What is 3D Ultrasound?
Traditional ultrasonography is performed with two-dimensional (2D) images of anatomy taken from multiple angles. This is done because ultrasound waves travel in a straight plane and cross through the structure in question in the same way that a knife cutting through fruit would. Naturally, since bodily structures and organs are three-dimensional (3D) objects we aim to acquire as many different imaging planes as possible in order to assess as much of the physical structure as possible. In an effort to expand our ability to see from all angles, ultrasounds can be performed using 3D imaging technology. 3D pictures give the healthcare team the ability to see structures (such as a fetus or a heart) as a model that can be rotated, sliced and assessed from all sides.
How Does 3D Ultrasound work?
These 3D images are built using a series of 2D imaging planes acquired in a particular sequence and pieced (or “stitched”) together with software, not unlike a panoramic photograph is made. 3D pictures are acquired without the need of any additional requirement of the patient and does not differ from the traditional ultrasound testing experience in any way. Because the resulting 3D model relies on data from the 2D images, quality plays a hugely important role in the accuracy of the final product. To put it simply, using any suboptimal 2D imaging to generate a 3D picture will result in subpar and potentially non-diagnostic images.
What Type of Ultrasounds Use 3D?
Cardiac Ultrasound
In regards to cardiac ultrasound, or echocardiography, 3D imaging of the heart valves is common. However, because optimal image quality is required for diagnostic 3D images, a transesophageal echocardiogram (images acquired by placing a transducer in the throat and under sedation like an endoscope) is often utilized for smaller heart structures, like valves, as it offers better definition to the upper portions of the heart, due to the esophagus’s proximity to the heart. Since these transesophageal 2D images enhance structure definition, 3D images acquired from this method often also result in a more high-definition model as well. In addition to heart valves, 3D is used to interrogate cardiac masses, measure chamber volumes and placement of intracardiac devices.
Three-dimensional echocardiography is commonly utilized in the pre-operative setting to offer surgeons a full three-hundred-and-sixty-degree view of the anatomy in question. It can also be used intra-operatively to assist in real time, for example to confirm proper placement and positioning of a new heart valve. Finally, 3D images can be used as an important piece of the follow-up analysis of surgical procedures post operatively.
Fetal Ultrasound
Because 3D ultrasound adds an extra dimension when compared to traditional ultrasound, the added detail is an exciting component for fetal ultrasounds. 3D ultrasound provides a realistic visualization of the fetal anatomy. Not only is this exciting for prospective parents to see the details and dimples of their soon to be newborn baby, but it provides clinicians with valuable, diagnostic information.
Three-dimensional sonography in the second and third trimesters allow obstetricians to assess fetal anatomy and identify any abnormalities. 3D images allow for assessment of the anatomy in a complete 360-degree view. Once a data set is obtained, the image can be rotated in order to provide a comprehensive review of anatomical structures like the stomach, bladder, and the heart. In addition, volume calculations are derived from 3D ultrasound images that provide crucial measurements for structures like the gestational sac and yolk sac. 3D ultrasound provides a detailed observation that allows providers to evaluate the development of the fetal anatomy and identify life threatening abnormalities (Kurjak et al., 2002). In addition, the mother’s anatomy is also able to be better assessed with 3D ultrasound. The uterus and ovaries are common points of interest for a 3D examination.
Additional Applications
While OBGYN and cardiac are the most common forms of 3D imaging, there are several other applications of three-dimensional ultrasound that are up and coming in the healthcare world. For example, fetal heart reconstruction is now possible where 3D ultrasound images are sent to a 3D printer (Cattapan et al., 2021). This is helpful in the setting of surgically treating congenital heart defects. Another example of applications of 3D ultrasound includes segmentation of the carotid artery. The carotid artery is a major artery that carries oxygenated blood to the brain. If this artery becomes blocked with atherosclerosis, or fatty plaque, a stroke can occur. Evaluating the presence and development of atherosclerosis can be done more efficiently through 3D ultrasound segmentation of the carotid artery (Jiang et al., 2020). Other applications include assessing tumors in areas like the esophagus, stomach, pancreas or rectum (Saftoiu & Gheonea., 2009). Furthermore, current research is being conducted to study the benefits of using 3D ultrasound to guide needle biopsies.
Why Does It Matter?
3D ultrasound allows for assessment of anatomy from every angle. It also allows for more accurate volume calculations in the body. In addition to optimal assessment of anatomical deformations, 3D ultrasound has been very influential in guiding surgeons throughout procedures, particularly in the field of cardiology. Where imaging modalities like CT and x-ray expose patients to high doses of radiation, 3D ultrasound yields similar information and simultaneously protects them from this type of exposure. As the demand for technology increases in the field of healthcare, ultrasound technologies continue to grow that allow an affordable, portable, and safe form of assessment for patients.
For more information on 2D and 3D sonography visit www.cure.edu.
Written by Alexandra Roberts, RDCS and Brandon Bentley, RCS
References
Arif, M., Moelker, A., & van Walsum, T. (2018). Needle Tip Visibility in 3D Ultrasound Images. Cardiovascular and interventional radiology, 41(1), 145–152. https://doi.org/10.1007/s00270-017-1798-7
Cattapan, C., Bertelli, F., Guariento, A., Andolfatto, M., Veronese, P., & Vida, V. L. (2021). 3D ultrasound-based fetal heart reconstruction: a pilot protocol in prenatal counselling. Revista espanola de cardiologia (English ed.), 74(6), 549–551. https://doi.org/10.1016/j.rec.2020.11.002
Jiang, M., Spence, J. D., & Chiu, B. (2020). Segmentation of 3D ultrasound carotid vessel wall using U-Net and segmentation average network. Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference, 2020, 2043–2046. https://doi.org/10.1109/EMBC44109.2020.9175975
Kurjak, A., Kupesic, S., & Kos, M. (2002). Three-dimensional sonography for assessment of morphology and vascularization of the fetus and placenta. Journal of the Society for Gynecologic Investigation, 9(4), 186–202.
Saftoiu, A., & Gheonea, D. I. (2009). Tridimensional (3D) endoscopic ultrasound - a pictorial review. Journal of gastrointestinal and liver diseases : JGLD, 18(4), 501–505.
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