Differences in Mean Values and Variance in Quantitative Analyses of Foveal OCTA Imaging

Abstract

Purpose Multiple approaches for quantifying parameters such as vessel density (VD) and vessel length density (VLD) in optical coherence tomography angiography (OCTA) en-face segmentations are currently available. While it is common knowledge that data gathered from different methods should not be directly compared to each other, a comparison of the different methods can help to further the understanding of differences between different methods of measurement. Here we compare a common method of semiautomatically quantifying VD and VLD with an automated method supplied by the manufacturer of an OCTA device and report on differences in performance in order to probe for and highlight differences in values gathered by both methods.

Methods OCTA was performed using the swept source PLEX Elite 9000 device, software version 2.0.1.47652 (Carl Zeiss Meditec Inc., Dublin, CA, USA). Scans of 3 mm × 3 mm from healthy volunteers centred on the fovea were acquired by a well-trained certified ophthalmologist. Scans with a signal strength of 8 out of 10 or higher were included. Quantitative parameters of the 3 mm × 3 mm cube scans were automatically generated and segmented into superficial capillary plexus (SCP) and deep capillary plexus (DCP) layers using layer segmentation produced by the instrument software and prototype analysis VD quantification software (Macular Density v.0.7.1, ARI Network Hub, Carl Zeiss Meditec Inc., Dublin, CA, USA) supplied by the manufacturer. An alternative approach of quantitative analysis of VD and VLD was performed manually with ImageJ (National Institutes of Health, Bethesda, Maryland, USA), as previously reported. VD was assessed as the ratio of the retinal area occupied by vessels. VDL was measured as the total length of the skeletonised vessels using 1-pixel centre line extraction of the blood vessels.

Results We report differences in standard deviation (SD) in OCTA parameters obtained using different methods. The standard deviation of VD and VLD measurements was statistically significantly different in VD of 3 mm × 3 mm DCP (p = 0.009), VLD of 3 mm × 3 mm SCP (p = 0.000), and VLD of 3 mm × 3 mm DCP (p = 0.021). No statistically significant differences were found in VD of 3 mm × 3 mm SCP (p = 0.128) or VLD of 3 mm × 3 mm SCP (p = 0.107).

Conclusions As expected, we were able to demonstrate significant differences in quantitative OCTA parameters gathered from the same images using different methods of quantification. Values gathered using different methods are not interchangeable. In scientific studies and in situations where long-term follow-up is necessary, the same device and the same method of quantification should be used to maintain retrospective comparability of measurements.

Zusammenfassung

Zweck Mehrere Ansätze zur Quantifizierung von Parametern wie Vessel Density (VD) und Vessel Length Density (VLD) in der optischen Kohärenztomografieangiografie (OCTA) sind derzeit verfügbar. Es ist ebenfalls bekannt, dass Daten, die mit verschiedenen Methoden erhoben wurden, nicht direkt miteinander vergleichbar sind. Diese Studie exploriert Unterschiede der verschiedenen Methoden, um zu einem besseren Verständnis der unterschiedlichen Messmethoden zu führen. Sie vergleicht eine gängige Methode zur halbautomatischen Bestimmung von VD und VLD mit einer automatischen Methode, welche vom Hersteller eines OCTA-Geräts bereitgestellt wird und berichtet über Unterschiede der mit den beiden Methoden ermittelten Werte.

Methoden Die OCTA-Aufnahmen wurden mit dem Swept Source PLEX Elite 9000, Softwareversion 2.0.1.47652 (Carl Zeiss Meditec Inc., Dublin, CA, USA) akquiriert. Scans von 3 mm × 3 mm von gesunden Probanden, zentriert auf die Fovea, wurden von einem geschulten Ophthalmologen erstellt. Scans mit einer Signalstärke von 8 von 10 oder höher wurden eingeschlossen. Quantitative Parameter der 3 mm × 3 mm-Scans wurden automatisch für den oberflächlichen Kapillarplexus (SCP) und tiefen Kapillarplexus (DCP) erstellt. Die Segmentierung wurde durch die geräteherstellereigene Software (Macular Density v.0.7.1, ARI Network Hub, Carl Zeiss Meditec Inc., Dublin, CA, USA) vorgenommen. Diese Software generiert auch VD- und VLD-Werte für den SCP und DCP. Ein alternativer Ansatz der quantitativen Analyse von VD und VLD wurde manuell mit ImageJ (National Institutes of Health, Bethesda, Maryland, USA) durchgeführt, wie bereits in anderen Publikationen berichtet.

Ergebnisse Wir berichten über Unterschiede in der Standardabweichung (SD) der OCTA-Parameter der unterschiedlichen Methoden. Die Standardabweichung der VD- und VLD-Messungen war statistisch signifikant unterschiedlich bei der VD von 3 mm × 3 mm des DCP (p = 0,009), bei der VLD von 3 mm × 3 mm des SCP (p = 0,000) und bei der VLD von 3 mm × 3 mm des DCP (p = 0,021). Keine statistisch signifikanten Unterschiede wurden bei der VD von 3 mm × 3 mm des SCP (p = 0,128) oder bei der VLD von 3 mm × 3 mm des SCP (p = 0,107) entdeckt.

Schlussfolgerungen Wie erwartet, konnten wir signifikante Unterschiede in den quantitativen OCTA-Parametern nachweisen, die aus denselben Bildern, aber mit unterschiedlichen Quantifizierungsmethoden gewonnen wurden. Die mit verschiedenen Methoden ermittelten Werte sind nicht austauschbar. In wissenschaftlichen Studien und in Situationen, in denen langfristig wiederholt Messungen durchgeführt werden, sollte dasselbe Gerät und dieselbe Quantifizierungsmethode verwendet werden, um die retrospektive Vergleichbarkeit der Messungen zu gewährleisten.

Key words

quantitative analysis - OCTA - retina

Schlüsselwörter

quantitative Analyse - OCTA - Retina

Publication History

Received: 10 October 2021

Accepted: 06 February 2022

Article published online:
26 April 2022

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