In vivo photoacoustic and fluorescence cystography using clinically relevant dual modal indocyanine green

Abstract

Conventional X-ray-based cystography uses radio-opaque materials, but this method uses harmful ionizing radiation and is not sensitive. In this study, we demonstrate nonionizing and noninvasive photoacoustic (PA) and fluorescence (FL) cystography using clinically relevant indocyanine green (ICG) in vivo. After transurethral injection of ICG into rats through a catheter, their bladders were photoacoustically and fluorescently visualized. A deeply positioned bladder below the skin surface (i.e., ~1.5-5 mm) was clearly visible in the PA and FL image using a laser pulse energy of less than 2 mJ/cm2 (1/15 of the safety limit). Then, the in vivo imaging results were validated through in situ studies. Our results suggest that dual modal cystography can provide a nonionizing and noninvasive imaging tool for bladder mapping.

Figure 1.

Experimental setups of a dual modal photoacoustic (a) and fluorescence (b) imaging system. AMP, Amplifier; OSC, oscilloscope; OPO, optical parametric oscillator; CNL, conical lens; CCL, concave lens; OC, optical condenser; UT, ultrasound transducer; WT, water tank; and UG, ultrasound gel.

Figure 2.

Photoacoustic (PA) and fluorescence (FL) properties of indocyanine green (ICG). (a) PA amplitudes vs. ICG concentration; (b) PA spectra of ICG by varying concentration; (c) FL intensities vs. ICG concentration; (d) FL intensities vs. LED output power.

Figure 3.

In vivo nonionizing and noninvasive photoacoustic (PA) cystography using indocyanine green (ICG). (a) Control PA MAP image of a rat's abdomen at 800 nm acquired before ICG injection. Only surround blood vessels are visible; (b) PA MAP image at 800 nm after ICG injection displaying the bladder (BD) filled with ICG, catheter, and blood vessels; (c) PA MAP image at 950 nm after ICG injection. The bladder disappeared due to the spectral response of ICG; (d–f) Depth-sensitive B-mode PA images of (a–c) cut along the dotted lines; (g) PA differential MAP image between (a) and (b); (h) PA differential MAP image between (b) and (c); (i) Depth-sensitive pseudo-colored PA MAP image of (b); (j) Photograph taken before PA imaging; (k) Photograph taken after PA imaging and skin removal.

Figure 4.

In vivo nonionizing and noninvasive fluorescence (FL) cystography using indocyanine green (ICG). (a) Combined FL and white-light image of ICG (15 μM) and water in plastic tubes; (b) Photograph taken before FL imaging and ICG injection; (c) Photograph taken after FL imaging and skin removal; (d) Control overlaid FL and white-light image of the rat's abdomen before ICG injection; (e) In vivo overlaid FL and white-light image after ICG injection; (f) In situ overlaid FL and white-light image after ICG injection and skin removal. BD, bladder.