Digital Watermarking of Medical Image Using R01 Information

2 3 4 5

Hyung-Kyo Lee Hee-Jung Kim Ki-Ryong Kwon Jong-Keuk Lee

Dept of Internet Business Andong Science College Dept of Elec and Comp Eng Pusan Univ of Foreign Studies

Dept of Computer Engineering Dongeui University E-mail krkwonpufsackr e952 1728hanmailnet

Conformance lnformation Object Definitions Service Class Specifications Data Structures and Encoding

Abstract-Recently the medicat image has been digitized by the development of computer science and digitization of the medical devices There are needs for database service o f the medical image and long term storage because of the construction of PACS (Picture Archiving and Communication System) following DICOM(Digita1 Imaging Communications i n Medicine) standards telemedicine and e t al Furthermore authentication and copyright protection are required to protect the illegal distortion and reproduction o f the medical information data In this paper we propose digital watermarking technique for medical image that prevents illegal forgery that can be caused after transmitting medical image data remotely A wrong diagnosis may be occurred if the watermark i s embedded into the whole area of image Therefore we embed the watermark into some area of medical image except the decision area that makes a diagnosis so called region of interest (ROI) area in our paper to increase invisibility The watermark is the value o f bit-plane i n wavelet transform of the decision area f o r certification method of integrity verification The experimental results show that the watermark emkdded by the proposed algorithm can survive successfully in image processing operations such as JPEG lossy compression

Keywords-PACS DICOM digital watermarking ROI

9 I O I I

1 INTRODUCTION ITH the development of information-communication and w computer technoloa there has been coim to digital

hospital age that can be received remote medical treatment in network by database of digital medical image HIS (Hospital lnformation System) and PACS based on DICOM standard pave the way to store medical image and search for data base and give remote medical treatment [I] A PACS offers some of information or functions (a) picture viewing at diagnostic reporting consultation and remote workstations (b) archiving on magnetic or optical media using short or long-term storage devices (c) communications using local or wide area networks or public communications services and (d) systems that include modality interfaces and gateways to HFDlS (Healthcare Facility and Departmental Information Systems) offering one integrated system to the user DICOM Standard is a set of rules (protocol) that allow medical images to be transmitted between instruments and computers of hospitals and users in network

Paint to Point Communication Support for Message Exchange Media Storage and File Format for Media Interchange Media Staraee Aodrcation Profiles

Table 1 shows the DICOM Standard[23j The American College of RadiologyNational Electrical Manufacturers Associations DICOM Standard has been developed to meet the needs of manufacturers and the users of medical imaging equipment for interconnection ofdevices on standard networks Its multiple parts provide a means for expansion and updating and the design of the standard was aimed at allowing simplified development for all types of medical imaging DlCOM also provides a means by which users o f imaging equipment may assess whether two devices claiming conformance will be able to exchange meaningful information

HIS and PACS provide to easily access manipulate and distribute medi~al data However there are some kinds of problems in HIS and PACS such as illegal reproduction of medical image proprietary rights and data authentication

TABLE I THE DlCOM STANDARD [Par t I Title

15 16 I7 I8

1 1 1 Introductioi~ and Overview

Security and Systein Maiiagetiient Profiles Content Mapping Resource Explaoatory Intonmanon Web Access to DlCOM Persistent Objects (WADO)

6 I Data Dictionary 7 I Messaee Exchanee

I 8 I Network Comniiinication Sua~ort for Messaee Exchanw

I I2 I Media F o r and Phvsical Media for Media lnlerchanae

I 14 I Gravscale Standard Disdav Function

0-7803- a940-905$2000 2005 IEEE - 404 -

Digital watermarking has been an emerged research area recently that originally focused on copyright protection Furthermore it has been exploited in a wide range of application such as video audio image and 3D graphic model

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Although there are only a few medical oriented watermarking studies in the literature to date digital watermarking will be a valuable tool for copyright protection with medical confidentiality protection patient and examination-related information hiding data integrity control and source identification in a variety of medical application^ following digital hospital age being capable of remote medical treatment Digital watermarking is the technology that embeds directly additional information by modifying imperceptible either the original data or some transformed version of them [4] I t is divided into two basic categories (a) Spatial domain watermarking Interchanges the lower order bits of the pixel values with the watermark or adds some fixed intensity value representing a visual watermark to the pixel values of an image (b) Frequency domain watermarking Inserts the watermark into the coefficients of a transformed image for example using the DFT (Discrete Fourier Transform) DCT (Discrete Cosine Transform) and DWT (Discrete Wavelet Transform) that is difficult to detect [5-91

Study of previous method is proposed a way to watermark medical images with encryption information of patient data (EEG PCG)in the spatial domain by swapping the gray level piset values with that of the watermark[lO]

In medical images ROI is an area which contains important information and must be stored without any distortion[l I] This paper suggested a digital watermarking method which specify ROI area in the original image Then compress the signature image by a progressive coding to generate a bitstream (bit) in the order of significance Embed the bit into pixels around the ROI in a spiral way to create the embedded image

In this paper we present a robust watermarking for medical imagethat embeds the watermark with ROI information into the adjacent area of ROI medical image Thus the watermark is embedded into parts surrounding ROI area The watermark is the value of bit-plane in DWT of the decision area for cerLificativn method of integrity vsrification The esperimental results show that the proposed technique could have the robustness against image processing operators like to JPEG lossy compression

11 PROPOSED METHOD

A Watermark Embedding Step

Figure I shows the procedure encoding the watermark ofROI information adjacent areaofROI medical image Generally ROI selects the centre area and especially when a doctors diagnose i t First thz mzdical image is separated into two parts ROI and non-ROI We embed the ROI image into the non-ROI part (black square region) ROI image is transformed into 3-level DWT and the wavelet coefficients in LL3 level are represented to Sbit plane Then each o f h i t - p h e information is matched to the size ofnon-ROI region and i t is used as the watermark using the embedding equation

B The Embedding Algorithm

The basic scheme is described as follows

Figure I Warermark embeddins steps

l Separate the hosr image H into ond p)

Consider the original image (host image) as H = h( i j ) 05 I J lt K ) where h ( i j ) 2 (0 I 2 2 ) L is the number ofbits used in the gray level of pixels

ROI image flo is = d( i j ) 05 i iN DltjltM) where h(ij) 2 (0 I 2 21

2) Transform ROl image H bv DWT(3-Level) fo obtain H 2 f h LL3

3)

represented in the form of the base 2 polynomial [ 121

Performance ampbit bit-plane of f 13

The gray level of an m-bit gray-scale image can be

1) of Hl m around the ROI of CI medical image

Embeddiq the waiermark vf ROI information (bir-plane

where LJtis the watermarked region Vi s the embedding region a is scale coefficient and x i is the watermark

C The Detection Alguritltni Figure 2 shows thc dzcoding procedure for extracting the watermark The original image stored in database server is required to extract the watermark If the watermark in the attacked image is failed to extract the image is re-transmitted to the user This procedure is reversed as the embedding procedure and it uses the subtraction of watermarked image and original image

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Figure 2 Watermark extracting sleps

1) Eriracrion is reversed the embedding

90

where C is watermarking image I is insert region a is scale coefticient and xi is watermark

4428 1 08886

111 EXPERIMENTAL RESULTS

80

Te evaluate our proposed algorithm we simulated with the medical images Brain and Spine that converted files of DICOM to image data using VisualGate and PiView 45 software supported by httpwwwinfinittcom In our scheme the extracted watermark is a visually recognizabfe pattern The viewer can compare the results with referenced watermark subjectively However the subjective measurement is dependent on factors such as the expertise ofthe viewers and the experimental conditions Therefore a quantitative measurement i s needed to provide objective judgment o f the extracting fidelity We define the similarity measurement between W(i j) insert watermark and extract watermark ( f j ] Where NC i s normalizad correlation PSNR is power signal-to-noise ratio and RMS is root mean square x ( j j ) is original image and (i j ) i s extract image

4287 1 08841

Figure 3 and 4 show an example o f the proposed watermarking approach Original medical images with size of 5 I 2 X 51 2 and ROI image with size of 256 X 256 and scale coefticient a is 01 The proposed technique successfully survives JPEG lossy compression

Figure 3-(a) is MRI 3rain image and (b) is watermarked image with 4674 dB of PSNR Figure 3 4 4 is an image operated by illegal processing and may be diagnosed as cerebral apoplexy Figure 34d) is estracted ROI from attack image Data integrity is confirmed by verifying some difference between the extracted watermark and the showing parts in the operated image Table 2 is variation of NC based JPEG compression rate of Figure 3-(b) We can know that information remains to high compression As similar as Figure 4-(a) is the MRI Spine image and (b) is watermarked image with 5222 dB of PSNR Figure 4-(c) i s an image operated by illegal processing and may be diagnosed as herniation of intervertebral Disk or Bulging Disk Figure 4-(d) is extracted ROI from Figure 4-fc) image

40

(C) Figure 3 MRI brain tmages (a) original image (b) watermarking image [c) attacked image and (d) extracted ROI from attack image

3927 07998

TABLE 2 VARIATION OF NC VALUE BASED P E G COMPRESSION RATE

4 I 8S 08657 4086 08507

50 4008 08181

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Authorized licensed use limited to Johns Hopkins University Downloaded on November 9 2009 at 1740 from IEEE Xplore Restrictions apply

Figure 2 Watermark extracting sleps

1) Eriracrion is reversed the embedding

90

where C is watermarking image I is insert region a is scale coefticient and xi is watermark

4428 1 08886

111 EXPERIMENTAL RESULTS

80

Te evaluate our proposed algorithm we simulated with the medical images Brain and Spine that converted files of DICOM to image data using VisualGate and PiView 45 software supported by httpwwwinfinittcom In our scheme the extracted watermark is a visually recognizabfe pattern The viewer can compare the results with referenced watermark subjectively However the subjective measurement is dependent on factors such as the expertise ofthe viewers and the experimental conditions Therefore a quantitative measurement i s needed to provide objective judgment o f the extracting fidelity We define the similarity measurement between W(i j) insert watermark and extract watermark ( f j ] Where NC i s normalizad correlation PSNR is power signal-to-noise ratio and RMS is root mean square x ( j j ) is original image and (i j ) i s extract image

4287 1 08841

Figure 3 and 4 show an example o f the proposed watermarking approach Original medical images with size of 5 I 2 X 51 2 and ROI image with size of 256 X 256 and scale coefticient a is 01 The proposed technique successfully survives JPEG lossy compression

Figure 3-(a) is MRI 3rain image and (b) is watermarked image with 4674 dB of PSNR Figure 3 4 4 is an image operated by illegal processing and may be diagnosed as cerebral apoplexy Figure 34d) is estracted ROI from attack image Data integrity is confirmed by verifying some difference between the extracted watermark and the showing parts in the operated image Table 2 is variation of NC based JPEG compression rate of Figure 3-(b) We can know that information remains to high compression As similar as Figure 4-(a) is the MRI Spine image and (b) is watermarked image with 5222 dB of PSNR Figure 4-(c) i s an image operated by illegal processing and may be diagnosed as herniation of intervertebral Disk or Bulging Disk Figure 4-(d) is extracted ROI from Figure 4-fc) image

40

(C) Figure 3 MRI brain tmages (a) original image (b) watermarking image [c) attacked image and (d) extracted ROI from attack image

3927 07998

TABLE 2 VARIATION OF NC VALUE BASED P E G COMPRESSION RATE

4 I 8S 08657 4086 08507

50 4008 08181

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( C ) Figure 5 MRI spine images [a) original image (b) walemarking linage (E) attacked image and (d) extracted RO[ from attack image

Iv CONCLUSION

Digital medical imaging technologies have become increasingly important in medical practice and health care for providing assistant toolsfor diagnosis treatment and surgery Due to the volume of medical images is huge and has grown rapidly especially on CT (computer tomography) and MRI (magnetic resonance imaging) the compression technique must be applied For the purposed algorithm of security watermarks are embedded into medical images Nevertheless the embedded watermarks may be removed or distorted by attacks In this paper we have proposed the technique of embedding the ROI image into the spatial domain of n o n 4 0 1 part of a medical image

ACKNOWLEDGMENT This work was supported by the Brain BusanZl Project in 2004

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