Figure 1.
Establishment of PA tomography's ability to visualize ICG-containing tissue.
(A) Using a human liver tissue-mimicking phantom (top), human plasma containing ICG at concentrations of 0.001, 0.01, 0.1, and 1.0 mg/mL was encapsulated into holes that were 5 mm in diameter and located at a depth of 5 mm from the surface; PA amplitudes were measured using the Vevo LAZR imaging system (middle). Fluorescence images of each ICG-containing plasma sample were also obtained (bottom). (B) Fluorescence imaging in a mouse model with subcutaneously implanted well-differentiated human hepatoma cells (HuH-7) identified ICG accumulation in the subcutaneous tumor (left). PA tomography enabled differentiation of tumor-specific PA signals from those of surrounding organs under the conditions of 800-nm excitation light and 54-dB PA gain (right).
Figure 2.
Photoacoustic tomography of surgically-resected hepatic tissue in humans.
(A) Fluorescence imaging identified uniform fluorescence of ICG on the cut surface of well-differentiated HCC tissue (left). PA tomography from the cut surface of the specimen visualized accumulation of ICG in cancerous tissues on US images (right, please see video S1). (B) Fluorescence imaging identified rim-type ICG fluorescence around CRLM lesions on the cut surface of the resected specimen (left). Photoacoustic tomography from the cut surface visualized accumulation of ICG in the peri-cancerous hepatic tissue on US images (right, please see video S2). Yellow squares and arrows in A and B indicate the site where a probe of the imaging system was attached and the boundaries between the tumors and non-cancerous liver parenchyma, respectively. (C) Photoacoustic amplitude of each ROI from the resected specimen (red bar indicates cancerous region; green bar, peri-cancerous region; and blue bar, non-cancerous hepatic parenchyma 2 mm from the tumor) according to the depth of the ROI from the sample's surface (depths of 1 to 5 mm). Indocyanine green accumulation was observed in the cancerous tissue in HCC specimens 1–4 (cancerous-type accumulation), while rim-type ICG accumulation was observed in HCC specimen 5, the ICC specimen, and CRLM specimens 1–4.
Table 1.
Tumor characteristics and results of fluorescence and PA imaging.
Figure 3.
Left, hematoxylin-eosin staining; middle, fluorescence images; and right, fusion images of ICG fluorescence, indicated in green, and hematoxylin-eosin staining. (A) In well-differentiated HC lesions, ICG fluorescence was identified mainly in the cancerous tissue, as demonstrated in Figure 2A. (B) Magnified view of (A). Indocyanine green had accumulated in the pseudoglands (arrowheads) and the cytoplasm of cancer cells (arrow). (C) Indocyanine green fluorescence was identified in the peri-cancerous hepatic parenchyma surrounding a CRLM lesion, as demonstrated in Figure 2B. (D) Magnified view of (C). Indocyanine green had accumulated in the cytoplasm of relatively small hepatocytes rather than in the intracellular spaces.
Figure 4.
Photoacoustic tomography from the body surface in NASH-HCC model mice.
(A) Spectrum computed tomography of a living NASH-HCC model mouse identified hepatic tumors with accumulation of ICG that had been intravenously injected 48 hours prior (IVIS Spectrum CT, PerkinElmer, Hopkinton, US; excitation 745 nm, emission 800 nm). (B) Photoacoustic tomography failed to visualize any cancer-specific PA signals on US images. (C, D) Three liver nodules were macroscopically identified in this mouse (C); one was visualized on fluorescence imaging (D). (E) Fluorescence microscopy identified ICG fluorescence (demonstrated in green in this fusion image with hematoxylin-eosin staining) in the cytoplasm of some of the cancerous cells in this NASH-HCC model mouse.