NIH researchers develop CT needle-guidance app for smartphones

Radiology researchers at the National Institutes of Health have created an app that uses a smartphone’s camera and gyroscope to optimize needle-insertion angle for planning and performing percutaneous CT-guided biopsies and ablations.

Lead author Sheng Xu, PhD, senior author Bradford Wood, MD, and colleagues describe their work in an article published online Sept. 27 in the American Journal of Roentgenology.

The app works by overlaying the interventionalist’s planned angle on the camera display in real time, they explain. The planned angle remains in place regardless of camera orientation (landscape or portrait), guiding placement of the actual needle during a procedure.

Needle placement can be performed either in front of or behind the device. If the screen is perpendicular to the planned path, the smartphone shows the Bull’s-Eye View mode, in which the angle is selected after the needle’s hub overlaps the tip in the camera, Xu and colleagues explain.

To validate the approach, the team conducted phantom studies, evaluating hardware accuracies, Guideline mode and Bull’s-Eye View mode. (The results are available to non-subscribers of AJR in the study abstract.)

‘Accurate, effective and easy’

Further, the researchers demonstrated the accuracy and efficacy of the method in a proof-of-concept clinical case with institutional review-board approval—namely, a biopsy performed at the NIH’s Center for Interventional Oncology.

For this the interventionalist set an axial angle of 52 degrees in the planning CT image, then sealed the smartphone in a sterile bag and held it near the patient to trace the insertion alongside the guidance display.

The resulting CT scan provided data to measure the actual angle of insertion, in the process confirming its accuracy and efficacy.

“Mobile devices can be useful for guiding needle-based interventions,” Xu et al. conclude. “The hardware is low cost and widely available. The method is accurate, effective and easy to implement.”

Laying out the rationale for pursuing their innovation, the authors note that numerous needle-guidance systems are commercially available.

“However, these systems have not been widely adopted in practice because of a variety of limitations, including cost, ergonomics and added procedural time or workflow complexity,” they point out.

Clinical trial underway

In their discussion, Xu and colleagues state their experimental results suggest that smartphone guidance can improve on conventional needle navigation and placement protocols.

“Although speculative, this tool could be more useful for inexperienced operators or those with minimal training in CT-guided procedures,” they write.

The authors state that a clinical trial is now being conducted to test the technique for accuracy and feasibility in regular clinical practice.

Looking ahead to potential future developments, they comment that most smartphones come equipped with an accelerometer.

“In theory, when both the gyroscope and the accelerometer are being used, all six degrees of freedom of the smartphone can be tracked, which could enable many image guidance applications, such as image fusion between the camera video and CT image,” they write. “Unfortunately, it takes double integrals to calculate the translation, which can be unstable and inaccurate with the current hardware technology. If position tracking of the needle becomes available, it may lead to major changes in the field of surgical navigation by offering low-cost solutions.”