Biomedical equipment revision
Question I: Define:a. drift
As components age and equipment undergoes changes in temperature
or humidity or sustains mechanical stress, performance gradually degrades. This
is called drift
b. Calibration
Process of comparing an unknown against a reference standard within
defined limits, accuracies and Uncertainties
c. Verification
Process of comparing an unknown against a reference standard at
usually one data point
d. Ultrasound
Mechanical vibration of frequency greater than 20 KHz
e. Acoustic Impedance
When an ultrasound wave meets a boundary between two different materials
some of it is refracted and some is reflected. The reflected wave is detected by the
ultrasound scanner and forms the image. The proportion of the incident wave that
is reflected depends on the change in the acoustic impedance, Z.
Acoustic Impedance, Z of a medium is defined as:
Z = c
Where  = the density of the material, kgm-3
c = speed of sound in that material, ms-1
f. Intensity reflection coefficient, 
At a boundary between mediums, the ratio of the intensity reflected, Ir to the intensity
incident, I0 is known as the intensity reflection coefficient, .
α=
𝐼𝑟
𝐼𝑜
The intensity of both the reflected and incident ultrasound waves depend on the acoustic
impedance, Z of the two mediums. Therefore the fraction of the wave intensity reflected
can be calculated for an ultrasound wave travelling from medium 1, (acoustic impedance Z1)
to medium 2 (acoustic impedance Z2).
𝛼=
𝐼𝑟
𝑍1 − 𝑍2 2
={
]
𝐼𝑜
𝑍1 + 𝑍2
If 2 mediums have a large difference in impedance, then most of the wave is reflected. If
they have similar impedance then none is reflected.
Question II: Answer
1-What to TEST for?
2-
3-
4-
5-
g. Performance Testing
h. Safety Testing
When to test equipment
a. prior to being accepted for use
b. During preventative maintenance.
c. After repairs.
Why we Need for Medical Equipment Testing?
a. Medical device incidents resulting in patient injury and death
• Ensure that the equipment is performing to the expected standards of
accuracy, reliability, free of hysteresis and linear (as designed).
• Safe and effective devices need to be available for
patient care
– Downtime costs money
• Regulations, accreditation requirements and standards.
Why do we do electrical safety?
a. Ensure patient safety
i. Protect against macroshock
ii. Protect against microshock
b. Test for electrical internal breakdown / damage to power cord, AC mains
feed, etc.
c. Meet codes & standards
i. Association of Medical Instrumentation (AAMI),
ii. The International Electrotechnical Commission (IEC),
iii. National Federation of Paralegal Associations (NFPA), etc.
d. Protect against legal liability
i. In case of a patient incident
Compare between Curvilinear, Rectilinear, Pseudo rectilinear chart recorder
6- Mention Writing Methods Used in Strip Chart Recorders.
a. Thermal, and Direct contact
i. Both of these types use a special writing stylus (rather than a pen
and a knife edge, also called writing edge)
ii. The mark on the paper by the contact of the stylus on the paper
along the knife edge,
iii. The stylus tip travels in a curvilinear path, but the resulting trace is
rectilinear because the knife edge is straight.
iv. The stylus can write anywhere along its length, so by keeping the
knife edge straight under the paper, we obtain the rectilinear
recording that shows waveshape as well as amplitude
b.
7- Mention writing systems are commonly used on PMMC recorders
a. direct contact,
b. thermal pen
c. ink pen
d. ink jet
e. Optical
8- Explain circuit for Servo recorders and recording potentiometers
 In potentiometeric measurements a three-terminal variable resistor (potentiometer)
is connected to produce an output voltage that is a function of both a reference
potential and position of the variable resistor’s wiper arm.
 A galvanometer will read zero when the unknown voltage and potentiometer
voltage are equal.
9- Explain A slide-wire potentiometer
10- Compare between Curvilinear recording, Rectilinear recording and Pseudo rectilinear
writing system
11- Compare between ultrasound and x-ray
ultrasound
Mechanical waves
Speed depends on the medium
safe
Frequency greater than 20 kHz
Cannot penetrate any substantial gas-layer.
Cannot penetrate mature
adult bone
(brain).
X-ray
Electromagnetic waves
Speed of light
Ionizing radiation have physiological effects
3×10 16 Hz to 3×10 19 Hz
Penetrate gas
Penetrate none
12- Explain different Writing Methods Used in Strip Chart Recorders
Question III: Complete:
i- The main components of x-ray unit are X-ray tube, X-ray electrical
power generator, Control unit, Film or digital system and additional
components are Table unit, Bucky film tray and grid system, and
Suspension system
ii- Main components of a modern x-ray tube are Glass Tube, Cathode- (which
consists of three parts Filament, Supporting wires and Focusing cup), and
Anode (two types Stationary and rotating).
iii- Properties of X-rays
b. X-rays travel in straight lines.
c. X-rays cannot be deflected by electric field or magnetic field.
d. X-rays have a high penetrating power.
e.
f.
g.
h.
Photographic film is blackened by X-rays.
Fluorescent materials glow when X-rays are directed at them.
Photoelectric emission can be produced by X-rays.
Ionization of a gas results when an X-ray beam is passed through
it.
iv. Minimum wavelength in the X-ray Spectra
min 
hc
eV
v. maximum frequency in the X-ray spectra:
f max 
eV
h
vi. Absorption mechanisms convert the energy of an acoustic wave to heat as the wave
propagates through a medium. A plane ultrasonic wave in an absorbing medium will lose
intensity as
I ( x)  I 0 e 2x
vii. Ultrasound systems must contain some form of the five system blocks.
–
Display - The system will have some way of displaying the data it acquires.
–
User Interface - It must have a user interface, this may be mechanical or
voice activated.
–
Transducer – Your ultrasound system will have a transducer to convert
electrical impulses to sound and back.
–
Image Processing - The ultrasound machine will have some sort of image
processing. This may be analog or digital.
–
Power Supply - Finally it will have a power supply, again analog or digital.
And Peripherals may include cameras, or printers.
viii. In the case of ultrasound two transducer function are recognized:
–
conversion of ac electric oscillation into acoustic vibration, and
–
Conversion of acoustic vibrations into ac oscillations of the same frequency.
–
These two functions are the transmitter and receiver transducers.
ix. Radiation is generated by means of:–
electromagnetic (EM)
–
ultrasound
–
electrons
And Displayed for interpretation on
–
Film
–
photograph or
–
computer display monitor
x. types of x-ray: diagnostic and therapeutic and diagnostic devices divided into still
picture, continuous picture and scan tomography
Question IV:
Draw a schematic diagram for:
-
Curvilinear recording
-
Rectilinear recording
-
Pseudo rectilinear writing system
i.
PARTS OF X RAY TUBE:
i- Glass Tube
ii- Cathode
i. Filament
ii. Supporting wires
iii. Focusing cup
iii- Anode
i. Stationary
ii. Rotating
j.
Main components of x-ray unit are:
i- X-ray tube
ii- X-ray electrical power generator
iii- Control unit
iv- Film or digital system
In addition to:
v- Table unit
vi- Bucky film tray and grid system
vii- Suspension system
k. Main components of a modern x-ray tube:
i- A heated filament releases electrons that are accelerated across a high
voltage onto a target.
ii- The stream of accelerated electrons is referred to as the tube current.
iii- X rays are produced as the electrons interact in the target.
iv- The x rays emerge from the target in all directions but are restricted by
collimators to form a useful beam of x rays.
v- A vacuum is maintained inside the glass envelope of the x-ray tube to
prevent the electrons from interacting with gas molecules.
l.
Sow with schematic diagram the main components of X-ray generator
m. CAT scan is an Abbreviation of Computerized Axial Tomography while CT scan is an
Abbreviation of Computer Tomography
n. CT Scan based on Reconstruction of a tomographic plane of the body (a slice) from a
large number of collected x-ray absorption measurements taken during a scan
around the body’s periphery. . Show with schematic diagram the basic idea of
tomography
Image Reconstruction
o. Compare the CT Generations and show your answer with schematic diagrams:i- First generation CT-scanner “Translate – Rotate” and has a Single Detector
Cell First Translation then Rotation.
First generation CT-scanner
“Translate – Rotate”
Translation
Rotation
• Single Detector Cell
• First Translation then Rotation.
ii- Second generation CT-scanner “Translate – Rotate” has an Array of
Detector Cell ( e.g. 20) First Translation then Rotation and Scan Time could
be reduced to 1/10
Second generation CT-scanner
“Translate – Rotate”
• Array of Detector Cell ( e.g. 20)
• First Translation then Rotation.
• Scan Time could be reduced to 1/10
iii- Third generation CT-scanner “Rotate – Rotate” has an Array of Detector
Cell ( e.g. 896) NO Translation movement and Scan Time Reduced
Third generation CT-scanner
“Rotate – Rotate”
• Array of Detector Cell ( e.g. 896)
• NO Translation movement.
• Scan Time Reduced.
iv- Fourth generation CT-scanner Tube rotates, Detector is stationary (full ring
of detectors)
Fourth generation CT-scanner
Tube rotates, Detector is stationary (full ring of detectors)
v- Fifth generation CT-scanner electron bean moves
Fifth generation CT-scanner
p. What is the main components of the CT show your answer with schematic diagram
i- Gantry
ii- Patient couch
iii- Control unit
iv- Consol
q. Show how data transfer from DAS to consol on the computer tomography in non
continuous rotation and continuous system show your answer with schematic
diagram
i- In non-continuous rotating system the data is transferred from the DAS to
the Console via parallel cable
Data Transfer from DAS to Console
In non-continuous rotating system the data is
transferred from the DAS to the Console via
parallel cable.
D.A.S.
CONSOLE
ii- In continuous rotating system the DAS data is: converted from parallel to
serial, transferred (via optical cable) converted back from serial to parallel.
Data Transfer from DAS to Console
In continuous rotating system the DAS data is:
• converted from parallel to serial,
• transferred (via slipring or optical)
• converted back from serial to parallel.
D.A.S.
Parallel
to
Serial
Serial
to
Parallel
CONSOLE
r.
I-
Give the function of collimator, wedage, slit and beam trimmer in the CT
i- Collimator: metal plate with a hole Limit x-ray beam
ii- Wedge: Limit x-ray beam Prevent detector overflow
iii- Slit: defines the slice thickness
iv- Beamtrimmer : Limit x-ray beam Used for thin slices (1 – 3 mm
Complete:
a. Short waves diathermy operates at a frequency of ----------, ---------, or
------- while microwave diathermy operates at a frequency of -----------or ----------b. Shortwave Diathermy Unit consists of --------, ---------, and ------c. Shortwave Diathermy (SWD) unit generates both -------------- field and
-------------- field and the ratio between them depends on
characteristics of both ---------- and --------------.
d. There are two types of short wave diathermy (SWD) Electrodes --------, and --------------- Selection of Appropriate Electrodes Can Influence
the Treatment.
e. In diathermy there are two coil arrangements: ---------- Coils and -------- Coils
II-
Chose :
a. In diathermy capacitor (Condenser) electrodes
i. Create stronger electrical field than magnetic field.
ii. Create stronger magnetic field than electrical field.
iii. Create magnetic field equal to electrical field.
b. the capacitive electrodes has
i. higher current density at the center than at the periphery
ii. higher current density at the periphery than at the center
iii. Homogeneous current density over the electrode surface
c. Increasing of the space between capacitive (Pad) electrodes Will
i. increase electric field but will decrease magnetic field
ii. increase magnetic field but will decrease electric field
iii. increase the current density but will decrease the depth of
penetration
iv. increase the depth of penetration but will decrease the
current density
d. The tissue that offers the greatest resistance to current flow develops
i. the lowest heat
ii. the most heat
iii. has no effect
e. Heating of biological tissue depends on
i. directly proportional to the resistance of the tissue and
inversely proportional to the current passing through it
ii. directly proportional to the resistance of the tissue and
inversely proportional to the square of the current passing
through it
iii. directly proportional to both the resistance of the tissue and
the current passing through it
iv. directly proportional to both the resistance of the tissue and
the square of the current passing through it
f. In diathermy induction coil
i. Create stronger electrical field than magnetic field.
ii. Create stronger magnetic field than electrical field.
iii. Create magnetic field equal to electrical field
III-
Write short assays about:
1. Physiologic Responses To Diathermy.
2. Different between diathermy heating and non heating effects.
3. Short wave diathermy unit.
4. Adjusting Resonance of SWD Unit (Tuning)
5. Capacitor electrode and its type
6. Induction method diathermy and its electrode.
7. Dose of diathermy
8. When Should Diathermy Be Used?
9. Microwave Diathermy
10. Best Treated areas for Microwave.
IV- Diathermy machine generate Peak Pulse Power = 800 W Pulse Duration = .4
ms, Pulse Frequency = 250 Hz, Find Pulse Period ,% on time, Mean Power
Answer
I-
Complete:
a. 27.122 MHz, 13.56MHz, 40.68MHz,2456MHz, 915 MHz.
b. Power Supply Powers Radio Frequency Oscillator (RFO), Power Amplifier
Generate Power To Drive Electrodes, Output Resonant Tank Tunes In The
Patient for Maximum Power Transfer.
c. Magnetic, Electric, generator, electrode.
d. Capacitor electrode, induction electrode.
e. Pancake Coils, Wraparound Coils
III- Write short assays about:
1- .
Physiologic Effects Are Those of Heat In General
a. Tissue Temperature Increase
b. Increased Blood Flow (Vasodilation)
c. Increased Venous and Lymphatic Flow
d. Increased Metabolism
e. Changes In Physical Properties of Tissues
f. Muscle Relaxation
g. Analgesia
2- .
Diathermy Heating:
•
Doses Are Not Precisely Controlled Thus The Amount of Heating Cannot Be
Accurately Measured
–
Basically means amount of heating patient receives cannot be directly
measured
•
Heating= Current2 X Resistance
Non-Thermal Effects:-
•
Pulsed SWD Used To Treat Soft Tissue Injuries and Wounds
•
Related To Depolarization of Damaged Cells
•
–
Loss of Cell Division
–
Loss of Proliferation
–
Loss of Regenerative capabilities
Repolarization Corrects Cell Dysfunction
•
Generates A Magnetic Field To Increase Na Pump Activity
3- .

Power Supply Powers Radio Frequency Oscillator (RFO)

RFO Provides Stable Drift-Free Oscillations at Given Frequency

Power Amplifier Generate Power To Drive Electrodes

Output Resonant Tank Tunes In The Patient for Maximum Power Transfer
4- .
Manual vs Automatic Tuning
a. When patient’s circuit (biologic tissue) oscillates at same frequency as
device frequency
b. Only when tuned will is the electromagnetic energy fully delivered
c. Most automatic
d. Can lose tuning due to movement at skin/electrode interface
Manual Tuning (adjusts patient circuit)
e. Set Output Intensity at 30-40%
f. Adjust Tuning Control Until Power Output Meter Reaches Max
g. Then Adjust Down to Patient Tolerance Which Is About 50%
h. If More Than 50% Patient Is Out of Resonance
5- .

Capacitor Electrodes:
-
Electrical Field Is The Lines of Force Exerted on Charged Ions That Cause
Movement From One Pole To Another,
-
Center Has Higher Current Density Than Periphery,
-
Patient Is Between Electrodes and Becomes Part of Circuit
-
Tissue Is Between Electrodes in a Series Circuit Arrangement

Air Space Plates
-
Two Metal Plates Surrounded By Plastic Guard
-
Can Be Moved 3cm Within Guard
-
Produce High-Frequency Oscillating Current
-
Sensation Of Heat In Direct Proportion To Distance Of Electrode From
Skin
-
Closer Plate Generates More Surface Heat
-
Parts Of Body Low In Subcutaneous Fat Best Treated

Pad Electrodes
-
Increasing The Spacing Will Increase The Depth Of Penetration But Will
Decrease The Current Density
-
Capacitive Method Good for Treating Superficial Soft Tissues
-
Creates A Stronger Magnetic Field Than Electrical Field
-
A Cable Or Coil Is Wrapped Circumferentially Around An Extremity Or
6- .
Coiled Within n Electrode
-
Passing Current Through A Coiled Cable Creates A Magnetic Field By
Inducing Eddy Currents (small circular electrical fields) That Generate
Heat

Cable Electrode
-
Two Arrangements: Pancake Coils,Wraparound Coils
-
Toweling Is Essential
-
Pancake Coil Must Have 6” in Center Then 5-10cm Spacing Between
Turns

Best Frequency
Drum Electrode
-
One Or More Monopolar Coils Rigidly Fixed In A Housing Unit
-
May Use More Than One Drum Depending On Area Treated
-
Penetration
-
Deeper Soft Tissues
-
Toweling Important
7- .
Patient Sensation Provides Basis For Recommendations Of Continuous SWD
-
Dose I (Lowest) (<38 W) - No Sensation of Heat
-
Dose II (Low) (~80 W)- Mild Heating Sensation
-
Dose III (Medium) (80-300 W) - Moderate or Pleasant Heating
Sensation
-
Dose IV (Heavy) (>300 W) -Vigorous Heating Within Pain Threshold
-
If The Skin Or Some Underlying Soft Tissue Is Tender And Will Not
8- .
Tolerate Pressure
-
In Areas Where Subcutaneous Fat Is Thick And Deep Heating Is
Required
a. Induction method
-
When The Treatment Goal Is To Increase Tissue Temperatures Over
A Large Area
9- .
-
Two FCC Assigned Frequencies-2456 MHz and 915 MHz
-
MWD Has Higher Frequency and Shorter Wavelength Than SWD
-
Generates Strong Electrical Field and Relatively Little Magnetic Field
-
Advantage: better focus wave on body, thereby more local heating
affects
-
Disadvantage: Depth Of Penetration Is Minimal In Areas With
Subcutaneous Fat > 1 cm
10- .
-
Tendons of foot, hand and wrist
-
AC and SC joints
-
Patellar tendon
-
Distal tendons of hamstrings
-
Achilles tendon
-
Other areas of low subcutaneous fat
iv. Pulse Period = 1 / 250 Hz = 4 ms
-
% on time = .4 / 4 = .10 or 10%
-
Mean Power = 10% of 800 = 80 W
1- Main components of magnetic resonance imaging (MRI):
a. Magnet
b. Coils
c. Radiofrequency source
d. Accessories
2- Types of magnets used in MRI:a. Permanent magnets
b. Electromagnets or Resistive magnets
c. Superconductivity magnets
3- Types of coils used in MRI
a. Volume coils
b. Hamlet coil
c. Shim Coil
d. Gradient coils
e. Surface Coils
4- Frequencies of Radio-frequency Source used in MEI:a. 60 MHZ
b. 90 MHz
c. 100 MHz