Patient and Probe Tracking During Freehand Ultrasound

Panorama Ultrasound for Navigation and Guidance of Epidural Anesthesia

Despite the common use of epidural anesthesia in obstetrics and surgery, the procedure can be challenging, especially for obese patients. We propose the use of an ultrasound guidance system employing a transducer-mounted camera to create 3-D panorama ultrasound volumes of the spine, thereby allowing identification of vertebrae and selection of puncture site, needle trajectory and depth of insertion. The camera achieves absolute position estimation of the transducer with respect to the patient using a specialized marker strip attached to the skin surface. The guidance system is validated first on a phantom against a commercial optical tracking system and then in vivo by comparing panorama images from human subjects against independent measurements by an experienced sonographer. The results for measuring depth to the epidural space, intervertebral spacing and registration of interspinous gaps to the skin prove the potential of the system for improving guidance of epidural anesthesia. The tracking and visualization are implemented in real time using the 3D Slicer software package.

Probe localization for freehand 3D ultrasound by tracking skin features

Ultrasound probe localization with respect to the patient's body is essential for freehand three-dimensional ultrasound and image-guided intervention. However, current methods for probe localization generally involve bulky and expensive equipment. In this paper, a highly cost-effective and miniature-mobile system is described for 6-DoF probe localization that is robust to rigid patient motion. In this system, skin features in the scan region are recorded at each ultrasound scan acquisition by a lightweight camera rigidly mounted to the probe. A skin map is built based on the skin features and optimal probe poses are estimated in a Bayesian probabilistic framework that incorporates a prior motion model, camera frames, and ultrasound scans. Through freehand scanning on three different body parts, it is shown that on average, for every probe travel distance of 10 mm, the translational and rotational errors are 0.91 ± 0.49 mm and 0.55 degrees ± 0.17 degrees, respectively. The 3D reconstructions were also validated by comparison with real ultrasound scans.

A needle tracking device for ultrasound guided percutaneous procedures

A novel tracking device is proposed for measuring the position and orientation of a needle with respect to an ultrasound probe. This device is intended to guide an operator during a percutaneous needle insertion so that the needle trajectory can be visually aligned with the target before insertion. The tracking device uses a pair of cameras to track the needle location so that a standard needle can be used without attaching a separate sensor to the needle. The main challenge is to calibrate the tracking system with sufficient accuracy. Calibration methods are described for each of the system parameters. A series of tests show that an overall error of 3.1 +/- 1.8 mm is achieved with two commercial cameras and an error of 6.5 +/- 5.7 mm is achieved with two inexpensive consumer cameras. An analysis of the source of errors reveals that the errors arise from all of the calibration steps. Overall system accuracy is therefore determined by both the quality of the cameras and the performance of calibration.