Chapter 5

Medical Equipments and Specifications

Chapter 5

Medical Equipments and Specifications

5.1 Organization of medical equipments

Biomedical devices includes an array of products that record, process, analyze,

display and transmit medical data. Such equipment and devices include

computerized tomographic (CT) scanners, and magnetic resonance imaging

(MRI) systems, cardiac monitoring systems, tissue and blood gas analyzers,

cardiac defibrillators and various laboratory analyzers, to name a few. There are

over 16,000 medical supply and device manufacturers across the globe that produces

medical equipments. The medical equipments are classified into following categories.

1. Laboratory Apparatus

2. Imaging and radiation therapy devices

3. Patient diagnostic devices

4. life support and therapeutic devices

5. Patient environmental and transport equipment

6. Other medical equipment

7. Non medical equipment

According to American Hospital Association standard, a 250 bed healthcare unit needs

to have 458 different equipments. These equipments are organized into following

departments.

Central Supply: Forty Suction units. Three wall sterlizers. One washer, Twenty

APP pumps. Three hypo/hyperthermia units. Three Circo electric beds. Twelve

infusion pumps.

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Clinical laboratory: One cell washer, Two blood banks, One slide stainer,

Coulters, Fourteen table top refrigerated centrifuges, Five incubators. Ten

nnicroscopes. Two balances fibrometer. Two shakers. Three rotators. Thirteen

heat blocks. Four dilutors and autocytometer. Four mixers, Three coleman 6C,

Turner 330, IL 313,11513, IL 143, IL 279, bilirubinometer, ABA—100,pH meter,

titrator, manual well system Electrophoresis unit, knife sharpener, microtome,

microtome/cryostat, paraffin bath. Tissue processor.

Dialysis: Two dialysis beds, table top centrifuge, Gould defibrillator with monitor,

EKG

Electrodia: Three EKG, defibrillator, stress test system, E for M DR 8, Suction

unit, Cardiology ultrasound diagnostic

Emergency: Exam table, electrosurgical unit, OR table , Dallons monitor with

recorder. Eight exam lamps, Datascope defibrillator, datascope monitor.

Labor and Delivery: Statham monitor, Dallons defibrillator with monitor, sterilizer.

Two OB tables, fetal monitor.

Nuclear Medicine: Gamma camera, well counter, rectilinear scanner, dose

calibrator. Two 70 mm cameras.

Nursen/: Six incubators, oxyzen monitor, warmer, Two apnea monitors, suction

unit, bilirubin Light.

Nursing: Four defibrillators. One monitor, exam lamp

Physical Therapy: Three hydrocollators. Six stimulators. Five whirlpools. Three

diathermies. Two UV lamps, traction unit, paraffin bath, medco sonolator.

Radiation Therapy: Superficial unit,cobalt unit.

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Radiology: Mobilizer, survey meter, defibrillator, Xerox 125, ultra sound B-

scanner, defibrillator with monitor, Three radiographic/fluoroscopic rooms, Two

radiographic rooms, Three mobile X-ray units. Two film processors.

Special care units: Eight beds Statham (ECG/HR), Eight beds Dallons

(ECG/HR), Defibrillator with monitor. Two cardiac output computers. Four

infusion pumps , spare recorder, spare monitor. Two external pacemakers

Special Procedures: injector. Two film changers. One special procedures room

Surgery/Recovery: Five OR tables, Five anesthesia machines, urological table.

Nine monitors, tele thermometer. Five ventilators, hypo/hypothermia,

electrosurgical units,002 insufflator. Five OR lights, Four fiberoptic sets. Four

warming cabinets. Two sterlizers. Two defibrillators. Two mobile X-ray units, OR

microscope. Two cast cutters , tonometer, Four monitor/recorders. Four drills,

cryogenic unit.

Following sections provide a brief description on the purpose and technical features of

the eguipments. Appendix 1 provides detailed specifications for equipments that are

common in most of healthcare units.

5.2 Infusion pump.

An infusion pump or perfusor, infuses fluids, medication or nutrients into a patient's

circulatory system. It is generally used intravenously, although subcutaneous, arterial

and epidural infusions are occasionally used. Infusion pumps can adminster fluids in

ways that would be impractically expensive or unreliable if performed manually by

nursing staff. For example, they can administer 1 milliliter per hour injections (too small

for a drip), injections every minute, injections with repeated boluses requested by the

patient, up to maximum number per hour (e.g. in patient-controlled analgesia), or fluids

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whose volumes vary by the time of day. The user interface of pumps usually requests

details on the type of infusion from the technician or nurse that sets them up:

1. Continuous infusion usually consists of small pulses of infusion, usually between

20 nanoliters and 100 microliters, depending on the pump's design, with the rate

of these pulses depending on the programmed infusion speed.

2. Intermittent infusion has a "high" infusion rate, alternating with a low

programmable infusion rate to keep the cannula open. The timings are

programmable.

3. Patient-controlled is infusion on-demand, usually with a preprogrammed ceiling

to avoid intoxication. The rate is controlled by a pressure pad or button that can

be activated by the patient. It is the method of choice for patient-controlled

analgesia (PCA).

4. Total parental nutrition usually requires an infusion curve similar to normal

mealtimes.

There are two basic classes of pumps. Large volume pumps can pump nutrient solutions

large enough to feed a patient. Small-volume pumps infuse hormones, such as insulin,

or other medicines, such as opiates. Within these classes, some pumps are designed to

be portable, others are designed to be used in a hospital, and there are special systems

for charity and battlefield use. Large-volume pumps usually use some form of peristaltic

pump. Classically, they use computer-controlled rollers compressing a silicone-rubber

tube through which the medicine flows. Another common form is a set of fingers that

press on the tube in sequence. Small-volume pumps usually use a computer-controlled

motor turning a screw that pushes the plunger on a syringe.

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The classic medical improvisation for an infusion pump is to place a blood pressure cuff

around a bag of fluid. The battlefield equivalent is to place the bag under the patient. The

pressure on the bag sets the infusion pressure. The pressure can actually be read-out at

the cuffs indicator. The problem is that the flow varies dramatically with the patient's

blood pressure (or weight), and the needed pressure varies with the administration route,

making this quite risky for use by an untrained person. Pressures into a vein are ususally

less than 8 Ibf/in^ (55 kPa. Epidural and subcutaneous pressures are usually less than

18lbf/in^(125kPa).

Places that must provide the least-expensive care often use pressurized infusion

systems. One common system has a purpose-designed plastic "pressure bottle"

pressurized with a large disposable plastic syringe. A combined flow restrictor, air filter

and drip chamber helps a nurse set the flow. The parts are reusable, mass-produced

sterile plastic, and can be produced by the same machines that make plastic soft-drink

bottles and caps. A pressure bottle, restrictor and chamber requires more nursing

attention than electronically-controlled pumps. In the areas where these are used,

nurses are often volunteers, or very inexpensive.

The restrictor and high pressure helps control the flow better than the improvised

schemes because the high pressure through the small restrictor orifice reduces the

variation of flow caused by patients' blood pressures.

An air filter is an essential safety device in a pressure infusor, to keep air out of the

patients' veins: doctors estimate that 0.55 cm^ of air per kilogram of body weight is

enough to kill (200-300 cm^ for adults) by filling the patient's heart. Small bubbles could

cause harm in arteries, but in the veins they pass through the heart and leave in the

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patients' lungs. The air filter is just a membrane that passes gas but not fluid or

pathogens. When an large air bubble reaches it, it bleeds off. Some of the smallest

infusion pumps use osmotic power. Basically, a bag of salt solution absorbs water

through a membrane, swelling its volume. The bag presses medicine out. The rate is

precisely controlled by the salt concentrations and pump volume. Osmotic pumps are

usually recharged with a syringe.

Spring-powered clockwork infusion pumps have been developed, and are sometimes

still used in veterinary work and for ambulatory small-volume pumps. They generally

have one spnng to power the infusion, and another for the alarm bell when the infusion

completes. Battlefields often have a need to perfuse large amounts of fluid quickly, with

dramatically changing blood pressures and patient condition. Specialized infusion pumps

have been designed for this purpose, although they have not been deployed.

Many infusion pumps are controlled by a small embedded system. They are carefully

designed so that no single cause of failure can harm the patient. For example, most

have batteries in case the wall-socket power fails. Additional hazards are uncontrolled

flow causing an overdose, uncontrolled lack of flow, causing an underdose, reverse flow,

which can siphon blood from a patient, and air in the line, which can starve a patient's

tissues of oxygen if it floats to some part of a patient's body. The range of safety features

varies widely with the age and make of the pump. A state of the art pump in 2003 may

have the following safety features:

1. Certified to have no single point of failure. That is, no single cause of failure

should cause the pump to silently fail to operate correctly. It should at least stop

pumping and make at least an audible error indication. This is a minimum

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requirement on all human-rated infusion pumps of whatever age. It is not

required for veterinary infusion pumps.

2. Batteries, so the pump can operate if the power fails or is unplugged.

3. Anti-free-flow devices prevent blood from draining from the patient, or infusate

from freely entering the patient, when the infusion pump is being set-up.

4. A "down pressure" sensor will detect when the patient's vein is blocked, or the

line to the patient is kinked. This may be configurable for high (subcutaneous and

epidural) or low (venous) applications.

5. An "air-in-line" detector. A typical detector will use an ultrasonic transmitter and

receiver to detect when air is being pumped. Some pumps actually measure the

volume, and may even have configurable volumes, from 0.1 to 2 ml of air. None

of these amounts can cause harm, but sometimes the air can interfere with the

infusion of a low-dose medicine.

6. An "up pressure" sensor can detect when the bag or syringe is empty, or even if

the bag or syringe is being squeezed.

7. Many pumps include an internal electronic log of the last several thousand

therapy events. These are usually tagged with the time and date from the pump's

clock. Usually, erasing the log is a feature protected by a security code,

specifically to detect staff abuse of the pump or patient.

8. Many makes of infusion pump can be configured to display only a small subset of

features while they are operating, in order to prevent tampering by patients,

untrained staff and visitors.

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5.3 Medical imaging

Medical imaging is Vne process by whicii physicians evaluate an area of the subject's

body that is not normally visible. Medical imaging may be "clinical", seeking to diagnose

and examine disease in specific human patients (see pathology). Alternatively, it may be

research-motivated, attempting to understand processes in humans or animal models.

Many of the techniques developed for medical imaging also have scientific and industrial

applications. Radiology is a diagnostic specialty within the field of medicine that employs

X-rays and other modalities for diagnostic imaging. Mathematically speaking, medical

imaging usually involves the solution of inverse problems. This means that we infer

cause (in this case properties of living tissue) from effect. The effect in this case is the

response to being probed by various means. In the case of ultrasonography the probe is

ultrasound; in the case of radiography, the probe is X-ray radiation.

In its most primitive form, imaging can refer to the physician simply feeling an area of the

body in order to visualize the condition of internal organs. This was used historically to

diagnose aortic aneurysms, fractures, enlarged internal organs, and many other

conditions. It remains an important step today in making initial assessments of potential

problems, although additional steps are often used to confirm a diagnosis. The primary

drawback of this approach is that findings are subject to interpretation, and while a

recorded image can be produced manually, in practice this is often not done. Following

are some of the imaging systems widely used in health care.

5.3.1 Ultrasound

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Medical ultrasonography uses high frequency sound waves of between 3.5 to 7.0

megahertz that are reflected by tissue to varying degrees to produce a 2D image,

traditionally on a TV monitor. This is often used to visualize the fetus in pregnant women.

Other important uses include imaging the abdominal organs, heart, male genitalia and

the veins of the leg. While it may provide less anatomical information than techniques

such as CT or MRI, it has several advantages which make it ideal as a first line test in

numerous situations, in particular that it studies the function of moving structures in real­

time. It is also very safe to use, as the patient is not exposed to radiation and the

ultrasound does not appear to cause any adverse effects. It is also relatively cheap and

quick to perform. Ultrasound scanners can be taken to critically ill patients in intensive

care units saving the danger of moving the patient to the radiology department. The real

time moving image obtained can be used to guide drainage and biopsy procedures.

Doppler facilities on modern scanners allow the blood flow in arteries and veins to be

assessed.

5.3.2 Radiographs

Radiographs, more commonly known as x-rays, are often used to determine the type

and extent of a fracture. With the use of radioactive dyes, such as barium, they can also

be used to visualize the structure of the intestines - this can help diagnose certain types

of colon cancer. X-rays are produced by bombarding a surface with high speed electrons

(in a vacuum). Upon discovery in 1895, X-Rays were advertised as the new scientific

wonder and seized upon by entertainers. Circus patrons viewed their own skeletons and

were given pictures of their own bony hands wearing silhouetted jewelry. While many

people were fascinated by this discovery, others feared that it would allow strangers to

look through walls and doors and phvacy. Early x-ray machines were used in stores to

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help sell shoes. These were known as fluoroscopes. However, as the harmful effects of

X-ray radiation were discovered, they fell out of use.

X-ray machines work by generating a beam of x-rays. The beam is projected on matter.

Some of the X-ray beam will pass through the object. The resulting shadow pattern of

the radiation is then detected by photographic film, semiconductor plates or image

intensifiers. Images taken with such devices are known as x-ray photographs or

radiographs. This can be used to diagnose broken or fractured bones. Imaging of the

digestive tract is done with the help of barium as a contrast medium. X-ray machines are

used to screen objects non-invasively. Luggage at airports is examined for possible

bombs and weapons. These machines are very low dose and safe to be around.

A film of carbon nanotubes that emits electrons at room temperature when exposed to

an electrical field has been fashioned into an X-ray device. An array of these emitters

can placed around a target item to be scanned and the images from each emitter can be

assembled by computer software to provide a 3-dimensional image of the target in a

fraction of the time it takes using a conventional X-ray device. The carbon nanotube

emitters also use less energy than conventional X-ray tubes leading to lower operational

costs. (Zhang, et al., 2005)

5.3.3 Computed tomoqraphv

A CT scan, also known as a CAT scan (Computed Axial Tomography scan), traditionally

produces a 2D image of the stuctures in a small section of the body. It uses X-ray

radiation, just like radiographs, and thus repeat scans are not recommended for children.

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In conventional CT machines, an X-Ray tube is physically rotated behind a circular

shroud (see the image above right); in the less used electron beam tomography (EBT)

the tube is far larger, note the internal funnel shape in the photo, with a hollow cross-

section and only the electron current is rotated. X-ray slice data is generated using an X-

ray source that rotates around the object; X-ray sensors are positioned on the opposite

side of the circle from the X-ray source. Many data scans are progressively taken as the

object is gradually passed through the gantry. They are combined together by the

mathematical procedure known as tomographic reconstruction.

Newer machines with faster computer systems and newer software strategies can

process not only individual cross sections but continuously changing cross sections as

the gantry, with the object to be imaged, is slowly and smoothly slid through the X-ray

circle. These are called helical or spiral CT machines. Their computer systems integrate

the data of the moving individual slices to generate three dimensional volumetric

information, in turn viewable from multiple different perspectives on attached CT

workstation monitors. The data stream representing the varying radiographic intensity

sensed reaching the detectors on the opposite side of the circle during each sweep—

360 degree in conventional machines, 220 degree in EBT—is then computer processed

to calculate cross-sectional estimations of the radiographic density, expressed in

Hounsfield units.

CT is used in medicine as a diagnostic tool and as a guide for interventional procedures.

Sometimes contrast materials such as intravenous iodinated contrast is used. This is

useful to highlight structures such as blood vessels that othenA ise would be difficult to

delineate from their surroundings. Using contrast material can also help to obtain

functional information about tissues. Pixels in an image obtained by CT scanning are

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displayed in terms of relative radiodensity. The pixel itself is displayed according to the

mean attenuation of the tissue that it corresponds to on a scale from -1024 to +3071 on

the Hounsfield scale. Water has an attenuation of 0 Hounsfield units (HU) while air is

-1000 HU, bone is typically +400 HU or greater and metallic implants are usually

+1000 HU. Improvements in CT technology have meant that the overall radiation dose

has decreased, scan times have decreased and the ability to reconstruct images (for

example, to look at the same location from a different angle) has increased over time.

Still, the radiation dose from CT scans is several times higher than conventional X-ray

scans. Presently, the cost of an average CT scanner is US$1.3 million.

Since its introduction in the 1970s, CT has become an important tool in medical imaging

to supplement X-rays and medical ultrasonography. Although it is still quite expensive, it

is the gold standard in the diagnosis of a large number of different disease entities.

Cranial CT: Diagnosis of cerebrovascular accidents and intracranial hemorrhage is the

most frequent reason for a "head CT" or "CT brain". Scanning is done without

intravenous contrast agents (contrast may resemble a bleed). CT generally does not

exclude infarct in the acute stage, but is useful to exclude a bleed (so anticoagulant

medication can be commenced safely). For detection of tumors, CT scanning with IV

contrast is occasionally used but is less sensitive than magnetic resonance imaging

(MRI). CT can also be used to detect increases in intracranial pressure, e.g. before

lumbar puncture or to evaluate the functioning of a ventriculoperitoneal shunt. CT is also

useful in the setting of trauma for evaluating facial and skull fractures. In the

head/neck/mouth area, CT scanning is used for surgical planning for craniofacial and

dentofacial deformities, evaluation of cysts and some tumors of the jaws/sinuses/ nasal

cavity /orbits, and for planning of dental implant reconstruction.

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Chest CT: CT is excellent for detecting both acute and chronic changes in the lung

parenchyma. For detection of airspace disease (such as pneumonia) or cancer, ordinary

non-contrast scans are adequate. For evaluation of chronic interstitial processes

(emphysema, fibrosis, and so forth), thin sections with high spatial frequency

reconstructions are used. For evaluation of the mediastinum and hilar regions for

lymphadenopathy, IV contrast is administered. CT angiography of the chest (CTPA) is

also becoming the primary method for detecting pulmonary embolism (PE) and aortic

dissection, and requires accurately timed rapid injections of contrast and high-speed

helical scanners. CT is the standard method of evaluating abnormalities seen on chest

X-ray and of following findings of uncertain acute significance.

Cardiac CT: With the advent of subsecond rotation combined with multi-slice CT (up to

64 slices), high resolution and high speed can be obtained at the same time, allowing

excellent imaging of the coronary arteries. It is uncertain whether this modality will

replace the invasive coronary catheterization.

Abdominal and pelvic CT: Many abdominal disease processes require CT for proper

diagnosis. The most common uses include diagnosis of renal/urinary stones,

appendicitis, pancreatitis, diverticulitis, abdominal aortic aneurysm, and bowel

obstruction. CT is also the first line for detecting solid organ injury after trauma. Oral

and/or rectal contrast is usually administered (more often iodinated contrast than barium

due to the tendency of barium to cause imaging artifacts that limit evaluation of

abdominal structures). CT has limited application in the evaluation of the pelvis. For the

female pelvis in particular, ultrasound is the imaging modality of choice. Nevertheless, it

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may be part of abdominal scanning (e.g. for tumors), and has uses in assessing

fractures.

5.3.4 Positron Emission Tomography:

Positron emission tomography (PET) is a nuclear medicine medical imaging technique

which produces a three dimensional image or map of functional processes in the body. A

short-lived radioactive tracer isotope which decays by emitting a positron, chemically

combined with a metabolically active molecule, is injected into the living subject (usually

into blood circulation). There is a waiting period while the metabolically active molecule

(usually a sugar) becomes concentrated in tissues of interest, then the subject is placed

in the imaging scanner. The short-lived isotope decays, emitting a positron. After

travelling up to a few millimeters the positron annihilates with an electron, producing a

pair of gamma ray photons moving in opposite directions. These are detected when they

reach a scintillator material in the scanning device, creating a burst of light which is

detected by photomultiplier tubes. The technique depends on simultaneous or coincident

detection of the pair of photons: photons which do not arrive in pairs (i.e., within a few

nanoseconds) are ignored. By measuring where the gamma rays end up, their origin in

the body can be plotted, allowing the chemical uptake or activity of certain parts of the

body to be determined. The scanner uses the pair-detection events to map the density of

the isotope in the body, in the form of slice images separated by about 5mm. The

resulting map shows the tissues in which the molecular probe has become concentrated,

and is read by a nuclear medicine physician or radiologist, to interpret the result in terms

of the patient's diagnosis and treatment. PET scans are increasingly read alongside CT

scans, the combination giving both anatomic and metabolic information (what the

structure is, and what it is doing). PET is used heavily in clinical oncology (medical

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imaging of tumours and the search for metastases) and in human brain and heart

research.

However, while other imaging scans such as CT and MR\, isolate organic anatomic

changes in the body, PET scanners are capable of detecting areas of molecular biology

detail (even prior to anatomic change) via the use of radiolabelled molecular probes that

have different rates of uptake depending on the type of tissue involved. The changing of

regional blood flow in various anatomic structures (as a measure of the injected positron

emitter) can be visualized and relatively quantified with a PET scan. In order to properly

interpret a PET scan result, the resolution of the scanner must be known. Typically,

determining the resolution of a PET scanner is done with tiny wires that have been

irradiated in a nuclear reactor or a particle accelerator. Another process involves using

tiny beads of zeolite that have been dipped into a saline solution containing technetium-

99m.

Radionuclides used in PET scanning are typically isotopes with short half lives such as

carbon-11, nitrogen-13, oxygen-15, and fluorine-18 (half-lives of 20 min, 10 min, 2 min,

and 110 min respectively). Due to their short half lives, the isotopes must be produced in

a cyclotron at or near the site of the PET scanner. Currently, 18-F is the only isotope

approved by the FDA for distribution in the US. Rubidium-82 is allowed limited use for

myocardial perfusion experiments. These isotopes are incorporated into compounds

normally used by the body such as glucose, water or ammonia and then injected into the

body to trace where they become distributed. PET as a technique for scientific

investigation is limited by the need for clearance by ethics committees to inject

radioactive material into participants, and also by the fact that it is not advisable to

subject any one participant to too many scans. Furthermore, due to the high costs of

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cyclotrons needed to produce the short-lived radioisotopes for PET scanning a few

hospitals and universities are capable of performing PET scans. PET is a valuable

technique for some diseases and disorders, because it is possible to target the radio­

chemicals used for particular bodily functions.

Oncology: PET scanning with the tracer (18F) fluorodeoxyglucose (FDG, FDG-PET) is

widely used in clinical oncology. This tracer mimics glucose and is taken up and retained

by tissues with high metabolic activity, such as the brain, the liver, and most types of

malignant tumour. As a result FDG-PET can be used for diagnosis, staging, and

monitoring treatment of cancers. However because individual scans are more expensive

than conventional imaging with CT and MRI, expansion of FDG-PET in cost-constrained

health services will depend on proper Health Technology Assessment. Oncology scans

using FDG make up over 90% of all PET scans in current practice.

Neurology: PET brain imaging is based on an assumption that areas of high radioactivity

are associated with brain activity. What is actually measured indirectly is the flow of

blood to different parts of the brain, which is generally believed to be correlated, and

usually measured using the tracer oxygen (150). Research continues into the use of

radiolabelled F-DOPA and FDDNP as more specific probes.

Cardiology: In clinical cardiology FDG-PET can identify so-called "hibernating

myocardium", but its cost-effectiveness in this role versus SPECT is unclear.

Neuropsychology / Cognitive neuroscience: To examine links between specific

psychological processes or disorders and brain activity.

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Pharmacology: In pre-clinical trials, it is possible to radio-label a new drug and inject it

into animals. The uptake of the drug, the tissues in which it concentrates, and its

eventual elimination, can be monitored far more quickly and cost effectively than the

older technique of killing and dissecting the animals to discover the same information.

PET scanners for rats and apes are marketed for this purpose.

5.4 Magnetic resonance imaging (IVIRI)

An MR! uses powerful magnets to excite hydrogen nuclei in water molecules in human

tissue, producing a detectable signal. Like a CT scan, an MR! traditionally creates a 2D

image of a small "slice" of the body. As an MRI does not use X-ray radiation, it is the

preferred imaging method for children and pregnant women. Magnetic resonance

imaging (MRI) - also called magnetic resonance tomography (MRT) - is a method of

creating images of the inside of opaque organs in living organisms as well as detecting

the amount of bound water in geological structures. It is primarily used to demonstrate

pathological or other physiological alterations of living tissues and is a commonly used

form of medical imaging. MRI has also found many niche applications outside of the

medical and biological fields such as rock permeability to hydrocarbons and certain non­

destructive testing methods such as produce and timber quality characterization.

In clinical practice, MRI is used to distinguish pathologic tissue (such as a brain tumor)

from normal tissue. One of the advantages of an MRI scan is that, according to current

medical knowledge, it is harmless to the patient. It utilizes strong magnetic fields and

non-ionizing radiation in the radio frequency range. Compare this to CT scans and

traditional X-rays which involve doses of ionizing radiation and may increase the chance

of malignancy, especially in children receiving multiple examinations. The typical MRI

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examination typically consists of 5-20 sequences, each of which are chosen to provide a

particular type of information about the subject tissues. This information is then

synthesized by the interpreting radiologist into a report for the clinical physician treating

the patient.

5.4.1 Diffusion MRI

Diffusion MRI measures the diffusion of water molecules in biological tissues. In an

isotropic medium (inside a glass of water for example) water molecules naturally move

according to Brownian motion. In biological tissues however, the diffusion is very often

anisotropic. For example a molecule inside the axon of a neuron has a low probability to

cross a myelin membrane. Therefore the molecule will move principally along the axis of

the neural fiber. Conversely if we know that molecules locally diffuse principally in one

direction we can make the assumption that this corresponds to a set of fibers.

Another application of diffusion MRI is diffusion weighted imaging (DWI). Following an

ischemic stroke, brain cells die, trapping water molecules inside them (cellular pumps

are no longer functioning). The resultant areas of restricted diffusion are detectable. This

finding appears within 5-10 minutes of the onset of stroke symptoms (as compared with

computed tomography, which often does not detect changes of acute infarct for up to 4-6

hours) and remains for up to two weeks. As such, DWI sequences are extraordinarily

sensitive for acute stroke.

Finally, it has been proposed that diffusion MRI may be able to detect minute changes in

extracellular water diffusion and therefore could be used as a tool for fMRI. The nerve

cell body enlarges when it conducts an action potential, hence restricting extracellular

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water molecules from diffusing naturally. Although this process works in theory, evidence

is only moderately convincing. If it could be made to work, diffusion fMRI would not

experience the temporal lag seen in BOLD fMRI.

5.4.2 Magnetic resonance anqioqraphv

Magnetic resonance angiography (MRA) is used to generate pictures of the arteries, in

order to evaluate them for stenosis (abnormal narrowing) or aneurysms (vessel wall

dilatations, at risk of rupture). The main uses of MRA is to evaluate the arteries of the

neck and brain, the thoracic and abdominal aorta, and the kidneys. A variety of

techniques can be used to generate the pictures, such as administration of a

paramagnetic contrast agent (such as gadolinium) or using a technique known as "flow-

related enhancement" (e.g. 2D and 3D time-of-flight sequences), where the only signal

on an image is due to blood which has recently moved into that plane.

5.4.3 Magnetic resonance spectroscopy

Magnetic resonance spectroscopy (MRS), also known as MRSI (MRS Imaging) and

Volume Selective NMR Spectroscopy, is a technique which combines the spatially-

addressable nature of MRI with the spectroscopically-rich information obtainable from

nuclear magnetic resonance (NMR). That is to say, MRI allows one to study a particular

region within an organism or sample, but gives relatively little information about the

chemical or physical nature of that region-its chief value is in being able to distinguish

the properties of that region relative to those of surrounding regions. MR spectroscopy,

however, provides a wealth of chemical information about that region, as would an NMR

spectrum of that region.

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Functional MRI (fMRI) measures signal changes in the brain that are due to changing

neural activity. The brain is scanned at low resolution but at a rapid rate (typically once

every 2-3 seconds). Increases in neural activity cause changes in the MR signal via a

mechanism called the BOLD (blood oxygen level-dependent) effect. Increased neural

activity causes an increased demand for oxygen, and the vascular system actually

overcompensates for this, increasing the amount of oxygenated hemoglobin

("haemoglobin" in British English) relative to deoxygenated hemoglobin. Because

deoxygenated hemoglobin reduces MR signal, the vascular response leads to a signal

increase that is related to the neural activity. The precise nature of the relationship

between neural activity and the BOLD signal is a subject of current research. The BOLD

effect also allows for the generation of high resolution 3D maps of the venous

vasculature within neural tissue.

While BOLD signal is the most common method employed for neuroscience studies in

human subjects, the flexible nature of MR imaging provides means to sensitize the

signal to other aspects of the blood supply. Alternative techniques weight the MRI signal

by cerebral blood flow (CBF) and cerebral blood volume (CBV). The CBV method

requires injection of a class of MRI contrast agents that are now in human clinical trials.

Because this method has been shown to be far more sensitive than the BOLD technique

in pre-clinical studies, it may potentially expand the role of fMRI in clinical applications.

The CBF method provides more quantitative information than BOLD signal, albeit at a

significant loss of detection sensitivity.

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5.4.4 Interventional MRI

Because of the lack of harmful effects on the patient and the operator, MR is well suited

for "interventional radiology", where the images produced by an MRI scanner are used

to guide a minimally invasive procedure intraoperatively and/or interactively. However,

the non-magnetic environment required by the scanner, and the strong magnetic

radiofrequency and quasi-static fields generated by the scanner hardware require the

use of specialized instruments. Often required is the use of an "open bore" magnet

which permits the operating staff better access to patients during the operation. Such

open bore magnets are often lower field magnets, typically in the 0.2 tesia range, which

decreases their sensitivity but also decreases the Radio Frequency power potentially

absorbed by the patient during a protracted operation. Higher field magnet systems are

beginning to be deployed in intraoperative imaging suites, which can combine high-field

MRI with a surgical suite and even CT in a series of interconnected rooms. Specialty

high-field interventional MR devices, such as the IMRIS system, can actually bring a

high-field magnet to the patient within the operating theatre, permitting the use of

standard surgical tools while the magnet is in an adjoining space.

5.4.5 Current Density Imaging

Current density imaging is a subbranch of MRI that endeavors to use the phase

information from the MRI images to reconstruct current densities within a subject.

Current density imaging works because electrical currents generate magnetic fields,

which in turn affect the phase of the magnetic dipoles during an imaging sequence. To

date no successful CDI has been performed using biological currents, however several

studies have been published which involve applied currents through a pair of electrodes.

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5.5 Blood gas monitor

This medical device measures the amount of a dissolved gas in a patient's blood. It is

often attached to a medical monitor so staff can directly read a patient's oxygenation at

all times. By far, the most common monitor measures oxygen perfusion, although

devices for measuring p02, pC02 (carbon dioxide) and pH values also exist. Typically it

has a small light-emitting diode and photodiode on a probe clipped to a part of the

patient's body. The red light reflects from the blood in a transparent part of the patient's

body, such as an ear-lobe or finger-nail. As a patient's oxygenation level drops, the

blood becomes more blue, reflecting less red light to the photodiode.

A blood-oxygen monitor customarily measures percent of normal. Acceptable normal

ranges are from 95 to 100 percent. For a patient breathing room air, at not far above sea

level, an estimate of arterial p02 can be made from the blood-oxygen monitor Sp02

reading. The monitor value bounces in time to the heart beat because the blood vessels

expand and contract with the heartbeat. Some monitors also measure heart rate.

Modern oxymeters can clip onto the finger of a patient and use optical properties of light

going through a nail to determine the amounts of these chemicals. Prior to the

oxymeter's invention, many complicated blood tests needed to be performed.

Blood oxygen monitors are of critical importance in emergency medicine and are also

very useful for patients with respiratory or cardiac problems.

5.6 Medical monitors:

A medical monitor is a medical device that displays a patient's vital signs continually,

without using paper. In critical care units of hospitals, it allows continuous supervision of

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a patient without continuous attendance. This improves patient care. IVIonitors resemble

oscilloscopes, or computer monitors and use superficially similar technology. However

medical monitors have been safety engineered so that failures are either apparent, or

unimportant.

Additionally, some monitors (e.g. ECG and EEG) actually touch patients, and are

electrical. There are strict limits on how much current and voltage they can apply when

the unit fails or becomes wet.

5.7 Medical ventilator

It is a device designed to provide mechanical ventilation to a patient. Ventilators are

chiefly used in intensive care medicine and emergency medicine (as standalone units)

and in anesthesia (as a component of an anesthesia machine). In its simplest form, a

ventilator consists of a compressible air reservoir, air and oxygen supplies, a set of

valves and tubes, and a disposable or reusable "patient set". The air reservoir is

pneumatically compressed several times a minute to deliver an air/oxygen mixture to the

patient; when overpressure is released, the patient will exhale passively due to the lungs'

elasticity. The oxygen content of the inspired gas can be set from 21 percent (ambient

air) to 100 percent (pure oxygen). Pressure and flow characteristics can be set

mechanically or electronically.

Ventilators may also be equipped with monitoring and alarm systems for patient-related

parameters (e.g. pressure and flow) and ventilator function (e.g. air leakage, power

failure), backup batteries, air and oxygen tanks, and remote control and alarms. The

pneumatic system is nowadays often replaced by a computer-controlled turbo pump.

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The failure of mechanical ventilation system may result in death, hence precautions

must be taken to ensure that mechanical ventilation systems are highly reliable. This

includes their power-supply provision. Mechanical ventilators are therefore carefully

designed so that no single point of failure can endanger the patient. They usually have

manual backup mechanisms to enable hand-driven respiration in the absence of power.

Some systems are also equipped with compressed-gas tanks and backup batteries to

provide ventilation in case of power failure or defective gas supplies, and methods to

operate or call for help if their mechanisms or software fails.

Modern ventilators are electronically controlled by a small embedded system to allow

exact adaptation of pressure and flow characteristics to an individual patient's needs.

Fine-tuned ventilator settings also serve to make ventilation more tolerable for the

patient. In Germany, Canada, and the United States, respiratory therapists are

responsible for tuning these settings.

5.8 Cardiac pump

A cardiac pump or cardiac bypass pump or heart-lung machine temporarily takes over

the function of breathing and pumping blood for a patient. It generally has two parts, the

pump and the oxygenator. The pump is usually several motor-driven rollers that

perstaltically massage a tube made of silicone rubber. The massage pushes the blood

through the tubing. This is commonly referred to as a roller pump. Another type of pump

is a centrifugal pump. The blood enters a small centrifuge, and propels the blood forward

via centrifugal force. The oxygenator varies, but usually is a passage through a silicone-

membrane simulated lung known as a true membrane oxygenator.

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Cardiac pumps are most often used in heart surgery, so that a patient's heart can be

disconnected from the body for longer than the twenty minutes or so it takes a prepared

patient to die. Although unprepared patients get brain damage in three to four minutes, a

patient can be prepared by cooling and drugs so that no damage will occur for twenty

minutes or more. Cardiac pumps are also sometimes used to keep babies with birth

defects alive, or to aerate bodies with transplantable organs.

Chronic use of cardiac pumps is contraindicated because the pressure profile of most

practical pumps is believed to cause circulatory damage to the brain, especially in

extended use. The pumps generate continuous pressure. When this pressure is set high

enough to aerate tissues in the foot, it can easily damage tissue in the brain. Likewise, if

set low enough to avoid damaging the brain, it often under-aerates some part of the

body, such as the feet.

In intensive care medicine, extracorporeal membrane oxygenation (ECMO) is a

technique of providing oxygen to patients whose lungs are so severely diseased that

they can no longer serve their function. An ECMO machine is similar to a heart-lung

machine. To initiate ECMO, cannulas are placed in large blood vessels to provide

access to the patient's blood. Anticoagulant drugs (usually heparin) are given to prevent

blood clotting. The ECMO machine continuously pumps blood from the patient through a

"membrane oxygenator" that imitates the gas exchange process of the lungs, i.e. it

removes carbon dioxide and adds oxygen. Oxygenated blood is then returned to the

patient.

ECMO can provide sufficient oxygenation for several days or even weeks, allowing

diseased lungs to heal while the potential additional injury of aggressive mechanical

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ventilation is avoided. It may therefore be life-saving for some patients. However, due to

the high technical demands, cost, and risk of complications (such as bleeding under

anticoagulant medication), ECMO is usually only considered as a last resort therapy.

5.9 Electrocardiagram

The electrocardiogram (ECG) is a surface measurement of the electrical potential

generated by electrical activity in cardiac tissue. Current flow, in the form of ions, signals

contraction of cardiac muscle fibers leading to the heart's pumping action. The ECG is a

valuable, non-invasive diagnostic tool which was first put to clinical use in 1913 with

Einthoven's invention of the string galvonometer. Einthoven's recording is known as the

"three lead" ECG, with measurements taken from three points on the body (defining the

"Einthoven triangle" — an equilateral triangle with the heart at the centre.) The difference

between potential readings from one and two what is used to produce the output ECG

trace. The third connection establishes a common ground for the body and the recording

device (oscilloscope.)

Establishing the correspondence between the ECG trace and the electrical events in the

heart is known as the inverse problem of electrocardiology: solving for the electric

sources from the potential generated by those sources on the surface of the body. The

inputs to ECG comes from self-sticking electrodes that are attached to the body of the

subject whose ECG is being taken. It is important for the cables connecting the

electrodes to the inputs of the circuit to be as short as possible and well shielded. RG-

174 50 Ohm coaxial cables with lemo connectors were chosen as these cables are good

to use for this project because they are sturdy, yet thin and light, and the lemo

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connectors are easy to plug and unplug into the aluminum sheet metal box that was

used to house the circuit. Because of the safety issues associated with electrically

connecting a person to an electronics device that runs off a significant power source,

diode protection was added to the inputs to the amplifier. Alternatively, to improve safety

the circuit could be redesigned and the protection diodes replaced with an optoisolator

circuit - this would provide complete galvanic isolation (upto several thousand Volts)

between the electrodes and the power supply.

For the output signal, a bulkhead BNC connector was mounted on the box containing

the circuit so that the output could be connected directly to an oscilloscope via correctly

terminated 50 Ohm coax cable. Two 9 Volt batteries were used for the power supply for

the amplifier (as well as for the pull-up of the output signal). The relevant terminals of the

batteries were connected to a switch mounted on the chassis for ease of powering up

and down. Decoupling capacitors were also used. The grounds of the circuit and the

input and output cables were connected to the metal box housing the circuit and

insulating feet were fitted to the box.

12-lead electrocardiogram (ECG) with ST-segment elevation in leads II, III and aVF,

suggestive of an inferior acute myocardial infarction (AMI). The ECG has a wide array of

uses:

• Determine whether the heart is performing normally or suffering from

abnormalities (eg. extra or skipped heartbeats - cardiac arrhythmia).

• May indicate acute or previous damage to heart muscle (heart attack) or

ischaemia of heart muscle (angina).

• Can be used for detecting potassium, calcium, magnesium and other electrolyte

disturbances.

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• Allows the detection of conduction abnormalities (heart blocks and bundle branch

blocks).

• As a screening tool for ischaennic heart disease during an exercise tolerance test.

• Can provide information on the physical condition of the heart (eg: left ventricular

hypertrophy, mitral stenosis).

• Can suggest non-cardiac disease (e.g. pulmonary embolism, hypothermia)

5.10 Blood pressure meters

Blood pressure is the pressure exerted by the blood on the walls of the blood vessels.

Unless indicated otherwise, blood pressure is understood to mean arterial blood

pressure, i.e. the pressure in the large arteries, such as the brachial artery (in the arm).

The pressure of the blood in other vessels is lower than the arterial pressure. The peak

pressure in the arteries during the cardiac cycle is the systolic pressure, and the lowest

pressure (at the resting phase of the cardiac cycle) is the diastolic pressure. Typical

values for the arterial blood pressure of a resting, healthy adult are approximately 120

mmHg systolic and 80 mmHg diastolic (written as 120/80 mmHg), with large individual

variations. Blood pressure is not static, but undergoes natural variations from one

heartbeat to another or in a circadian rhythm; it also changes in response to stress,

nutritional factors, drugs, or disease.

Blood pressure (BP) is most accurately measured invasively by placing a cannula into a

blood vessel and connecting it to an electronic pressure transducer. This invasive

technique is regularly employed in intensive care medicine, anesthesiology, and for

research purposes, but it is associated with complications such as thrombosis, infection.

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and bleeding. Therefore, the less accurate techniques of manual or oscillometric

measurement predominate in routine examinations.

Most often, arterial blood pressure is measured manually using a sphygmomanometer.

This is an inflatable (Riva Rocci) cuff placed around the upper arm, at roughly the same

vertical height as the heart in a sitting person, attached to a manometer. The cuff is

inflated until the artery is completely occluded. Listening with a stethoscope to the

brachial artery at the elbow, the examiner slowly releases the pressure in the cuff. When

blood flow barely begins again in the artery, a "whooshing" or pounding sound (first

Korotkoff sound) is heard. The pressure is noted at which this sound began. This is the

systolic blood pressure. The cuff pressure is further released until no sound can be

heard (fifth Korotkoff sound). This is the diastolic blood pressure.

Oscillometric methods are used in long-term measurement as well as in clinical practice.

Oscillometric measurement (also termed NIPB = Non-Invasive Blood Pressure) is

incorporated in many bedside patient monitors. It relies on a cuff similar to that of a

sphygmomanometer, which is connected to an electric pump and a pressure transducer.

The cuff is placed on the upper arm and is automatically inflated. When pressure is

gradually released, the small oscillations in cuff pressure that are caused by the cyclic

expansion of the brachial artery are recorded and used to calculate systolic and diastolic

pressures. Values are usually given in millimetres of mercury (mmHg). Incidentally, the

absolute BR is obtained by adding the Atmospheric pressure (e.g., 760 mm Hg at sea

level) to the values obtained by the sphygmomanometer. If the BR had not been greater

than the atmospheric pressure, the blood would have never flown through the vessels!

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5.11 Defibrillator

A defibrillator is a medical device used in the defibrillation of the heart. It consists of a

central unit and a set of two electrodes. The central unit provides a source of power and

control. The two electrodes are placed directly on or in the patient. The device is

designed to deliver an electric shock to the patient, in an effort to stop ventricular

fibrillation. There are two types of defebrillator.

Internal Defibrillators: The device may be implanted directly in the user of the device. If

so, it is known as an implantable cardioverter-defibrillator or (much less frequently) an

internal cardiac defibrillator (ICD). This type of defibrillator is designed to provide

immediate defibrillation to high-risk patients. By actively monitoring the pulse rate,

rhythm, and waveform, and by comparing atrial and ventricular activity, in ICD can detect

ventricular fibrillation, and immediately initiate defibrillation.

External Defibrillators: External defibrillators are typically used in hospitals or

ambulances, but are increasingly common outside the medical realm, as automated

external defibrillators become safer and cheaper. There are a variety of technologies

and form factors in use for external defibrillators, and recent progress in cardiac

research has led to substantial improvements in the underlying technology.

Biphasic Defibrillation: Until recently, external defibrillators relied on monophasic

shock waves. Electrical pulses are sent rapidly from one electrode to the other,

only in one direction. Biphasic defibrillation, however, alternates the direction of

the pulses, completing one cycle in approximately 10 milliseconds. Biphasic

defibrillation was originally developed and used for implantable cardioverter-

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defibrillators. When applied to external defibrillators, biphasic defibrillation

significantly decreases the energy level necessary for successful defibrillation.

This, in turn, decreases risk of burns and myocardial damage.

Automated External Defibrillators: An Automated External Defibrillator (AED) is a

self-contained defibrillator device designed for portability and ease of use. AEDs

are generally shaped like a briefcase, so that they may be carried easily by a

handle. An AED contains a battery, a control computer, and electrodes. Upon

placing the electrodes on the patient, the control computer in an advanced

system will assess the patient, determining the type of rhythm or arrhythmia

present. It will then set appropriate power levels and deliver a shock. If the

patient does not require defibrillation, many units will not allow a shock to be

administered. Current AED devices are designed for emergency medical

technicians, home users, public safety officers and other people with minimal

medical knowledge. AEDs are available for $1000 for a basic model to several

thousand dollars for a more fully-featured or durable model.

5.12 Centrifuges

A centrifuge is a piece of equipment that puts a substance in circular motion in order for

the centrifugal force to separate a fluid from a fluid or from a solid substance. Generally,

a motor drives the rotary motion of the sample. There are many different kinds of

centrifuges, often for very specialised purposes. Simple centrifuges are used in biology

and biochemistry for isolating and separating biocompounds on the basis of molecular

weight. These will tend to rotate at a slower rate than an ultracentrifuge, and have larger

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rotors, and be optimized for holding large quantities of material at intermediate

acceleration.

5,13 Tonometer

A tonometer is an instrument used by eye care professionals to measure the intraocular

pressure of a patient's eye. This pressure measurement is an important part of every eye

examination because an increase in pressure may signal the onset of glaucoma, a sight-

threatening disease. Pressure is measured in millimeters of mercury, and, as a general

guideline, pressure above 21 millimeters is considered to be elevated pressure, though

not all persons with that reading have glaucoma.

The most popular tonometry test is with the noncontact tonometer, often referred to as

the "air-puff' test. The patient looks through a machine as it blows a gentle puff of air at

the eye. This puff of air flattens the cornea slightly in order to give the pressure reading.

The machine is gas pressurized and does not require direct contact with the eye.

Another form of tonometry, and one of the most accurate, is the contact tonometer, an

instrument that looks like a pen. When using the contact tonometer, numbing eye-drops

are administered, and then the tip of the tonometer touches the eye and measures the

pressure.

An applanation tonometer measures the force required to flatten a small area of central

cornea. A topical anesthetic and fluorescein dye are instilled before the measurement is

taken. One type of applanation tonometer attaches to a slit lamp, while another is hand­

held. The Schiotz tonometer measures the amount the cornea is indented by a fixed

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weight that artificially raises the pressure. It is a simple, portable instrument, but is

considered to be somewhat less accurate than other types of measuring devices.

5.14 Other medical equipments

Following are some additional equipments used in laboratory.

Autoclaves; Autoclaves generate steam from water at a temperature above 100 in

aclosed chamber. At these temperatures,the steam is above atmospheric pressure and

the conditions are Optimal for the sterlization of laboratory equipment. There are two

types. The non-jacketed autoclave, which exists in vertical and horizontal versions, is

simpler and has some practical disadvantages but it is cheaper than a steam jackated

autoclave with automatic air and condeser discharge. Sterlization of porous materials,

like laundry and bandages, is more difficult, since air in these materials must be replaced

by steam. This replacement is improved by evacuating the closed chamber of

autoclave containing the materials to sterlized. With modern autoclaves, the chamber

can be repeatedly evacuated so that the pressure in the chamber falls to 5.5kPa. The

chamber is then heated to evaporate water for sterlization.

Hot-air-ovens: Hot air ovens are used mainly for drying laboratory equipment and

surgical devices in dry air.There are two types of hot air oven,with and without internal

air corculation of dry air.

Incubators: Incubators are used mainly used for bacterial culture. The incubator must

maintain a constant temperature(33 to 37 degree C for bacterial culture ).

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Water -baths: Water baths are used for investigations at 25 deg.SO ,37,42,56 degrees.

Water bath maintains constant temperature within narrow range during the

investigation.

Balances: Balances are used to measure the weight or mass of a substance. There are

several types of balances that find use in healthcare. Some them include Spring balance.

Sliding weight balance. Parallel-guidance balance, Equal-lever-arm balance. Unequal -

lever- arm balance. Electromagnetic balance.

Cell counters: Cell counters are used for haematological measurement.semi- automated

and automated cell counting has proved to be much more reliable microscopic cell

counting. A far greater number of cells can be counted rapidly in a specimen by an

analyser system.

Photometers: Photometer can be used for the determination of a great number of

analytes in body fluids.

Filters: Filters absorb light of different wavelengths.allowing only light with narrow range

of wave lengths to pass through.filters for a photometer have a band width of about 2nm.

Cuvettes: A cuvette is the transparent container used to hold test solution.cuvettes

may be made out of quartz glass or transparent plastic. Such as polyamide.

This chapter has provided a brief description of medical equipments along with technical

specifications. This information would enable Clinical Engineering department or

associated department responsible for maintenance of equipments to plan for spare

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parts, estimate frequency of failures and technology connplexity, Technician Skill and

training needs etc.

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