Abstract –– In this paper, we present a framework for monitoring and quantifying blood flow in coronary artery bypass surgery, by employing a combination of ultrasound measures. An acquisition module is described, detailing both hardware and software characteristics. The system aims to perform signal acquisitions from 1 to 4 channels and transmit them to a remote station; hence a software control tool to attain an efficient transmission is described.

Keywords –– Ultrasonics, telemedicine, internet, bypass,

cardiovascular disease

I. INTRODUCTION

Unfortunately, studies carried out in recent years on

cardiovascular diseases (CVDs) have shown that the number of people suffering from these kinds of diseases is increasing worryingly. In fact, according to World Health Organization, an estimated 17.1 million people died from CVDs in 2004, representing 29% of all global deaths and by 2030 24 million people will die from CVDs [1]. Nowadays, CVDs are the number one cause of death globally.

Despite the efforts to prevent and control these diseases,

in most of the cases, surgeries are required [2, 3]. One of the most famous procedures to enhance the quality of life of people suffering from CVDs is known as Coronary artery bypass surgery (Bypass), and can be described as a surgical technique to avoid the total obstruction of one of the veins that irrigate the heart. The bypass technique improves the blood flow to the heart by using a vein from the leg or an artery from the chest, usually, saphenous vein or the internal thoracic artery respectively. The goal is to create an alternative route by means of sewing the internal thoracic artery around the disease artery.

Due to high complexity of such a procedure, it is

critical to have accurate measures and continual monitoring of vital signs. Currently, in order to know when a bypass is working correctly, doctors use very intuitive methods such as taking patient's pulse if deals with an artery, or just observing the blood irrigation if deals with a vein. There exist other methods which can also be considered to help doctors to get a more accurate measure on the bypass state:

• Electrocardiography • Doppler Effect technique (DET) • Transit Time (TT) • Elastography

Electrocardiography [3] is a representation of the

electrical activity of the heart over time. The heart movements are observed from twelve electrodes located on the skin.

Doppler Effect (DET) [4], also called

"echocardiogram", consists of a transducer which sends ultrasound signals in a sense, so in opposite sense; it receives the echo signals produced by moving erythrocytes. As a result, by calculating the frequency derives, relative velocity of the objects is found. The transducer's location must be as parallel as possible to the blood flow.

Fig. 1. DET applied to blood flow evaluation.

Transit time (TT) [5], is based on measuring the movement velocity of an ultrasonic pulse in the same sense and against the blood flow. In Anastomosis interventions, the TT technique is used to measure the times employed by an ultrasonic pulse to go through a vein or an artery.

Fig. 2. Transducer applied to blood flow evaluation in TT.

Transducer 1 Transducer 2

Telemetering Acquistion Module for Ultrasonic Cardiovascular Diagnostic

Miguel Angel Rodríguez-Hernández, Gustavo Adolfo Hernández-Peñaloza

ITACA, Universitat Politècnica de València (UPV), Valencia, Spain Email: marodrig@upvnet.upv.es;

This work has been partially supported by CYTED (Project Sucodic) and by the National Plan of the Spanish Ministry of Science & Innovation (R&D Project DPI2008-05213).

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Elastography allows determining the elasticity of an

object, in our case vascular tissue [6]. This ultrasonic system aims for the non-invasive remote evaluation of tissue elasticity by using multiple distributed ultrasonic transducers. In cardiovascular medicine it is used to characterize vascular functions, can detect atheromatous plaques in the presence of lipids.

Fig. 3. Principle of elastography.

There exist medical imaging techniques based on DET developed for diagnostic in patient consultations [7]. However, these machines can not be located directly at the surgery room. Although some systems based on continuous and pulsed Doppler sonograms have been developed for bypass assessment, this technique is not enough by itself to quantify the blood flow; therefore in order to have an accurate flow evaluation, a complementary technique is required.

The combination of DET, TT and elastography, allows

on one side, to quantify the blood flow through bypass hence warrants the surgery success, so reducing patient death probabilities. On the other side, take into account an elastic quantitative characterization of vascular tissue by employing ultrasound elastography technique increases certainty on the diagnostic, and blood flow in vascular system.

Systems combining DET and TT applied to flow

assessment for coronary bypass surgery have been reached by few companies around the world like Medi-Stim ASA, but with a high economical cost. Then, Sucodic project treats to develop an alternative and low cost system to help in cardiovascular surgery combining four measures based on electrocardiography, DET, TT and elastography.

This paper describes the module that performs the signal

acquisitions for the four measurement types. This module allows acquiring, displaying in time and frequency, saving and sending via internet, the signals obtained from the transducers. Additionally the acquisition system can be

remote controlled via internet. The measurement units for this system are developed by other the project partners. However, this work is mainly focused on show the software characteristics of the acquisition system that is an improvement of a previous work [8].

Then the whole objective is the development of a low

cost system for blood flow assessment in bypass surgery by using multiple distributed ultrasonic transducers (DET, TT and elastography). The system has a double functionality, on a hand, it enhance the diagnostic and success of bypass surgery by processing and representing the acquired measures. On the other hand, it allows to doctors and patients save time by means of sending reports as well as being controlled from a remote point.

The main design aspects of this measurement

telemetering system are explained. The remainder of this paper is organized as follows: In section II, the hardware prototype for acquisition is explained. In section III, the software characteristics are shown. At the end, some conclusions of the paper are presented.

II. HARDWARE FOR DATA ACQUISITION

A hardware prototype has been assembled previously to the development of the control software for the acquisition module. All the components of this module are commercial elements thus this part the work consisted in the selection and connection of the different elements. The system is composed of a central station (PC) a remote station (PC) and an acquisition card Adlink technology PCI-9810 [9].

Analogue to digital conversion (A/D) is performed by means of the card PCI-9810 which has a 32 bit PCI bus connected to the PC computer which acts as station. The most significant characteristics of this card are: 20 MHz as maximum value in sampling frequency and 10 bit resolution per sample, 4 simultaneous A/D channels and 32 Kilo-samples in internal memory for data storage.

The station contains the A/D converter card plugged in a slot of PCI and software. The output of the ultrasonic unit used in this prototype is connected to one of the four inputs of the A/D converter card. It is possible to have four ultrasonic units in testing tasks simultaneously, which transmit the ultrasonic information to the central station. Specific software for central and remote stations is described in section IV. A general outline of the telemetering system is shown in figure 4.

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Fig. 4. Telemetering system framework.

III. CONTROL SOFTWARE DEVELOPED FOR MONITORING

The software designed for this system has two principal functions: on one hand, it represents the data received from the ultrasonic unit, allowing tracking the blood flow. This is critical when a bypass surgery is performed. In the other hand, the software allows packing and sends the measures as reports to a remote station. Then the measures can be

followed via internet by other doctors or students interested in the bypass surgery.

The module presented here could be connected to other

diagnostic systems. Thus, it could be used in other telemedicine environments. As an application, let it suppose the patient takes his measures from home and sends it to the hospital, where it will be analyzed by the doctors. By this procedure, the patient can know his current state, hence, saving time and money, and the treatment evolution can be monitored by doctors, and even, they can request a new measurement if it is necessary. The software controls the general aspects of the whole system. It can set and program measures from 1 to 4 channels.

The received data are decoded, represented and saved

into a standard ASCII format. We establish two software versions. The first, has been created for remote stations that do not carryout data acquisition, whereas the second, has been developed for the base stations, which have the A/D device installed.

Fig. 5. Main screen of the software system for remote scheduling.

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Visual Basic is the programming language chosen to develop this software. The system consists of several control groups and displays. The main screen of the remote stations is shown in figure 5; this tool allows programming the connections as well as the time to measure in the other stations. The option to program connections allows creating a scheduling which is useful in cases where periodic reports are required. Apart from this, the measures option allows make the readings schedule, and perform real time representations. Other options include erasing measurements in remote stations, configure the A/D card, visualize and send data readings.

The base and remote stations software allows that

measurements obtained in a room can be follow in real time in different other places, via internet. The language of the actual version of the software is Spanish, but in a new version could be included any other language like English.

The main screen for base stations is shown in figure 6.

A dynamic library (PCIDASK.dll) is required to carry out this software, and can be found in [9]. In the top we can see the menus, where we can find reports about connections and measures performed, as well as change the kind of transmission protocol. Also we can know the connection state, the next connections and measures, in the “Estado actual” frame. In the bottom, we can find the displays that show data behaviour over time (electrocardiography) and

frequency (DET). In addition to all options available for remote station, we also can calibrate the A/D card from this software.

For data transmission, a versatile data frame has been designed. Data reports can be transmitted by using either Transmission Control Protocol (TCP), or User Datagram Protocol (UDP). TCP is a connection-oriented protocol; therefore a virtual window is created between the stations using one port of each station. Reliable communication is warranted by error checking and acknowledges messages. On the other hand, UDP, is not a connection-oriented protocol; is based on datagram exchange, hence the communication is unreliable, and some messages can be lost. Nonetheless, UDP overhead is much lower than TCP.

The growing use of internet as transmission medium has extended and nowadays it is the main way to send information. The design software takes advantage of that, and therefore the data exchange is performed online. A specifically data frame format has been designed to optimize the transmission. The data frame for message exchanging is described in figure 7, which is composed by an A/D configuration block that contains the acquisition parameters. The second and third block consists of the connections and measures programming respectively. The final block is formed by the data measures.

Fig. 6. Main screen of the software system for data acquisition and representation.

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Fig. 7. Frame format for data transmitting.

The whole acquisition system operation is described in figure 8. When we start the procedure, we must to mark at least one of the labs of “controles” frame. Once we do this, the corresponding frame is enabled to fill. Also the program checks if the input data is correct, then it saves the scheduling, and checks the connection. If all things are correct, the data frame is sent.

Fig. 8. Software operation scheme. .

IV. CONCLUSIONS

In this paper, an acquisition module is presented, which has been designed as a data remote transmission tool, in ultrasonic cardiovascular diagnosis applications. It was developed as a part of the consortium project entitled “Sucodic (Desarrollo de sistemas ultrasónicos y computacionales para diagnóstico cardiovascular”) financed by CYTED.

The hardware of the module is composed by two personal

computers with internet cards and an additional card with four A/D converters. The system is completed by a specifically developed software to control the hardware stage and to manage the signal information. Some of the most important software characteristics have been described, including the data frame format that has been designed for this system. Other system characteristics have been also shown, as its capability of signals representations in time and frequency.

The system is intended to track and program several ultrasound measures during a bypass surgery procedure. The objective pursued is to track local as well as remotely, and quantifying, the blood flow during such a procedure. The integration of the hardware and software modules detailed here, with some commercial devices, is employed as an acquisition tool within the Sucodic project.

REFERENCES

[1] World Health Organization (WHO), The global burden of disease. Last Update fact sheet, 1999.

[2] World Health Organization (WHO), Prevention of cardiovascular disease: guideline for assessment and management of cardiovascular risk. ISBN 978 92 4 154717 8, 2007.

[3] L. B. Mongero, J. R. Beck, On bypass: Advanced Perfusion Techniques, Humana Press, 2008. ISBN: 1588296369. 580 pages

[4] Evans D and McDicken W.N. Doppler Ultrasound. Physics, Instrumentation And Signal Processing. John Wiley & Sons LTD.2000.

[5] Bednarik, J.A., May, C.N., Evaluation of a Transit-Time System for the Chronic Measurement of Blood Flow in Conscious Sheep, J Appl. Physiol.1995;78(2): 524-530. (Howard Florey Institute of Experimental physiology and Medicine, Univ. of Melbourne, Parkville 3052, Australia) 26V.

[6] Ophir et al, Elastography . A method for imaging the elasticity in biological tissues” Ultrasonic Imaging , vol 13, pp. 111-134,1991.

[7] Fu D. et al, Non invasive quantitative reconstruction of tissue elasticity using an iterative forward approach, Ultrasound in Medicine and Biology, vol 45-6, pp.1495-1509, 2000.

[8] M. Rodríguez, A. Ramos, P. Sanz, D. Zaplana, J. San Emeterio, Ultrasonic system for remote non-destructive testing using mobile telephony NDT and E International, vol. 36, no. 2, enero 2003, pp. 85-92, ISSN: 0963-8695

[9] Adlink catalogue. http://www.adlink.com

Yes

Program

Any tab marked?

You must mark some labs

Correct settings?

You must fill in a correct way

Save settings & show state

Connected ?

Check connection

Send dataframe

No

No

No

Yes

Yes

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