Feasibility of Angiographic CT in Peri-Interventional Diagnostic Imaging: A Comparative Study with Multidetector CT

Discussion

After neuroendovascular procedures and within the angiography suite, ACT provides cross-sectional CT-like images and enables an immediate detection of hemorrhage or hydrocephalus.^1,2,10 To the best of our knowledge, this is the largest retrospective study exploring the potential of ACT in the emergency diagnosis and the first evaluating the power of ACT in the detection of ischemic lesions.

In accordance with previous studies, in which ACT was proved to be as reliable as MDCT for the detection of ICH, in our collective experience, ACT showed no statistical significance in the evaluation of SAH, IPH, or IVH in comparison with MDCT. Most ratings regarding ACT were “diagnostic,” with 90.3%, 83.9%, and 80% for SAH, IPH, and IVH, respectively. As seen in Fig 1, after intracranial angioplasty and stent placement, a peri-interventional complication like SAH and subarachnoidal contrast agent accumulation can be easily detected in the ACT image. This is 1 of the 5 cases in our series (3 SAHs, 2 IPHs) in which the hemorrhage occurred within the angiography suite during treatment. In such cases, detecting the hemorrhage as soon as possible is crucial for the further management of the patient in the intensive care unit. Additionally, potentially dangerous transfer of the patient to the MDCT scanner would then not be necessary. Figure 2 shows an example in which ACT correctly depicts IPH and IVH after rupture of a venous aneurysm before treatment. Correct EVD placement can be verified in both examinations. In Fig 4, SAH and IVH, after rupture of an internal carotid artery aneurysm, can be accurately diagnosed in the ACT examination.

Regarding the ventricular system and the subarachnoidal spaces, ACT also proved to be a reliable tool. For the infratentorial ventricular spaces, there are some limitations through beam hardening and bone-blooming artifacts; however, ACT can be compared with MDCT in the evaluation of these structures in the supratentorial compartment (Figs 1, 2, and 4).

Concerning the evaluation of gray matter and the detection of ischemic lesions, ACT was not reliable. Most scores on our study are “identifiable, but not diagnostic,” and there are a large number of examinations in which gray matter structures, like the basal ganglia or the insular cortex, are “not identifiable” at all. Acute ischemic lesions can hardly be detected in ACT, and even bigger older lesions can be overlooked. As depicted in Fig 1, the patient has an older right frontal infarction, which can be easily detected in the MDCT examination but is practically undetectable in the ACT examination. In Fig 3, ACT shows a demarcated thalamic infarction, after recanalization of a basilar artery thrombosis. MDCT performed 2 hours later confirmed the thalamic infarction but, furthermore, depicted an acute large posterior cerebral artery territory infarction, whose early signs were undetectable in the ACT scan.

The position of the EVD catheter tip can be accurately determined with ACT. This feature is especially useful in cases of ruptured aneurysm and SAH. After placement of the EVD, the patient can be directly transferred to the angiography suite. The position of the EVD catheter tip can be verified within the angiography suite, before or after the diagnostic angiography or endovascular treatment of the ruptured aneurysm. Thus, precious time is saved, and the additional transfer of the patient to the MDCT scanner can be avoided.

Weighted κ statistics showed substantial agreement among ACT and perfect agreement among MDCT observer ratings. Because ACT provides us with cross-sectional CT-like images, even less experienced neuroradiologists (in our study, A.X.), however familiar with the interpretation of MDCT images, can successfully diagnose abnormalities in ACT examinations.

Contrary to other studies, we did not face any problems with motion artifacts in our patients because all patients had intubation narcosis before endovascular treatment.

Regarding the effective dose, the use of a 20-second ACT protocol in our study resulted in lower CTDI_w values (manufacturer's information, ∼35 mGy), as opposed to conventional cranial CT (reference value: CTDI_w ∼60 mGy).¹² This is still higher than that in the usual rotational angiography scans (5-second 3D-DSA, CTDI_w ∼9 mGy), but use of the 20-second protocol is necessary to achieve low-contrast resolution.^13,14 Contrary to Kyriakou et al,¹⁴ who applied the high-dose ACT protocol (CTDI_w ∼75 mGy) in their study, we used the low-dose protocol solely for the purposes of our study.

An additional characteristic of ACT, which was not evaluated in our series but was very useful in the cases we treated with intracranial stent placement, is the depiction of small high-contrast objects like intracranial stents by means of ACT. With the same rotational dataset used in our study, we can produce thin cross-sectional images of <0.1-mm isotropic voxel size; these images have a quality superior to that of conventional MDCT or even DSA images.^15–17 This is a valuable feature following intracranial angioplasty with stent placement because the same dataset, used to provide ACT images for the detection of hemorrhage, can be used to depict deployment characteristics and stent conformability (Fig 1).