3D ultrasound imaging has attained a high level of quality, but its dependence on the examiner continues to be a problem. The ability to visualize structures in three dimensions plays a major role in this regard. The ability to form a three-dimensional mental picture varies greatly among different examiners, and it can be learned only to a degree. Examiners who are poor visualizers will have great difficulties in conducting examinations and interpreting the findings. This leads to yet another problem: documentation and reporting the findings to another physician. Even if the sonographer has acquired a good three-dimensional impression of the disease process, it is still difficult to share that impression with another physician. This problem is particularly acute in cases where the recipient of the ultrasound report will also carry out the breast surgery. As a rule, the ultrasound documentation consists of two-dimensional images that show a lesion in cross section but do not convey a spatial impression of the lesion or its location in the tissue. This also makes it difficult to compare ultrasound findings with the results of other studies such as mammography or MRI. A common makeshift solution is to make line drawings of the lesion and describe its location as accurately as possible. But because malignant tumors are not simple geometric figures, it is very difficult to document and describe their shape and extent, especially if the lesions are multifocal. Given the complexity of breast anatomy, then, a reasonable approach is to represent the lesion and the surrounding organ in three dimensions. This can be accomplished by acquiring and storing three-dimensional image data and rendering the images in an extended or three-dimensional format. This also permits other examiners to repeat the breast examination and review suspicious findings even when the patient herself is no longer available.

Another problem of ultrasound is that the small field of view under the transducer demonstrates only a small section of the whole breast. A sectional image of the lesion without the surrounding tissue makes planning for surgery and also comparison with mammography and MRI difficult. A panoramic scan enables the investigator to produce a two-dimensional cross-sectional image of the whole breast. In comparison with the small field of view under the real-time transducer, this allows much better recognition of the whole breast anatomy and the localization of a lesion within the breast.

In conventional ultrasound sound is always transmitted in one direction only, producing a simple scan image. One of the important physical limitations of ultrasound is that good reflection of sound is only given if the ultrasonic beam hits structures in a perpendicular angle. If the angle of sound inclination is oblique, refraction occurs and the structure cannot be displayed. Breast anatomy is rather complex with many reflectors in variable directions. Therefore conventional ultrasound is limited with regard to demonstrating all breast structures. Compared with simple scanning, a compound image is created by image reconstruction from multiple scan directions. This improves the display of architectural details considerably.

Fig. 18.1 Invasive ductal carcinoma, size 12 × 17 × 14 mm. Sectional planes reconstructed from the volume acquisition: sagittal (upper left), transverse (upper right), horizontal (C scan, lower left), and transparent display (lower right). The slice thickness for the transparent mode has been selected to large. Therefore the tumor is partly covered from the surrounding breast tissue. The C scanning plane clearly shows the typical retraction pattern of carcinomas.