Armin Schneider, Hubertus Feussner, in Biomedical Engineering in Gastrointestinal Surgery, 2017
5.4.6 3D/4D Ultrasound
3D US is a volumetric imaging technology that provides a 3D view of internal structures. Dynamic volumetric imaging, also known as “4D US” or “real-time 3D US,” extends the visualization with a time frame so that it is able to display motion instead of a static 3D data set.
3D data are usually acquired as a large number of consecutive tomographic images through movement of an US transducer array. Each tomographic image has to be gathered along with its positional information to construct a 3D data set. Accurate positional information is obtained through an electromagnetic position sensor, an electric gyro attached to the probe, or by defining previous movement (Table 5.6).
|Typical applications||Strengths and weaknesses||Recent developments||Research potential and future trends|
|Obstetrics, cardiovascular medicine
|Vague depiction of internal structures||USCT/Warm bath US||Optimizing 3D US, Increasing image quality|
Static 3D images can be acquired manually by moving a 2D transducer across a ROI, or automatically through the use of a 3D transducer that sweeps a 2D array of beams across the ROI. 3D/4D US requires rapid automatic sweeps of multiple adjacent 2D cross-sections.
The software is the core of volumetric imaging technologies, especially 4D visualizations, which need highly optimized algorithms. For applications like scanning a heart, a gated technique is applied to avoid distortion of a 3D data set due to movement. Tomographic images are rearranged according to the phase of the cardiac cycle and a 3D data set is constructed with only tomographic images at the same phase of the cardiac cycle. The heart can be seen beating three-dimensionally by reconstructing many 3D data sets into a single cardiac cycle.
Strengths and Weaknesses
3D images provide examiners with an abundance of information, reducing the amount of interpretation needed and limiting the probability of misdiagnoses.
Compared to common US modifications, the amount of data involved is much higher. The depiction of one ROI demands up to 20 GB of data storage. Despite the increasing capability of computers, the processing time of data sets is still a limiting factor.
Recent Developments and Current Research
US travels through soft tissue at an average speed of 1540 m/s, which limits 3D scanning speed. The parallel receiving technique uses one broad US beam that is transmitted; its echoes are received as plural ultrasonic beams. In a 2D array probe, a high degree of parallel receiving is used and high-speed 3D scanning is possible. As a result, the profound advancements in 3D/4D imaging are mainly due to a general evolution of electronics and transducer arrays from linear systems to 1.25D, 1.5D, 1.75D, and 2D arrays and the latest matrix phase transducers, which are a current field of research .
Currently, there are plans to make 4D US available through handheld devices, which has already been achieved in high-end devices .
Today, the relevance of 3D/4D US systems is still low due to high purchasing costs and technological performance issues. In the future, the relevance of these systems is expected to rise as a result of technical improvements and mass-market adoption.