Percutaneous needle procedures (PNPs) are minimally invasive procedures that use imaging guidance to diagnose or treat medical conditions. In the treatment of liver cancer, PNPs are becoming increasingly used due to their shorter recovery times and lower complication rates. However, needle placement during PNPs can be challenging due to a lack of direct visualization of the target and liver tissue deformation caused by respiratory motion, patient (re)positioning, and needle insertion. Currently, no imaging modality provides continuous, qualitative visualization while maintaining acceptable radiation levels. Continuous feedback during PNPs could improve needle placement accuracy by enabling real-time adjustments in response to tissue deformation. Previous studies have used external- and internal markers for continuous feedback, but these markers have not been able to fully capture tumor displacement and the underlying causes of deformation. Endovascular insertion is a potential solution to this problem - it involves placing the marker close to the tumor by inserting it through the blood vessels. Here, we present exploratory research that aims to investigate the possibility of using an endovascular marker to capture the displacement of a liver tumor during a PNP.

An ex-vivo porcine liver with artificially created tumors and endovascular catheter markers was used. In the first experiment, robotic-assisted needle insertion was performed on seven tumors with a 13-gauge ablation needle. The second experiment involved simulating respiratory motion with an inflatable sachet to mimic the lungs and create a representable blow zone (the area affected by the inflated sachet). The displacement of the tumor- and endovascular catheter markers were tracked in the x-, y-, and z-directions using a C-arm system making Cone Beam Computed Tomography (CBCT). The x- and y-directions represents the horizontal plane within the liver, and the z-direction is the vertical plane (the direction of the ablation needle). The average offset in millimeters was calculated to quantify the error between the tumor- and catheter marker displacement.

The results of needle insertion showed that catheter markers placed 8-28 mm from the tumor could deduce tumor displacement in the x-direction, with a maximum offset of 1.23 mm. The catheter markers placed 8-13 mm from the tumor were also able to deduce displacement in the z-direction with a maximum offset of 0.23 mm and in Euclidean distance (total path length as measured using Pythagoras' theorem) with a maximum offset of 0.73 mm. Furthermore, the results indicated that, on average, catheter markers placed 8-28 mm from the tumor were able to accurately deduce tumor displacement for needle insertion depths of 0-15 mm. During respiratory motion simulation, tumor- and catheter marker displacement was influenced more by blow zone location than the distance between them. To apply these findings to the human body, it is recommended that the endovascular marker will be positioned in the same sagittal (longitudinal) and coronal (frontal) plane as the tumor. In this study, catheter markers could be used to deduce tumor displacement for inflation volumes of 0-500 ml, which is the typical resting breathing volume.

In conclusion, this study demonstrated that the ability to use endovascular catheter markers to deduce tumor displacement during a percutaneous needle procedure is influenced by the distance between the tumor- and the catheter marker, the depth of the needle, the inflation volume of simulated lungs, and whether the marker is positioned in the same sagittal and coronal plane in relation to the tumor. Future research should focus on determining the optimal number and location of endovascular markers, including a bigger variation and spread of tumor locations, and adjusting insertion techniques, to further realize the clinical applicability of endovascular catheter markers in percutaneous needle procedures.