Small animal photoacoustic imaging application example

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Application of small animal photoacoustic imaging system

Author: Huijia biological instrument (Shanghai) Co., Ltd. Di Junhui

Near-infrared small animal photoacoustic imaging can be widely used in the development of new contrast agents (probes), nano-material clinical application analysis, cardiovascular, drug metabolism, early disease diagnosis, tumor efficacy observation, gene expression research, stem cell and immune research, etc. field.

Optical contrast agent application

Many components in our body are endogenous contrast agents. For example, hemoglobin is a good endogenous contrast agent, and hemoglobin carrying oxygen will absorb more at other wavelengths, so according to this principle, light The sound can measure hemoglobin concentration and blood oxygen saturation. The soft tissue in the body and the neovascularization in the tumor are also good contrast agents. The principle of tumor angiogenesis is also based on the very active vascular activity, so the hemoglobin concentration is higher than the internal structure of the tumor, and the tumor can be implemented based on the photoacoustic wavelength of hemoglobin detection. Analysis of angiogenesis.

  

Exogenous contrast agents, as long as they absorb between 680nm and 950nm, can be detected by photoacoustic imaging systems. For example, commonly used ICGs, almost all nanomaterials, etc., can be produced in photoacoustic systems. Good detection signal. ,


2. Applications in nanomaterials (new contrast agents)


Nanomaterials have better light absorption in the near infrared due to their uniform dispersibility and nanometer size, which is also the basis of photoacoustic imaging. Endra Nexus 128, because its excitation wavelength is at 680-950 nm, all nanomaterials include carbon nanotubes, gold nanorods, gold nanocages, and gold nanospheres. Both can have corresponding light absorption at this wavelength, which is very beneficial for the research of novel nanoprobes.
Because the Endra Nexus 128 photoacoustic system features non-invasive detection and because it is true 3-D imaging, it is ideal for continuous observation of experimental animals. After the probe is injected into the experimental animal, the experimental animal can be intermittently scanned to obtain dynamic information that the probe is ingested, absorbed, and cleared in the body.

For example, in order to study the dynamic distribution process of gold nanorods in mouse transplanted tumors, the animals were scanned every 15 minutes after the injection of the nano-probes, and the scan was performed 5 times for a total time of 75 minutes. The scanned photoacoustic image can be fused in the software and generate corresponding dynamic curves for our analysis.
From the interface of software analysis, it can be seen that Nexus 128 can realize all aspects of probe experimental research, including comparing the absorption time of different probes, comparing the absorption time of different regions of the tumor, testing the concentration of probes at different absorption times, and testing the target. The 3-D distribution of the probe inside the tumor, and the like. These applications are critical for probe development and preclinical evaluation.

3. Anatomy application

Since the muscles, bones, and proteins of the living organism have a certain degree of absorption in the near-infrared region, as an endogenous contrast agent, different photoacoustic signals can be presented under photoacoustic scanning, and thus can be used as a means of anatomical imaging. . In the photoacoustic imaging of the figure below, we can clearly see the various anatomical structures of the mouse.


4. Oncology applications

4.1 Tumor Morphology Due to its high resolution, photoacoustic can exert its unique advantages in tumor morphology research. At the same time, since photoacoustic detection is a non-invasive and non-destructive detection method, there is no harm to the experimental materials, so the interpretation of the research results is more scientific and reasonable.

4.2 Tumor perfusion Due to the different peripheral and internal structures of the tumor, these two different regions may cause different behaviors for the absorption of contrast agents. Peripheral perfusion of tumors is usually faster, because there are more angiogenesis and metabolism, so the clearance rate is fast, and the curve shows a pattern of rapid rise and fall. On the contrary, due to slow metabolism, the perfusion shows slow rise and fall. Mode, and the overall signal peak is much lower than the tumor peripheral signal. This can be used for tumor state determination. If these two peaks are gradually close in time, it indicates that the tumor is inhibited and progresses toward a good prognosis, and vice versa.

4.3 Probe Absorption - Dynamic Scanning

For any commercially available probe and contrast agent, the Endra Nexus 128 can perform dynamic scans accordingly. Then analyze the ingestion, absorption, and removal processes in the accompanying professional software. The following figure is a dynamic process of absorption and clearance in a tumor model of a mouse using human ICG as an example.
Figure 1: Comparison of photoacoustic images before and after intravenous ICG. Figure 2: Status of ICG distribution in different regions of the tumor.
Figure 3: Comparison of dynamic process of ICG uptake in different regions. The above picture shows the peripheral of the tumor. It can be seen that the ICG absorbs faster and reaches the peak and then decreases. The lower graph shows the internal dynamics curve of the tumor, showing that the absorption is slow until the last scan signal. Still rising.

4.4 Tumor treatment

Since the Nexus 128 can observe tumor morphology and can also detect tumor perfusion and dynamic scanning, it can be applied to the evaluation of tumor treatment. It is possible to directly or semi-quantitatively determine whether the tumor is inhibited from the size of the tumor, or to evaluate the efficacy of the antitumor drug by changes in the internal and external structures of the tumor.

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