Radiation dose and image quality in intraoperative CT (iCT) angiography of the brain with stereotactic head frames

Detection of remnants in clipped unruptured intracranial aneurysms by intraoperative CT-angiography and postoperative DSA: clinical relevance and follow-up

BACKGROUND

Aneurysm clipping is routinely performed with high efficacy and low complication rates in specialized neurovascular centers. Postoperative aneurysm remnants bear the risk of growth/rupture. Study aim was to analyze remnants in postoperative angiography (pDSA) and follow-up (FU) and to evaluate whether use of intraoperative CT-angiography (iCTA) can intraoperatively detect remnants and enable therapeutic consequences.

METHODS

All patients undergoing elective aneurysm clipping at our center between 11/2012 and 12/2019 were included for FU in 01/2024. All patients received Indocyanin-green-videoangiography (ICGVA) and postoperative angiography (pDSA). After iCTA implementation in 10/2016, the majority of patients received additionally iCTA. Baseline characteristics, treatment-related morbidity/outcome, resulting operative conclusions in distinct cohorts with/without iCTA, and management of remnants according to Sindou classification were analyzed.

RESULTS

270 patients (367 enrolled/97 excluded) were clipped using iCTA in 74 patients. In 12/270 patients (4.5%) clip repositioning was performed due to ICGVA results, but iCTA further detected large remnants intraoperatively in 3/74 patients (4.1%) correctly resulting in re-clipping in two patients and recommendation for endovascular therapy in one patient. The specificity, sensitivity, and accuracy for detection of Sindou grade (SG) III-IV remnants by iCTA were 100%, 75%, and 98.6%, respectively. Overall, pDSA detected SG I-II remnants in 32/270 (11.9%) and SG III-V remnants in 8/270 (3.0%) patients with 3/270 requiring retreatment (n = 1 resurgery, n = 2 endovascular therapy). Frequency of SG I-V and III-V remnants were slightly lower in iCTA than non-iCTA group (10.8 vs. 16.3%, p < 0.173 and 1.4 vs. 3.6%, p < 0.306). All SG I-II and five SG III-V remnants did not reveal growth/rupture after a mean FU of 29 months.

CONCLUSIONS

Aneurysm remnants after clipping are rare and predominantly small (SGI-II)-not harbouring a risk of growth/rupture during short-term FU. Intraoperative CTA can detect large aneurysm remnants (SG III-IV) and may prompt adjustment of surgical strategy in individual cases.

Optimizing Radiation Dose and Image Quality in Stroke CT Protocols: Proposed Diagnostic Reference Levels for Multiphase CT Angiography and Perfusion Imaging

OBJECTIVE

In suspected acute ischemic stroke, it is now reasonable to expand the conventional "stroke protocol" (non-contrast computed tomography (NCCT), arterial CT angiography (CTA), and optionally CT perfusion (CTP)) to early and late venous head scans yielding a multiphase CTA (MP-CTA) to increase diagnostic confidence. Diagnostic reference levels (DRLs) have been defined for neither MP-CTA nor CTP. We therefore present dosimetry data, while also considering image quality, for a large, unselected patient cohort.

METHODS

A retrospective single-center study of 1790 patients undergoing the extended stroke protocol with three scanners (2× dual-source, DSCT; 1× single-source, SSCT) between 07/21 and 12/23 was conducted. For each sequence, we analyzed the radiation dose (volumetric CT dose index (CTDIvol); dose length product; effective dose); objective image quality using manually placed regions of interest (contrast-to-noise ratio (CNR)); and subjective image quality (4-point scale: 1 = non-diagnostic, 4 = excellent). The DRL was defined as the 75% percentile of the CTDIvol distribution. The Kruskal-Wallis test was used initially to test for overall equality of median values in each data group. Single post-test comparisons were performed with Dunn's test, with an overall statistical significance level of 0.05.

RESULTS

Dosimetry values were significantly higher for SSCT (p < 0.001, each). Local DRLs ranged between 37.3 and 49.1 mGy for NCCT, 3.6-5.5 mGy for arterial CTA, 1.2-2.5 mGy each for early/late venous CTA, and 141.1-220.5 mGy for CTP. Protocol adjustment (DSCT-1: CTP) yielded a 28.2% dose reduction. The highest/lowest CNRs (arterial/early venous CTA, respectively) were recorded for SSCT/DSCT-2 (p < 0.001). Subjective image quality was rated excellent except for slightly increased MP-CTA noise at DSCT-2 (median = 3).

CONCLUSIONS

Our data imply that additive MP-CTA scans only yield a minor increase in radiation exposure, particularly when using DSCT. CTP should be limited to selected patients.

Detection of impending perfusion deficits by intraoperative computed tomography (iCT) in aneurysm surgery of the anterior circulation

Background

The aim of our study was to evaluate the additional benefit of intraoperative computed tomography (iCT), intraoperative computed tomography angiography (iCTA), and intraoperative computed tomography perfusion (iCTP) in the intraoperative detection of impending ischemia to established methods (indocyanine green videoangiography (ICGVA), microDoppler, intraoperative neuromonitoring (IONM)) for initiating timely therapeutic measures.

Methods

Patients with primary aneurysms of the anterior circulation between October 2016 and December 2019 were included. Data of iCT modalities compared to other techniques (ICGVA, microDoppler, IONM) was recorded with emphasis on resulting operative conclusions leading to inspection of clip position, repositioning, or immediate initiation of conservative treatment strategies. Additional variables analyzed included patient demographics, aneurysm-specific characteristics, and clinical outcome.

Results

Of 194 consecutive patients, 93 patients with 100 aneurysms received iCT imaging. While IONM and ICGVA were normal, an altered vessel patency in iCTA was detected in 5 (5.4%) and a mismatch in iCTP in 7 patients (7.5%). Repositioning was considered appropriate in 2 patients (2.2%), where immediate improvement in iCTP could be documented. In a further 5 cases (5.4%), intensified conservative therapy was immediately initiated treating the reduced CBP as clip repositioning was not considered causal. In terms of clinical outcome at last FU, mRS0 was achieved in 85 (91.4%) and mRS1-2 in 7 (7.5%) and remained mRS4 in one patient with SAH (1.1%).

Conclusions

Especially iCTP can reveal signs of impending ischemia in selected cases and enable the surgeon to promptly initiate therapeutic measures such as clip repositioning or intraoperative onset of maximum conservative treatment, while established tools might fail to detect those intraoperative pathologic changes.