Ultrasound Imaging Modes PDF

Ultrasound Imaging Modes Echo Display Modes: A-Mode – (A for amplitude) B-Mode – (B for brightness) M-Mode – (M for motion) Ultrasound Pulse Timing The ultrasound pulse is typically 2-3 wavelengths long. The length of the pulse is called the spatial pulse length, SPL. 𝑆𝑃𝐿 = 𝑛𝜆 – n...

Ultrasound Imaging Modes Echo Display Modes: A-Mode – (A for amplitude) B-Mode – (B for brightness) M-Mode – (M for motion) Ultrasound Pulse Timing The ultrasound pulse is typically 2-3 wavelengths long. The length of the pulse is called the spatial pulse length, SPL. 𝑆𝑃𝐿 = 𝑛𝜆 – n is the number of cycles. Ultrasound pulse timing Pulse duration, PD, is a measure of the time period of the pulse 𝑃𝐷 = 𝑛𝑇𝑝 – Tp in the pulse period. After the pulse, some time passes before the next pulse to allow for receiving of the signals. Ultrasound Pulse Timing Pulse Repetition Period (PRP): The time interval between the transmission pulses. Pulse Repetition Frequency (PRF): is the frequency of the repetition of the pulses. Relationship Between PRP and PRF: PRF = 1/PRP Key Points:  PRP and PRF are inversely related. Shorter PRP = Higher PRF. Duty Factor (DF): DF is the fraction or percentage of time an ultrasound system spends transmitting a pulse during each transmit-receive cycle. Formula: DF=Pulse Duration (PD)/Pulse Repetition Period (PRP) Key Points: DF is a ratio (unitless) or percentage. A higher DF means more time is spent transmitting. It helps determine the efficiency of ultrasound signal usage. Image Depth Image depth (Dmax) is the maximum distance the ultrasound can travel, reflect, and return to the transducer within a single pulse cycle. Key Points: The transducer sends pulses and waits for echoes before the next pulse. Relation: Image depth decreases as pulse repetition frequency (PRF) increases. High-frequency pulses reduce Dmax, limiting how deep the ultrasound can image. Spatial Resolution Spatial resolution refers to the smallest distance between two objects that can still be distinguished as separate in an ultrasound image. Types of Resolution: 1. Axial Resolution: is measured along the direction of the ultrasound beam. 2. Lateral Resolution: Perpendicular to the beam's direction.  3. Sectional Thickness (Elevational Resolution): Depth or thickness of the imaging slice. This determines the clarity and detail of the ultrasound image. Axial Resolution Axial resolution is the ability to distinguish two close surfaces along the direction of the ultrasound beam. Key Points: Depends on Spatial Pulse Length (SPL): Shorter SPL improves axial resolution. Improved by Higher Frequency: Higher frequencies produce shorter wavelengths, reducing SPL and improving resolution. Lateral Resolution Lateral resolution is the ability to distinguish two points that are side by side (perpendicular to the ultrasound beam). Key Points: Governed by Beam Width: Narrower beam width improves lateral resolution. Depends on Transducer Aperture: Aperture (number of active element groups) affects beam width during transmission. Varies with Distance: Best resolution is in the focal region; resolution decreases farther from the transducer. Improved by Higher Frequency: Higher frequency narrows the beam, enhancing lateral resolution. Doppler Imaging Doppler imaging uses the Doppler effect to measure the velocity of blood flow in the body. Doppler Effect: The change in sound frequency when a source (blood) moves relative to a detector. ○ Higher frequency (pitch) is detected when the source (e.g., blood cells) approaches. ○ Lower frequency (pitch) is detected when the source moves away. Application: Measures blood velocity accurately by analyzing these frequency shifts.