week 4 UT 200 day 1

Why Continuous Wave (CW) cannot determine reflector depth

CW transmits sound constantly, causing outgoing and returning signals to overlap with no way to measure transit time.

Fundamental operating principle of Pulsed Wave (PW) ultrasound

Transmit and listen: emits a brief sound burst and measures the exact arrival time of returning echoes to calculate depth.

Pulse Duration (PD) definition

The actual time from the start of a pulse to the end of that pulse (transmit or "on" time only).

Pulse Duration (PD) formulas

PD = n * P or PD = n / f (where n = number of cycles, P = period, and f = frequency).

What determines Pulse Duration (PD) and can it be adjusted?

Determined solely by the sound source; cannot be altered by the sonographer.

Pulse Repetition Period (PRP) definition

The total time from the start of one pulse to the start of the next pulse (PD + listening/receive time).

What determines Pulse Repetition Period (PRP) and can it be adjusted?

Determined by the sound source and imaging depth; sonographer alters PRP by adjusting depth.

Relationship between imaging depth and PRP

Direct relationship: increasing imaging depth increases listening time, thereby increasing PRP.

Pulse Repetition Frequency (PRF) definition

The number of pulses transmitted into the body by the ultrasound system each second.

PRF formula and mathematical relationship to PRP

PRF = 1 / PRP (reciprocal relationship; PRF * PRP = 1).

Units of Pulse Repetition Frequency (PRF)

Hertz (Hz) or pulses per second.

What determines PRF and can it be adjusted?

Determined by the sound source via imaging depth; sonographer changes PRF by altering depth.

Relationship between imaging depth and PRF

Inverse relationship: increasing imaging depth decreases PRF.

Does transducer operating frequency determine or affect PRF?

No; PRF is strictly related to imaging depth, not transducer operating frequency.

Duty Factor (DF) definition

The percentage or fraction of time that the ultrasound system is actively transmitting sound.

Duty Factor (DF) formula

Duty Factor (%) = (PD / PRP) * 100.

Typical Duty Factor value for Continuous Wave (CW) ultrasound

1.0 or 100% (transmits continuously without listening time).

How does increasing imaging depth affect Duty Factor?

Increasing depth increases PRP, which decreases the Duty Factor (inverse relationship).

Spatial Pulse Length (SPL) definition

The physical distance a pulse occupies in space from its start to its end.

Spatial Pulse Length (SPL) formula

SPL = n * lambda (number of cycles in pulse * wavelength).

Units of Spatial Pulse Length (SPL)

Millimeters (mm).

What determines Spatial Pulse Length (SPL) and can it be adjusted?

Determined by both the sound source and the medium; cannot be altered by the sonographer.

Why shorter Spatial Pulse Length (SPL) is clinically desirable

Shorter pulses create less overlap between structures along the beam axis, yielding better axial resolution.

How higher frequency affects SPL and pulse duration

Higher frequency means shorter period and shorter wavelength, resulting in shorter PD and shorter SPL.

Parameters determined SOLELY by the sound source

Pulse Duration (PD), Pulse Repetition Period (PRP), Pulse Repetition Frequency (PRF), and Duty Factor (DF).

The only pulsed wave parameter determined by BOTH the sound source and the medium

Spatial Pulse Length (SPL).

Pulsed wave parameters altered by adjusting imaging depth

Pulse Repetition Period (PRP), Pulse Repetition Frequency (PRF), and Duty Factor (DF).

Pulsed wave parameters that CANNOT be altered by adjusting imaging depth

Pulse Duration (PD) and Spatial Pulse Length (SPL).

Assumed average propagation speed of sound in soft tissue

1.54 mm/μs or 1,540 m/s.

The Range Equation for reflector depth (D)

D = (1.54 mm/μs * t) / 2 = 0.77 * t (where t is round-trip time in μs).

The 13 μs Rule in soft tissue

It takes exactly 13 μs of round-trip time for sound to travel to a reflector at 1 cm depth and return to the transducer.

One-way transit time for sound to travel 1 cm in soft tissue

6.5 μs.

Total distance sound travels during a 13 μs round trip to a 1 cm reflector

2 cm (1 cm out + 1 cm back).

Formula to calculate round-trip time from imaging depth in soft tissue

Round-trip time (μs) = Depth (cm) * 13 μs/cm.

Formula to calculate total distance traveled from reflector depth

Total distance traveled (cm) = Depth (cm) * 2.