Biomedical Instrumentation

Archive for the ‘Recorder Equipments’ Category

Apex cardiograph: An apex cardiograph records the chest-wall movements over the apex of the heart. These movements are in the form of vibrations having a frequency range of 0.1 to about 20 Hz. The transducer required for recording these movements is similar to that employed for a phonocardiography but which has a frequency response much below the audio range. It can be air coupled microphone or a contact microphone. The apex cardiograph has limited applications. It is, however, useful in the diagnosis of the enlargement of the heart chambers and some type of valvular disorders.

Ballistocardiography: A ballistocardiography is a machine that records the movement imparted to the body with each beat of the heart cycle. These movements occur during the ventricular contraction of the heart muscle when the blood is ejected with sufficient force. In BCG, the patient is made to lie on a table top which is spring suspended or otherwise mounted to respond to very slight movements along the head axis. Sensing devices are mounted on the table to convert these movements into corresponding electrical signals. The sensors usually are piezo-electric crystals, resistive elements or permanent magnets, moving with respect to fixed coils. In all such cases, the output of the sensor is amplified and fed to an oscilloscope or to a chart recorder. BCG has so far been used mainly for research purpose only. It is rarely used in routine clinical applications.

Electroretinograph: It is found that an electrical potential exists between the cornea and the back of the eye. This potential changes when the eye is illuminated. The process of recording the change in potential when light falls on the eye is called Electroretinograph. ERG potentials can be recorded with a pair of electrodes. One of the electrodes is mounted on a contact lens and is in direct contact with the cornea. The other electrode is placed on the skin adjacent to the outer corner of the eye. A reference electrode may be placed on the forehead. A general purpose direct writing recorder may be used for recording electroretinograms.

Dear all! Opthalmoscopy is used to inspect the interior of the eye. It permits visualization of the optic disc, vessels, retina, choroids and ocular media. Direct Opthalmoscopy and indirect Opthalmoscopy are the two methods used.

Direct Opthalmoscopy: In a darkened room, the examiner projects a beam of light from a hand-held Ophthalmoscope through the patient’s pupil to view an upright image of the retina structure. The Ophthalmoscope has rotating lenses on top to magnify a particular area being viewed up to 15 times. With papillary dilation, about half the fundus may be seen, while about 15 percent of the fundus may be seen without papillary dilation. The resolving power of direct Opthalmoscopy is about 70µm. smaller objects, such as capillaries, small hemorrhages are micro aneurysms, cannot be seen.

Indirect Opthalmoscopy: Indirect Opthalmoscopy is usually performed by using a binocular ophthalmoscope. The patient’s retina is illuminated by a light source from headset of the binocular instrument. Prisms within the instrument make it possible to see a stereoscopic image. The entire fundus may be examined by indirect Opthalmoscopy with pupil dilation and sclera indentation. Indirect Opthalmoscopy provides a significantly wider field of view than direct Opthalmoscopy. But because of direct Opthalmoscopy’s higher resolution both are commonly used during an eye examination. Although indirect Opthalmoscopy only has 200µm resolving power, it is more advantageous than direct Opthalmoscopy in that the stereoscopic image allows detection and evaluation of minimal elevations of the sensory retina and retina pigment epithelium. These images also allow the only direct view of the living network of the blood vessels and can help diagnose atherosclerosis, hypertension, and diabetes mellitus, and other systemic and eye-specific disorders.

Electro-Oculogram: The resting potential of the front of the retina is electropositive with respect to the back of the retina. This makes the cornea positive compared to the back of the eye. If the eye looks left, this positive cornea makes an electrode to the left of the eye more positive than an electrode to the right of the eye. Electrodes above and below the eye can determine the vertical direction of the gaze. This electro- Oculogram is useful for measuring changes in direction of gaze but cannot measure absolute direction of the gaze because variation in skin potential is larger than EOG signal.

Dear readers! Electroencephalograph is an instrument for recording the electrical activity of the brain, by suitable placing surface electrodes on the scalp. EEG, describing the general function of the brain activity, is the superimposed wave of neuron potentials operating in a non-synchronized manner in the physical sense. Its stochastic nature originates just from this and the prominent signal groups can be empirically connected to diagnostic conclusions.

Monitoring the electroencephalogram has proven to be an effective method of diagnosing many neurological illnesses and diseases, such as epilepsy, tumor, cerebovascular lesions, ischemia and problems associated with trauma. It is also effectively used in the operating room to facilitate anesthetics and to establish the integrity of the anaesthetized patient’s nervous system. This has become possible with advent of small, computer-based EEG analyzers. Consequently, routine EEG monitoring in the operating room and intensive care units is becoming popular. Several types of electrodes may be used to record EEG. These include: peel and stick electrodes, silver plated cup electrodes and needle electrodes.

EEG electrodes are smaller in size than ECG electrodes. They may be applied separately to the scallop or may be mounted in special bands, which can be placed on the patient’s head. In case, electrode jelly or paste is used to improve the electrical contact. If the electrodes are intended to be used under the skin of the scalp, needle electrodes are used. EEG electrodes give high skin contact impedance as compared to ECG electrodes. Good electrode impedance should be generally below 5 kilohms. Impedance between a pair of electrodes must also be balanced or the difference between them should be less than 2 kilohms. EEG preamplifiers are generally designed to have a very high value of input impedance to take care of high electrode impedance.

EEG signals picked up by the surface electrodes are usually small as compared with the ECG signals. They may be several hundred micro volts, but 50 micro volts peak to peak are the most typical. The brain waves, unlike the electrical activity of the heart, do not represent the same pattern over and over again. Therefore, brain recordings are made over a much longer interval of time in order to be able to detect any kind of abnormalities. My dear friends! I am sure this article will enhance your knowledge regarding the electroencephalograph.

Dear friends! Lines of ultrasonic information are not generated in TV compatible format, consequently to use conventional TV monitors to display the image; some kind of scan conversion must be performed. The majorities of scanners digitize the image information and use a digital memory as a buffer store. The memory can be updated whenever necessary and can be read to give a standard video output.

Digitization of the echo information can be performed at a number of points in the signal dynamic range is about 20 db and the required digitization rate, about 1MHz. Both these criteria are easily met with readily available analog to digital converts. Alternatively, there is a growing interest in reducing the amount of undesirable information and digitization just after the radio frequency amplifier is becoming more popular. The dynamic range of 40 db and digitization rate of 10MHz would require expensive analog to digital converters. The advantage of digitization at this rate is that the phase information in the carrier is not lost and frequency changes can be used to modulate the image.

Because of the fairly low speed of the ultrasound in soft tissues and the requirements that all the echoes from the preceding pulse must be received before the next pulse can be delivered, the image line rate is limited. For penetration of 30cm, the maximum line rate is 5 KHz. With a frame rate of 20 frames per second for non-jerky real time imaging, the line density per frame is limited to 200. For some scanners, this trade-off between line rate, frame rate and line density produces a display with visible gaps between the lines of real ultrasonic information. Often these gaps are filled with lines calculated inside the machine by interpolation of real information. This improvement in aesthetic appearance does not affect the diagnostic accuracy.

Digital scan converters are microprocessor based and offer several additional benefits to the user. Alphanumeric information concerning the patient, date and equipment parameters such as transducer frequency, gain settings and location of the scan plane can be conveniently entered and displayed along with the ultrasound image. My dear friends! I am sure this article will enhance your knowledge regarding the digital scan converter.

Dear friends! There are numerous types of ECG recorders are available. Many of these are portable units, while the others are permanent installations.  The types of recorders are discussed below:

Single Channel Recorders: The most frequently used type of ECG recorder is the portable single channel unit. For hospital use this recorder is usually mounted on a cart so that it can be wheeled to the bedside of a patient with relative case. If the electrocardiogram of a Patient is recorded in the twelve standard lead configurations, the resulting paper strip is form 3 to 6ft long. Even if folded in accordion fashion, the strip is still inconvenient to read and store. Therefore, it is usually cut up, and sections of recording from twelve mounted leads. Because it is easy to mix up the cut sections, the lead for each trace is encoded in the paper, using the marker pen, during the recording process. The code markers consist of short marks and the long marks and look similar to Morse code. No standard code has been established for this purpose, however. The cut sections of the electrocardiogram can be mounted by inserting them in pockets of a special folder with cutouts to make the trace visible. It should be noted that the recordings from the three limb leads are longer than those from the other lead selections in order to show several complexes, they are called as rhythm strips. Commercial systems are available to simplify the mounting by die-cutting the paper strip and using mounting cards with adhesive pads. With the automatic three-channel recorders mounting is greatly simplified.

Three Channel Recorders: Where large numbers of electrocardiograms are recorded and mounted daily, substantial savings in personnel can be achieved by the use of automatic three channel recorders. These devices not only record three leads simultaneously on a three-channel recorder, but they also switch automatically to the next group of three leads. An electrocardiogram with twelve standard leads, therefore, can be recorded automatically as a sequence of four groups of three traces. The time required for the actual recording is only about ten seconds. The groups of leads recorded and the time at which the switching occurs are automatically identified by code markings at the margin of the recording paper.  My dear friends! I am sure this article will enhance your knowledge regarding ECG recorders.