Automatic Alignment of Cranial CT Examinations to the Anterior Commissure/Posterior Commissure (ACPC) Reference Plane for Reliable Interpretation and Quality Assurance

Abstract

Alignment of cranial CT scans (cCTs) to a common reference plane simplifies anatomical-landmark-based orientation and eases follow-up assessment of intracranial findings. We developed and open sourced a fully automated system, which aligns cCTs to the Anterior Commissure/Posterior Commissure (ACPC) line and exports the results to the PACS. FMRIB’s Linear Image Registration Tool (FLIRT) with an ACPC-aligned atlas is used in the alignment step. Five mm mean slabs are generated with the top non-air slice as the starting point. For evaluation, 301 trauma cCTs from the CQ500 dataset were processed. In visual comparison with the respective ACPC-aligned atlas, all were successfully aligned. Image quality (IQ) and ease of identification of the central sulcus (CS) were rated on a Likert scale (5 = excellent IQ/immediate CS identification). The median IQ was 4 (range: 2–4) in the original series and 5 (range: 4–5) in the ACPC-aligned series (p < 0.0001). The CS was more easily identified after fatbACPC (original scans: 4 (range: 2–5); ACPC-aligned: 5 (range: 4–5); p < 0.0001). The mean rotation to achieve alignment was |X| = 6.4 ± 5.2° ([–X,+X] = –26.8°–24.2°), |Y| = 2.1 ± 1.7° ([-Y,+Y] = –8.7°–9.8°), and |Z| = 3.1 ± 2.4° ([–Z,+Z] = –14.3°–12.5°). The developed system can robustly and automatically align cCTs to the ACPC line. Degrees of deviation from the ideal alignment could be used for quality assurance.

Key Points:

• fatbACPC automatically aligns cranial CT scans to the Anterior Commissure/Posterior Commissure plane.

• ACPC-aligned images simplify anatomical-landmark-based orientation.

• fatbACPC does not impact image quality.

• fatbACPC is robust, fully PACS-integrated, and Open Source: https://github.com/BrainImAccs

Citation Format

• Rubbert C, Turowski B, Caspers J. Automatic Alignment of Cranial CT Examinations to the Anterior Commissure/Posterior Commissure (ACPC) Reference Plane for Reliable Interpretation and Quality Assurance. Fortschr Röntgenstr 2021; 193: 61 – 67

Zusammenfassung

Die Ausrichtung kranialer CTs (cCTs) an einer etablierten Referenzebene unterstützt die Orientierung anhand anatomischer Landmarken und vereinfacht die Verlaufsbeurteilung von Pathologien. Wir haben ein vollautomatisches System als Open Source entwickelt, welches cCTs an der Commissura anterior/Commissura posterior (ACPC) ausrichtet und in das PACS exportiert. Im Ausrichtungsschritt wird das FMRIB Linear Image Registration Tool (FLIRT) mit einem ACPC-orientierten Atlas genutzt. 5mm-Mittelwert-Scheiben mit der obersten soliden Schicht als Ausgangspunkt werden generiert. Zur Evaluation wurden 301 Trauma-cCTs des CQ500-Datensatzes genutzt. Im visuellen Vergleich mit dem ACPC-orientierten Atlas wurde alle cCTs erfolgreich ausgerichtet. Bildqualität (BQ) und der Aufwand, den Sulcus centralis (SC) zu identifizieren, wurden auf einer Likert Skala eingestuft (5 = optimale Bildqualität/auf Anhieb zu identifizierender SC). Die mediane BQ betrug 4 (Spannbreite: 2–4) in den originalen Serien und 5 (4–5) in den ACPC-ausgerichteten Serien (p < 0,0001). Der SC war nach fatbACPC einfacher zu identifizieren (Original: 4 (2–5); ACPC: 5 (4–5); p < 0,0001). Die mittlere Rotation betrug |X| = 6,4 ± 5,2° ([–X,+X] = –26,8°–24,2°), |Y| = 2,1 ± 1,7° ([–Y,+Y] = –8,7°–9,8°) und |Z| = 3,1 ± 2,4° ([–Z,+Z] = –14,3°–12,5°). Das entwickelte System kann cCTs verlässlich und automatisch an die ACPC-Linie anpassen. Abweichungen von der idealen Ausrichtung könnten zur Qualitätssicherung genutzt werden.

Kernaussagen:

• fatbACPC richtet kraniale CT Untersuchungen automatisch an der Anterior Commissure/Posterior Commissure Referenzebene aus.

• ACPC-ausgerichtete Bilder erleichtern die Orientierung an anatomischen Landmarken.

• fatbACPC setzt die Bildqualität nicht herab.

• fatbACPC ist robust, vollständig PACS-integrierbar und Open Source: https://github.com/BrainImAccs

Key words

multidetector computed tomography - neuroimaging - software - rotation - follow-up studies

Publication History

Received: 05 September 2019

Accepted: 20 April 2020

Article published online:
09 June 2020

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