Ultrasound Physics with Sononerds Unit 12a

This paragraph introduces Unit 12A, focusing on transducer types and characteristics. It discusses how transducers create images and key definitions that are essential for understanding their operation. The unit is divided into two parts: 12A covering transducer characteristics and imaging principles, and 12B exploring resolution, specifically elevational resolution, and its relation to transducer construction. The lecture begins with definitions that provide context for the study of different transducers and their field of view shapes, such as sector, blunted sector, rectangular, and others. It also touches on the importance of the transducer's footprint and the role of crystals (PZT elements) in transducers, including single-element and array types.

The second paragraph delves into the specifics of array transducers, explaining the arrangement of crystals in 1D, 1.5D, and 2D arrays and how these configurations impact imaging capabilities. It discusses the benefits of 1.5D arrays in controlling beam thickness and the potential for 2D arrays to create 3D imaging. The paragraph also introduces the concept of channels in transducers, which include the crystal, connecting wire, and machine electronics, emphasizing their role in activating elements and receiving echoes. Furthermore, it explains the idea of multi-focus in annular array transducers and the trade-off between temporal and lateral resolution.

This paragraph discusses the evolution of focusing and steering mechanisms in transducers. It starts with the obsolescence of multi-focus fixed transducers and transitions to electronic focusing, which is predominant in modern systems. Electronic focusing is possible with array transducers and allows for adjustable focus by manipulating electrical voltage patterns. The paragraph also explains beam steering, introducing manual, mechanical, and electronic (phasing) steering methods, and how they expand the field of view for comprehensive imaging.

The fourth paragraph focuses on mechanical steering, which uses a motor within the transducer to physically move the PZT element and create new scan lines for imaging. It highlights the issues associated with mechanical steering, such as the need for oil to maintain the motor and the risk of oil leakage or air intrusion, which can affect transducer performance. The paragraph contrasts mechanical steering with electronic steering, which is more common in modern ultrasound systems.

This paragraph explores electronic steering in depth, explaining how it uses phasing to steer the beam through delays in crystal activation. It describes how the slope of the voltage pattern affects the direction of the beam and how all elements are needed for beam formation in phased transducers. The paragraph also touches on combined mechanical and electronic steering, which is primarily found in 2D array transducers used for 3D imaging.

The sixth paragraph introduces the concept of sequencing, where small groups of elements are activated to create a beam across the transducer surface, in contrast to phasing. It discusses the impact of damaged PZT crystals on imaging, explaining how damage can result in dropouts or reduced image quality. The paragraph emphasizes the importance of transducer care to prevent damage and the different effects of crystal damage on sequencing versus phased transducers.

The seventh paragraph discusses 3D and 4D imaging, explaining the transition from 2D pixel-based images to 3D voxel-based images for volume measurement. It highlights the use of 3D imaging in determining the volume of fluid or soft tissue and the popular perception of 3D imaging for creating lifelike images of fetuses. The paragraph also explains 4D imaging as the addition of real-time movement to 3D images, requiring significant processing power and resulting in lower frame rates.

This paragraph outlines the exploration of various ultrasound transducer types, focusing on six key transducers: mechanical, annular, phased array, linear, convex, and vector. It emphasizes the importance of understanding the image shape, crystal shape, number, and potential impact of damaged PZT crystals on different transducers. The paragraph also covers how beams are steered and focused, common applications, and the evolution of ultrasound technology from obsolete to modern transducers.

The eighth paragraph discusses two types of mechanical transducers: the mechanical sector and the mechanical annular array transducers. The mechanical sector transducer, with its circular PZT crystal and motor, creates a sector-shaped image and is prone to issues due to its mechanical nature. The annular array transducer, with its concentric circle crystals, also creates a sector-shaped image but offers better lateral resolution. Both transducers are now mostly obsolete but were instrumental in the development of modern ultrasound technology.

The ninth paragraph introduces the linear switched array and phased array transducers. The linear switched array, with its rectangular crystals, uses sequencing for imaging and is limited in steering capabilities. It has been largely replaced by modern transducers. The phased array transducer, with its rectangular crystals, utilizes electronic steering and focusing, offering adjustable focus and improved imaging capabilities, particularly in cardiac applications.

This paragraph discusses the linear sequential array and curved linear sequential array transducers. The linear sequential array uses rectangular crystals and electronic focusing for vascular and small-part imaging. It can also perform wide scans or convex scans with phasing. The curved linear sequential array, also known as the convex transducer, has a blunted sector image shape due to its curved surface and is commonly used for abdominal, vascular, and OB/GYN applications.

The fourteenth paragraph covers the vector array transducer, which combines elements of phased and linear sequential array transducers, and the 3D transducer. The vector array transducer creates a flat top sector or trapezoid sector image and uses electronic steering and focusing with groups of elements. The 3D transducer, made up of 2D arrays, captures information from all three planes simultaneously and renders a 3D image, often used for applications like IUD placement and fetal ultrasounds.

The final paragraph concludes the lecture on transducer types, emphasizing the importance of understanding the six key transducers: mechanical, annular, phased, linear, convex, and vector. It advises learners to focus on the provided charts and definitions to grasp how images are created and the capabilities of each transducer. The paragraph also mentions the second section of Unit 12, which will delve deeper into elevational resolution. Additionally, it encourages learners to use the workbook activities and 'nerd check' questions for practice and self-assessment.