Extended Field of View in Breast Sonography

Introduction

The size of the field of view (FOV), i. e. the bidimensional space on the monitor of the scanner where the anatomic area explored is displayed, is notoriously small, particularly for high-resolution, linear transducers. Consequently, the operator has to continuously move the probe with to-and-fro, rotational, and angulate movements to explore the entire breast and to define the anatomical relationship between the various normal and abnormal structures encountered. The simultaneous display of various normal and abnormal findings can be difficult or even impossible. Additionally, when the examination has been completed, it becomes difficult for the operator to reconstruct mentally the whole spectrum of findings from the collection of (printed or electronic) images.

The FOV of a linear probe is rectangular and it is limited by the frontal length of the probe, usually four centimetres. It is possible to increase the scan panoramic view by freezing the scan and then moving to the adjacent section with a splicing manoeuvre (dual imaging), by using a larger probe (for example 6 cm in length), or finally by using a trapezoid scan, where the FOV is progressively larger in its deepest part (image bottom). Nevertheless, these techniques often cannot significantly achieve a wide enough FOV to cover the area of interest, particularly when imaging the breast. The breast is large, in comparison with the length of commonly-used sonography transducers, and it is impossible to depict it entirely at once or to display multiple abnormalities in a single image. Consequently it is sometimes difficult to define, to measure, and to render in the final report, the topography and spatial relationship of the abnormalities encountered. This is particularly evident in the case of multifocal disease and of locally-advanced breast cancer.

Real-time, extended-FOV (EFOV) sonography is based on electronically extending the acquired image plane to obtain wide, high-quality gray-scale (eventually also with colour or power-Doppler) images. In this pictorial essay we illustrate the possibilities, limitations, pitfalls, and practical value of real-time, EFOV reconstruction in the sonographic evaluation of various breast abnormalities. Institutional review board permission to use anonymous images without individual consent was obtained for the purpose of this paper. To our knowledge there is no published paper dealing with EFOV scanning of the breast; we could only find an exhibit abstract (Krämer S et al. Ultraschall in Med 1999; 20: S 104).