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Fully automatic, multiorgan segmentation in normal whole body magnetic resonance imaging ( MRI ), using classification forests ( CF s), convolutional neural networks ( CNN s), and a multi‐atlas ( MA ) approach
Author(s) -
Lavdas Ioannis,
Glocker Ben,
Kamnitsas Konstantinos,
Rueckert Daniel,
Mair Henrietta,
Sandhu Amandeep,
Taylor Stuart A.,
Aboagye Eric O.,
Rockall Andrea G.
Publication year - 2017
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12492
Subject(s) - magnetic resonance imaging , convolutional neural network , hausdorff distance , artificial intelligence , segmentation , computer science , pattern recognition (psychology) , sørensen–dice coefficient , image segmentation , medicine , radiology
Purpose As part of a program to implement automatic lesion detection methods for whole body magnetic resonance imaging ( MRI ) in oncology, we have developed, evaluated, and compared three algorithms for fully automatic, multiorgan segmentation in healthy volunteers. Methods The first algorithm is based on classification forests ( CF s), the second is based on 3D convolutional neural networks ( CNN s) and the third algorithm is based on a multi‐atlas ( MA ) approach. We examined data from 51 healthy volunteers, scanned prospectively with a standardized, multiparametric whole body MRI protocol at 1.5 T. The study was approved by the local ethics committee and written consent was obtained from the participants. MRI data were used as input data to the algorithms, while training was based on manual annotation of the anatomies of interest by clinical MRI experts. Fivefold cross‐validation experiments were run on 34 artifact‐free subjects. We report three overlap and three surface distance metrics to evaluate the agreement between the automatic and manual segmentations, namely the dice similarity coefficient ( DSC ), recall ( RE ), precision ( PR ), average surface distance ( ASD ), root‐mean‐square surface distance ( RMSSD ), and Hausdorff distance ( HD ). Analysis of variances was used to compare pooled label metrics between the three algorithms and the DSC on a ‘per‐organ’ basis. A Mann–Whitney U test was used to compare the pooled metrics between CF s and CNN s and the DSC on a ‘per‐organ’ basis, when using different imaging combinations as input for training. Results All three algorithms resulted in robust segmenters that were effectively trained using a relatively small number of datasets, an important consideration in the clinical setting. Mean overlap metrics for all the segmented structures were: CF s: DSC = 0.70 ± 0.18, RE = 0.73 ± 0.18, PR = 0.71 ± 0.14, CNN s: DSC = 0.81 ± 0.13, RE = 0.83 ± 0.14, PR = 0.82 ± 0.10, MA : DSC = 0.71 ± 0.22, RE = 0.70 ± 0.34, PR = 0.77 ± 0.15. Mean surface distance metrics for all the segmented structures were: CF s: ASD = 13.5 ± 11.3 mm, RMSSD = 34.6 ± 37.6 mm and HD = 185.7 ± 194.0 mm, CNN s; ASD = 5.48 ± 4.84 mm, RMSSD = 17.0 ± 13.3 mm and HD = 199.0 ± 101.2 mm, MA : ASD = 4.22 ± 2.42 mm, RMSSD = 6.13 ± 2.55 mm, and HD = 38.9 ± 28.9 mm. The pooled performance of CF s improved when all imaging combinations (T2w + T1w + DWI ) were used as input, while the performance of CNN s deteriorated, but in neither case, significantly. CNN s with T2w images as input, performed significantly better than CF s with all imaging combinations as input for all anatomical labels, except for the bladder. Conclusions Three state‐of‐the‐art algorithms were developed and used to automatically segment major organs and bones in whole body MRI ; good agreement to manual segmentations performed by clinical MRI experts was observed. CNN s perform favorably, when using T2w volumes as input. Using multimodal MRI data as input to CNN s did not improve the segmentation performance.