Evaluation of 3D ultrasound for image guidance

Reliability of tomographic 3D ultrasound in measuring internal carotid artery plaque volume

BACKGROUND

Tomographic 3D ultrasound (t3DUS) is a promise imaging technique for quantifying carotid plaque through measuring the degree of stenosis and plaque volume. Carotid plaque volume (CPV) could add benefit in predicting the potential risk of stroke.

PURPOSE

To assess the reproducibility and accuracy of t3DUS for measuring CPV within the internal carotid artery in patients undergoing carotid endarterectomy.

MATERIAL AND METHODS

t3DUS was used to obtain CPV in vivo from 25 symptomatic patients prior to surgery. Ex vivo CPV from the carotid endarterectomy specimen was then measured using a validated saline displacement method as a reference standard. CPV for each patient was measured twice using both methods (total n = 50 per technique). Intraclass correlation coefficient (ICC) and Bland-Altman plot were used to establish bias and limit of agreement between CPV measurements.

RESULTS

There was an excellent agreement between t3DUS and reference test with respect to measuring CPV with an ICC value of 0.98 (95% confidence interval = 0.97-0.99, P < 0.001). Bias in measurements was 0.02 ± 0.11 cm3 (95% limit of agreement = -0.19 to 0.25). Intra-observer agreement of t3DUS CPV measurements was excellent with an ICC value of 0.95 (95% confidence interval = 0.92-0.97, P < 0.001). Bias in measurements was 0.004 ± 0.07 cm3 (95% limit of agreement = -0.14 to 0.15).

CONCLUSION

t3DUS is a reproducible imaging method and showed excellent agreement with the reference standard with respect to measuring CPV. These findings suggest that t3DUS has the potential to be a valuable non-invasive tool for assessing carotid plaque burden and predicting the risk of stroke.

3D ultrasound guided navigation system with hybrid image fusion

A prototype of a navigation system to fuse two image modalities is presented. The standard inter-modality registration is replaced with a tracker-based image registration of calibrated imaging devices. Intra-procedure transrectal US (TRUS) images were merged with pre-procedure magnetic resonance (MR) images for prostate biopsy. The registration between MR and TRUS images was performed by an additional abdominal 3D-US (ab-3D-US), which enables replacing the inter-modal MR/TRUS registration by an intra-modal ab-3D-US/3D-TRUS registration. Calibration procedures were carried out using an optical tracking system (OTS) for the pre-procedure image fusion of the ab-3D-US with the MR. Inter-modal ab-3D-US/MR image fusion was evaluated using a multi-cone phantom for the target registration error (TRE) and a prostate phantom for the Dice score and the Hausdorff distance of lesions . Finally, the pre-procedure ab- 3D-US was registered with the TRUS images and the errors for the transformation from the MR to the TRUS were determined. The TRE of the ab-3D-US/MR image registration was 1.81 mm. The Dice-score and the Hausdorff distance for ab-3D-US and MR were found to be 0.67 and 3.19 mm. The Dice score and the Hausdorff distance for TRUS and MR were 0.67 and 3.18 mm. The hybrid navigation system showed sufficient accuracy for fusion guided biopsy procedures with prostate phantoms. The system might provide intra-procedure fusion for most US-guided biopsy and ablation interventions.