Fig. 1

Comparison of optical absorption spectra of different photoacoustic agents A: The absorption peaks of ICG and ICG-RIT were 780-800 nm; B: The light absorption peaks of methylene blue, methemoglobin, oxyhemoglobin and deoxyhemoglobin were located at 660-680 nm, 620-640 nm and below 600 nm, respectively."

Fig.2

The diagram of the structure of hand-held photoacoustic signal sensing system"

Fig. 3

The structure of hand-held photoacoustic imaging system"

Tab. 1

Amplitudes of ICG-RIT phantoms with different concentrations at different depths"

Fig. 4

Amplitudes of ICG-RIT phantoms with different concentrations at different depths"

Fig. 5

Photoacoustic signals of 25% concentration ICG-RIT phantoms at different depths A: PA signal amplitude was 11.20 mV; Depth was 6.15 mm; B: PA signal amplitude was 8.99 mV; Depth was 17.37 mm; C: PA signal amplitude was 7.00 mV; Depth was 28.56 mm; D: PA signal amplitude was 6.25 mV; Depth was 43.50 mm; E: PA signal amplitude was 2.75 mV; Depth was 62.22 mm."

Fig. 6

Photoacoustic signals of 6.25% concentration ICG-RIT phantoms at different depths A: PA signal amplitude was 13.24 mV; Depth was 6.81 mm; B: PA signal amplitude was 12.25 mV; Depth was 14.73 mm; C: PA signal amplitude was 5.00 mV; Depth was 19.14 mm; D: PA signal amplitude was 2.74 mV; Depth was 33.00 mm; E: Photoacoustic signal at 46.95 mm depth was not used because of the low differentiation."

Fig.7

Lymph nodes in NIR fluorescence imaging system A: Lymph drainage in the NIR fluorescence imaging system after subareolar injection of ICG-RIT; B: Image of excised SLN in the NIR fluorescence imaging system; C:Visual inspection of the excised SLN."

Fig. 8

Photoacoustic signals SLN at different depths A: The photoacoustic signal of axillary fat; B: PA signal amplitude was 99 mV; Depth was 9.18 mm; C: PA signal amplitude was 72 mV; Depth: 17.37 mm; D: PA signal amplitude was 59 mV; Depth was 25.60 mm; E: PA signal amplitude was 31 mV; Depth was 32.72 mm."

Fig. 9

Photoacoustic images and ultrasound images of SLN at different depths A, B: Both PAI and US imaged SLN under about 1 cm thick axillary fat; C, D: Both PAI and US imaged SLN under about 2.5 cm thick axillary fat; E: No significant SLN signal was found in PAI under about 4 cm thick axillary fat; F: US imaged SLN under about 4 cm thick axillary fat."

Fig. 10

Amplitudes and photoacoustic images after injection of ICG-RIT A, B: No significant signal of the popliteal LNs in the PASS and PAI was observed with no ICG-RIT injection; C, D: Characteristic photoacoustic signal in the PASS and PAI of the popliteal LNs was detected at 10.05 mm depth after ICG-RIT injection; E, F: No significant signal of the iliac LNs in the PASS and PAI was observed after ICG-RIT injection; G, H: No obvious staining of the popliteal LNs and the iliac LNs dissected along photoacoustic signal."

Fig. 11

Amplitudes and photoacoustic images after injection of MB A, B: Characteristic photoacoustic signal in the PASS and PAI of the popliteal LNs was detected at 6.93 mm depth after MB injection; C, D: Characteristic photoacoustic signal in the PASS and PAI of the iliac LNs was detected at 14.67 mm depth after MB injection; E, F: Obvious staining of the popliteal LNs and the iliac LNs dissected along photoacoustic signal."

Fig. 12

Amplitudes of ex vivo lymph nodes A: ICG-RIT injection ex vivo popliteal LNs PA signal amplitude was 2.50 mV; B: ICG-RIT injection ex vivo popliteal LNs PA signal amplitude was 0 mV; C: MB injection ex vivo popliteal LNs PA signal amplitude was 20.25 mV; D: MB injection ex vivo popliteal LNs PA signal amplitude was 7.74 mV."

Tab. 2

Amplitude differences between ICG-RIT and MB at different level lymph nodes"