The latest in ultrasound: three-dimensional imaging. Part 1

The state-of-the-art of three-dimensional ultrasound is reviewed to evaluate technological achievements and future possibilities in diagnosis and in the follow-up of medical or invasive therapy.

The problems related to volumetric acquisitions in the tissues of interest to provide three-dimensional images are considered. Three-dimensional images are easier to achieve with computed tomography because the scanning system of this technique is automatic and thus provides sequential slices. The same is true for magnetic resonance imaging which can aquire volumes directly. The problem with ultrasound lies in the fact that the scans are manual and therefore less precise. To obtain three-dimensional images these devices are commonly used: manual scanning probes connected to spatial magnetic evidencers with remote processing; manual scanning probes connected to spatial magnetic evidencers placed on the patient's examination table with processing internal to the ultrasound unit; mechanical probes that can provide volumetric scans; 'matrix' probes. Recent contributions are discussed relative to three-dimensional applications to cardiology (cardiac valve studies), obstetrics (malformations), gynecology (uterine malformations and extensive ovarian disease studies), gastroenterology (diagnosis of pancreatic and hepatoabiliary tumor extent), uro-nephrology (detection of stones, prostatic tumors) and finally in the study of rectal carcinomas.

Nearly all the papers about three-dimensional ultrasound are works in progress because the technique has not been standardized yet and some of its future diagnostic possiblities are difficult to foresee. Moreover, 'matrix' probes are still in the experimental stage. Nevertheless, this technique seems to be able to yield the best results in: fetal malformations; calculating the volumes of normal and diseased organs; the follow-up of masses treated with irradiation/chemotherapy or with alcohol or chemoembolization; the spatial reconstruction of extensive lesions; the detection of small lesions (metastases); the study of some complex functions such as cardiac valve dynamics. But the real problem with three-dimensional sonography is not its efficiency but rather its efficacy, that is which actual role this technique can play in diagnosis and which information it can add to that obtained with two-dimensional imaging.