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Medical Physics A2

Total questions: 80

Worksheet time: 45mins

Name
Class
Date
1.

A piezoelectric crystal generates an e.m.f. when:

a)

A constant p.d. is applied

b)

It is heated

c)

Its shape changes

d)

Its density increases

2.

Ultrasound waves are generated in a transducer by:

a)

Magnetic induction

b)

Piezoelectric effect

c)

Photoelectric effect

d)

Thermionic emission

3.

Which property makes piezoelectric crystals suitable for ultrasound?

a)

They are magnetic

b)

They fluoresce

c)

They change shape under p.d.

d)

They are low density

4.

Ultrasound imaging relies on:

a)

Transmission of visible light

b)

Reflection of sound

c)

Scattering of gamma rays

d)

Refraction of light

5.

Specific acoustic impedance is defined as:

a)

Z = ρ/c

b)

Z = c/ρ

c)

Z = ρc

d)

Z = ρc²

6.

In I = I₀e^(-μx), μ represents:

a)

Density

b)

Attenuation coefficient

c)

Acoustic impedance

d)

Absorption length

7.

The reflection coefficient at a boundary depends on:

a)

Frequency

b)

Acoustic impedances

c)

Crystal thickness

d)

Amplitude

8.

If Z₁ = Z₂ at a boundary, reflection coefficient is:

a)

0

b)

1

c)

0.5

d)

Undefined

9.

Ultrasound attenuation increases with:

a)

Lower frequency

b)

Higher frequency

c)

Lower impedance

d)

Smaller μ

10.

The intensity reflection coefficient is maximum when:

a)

Z₁ ≈ Z₂

b)

Z₁ ≫ Z₂

c)

Z₁ ≪ Z₂

d)

Z₁ = 0

11.

The frequency of ultrasound used in imaging is:

a)

20 Hz–20 kHz

b)

20 kHz–20 MHz

c)

2 GHz–20 GHz

d)

>200 MHz

12.

Which factor does NOT affect ultrasound resolution?

a)

Frequency

b)

Wavelength

c)

Acoustic impedance

d)

Transducer design

13.

Gel is used in ultrasound scanning to:

a)

Amplify sound

b)

Match impedances

c)

Cool the transducer

d)

Increase frequency

14.

Which factor reduces penetration depth of ultrasound?

a)

Low μ

b)

High frequency

c)

Low density

d)

Shorter path

15.

The time for an echo to return depends on:

a)

Density

b)

Speed of sound

c)

Attenuation coefficient

d)

Acoustic impedance

16.

An ultrasound pulse must be:

a)

Long

b)

Short

c)

Long for less attenuation

d)

Short for less impedance

17.

Ultrasound images display:

a)

Tissue temperature

b)

Boundaries between tissues

c)

Electrical signals

d)

Nuclear density

18.

Which equation represents attenuation?

a)

I=I₀e^(μx)

b)

I=I₀e^(-μx)

c)

I=I₀μx

d)

I=I₀/μx

19.

What is measured in rayls?

a)

Acoustic impedance

b)

Attenuation coefficient

c)

Frequency

d)

Pressure

20.

Increasing density with constant c will:

a)

Reduce impedance

b)

Increase impedance

c)

Reduce reflection

d)

Reduce attenuation

21.

Resolution increases with:

a)

Higher frequency

b)

Lower frequency

c)

Longer wavelength

d)

Lower intensity

22.

Which interaction produces ultrasound echoes?

a)

Refraction

b)

Reflection

c)

Absorption

d)

Diffraction

23.

In IR/I₀ = (Z₁-Z₂)²/(Z₁+Z₂)², the answer represents

a)

Transmission fraction

b)

Reflection fraction

c)

Attenuation

d)

Absorption

24.

If attenuation is too high:

a)

Image improves

b)

No echoes return

c)

Resolution increases

d)

Wavelength increases

25.

Detection transducer function:

a)

Convert echoes to e.m.f.

b)

Store energy

c)

Absorb sound

d)

Amplify voltage

26.

X-rays are produced when:

a)

Electrons recombine

b)

Electrons hit target

c)

Gamma decay

d)

Photoelectric effect

27.

Minimum wavelength is determined by:

a)

Target metal

b)

Accelerating potential

c)

Tube current

d)

Crystal

28.

Increasing p.d. gives:

a)

Shorter λmin

b)

Longer λmin

c)

Lower intensity

d)

No change

29.

Energy of X-ray photon:

a)

E=hf

b)

E=mc²

c)

E=½mv²

d)

E=QV

30.

Target metal usually:

a)

Aluminium

b)

Tungsten

c)

Copper

d)

Lead

31.

Purpose of tungsten target:

a)

Emit electrons

b)

Stop electrons and emit X-rays

c)

Reduce attenuation

d)

Shield radiation

32.

Bremsstrahlung spectrum arises from:

a)

Ionisation

b)

Deceleration

c)

Photoelectric

d)

Scattering

33.

In imaging, contrast depends on:

a)

Tube voltage

b)

Current

c)

Ultrasound frequency

d)

Target thickness

34.

High tube voltage gives:

a)

High contrast

b)

Low contrast

c)

No contrast

d)

Infinite resolution

35.

Low-energy X-rays are removed using:

a)

Filters

b)

Detectors

c)

Transducers

d)

Photodiodes

36.

X-ray intensity decreases as:

a)

I=I₀μx

b)

I=I₀e^(-μx)

c)

I=I₀/x

d)

I=μ/I₀

37.

μ depends on:

a)

Target

b)

Absorber

c)

Voltage

d)

Waveform

38.

Increasing thickness:

a)

Increases intensity

b)

Reduces intensity

c)

No effect

d)

Increases λ

39.

CT images are produced by:

a)

Single picture

b)

Multiple 2D slices

c)

Ultrasound

d)

Gamma scattering

40.

A single slice in CT uses:

a)

Rotating X-ray source

b)

Fixed X-ray

c)

PET gamma rays

d)

Piezoelectric

41.

A 3D CT image is built from:

a)

Echoes

b)

2D slices

c)

Gamma rays

d)

Refraction

42.

Higher μ means:

a)

Lower absorption

b)

Higher absorption

c)

Higher transmission

d)

No attenuation

43.

Half-value thickness is:

a)

Thickness for 50% reduction

b)

Stop all X-rays

c)

Double intensity

d)

Complete reflection

44.

Tube current affects:

a)

Wavelength

b)

Intensity

c)

Contrast

d)

Resolution

45.

Main risk of X-rays:

a)

Heating

b)

Ionisation

c)

Vibration

d)

Magnetic effects

46.

Reduce patient dose by:

a)

Increasing time

b)

Using filters

c)

Increasing p.d.

d)

No collimation

47.

CT differs from X-ray because:

a)

CT uses ultrasound

b)

CT combines multiple angles

c)

CT has no radiation

d)

CT uses impedance

48.

CT detectors measure:

a)

Echoes

b)

Transmitted intensity

c)

Reflected rays

d)

Magnetic resonance

49.

Higher tube voltage produces:

a)

Longer λ

b)

Shorter λ

c)

Higher attenuation

d)

Lower energy

50.

Bone vs tissue contrast arises because:

a)

Different impedances

b)

Different μ values

c)

Different resonances

d)

Different reflection

51.
A tracer is:
a)
Fluorescent dye
b)
Radioactive substance
c)
Gel
d)
CT slice
52.
PET tracers decay by:
a)
α
b)
β⁺
c)
β⁻
d)
γ only
53.
Positron annihilation produces:
a)
1 photon
b)
2 gamma photons
c)
2 positrons
d)
1 neutron
54.
The annihilation photons travel:
a)
Random
b)
Opposite
c)
90°
d)
Circles
55.
The energy of each photon:
a)
511 keV
b)
1 MeV
c)
13.6 eV
d)
2.2 MeV
56.
PET images are formed by:
a)
Measuring attenuation
b)
Detecting annihilation photons
c)
Using X-rays
d)
Using echoes
57.
Momentum conservation means:
a)
Photons move together
b)
Photons opposite
c)
Energy lost
d)
Speed decreases
58.
PET is sensitive because:
a)
Detects back-to-back photons
b)
Variation in impedance
c)
Reflection
d)
CT slices
59.
PET identifies active tissue because:
a)
Tracers accumulate in active regions
b)
Scatter less
c)
Absorb less
d)
Reduce μ
60.
PET is superior for:
a)
Impedance
b)
Functional imaging
c)
Attenuation
d)
Structural only
61.
Relevant particle pair:
a)
Proton-antiproton
b)
Electron-positron
c)
Neutron-antineutron
d)
Photon-photon
62.
Radiation hazard in PET:
a)
Ultrasound
b)
Radioactive tracers
c)
Transducers
d)
Tungsten
63.
Detectors are arranged:
a)
Line
b)
Ring
c)
Square
d)
Random
64.
Time-of-flight PET improves by:
a)
Absorption
b)
Arrival times
c)
Echoes
d)
Voltage
65.
If only one photon detected:
a)
Valid
b)
Rejected
c)
Doubled
d)
Stored
66.
Annihilation ensures:
a)
Conserve charge & momentum
b)
Violate charge
c)
Produce neutrons
d)
Create protons
67.
Gamma rays escape body because:
a)
Scatter
b)
High energy
c)
Reflect
d)
Refract
68.
PET tracer decay:
a)
Proton→neutron+e⁻
b)
Proton→neutron+β⁺
c)
Neutron→proton+β⁻
d)
Electron capture
69.
PET resolution depends on:
a)
Impedance
b)
Detector ring
c)
Tungsten target
d)
Gel
70.
A limitation of PET is:
a)
High radiation dose
b)
Poor function
c)
Low specificity
d)
No gamma detection
71.
An ultrasound wave I₀=10 W m⁻² passes 4 cm tissue (μ=0.15 cm⁻¹). Transmitted intensity?
a)

5.5 W m⁻²

b)
6.7 W m⁻²
c)
2.2 W m⁻²
d)
8.9 W m⁻²
72.
Two tissues Z₁=1.6×10⁶, Z₂=6.0×10⁶. Reflection coefficient?
a)
0.28
b)
0.43
c)
0.62
d)
0.18
73.
Ultrasound beam 12 W m⁻², μ=0.20 cm⁻¹, thickness 5 cm. Transmitted intensity?
a)
5.4 W m⁻²
b)

4.4 W m⁻²

c)
7.2 W m⁻²
d)
2.8 W m⁻²
74.
X-ray beam 100 W m⁻² passes 2 cm bone (μ=0.35 cm⁻¹). Transmitted intensity?
a)
36 W m⁻²
b)
50 W m⁻²
c)
70 W m⁻²
d)
28 W m⁻²
75.
At a boundary Z₁=1.5×10⁶, Z₂=1.7×10⁶. Transmission fraction?
a)
0.99
b)
0.96
c)
0.89
d)
0.75
76.
Ultrasound I₀=8 W m⁻², 3 cm tissue μ=0.25, then bone Z=6.5×10⁶ vs tissue 1.5×10⁶. Final transmitted?
a)

2.3 W m⁻²

b)

2.8 W m⁻²

c)
3.0 W m⁻²
d)
4.4 W m⁻²
77.
X-rays I₀=200 W m⁻², 6 cm tissue μ=0.12 cm⁻¹. Transmitted intensity?
a)
72 W m⁻²
b)
88 W m⁻²
c)

97 W m⁻²

d)
65 W m⁻²
78.
Ultrasound I₀=5 W m⁻², 2 cm μ=0.40, then 3 cm μ=0.20. Final intensity?
a)
2.0 W m⁻²
b)

1.2 W m⁻²

c)
0.9 W m⁻²
d)
1.8 W m⁻²
79.
X-rays I₀=50 W m⁻², 1 cm tissue μ=0.15, then 2 cm bone μ=0.40. Transmitted intensity?
a)
28 W m⁻²
b)

19 W m⁻²

c)
35 W m⁻²
d)
24 W m⁻²
80.
Ultrasound I₀=6 W m⁻², 2.5 cm tissue μ=0.20. % transmitted?
a)
0.45
b)
0.53
c)
0.61
d)
0.7

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