MachineX: Medical Image Analyses for Malaria Detection

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In this blog we will see the implementation of a neural network which will help us to detect malaria in a blood sample.

In our previous blog MachineX: Malaria detection using Artificial Intelligence , we had talked about why Ai is important to make it more accurate and how.

Now before we begin, I’d like to point out that I am neither a doctor nor a healthcare researcher and I’m nowhere near to being as qualified as they are. I do have interests though in applying AI for healthcare research. The intent of this article is not to dive into the hype that AI would be replacing jobs and taking over the world, but to showcase how AI can be useful in assisting with malaria detection, diagnosis and reducing manual labor with low-cost effective and accurate open-source solutions.

This is what our training data is look like

Note: I am using google colab and the code will be according to the same , i recommend you all to use google colab for ease.

lets go to the code:

Code

Initialization

%reload_ext autoreload
%autoreload 2
%matplotlib inline

Virtual machine testing on google colab

If Google’s servers are crowded, you’ll eventually have access to only part of a GPU. If your GPU is shared with another Colab notebook, you’ll see a smaller amount of memory made available for you.

!/opt/bin/nvidia-smi
!nvcc --version

When I started running the experiments described here, I was lucky: I had 11441 MB RAM! My output looked like this:

Mon Nov  4 05:40:26 2019       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 418.67       Driver Version: 418.67       CUDA Version: 10.1     |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  Tesla K80           Off  | 00000000:00:04.0 Off |                    0 |
| N/A   49C    P8    30W / 149W |      0MiB / 11441MiB |      0%      Default |
+-------------------------------+----------------------+----------------------+
                                                                               
+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID   Type   Process name                             Usage      |
|=============================================================================|
|  No running processes found                                                 |
+-----------------------------------------------------------------------------+
nvcc: NVIDIA (R) Cuda compiler driver
Copyright (c) 2005-2018 NVIDIA Corporation
Built on Sat_Aug_25_21:08:01_CDT_2018
Cuda compilation tools, release 10.0, V10.0.130

Import libraries

Here we import all the necessary packages. We are going to work with the fast.ai V1 library which sits on top of Pytorch 1.0. The fast.ai library provides many useful functions that enable us to quickly and easily build neural networks and train our models.

from fastai.vision import *
from fastai.metrics import error_rate
from fastai.callbacks import SaveModelCallback

# Imports for diverse utilities
from shutil import copyfile
import matplotlib.pyplot as plt
import operator
from PIL import Image
from sys import intern   # For the symbol definitions

Some util functions: Export and restoration

Now here is an export network for deployment and one for create an copy

# Export network for deployment and create a copy

def exportStageTo(learn, path):
    learn.export()
    # for backup
    copyfile(path/'export.pkl', path/'export-malaria.pkl')
    
#exportStage1(learn, path)

Restoration of a deployment model, for example in order to continue fine-tuning

# Restoration of a deployment model, for example in order to continue fine-tuning

def restoreStageFrom(path):
  # Restore a backup
  copyfile(path/'export-malaria.pkl', path/'export.pkl')
  return load_learner(path)
  
#learn = restoreStage1From(path)

Now let’s download the NIH dataset , on which we will work today:

!wget  --backups=1 -q https://ceb.nlm.nih.gov/proj/malaria/cell_images.zip
!wget  --backups=1 -q https://ceb.nlm.nih.gov/proj/malaria/malaria_cell_classification_code.zip
!ls -al

The backups=1 parameter of wget will allow you to repeat the command line many times, if a download fails, without creating a lot of new versions of the files.

The ouput of the last line should be like thi:

total 690400
drwxr-xr-x 1 root root      4096 Nov  4 10:09 .
drwxr-xr-x 1 root root      4096 Nov  4 05:34 ..
-rw-r--r-- 1 root root 353452851 Apr  6  2018 cell_images.zip
-rw-r--r-- 1 root root 353452851 Apr  6  2018 cell_images.zip.1
drwxr-xr-x 1 root root      4096 Oct 30 15:14 .config
drwxr-xr-x 5 root root      4096 Nov  4 07:26 data
-rw-r--r-- 1 root root     12581 Apr  6  2018 malaria_cell_classification_code.zip
-rw-r--r-- 1 root root     12581 Apr  6  2018 malaria_cell_classification_code.zip.1
drwxr-xr-x 1 root root      4096 Oct 25 16:58 sample_data

Lets unzip the NIH cell images dataset:

!unzip cell_images.zip

This will produce a very large verbose output, that will look like this:

Archive:  cell_images.zip
   creating: cell_images/
   creating: cell_images/Parasitized/
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_144104_cell_162.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_144104_cell_163.png  
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 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_144104_cell_167.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_144104_cell_168.png  
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 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145422_cell_167.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145422_cell_168.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145422_cell_169.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145609_cell_144.png  
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 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145938_cell_168.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145938_cell_169.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145938_cell_170.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145938_cell_171.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145938_cell_172.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145938_cell_173.png  
 extracting: cell_images/Parasitized/C100P61ThinF_IMG_20150918_145938_cell_174.png  
and .......... so on

Prepare your data

Change the name of the cell_images folder to train, and then mv it on top of a new data folder, so fast.ai can use it to automatically generate train, validation and test sets, without any further fuss

!mv cell_images train
!mkdir data
!mv train data

Deep dive on data folder

Install the tree command if you haven’t it:

!apt install tree

lets run the command now

!tree ./data --dirsfirst --filelimit 10

this will show an tree structure of your folder:

./data
└── train
    ├── Parasitized [13780 exceeds filelimit, not opening dir]
    └── Uninfected [13780 exceeds filelimit, not opening dir]3 directories, 0 files

Variable Initialization

bs = 256                # Batch size, 256 for small images on a T4 GPU...
size = 128              # Image size, 128x128 is a bit smaller than most of the images...
path = Path("./data")   # The path to the 'train' folder you created...

create training and validation data bunches

With fast.ai it is not necessary: if you only have a ‘train’ folder, you can automatically split it while creating the DataBunch by simply passing a few parameters. We will split the data into a training set (80%) and a validation set (20%). This is done with the valid_pct = 0.2 parameter in the ImageDataBunch.from_folder() constructor method:

Limit your augmentations: it’s medical data! You do not want to phantasize data…

Warping, for example, will let your images badly distorted, so don’t do it!

This dataset is big, so don’t rotate the images either. Lets stick to flipping…


tfms = get_transforms(max_rotate=None, max_warp=None, max_zoom=1.0)
# Create the DataBunch!
# Remember that you'll have images that are bigger than 128x128 and images that are smaller,   
# so squish them all in order to occupy exactly 128x128 pixels...
data = ImageDataBunch.from_folder(path, ds_tfms=tfms, size=size, resize_method=ResizeMethod.SQUISH, 
                                  valid_pct = 0.2, bs=bs)
#
print('Transforms = ', len(tfms))
# Save the DataBunch in case the training goes south... so you won't have to regenerate it..
# Remember: this DataBunch is tied to the batch size you selected. 
data.save('imageDataBunch-bs-'+str(bs)+'-size-'+str(size)+'.pkl')
# Show the statistics of the Bunch...
print(data.classes)
data

The print() will output the transforms and the classes:

Transforms =  2
['Parasitized', 'Uninfected']

and the data command in the last will simply output the return value of the ImageDataBunch instance:

ImageDataBunch;

Train: LabelList (22047 items)
x: ImageList
Image (3, 128, 128),Image (3, 128, 128),Image (3, 128, 128),Image (3, 128, 128),Image (3, 128, 128)
y: CategoryList
Uninfected,Uninfected,Uninfected,Uninfected,Uninfected
Path: data;

Valid: LabelList (5511 items)
x: ImageList
Image (3, 128, 128),Image (3, 128, 128),Image (3, 128, 128),Image (3, 128, 128),Image (3, 128, 128)
y: CategoryList
Uninfected,Parasitized,Parasitized,Parasitized,Parasitized
Path: data;

Test: None

A look on augmented Databunches

data.show_batch(rows=5, figsize=(15,15))

ResNet18

The ResNet18 is much smaller, so we’ll have more GPU RAM for us. We will create the DataBunch again, this time with a bigger batch size.

I had also used ResNet50 , It was giving an 92% accuracy.

But ResNet18 is good fit for this data and in this blog we are going to use that,

Now, create the learner:

learn18 = cnn_learner(data, models.resnet18, metrics=error_rate)

If you Colab environment doesn’t have the pretrained data for the ResNet18, fast.ai will automatically download it:

Downloading: "https://download.pytorch.org/models/resnet18-5c106cde.pth" to /root/.torch/models/resnet18-5c106cde.pth
46827520it [00:01, 28999302.58it/s]

Lets have an look on the model:

learn18.model

This will list the structure of your net. It is much smaller than the ResNet34, but still has a lot of layers. The output will look like this:

Sequential(
  (0): Sequential(
    (0): Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3), bias=False)
    (1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
    (2): ReLU(inplace=True)
    (3): MaxPool2d(kernel_size=3, stride=2, padding=1, dilation=1, ceil_mode=False)
    (4): Sequential(
      (0): BasicBlock(
        (conv1): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
        (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
        (relu): ReLU(inplace=True)
        (conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
        (bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      )
      (1): BasicBlock(
        (conv1): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
        (bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
        (relu): ReLU(inplace=True)
        (conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
        (bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      )
    )
    (5): Sequential(
      (0): BasicBlock(
        (conv1): Conv2d(64, 128, kernel_size=(3, 3), stride=(2, 2), padding=(1, 1), bias=False)
        (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
        (relu): ReLU(inplace=True)
        (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
        (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
        (downsample): Sequential(
          (0): Conv2d(64, 128, kernel_size=(1, 1), stride=(2, 2), bias=False)
          (1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
        )
      )
      (1): BasicBlock(
        (conv1): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
        (bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
        (relu): ReLU(inplace=True)
        (conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
        (bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
      )
    )
    (6): Sequential(
      (0): BasicBlock(
        (conv1): Conv2d(128, 256, kernel_size=(3, 3), stride=(2, 2), padding=(1, 1), bias=False)
        (bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
        (relu): ReLU(inplace=True)
        (conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), bias=False)
        (bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
        (downsample): Sequential(
          (0): Conv2d(128, 256, kernel_size=(1, 1), stride=(2, 2), bias=False)
          (1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)

.......... and so on

Let’s train it

We will again use the fit_one_cycle HYPO training strategy. Limit the training to 10 epochs to see how this smaller network behaves:

learn18.fit_one_cycle(10, callbacks=[SaveModelCallback(learn18, every='epoch', monitor='accuracy', name='malaria18-1')])
# save a stage
learn18.save('malaria18-stage-1')
# for a deployment purpose, lets export the model
exportStageTo(learn18, path)

This table below shows that the network learned to an accuracy of roughly 96.1% and suggests that the network should not be trained further: the loss between epoch #8 and #9 shows a 0.005 decrease but the accuracy has remained the same, suggesting that the network has started overfitting.

epoch 	train_loss 	valid_loss 	accuracy 	time
0 	0.543975 	0.322170 	0.901107 	01:08
1 	0.354574 	0.198226 	0.927055 	01:07
2 	0.256173 	0.173847 	0.938487 	01:08
3 	0.197873 	0.157763 	0.943930 	01:09
4 	0.163859 	0.148826 	0.947197 	01:08
5 	0.143582 	0.142058 	0.948104 	01:08
6 	0.130425 	0.134914 	0.949918 	01:09
7 	0.118313 	0.132691 	0.951551 	01:09
8 	0.112078 	0.132101 	0.952459 	01:09
9 	0.107859 	0.131681 	0.952096 	01:09

Let’s generate a ClassificationInterpretation and look at the confusion matrix and the loss curves.

interp = ClassificationInterpretation.from_learner(learn18)

losses,idxs = interp.top_losses()

len(data.valid_ds)==len(losses)==len(idxs)

Let’s have an look on confusion matrix:

interp.plot_confusion_matrix(figsize=(5,5), dpi=100)

Let’s look at the losses:

learn18.recorder.plot_losses()

ResNet18 started overfitting a bit after about 290 batches.

Remember that our bs is 512 here and was 256 for the ResNet34.

Fine tuning the model

Here we will introduce another fast.ai HYPO: automatically chosen variable learning rates. We will let fast.ai choose which learning rate to use for each epoch and each layer, providing a range of learning rates we consider adequate. We will train the network for 30 epochs.

# Unfreeze the network
learn18.unfreeze()
learn18.fit_one_cycle(30, max_lr=slice(1e-4,1e-5), 
                    callbacks=[SaveModelCallback(learn, every='epoch', monitor='accuracy', name='malaria18')])
# save this stage too
learn18.save('malaria18-stage-2')
# expert the model for deployment
exportStageTo(learn18, path)

Here , our fast.ai model achieved the accuracy of approx 97% after some fine tunning , that is quite good enough .

The validation loss, however, was becoming worse for the last epochs. This indicates that we have been overfitting from about epoch #20 on.

So if we want to deploy the model , choose the one with 20 epochs and note that this is the best accuracy at least with this network ,we can you different network for better result.

Results

interp = ClassificationInterpretation.from_learner(learn18)

losses,idxs = interp.top_losses()

len(data.valid_ds)==len(losses)==len(idxs)

interp.plot_confusion_matrix(figsize=(5,5), dpi=100)

learn.recorder.plot_losses()

This is better than what we’ve had before. Let’s look at the loss curves:

Here we see that the network seems to start to overfit after 500 batches, which would confirm our suspicion inferred from the results table above. If you look at the curves above, you’ll see that the validation loss starts to grow in the last third of the training, suggesting that this part of the training only overfitted the network.

Now i will give this task to you guys , tune the network or use any technique and control this situation.

Hint: save your model after every epoch.

Happy learning 🙂

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