A clinical ultrasonic scanner has been adapted to PAT, combining the high contrast of optical imaging and the high resolution of US imaging [9][10][11].…”

Handheld probe integrating laser diode and ultrasound transducer array for ultrasound/photoacoustic dual modality imaging

“…This association allowed to achieve valuable results, since ultrasound can provide complementary information, such as anatomy and structures, deep inside the interrogated medium with a likewise sub-millimeter resolution [10]. Until now, bulky lasers were used, making the proposed dual modality imaging systems large, costly, and with low frame rate imaging, complicating their clinical integration [11]. There is a growing need to develop photoacoustic imaging systems (PAI) that are compact, affordable and offering real-time imaging which will contribute to make photoacoustics a standard technique for clinical applications such as breast tumor, melanoma imaging and rheumatoid arthritis.…”

Hybrid photoacoustic and ultrasound section imaging with optical ultrasound detection

“…One obvious reason for this combination is the possibility of using the same equipment, piezoelectric transducers, for the generation of sound in the US mode and for the detection of PA and US signals. Common implementations use commercial ultrasound devices, to which a pulsed laser source is added [3][4][5]. One advantage of such a combined system is the real-time two-dimensional imaging capability of the US array.…”