Biomedical Instrumentation

Archive for August, 2009

To operate effectively with or as a part of the medical instrumentation system, a computer or microprocessor must properly interface with the various devices comprising the rest of the system. Input data must be requested and are received in an acceptable form and output signals must be provided wherever control functions are required or where data must be transmitted to other equipment. Many biomedical instruments with which a computer may be interfaced generate analog data in the form of voltages proportional to the variables represented. For computer entry, these analog signals must be converted into digital form.

Interfacing a computer with other devices that handle data in digital form involves both hardware and software. The software is usually a part of the computer’s system software and is often an extension of the input-output package that controls the flow of information to and from such peripheral devices as disks and magnetic tape drives. Programs are included to monitor input lines, generate commands, identify the various sources of input data, accept each word of data as it arrives, and route it to the arithmetic unit or memory as appropriate.Interfacing hardware is required to format the data, provide buffer registers to temporarily hold each word until it can be dealt with, and where necessary, convert input or output signals from one system of logic to another.

Formatting is the arranging of data into a form that can be accepted and recognized by the computer or device receiving computer output. It involves such factors as the number of bits to be received or sent out at a time and the way in which the bits of a word are arranged among the input or output lines. Data may be received or sent out in either serial form or parallel form. When the digital medical devices with which the computer must be interface can be controlled so that transfer of data always occurs in time corresponding with computer’s internal clock, the I/O operation is said to be synchronous. I am sure this article will enhance your knowledge regarding interfacing techniques of computer with modern medical equipment.

Dear readers! The first biomedical instruments incorporating microprocessors began to appear on the market around 1975. While the first devices were mainly laboratory type instruments, microprocessors are the advance technology which is now used in all areas of biomedical instrumentation. Although microprocessors were originally advocated mainly as replacement for controllers using digital logic, it was soon found that the new technology could be extended much further. Following are some examples of the ways in which microprocessors are employed in contemporary medical instruments.

Calibration: Many instruments require zeroing and recalibration at certain time intervals, sometimes every few hours. A software or hardware timer in a microprocessor system can initiate a calibration cycle. As with manual calibration, this cycle requires the introduction of a blank and standard, each of which might be in the form of a voltage, gas or liquid. In manual calibration methods, zero and gain control potentiometers are normally adjusted until the readout indicates the proper values. Microprocessor equipped devices usually perform the calibration in digital form. During the calibration, offset and gain correction factors are determined and stored in memory to be applied to the measured data during the measurement.

Table lookup and averaging: In analog system, nonlinear functions are usually implemented by straight-line approximations. In microprocessor-equipped systems, table lookup with interpolation can be used. This procedure is less limited and more accurate and also permits the determination of parameters that are independent on more than one variable. Also microprocessors can easily average data overtime or over successive measurements and can thus decrease statistical variations.

Formatting and printout: Because medical equipment using microprocessors usually processes data in digital form, the microprocessors can be utilized to format the data, convert the raw data into physical units, and printout the results in a form that does not require further transcribing or processing. My dear friends! I am sure this article will enhance your knowledge regarding the usage of microprocessors in biomedical instrumentation.

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 readers! To become emotionally healthy, you must function well in three spheres-in relations to yourself, to others, and to society. In becoming emotionally healthy, you first need to know yourself, you need to examine you thoughts, needs, values, and feelings. You also need to discover the various aspects of your personality and to recognize the stages of life that await you. The relationship with self is the most important and must be positive before the relationships with others and society can be truly rewarding.

Your thoughts shape your life. If you think distorted, negative thoughts, you probably will feel unhappy. Through positive thought processes you can also begin to work on to next task in becoming emotionally healthy-identifying the needs. Some people don’t even know they have needs, but everyone does, and recognizing them and learning how to meet them fosters emotional health. The psychologist has described a hierarchy of needs that provides an excellent start. People will struggle to meet their basic needs before they can begin to think about higher things. Hunger is such a need.

People who are hungry may not be able to meet their need for love. Once the basic need for food is met, however, other needs naturally arise. In other words, needs form a hierarchy, and when you have met the most basic ones, you become more aware of, and can strive to meet, the higher ones. Most primitive are related to survival-needs for food, clothing, and shelter. Next are the needs to feel physically safe and secure. If safe and secure, people are free to notice their needs to be loved, to feel emotionally secure.

If those needs are met, they can be in touch with their needs for respect and esteem; and given that, they can seek to achieve the ultimate-self actualization, or the realization of their full potential. Only a few people perhaps 1 to 2 percent ever evolve that far. My dear friends! I am sure this article will enhance your knowledge of becoming emotionally healthy.