**1. Introduction**

I sincerely hope that you will enjoy and gain much benefit in reading this book. I would like to take this opportunity to thank all the authors who worked so hard and gave a lot of time in contributing to this book. The professional support given by the editorial board and the officials of InTech at every stage of this project was excellent. Finally, I would like to extend my sincere gratitude to my dear friend and colleague, Mr Andrew Fairhead, Honorary lec‐ turer and Former ultrasound Engineer at NHS Grampian, for his valuable comments and

**Gunti Gunarathne (PhD, FIET)**

Robert Gordon University, UK.

School of Engineering,

support throughout this project.

VIII Preface

Soon after the discovery of x-rays, physicians recognized the importance of using imaging to guide interventional procedures. As imaging technology became more advanced with the development of fluoroscopic, CT, MR and ultrasound systems, image-guided interventions have become a critical tool for physicians in dealing with complex interventional and surgical procedures. Today, image-guided procedures make use of computer-based systems to provide real-time three-dimensional (3D) information of the anatomy of the patient being treated. The information is presented in various ways, such as virtual graphical image overlays, or multiscreen approaches to help the physician precisely visualize and target the anatomical site.

Since the development of Computed Tomography (CT) in the early 1970s, the availability of 3D anatomical information has revolutionized diagnostic radiology by providing physicians with 3D images of anatomical structures. The pace of development has continued with the development of 3D magnetic resonance imaging (MRI), positron Emission Tomography (PET), and multi-slice and cone beam CT imaging. These imaging modalities have stimulated the development of a wide variety of image-guided interventional procedures.

Although 2D ultrasound (2D US) imaging has been used extensively for interventional procedures, such as biopsy and guidance of ablation procedures, 3D ultrasound is slowly growing in clinical applications [1]. Today, the majority of US-based diagnostic and interven‐ tional procedures are still performed using conventional 2D imaging. Over the past two decades, university-based investigators and commercial companies have utilized both 1D and 2D arrays while developing 3D ultrasound (3D US) imaging techniques. 3D US techniques have been increasingly used in diagnosis, minimally invasive image-guided interventions and intra-operative use of imaging [2-4]. Today, most US system manufacturers provide 3D US imaging capability as part of the systems. Advances in 3D US imaging technology have resulted in high quality 3D images of complex anatomical structures and pathology, which are used in diagnosis of disease and to guide interventional and surgical procedures [5-9].

© 2013 Fenster et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Fenster et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In this chapter we focus on the recent development of 3D US imaging as it applies to imageguided interventions. The chapter will briefly review how 3D US images are obtained and then will provide two examples of recent development of 3D US- guided interventional procedures.

These mechanical 3D scanning systems allow the user to optimize the image resolution by

3D Ultrasound Imaging in Image-Guided Intervention

http://dx.doi.org/10.5772/55230

3

Two approaches have been used in the development of mechanical 3D US scanning systems: integrated 3D US transducers with the scanning mechanism within the transducer housing; and external mechanical fixtures that hold the housing of a conventional 2D US transducers. Both approaches have been successfully used for a variety of clinical applications including

Most US system manufacturers offer integrated 3D US transducers that are based on a mechanically-swept transducer or "wobbler". In these systems a 1D US array is wobbled or swept back and forth inside the 3D transducer housing. Digital 2D US images that are generated while the 1D US array is wobbled, which are used in the 3D US image reconstruction. These 3D transducers are larger than conventional 2D US transducers. These types of 3D US transducers are convenient to use but require a special US machine that can control the 3D

Many interventional 3D US-guided interventional systems are currently using external fixtures for mechanical 3D scanning since researchers typically do not get access to the control of the US system for development of novel interventional systems. In this approach, a motorized custom made fixture is used to house the conventional 2D US transducer. A computer is used to control the motor to cause the US transducer to tilt or "wobble". The video stream from the US machine is digitized using an analogue or digital frame grabber. Since the relative angle between the acquired 2D images is known, a 3D image can be reconstructed as

Although the external mechanical 3D scanning fixtures are bulkier than integrated 3D transducers, they can be used with any US manufacturer's transducer, obviating the need to purchase a special 3D US machine. In addition, the external fixture approach can take advant‐ age of improvements in the US machine (e.g., image compounding, contrast agent imaging) and flow information (e.g., Doppler imaging) without any changes in the scanning mechanism.

Both approaches used in mechanical 3D US scanning allow short imaging times, ranging from about 3 to 0.2 3D images/s. The 3D images are of high quality and also include B-mode and

Figure 1a is a diagram of the mechanical tilt approach of a conventional 1D array US transducer about an axis parallel to the face of the transducer, and 1b shows the tilting axis away from the face of the transducer. The latter approach is typically used in integrated 3D scanning mech‐ anisms. In both approaches, the acquired 2D US images are arranged as a fan with an adjustable angular spacing, e.g., 1.0°. To generate a 3D image, the housing of the 3D probe or external fixture remains fixed on the skin of the patient while the US transducer is wobbled. The time required to generate a 3D US image depends on the 2D US image update rate and the number of 2D images needed to generate the 3D image. The 2D US image update rate depends on the US machine settings (i.e., depth setting and number of focal zones) and number of acquired 2D US images is determined by the chosen angular separation between the acquired 2D images,

adjusting the angular or spatial interval between the acquired 2D image [10].

interventional applications.

the 2D images are acquired.

Doppler information.

*2.2.1. Wobbling or tilting mechanical 3D US scanners*

scanning and reconstruct the acquired 2D images into a 3D image.
