The pandemic situation has accelerated digitalization to many countries. However, people living in rural areas are having an inconvenience to access medical technologies due to unavailability of specialists and also shortage of medical equipments. ¹ In Malaysia rural clinics, for example, there are still X-ray facilities that produce physical X-ray films. The films are then sent using courier services to the nearest available hospital for diagnosis by radiologists, making the whole process becomes inefficient. Moreover, purchasing new digital X-ray facilities for rural clinics may not be cost beneficial since the population numbers are low.

Digital technology has seen growth that leads to telemedicine. ^{2 – 4} Telemedicine makes use of communication technology in healthcare and can be cost effective. However, telemedicine is not commonly practiced in Malaysia ⁵ despite its potential to address healthcare shortcomings in the rural areas. In this paper, we propose a proof of concept work to digitalize physical X-ray films via digital photo capture so that their digital versions can be sent via email or cloud for evaluation by a radiologist elsewhere. This may improve efficiency in remote diagnosis as well as reducing physical storage. ⁶

A study by ¹ had described a simple implementation of 70 digitized chest X-ray films using a digital camera with an application of lossy compression technique. The digitized images had been shown in random order to two radiologists for diagnosis at 8 weeks after image capture. Then, lossy compression of different percentages were applied. The compressed images were again shown to the same radiologists in a random order for diagnosis at 8 weeks after the compression. The study achieved a mean percentage of 90% correct diagnosis with compression levels up to 20%. But with a compression of 40% and 50%, the correct percentages were 84% and 80%, respectively.

A similar study by ⁷ used an 8-megapixel smartphone on 44 X-ray films consisting of 16 chest and 28 musculo-skeletal. The digitize X-ray films were shown in random order to two radiologists for diagnosis through a LCD cellphone. The accuracy of diagnosis was reported as high. Also it was reported that a diagnosis was difficult when involving uncommon and difficult pathology cases.

These studies purely implemented digital photo capture of X-ray films and performed diagnosis without requiring online transmission. For sending images over the network, small file size with good resolution is best. However, there can be different resolutions due to differences in digital imaging software and hardware, hence, producing different qualities of digital X-ray films. ⁸ These variations open an opportunity to explore image enhancement techniques on images of digitized X-ray films. ^{9 – 15} In this paper, we investigate the use of CLAHE image processing techniques as a proof of concept and we validate the output via quantitative metrics and qualitative evaluation by a medical practitioner.

Figure 1 shows the flow of our proposed methodology, which includes, data collection and digitalization, image enhancement and compression, and evaluation. These would be discussed in the preceding sections.

Table 1 shows the average PSNR and MSE values for each image enhancement and image compression pairs. From this table the results show that CLAHE-DCT gave the lowest average MSE of 35.59 and the highest average PSNR values of 32.85dB compared to other methods. Nevertheless, CLAHE-FFT, MMCLAHE-DCT and MMCLAHE-FFT also attained comparable good values of PSNR at 32.67dB, 31.98dB, and 31.80dB, respectively. Also CLAHE-FFT produced comparable low average MSE results at 36.96. Both MMCLAHE-DCT and MMCLAHE-FFT attained MSE values of 57.16 and 58.71, respectively.

Figure 3 shows samples of processed CXR with a pneumothorax at High resolution level. They are labelled as A, B, C, D, E, F from top-left to bottom-right. Samples of processed CXR for CLAHE and MMCLAHE are in Figure 3 (A, B, C, and D).

On the contrary, both N-CLAHE FFT and N-CLAHE DCT attained the highest MSE and the lowest PSNR values at about 6533 and 10dB, respectively. It can be seen in Figure 3 (E and F) that the N-CLAHE method had produced an overexposure on the digitized CXR.

For qualitative evaluation, samples of Figure 3 were presented to the medical practitioner. Generally, the practitioner was extremely satisfied with the quality of the digitized and processed CXR. Images C and D (using MMCLAHE) were said to be better than Images A and B (using CLAHE). Images E and F (using N-CLAHE) were the worst among all due to overexposure.

Table 2 shows the results of blind qualitative evaluation where nine images were randomly selected for diagnosis. All diagnosis of the presented digitized CXR had managed to be identified without any difficulties except for Image 7. The true diagnosis for Image 7 was Normal. However, the diagnosis reported that there might be some abnormalities present even though Image 7 was a High resolution MMCLAHE-FFT enhanced image. Thus, a simple accuracy attained by the qualitative evaluation is 89.9%, which is comparable to the work of Refs. 1 and 7.

Also, for Image 6, which was a Medium resolution CLAHE-FFT, it was highlighted that further testing would be required to confirm the diagnosis of Infiltration. Nonetheless it was generally concluded that no pathological differences were observed between all processed CXR and all digitalized CXR.

In this paper, we presented the results of image processing techniques using CLAHE and its variations to enhance digitized X-ray films. Twenty-one physical X-ray films had been digitized via mobile phone capture at Low, Medium, and High resolutions. Three different image enhancement methods with two different image compression techniques had been compared. Results of quantitative evaluation indicated that N-CLAHE may not be a suitable method due to producing an overexposure. Also, the performance of DCT or FFT did not affect the quality of output.

Results of qualitative evaluation further validated the accuracy of the digitized X-ray with a medical practitioner. It had been found that the accuracy of correct diagnosis is close to the work by others in literatures. The overall presentation of the digitized X-ray had been found to be acceptable though some images might require further testing to confirm a diagnosis. Nevertheless, this paper had shown potential improvements with the proposed methods of enhancement that in turn may contribute to an increase efficiency in healthcare processes at rural clinics.

Mohd-Isa W: Conceptualization, Formal Analysis, Project Administration, Supervision, Writing – Original Draft Preparation, Writing – Review & Editing; Joseph J: Data Curation, Investigation, Methodology, Investigation; Hashim N: Conceptualization, Project Administration; Salih N: Formal Analysis, Validation.

Figshare: CLAHE-Enhanced X-ray Images DOI: https://doi.org/10.6084/m9.figshare.c.5490822. ²⁵

This project contains the following data: -

A collection of processed chest X-ray digitized images with CLAHE, MMCLAHE, N-CLAHE techniques and FFT and DCT compression.

Data are available under the terms of the Creative Commons Zero “No rights reserved” data waiver (CC BY 4.0 Public domain dedication).

Figshare. CLAHE-Enhanced X-ray Images

This project contains the following data: -

Processed images after digitization of physical X-ray films using CLAHE, MMCLAHE, N-CLAHE, and DCT and FFT compression.

Data are available under the terms of the Creative Commons Zero “No rights reserved” data waiver (CC BY 4.0 Public domain dedication).