Cone beam CT guidance provides superior accuracy for complex needle paths compared with CT guidance

Abstract

Objective: To determine the accuracy of cone beam CT (CBCT) guidance and CT guidance in reaching small targets in relation to needle path complexity in a phantom.

Methods: CBCT guidance combines three-dimensional CBCT imaging with fluoroscopy overlay and needle planning software to provide real-time needle guidance. The accuracy of needle positioning, quantified as deviation from a target, was assessed for inplane, angulated and double angulated needle paths. Four interventional radiologists reached four targets along the three paths using CBCT and CT guidance. Accuracies were compared between CBCT and CT for each needle path and between the three approaches within both modalities. The effect of user experience in CBCT guidance was also assessed.

Results: Accuracies for CBCT were significantly better than CT for the double angulated needle path (2.2 vs 6.7 mm, p<0.001) for all radiologists. CBCT guidance showed no significant differences between the three approaches. For CT, deviations increased with increasing needle path complexity from 3.3 mm for the inplane placements to 4.4 mm (p=0.007) and 6.7 mm (p<0.001) for the angulated and double angulated CT-guided needle placements, respectively. For double angulated needle paths, experienced CBCT users showed consistently higher accuracies than trained users [1.8 mm (range 1.2-2.2) vs 3.3 mm (range 2.1-7.2) deviation from target, respectively; p=0.003].

Conclusion: In terms of accuracy, CBCT is the preferred modality, irrespective of the level of user experience, for more difficult guidance procedures requiring double angulated needle paths as in oncological interventions.

Advances in knowledge: Accuracy of CBCT guidance has not been discussed before. CBCT guidance allows accurate needle placement irrespective of needle path complexity. For angulated and double-angulated needle paths, CBCT is more accurate than CT guidance.

Figure 1.

Outline of the interventional three-dimensional abdominal phantom showing an internal target (black dot) and three corresponding needle paths: dotted/dashed line, inplane path; dashed line, angulated path; and solid line, double angulated path. Grey spots represent the corresponding skin entry points. The axes indicate the right (R), head (H) and anterior (A) sides of the phantom.

Figure 2.

(a) CT image used for measurement of deviation between target centre and needle tip in an angulated needle placement. Slice thickness is 3 mm. (b) Enlargement of the CT image in (a) with distance measurement indicated in black. (c) Axial view of CBCT volume with measurement of distance between target centre and tip of angulated placed needle in white. All images show the same target with the needle following an angulated needle path placed by the same interventional radiologist.

Figure 3.

Boxplot showing deviation of the needle tip from target point for both cone beam CT (grey) and CT-guided procedures (white) for the three needle paths separately.