Compression assessment based on medical image quality concepts using computer-generated test images

Anterior ophthalmic imaging

Improvements in imaging chips and computer processing power have brought major advances in imaging of the anterior eye. Digitally captured images can be visualised immediately and can be stored and retrieved easily. Anterior ocular imaging techniques using slitlamp biomicroscopy, corneal topography, confocal microscopy, optical coherence tomography (OCT), ultrasonic biomicroscopy, computerised tomography (CT) and magnetic resonance imaging (MRI) are reviewed. Conventional photographic imaging can be used to quantify corneal topography, corneal thickness and transparency, anterior chamber depth and lateral angle and crystalline lens position, curvature, thickness and transparency. Additionally, the effects of tumours, foreign bodies and trauma can be localised, the corneal layers can be examined and the tear film thickness assessed.

Imaging and image management: A survey on current outlook and awareness in pathology practice

BACKGROUND

Flexibility of digital photography enables it to be an integral part of pathology practice. An assessment of guidelines of imaging is essential for proper usage of photographs.

OBJECTIVES

The purpose of the study was to assess awareness of oral pathologists about various aspects of medical photography.

METHODS

Questionnaire based on the availability of facilities, usage, technical details and ethical issues of medical photography was sent to postgraduate students and teaching faculties of Oral Pathology in various localities in India.

RESULTS

Photographs were taken mostly for the purposes of publication, medical documentation and education. Significant number of postgraduate students and faculties of Oral Pathology didn't receive any training or hadn't gone through any publications/books (P = 0.000) about medical photography. Consent for patient photography was taken by significant number of respondents (P = 0.000) but in a verbal form. Majority of people used image editing software, but 19.0% of faculties and 21.1% of postgraduate students were unaware of deleterious effect of image editing. Firm and sensible instructions concerning image storage, sharing and accessibility were not yet created.

CONCLUSION

This survey drew attention towards lack of proper understanding about the technical details, medical protocols and ethical issues related to medical photography. These findings recommend implementation of basic training for medical photography and policy for image management for students and faculties in every health care institution.

Design of a lossless image compression system for video capsule endoscopy and its performance in in-vivo trials

In this paper, a new low complexity and lossless image compression system for capsule endoscopy (CE) is presented. The compressor consists of a low-cost YEF color space converter and variable-length predictive with a combination of Golomb-Rice and unary encoding. All these components have been heavily optimized for low-power and low-cost and lossless in nature. As a result, the entire compression system does not incur any loss of image information. Unlike transform based algorithms, the compressor can be interfaced with commercial image sensors which send pixel data in raster-scan fashion that eliminates the need of having large buffer memory. The compression algorithm is capable to work with white light imaging (WLI) and narrow band imaging (NBI) with average compression ratio of 78% and 84% respectively. Finally, a complete capsule endoscopy system is developed on a single, low-power, 65-nm field programmable gate arrays (FPGA) chip. The prototype is developed using circular PCBs having a diameter of 16 mm. Several in-vivo and ex-vivo trials using pig's intestine have been conducted using the prototype to validate the performance of the proposed lossless compression algorithm. The results show that, compared with all other existing works, the proposed algorithm offers a solution to wireless capsule endoscopy with lossless and yet acceptable level of compression.

The effect of image content on detail preservation and file size reduction in lossy compression

OBJECTIVES

To demonstrate the effect of image content on image detail preservation and file size reduction.

METHODS

The first set, containing 16 in vitro images with variable projection geometry, exposure time, bone level and number of teeth, was compressed with three compression modes: JPEG quality factor (JPQF), JPEG2000 quality factor (J2QF) and JPEG2000 compression ratio (J2CR). Image detail degradation was evaluated by local mean square error (MSE) on a standardized region of interest (ROI), containing bone. The second set, containing 105 clinical bitewings, was compressed with the same compression modes at 3 quality factors/compression ratios and local MSEs were calculated on two ROIs, containing bone and crown.

RESULTS

For the first image set, nearly constant MSE was found for the JPQF and J2QF compression modes, while file size depended on projection geometry, exposure time, bone level and the number of teeth. In contrast, file size reduction was nearly constant for the J2CR compression mode, while MSE depended on the abovementioned factors. Similarly, for the second image set, nearly constant MSE and variation of file size reduction were found for JPQF and J2QF but not for the J2CR compression mode. All of these results were consistent for all three quality factors/compression ratios.

CONCLUSIONS

Constant image detail preservation, crucial for diagnostic accuracy in radiology, can only be assured in QF compression mode in which the file size of the compressed image depends on the original image content. CR compression mode assures constant file size reduction, but image detail preservation depends on image content.

The impact of image information on compressibility and degradation in medical image compression

The aim of the study was to demonstrate and critically discuss the influence of image information on compressibility and image degradation. The influence of image information on image compression was demonstrated on the axial computed tomography images of a head. The standard Joint Photographic Expert Group (JPEG) and JPEG 2000 compression methods were used in compression ratio (CR) and in quality factor (QF) compression modes. Image information was estimated by calculating image entropy, while the effects of image compression were evaluated quantitatively, by file size reduction and by local and global mean square error (MSE), and qualitatively, by visual perception of distortion in high and low contrast test patterns. In QF compression mode, a strong correlation between image entropy and file size was found for JPEG (r=0.87, p < 0.001) and JPEG 2000 (r=0.84, p < 0.001), while corresponding local MSE was constant (4.54) or nearly constant (2.36-2.37), respectively. For JPEG 2000 CR compression mode, CR was nearly constant (1:25), while local MSE varied considerably (2.26 and 10.09). The obtained qualitative and quantitative results clearly demonstrate that image degradation highly depends on image information, which indicates that the degree of image degradation cannot be guaranteed in CR but only in QF compression mode. CR is therefore not a measure of choice for expressing the degree of image degradation in medical image compression. Moreover, even when using QF compression modes, objective evaluation, and comparison of the compression methods within and between studies is often not possible due to the lack of standardization of compression quality scales.

Lossy JPEG compression: easy to compress, hard to compare

OBJECTIVES

To review the literature on lossy compression in dental radiography and to discuss the importance and suitability of the methodology used for evaluation of image compression.

METHODS

A search of Medline (from 1966 to October 2004) was undertaken with the search expression "(Radiography, dental) and compression". Inclusion criterion was that the reference should be evaluating the effect of lossy image compression on diagnostic accuracy. For all included studies, information in relation to mode of image acquisition, image content, image compression, image display, and method of image evaluation was extracted.

RESULTS

12 out of 32 papers were included in the review. The design of these 12 studies was found to vary considerably. Parameters used to express the degree of information loss (DIL) were either or both compression ratio (CR) and compression level (CL). The highest acceptable CR reported in the studies ranged from 3.6% to 15.4%. Furthermore, different CR values were proposed even for the same diagnostic task, for example, for caries diagnosis CR ranged from 6.2% to 11.1%.

CONCLUSION

Lossy image compression can be used in clinical radiology if it does not conflict with national law. However, the acceptable DIL is difficult to express and standardize. CR is probably not suitable to express DIL, because it is image content dependent. CL is also probably not suitable to express DIL because of the lack of compression software standardization.

The effect of digital image resolution and compression on anterior eye imaging

AIM

To determine the theoretical and clinical minimum image pixel resolution and maximum compression appropriate for anterior eye image storage.

METHODS

Clinical images of the bulbar conjunctiva, palpebral conjunctiva, and corneal staining were taken at the maximum resolution of Nikon:CoolPix990 (2048x1360 pixels), DVC:1312C (1280x811), and JAI:CV-S3200 (767x569) single chip cameras and the JVC:KYF58 (767x569) three chip camera. The images were stored in TIFF format and further copies created with reduced resolution or compressed. The images were then ranked for clarity on a 15 inch monitor (resolution 1280 x 1024) by 20 optometrists and analysed by objective image analysis grading. Theoretical calculation of the resolution necessary to detect the smallest objects of clinical interest was also conducted.

RESULTS

Theoretical calculation suggested that the minimum resolution should be > or = 579 horizontal pixels at 25x magnification. Image quality was perceived subjectively as being reduced when the pixel resolution was lower than 767 x 569 (p<0.005) or the image was compressed as a BMP or <50% quality JPEG (p<0.005). Objective image analysis techniques were less susceptible to changes in image quality, particularly when using colour extraction techniques.

CONCLUSION

It is appropriate to store anterior eye images at between 1280 x 811 and 767 x 569 pixel resolution and at up to 1:70 JPEG compression.

Integrating images into the electronic patient record of the hospital authority of Hong Kong

Over a period of 10 years the Hospital Authority has developed an integrated clinical information system (The Clinical Management System-CMS), including a territory-wide longitudinal electronic patient record (ePR). The CMS and ePR are used by over 4000 doctors and 20,000 other clinicians to document and review care. The ePR currently has nearly 3TB of data covering 44 million episodes for 6.4 million patients. To date the CMS has largely dealt with textual data. However, PACS technology is increasingly being adopted in the HA. This paper describes our strategy for taking the hospital image archives and making them available throughout the Authority as part of the longitudinal patient record, leveraging the ePR to distribute radiological and other images in a manner which is integrated, affordable and sustainable.