Residency · Residency · Interventional Radiology
Cone-Beam CT in Interventional Radiology
Introduction
Cone-beam computed tomography (CBCT) is an advanced imaging capability integrated into modern angiographic systems that provides three-dimensional, cross-sectional imaging during interventional procedures. By performing a rotational acquisition with the C-arm, CBCT bridges the gap between fluoroscopic guidance and conventional CT, enabling real-time volumetric assessment without transferring the patient.
Physics and Image Acquisition
Principles of CBCT
A cone-shaped X-ray beam and flat-panel detector rotate around the patient, typically through a 200-degree arc. Multiple projection images (150-600 frames) are acquired during the rotation over 5-20 seconds. Volumetric data is reconstructed using a Feldkamp-Davis-Kress (FDK) filtered back-projection algorithm. Spatial resolution approaches 0.1-0.2 mm, superior to multidetector CT for high-contrast structures.
Acquisition Protocols
| Protocol | Contrast | Acquisition | Primary Application |
|---|---|---|---|
| Non-contrast CBCT | None | Single rotation | Device position, lipiodol retention, bony anatomy |
| Contrast-enhanced CBCT | Selective arterial injection | Delayed rotation | Tumor vascularity, feeder identification |
| Dual-phase CBCT | Selective injection | Arterial + delayed | Tumor vs. parenchyma differentiation |
Non-contrast CBCT: assessment of device position, bony anatomy, or dense materials (e.g., lipiodol retention). Contrast-enhanced CBCT: selective arterial injection with delayed rotational acquisition to map tumor vascularity and perfusion. Dual-phase CBCT: arterial and delayed acquisitions to differentiate tumor enhancement from surrounding parenchyma.
Image Quality Considerations
Cone-beam artifacts: scatter, beam hardening, and truncation artifacts are more pronounced than in conventional CT. Motion artifacts from respiration can degrade image quality; breath-hold or respiratory gating is essential. Soft tissue contrast is inferior to multidetector CT due to increased scatter and limited dynamic range. Metal artifacts from coils, stents, or dense embolic material can obscure adjacent structures.
Clinical Applications
Hepatic Interventions
Transarterial chemoembolization (TACE): CBCT identifies feeding arteries to hepatocellular carcinoma and confirms completeness of lipiodol deposition. Radioembolization (Y-90): CBCT during mapping angiography verifies catheter position and detects extrahepatic perfusion. Intraprocedural CBCT changes management in up to 30% of TACE cases by identifying additional tumors or feeders not seen on DSA.
Percutaneous Procedures
Needle guidance: CBCT provides real-time confirmation of needle trajectory for biopsies, ablations, and drainages. Overlay of CBCT datasets onto live fluoroscopy creates 3D roadmaps for navigating complex anatomy. Particularly valuable for lesions not visible on fluoroscopy or ultrasound.
Vascular Interventions
Assessment of stent deployment and apposition in aortic endografts. Identification of endoleak sources following endovascular aneurysm repair. Evaluation of intracranial stent placement and coil packing in neurointerventional procedures.
Musculoskeletal Applications
Vertebroplasty/kyphoplasty: CBCT confirms cement distribution and detects early cement leakage. Assessment of screw placement in minimally invasive spine procedures. Guidance for sacroiliac joint and facet injections in challenging anatomy.
Dose Considerations
A single CBCT acquisition delivers approximately 3-10 mGy to the skin, comparable to 1-3 minutes of fluoroscopy. Cumulative dose increases significantly when multiple CBCT runs are performed. Dose reduction strategies include: Reducing number of projection images per rotation. Lowering mA and kVp settings when high-contrast structures are the target. Limiting the number of CBCT acquisitions to those that will change management.
Integration with Navigation Systems
CBCT datasets can be fused with preprocedural CT, MRI, or PET-CT for multimodality guidance. Electromagnetic navigation systems use CBCT-derived 3D maps for catheter tracking without continuous fluoroscopy. Augmented fluoroscopy overlays CBCT-derived vascular maps onto live imaging, reducing contrast and radiation exposure.
Limitations
Limited field of view compared to conventional CT (typically 25 cm or smaller). Longer acquisition time increases susceptibility to motion artifact. Inferior soft tissue contrast compared to multidetector CT. Requires a trained operator to optimize acquisition parameters and interpret volumetric data. Not a substitute for diagnostic CT in most clinical scenarios.
Key Clinical Pearls
CBCT during TACE can detect additional tumors missed on preprocedural imaging and DSA, changing treatment strategy in a significant proportion of cases. For Y-90 radioembolization, CBCT is essential for confirming catheter position and detecting non-target perfusion that could result in radiation injury to the lungs or GI tract. Breath-hold technique is critical for hepatic CBCT; even small respiratory motion degrades image quality and reduces diagnostic accuracy. When using CBCT for needle guidance, a single acquisition with 3D overlay can replace multiple fluoroscopic spot checks, potentially reducing overall dose.
References
- Tacher V, Radaelli A, Lin M, Geschwind JF. How I Do It: Cone-Beam CT during Transarterial Chemoembolization for Liver Cancer. Radiology. 2015;274(2):320-334.
- Wallace MJ, Kuo MD, Glaiberman C, et al. Three-Dimensional C-Arm Cone-Beam CT: Applications in the Interventional Suite. J Vasc Interv Radiol. 2009;20(7 Suppl):S523-S537.
- Orth RC, Wallace MJ, Kuo MD. C-Arm Cone-Beam CT: General Principles and Technical Considerations for Use in Interventional Radiology. J Vasc Interv Radiol. 2008;19(6):814-820.
- Meyer BC, Frericks BB, Voges M, et al. Visualization of Hypervascular Liver Lesions During TACE: Comparison of Angiographic C-Arm CT and MDCT. AJR Am J Roentgenol. 2008;190(4):W263-W269.