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A Telemedicine Platform for Cardiovascular Ultrasound

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A Telemedicine Platform for Cardiovascular Ultrasound
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  A Telemedicine Platform for Cardiovascular Ultrasound Carlos Costa a , José Luís Oliveira a , Augusto Silva a , Vasco Gama Ribeiro b , José Ribeiro b   a University of Aveiro, Electronic and Telecommunications Department / IEETA, 3810-193 Aveiro, Portugal b  CHVNG, Cardiology Department, V. N. Gaia, Portugal Abstract This paper describes the design, implementation and current exploitation of a PACS solution for echocardiographic applications. The developed software package, denominated as Himage (Healthcare Image), provides an efficient digital archive that enables the acquisition, storage and visualization of DICOM cardiovascular ultrasound sequences. On the other hand, the system includes capabilities that allow the establishment of remote and cooperative telemedicine sessions. The system has been used with success across several institutions both at national and at transcontinental internetworking scenarios. The Himage great advantage is its compression rate that allows maintaining all the available exams online with diagnostic quality, and allows the transmission of these exams through low-bandwidth channels, both in synchronous and asynchronous telemedicine sessions. Keywords: PACS, DICOM, Telemedicine, Cardiovascular Ultrasound, Cardiology Image 1. Introduction The echocardiography is a rather demanding medical imaging modality when regarded as digital source of visual information. The date rate and volume associated with a typical echo poses several problems in the design and deployment of telematic PACS structures, especially in wide areas interaction environments. We know that, for example, an uncompressed echocardiography study size can fluctuate between 50 and 500Mbytes, depending from equipment technical characteristics, human factor and procedure type [1]. Digital video compression is a technology of the utmost importance when considering issues like storage and transmission delay. In this case, given the time-space redundancy that characterizes this type of video signals there are important gains by choosing a compression methodology that copes with both intra-frame and inter-frame redundancies, like the MPEG family encoders [2]. The definition of an adequate trade off between compression factor and diagnostic quality is a fundamental constraint in the design of both the digital archive and the telecommunications platform. In the following paragraphs we will present the architecture of a Digital Video Archive and Communication System, that preserves the images srcinal quality, that allows the on-line access to the whole cardiovascular ultrasounds history, and that supports and extends the DICOM standard. Connecting Medical Informatics and Bio-Informatics R. Engelbrecht et al. (Eds.) ENMI, 20051213Section 7: Imaging Informatics  2. Materials and Methods The PACS architecture described in this paper was developed in the Central Hospital of V.N.Gaia - Cardiology Department (Portugal) IT infrastructure. This healthcare unit is supported by two digital laboratories. The Cardiac Catherization Laboratory ( cathlab ) produces about 3000 procedures/year. The srcinal cathlab  PACS [3] (embryo of Himage), installed in 1997, allowed the storage of 12-14 months of XA procedures based on DICOM JPEG-lossy 95 (35 Mbytes/exam). The other unity is the Cardiovascular Laboratory ( echolab ) with 6000 procedures/year. The echolab  PACS module, installed in 2001, allowed the storage of 14-16 months of US procedures making use of DICOM JPEG-lossy 85 (10 Mbytes/exam). This volume of information is difficult to handle, namely if it is desired permanent availability and cost-effective transmissions times for remote connections. Also in 2001, starts a transcontinental project to develop a telematic platform capable of establishing cooperative telemedicine sessions between the Cardiology Departments of the Central Hospital of Maputo (Mozambique) and the CHVNG, to coronary ultrasounds. The telemedicine platform should support both real-time and store and forward sessions, promoting in any case the remote access and sharing of clinical data. Pushed by this project, we start developing a new PACS software solution to support the local storage and transmission of coronary US between both sites. 3. Network Platform Implementation The clinical partners are equipped with echocardiography machines including standard DICOM3.0 output interfaces and videoconference platforms. It was installed a network infrastructure with two computer servers in the Eduardo Mondlane Medicine Faculty. The Portuguese Medical partner provided the clinical training and ensures the remote support to diagnostics and therapeutic decisions, in offline and/or real-time sessions [4]. The clinical modus operandi , the geographic distance and the scarce telecommunications resources available, imposed us strict rules on the planning and implementation of the PACS system. The lack of telecommunications structures between the two interlocutors, with minimum technical requirements, was a crucial problem. Analysing the few communications platform possibilities, the adopted solution was the public ISDN network. However, and because the Maputo public ISDN was very recent and experimental (2002), the necessity of a backup circuit takes us to the inevitable space segment through satellite communication services, based in portable terminals INMARSATB that allow ISDN 64Kbps point-to-point connections and permanent availability. The utilization Internet as eventual valid alternative was also contemplated, but the quality-of-service was not acceptable. However, the expected future resource to a shared network obligated the implementation of security mechanisms, namely the resource to public key cipher supported by Public Key Infrastructures (PKI) and digital certificates. 4. Image Compression Guaranteed the minimum communications platform (bandwidth and availability), it was necessary to focus on the image data amount problem. The first approach of using the existent DICOM JPEG lossy format [5], with above expressed study volumes, resulted in an incorporable cost-time transmission solution to the project consortium. Typically, the methodology to find the “best” compression encoder (and settings) was based on successive evaluations of compression codec/factor versus desired diagnostic image quality to each specific modality and respective utilization scenario [6]. The novelty of our compression approach starts by embedding each storage server with highly efficient MPEG4 encoding software. If the JPEG explores exclusively the intra- Connecting Medical Informatics and Bio-Informatics R. Engelbrecht et al. (Eds.) ENMI, 20051214Section 7: Imaging Informatics  frame information redundancy, the MPEG4 encoding strategy takes full advantage of object texture, shape coding and inter-frame redundancy and led to best results. Since MPEG4 is not a DICOM native coding standard, subsequent image transmission, decoding and reviewing is accomplished through a DICOM private transfer syntax mechanisms enabled between storage servers and diagnostic clients terminals equipped with the echocardiography viewing software. In order to achieve full compliance all the other DICOM information elements and structure were kept unchanged. 5. DICOM Private Transfer Syntax Because we also develop solutions to other medical image modalities and have other telemedicine projects, it was decide not to insert the MPEG4 directly in the TLV (Tag Length Value) DICOM data structure, i.e. solve the US “specific problem”. Instead of that, it was developed a multimedia container that dynamically support different (versions) encoders (Figure 1). The container has a simple structure, including a field to store the encoder ID code. When it is necessary to decompress the images, the Himage-PACS solicits the respective decoder service to the operating system (like other multimedia application). The exposed approach represents an optimized high level software solution. If, for instance, in 5-10 years appears a more efficient image codec, we just need to change one parameter in the “Himage Convertion Engine” (i.e. set the new codec ID) to setup. - - --- - -- ---- -- -- - ----- ---- ---- -- ------- --- - - ---- - --- -- --- - - - --- - - ---- - --- -----  --- - - --- ---- - - --- - -----  --- - --- DICOMPrivate SyntaxImageEncapsulatedEncoder (MPEG4 – US) Himage Conversion Engine DICOM Default Transfer Syntax   - - --- - -- ------ -- - ----- ---- ---- -- ---- Encoder Code - - - - - - - - Encoder Code - - - - - - - - ImageRAWDevelopedContainer  Figure 1 - Conversion of DICOM “default transfer syntax” in “private syntax” The Figure 2 shows a DICOM partial overlap dump, “default transfer syntax” versus “private syntax”, of a US 25 frames image sequence with a RGB 576*768 matrix. It is possible to observe two important aspects. First, the DICOM DefaultTransferSyntaxUID identifier (1.2.840.10008.1.2) is replaced by a private PrivateTransferSyntaxUID (1.2.826.0.1.3680043.2.682.1.4). This private UID is based on the root UID 1.2.826.0.1.3680043.2.682 requested by our workgroup. Second, the “PixelData” field size “is reduced” 120 times (33177600/275968). Figure 2 - DICOM dump: DICOM “default transfer syntax” vs “private syntax” Connecting Medical Informatics and Bio-Informatics R. Engelbrecht et al. (Eds.) ENMI, 20051215Section 7: Imaging Informatics  6. Results With this new system, more than 12000 studies have been performed so far. For example, a typical Doopler color run (RGB) with an optimized time-acquisition (15-30 frames) and a sampling matrix (480*512), rarely exceed 200-300kB. The compression ratio starts in 1:65 to a unique acquired cycle, but can reach the 1:100 to 5 cardiac cycles. For the previous values, and even for a heavy work-loaded echolab, it is possible to have all historic procedures online or distribute them with reduced transfer time over the network, which is a very critical issue when we are dealing with costly or low bandwidth connections. The achieved compression rate does not compromise diagnostic quality, according to the results of user’s assessment, and reduces significantly the waiting time to download and display of images. 7. Image Quality Evaluation The new DICOM-MPEG4  private transfer syntax  offers an impressive trade off between image quality and compression factors spanning a wide range of bit-rates. Two studies were carried on assessing the DICOM cardiovascular ultrasounds image quality of MPEG4 (768kbps) format when blindly compared with the uncompressed srcinals. Qualitative and quantitative results have been present in [7]. An impressive fact coming out from this study was that, in a simultaneous and blind display of the srcinal against the compressed cine-loops, 37% of the trials have selected the compressed sequence as the best image. The quantitative and qualitative assessment of compressed images shows us that quality is kept at high standards without ever impairing its diagnostic value. Using compression factors of the same magnitude in other DICOM coding standards JPEG [8] MPEG1 [9] will lead to a severe decrease on image quality. 8. Himage-PACS Software The Himage different modules contemplate the acquisition of images uncompressed in DICOM3.0 ( default transfer syntax ) sent by the ecocardiograph machines, their processing and creation of our DICOM  private syntax.  Thereafter, every procedure is stored in the Himage-PACS, i.e. the alphanumeric data (extract from DICOM files) are added to the database and the images saved in the storage server. The uncompressed images are kept in the server during six months. However, the compressed DICOM  private syntax  image version is permanently available. The Himage client software (Figure 3) is enabled with several facilities, besides the customization to handle DICOM 3.0 and our DICOM  private syntax . Graphically, the main window includes a list box with the patient’s in the Himage database and a simultaneous cine preview of three sequences. In a second graphical application layer we have available the communications, report and DICOM viewer modules. In the main window toolbar, the user can “switch” to the database area containing the studies received from remote institutions. Other specific functionalities have been included like, for example, the traditional image manipulation tools (contrast/brightness), the printing capacities and the exportation of images in distinct formats (DICOM3.0, AVI, BMP,…). It is also possible to record in a CDROM/DVD the uncompressed DICOM default transfer syntax format. In the main window exists a “send select” button that allows the selection and mark of sequences that are sent to the communication module. This functionality allows the creation of customized study packages, with more than one study, to be sent to predefined remote institutions. With this facility the physician can select images sequences, make annotations, append extra comments and send the examination over the network to the remote unit. Connecting Medical Informatics and Bio-Informatics R. Engelbrecht et al. (Eds.) ENMI, 20051216 Section 7: Imaging Informatics  According to predefined security rules, remote sessions can easily be set up since the departmental network is made accessible both by conventional TCP/IP and by the DICOM own communications methods. In the Himage DICOM viewer window it is possible to visualize the image sequences and select image frames (from distinct sequences) that are sent to the report area. In this last module, the user can arrange the images location or delete some frames with a drag-and-drop functionality. At the end, the output images matrix (2x3) is used jointly with the clinician report to generate a RTF file, compatible with any common text editor. Figure 3 - Himage-PACS client modules: database, viewer, report and communications windows 9. Transcontinental Telemedicine Project The sessions can be conference-based teleconsultations for analysis of real-time clinical cases, or analysis of previously transferred exams files (DICOM  private transfer syntax ). In the last case the remote physician can select echo images sequences, make annotations, append extra comments and send to the Gaia Hospital. This information is stored in one dedicated server and is accessible by the Gaia cardiovascular ultrasound specialists. Both methods can be used at same time, the physician in Gaia can open and examine a clinic record file previously sent by the remote place, and use videoconferencing equipment to face to face consultation and decide the therapy. The communication relies on 2x64 Kbps ISDN channels (1 full US exam takes typically 2-5 min using a 64kb channel). Connecting Medical Informatics and Bio-Informatics R. Engelbrecht et al. (Eds.) ENMI, 20051217 Section 7: Imaging Informatics
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