Using Machine Learning to Diagnose Chest X-rays and Interpret Patient Symptoms and Medical History

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Using Machine Learning to Diagnose Chest X-rays and Interpret Patient Symptoms and Medical History

Rohan Bhansali

Senior at Loudoun Academy of Science Director at Connect AI Ashburn, United States

Abstract Chest X-rays are the most frequently used medical imaging procedure and contain among the most significant and perilous diseases. Hospitals, especially those that are understaffed or have underqualified radiologists, would benefit greatly from an automated method of diagnosing these X-rays, which would drastically lower healthcare costs as well. This paper explores a combination of past, present, and future research that implements artificial intelligence towards this goal of automated diagnoses. Additionally, the importance of chest X-rays in light of COVID-19 is also analyzed.

KeywordsChest X-rays, radiology, artificial intelligence, machine learning

I. APPLYING ARTIFICIAL INTELLIGENCE TO DIAGNOSING CHEST X-RAYS

Thoracic radiographs are the most commonly utilized medical diagnostic tool, with over two billion performed annually [17]. However, there is a global shortage of radiologists to analyse these X-rays, as exemplified by the nearly two thirds of the worlds population that lacks radiologists. This problem is further exacerbated in poor countries such as Rwanda, where eleven radiologists care for twelve million inhabitants, and Liberia, where, despite a population of four million, there are merely two practicing radiologists [10].

The cardiopulmonary diseases that are typically detected through these radiographs tend to be among the most lethal; they include pneumonia, a contagion that hospitalizes over a million Americans annually, of which approximately fifty thousand expire [14]; tuberculosis, which currently afflicts one fourth of the worlds population and kills an annual average of

1.3 million people worldwide [3]; and lung carcinoma, the deadliest cancer for both men and women, with over one hundred and fifty thousand annual deaths attributed to the disease [13].

The frequency of chest X-rays and the deadly nature of the diseases associated with them make their accurate diagnosis imperative. However, radiologists, though professionally trained, are subject to human limitations that include fatigue, inattentiveness and bias. Consequently, a model with automated diagnostic capabilities would have enormous consequences; for example, in areas with a deficiency of radiologists, the model could essentially replace the radiologists and provide a diagnosis of patients X-rays with symptoms and history taken into consideration, just as a radiologist would. A model with this capability would also be extremely versatile as it could be implemented in areas where

there are not insufficiencies of radiologists; in these areas, the model could act as a confirmation to the radiologists and could also expedite the diagnostic process and reduce the costs associated with it. However, to fully simulate the clinical process of diagnosis, a model must meet several criteria.

A. Model Criteria

First, the model must differentiate between anteroposterior (AP) and posteroanterior (PA). Although AP and PA X-rays are both frontal radiographs, they are fundamentally different in terms of the method by which they are performed and the resultant radiograph. PA X-rays are taken from the back to the front whereas AP X-rays are taken from the front to the back. AP X-rays are generally not preferred except in scenarios in which the patient is too weak or is unable to assume an erect position [15]. AP X-rays are much more difficult to read as radiologists must make several adjustments to account for the differing view. For example, AP X-rays tend to return the appearance of mild cardiomegaly (enlargement of the heart) because the X-rays diverge as they pass through the mediastinum, resulting in an overall magnification of the anterior structures of the thorax, among which is the heart.

Second, the model must take into account the lateral X-rays as they are significant for at least 15% of diagnoses and often reveal information that a frontal X-ray does not [9]. Lateral X- rays are especially useful in situations where the frontal X-ray is AP; due to their aforementioned difficulty in interpretation, the lateral view often provides clarification and further detail. Third, the model would need to also account for patient information, including symptoms and medical history. The importance of these factors in the diagnosis can be highlighted by the example of a patients chest X-ray showing signs of congested lung vasculature. The radiologist analyzing the roentgenogram could potentially diagnose it as an acute illness like multifocal pneumonia; however, if the radiologist knew that the patient has a heart condition and is exhibiting shortness of breath, it would be much more likely that the patient is affected by pulmonary edema. However, without the knowledge of the patient and the patients symptoms and history, the radiologist would have provided a misdiagnosis which ultimately could have led to the expiration of the patient.

B. Existing Chest X-ray Datasets

Several datasets have been released to further the development of machine learning in thoracic radiograph diagnosis. One of the earliest and most significant datasets was the ChestX-ray14 dataset, a large set of thoracic radiographs released by the National Institute of Health. The dataset, which was, at the time of its initial publication, the largest dataset of chest X- rays, contained 112,210 X-ray images in DICOM format from 30,805 patients [20]. The dataset was especially notable for the role it played in the development CheXNeXt, a deep learning algorithm designed by researchers belonging to Stanford Universitys Machine Learning Group. CheXNeXt is a 121- layer convolutional neural network that was trained and validated using the aforementioned ChestX-ray14 dataset [16]. The model took a frontal X-ray as an input and outputted a vector of disease probabilities and a heat map of where the findings of the radiograph were localized.

Fig. 1. A visual representation of CheXNeXt, with the inputted X-ray and outputted heat map and disease probability.

The model was tested with a set of 420 chest X-rays, which it diagnosed in 90 seconds; conversely, the four board- certified radiologists against whom CheXNeXt was being compared required approximately four hours. Although CheXNeXt wasz remarkable in terms of the accuracy it achieved, it was limited in that it did not differentiate between AP and PA X-rays, account for lateral chest X-rays or consider patient information. However, despite its shortcomings, CheXNeXt was revolutionary as it was the first model to conclusively provide evidence for the potential of such a model matching, and occasionally surpassing) the accuracy of radiologists.

Another prominent dataset is MIMIC-CXR, the largest collection of thoracic radiographs released to date [10]. The dataset contains 371,920 thoracic radiographs with positive and negative labels for the following diseases/findings: no finding, enlarged cardiomediastinum, cardiomegaly, airspace opacity, lung lesion, pulmonary edema, consolidation, pneumonia, atelectasis, pneumothorax, pleural effusion, pleural other, fracture and support devices. The DICOM- formatted images were obtained from 227,943 radiologic imaging studies conducted at the Beth Israel Deaconess Medical Center and were de-identified using an algorithm that removed dates and potential patient identifiers. Subsequently, the images were labelled with information from their corresponding radiology report using the CheXpert labele developed by researchers at Stanford University. The dataset has been published for researcher use and is intended to be fully disseminated in the near future. As a prerequisite to gaining access to the data, completing a course in human ethics is mandatory; additionally, the researchers must agree to citing the data in any publication that makes use of it.

II. EXISTING RESEARCH

A recently published model developed by researchers at Philips Research Institute was able to build upon the research done by Rajpurkar, et al.; in their research, three separate networks were trained for PA, AP and lateral X-ray images [18]. These networks were then paired together for two different models. One model was composed of a PA and lateral network, while the other model was composed of an AP and lateral network. The model operated by accepting two different inputs: a frontal X-ray and a lateral X-ray. Subsequently, the images were independently analyzed through separate networks with the final output being a fusion of the outputs of the individual networks. Each network was designed based on the DenseNet-121 architecture. A sigmoid operation was applied to each of the fourteen outputs and the networks were trained using a binary cross-entropy loss function.

TABLE I.

AUC Comparison Between Radiologists and CheXNeXt
Pathology Radiologists CheXNeXt
Atelectasis 0.808 0.862a
Cardiomegaly 0.888 0.831
Consolidation 0.841 0.893a
Edema 0.910 0.924a
Effusion 0.900 0.901a
Emphysema 0.911 0.704
Fibrosis 0.897 0.806a
Hernia 0.985 0.851
Infiltration 0.734 0.886a
Mass 0.886 0.909a
Nodule 0.899 0.894a
Pleural thickening 0.779 0.798a
Pneumonia 0.823 0.851a
Pneumothorax 0.940 0.944a

a. CheXNeXt performed statistically equal to or better than the radiologists

Fig. 2. A visual representation of the dual convolutional neural networks. While this model was successful in implementing lateral X- rays, something that prior research had been unable to accomplish, it still did not account for patient information, which would be the focus of future research in this field [18].

III. X-RAY IMAGE PROCESSING TECHNIQUES Unfortunately, as with many other medical classification

problems, there is a lack of publicly available COVID-19 X-ray scans. A lack of training data can significantly restrict the

performance of deep neural models and lead to overfitting. One potential solution that has been explored to this problem is the use of generic data augmentation techniques. Generic data augmentation involves manipulating the original images in the dataset through various methods of cropping, rotating, and zooming, in order to artificially grow the dataset while preserving the distinguishing features that are present in the images. Generic data augmentation has been shown to be especially useful in fine-grained datasets, or datasets that have low sample sizes and high degrees of similarities between images [19]. The primary concern in the application of data augmentation is that of over-fitting occurring. Thus, it is important that studies which employ data augmentation analyze differences in training and validation metrics over the runtime in order to rule out overfitting.

In mathematical terms, the Laplace filter is a filter that is defined by the divergence of a scalar fields gradient. In image processing, it is used for enhancing an images edges to help in its detection. Because derivative filters, among them the Laplace filter, are sensitive to noisy images, they are often performed in association with a smoothing filter to remove noise. The filter operates by calculating a sum of differences across multiple neighboring pixels to replace the magnitude of each individual pixel. This is how it effectively locates edges and simultaneously removes noise from images. In the presence of a bright spot located in a dark region of the image, the Laplace filter will return an even brighter spot to highlight the disparity. The Laplace filter is utilized in Image Preprocessing since it has shown the ability to improve the recall rate of CNNs when tested on X-ray images [2].

IV. CONCLUSION

A model with the capability to instantaneously and accurately diagnose X-rays would have immense benefits in health-care environments as they would drastically reduce the number of diagnostic-related deaths, lower health-care costs and decrease the amount of time needed by radiologists to analyse the radiographs. Additionally, areas with minimal medical staff would greatly benefit from a model that effectively replaces radiologists. There exist many limitations in the diagnosis of chest X-rays, such as inadequate data, insufficient accuracy, and misleading results.

ACKNOWLEDGMENT

I would like to thank Mr. Writer of the Academies of Loudoun for his mentorship in writing this paper.

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