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Year : 2020  |  Volume : 16  |  Issue : 2  |  Page : 276-279

In vivo microscopy of arterial distribution embolic particles in rabbit mesenteric artery

Department of Vascular and Interventional Radiology, First Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China

Date of Submission29-Jun-2019
Date of Decision01-Jan-2020
Date of Acceptance20-Jan-2020
Date of Web Publication28-May-2020

Correspondence Address:
Caifang Ni
Department of Vascular and Interventional Radiology, First Affiliated Hospital of Soochow University, No. 188 Shizi Street, Suzhou 215006
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcrt.JCRT_435_19

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 > Abstract 

Purpose: To study the arterial distribution of embosphere microsphere (EM) and polyvinyl alcohol (PVA) particles in rabbit mesenteric artery using in vivo microscopy.To study the arterial distribution of embosphere microsphere (EM) and polyvinyl alcohol (PVA) particles in rabbit mesenteric artery using in vivo microscopy.
Methods: Sixteen New Zealand rabbits were divided into four groups, namely large PVA (560–710 μm), small PVA (150–350 μm), large EM (500–700 μm), and small EM (100–300 μm). The mesenteric arteries of the experimental animals were embolized under fluoroscopic guidance and visualized using in vivo microscopy. The embolized vessel diameter and arterial distribution of embolic agents were compared.
Results: The diameters of occluded vessels in large PVA, small PVA, large EM, and small EM groups were 430.60 ± 67.30, 200.95 ± 70.54, 387.79 ± 92.51, and 143.81 ± 39.65 μm, respectively. PVA occluded significantly larger vessels than EM when the particle size was similar (P < 0.001). The proportion of EM at the bifurcation of the artery was significantly higher than that of PVA particles (large PVA < large EM, χ2 = 4.325, P < 0.038; small PVA < small EM, χ2 = 6.68, P < 0.01).
Conclusion: Both PVA and EM could occlude vessels smaller than the particle size, and EM resulted in deeper penetration. The location of embolic particles in the artery is mainly related to the shape of particles.

Keywords: Animal experiment, arterial distribution, embolic particle, embolization treatment, microscope

How to cite this article:
Li W, Yang J, Gu C, Yin Y, Li Z, Ni C. In vivo microscopy of arterial distribution embolic particles in rabbit mesenteric artery. J Can Res Ther 2020;16:276-9

How to cite this URL:
Li W, Yang J, Gu C, Yin Y, Li Z, Ni C. In vivo microscopy of arterial distribution embolic particles in rabbit mesenteric artery. J Can Res Ther [serial online] 2020 [cited 2020 Jul 16];16:276-9. Available from: http://www.cancerjournal.net/text.asp?2020/16/2/276/285186

 > Introduction Top

Transcatheter embolization has developed into one of the most important techniques for interventional radiology.[1] With the advent of microcatheters and new embolic materials, interventional embolization has been widely applied in tumor therapy and gastrointestinal bleeding.[2],[3] The basic goal of embolization is to block, reduce, or slow blood flow.[4] Imaging examinations are often used to evaluate the distribution of embolic agents,[5],[6],[7] and histopathology analysis is another commonly used method.[8] In this study, we described our preliminary findings of the size of the occluded vessels and the distribution of embolic particles in rabbit mesenteric artery usingin vivo microscopy.

 > Materials and Methods Top

In vivo microscope

The in vivo microscope is specialized equipment for observing dynamic microcirculation. It is modified from the traditional microscope, and its light can pass through tissues using a high-throughput light microscope with long focal length. After anesthesia, the organs or tissues of the experimental animal are placed on the observation window and viewed through an objective lens.[9]

Embolic particles

The embolic agents used in this study were nonspherical polyvinyl alcohol particles (PVAs; Alicon, Hangzhou, China) and embosphere microspheres (EMs; Biosphere Medical, Rockland, USA). Both PVA and EM are commonly used as permanent embolic agents in the management of arteriovenous malformations and hypervascular tumors. There were two granulometric size ranges of PVA, 560–710 μm [large PVA, [Figure 1]a and 150–350 μm [small PVA, [Figure 1]b and [Figure 1]c), compared with similar size ranges of EM, 500–700 μm [large EM, [Figure 1]d and 100–300 μm [small EM, [Figure 1]e and [Figure 1]f.
Figure 1: Embolic agents in rabbit mesenteric artery (a) a large PVA particle at the bifurcation of the artery; (b and c) small PVA particle in the artery; (d) large microspheres at the bifurcation of the artery; (e and f) small EMs at the bifurcation of the artery. PVA = Polyvinyl alcohol, EM = Embosphere microsphere

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Experimental animals

All experiments in our study were approved by the Institutional Animal Care and Use Board of our institution and were performed according to facility regulations on animal care and experiments. Sixteen adult New Zealand white rabbits, each weighing 2.5–3.0 kg, were divided into four groups of four rabbits each.

Embolization procedure

All animals were not fed for 12 h before operation and anesthetized with intramuscular injection of xylazine hydrochloride (Shengda Animal Medicine, Dunhua, China) at a dose of 0.2 mL/kg. After sterilizing the left groin region and skin cutting, the left femoral artery was isolated, and a self-made sheath was introduced. Routine angiography was performed before embolization with a 2.7 F microcatheter (Progreat; Terumo Corporation, Tokyo, Japan) to confirm the anatomy of mesenteric artery. For angiography, 3 mL of contrast medium (Ioversol; Hengrui Pharma, China) was injected at a rate of 1 mL/s and using pressure of 300 pounds per square inch. Then, the branches of the mesenteric artery, which were the feeding arteries of the jejunum and ileum, were superselectively catheterized.

The suspensions of PVA and EM were prepared as previously described. Briefly, one bottle of embolic particles was poured into a 20-mL syringe. Then, PVA particles were compressed to remove the air, and the supernatant fluid of EM was expressed through the tip. After that, the syringe was filled to 20-mL total volume with a 1:1 saline and contrast mixture. For each embolic agent, the total 20-mL suspension was divided into ten 2-mL syringes after agitation. Afterward, the suspension was delivered into the feeding arteries of the jejunum and ileum at a rate of 0.1 mL/s via the microcatheter with a 2-mL syringe, each of which was followed by a 5-mL saline flush. Approximately 6 mL of suspension was injected in each animal.

Microscopic examination

A standard compound binocular microscope (NK200; Nanguang, Suzhou, China) was modified forin vivo microscopy and equipped for transillumination and epi-illumination. After embolization, animals were transferred to the laboratory. If necessary, xylazine hydrochloride was intramuscularly injected at the dose of 0.1 mL/kg. After sterilizing, experimental animals underwent a midline abdominal incision. The procedures of in vivo microscopy have been described in previous studies.[10] The jejunum and ileum were gently exteriorized through the incision and positioned over a window of mica on a specially designed microscope tray. Throughout the observation period, the jejunum, ileum, and mesenteric region were constantly irrigated with normal saline at body temperature. The microscopic images were obtained using ×4, ×8, ×10, ×20, and ×40 dry objectives and ×10 oculars, and the video images were recorded and stored in the computer connected to the microscope.

To evaluate the location of embolic agents and the diameter of occluded vessels, images of the occluded vessels were recorded and stored in the computer for further measurement. In our study, the positions of embolic agents in the arteries were divided into the point of bifurcations and side branches of vessels. The diameter of vessels was measured as the internal diameter of the vessel lumen. Furthermore, both the proximal and distal diameters of occluded vessels were measured at a point where they were 0.5–1.0 mm away from the particle, which is in relation to the size of the particles.

Statistical analysis

Quantitative data were expressed as means ± standard deviation. Mann–Whitney and Kruskal–Wallis tests were performed for comparisons of the diameter of the occluded vessels. A Chi-square test was performed to compare the location of occlusion between each type of microsphere. Statistical significance was set at P < 0.05 (two-sided). The data were analyzed with SPSS statistical software (version 25.0; IBM Corporation, Armonk, NY, USA).

 > Results Top

Observed embolic agent

A total of 715 embolic agents were observed and recorded using anin vivo microscope. The number of embolic agents in each group is shown in [Table 1].
Table 1: Comparison of the proportion of location according to the kind and size range of embolic agents

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Diameter of occluded vessel

The diameter of occluded vessels was 430.60 ± 67.30 μm (median 440.34 μm) in large PVA group, 200.95 ± 70.54 μm (median 175.05 μm) in small PVA group, 387.79 ± 92.51 μm (median 376.16 μm) in large EM group, and 143.81 ± 39.65 μm (median 138.65 μm) in small EM group.

For the same kind of embolic agents, large agents occluded significantly larger vessels than small particles (both P < 0.001). For agents with similar size, nonspherical PVA particles occluded significantly larger vessels than spherical EM (both P < 0.001) [Figure 2].
Figure 2: Comparison of the diameter of the vessels occluded by different embolic agents. MW = Mann–Whitney U-test, PVA = Polyvinyl alcohol, EM = Embosphere microsphere

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Location of embolic agent

The location of embolic agents was observed with a low-power microscope. In general, 527 (73.71%) embolic agents were located at the bifurcation of the artery [Figure 1]a, [Figure 1]b, [Figure 1]c, [Figure 1]d, [Figure 1]e, black arrows], and 188 (26.29%) embolic agents were located at the side branch of vessels [Figure 1]c, e, and [Figure 1]f, white arrows].

For the same kind of embolic agents, the proportion of large agents located at the bifurcation of the artery was higher than that of small agents but with no statistical significance. For agents of similar size, the proportion of spherical EM at the bifurcation of the artery was significantly higher than that of nonspherical PVA particles [Table 1].

 > Discussion Top

In clinical practice, transcatheter embolization is now widely used in the management of many kinds of disease, especially for the treatment of hepatocellular carcinoma.[11],[12] However, in most situations, interventional radiologists have to rely on their own clinical experience when choosing the embolic agent.

The results of our study showed that both PVA and EM could occlude vessels much smaller than the particle size. In addition, most of these embolic particles were located at the bifurcation of artery, which, to our knowledge, had not been reported in previous studies. Compared to PVA particles, EMs occluded significantly smaller vessels when their particle size was similar (P < 0.001), and PVA particles were more likely to be located at the bifurcation, which had not been described in previous studies.

Several animal studies were conducted to evaluate the arterial distribution of embolic agents and the size of occluded vessels.[6],[13] However, most of these studies were based on the imaging and histological findings. In our study, we used anin vivo microscope that allowed direct observation of embolic particles. The embolic particles in our study were embolic agents commonly used in clinical practice. Since these embolic agents are not a precise size but within a granulometric size range, we decided to use those embolic agents with significantly different granulometric size ranges.

Our findings were quite different from those in previous experiments. With the application ofin vivo microscopy, the location of embolic particles could be directly observed, as well as the diameter of occluded vessels. Interestingly, we found that the diameter of distal part of embolic agents in the vessel was much smaller than the granulometric size of embolic particles, and in most cases, the diameter of proximal area of embolic agents was similar or smaller than the granulometric size of embolic particle [Figure 1]f. To reduce error, the diameter of occluded vessels was calculated as the mean of the proximal diameter and the diameter of the distal branches of occluded vessels.

In earlier studies, some scholars believed that PVA particles would remain in vessels similar to their own size.[14],[15] The possible reasons for the different results between our study and previous studies are as follows. First, the target organs were different in our study. Second, histologic findings were usually based on the section with embolic particles while ignoring those sections without embolic particles, whereasin vivo microscopy allows for the vessels and embolic agents to be directly observed. Third, PVA particles are nonspherical and easier to aggregate with each other, leading to the formation of larger particles. Regarding the location of embolic particles, the proportion of embolic agents at the bifurcation of the artery might be mainly related to the shape of embolic agents. We assumed that PVA particles that are nonspherical might result in increased friction between PVA particles and vessel walls, which might make PVA particles more resistant to moving forward to the next bifurcation.

Based on these findings, it is important to recognize that the embolic particles could have penetrated deeper than we thought. In clinical practice, interventional radiologists should pay more attention to the choice of optimal embolic particles, according to the size of the target vessels. Our study has several limitations. First, the results of our experiments in rabbits cannot be translated directly to humans due to the differences of the patterns and the diameters of arteries between humans and rabbits. Second, the long-term effects of embolization could not be evaluated because the animals were sacrificed immediately afterin vivo microscopy. Third, only two size ranges of each kind of embolic agent were examined in our study. Fourth, only the mesenteric artery was studied in our experiments, since it can be easily observed using anin vivo microscope. However, the embolized vessel diameter may differ in different organs.[15] Fifth, the range of ischemic changes was not observed in the present study, and further studies regarding this matter should be performed.

 > Conclusion Top

In vivo microscopy shows promise for comparative studies of embolic agents. Both PVA and EM could occlude the vessels smaller than the particle size, and when compared with nonspherical PVA particles, spherical EMs resulted in deeper penetration. In addition, the location of embolic particles in the artery is mainly related to the shape of particles. Moreover, further investigations in different organs with different embolic agents are needed.

This study was supported by Six One Projects for high-level health personnel in Jiangsu Province (grant number LGY2018077), Jiangsu Provincial Medical Youth Talent (QNRC2016711), and Suzhou Science and Technology Plan (SYS201611 and KJXW2016005).

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

 > References Top

Sheth RA, Sabir S, Krishnamurthy S, Avery RK, Zhang YS, Khademhosseini A, et al. Endovascular embolization by transcatheter delivery of particles: Past, present, and future. J Funct Biomater 2017;8. pii: E12.  Back to cited text no. 1
Huang Y, Jia Z, Tu J, Shen T, Tian F, Jiang G. Supplemental conventional transarterial embolization/chemoembolization therapy via extrahepatic arteries for hepatocellular carcinoma. J Cancer Res Ther 2017;13:720-4.  Back to cited text no. 2
Dutta R, Mahato RI. Recent advances in hepatocellular carcinoma therapy. Pharmacol Ther 2017;173:106-17.  Back to cited text no. 3
Angle JF, Siddiqi NH, Wallace MJ, Kundu S, Stokes L, Wojak JC, et al. Quality improvement guidelines for percutaneous transcatheter embolization: Society of Interventional Radiology Standards of Practice Committee. J Vasc Interv Radiol 2010;21:1479-86.  Back to cited text no. 4
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Laurent A, Wassef M, Namur J, Ghegediban H, Pelage JP. Arterial distribution of calibrated tris-acryl gelatin and polyvinyl alcohol embolization microspheres in sheep uterus. Cardiovasc Intervent Radiol 2010;33:995-1000.  Back to cited text no. 6
Thompson JG, van der Sterren W, Bakhutashvili I, van der Bom IM, Radaelli AG, Karanian JW, et al. Distribution and detection of radiopaque beads after hepatic transarterial embolization in swine: Cone-beam CT versus microCT. J Vasc Interv Radiol 2018;29:568-74.  Back to cited text no. 7
Laurent A, Wassef M, Chapot R, Houdart E, Merland JJ. Location of vessel occlusion of calibrated tris-acryl gelatin microspheres for tumor and arteriovenous malformation embolization. J Vasc Interv Radiol 2004;15:491-6.  Back to cited text no. 8
McCuskey RS. A dynamic and static study of hepatic arterioles and hepatic sphincters. Am J Anat 1966;119:455-77.  Back to cited text no. 9
Kan Z, Ivancev K, Lunderquist A, McCuskey PA, McCuskey RS, Wallace S.In vivo microscopy of hepatic metastases: Dynamic observation of tumor cell invasion and interaction with Kupffer cells. Hepatology 1995;21:487-94.  Back to cited text no. 10
Wang H, Liu Y, Shen K, Dong Y, Sun J, Shu Y, et al. A comparison between radiofrequency ablation combined with transarterial chemoembolization and surgical resection in hepatic carcinoma: A meta-analysis. J Cancer Res Ther 2019;15:1617-23.  Back to cited text no. 11
Zhou J, Liu Y, Ren Z, Zhang Y, Zhang M. Transarterial chemoembolization with gelatin sponge microparticles for Barcelona Clinic Liver Cancer Stage C and large hepatocellular carcinoma: Initial clinical experience. J Cancer Res Ther 2017;13:767-72.  Back to cited text no. 12
Laurent A, Wassef M, Saint Maurice JP, Namur J, Pelage JP, Seron A, et al. Arterial distribution of calibrated tris-acryl gelatin and polyvinyl alcohol microspheres in a sheep kidney model. Invest Radiol 2006;41:8-14.  Back to cited text no. 13
Quisling RG, Mickle JP, Ballinger WB, Carver CC, Kaplan B. Histopathologic analysis of intraarterial polyvinyl alcohol microemboli in rat cerebral cortex. AJNR Am J Neuroradiol 1984;5:101-4.  Back to cited text no. 14
Verret V, Ghegediban SH, Wassef M, Pelage JP, Golzarian J, Laurent A. The arterial distribution of Embozene and Embosphere microspheres in sheep kidney and uterus embolization models. J Vasc Interv Radiol 2011;22:220-8.  Back to cited text no. 15


  [Figure 1], [Figure 2]

  [Table 1]


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