June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
4D longitudinal choroidal thickness quantification improves reproducibility
Author Affiliations & Notes
  • Ipek Oguz
    The University of Iowa, Iowa City, IA
  • Li Zhang
    The University of Iowa, Iowa City, IA
  • Kyungmoo Lee
    The University of Iowa, Iowa City, IA
  • Michael David Abramoff
    The University of Iowa, Iowa City, IA
  • Milan Sonka
    The University of Iowa, Iowa City, IA
  • Footnotes
    Commercial Relationships Ipek Oguz, None; Li Zhang, None; Kyungmoo Lee, None; Michael Abramoff, IDx LLC (C), IDx LLC (I), University of Iowa (P); Milan Sonka, University of Iowa (P)
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 5288. doi:
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    • Get Citation

      Ipek Oguz, Li Zhang, Kyungmoo Lee, Michael David Abramoff, Milan Sonka; 4D longitudinal choroidal thickness quantification improves reproducibility. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5288.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

Accurate and reproducible measurement of choroidal thickness is important for longitudinal studies of disease mechanisms and management. Joint segmentation of multiple 3D scans over time (termed 3D+time or 4D) has the potential to improve accuracy.

 
Methods
 

Topcon SS OCT scans were acquired every 2 weeks during anti-VEGF induction (7 scans/subject). Bruch’s membrane (BM) was segmented using the Iowa Reference Algorithms (www.iibi.uiowa.edu/octexplorer) to flatten the images. In the 3D approach, upper and lower surfaces of the choroid were segmented for each scan independently, using a graph-based algorithm. In the 4D approach, the 7 scans were segmented jointly by linking the individual graphs based on temporal registration. These links encourage temporal coherence of the segmentation while allowing up to 52μm surface position variation between each successive timepoint pair. Paired t-tests were used to compare choroidal thickness measurements obtained from the 3D and 4D approaches.

 
Results
 

15 patients with exudative AMD were included. Compared to independent 3D segmentations, choroidal thickness was substantially more reproducible in 4D (standard deviation of thickness was 2.43μm in 4D vs. 7.05μm in 3D, p<0.001). The mean thickness (50.6 vs. 49.2μm) and temporal thinning rate (4.28 vs. 7.43μm/12 weeks) were not significantly different between the two methods (p=0.34, p=0.23), suggesting that the 4D approach is less affected by measurement noise and not exhibiting measurement bias, leading to increased temporal sensitivity.

 
Conclusions
 

We have developed the first automated 4D method for jointly quantifying choroidal thickness in longitudinal OCT studies. Our method is robust to image noise and produces more reliable choroidal thickness measurements than a sequence of independent 3D segmentations.  

 
Fig. 1: Choroidal thickness computed in 3D and 4D. Colors denote individual patients. 4D results show significantly smaller measurement variability over time.
 
Fig. 1: Choroidal thickness computed in 3D and 4D. Colors denote individual patients. 4D results show significantly smaller measurement variability over time.
 
 
Fig. 2: Choroidal segmentation consistency and accuracy. (a) 4D (red) and 3D (blue) segmentations generally agree with each other, except for areas of high ambiguity (white rectangle). Note that the 3D approach erroneously cuts through choroidal vessels. (b,c) The 7 individual 3D segmentations show up to 280μm local differences, while the 4D joint segmentation resolves these discrepancies and offers segmentation consistency.
 
Fig. 2: Choroidal segmentation consistency and accuracy. (a) 4D (red) and 3D (blue) segmentations generally agree with each other, except for areas of high ambiguity (white rectangle). Note that the 3D approach erroneously cuts through choroidal vessels. (b,c) The 7 individual 3D segmentations show up to 280μm local differences, while the 4D joint segmentation resolves these discrepancies and offers segmentation consistency.

 
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