1. Optic Nerve Sheath Diameter Measurement Techniques: Examination Using a Novel Ex-Vivo Porcine Model
- Author
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Ashot E. Sargsyan, Jonathan B. Clark, Kurt H. Bockhorst, Jeffrey P. Sutton, Larry A. Kramer, Derek M. Nusbaum, R. Blaine Easley, Erik L. Antonsen, Kathleen K. Kibler, and Kenneth Martin Brady
- Subjects
Optic nerve sheath ,Materials science ,Diameter measurement ,Intracranial Pressure ,medicine.diagnostic_test ,Swine ,business.industry ,Ultrasound ,Public Health, Environmental and Occupational Health ,Optic Nerve ,Magnetic resonance imaging ,Anatomy ,In Vitro Techniques ,Surgical Instruments ,Magnetic Resonance Imaging ,Models, Animal ,medicine ,Optic nerve ,Animals ,Image acquisition ,Calipers ,Nuclear medicine ,business ,Ultrasonography ,Intracranial pressure - Abstract
Background Ultrasound (U/S) and MRI measurements of the optic nerve sheath diameter (ONSD) have been proposed as intracranial pressure measurement surrogates, but these methods have not been fully evaluated or standardized. The purpose of this study was to develop an ex-vivo model for evaluating ONSD measurement techniques by comparing U/S and MRI measurements to physical measurements. Methods The left eye of post mortem juvenile pigs (N = 3) was excised and the subdural space of the optic nerve cannulated. Caliper measurements and U/S imaging measurements of the ONSD were acquired at baseline and following 1 cc saline infusion into the sheath. The samples were then embedded in 0.5% agarose and imaged in a 7 Tesla (7T) MRI. The ONSD was subsequently measured with digital calipers at locations and directions matching the U/S and direct measurements. Results Both MRI and sonographic measurements were in agreement with direct measurements. U/S data, especially axial images, exhibited a positive bias and more variance (bias: 1.318, 95% limit of agreement: 8.609) compared to MRI (bias: 0.3156, 95% limit of agreement: 2.773). In addition, U/S images were much more dependent on probe placement, distance between probe and target, and imaging plane. Conclusions This model appears to be a valid test-bed for continued scrutiny of ONSD measurement techniques. In this model, 7T MRI was accurate and potentially useful for in-vivo measurements where direct measurements are not available. Current limitations with ultrasound imaging for ONSD measurement associated with image acquisition technique and equipment necessitate further standardization to improve its clinical utility.
- Published
- 2014
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