Three-dimensional ultrasound imaging

Ultrasound is an inexpensive and widely used imaging modality for the diagn osis and staging of a number of diseases. In the past two decades, it has b enefited from major advances in technology and has become an indispensable imaging modality, due to its flexibility and non-invasive character. In the last decade, research investigators and commercial companies have further advanced ultrasound imaging with the development of 3D ultrasound. This new imaging approach is rapidly achieving widespread use with numerous applica tions. The major reason for the increase in the use of 3D ultrasound is related to the limitations of 2D viewing of 3D anatomy, using conventional ultrasound . This occurs because: (a) Conventional ultrasound images are 2D, yet the a natomy is 3D, hence the diagnostician must integrate multiple images in his mind. This practice is inefficient, and may lead to variability and incorr ect diagnoses. (b) The 2D ultrasound image represents a thin plane at some arbitrary angle in the body. It is difficult to localize the image plane an d reproduce it at a later time for follow-up studies. In this review article we describe how 3D ultrasound imaging overcomes thes e limitations. Specifically, we describe the developments of a number of 3D ultrasound imaging systems using mechanical, free-hand and 2D array scanni ng techniques. Reconstruction and viewing methods of the 3D images are desc ribed with specific examples. Since 3D ultrasound is used to quantify the v olume of organs and pathology, the sources of errors in the reconstruction techniques as well as formulae relating design specification to geometric e rrors are provided. Finally, methods to measure organ volume from the 3D ul trasound images and sources of errors are described.