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Multiscale photoacoustic tomography using reversibly switchable bacterial phytochrome as a near-infrared photochromic probe.

Yao J, Kaberniuk AA, Li L, Shcherbakova DM, Zhang R, Wang L, Li G, Verkhusha VV, Wang LV - Nat. Methods (2015)

Bottom Line: BphP1 binds a heme-derived biliverdin chromophore and is reversibly photoconvertible between red and near-infrared light-absorption states.We combined single-wavelength PAT with efficient BphP1 photoswitching, which enabled differential imaging with substantially decreased background signals, enhanced detection sensitivity, increased penetration depth and improved spatial resolution.This technology is promising for biomedical studies at several scales.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA.

ABSTRACT
Photoacoustic tomography (PAT) of genetically encoded probes allows for imaging of targeted biological processes deep in tissues with high spatial resolution; however, high background signals from blood can limit the achievable detection sensitivity. Here we describe a reversibly switchable nonfluorescent bacterial phytochrome for use in multiscale photoacoustic imaging, BphP1, with the most red-shifted absorption among genetically encoded probes. BphP1 binds a heme-derived biliverdin chromophore and is reversibly photoconvertible between red and near-infrared light-absorption states. We combined single-wavelength PAT with efficient BphP1 photoswitching, which enabled differential imaging with substantially decreased background signals, enhanced detection sensitivity, increased penetration depth and improved spatial resolution. We monitored tumor growth and metastasis with ∼ 100-μm resolution at depths approaching 10 mm using photoacoustic computed tomography, and we imaged individual cancer cells with a suboptical-diffraction resolution of ∼ 140 nm using photoacoustic microscopy. This technology is promising for biomedical studies at several scales.

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Longitudinal PACT monitoring of cancer metastasis in a mouse liver (n = 6). (a) Whole-body PACT images of the liver region of a representative nude mouse acquired repeatedly for 30 days after the injection of BphP1-expressing U87 cells into the right liver lobe (n = 6). Differential signals (shown in color) are overlaid on top of the structural signals from the blood (shown in gray). The white arrows in the Day 21 and Day 30 images indicate secondary tumors due to metastasis. A global threshold was applied to all the differential images with a threshold level at three times the noise level. All the images were first thresholded and then normalized across the measurements. (b) Increase in areas of the primary and secondary tumors. Error bars: standard errors of the results from 6 animals. (c) Representative H&E histological images of the mouse liver lobes with the primary tumor (PT, top panel) and secondary tumors (ST, bottom panel).
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Figure 4: Longitudinal PACT monitoring of cancer metastasis in a mouse liver (n = 6). (a) Whole-body PACT images of the liver region of a representative nude mouse acquired repeatedly for 30 days after the injection of BphP1-expressing U87 cells into the right liver lobe (n = 6). Differential signals (shown in color) are overlaid on top of the structural signals from the blood (shown in gray). The white arrows in the Day 21 and Day 30 images indicate secondary tumors due to metastasis. A global threshold was applied to all the differential images with a threshold level at three times the noise level. All the images were first thresholded and then normalized across the measurements. (b) Increase in areas of the primary and secondary tumors. Error bars: standard errors of the results from 6 animals. (c) Representative H&E histological images of the mouse liver lobes with the primary tumor (PT, top panel) and secondary tumors (ST, bottom panel).

Mentions: We longitudinally imaged the growth of a BphP1-expressing U87 tumor in a mouse liver and monitored tumor metastases in the liver lobes for a month (n = 6) (Fig. 4a). The differential PA images detected the growth of a primary tumor in the right liver lobe, and later the secondary tumors resulted from metastatic spread to other liver lobes (Fig. 4a). The smallest secondary tumor had an average diameter of ~300 µm. Assuming that the mean diameter of U87 cells is ~10 µm, each resolution voxel of the secondary tumor corresponds to ~3000 U87 cells. The CNR of the above-mentioned tumor is ~15 in the differential image, suggesting it is possible to detect as few as ~200 cells at this depth. Over one month, we observed an exponential growth of the primary tumor, and a delayed exponential growth of the secondary tumor (Fig. 4b). There was no difference between the growth rates of the primary tumor (from day 0) and secondary tumors (from day 7). The cross-sectional area doubling times of the primary tumor and secondary tumors are respectively 8.0 ± 1.2 days and 7.2 ± 2.7 days, suggesting cell doubling times of 5.3 ± 0.8 days and 4.8 ± 1.8 days. After the PA imaging, we histologically confirmed the relative locations of the tumors (Fig. 4c).


Multiscale photoacoustic tomography using reversibly switchable bacterial phytochrome as a near-infrared photochromic probe.

Yao J, Kaberniuk AA, Li L, Shcherbakova DM, Zhang R, Wang L, Li G, Verkhusha VV, Wang LV - Nat. Methods (2015)

Longitudinal PACT monitoring of cancer metastasis in a mouse liver (n = 6). (a) Whole-body PACT images of the liver region of a representative nude mouse acquired repeatedly for 30 days after the injection of BphP1-expressing U87 cells into the right liver lobe (n = 6). Differential signals (shown in color) are overlaid on top of the structural signals from the blood (shown in gray). The white arrows in the Day 21 and Day 30 images indicate secondary tumors due to metastasis. A global threshold was applied to all the differential images with a threshold level at three times the noise level. All the images were first thresholded and then normalized across the measurements. (b) Increase in areas of the primary and secondary tumors. Error bars: standard errors of the results from 6 animals. (c) Representative H&E histological images of the mouse liver lobes with the primary tumor (PT, top panel) and secondary tumors (ST, bottom panel).
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Related In: Results  -  Collection

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Figure 4: Longitudinal PACT monitoring of cancer metastasis in a mouse liver (n = 6). (a) Whole-body PACT images of the liver region of a representative nude mouse acquired repeatedly for 30 days after the injection of BphP1-expressing U87 cells into the right liver lobe (n = 6). Differential signals (shown in color) are overlaid on top of the structural signals from the blood (shown in gray). The white arrows in the Day 21 and Day 30 images indicate secondary tumors due to metastasis. A global threshold was applied to all the differential images with a threshold level at three times the noise level. All the images were first thresholded and then normalized across the measurements. (b) Increase in areas of the primary and secondary tumors. Error bars: standard errors of the results from 6 animals. (c) Representative H&E histological images of the mouse liver lobes with the primary tumor (PT, top panel) and secondary tumors (ST, bottom panel).
Mentions: We longitudinally imaged the growth of a BphP1-expressing U87 tumor in a mouse liver and monitored tumor metastases in the liver lobes for a month (n = 6) (Fig. 4a). The differential PA images detected the growth of a primary tumor in the right liver lobe, and later the secondary tumors resulted from metastatic spread to other liver lobes (Fig. 4a). The smallest secondary tumor had an average diameter of ~300 µm. Assuming that the mean diameter of U87 cells is ~10 µm, each resolution voxel of the secondary tumor corresponds to ~3000 U87 cells. The CNR of the above-mentioned tumor is ~15 in the differential image, suggesting it is possible to detect as few as ~200 cells at this depth. Over one month, we observed an exponential growth of the primary tumor, and a delayed exponential growth of the secondary tumor (Fig. 4b). There was no difference between the growth rates of the primary tumor (from day 0) and secondary tumors (from day 7). The cross-sectional area doubling times of the primary tumor and secondary tumors are respectively 8.0 ± 1.2 days and 7.2 ± 2.7 days, suggesting cell doubling times of 5.3 ± 0.8 days and 4.8 ± 1.8 days. After the PA imaging, we histologically confirmed the relative locations of the tumors (Fig. 4c).

Bottom Line: BphP1 binds a heme-derived biliverdin chromophore and is reversibly photoconvertible between red and near-infrared light-absorption states.We combined single-wavelength PAT with efficient BphP1 photoswitching, which enabled differential imaging with substantially decreased background signals, enhanced detection sensitivity, increased penetration depth and improved spatial resolution.This technology is promising for biomedical studies at several scales.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA.

ABSTRACT
Photoacoustic tomography (PAT) of genetically encoded probes allows for imaging of targeted biological processes deep in tissues with high spatial resolution; however, high background signals from blood can limit the achievable detection sensitivity. Here we describe a reversibly switchable nonfluorescent bacterial phytochrome for use in multiscale photoacoustic imaging, BphP1, with the most red-shifted absorption among genetically encoded probes. BphP1 binds a heme-derived biliverdin chromophore and is reversibly photoconvertible between red and near-infrared light-absorption states. We combined single-wavelength PAT with efficient BphP1 photoswitching, which enabled differential imaging with substantially decreased background signals, enhanced detection sensitivity, increased penetration depth and improved spatial resolution. We monitored tumor growth and metastasis with ∼ 100-μm resolution at depths approaching 10 mm using photoacoustic computed tomography, and we imaged individual cancer cells with a suboptical-diffraction resolution of ∼ 140 nm using photoacoustic microscopy. This technology is promising for biomedical studies at several scales.

Show MeSH
Related in: MedlinePlus