  Current commercial matrix transducers for 3D DCE-US do not display
side-by-side B-mode and contrast-mode images when capturing volumetric data,
thus leaving the operator with no position feedback during lengthy
acquisitions. The purpose of this study was to investigate the use of
transducer tracking to provide positioning feedback and to re-align images to
improve quantification. An interventional tracking system was developed in
house using an infrared camera and a 3D-printed tracking target attached to a
X6-1 matrix transducer. The system displays a virtual probe on a separate
screen and allows to capture a reference position to provide operator feedback
when no B-mode image is available. To test this set-up, five experienced
operators were asked to locate an image landmark within a volunteer liver in
B-mode images using the X6-1 connected to an EPIQ7 system. Operators were then
asked to maintain the transducer position for 4 minutes under three feedback
methods: i) B-mode, ii) display of real-time virtual transducer, iii) blind.
The magnitude of displacement over the cine was computed as an estimate of the
imaging position error. We also investigated whether transducer coordinates can
be used to re-align images due to motion and improve contrast ultrasound
perfusion repeatability. A total of 8 patient data were obtained under an IRB
for this. Results suggest that tracking can assist operators maintain a steady
position during a lengthy acquisition. With blinded acquisition, an average
displacement of 4.58 mm (S.D. 2.65 mm) was noted. In contrast, the average
displacement for tracking-feedback was comparable to B-mode at 3.48 mm (S.D.
0.8 mm). We also observed that perfusion parameters had better repeatability
after re-alignment.
