AUTHOR=Netteland Dag Ferner , Aarhus Mads , Smistad Erik , Sandset Else Charlotte , Padayachy Llewellyn , Helseth Eirik , Brekken Reidar 

TITLE=Noninvasive intracranial pressure assessment by optic nerve sheath diameter: Automated measurements as an alternative to clinician-performed measurements

JOURNAL=Frontiers in Neurology

VOLUME=Volume 14 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2023.1064492

DOI=10.3389/fneur.2023.1064492

ISSN=1664-2295

ABSTRACT=Introduction: 
Optic nerve sheath diameter (ONSD) has shown promise as a non-invasive parameter for estimating intracranial pressure (ICP). In this study we evaluate a novel automated method of measuring the ONSD in transorbital ultrasound imaging.

Methods: 
From adult traumatic brain injury (TBI) patients with invasive ICP monitoring, bedside manual ONSD measurements and ultrasound videos of the optic nerve sheath complex were simultaneously acquired. Automatic ONSD measurements were obtained by processing of the ultrasound videos by a novel software based on a machine learning approach for segmentation of the optic nerve sheath. Agreement between manual and automated measurements, as well as their correlation to invasive ICP, was evaluated. Furthermore, the ability to distinguish dichotomized ICP for manual and automatic measurements of ONSD was compared, both for ICP dichotomized at ≥20mmHg and at the 50th percentile (≥14mmHg). Finally, we performed exploratory subgroup analysis based on the software’s judgement of optic nerve axis alignment to elucidate reasons for variation in agreement between automatic and manual measurements.

Results: 
A total of 43 ultrasound examinations were performed in 25 adult TBI patients, resulting in 86 image sequences covering right and left eyes. The median pairwise difference between automatically and manually measured ONSD was 0.06mm (IQR -0.44mm-0.38mm; p=0.80). The manually measured ONSD showed a positive correlation with ICP, while automatically measured ONSD, showed a trend towards, but not a statistically significant correlation with ICP. When examining for ability to distinguish dichotomized ICP, manual and automatic measurements performed with similar accuracy both for an ICP cut-off at 20mmHg (Manual: AUC 0.74, 95%CI 0.58-0.88; Automatic: AUC 0.83, 95%CI 0.66-0.93) and for an ICP cut-off at 14mmHg (Manual: AUC 0.70, 95%CI 0.52-0.85; Automatic: AUC 0.68, 95%CI 0.48-0.83). In the exploratory subgroup analysis, we found that the agreement between measurements was higher in the subgroup where the automatic software evaluated the optic nerve axis alignment as good as compared to intermediate/poor.

Conclusions: 
The novel automated method of measuring the optic nerve sheath diameter on ultrasound videos using segmentation of the optic nerve sheath showed a reasonable agreement with manual measurements and performed equally well in distinguishing high and low ICP.