WASHINGTON — Researchers have developed a new endoscope that combines ultrasound with optical coherence tomography (OCT) to assess the structural characteristics of the lining of the uterus, called the endometrium, in unprecedented detail. The new probe could one day help doctors diagnose infertility issues related to endometrial receptivity with greater accuracy than current imaging technologies while reducing the need for invasive biopsies.
“This tool combines the two techniques of ultrasound and OCT, which allows it to obtain more information and provide a more accurate assessment of the condition of the endometrium than traditional vaginal ultrasound,” said said research team leader Xiaojing Gong of the Chinese Academy Shenzhen Institutes of Advanced Technology. Sciences. “It has the potential to be used for basic endometrial research and to advance the clinical assessment of endometrial responsivity and other endometrial-related diseases.”
In the magazine Optica Publishing Group Express Biomedical Optics, the researchers report the ability of their dual-mode endoscope to differentiate between healthy and injured endometrial tissue in rabbit models based on surface features and depth information. This is the first in vivo demonstration of intrauterine endoscopic imaging in small animals, with a probe measuring just 1.2 mm in diameter.
The endometrium plays a vital role in the ability of a blastocyst to implant in a uterus and develop into a healthy fetus. Implantation failure is recognized as a major bottleneck in the reproductive process, with impaired endometrial receptivity accounting for approximately two-thirds of implantation failures.
By providing detailed structural information about the endometrium, the probe could offer a less invasive way to determine whether endometrial problems are the cause of infertility, which affects around 10-20% of women worldwide, as well as help diagnose other uterine health problems.
“The system can obtain the information of endometrial thickness, endometrial echo pattern and endometrial surface damage information, which plays an important role in the evaluation of the endometrial receptivity,” Gong said. “It also has the potential to detect diseases of the uterus, such as endometrial cancer and uterine fibroids.”
Create a better probe
The current gold standard for assessing endometrial receptivity is through biopsies, which involve surgically removing and analyzing a small sample of tissue. Endoscopic imaging is a less invasive method, but current endoscopes can only identify larger defects in the uterus, such as anatomical malformations or polyps, and not assess endometrial structure. A vaginal ultrasound can provide information about endometrial thickness and other structural features, but lacks the resolution and contrast needed to comprehensively assess endometrial receptivity.
OCT is an imaging technique that uses relatively long wavelength light (commonly known as near infrared light) to produce high resolution images from a scattering medium. It has been adapted for diagnostic tools in several medical fields including ophthalmology, cardiology and dermatology. Previous studies have shown that OCT imaging can be used to identify endometrial structural features associated with implantation failures.
For the new study, the researchers enhanced a prototype they had previously developed to combine OCT and ultrasound imaging in a single probe. The OCT modality provides detailed information about the superficial endometrium, including its surface information, while ultrasound provides information about its entire thickness. Since several characteristics of the endometrium affect implantation success, the combination of these imaging modalities provides a more accurate picture of endometrial receptivity than either mode individually.
The catheter is designed to cross the cervix, enter the uterine cavity and inject water to facilitate high resolution imaging. A series of tiny, custom-designed optical and ultrasound components are arranged within the catheter to achieve both ultrasound and OCT mode. The improved probe also uses single-mode fiber, which offers higher resolution and lower noise for OCT mode. Additionally, the researchers used a metal coil to allow the probe to rotate for a full 360-degree field of view once inside the uterus.
“The imaging catheter can realize the rotation and retraction scan through the rotation-retraction unit at the rear end and obtain the three-dimensional ultrasound-OCT image of the uterus,” Gong said.
A powerful combination
To test the endoscope, the researchers used it to image the uterine lining of four anesthetized rabbits. Some of the rabbits were healthy while others had undergone a procedure to wash out the endometrium with ethanol for varying lengths of time, causing varying degrees of tissue damage.
The researchers quantified the characteristics of the endometrium, including its thickness, distribution and surface roughness separately in ultrasound and OCT modalities. OCT images showed that healthy endometrial tissues had a smoother and more continuous surface, while damaged tissues were rougher. In ultrasound images, the endometrium was found to be thicker in healthy tissue and thinner in damaged areas. Although each modality provided valuable information on its own, it was not until the researchers combined the information from each that they were able to fully and accurately assess the degree of tissue damage.
“These results demonstrated the importance of bimodality in detecting the extent of endometrial damage,” Gong said. “The variance is too large and it is difficult to distinguish the degree of injury through a single mode of information. However, the combination of information from the two modalities can differentiate the degree of damage.
The probe also provided echo patterns that were similar to what can be obtained with a vaginal ultrasound but with better resolution. Additionally, the images revealed physical features such as polyp-like formations as small as 200 microns, demonstrating the probe’s ability to discern tiny lesions that could affect endometrial health.
The researchers plan to add a photoacoustic mode to increase the probe’s ability to observe blood flow and information about the vascular networks of the uterine lining. Additionally, they are working to improve the size, resolution, and imaging range of the imaging catheter to make it more practical for clinical use in humans.
Paper: J. Zhang, M. Du, J. Fang, S. Lv, W. Lou, Z. Xie, Z. Chen, X. Gong, “In vivo evaluation of the endometrium by dual-modality intrauterine endoscopy, ” Biomedical. Opt. Express, Flight. 13, issue 5, pages 2554-2565 (2022) DOI: https://doi.org/10.1364/BOE.453191
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In vivo evaluation of the endometrium by dual-modality intrauterine endoscopy
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