Clinical Evaluation of an Innovative Metal-Artifact-Reduction Algorithm in FD-CT Angiography in Cerebral Aneurysms Treated by Endovascular Coiling or Surgical Clipping

Abstract

Treated cerebral aneurysms (IA) require follow-up imaging to ensure occlusion. Metal artifacts complicate radiologic assessment. Our aim was to evaluate an innovative metal-artifact-reduction (iMAR) algorithm for flat-detector computed tomography angiography (FD-CTA) regarding image quality (IQ) and detection of aneurysm residua/reperfusion in comparison to 2D digital subtraction angiography (DSA). Patients with IAs treated by endovascular coiling or clipping underwent both FD-CTA and DSA. FD-CTA datasets were postprocessed with/without iMAR algorithm (MAR+/MAR−). Evaluation of all FD-CTA and DSA datasets regarding qualitative (IQ, MAR) and quantitative (coil package diameter/CPD) parameters was performed. Aneurysm occlusion was assessed for each dataset and compared to DSA findings. In total, 40 IAs were analyzed (ncoiling = 24; nclipping = 16). All iMAR+ datasets demonstrated significantly better IQ (pIQ coiling < 0.0001; pIQ clipping < 0.0001). iMAR significantly reduced the metal-artifact burden but did not affect the CPD. iMAR significantly improved the detection of aneurysm residua/reperfusion with excellent agreement with DSA (naneurysm detection MAR+/MAR−/DSA = 22/1/26). The iMAR algorithm significantly improves IQ by effective reduction of metal artifacts in FD-CTA datasets. The proposed algorithm enables reliable detection of aneurysm residua/reperfusion with good agreement to DSA. Thus, iMAR can help to reduce the need for invasive follow-up in treated IAs.

Keywords: cerebral aneurysm; endovascular coiling; flat-detector computed tomography angiography; metal-artifact-reduction algorithm; surgical clipping.

Figure 1

Flowchart of the iMAR technique. The interpolation-based iMAR technique is described in detail by Meyer et al. [21,22].

Figure 2

A 63-year-old patient with an aneurysm of the basilar artery in the initial DSA ((A) red arrow) with consecutive treatment via endovascular coiling (B). Six months later, DSA control revealed a reperfusion in the aneurysm center ((C) red arrow). The aneurysm was not assessable in iMAR− FD-CTA due to severe metal artifacts (D). After application of iMAR and the following significant metal artifact reduction, FD-CTA also demonstrated reperfusion in the aneurysm center ((E) red arrow).

Figure 3

An 84-year-old patient with an aneurysm of the anterior communicating artery in the initial DSA ((A) red arrow) with consecutive treatment via endovascular coiling (B). Six months later, DSA control revealed a reperfusion at the aneurysm base ((C) red arrow). The aneurysm was not assessable in iMAR− FD-CTA due to severe metal artifacts (D). Thanks to a significant metal artifact reduction, iMAR+ FD-CTA also demonstrated the basal aneurysm reperfusion in accordance with the DSA ((E) marked with red dotted line).

Figure 4

An 80-year-old patient with an aneurysm of the right posterior communicating artery treated via intracranial clipping. DSA control revealed a small residuum at the aneurysm neck ((A) red arrow). The aneurysm was not assessable in iMAR− FD-CTA due to severe metal artifacts (B). After application of iMAR and the following significant metal artifact reduction, FD-CTA also demonstrated the small residuum ((C) red arrow).

Figure 5

Side-by-side examples of FD-CTA images without/with application of the iMAR (iMAR−/iMAR+) in patients with treated intracranial aneurysms via endovascular coiling. Upper row shows a patient with a treated aneurysm of the anterior communicating artery, basal row shows a patient with a treated aneurysm of the internal carotid artery. In the iMAR− images of both cases, the parent vessels are not (upper case) or poorly differentiable (basal case), whereas in the iMAR+ images, the parent vessels are very well differentiable.

Figure 6

Exemplary CPD measurement in iMAR−/+ FD-CTA images. CPD is indicated by the red arrow.

Figure 7

Evaluation of IQ regarding diagnostic value in patients with coiled (A) and clipped (B) IAs. The iMAR algorithm significantly improves IQ. Evaluation of IQ regarding metal-artifact burden in patients with coiled (C) and clipped (D) IAs. The iMAR algorithm significantly reduced metal-artifact burden in all cases. (E) Number of detected aneurysm reperfusions in patients treated via endovascular coiling. iMAR+ FD-CTA allows better aneurysm reperfusion detection with good agreement with DSA reference in comparison with iMAR− images. (F) Number of detected aneurysm residua in patients treated via surgical clipping. iMAR+ FD-CTA allows better aneurysm residua detection in comparison with iMAR− images. p-values less than 0.0001 are marked with “****”.