Name that array
This array fires neighboring groups of elements sequentially and produces a standard rectangular grayscale image.
What is a linear sequential array?
This type of resolution improves when frame rate increases.
What is temporal resolution?
This component creates the electrical voltages that excite the PZT during transmission.
What is the pulser?
This is the smallest building block of a digital image.
What is a pixel?
Dynamic range is expressed in this relative unit.
What are decibels, or dB?
This array has a small footprint, produces a sector-shaped image, and electronically steers and focuses its beam.
What is a linear phased array?
A sonographer wants to follow rapidly moving cardiac structures. Name two adjustments that can increase frame rate.
What are narrowing the sector and reducing the number of transmit focal zones?
Reducing unnecessary depth or line density can also help.
The superficial image looks appropriately bright, but deeper tissues are too dark because of attenuation. This receiver function allows depth-specific correction.
What is compensation, or TGC/DGC?
A system uses 7 bits per pixel. This is the maximum number of gray levels it can represent.
What is 128 gray levels?
2⁷ = 128.
A very narrow displayed dynamic range produces this appearance: many intermediate grays or mostly black and white.
What is mostly black and white, with high image contrast?
Combining linear sequential and linear phased technologies, this array produces a trapezoidal image with a flat near field.
What is a vector array?
A system uses 100 transmissions per frame with a PRP of 0.2 ms. Calculate its frame time and frame rate.
What are 20 ms per frame and 50 frames per second?
100 × 0.2 ms = 20 ms = 0.020 seconds.
Frame rate = 1 ÷ 0.020 = 50 frames/second.
Name the five traditional receiver operations in their correct order.
What are amplification, compensation, compression, demodulation, and reject?
A sonographer selects a region of interest, and the system rescans that region with finer sampling. Name this type of magnification.
What is write magnification, or write zoom?
A signal has a dynamic range of 105 dB and undergoes 35 dB of compression. This is its resulting dynamic range.
What is 70 dB?
105 − 35 = 70 dB.
During reception, the system continually adjusts delays to align echoes from different depths before combining them. Name this process and state whether it requires another transmitted pulse.
What is dynamic receive focusing, which does not require another transmitted pulse?
A sonographer increases scan-line density to show more spatial detail. With all other settings unchanged, these two imaging characteristics decrease.
What are frame rate and temporal resolution?
An echo signal has an amplitude of 12 units and noise has an amplitude of 3 units. Receiver gain triples both. State the new signal-to-noise ratio and whether it improved.
What is 4:1, with no improvement?
Before: 12 ÷ 3 = 4:1.
After: 36 ÷ 9 = 4:1.
One technique combines views acquired from different angles. Another combines information from successive frames. Name both techniques and their shared temporal-resolution tradeoff.
What are spatial compounding and temporal compounding/persistence, which can reduce temporal resolution?
After 45 dB of compression, a signal has a dynamic range of 55 dB. This was its original dynamic range.
What is 100 dB?
55 + 45 = 100 dB.
A fluid-filled cyst appears to contain echoes because sound outside the main beam strikes a strong adjacent reflector. Name the two lobe artifacts that can cause this positioning error and one scanning action to help investigate it.
What are side lobes and grating lobes, and rescanning in another plane or changing the insonation angle?
Originally, a system uses 120 transmissions per frame with a PRP of 0.1 ms. After an adjustment, it uses 60 transmissions with a PRP of 0.2 ms. Determine whether frame rate changes and calculate its value.
What is no change—approximately 83 frames per second?
Original: 120 × 0.1 = 12 ms/frame.
Adjusted: 60 × 0.2 = 12 ms/frame.
Frame rate = 1 ÷ 0.012 ≈ 83.3 frames/second.
A sonographer raises the reject threshold to eliminate weak echoes. Explain why this may remove useful anatomy as well as noise.
What is reject suppresses signals based on amplitude, so it cannot distinguish weak meaningful echoes from weak noise?
An image looks smoother after the system fills gaps using neighboring pixel values. Name the process and explain whether it collected new echoes.
What is fill-in interpolation, which estimates values without acquiring new echo measurements?
An ultrasound image shows many shades of gray and subtle differences between tissues. Describe its dynamic range, image contrast, and contrast resolution.
What are wide dynamic range, low image contrast, and good contrast resolution?
Chapter 16, slides 14–15.