Precisely Mapping Choroidal Tumour Margins

Abstract

Purpose : Assessing the malignant potential of choroidal tumours relies on accurate mapping of tumour margins. Standalone images taken using colour fundus photography (CFP), ultrawidefield scanning laser ophthalmoscopy (UWF SLO) or enhanced-depth imaging optical coherence tomography (EDI-OCT) are most commonly used to do this. Each of these methods has limitations: conventional EDI-OCT can only image tumours up to ~9mm in basal diameter and can be difficult to interpret without en face projections; tumour margin delineation with CFP or UWF SLO can be confounded by pigmentation and overlying retinal and pigment epithelial change. Our group has developed machine learning tool to co-register retinal images captured on different modalities, enabling assessment of the concordance between modalities in tumour margin mapping. Preliminary data using this technology is presented here.

Methods : Non-mydriatic retinal photography (Canon CR6-45NM), UWF SLO (Optos), EDI-OCT (Spectralis, Heidelberg) images of choroidal naevi from 9 people were co-registered using a software application developed by our team. Tumour margins were annotated independently for each image type by an ocular oncologist masked to patient identity. Dense raster EDI-OCT B-scans were annotated to delineate cross-sectional tumour measurements. These measurements were rendered as an en face projection for tumour margin and area determination.

Results : Mean tumour area was 21.9 mm² (SD=16.6 mm²) based on EDI-OCT B-scan measurements. Tumour area measurements were, on average, larger for EDI-OCT (ground truth) than for CFP and UWF SLO: absolute difference 2.3 mm² (SD = 4.7 mm²) and 2.7 mm² (SD = 3.1 mm²), respectively. These differences were greater than 1 mm² (pre-defined threshold of clinical relevance) in 4 out of 9 cases (45%). Figure 1 shows the discrepancy in tumour margin and area for a representative choroidal naevus between co-registered CFP, UWF SLO and OCT images.

Conclusions : There is discrepancy between tumour margin boundaries defined by EDI-OCT (the reference standard) and CFP as well as UWF SLO. Co-registered images with en-face projection of EDI-OCT B scans may allow more accurate delineation of tumour margins. Further studies are needed.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Figure 1.(A) Representative choroidal naevus on CFP, UWF SLO and IR/OCT imaging.(B) Manual annotation of the naevus for each imaging modality. *Annotation for the IR/OCT image is based on margins labelled on EDI-OCT B-scans (C) Comparison of lesion areas