chapter 13 real time imaging

Definition: Real time imaging is the identification and precise localization of moving targets from instant to instant.
Conceptual Understanding:
- It can be viewed as the inverse of time between the beginning of one frame to the next.
- A comparison can be made to a movie versus a still picture.

Definition: Frame rate is defined as the number of frames (images) produced per second.
- Measured in Hertz (Hz).
- The relationship between time for one frame and frame rate:
- \text{Time of 1 frame} \times \text{Frame rate} = 1
- For a real-time effect, the frame rate should be greater than 20 Hz, typically between 20-100 Hz.
Factors Affecting Frame Rate:
- Speed of sound in the medium (higher speed leads to higher frame rate).
- Fixed speed of sound at 1540 m/s.
- Shallow depth produces a higher frame rate.
- The number of pulses per frame is inversely related.
Calculation of Frame Rate:[
- \text{Frame rate} = \frac{\text{PRF}}{\text{number of foci} \times \text{number of pulses for each frame}}
- \text{Frame rate} = \frac{1}{\text{Time for 1 frame}}
- Frame rate is inversely proportional to the time of 1 frame
- SETTINGS DETERMINING FRAME RATE

Two key system settings:
1. Imaging depth
2. number of pulses per frame
  1. Both settings are within the control of the sonographer.

The relation between depth and temporal resolution:
- Lower depth yields better temporal resolution.
- Shorter time to receive reflected signals from shallower depths results in higher frame rates and improved temporal resolution.

Visual Representation:
- Fig. 13.2 illustrates imaging depth and the time per frame (Tframe) relationship.
- Thinner images (upper) show higher frame rates compared to deeper images (lower).

Shallow Imaging:
- Short go-return time.
- Shorter Tframe.
- Higher frame rate.
- Superior temporal resolution.
Deep Imaging:
- Long go-return time.
- Longer Tframe.
- Lower frame rate.
- Inferior temporal resolution.
Mathematical Takeaway: Time per frame is inversely proportional to the pulse repetition frequency (PRF).

Pulses per frame and frame rate are inversely related.
Pulses per frame and temporal resolution are inversely related.
Pulses per frame and time of frame are directly related.
Dependents of Pulses per Frame:
- Sector width (wider width leads to more pulses).
- Line density (higher density requires more time per frame leading to a lower frame rate).
- Number of focal points.

Implications:
- Multi-focus requires three times as many pulses for each image, leading to a decreased frame rate compared to single focus.
Visual Comparison:
- Figs. 13.3 & 13.4 differentiate single focus (upper) and multi-focus (lower) impact on frame rate.

Single Focus:
- One pulse per scan line.
- Leads to shorter Tframe and higher frame rate.
- Superior temporal resolution but poorer lateral resolution.
Multi-focus:
- Multiple pulses per scan line.
- Results in longer Tframe, lower frame rate, and diminished temporal resolution but improved lateral resolution.

Definition: Number of pulses required to create an image.
Increasing sector size increases the number of pulses required thus decreasing temporal resolution.
Relationship: Frame rate and field of view are inversely correlated.
- Small sector size = high frame rate.
- Wide sector size = low frame rate.

Narrow Sector:
- Fewer pulses per frame, leading to shorter Tframe and higher frame rate.
Wide Sector:
- More pulses per frame, resulting in a longer Tframe and lower frame rate.

Definition: Space between scan lines.
- Low line density = widely spaced lines.
- High line density = tightly packed lines.
Impact: Line density and frame rate are inversely related.
- Benefit: Higher line density improves spatial resolution.

Low Line Density:
- Widely spaced lines allow for higher frame rates.
High Line Density:
- Tightly packed lines create a longer Tframe leading to lower frame rates and high spatial resolution.

More focal points mean that more time is needed for each scan, reducing frame rate and resolution.
However, it improves the accuracy and lateral resolution of the image.

Higher Temporal Resolution:
1. Shallow imaging.
2. Single focus.
3. Narrow sector size.
4. Low line density.
Lower Temporal Resolution:
1. Deeper imaging.
2. Multiple focal points (improving lateral resolution).
3. Wide sector size.
4. High line density (improving spatial resolution).

Definition: The ability of the imaging system to accurately locate the position of a moving object instantaneously.
Temporal pertains to accuracy in time.
Relationship to Frame Rate:
- Higher frame rates lead to better temporal resolution, while lower frame rates yield less temporal resolution.
Units: Measured in Hz or per second.

Four settings that affect temporal resolution:
1. Imaging depth.
2. Number of pulses per scan line (in multi-focus systems).
3. Sector size.
4. Line density (lines per degree of the sector).

Depth and temporal resolution are inversely related:
- Shallower imaging increases frame rate and improves temporal resolution.
- Deeper imaging reduces frame rate and degrades temporal resolution.

High Temporal Resolution:
- High frame rate, shallow imaging, fewer pulses, single focusing, narrow sector, low line density.
Low Temporal Resolution:
- Low frame rate, deep imaging, more pulses, multi-focusing, wide sector, high line density.

Notable trade-offs occur between image quality and temporal resolution:
- Multi-focusing improves lateral resolution but degrades temporal resolution.
- Increasing line density can enhance spatial resolution but degrades temporal resolution.
- Altering sector size or imaging depth does not affect image quality.