How I do it: Cone-beam CT during transarterial chemoembolization for liver cancer

Abstract

Cone-beam computed tomography (CBCT) is an imaging technique that provides computed tomographic (CT) images from a rotational scan acquired with a C-arm equipped with a flat panel detector. Utilizing CBCT images during interventional procedures bridges the gap between the world of diagnostic imaging (typically three-dimensional imaging but performed separately from the procedure) and that of interventional radiology (typically two-dimensional imaging). CBCT is capable of providing more information than standard two-dimensional angiography in localizing and/or visualizing liver tumors ("seeing" the tumor) and targeting tumors though precise microcatheter placement in close proximity to the tumors ("reaching" the tumor). It can also be useful in evaluating treatment success at the time of procedure ("assessing" treatment success). CBCT technology is rapidly evolving along with the development of various contrast material injection protocols and multiphasic CBCT techniques. The purpose of this article is to provide a review of the principles of CBCT imaging, including purpose and clinical evidence of the different techniques, and to introduce a decision-making algorithm as a guide for the routine utilization of CBCT during transarterial chemoembolization of liver cancer.

Figure 1:

CBCT imaging involves the rotation of a C-arm equipped with a flat panel detector around the patient. Multiple 2D projections are acquired and reconstructed to generate a 3D volumetric data set.

Figure 2:

Configuration of angiography suite during TACE. The C-arm is aligned with the table and positioned at the head end, and accessory equipment (eg, shielding screens, intravenous poles) is positioned in such way that it can be easily removed to allow for 3D scanning. The large monitor shows patient monitoring information and different imaging inputs, including live fluoroscopy, 2D angiography, and the results of the embolization planning and guidance software overlaid on live fluoroscopy images.

Figure 3:

Example of a DEB-TACE procedure shows the various steps (ie, visualization, targeting, and assessing response). The patient is a 61-year-old man with a unifocal HCC in segment 4 of the liver (arrowhead), seen on preprocedural contrast-enhanced MR images as a hypervascular tumor in the arterial phase (A) and as a hypoattenuating tumor in the portal venous phase (B). Pretreatment right hepatic angiograms show a tumor blush (arrowhead, C and D). Pretreatment DP-CBCT images demonstrate the 3D hepatic arterial anatomy (arrowhead) in the arterial phase (E), and the tumor enhancement (arrowhead) in the delayed phase (F). The patient underwent a first DEB-TACE treatment. After DEB-TACE, DP-CBCT was performed to assess technical success of embolization. The early arterial (G) and delayed parenchymal (H) phases images predicted intraprocedurally the same tumor response (arrowhead) when compared with the post-TACE follow-up contrast-enhanced MR images obtained 1 month later in the arterial (I) and portal venous (J) phases.

Figure 4:

Example of a conventional TACE procedure that highlights the same steps as shown in Figure 3. The patient is an 81-year-old man with a unifocal HCC in the right lobe of the liver (arrowhead) seen in the arterial (A) and portal (B) venous phases of the preprocedural contrast-enhanced MR images. Pretreatment right hepatic angiogram and fluoroscopy show a tumor blush (arrowhead, C and D). Pretreatment DP-CBCT images depict the 3D hepatic arterial anatomy (arrowhead) in the arterial phase (E) and the tumor enhancement (arrowhead) in the delayed venous phase (F). The patient underwent a first conventional TACE treatment. After TACE, nonenhanced CBCT (Lip-CBCT) was performed to assess lipiodol deposition into the tumor (arrowhead, G), which was similar to the nonenhanced follow-up multidetector CT study (H). The incomplete lipiodol uptake (arrowhead) was predictive of poor tumor response on the 1-month follow-up contrast-enhanced MR images in both the arterial (I) and portal venous (J) phases.

Figure 5:

Example of a superselective DEB-TACE procedure performed using software guidance technology. The patient is a 79-year-old man with a unifocal HCC in segment 4 of the liver (arrowheads), seen in the arterial (A) and portal venous (B) phases of the preprocedural contrast-enhanced MR images. Pre-TACE DP-CBCT images demonstrate the 3D hepatic arterial anatomy (arrowhead) in the arterial phase (C) and the tumor enhancement (arrowhead) in the delayed venous phase (D). Software allowed tumor segmentation and 3D roadmap generation to reach the targeted tumor (E). The patient subsequently underwent successful DEB-TACE therapy. After DEB-TACE, nonenhanced CBCT (Deb-CBCT) was performed to assess contrast medium saturation at the tumor margin (arrowhead, F). The degree of contrast medium saturation at the tumor margin predicted tumor response on the 1-month follow-up contrast-enhanced MR images in both the arterial (G) and portal venous (H) phases.

Figure 6:

A suggested algorithm for the optimal use of different CBCT techniques during each successive step of diagnostic, intraprocedural (“see”, “reach” the targeted tumors, and “assess” treatment success), and follow-up imaging. For example, a patient with multiphasic multidetector (M-MDCT) diagnostic imaging would benefit from intraprocedural CBCT-AP plus DP-CBCT to “see” and “reach” the tumor, or a patient with contrast-enhanced MR imaging (CE-MRI) would benefit from DP-CBCT. According to treatment type, conventional TACE (C-TACE) or DEB-TACE, Lip-CBCT would help to assess intraprocedural treatment success after conventional TACE just as DP-CBCT or Deb-CBCT after DEB-TACE. Finally, follow-up diagnostic imaging based on multiphasic multidetector CT or contrast-enhanced MR imaging would be performed at 4–6 weeks after treatment.