Introduction:
Abdominal aortic aneurysm (AAA) monitoring can be conducted using the comparatively new technique of three-dimensional ultrasound (3D-US), which may have higher accuracy than traditional two-dimensional ultrasound (2D-US) assessment. Ultrasound is a good tool for estimating the greatest possible diameter of an abdominal aortic aneurysm, which is important in determining the requirements for treatment at presentation or during long-term monitoring. Traditionally, two-dimensional (2D) ultrasound has been used to diagnose AAAs and monitor them over an extended period without the radiation risk and expense of computed tomography (CT). The measurement of aneurysm diameter and volume using three-dimensional (3D) ultrasonography may provide a more precise means of assessing AAAs.
What Is Aneurysm?
An aneurysm develops when the wall of an artery weakens, resulting in an excessively large bulge. Blood is transported from the heart to the rest of the body via arteries and returned to the heart and lungs via veins. The most dangerous possibility associated with an aneurysm is that it can burst, perhaps leading to a stroke or severe bleeding that might be fatal. A big aneurysm can cause blood clots and impair blood flow.
Although aneurysms can occur in any blood vessel, they typically develop in the arteries that supply the brain or in the abdominal or chest regions of the aorta, the major blood vessel that delivers blood from the heart.
The different types of aneurysms include aortic aneurysms, abdominal aortic aneurysms, carotid aneurysms, popliteal aneurysms, cerebral aneurysms, thoracic aortic aneurysms, and mesenteric artery aneurysms.
What Is 3D Ultrasound?
Conventional two-dimensional grayscale ultrasound images can be transformed into a volumetric dataset using a technique called three-dimensional ultrasound. The 3D image may be further examined subsequently. The method was created to solve problems, especially in obstetric and gynecologic examinations and also in vascular abnormalities.
What Are the Methods for Producing 3D-US Pictures?
Three primary methods exist for obtaining 3D-US information: mechanical, matrix, and freehand.
A motor housed inside the mechanical three-dimensional ultrasound transducer operates, capturing a sequence of two-dimensional pictures. These 2D photos are then gradually integrated into a 3D volume reconstruction. When compared to a matrix transducer, the imaged volume is comparatively small. As a result, this technology can only photograph limited portions of the structure.
Typically, a matrix 3D-US transducer that is sold commercially consists of up to 9,000 piezoelectric crystal grids. Compared to mechanical transducers, the imaging volume is greater, and image acquisition is far faster, taking only around a second. All three picture planes can be used for image acquisition because of the grid of crystals and electrical sequencing. When comparing the image resolution to the mechanical transducer, it is marginally lower. In matrix scanning, the fixed crystal grid can capture images at a greater and longer range than a mechanical probe, but the volume is still constrained. As a result, the anatomy of lengthy vessels is not always visible in a single collection.
Position sensors and conventional 2D transducers connected to an independent tracking device are used in "Freehand" 3D-US. Using sensors installed on a traditional 2D transducer that is monitored by an optical system or in a magnetic field is the most widely used method. The system can discern the position of the probe, which makes it possible to reconstruct the US pictures into a three-dimensional volume. Because transducers may be moved to cover a wide area of interest and avoid obstructions such as intestinal gas and acoustic shadowing, this approach allows the technician more freedom.
How Is 3D Ultrasound Used in the Management of Aneurysms?
Three primary 3D-US applications that are pertinent to AAA have been investigated in various studies.
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Assessing AAA size, including maximal diameter and volume.
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Endoleak detection after endovascular aneurysm repair (EVAR).
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Rupture risk prediction models.
1. Assessing AAA Size:
While AAA diameter is the standard indication for treatment, there is still disagreement over the best imaging modality. The primary source of operator variability in ultrasonic imaging is the difference in scanning plane orientation among operators. 3D-US can overcome these drawbacks because it allows the diameter of the AAA to be measured along its true axis, as is made possible by CTA (computed tomography angiography). Enabling measurements in orthogonal planes lessens the reliance on the user and may improve the accuracy and consistency of measurements.
Following endovascular aneurysm repair (a less invasive procedure for addressing aortic aneurysms with a stent graft), aneurysm shrinkage measured by maximal diameter is regarded as effective aneurysm elimination. 3D data obtained with a mechanical or matrix transducer needs to be postprocessed employing specialized software in order to measure AAA volume. With this technology, the entire length of AAA cannot be scanned in a single scan. The exact position of the maximum AAA diameter must be used as an indicator to establish a "partial volume" in order to make up for it.
2. Finding Endoleaks Following EVAR (Endovascular Aneurysm Repair):
Since EVAR was initially begun, CTA has been regarded as the "gold standard" for post-EVAR monitoring and has been included in all follow-up programs. In order to detect endoleaks, ultrasound techniques are gradually taking the place of CTA as a non-intrusive, safe, radiation-free, and affordable alternative. The fact that ultrasound is operator-dependent and requires an expert to comprehend two-dimensional pictures in 3D is a typical criticism of the system. This could make it difficult to interpret complex scans. This inaccuracy can be minimized by using a 3D system that supports multiplanar reconstructions.
Compared to uniplanar angiography or regular CEUS, 3D-CEUS (contrast-enhanced ultrasound) provided a more accurate means of detecting and classifying endoleaks. While its widespread application for completion imaging looks improbable, 3D-CEUS is still an option for patients who face a possibility of renal injury from X-ray contrast.
3. Rupture Risk Prediction Models:
The finding that small aneurysms may rupture while much larger aneurysms remain intact for years emphasizes the need for rupture risk prediction, even if it is evident that the likelihood of AAA increases with maximum aneurysm diameter. Additional indicators of rupture risk include AAA morphology, aneurysm volume, biomechanical evaluation of AAAs, and intraluminal thrombus volume. Thus far, these metrics have depended on CTA. It would be beneficial to be able to extract physiological parameters from a noninvasive, low-cost, radiation-free method that could be related to rupture risk. Considering only three pertinent studies, it is evident that the use of 3D-US for this purpose is still in its early stages.
Conclusion:
3D ultrasound is a great way to visualize an aneurysm. It is less expensive than the alternatives, faster, radiation-free, and less stressful for the patient. Three-dimensional ultrasound measurement of the aneurysm diameter has demonstrated encouraging results, enhancing accuracy and consistency. Nevertheless, there are not enough studies assessing 3D-US in a clinical setting, which might prevent this new modality from being used to its full potential.
