Photoacoustic and Ultrasound Imaging with Nanosized Contrast Agents - Nanotechnology for Biomedical Imaging and Diagnostics - page 300

nanoparticles were successfully developed as a dual-modality PA and US contrast
agent [143]. Upon laser irradiation and its consequent liquid-to-gas phase transition
of liquid PFC, significant PA signals were generated. The generated gaseous phase
enhances the US contrast.

10.5.5 dual-modality Photoacoustic and fluorescence contrast
agents and activatable Probe

As another dual-modality imaging capability of hybrid PAT, FL imaging has been
combined with PAT [126, 144-146]. As mentioned previously, the conversion
efficiency between specific optical absorption and heat of a given molecule deter-
mines the amplitudes of initially generated PA pressure waves (see section “Principles
of PAT”). Thus, it is expected that a material with high nonradiative quantum yield is
a good candidate as a PA contrast agent. In other words, if the quantum yield between
radiative and nonradiative energy release is properly controlled, the dual-modality PA
and FL imaging is highly feasible using a single contrast agent. For example, owing
to its moderate FL quantum yield (e.g., ~12% in dMSo and <2% in water), ICg (an
FdA-approved organic dye) was used as a multimodal contrast agent for both FL and
PA imaging. recently, Walter et al . demonstrated that FL quenching of nIr fluorescent
dyes in nanoparticles significantly enhanced the PA contrast, a way to convert a highly

(a)

Phospholipid surface

NIR dye

Ligand

PEG2000

O

FF
N

CN

B

N

N N

e

CN

F F

PPCy-C8

O

Peruorocarbon

(b) (c) (d)

24 h

LN3

C1

LN2

LN1

figure 10.11 dual-modality photoacoustic (PA) and fluorescence (FL) contrast agents.
(a) Schematic of dye-loaded perfluorocarbon nanoparticles and its chemical structure. (b) In vivo
noninvasive PA mapping of sentinel lymph node in small animals. In vivo (c) intensity- and
(d) lifetime-based FL mapping of the sentinel lymph node in a rat. (reprinted with permission from
ref. [144]. © American Chemical Society.) ( See insert for color representation of the figure.) .)