Medical Devices Have Multiple Functions Biology Essay

Published: Last Edited:


Medical devices have multiple functions, they are useful to have a look inside the body, to control vital signs and provide treatment. It is important that these devices working correct and have no deviations in their measurements and resolution otherwise these proceeds of the treatment and cure of patients can be wrong.

In the experiment will be examined this importance by evaluate the functions and resolutions of ultrasound devices, the treatment of diathermy and of the defibrillator. Further will be quantify the vital sign monitors if they represent the real situation, because it is essential that vital signs are accurate. The reason of that is that vital signs are the first signs for diseases [DHO].

In the experiment is conclusively dealt with the function of the electrocardiography and how is the correlation of the leads.

2. Theory

1.2 Ultrasound

Ultrasound is one of the medical devices which provide a look inside the body without to injure the patient. The concept of ultrasound is to use ultrasound waves with a frequency above 20.000 Hz which propagate through the tissue in the body [UfS]. One part of the wave will reflect and travels back to the detector. The result will be an image which represents the environment inside the body. It is a complete non-radiation variant compare to some other imaging alternatives. This treatment provides also measurements about specific tissue parameters like elasticity or the blood flow. The resolution of an image is an important factor. It plays a big role to use an ultrasound image for diagnosis.

1.2.1 B-Mode

For testing the phantom was use the B-Mode. The B is standing for Brightness. The amplitude of each returning signal is not simply displayed. Instead the amplitude controls the brightness of the spot which represent this reflection; this also means the echo intensity. The highest amplitude stands for almost white, the smallest amplitude stands for almost black. Intermediate amplitudes give a various of grey. White areas in the image represent bone, gas, air or lime; the black areas represent liquid. The higher the frequency the lower the wavelength. This means the lower the depth to lead the wave into the body. However the resolution of the image is better. The formula to calculate the frequency f [Hz] with using the velocity c [] and the wavelength Î» [mm] shows the correlation between the frequency and the wavelength which given by:



2.1.2 Resolution

Ultrasound systems have the property to distinguish between two points at a particular depth in tissue. It is the axial resolution and lateral resolution, which is definite predominantly by the transducer [RUS].

The lateral resolution is defined as the minimum distance which can be differentiated between two reflectors located perpendicular to the direction of the ultrasound beam. The lateral resolution is high when the width of the beam of ultrasound is narrow [RUS]. The lateral resolution LR is depended on the wavelength Î», the aperture and the focal length which shows the following formula:


The axial (longitudinal) resolution is the minimum distance which can be distinguished between two reflectors. In this experiment was the aim to control the resolution of the screen with the real situation.

2.1.3 Colour Doppler

Commonly the Doppler is used to measure the blood flow. The principle is that the ultrasound wave will be reflected for a moving surface, the surface is altered slighty in a manner. The doppler frequency will be calculate by


Thereby is the normal frequency [Hz], v is the velocity of blood cells [], c is the speed of sound [1450]. The smaller the angle Î± the better the measurement. Best measurements will be getting by using an angle under 30Â°. By using an angle of 90Â° no doppler effect will be measured because the cosinus of 90Â° is zero. The consequence is that the frequency will be also zero [].

The colour Doppler represents the direction of the blood flow with the help of the colours blue and red. For the Doppler experiment was the aim to find out the relationship between the transducer moving direction and the colour changing of the regions of interests.

2.1.4 Elastography

The elastography function will used to measure the softness of the scanned tissue, the elasticity [Kpa]. With the aid of the elastography function in ultrasound device can be made a much better diagnosis for e.g. cancer tissue. The aim was to quantify the elastography appearances among the machines.

2.1.5 Dynamic range and time gain compensation

For efficient and accurate diagnosis of ultrasound images, the appropriate time gain compensation (TGC) and dynamic range (DR) in decibel control of ultrasound echo signals are important. TGC is used for compensating the attenuation of the sound beam as it passes through tissue, and DR is for controlling the image contrast [TCG]. DR compressed the gray scale information into a usable range for the display on the screen. A wider dynamic range provides more shades of gray, while in a narrow dynamic range appears more black and white shades [UPT]. In this part of the ultrasound experiment would just present how does it look like and if the difference are recognizable on the screen.

2.2 Diathermy and Defibrillation

The principle of diathermy is the use of high frequency electric current to produce heat. This principle is either to cut, to destroy tissue or to produce coagulation. The effect of the diathermy depends on the current intensity and the wave form. Coagulation produced interrupted pulses and has a square wave-form. It will be divided in Fulgurate which is used to stop bleeding and desiccate to dry tissue. Cutting produced a continuous current and has a sinus wave-form. The electrical frequency used a range of 300 kHz to 3 MHz.

Diathermy is divided in two treatments. In Monopolar und Bipolar diathermy. The monopolar principal used an electrical plate which acts as indifferent electrode. The current passes from the instrument through the body of the patient to the electrical plate.

The bipolar diathermy used an instrument which has two electrodes combined in one tool like a pincette. The current passes between the tips and not through the whole body [PSP]. In this experiment the monopolar treatment was applied and exanimate the variety of energy which is necessary for cutting or coagulating.

The principle of defibrillator is to deliver high current (pulse) to the heart and to depolarize the muscle of the heart.

Two modes are use to activate the heart. One of them is the synchronize-mode. This mode will use to shock the heart of the R-Wave (absolute refactory period) [WHO]. In this area it will be not hurt the ventricle. The delay time represent the time to find the peak of the R-wave (input) to the output of the shock and is indicated in millisecond. The energy which produces the pulse is indicated in Joule. The other mode is the disynchronize-mode. This mode will applied when ventricular fibrillation occurs. By ventricular fibrillation the normal heart rhythm is abnormal and consequently the R-wave is not to identify. The aim was to understand the principle of the defibrillator and to understand the difference between the two modes, to test the energy which is necessary for the shock and how long the delay time is.

2.3 Vital signs monitoring

The most common monitoring vital signs are the heart rate, the blood pressure, the oxygen saturation, the temperature and the respiratory rate. The benefit to monitor these vital signs is to make a diagnosis directly and if necessary to react directly with counter-measure to balance the vital sign.

The purpose in this experiment was to find differences of vital sign measure results between different monitoring items.

It would measure the blood pressure and the oxygen saturation. The blood pressure is recorded as two numbers, the systolic and the diastolic number. The systolic value is the pressure in the heart when the heart muscles contracts. This value is also the highest value of the two numbers. The diastolic value measured the pressure when the heart muscle is resting between beats and the ventricle is refilling with blood. The blood pressure is measured mmHg.

The second vital sign which was measured was the oxygen saturation. Oxygen is carried in the blood attached to haemoglobin molecules. The oxygen saturation is a measure of how much oxygen the blood is carrying as a percentage of the maximum it could carry. It is referred to as SPO2. Healthy people have an oxygen level above 95 %.

The oxygen level will titrate about two separate light sensors which will send to the blood circle in the capillaries. These rays reflect the oxygen concentration in the blood [Nonin] and can calculate by the following formula where T is the transmission coefficient, A0 the input of the ray and A1 the output of the ray:



Two separate lights provide two different trans-mission coefficients. By dividing (3) with (4) it will give the oxygen level in percent:


oxygen measure principle.png

Fig. : Principle to measure the oxygen level in the blood Reference?

2.4 Electrocardiograph

An electrocardiograph (ECG) is designed to recognize and record the electrical activity of the heart which means the potential difference in the body. This method is useful to check non-invasive the rhythm of the heart and can make diagnosis about abnormal heart rhythm which may be affected by underlying heart disease.

Ten electrodes are connected to the body, two for the legs, two for the arms and six for the chest. Electrical potential will be measured between two references. Here was use the bipolar lead after "Einthoven". In this treatment the electrical potential difference will be calculate between the limbs.

The six different leads provide a look of the heart of the frontal plane. That gives information about the current flow right, left, inferior, or superior.

The unipolar leads of V1, V2, V3, V4, V5, V6 are located on the chest (precordial leads) and provide a view of the electrical activity of the heart from the horizontal plane, which gives information about the current flow right, left, anterior, or posterior [ECG]. A three-dimensional view will provide through the frontal plane and the horizontal plane. By doing this, problems of the heart can specific localized and will shown in the graph report on the ECG [KY]. The right leg electrode (RL) is the neutral electrode. It is there to complete the electrical circuit and plays no role in the ECG itself. These data can be store either by SD-Card or USB-Stick or printing it. The goal was to find out the correlation between the leads.

3. Experimental procedure

3.1. UltrasoundUltrasound.jpg





Transducer: Linear Array 7.5 MHz & 10 MHz

Fig. : Experimental assembly of the ultrasound study


For the beginning the experiment must be prepared. It is necessary to check roughly whether all elements on the array are working properly, that means no crack in the elements. It was firstly done by scanning a simple plastic item. The elements are cracked if a black sign will be visible on the screen which is disturbing the image. The control check didn't show any conspicuousness.

The axial resolution would be realized for the HITACHI EUB-405 with a 7.5 MHz linear array by using the B-Mode. The transducer would lead over the surface of the phantom. The screen represents the dots which are contained in the phantom. By using the measure tool could quantify the smallest possible distance between two dots.

The same principle would used for the ULTRASONIX SonixTablet with a 10 MHz linear array by using the B-Mode.

In the experiment the phantom is water coupled and therefore no blood flow inside the phantom. For the measurement of the colour changing, the transducer was moving on the surface of the phantom instead of the blood flow. This was done by using the ULTRASONIX device.

The elastography appearances couldn't compare between the devices because just the ULTRASONIX EUB-405 provides the elastography function.

Dynamic range TGC??

3.2 Diathermy and Defibrillatordiathermy.jpg

Equipment for the Diathermy:

Valleylab: Force ETTM Electrosurgical Generator

METRON: QA-ES MKII Electrosurgical Analyzer


Fig. : Experimental assembly of the diathermy studyThe implementation of diathermy experiment would realize by monopolar- mode. Instead of a patient meat was used to cut and coagulate tissue. The meat was lying on the indifferent electrode. The surface of this electrode

is bigger than the surface of the electrode on the instrument. The

instrument and the analyzer were connected to the electrosurgical generator. The analyzer calculated the current which is travelling through the body by cutting or coagulating the tissue by using a particular amount of power (watt). The watt was controlled by the generator.

Equipment for the Defibrillator

HP Hewlett Packard: Codemaster XL Plus Defibrillator

DYNATECH-NEVADA. Impulse 3000 Defibrillator Analyzer


The synchronized and di-synchronized shock would simulate. For the synchronized-mode the first step is to choose the energy up to 200 Joule. After verifying that the synchronized mode pulse appears reliably on the R wave, the paddle was hold and pressed the discharge buttons; a shock was delivered only when the control circuits sense the next R wave. The delivery of energy is synchronized with and shortly follows the peak of the R wave, preventing discharge during the vulnerable period of ventricular depolarization, which is represented by the T wave. The same procedure was realized by the di-synchronized mode. However, no measurements about it would be done.

3.3 Vital signs


SpaceLabs Healthcare: èlance Vital Signs Monitors

Welch Allyn: Spot Vital Signs Monitor 300 Series


The blood pressure was measured on the upper arm in the brachial artery of the same person with the two vital sign monitors and the results were compared. The same principle was implemented with the measurement of the oxygen saturation. It was measured of the right forefinger of the same person.

3.4 ElectrocardiographLionheart.jpg


10 leads

Simulator "Lionheart 3"

The Bipolar limb leads:

View I. = LA-RA

View II. = LL-RA

View III. = LL-LA

The Unipolar Limb leads:

Fig. Simulator and the 10 electrodesaVR provides a view of the heart from RA

aVL provides a view of the heart from LA

aVF provides a view of the heart from below, LL


A simulator was used instead of a patient and connected with the leads. Fig. showed this simulator.

To understand the correlation of the leads each electrode was detach from the simulator and it was checked which leads are going lost.

4. Results and Discussion

4.1 Ultrasound

The Hitachi EUB-525 has an average axial resolution of 0.85 mm by using a linear array with 7.5 MHz. It would measure the smallest axial distance of two dots.

The axial resolution of the ULTRASONIX SonixTablet has an average deviation of 0.65 mm by using a linear array of 10 MHz.

The normal axial resolution of the Phantom, smallest distance between two dots, amounts 0.5 mm.

Consequently could be proved that the axial resolution of the Hitachi EUB-525 ultrasound device has an error which a deviation of 0.35 mm per measured distance. The ULTRASONIX has an average error of 0.65 mm per measured distance. The table below shows the individual measurements.

Measurements between two dots


Hitachi 7.5 MHz

Ultrasonix 10MHz


0.9 mm

0.68 mm


0.8 mm

0.68 mm



0.47 mm


0.85 mm

0.65 mm

Based on these measurements can be say that both devices have a resolution error. However it has to be considering that the measurements contains readings errors produced by human as well.

For the Colour Doppler could find out that the red colour represent object which are travelling toward the transducer, the blue colour demonstrate objects which moving away.

4.2. Vital signs

The blood pressure measurements from the same person have shown that between the Welch Ally and Èlence no differences are exists in the blood pressure display. Both devices measured a blood pressure of 95/61 mmHg.

The same result was shown for the oxygen saturation. Both measurements have shown the same amount of oxygen percent in the blood, which was 100 %. In this way have both devices concurrent results of their measurements.

4.3. Electrocardiography

The result of particular correlation between the specifically electrodes shows the table below.

If the connection to the leg leads is lost, every signal from the chest leads drop away. A further confirmation is that the RL plays no rule because if this lead lost nothing happens with the other signals. Also shows the table if the equation of the views I, II and II are unplugged, every signal goes lost.

The table represent the leads by Einthoven and their dependence among themselves.

4.4. Diathermy

The table shows the measurements of the generator and the analyzer for current, power and voltage by using the monopolar-mode for cutting or coagulation.









75 W

599 mA

73 W

744 V

45 W

471 mA

45 W

410 V





80 W

614 mA

76 W

544 V

40 W

423 mA

36 W

602 V

It is showing that the analyzer presents a divergence of an average about 2.5 watt per measurement compares to the generator.

4.5 Defibrillator

By using an input of 20 Joule for the synchronized-mode it gives an output of 21.1 Joule and a delay time from 20 ms.

20 to 30 ms is the best value for the delay time.

To find out which minimum amount of energy is necessary to implement a shock was not possible because of the shortage of time.

5. Conclusion

The experiment highlights different medical devises for treatment and diagnosis.

The experiment has proven that the ultrasound device and the diathermy analyzer have both an error in the measurements. For Ultrasound is the resolution important. Unfortunately the axial resolution of the devices varieties compare to the reality resolution. This may have serious consequences for the diagnosis and treatment for the patient.

For the diathermy analyzer could proven also a systematic error which means varieties of the measurements of the power compare to the generator. This error should be solving because differences between the measured power and the actually power can effects unwanted hurt to the patient.

A good result could obtain for the vital sing monitors. Both vital sign monitors from different companies haven't any divergences in the measurements of blood pressure and the oxygen level in the blood.

Showing of the correlation of the leads could be done. It can prove that the chest leads are the most important ones. Disconnect them introduce brakes the system of the electrocardiograph and no measurements of the heart are possible.