Chapter 6 MI Medical Imaging Technology

Question 1

State the components of a simple x-ray system.

Answer 1

1. A high voltage generator
2. An x-ray tube
3. A collimator
4. An intensifying screen and film

Question 2

How does an x-ray work? (4 steps)

Answer 2

1) The x-ray tube generates x rays that are restricted by the aperture (an opening or an open space) in the collimator.
2) The aluminium filter removes low-energy x-rays that would not penetrate the body.
3) Scattered secondary radiation is trapped by the grid, whereas primary radiation strikes the screen phosphor.
4) The resulting light exposes the film.

Question 3

What is a computed tomography?

Answer 3

Computed tomography (CT) generates anatomical imaging, which is digitally reconstructed

Question 4

How does a CT work?

Answer 4

The timing, anode voltage kV and beam current mA are controlled by a dedicated microcomputer. The high voltage dc power supply drives an x-ray tube that can be mechanically rotated along the circumference of a gantry. The x-rays pass through the patient, who is lying in a tube through the centre of the gantry. Imaging upon several of as many as 1000 detectors fixed in place around the circumference of the gantry

Question 5

What is the imaging of a CT based on?

Answer 5

Imaging is based on Back projection reconstruction

Question 6

What is an MRI?

Answer 6

MRI is a medical imaging technique used in radiology to visualize detailed internal structures.

Question 7

How does an MRI work?

Answer 7

It uses a powerful magnetic field to align the magnetization of some atoms in the body, then uses radio frequency fields to systematically alter the alignment of this magnetization.

It provides good contrast between the different soft tissues of the body make it especially useful in brain muscle, heart and cancer compared with other medical imaging techniques such as CT or X-ray

Question 8

How does a compass needle behave in a large magnetic field?

Answer 8

A) The compass needle (a small magnet) aligns itself with a N/S-S/N direction when placed in a large magnetic field.
B) When another strong magnet is brought near the aligned compass needle the magnetic fields of all three magnets interact in such a way that the mobile, weakest magnet (the compass needle) realigns itself away from its original orientation.
C) When the perturbing magnetic field is removed suddenly the compass needle magnet realigns itself with the large external magnet field, but before realigning, it wobbles around the point of stability and gradually comes to rest.

Question 9

Why use MRI?

Answer 9

1. Utilizes non ionizing radiation. (unlike x-rays).
2. Ability to image in any plane. (unlike CT scans).
3. Very low incidents of side effects.
4. Ability to diagnose, visualize, and evaluate various illnesses

Question 10

What are the components of an MRI and state its function?

Answer 10

1. A magnet which produces a very powerful uniform magnetic field.
2. Gradient Magnets which are much lower in strength.
3. Equipment to transmit radio frequency (RF).
4. A very powerful computer system, which translates the signals transmitted by the coils.

Question 11

What is an ultrasound?

Answer 11

Ultrasound is acoustic waves with frequencies of 20 kHz to hundred MHz.

Question 12

What is the range of frequency used in most ultrasound scan?

Answer 12

1Mhz to 15 MHz

Question 13

Why is ultrasound considered as a noninvasive technique?

Answer 13

Since the sound waves are applied to external of the body, ultrasound is considered as a noninvasive technique.

Question 14

Is ultrasound safe?

Answer 14

Ultrasound is generally considered safe for human body, even for pregnancy scans.

Question 15

The ultrasound is more sensitive to variations in ____________?

Answer 15

Ultrasound scan is more sensitive to variations in soft tissue types than radiograph

Question 16

How does ultrasound capture images?

Answer 16

The waves propagate into the tissues of the body and reflects from interfaces between types of different acoustic properties.

Question 17

Describe the block diagram of an ultrasonic imaging equipment

Answer 17

see notes

Question 18

What are acoustic waves?

Answer 18

Acoustic (sound) waves are vibrations of the molecules of a medium that is able to support the propagation.

Question 19

When are waves known as ultrasonic radiation?

Answer 19

When the frequency of the vibration is above the audible hearing range

Question 20

What is the wave equation in one-direction?

Answer 20

p = pm x cos(wt-kx)

pm is the magnitude of the pressure wave
w is the angular frequency of the wave
k is the propagation constant
x is the x-direction axis

Question 21

What type of waves do ultrasonic waves produce in practice?

Answer 21

Sinusoidal waves

Question 22

What are dashed lines called?

Answer 22

Constant phase fonts

Question 23

Ultrasound waves propagates in which direction (x or y)?

Answer 23

The ultrasound wave propagates in x direction

Question 24

What is the formula for ultrasound wave velocity?

Answer 24

c = dx/dt = w/k

where c is the ultrasound wave velocity, which propagates in x direction.

Question 25

What is the velocity of the acoustic wave in the water 20C?

Answer 25

It is about
c = 1.5 x 10^3 m/sec

Question 26

What is the velocity of the acoustic wave in air?

Answer 26

It is about
c = 340m/sec

Question 27

What are the formulas for acoustic impedance?

Answer 27

Z = pressure/velocity = p/v

where p is the pressure
v is the velocity of particle of medium

Z = pc

where Z is the impedance
p is the density
c is the acoustic velocity

Question 28

What is the formula for velocity of particle?

Answer 28

v = Vm x cos(wt - kx)

Question 29

What are the two important items when studying the reflection of waves?

Answer 29

(1) the angle that the reflected wave has as it leaves the interface

(2) the angle that the transmitted waves takes as it propagates into the new region.

Question 30

What is the key principle of operation for ultrasonic imaging equipment?

Answer 30

The key principle of operation for ultrasonic imaging equipment is the principle of traveling wave reflection, commonly known in the audio spectrum as echo.

Question 31

The ultrasound instrumentation is based on detection of?

Answer 31

The reflected echoes from various interfaces in the body

Question 32

What are the 3 requirements of ultrasound detection? (GRP)

Answer 32

(1) Generation of an ultrasonic beam
(2) Reception of the returning echo
(3) Processing the signal for display

Question 33

How is ultrasound generated?

Answer 33

Through the piezoelectric effect. When a voltage is applied across the conducting plates, the molecules twist to align with the electric field, thereby thickening the material. If the polarity is reversed, the molecules twist back in the opposite direction, creating a decrease in the crystal thickness. The flipping back and forth of polarity causes expansion and contraction of the crystal, which creates mechanical vibration (sound waves). Reversely, it produces a voltage across their two surfaces when deformed (oscillation).

Question 34

What does the voltage generator in ultrasonic imaging device do?

Answer 34

The voltage generator in ultrasonic imaging devices hits piezoelectric transducer with a short pulse and causes it to oscillate at its resonant frequency.

Question 35

Where does the pulse of ultrasonic energy travel?

Answer 35

The pulse of ultrasonic energy travels into tissue. It is reflected from tissue boundaries, causing echoes. By the time the echoes reach the transducer, the pulse generator has turned off, and the echoes creates an oscillation in the transducer again.

Question 36

In medical ultrasound system, the ultrasound waves are generated using a special material called:
(a) superconductive material.
(b) piezoelectric material.
(c) semiconducting material.
(d) biodegradable material.

Answer 36

(b) piezoelectric material.

Question 37

Which of the following imaging modalities cannot be used safely for a patient who has cardiac pacemaker and metal implant?
(a) X-ray
(b) Ultrasound
(c) Computed Tomography (CT)
(d) Magnetic Resonance Imaging (MRI)

Answer 37

(d) Magnetic Resonance Imaging (MRI)

Question 38

Which type of waveform is suitable for use to effectively produce sharp cutting during electrosurgery?
(a) Damped Sinusoids
(b) Triangular Wave
(c) Continuous Wave
(d) Blended Wave

Answer 38

(c) Continuous Wave

Question 39

In X-ray imaging system, there is usually an Aluminium filter for the ray. State the purpose of the filter.

Answer 39

To remove low energy X-ray that would not penetrate the body. OR to avoid beam hardening effect.

Question 40

Why is an acoustic matching layer needed in an ultrasound transducer?

Answer 40

Density of air is much lower than water, and speed of ultrasound in air is much slower than in water. An acoustic matching layer is needed for reducing impedance mismatch which causes partial reflection in the transducer, which would reduce the efficiency of the transducer

Question 41

For the 4 types of imaging methods (CT, X-ray, MRI, and ultrasound), categorize them in a table showing which use or do not use ionizing radiation.

Answer 41

Ionizing - CT, X-ray
Non-ionizing - MRI, Ultrasound

Question 42

What can an MRI detect?

Answer 42

MRI can be used to detect brain tumors, traumatic brain injury, developmental anomalies, multiple sclerosis, stroke, dementia, infection, and the causes of headache.

Question 43

What are the formed elements in the blood?
(a) It is Red blood Cells (erythrocytes)
(b) It is White Blood Cells (leukocytes)
(c) It is Platelets (thrombocytes)
(d) All of (a), (b) and (c).

Answer 43

(d) All of (a), (b) and (c).

Question 44

Which statement about blood plasma is incorrect?
(a) Blood plasma contains formed blood elements.
(b) Blood plasma contains proteins which are used for organic repair.
(c) The nutrients found in blood plasma includes glucose, lipids and amino-acids.
(d) Enzymes, hormones and antibodies are found in blood plasma.

Answer 44

(a) Blood plasma contains formed blood elements.

Question 45

The spectrophotometric technique that can detect extremely small quantities of some substances is:
(a) Atomic-emission flame spectrophotometry.
(b) Atomic-absorption flame spectrophotometry.
(c) Fluorometry.
(d) Colorimetry.

Answer 45

(c) Fluorometry.

Question 46

In a hospital, patient’s samples are sent to the medical laboratory for analysis.

Briefly describe the four major sections of a typical medical laboratory and their functions.

Answer 46

Chemistry Section
Performs analyses of patient specimens such as blood, urine and cerebrospinal fluid (CSF).

Haematology Section
Performs measurements on blood including counting formed blood elements and clotting studies.

Microbiology Section
Performs studies on body tissues and fluids to determine the presence of pathological microorganisms.

Blood Bank
Performs automatic classification of blood products, and the storage of blood.

Question 47

Spectrophotometers are able to detect the presence of metallic elements in a patient’s specimen. Sketch and briefly explain the principle of the atomic-emission flame photometer, which is one type of spectrophotometer.

Answer 47

1. The patient sample is dissolved in a solvent and nebulised into the flame.
2. About 1% of the atoms are raised to excited state and emits photons.
3. A wavelength selector allows only the photons with the desired wavelength to reach the photometer.
4. The photometer indicates the intensity and hence the amount of metallic element present.
5. Elements detectable are Li+, Na+, K+, Ca2+.

Question 48

A blood cell analyser based on an aperture impedance change is shown in Figure 1. Describe in detail how the analyser measures the formed elements in the blood sample.

Answer 48

1. This analyzer is based on impedance change. An external electrical voltage is applied between both chambers
2. An aperture tube sucks in a diluted anti-coagulated blood solution into a tube.
3. The tube has a small aperture of about 100 microns.
4. Electrodes inside and outside the tube measure the resistance of the aperture.
5. Since formed elements have higher resistance than the solution, a spike increase in resistance is produced whenever a formed element goes through the aperture.
6. The resistance spikes are counted which corresponds to the number of formed elements flowing through.