Fully automated identification of brain abnormality from whole-body FDG-PET imaging using deep learning-based brain extraction and statistical parametric mapping

Abstract

Background: The whole brain is often covered in [¹⁸F]Fluorodeoxyglucose positron emission tomography ([¹⁸F]FDG-PET) in oncology patients, but the covered brain abnormality is typically screened by visual interpretation without quantitative analysis in clinical practice. In this study, we aimed to develop a fully automated quantitative interpretation pipeline of brain volume from an oncology PET image.

Method: We retrospectively collected 500 oncologic [¹⁸F]FDG-PET scans for training and validation of the automated brain extractor. We trained the model for extracting brain volume with two manually drawn bounding boxes on maximal intensity projection images. ResNet-50, a 2-D convolutional neural network (CNN), was used for the model training. The brain volume was automatically extracted using the CNN model and spatially normalized. For validation of the trained model and an application of this automated analytic method, we enrolled 24 subjects with small cell lung cancer (SCLC) and performed voxel-wise two-sample T test for automatic detection of metastatic lesions.

Result: The deep learning-based brain extractor successfully identified the existence of whole-brain volume, with an accuracy of 98% for the validation set. The performance of extracting the brain measured by the intersection-over-union of 3-D bounding boxes was 72.9 ± 12.5% for the validation set. As an example of the application to automatically identify brain abnormality, this approach successfully identified the metastatic lesions in three of the four cases of SCLC patients with brain metastasis.

Conclusion: Based on the deep learning-based model, extraction of the brain volume from whole-body PET was successfully performed. We suggest this fully automated approach could be used for the quantitative analysis of brain metabolic patterns to identify abnormalities during clinical interpretation of oncologic PET studies.

Keywords: Brain FDG-PET; Brain segmentation; Convolutional neural network; Deep learning; FDG-PET; Quantitative PET analysis.

Fig. 1

Brief outline of the automatic brain extraction. We trained the model with two manually drawn bounding boxes on maximal intensity projection (MIP) images. ResNet-50, a convolutional neural network (CNN) was used for learning model. Internal validation of model was performed. Finally, the brain volume was extracted and spatially normalized to the template space

Fig. 2

Representative results of the automatic brain extractor. a, b In both of the “torso”, PET covering up to mid-thigh and “total-body” PET covering whole heights of body the extractor successfully located the brain. c The extractor was also capable of identifying brain when the artifact caused by radiopharmaceutical injection was projected to the brain at the MIP image. d When the brain volume was not fully included, the extractor classified the image as “not containing entire brain”

Fig. 3

Quantitative analysis of the extracted brain. The voxel-wise T test successfully identified the metastatic lesions in the brain at three of four subjects in the case group (uncorrected P < 0.001). The graphics on the left side show the brain regions that show hypometabolism compared to the control group. The image on the right side shows the corresponding FDG-PET image. a, b, c In all of the three successful cases, the analysis revealed hypometabolic lesions due to edematous change around the lesion. d In the other case with unsuccessful result, the statistical analysis showed diffuse hypometabolism in frontoparietal lobe, instead of focal metabolic defect at the metastatic site