1. CS 698 | Current Topics in Data Science
Dr. Usman Roshan
Deep Convolutional Neural Networks for Lung Cancer Detection
Paper Presentation | Spring 2018
Fadi G. Farhat
February 15th, 2018
New Jersey Institute of Technology

2. Authors Albert Chon • Peter Lu Niranjan Balachandar
Department of Computer Science
Stanford University

3. Introduction:
Lung cancer is one of the most common and deadliest cancers
225,000 cases; 150,000 deaths; $12 billion in healthcare costs yearly in the United States
Only 17% of people in the U.S. diagnosed with lung cancer survive five years after the diagnosis
Current diagnostic methods include biopsies and imaging, such as CT scans
Early detection of lung cancer significantly improves the chances for survival; difficult to do with fewer symptoms

4. Objective:
Binary classification problem to detect the presence of lung cancer in patient CT scans of lungs with and without early stage lung cancer
Build an accurate classifier using 2D and 3D convolutional neural networks
Classifier could speed up and reduce costs of lung cancer screening; allow early detection; improve survival
Computer-aided diagnosis (CAD) system will take as input patient chest CT scans, and outputs whether or not the patient has (early stage) or is likely to develop lung cancer

5. Challenges:
CAD system must detect the presence of a tiny nodule (less than 10 mm in diameter for early stage) from a large 3D lung CT scan (around 200 mm x 400 mm x 400 mm)
Example of an early stage
lung cancer nodule (~5mm)
CT scan is filled with noise
from surrounding tissues,
bone, air, water, blood

6. Data:
Primary dataset: patient lung CT scan dataset from Kaggle’s Data Science Bowl 2017
Labeled data for 2101 patients; divided into training set of 1261, validation set of 420, and test set of 420
Data consists of CT scan data (100 to 400 2D slice images per patient) and a label (0 for no cancer, 1 for cancer); Kaggle dataset does not have labeled nodules!

7. Data (cont.):
Secondary dataset: patient lung CT scan data with labeled nodules from the LUng Nodule Analysis 2016 (LUNA16) Challenge
LUNA16 dataset has labeled data for 888 patients; divided into training set of 710, validation set of 178
Data consists of CT scan data and a nodule label (list of nodule center coordinates and diameter)

8. Approach:
Preprocess the 3D CT scans using segmentation, normalization, down-sampling, and zero-centering
Train a U-Net (2D Convolutional Networks for Biomedical Image Segmentation) for nodule candidate detection
Input regions around nodule candidates detected by the U-net into 3D CNNs to classify the CT scans as positive or negative for lung cancer

9. Preprocessing & Segmentation:
Convert the pixel values in each
image to Hounsfield units (HU),
a measurement of radiodensity,
then stack 2D slices into a single 3D image
bone:
tissue:

10. Preprocessing & Segmentation:
Use segmentation to mask out the bone, outside air, and other substances that would make the data noisy; retain only lung tissue information
Watershed and Thresholding segmentation tested; Thresholding used
original thresholding watershed

11. Preprocessing & Segmentation:
Normalize the 3D image by applying linear scaling
Down-sample each 3D image by a scale of 0.5 in each of the three dimensions
Zero-center the data by subtracting the mean of all the images from the training set

12. U-Net for Nodule Detection:
Find small boxes containing top cancerous nodule candidates
Train a modified version of the U-Net on the LUNA16 data
Model is trained to output images (256x256) where each output pixel has a value between 0 and 1 indicating the probability the pixel belongs to a nodule
Trained U-Net is then applied to the segmented Kaggle CT scan slices to generate nodule candidates

13. U-Net for Nodule Detection:

14. U-Net for Nodule Detection:

15. U-Net for Nodule Detection:
U-Net produces a strong signal for the actual nodule, but also produces a lot of false positives
U-Net labeled input U-Net predicted output true nodule location

16. U-Net for Nodule Detection:
Solution: Locate top 8 (most active) nodule candidates (32x32x32 volumes) and save them
Top sectors not permitted to overlap to prevent them from simply being clustered in the brightest region of the image
Combine these sectors into a single 64x64x64 volume and use as input to classifiers, which assign a label (cancer or not cancer)

17. Malginancy Classifiers:
Linear classifier used as a baseline, then a vanilla 3D CNN, and a GoogleNet-based 3D CNN were applied
Each classifier used weighted loss (weight for a label is the inverse of the frequency of the label in the training set)
CNNs use ReLU activation and droupout after each convolutional layer during training
ReLU = Rectified Linear Unit

18. Malginancy Classifiers (cont.):
Vanilla 3D CNN (left) and GoogleNet 3D CNN (right) architectures

19. Results:
Kaggle test set accuracy, sensitivity, specificity, and AUC of ROC
Sensitivity: true
positive rate
Specificity: true negative rate
AUC: Area Under the ROC Curve
ROC: Receiver Operating
Characteristic
FPR vs. TPR for diff. cutoff points

20. Results (cont.):
Observation: activations showing that cancerous nodule presence (and location) is detected in some outputs

21. Conclusions:
The deep 3D CNN models, and in particular the GoogleNet-based model, performed the best on the test set
State-of-the-art performance AUC of 0.83 not achieved; models performed well considering that less labeled data was used (than most state-of-the-art CAD systems)
Current model could be extended to determine the exact location of the cancerous nodules, and not only whether or not the patient has cancer (slide 20)

22. Future Work:
Use Watershed method instead of Thresholding as the initial lung segmentation
Make the networks deeper
Perform more extensive hyper-parameter tuning
Generalize: extend models to 3D images for other cancers