[Evaluation of the accuracy of volume navigation of sonography and computed tomography using a phantom]

In case of superimpositions of gas in the gastrointestinal tract or the ribs, tissue changes well detectable on computed tomography (CT) cannot be identified sonographically in a number of cases. Combining ultrasonography and CT provides enhanced information compared to sole sonography and volume navigation may be used as an effective tool. Tissue samples easily and safely obtained under sonographic guidance are often necessary to confirm the diagnosis of a suspicious focus. In these cases, the spatial fusion of CT and sonography may also be employed for improved visualization of foci by eliminating superimposition of sonographic images which is a limitation of ultrasound. This study investigated the potential benefit and improved informative value of the fusion of CT and sonography in case of superimpositions and aimed at determining the registration method with the best accuracy.

Sixteen models (10 models with peas [low contrast], 6 models with wooden spheres [high contrast] as round structures) were created. These models were examined by computed tomography and fused using 3 volume navigation protocols. Subsequently, volume-guided sonography was performed. The deviation of the specimens was measured.

In total, 1026 measurements of the pea models and 648 measurements of the wooden sphere models were carried out. A fusion accuracy of 100 % was observed in 9.9 % (102/1026) resp. 9.9 % (64/648) of the models. In 85.4 % (876/1026) resp. 94.1 % (610/648) the deviation was < 5 mm and in 98.1 % (1006/1026) resp. 99.4 % (644/648) it was < 10 mm. The registration protocol in which all reference points were used for spatial fusion proved to be the most accurate CONCLUSION: The registration protocols for volume-guided ultrasound have sufficient biopsy accuracy to merge identical sites and provide the basis for improved volume-navigated biopsy sampling.