Psychophysical evaluation of in-situ ultrasound visualization.

We present a novel psychophysical method for evaluating ultrasonography based on Real-Time Tomographic Reflection (RTTR), in comparison to Conventional Ultrasound (CUS). The method measures the user's perception of the location of an ultrasound-imaged target independently from assessing the action employed to reach it. Three experiments were conducted with the Sonic Flashlight (SF), an RTTR device, and CUS. The first two experiments determined subjects' perception of target location with a triangulation-by-pointing task. Depth perception with the SF was comparable to direct vision, while CUS caused considerable underestimation of target depth. Binocular depth information in the SF was shown to significantly contribute to its superiority. The third experiment tested subjects in an ultrasound-guided needle insertion task. Because the SF provides visualization of the target at its actual location, subjects performed insertions faster and more accurately by using the SF rather than CUS. Furthermore, the trajectory analysis showed that insertions with the SF generally went directly to the target along the desired path, while CUS often led to a large deviation from the correct path consistent with the observed underestimation of target depth. These findings lend great promise to the use of RTTR-based imaging in clinical practice and provide precise means of assessing efficacy.