Abstract

CT-guided percutaneous ablation for liver cancer treatment is a relevant technique for patients not eligible for surgery and with tumors that are inconspicuous on US imaging. The lack of real-time imaging and the use of a limited amount of CT contrast agent make targeting the tumor with the needle challenging. In this study, we evaluate a registration framework that allows the integration of diagnostic pre-operative contrast enhanced CT images and intra-operative non-contrast enhanced CT images to improve image guidance in the intervention. The liver and tumor are segmented in the pre-operative contrast enhanced CT images. Next, the contrast enhanced image is registered to the intra-operative CT images in a two-stage approach. First, the contrast-enhanced diagnostic image is non-rigidly registered to a non-contrast enhanced image that is conventionally acquired at the start of the intervention. In case the initial registration is not sufficiently accurate, a refinement step is applied using non-rigid registration method with a local rigidity term. In the second stage, the intra-operative CT-images that are used to check the needle position, which often consist of only a few slices, are registered rigidly to the intra-operative image that was acquired at the start of the intervention. Subsequently, the diagnostic image is registered to the current intra-operative image, using both transformations, this allows the visualization of the tumor region extracted from pre-operative data in the intra-operative CT images containing needle. The method is evaluated on imaging data of 19 patients at the Erasmus MC. Quantitative evaluation is performed using the Dice metric, mean surface distance of the liver border and corresponding landmarks in the diagnostic and the intra-operative images. The registration of the diagnostic CT image to the initial intra-operative CT image did not require a refinement step in 13 cases. For those cases, the resulting registration had a Dice coefficient for the livers of 91.4%, a mean surface distance of 4.4 mm and a mean distance between corresponding landmarks of 4.7 mm. For the three cases with a refinement step, the registration result significantly improved (p<0.05) compared to the result of the initial non rigid registration method (DICE of 90.3% vs 71.3% and mean surface distance of 5.1 mm vs 11.3 mm and mean distance between corresponding landmark of 6.4 mm vs 10.2 mm). The registration of the preoperative data with the needle image in 16 cases yielded a DICE of 90.1% and a mean surface distance of 5.2 mm. The remaining three cases with DICE smaller than 80% were classified as unsuccessful registration. The results show that this is promising tool for liver image registration in interventional radiology.

Highlights

  • Primary liver cancer is one of the most fatal cancers

  • We propose to register the diagnostic image to the CT image with needle in situ in two stages: first the diagnostic image (D) is registered to the first complete liver operative image (F), which enables integration of the tumor in the planning CT image, and subsequently the initial operative image is registered to the limited field-of-view image with the needle (N)

  • The field of view of the 3D abdominal images is larger than the region of interest i.e. the liver

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Summary

Introduction

Primary liver cancer is one of the most fatal cancers. The 5-year survival rate of patients without treatment is 15% [1,2,3]. Not all the patients are eligible for such an invasive procedure. Invasive approaches such as radiofrequency ablation (RFA), microwave ablation, radiotherapy, chemoembolization, and high-intensity focused ultrasound are alternatives in case surgery is not an option [1, 4]. In chemoembolization drugs are brought to the tumor via a catheter in the arterial system, and in case of ablation, a needle is introduced percutaneously into the tumor. Such treatments, being minimally invasive, require image-guidance during the intervention. These techniques are suitable for patients with tumors detected in early stages (< 3 cm in diameter) [4, 5]

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