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How much will linked deformable registrations decrease the quality of multi-atlas segmentation fusions?

Sjöberg C, Johansson S, Ahnesjö A - Radiat Oncol (2014)

Bottom Line: The median decrease of the DSC was in the range 2.8% to 8.4% compared to direct registrations for all structures while reducing the computer calculation time to that of a single deformable registration.Linking several registrations showed a DSC decrease almost linear to the number of links, suggesting that extrapolation to zero links provides an observer independent measure of the inherent precision with which the segmentation guidelines can be applied.Linking pre-made registrations of multiple atlases via a runtime registration of a single atlas provides a feasible method for reducing computation time in multi-atlas registration.

View Article: PubMed Central - PubMed

Affiliation: Section for Medical Radiation Physics, Department of Radiology, Oncology and Radiation Sciences, Uppsala University, Akademiska Sjukhuset, Sjukhusfysik Ing. 82, SE-751 85, Uppsala, Sweden. carl.sjoberg@onkologi.uu.se.

ABSTRACT

Background and purpose: Multi-atlas segmentation can yield better results than single atlas segmentation, but practical applications are limited by long calculation times for deformable registration. To shorten the calculation time pre-calculated registrations of atlases could be linked via a single atlas registered in runtime to the current patient. The primary purpose of this work is to investigate and quantify segmentation quality changes introduced by such linked registrations. We also determine the optimal parameters for fusing linked multi-atlas labels using probabilistic weighted fusion.

Material and methods: Computed tomography images of 10 head and neck cancer patients were used as atlases, with parotid glands, submandibular glands, the mandible and lymph node levels II-IV segmented by an experienced radiation oncologist following published consensus guidelines. The change in segmentation quality scored by Dice similarity coefficient (DSC) for linking free-form deformable registrations, modeled by B-splines, was investigated for both single- and multi-atlas label fusion by using a leave-one-out approach.

Results: The median decrease of the DSC was in the range 2.8% to 8.4% compared to direct registrations for all structures while reducing the computer calculation time to that of a single deformable registration. Linking several registrations showed a DSC decrease almost linear to the number of links, suggesting that extrapolation to zero links provides an observer independent measure of the inherent precision with which the segmentation guidelines can be applied.

Conclusions: Linking pre-made registrations of multiple atlases via a runtime registration of a single atlas provides a feasible method for reducing computation time in multi-atlas registration.

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Related in: MedlinePlus

Illustration of registration linking. Segmentation transfers for the case of i = 1, k = 2 and N = 10 are displayed.
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Fig1: Illustration of registration linking. Segmentation transfers for the case of i = 1, k = 2 and N = 10 are displayed.

Mentions: The quality drop when linking registrations via one intermediate image was assessed for both individual segmentations and fused segmentations. Using the leave-one-out approach a fixed image Ai and an intermediate image Ak, k ≠ i was selected. The other atlas images were in turn used as moving images Aj, j ≠ i, k, thus for N = 10 a total of 10 ⋅ 9 ⋅ 8 = 720 combinations of registrations were possible. The segmentations from the moving images were transformed using the composed transformation Ti ← I(1) ← j = Ti ← k ∘ Tk ← j applied to the labeled images Lj and results were compared with results using direct registrations Ti ← j. Figure 1 demonstrates this process with i = 1 and k = 2 . The quality loss was then quantified by comparing the resulting DSC values with those acquired based on direct registrations.Figure 1


How much will linked deformable registrations decrease the quality of multi-atlas segmentation fusions?

Sjöberg C, Johansson S, Ahnesjö A - Radiat Oncol (2014)

Illustration of registration linking. Segmentation transfers for the case of i = 1, k = 2 and N = 10 are displayed.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4279807&req=5

Fig1: Illustration of registration linking. Segmentation transfers for the case of i = 1, k = 2 and N = 10 are displayed.
Mentions: The quality drop when linking registrations via one intermediate image was assessed for both individual segmentations and fused segmentations. Using the leave-one-out approach a fixed image Ai and an intermediate image Ak, k ≠ i was selected. The other atlas images were in turn used as moving images Aj, j ≠ i, k, thus for N = 10 a total of 10 ⋅ 9 ⋅ 8 = 720 combinations of registrations were possible. The segmentations from the moving images were transformed using the composed transformation Ti ← I(1) ← j = Ti ← k ∘ Tk ← j applied to the labeled images Lj and results were compared with results using direct registrations Ti ← j. Figure 1 demonstrates this process with i = 1 and k = 2 . The quality loss was then quantified by comparing the resulting DSC values with those acquired based on direct registrations.Figure 1

Bottom Line: The median decrease of the DSC was in the range 2.8% to 8.4% compared to direct registrations for all structures while reducing the computer calculation time to that of a single deformable registration.Linking several registrations showed a DSC decrease almost linear to the number of links, suggesting that extrapolation to zero links provides an observer independent measure of the inherent precision with which the segmentation guidelines can be applied.Linking pre-made registrations of multiple atlases via a runtime registration of a single atlas provides a feasible method for reducing computation time in multi-atlas registration.

View Article: PubMed Central - PubMed

Affiliation: Section for Medical Radiation Physics, Department of Radiology, Oncology and Radiation Sciences, Uppsala University, Akademiska Sjukhuset, Sjukhusfysik Ing. 82, SE-751 85, Uppsala, Sweden. carl.sjoberg@onkologi.uu.se.

ABSTRACT

Background and purpose: Multi-atlas segmentation can yield better results than single atlas segmentation, but practical applications are limited by long calculation times for deformable registration. To shorten the calculation time pre-calculated registrations of atlases could be linked via a single atlas registered in runtime to the current patient. The primary purpose of this work is to investigate and quantify segmentation quality changes introduced by such linked registrations. We also determine the optimal parameters for fusing linked multi-atlas labels using probabilistic weighted fusion.

Material and methods: Computed tomography images of 10 head and neck cancer patients were used as atlases, with parotid glands, submandibular glands, the mandible and lymph node levels II-IV segmented by an experienced radiation oncologist following published consensus guidelines. The change in segmentation quality scored by Dice similarity coefficient (DSC) for linking free-form deformable registrations, modeled by B-splines, was investigated for both single- and multi-atlas label fusion by using a leave-one-out approach.

Results: The median decrease of the DSC was in the range 2.8% to 8.4% compared to direct registrations for all structures while reducing the computer calculation time to that of a single deformable registration. Linking several registrations showed a DSC decrease almost linear to the number of links, suggesting that extrapolation to zero links provides an observer independent measure of the inherent precision with which the segmentation guidelines can be applied.

Conclusions: Linking pre-made registrations of multiple atlases via a runtime registration of a single atlas provides a feasible method for reducing computation time in multi-atlas registration.

Show MeSH
Related in: MedlinePlus