US physics II quiz 4

Ultrasound

bidirectional

transducer

converts one form of energy into another

transmission

Electrical → Sound

reception

Sound → Electrical

Transducer connection

Energy conversion → Sound beam → Image formation

PZT (Piezoelectric element)

performs the energy conversion that creates ultrasound imaging

PZT transmission

Voltage → Sound

pulse leaves transducer

creates ultrasound wave

PZT reception

Sound → Voltage

echo returns to transducer

creates electrical signal

↑ Damping

↓ Pulse Duration

↑ Bandwidth

↓ Q Factor

Q-Factor (Quality Factor)

Measures how efficiently a transducer produces

a narrow range of frequencies

High Q-factor

– Narrow bandwidth

– Longer pulse

– More sensitive

Low Q-factor

– Wide bandwidth

– Shorter pulse

– Better for imaging

Imaging transducers prefer

Low Q + Wide bandwidth

A transducer is modified to increase damping. Which change is MOST likely to

occur?

a) Narrower bandwidth and higher Q factor

b) Narrower bandwidth and lower Q factor

c) Wider bandwidth and lower Q factor

d) Longer pulse duration

Wider bandwidth and lower Q factor

Mechanical Transducers

■ Physical movement creates image

■ Beam direction changed mechanically

(sweep/steering)

■ Typically fixed focus

Array (Electronic) Transducers

■ Multiple active elements

■ Electronic steering & focusing

■ Most common in modern ultrasound

(provides greater beam control)

Linear

FOV: rectangular

Used for vascular, small parts

Curvilinear

FOV: curved / blunted sector

Used for abdomen, OB

Phased Array

FOV: sector

Used for cardiac

Vector

FOV: trapezoidal

Used for small acoustic windows

Higher frequency

↑ Resolution, ↓ Penetration

Lower frequency

↓ Resolution, ↑ Penetration

Thyroid →

higher frequency

Abdomen →

lower frequency

Cardiac →

lower frequency + phased array

Transducer design determines

image performance

Frequency →

Resolution & penetration

Beam shape →

Field of view

Focusing →

Lateral resolution

Array design →

Slice thickness control

Footprint →

Acoustic window access

A sonographer is scanning through a narrow acoustic window and needs the ability to electronically steer and focus the beam.

Which transducer is MOST appropriate?

a) Mechanical transducer

b) Curvilinear array

c) Phased array

d) Sequential linear array

Phased array

Beam is

narrowest at the focus

Near Zone (Near Field / Fresnel Zone)

Beam narrows with depth

Focus (Focal Point)

– Narrowest part of beam

– Best lateral resolution

Focal Length (Near Zone Length)

Distance from transducer to focus

Far Zone (Far Field / Fraunhofer Zone)

Beam diverges with depth

Focal Zone

Region around the focus where the beam

remains narrow

Focal Depth (Near Zone Length)

■ ↑ Transducer Diameter → ↑ Focal Depth

■ ↑ Frequency → ↑ Focal Depth

Beam Divergence (Far Zone)

■ ↑ Transducer Diameter → ↓ Divergence

■ ↑ Frequency → ↓ Divergence

Which transducer would produce the least divergence?

■ 5 MHz with 5 mm diameter

or

■ 15 MHz with 20 mm diameter?

15 MHz with 20 mm diameter?

Which change would produce the deepest focus and least beam divergence?

a) ↓ Frequency + ↓ Diameter

b) ↑ Frequency + ↓ Diameter

c) ↓ Frequency + ↑ Diameter

d) ↑ Frequency + ↑ Diameter

↑ Frequency + ↑ Diameter

More rows of elements →

greater beam control

1D Array

Lateral only, Standard imaging

1.5D Array

Lateral + Elevational, Improved slice thickness control

2D Array

Multi-directional control, 3D / 4D imaging

A cyst appears partially filled with echoes that are actually coming from tissue outside the imaging plane.

Which transducer design MOST directly helps?

a) 1D array

b) 1.5D array

c) 2D array

d) Harmonic imaging

1.5D array

Which transducer array is MOST associated with 3D imaging?

a) 1D array

b) 1.5D array

c) 2D array

d) Sequential linear

2D array

A sonographer adds additional focal zones.

What is the MOST likely result?

a) Improved temporal resolution

b) Improved lateral resolution with reduced

frame rate

c) Improved axial resolution

d) Increased penetration

Improved lateral resolution with reduced

frame rate

Steering changes

beam direction, not beam width

Which problem is MOST directly improved by harmonic imaging?

a) Beam thickness

b) Contrast resolution

c) Spatial pulse length

d) Axial resolution

Contrast resolution

Harmonic imaging MOST commonly improves:

a) Temporal resolution

b) Contrast resolution

c) Penetration depth

d) Slice thickness artifact

Contrast resolution

Which concept MOST directly improves slice thickness

artifact?

a) Harmonic imaging

b) Increased dynamic range

c) Improved elevational control

d) More damping

Improved elevational control

A sonographer is imaging a small moving cardiac structure through a narrow acoustic window and wants to optimize image quality.

Which combination is MOST appropriate?

a) Linear array + multiple focal zones

b) Curvilinear array + harmonic imaging

c) Phased array + electronic focusing

d) Mechanical transducer + increased damping

Phased array + electronic focusing