General Physics Pulsed Wave Operation Padmini Arora Ultrasound Continuous Wave: ➔ Wave that’s “on” for indefinite amount of time with constant amplitude ➔ Also referred to as undamped wave ➔ Cannot create anatomical images Pulsed Wave: ➔ To create anatomical images in diagnostic ultrasound ➔ Pulses separated by gap in time ➔ Pulses = a few cycles of ultrasound ➔ Also called damped wave ➔ Pulse is like an individual train car ➔ Pulsed wave is like the train ➔ Transmit time: talking time OR “on” time ➔ Receive time: listening time OR “off” time Pulsed Ultrasound Parameters for Pulsed Ultrasound besides the other sound wave parameters from Ch. #3: 1. 2. 3. 4. 5. Pulse Duration Spatial Pulse Length Pulse Repetition Period Pulse Repetition Frequency Duty Factor Pulse Duration [PD] ➔ Definition: Time it takes for one pulse to occur [n] ➔ ➔ ➔ ➔ ➔ ➔ ➔ ➔ ➔ ⟡ Period [time for one cycle] ∗ # of cycles in pulse ⟡ Single “on” time Formula: PD [µs] = n ∗ T [µs] Unit: microseconds, milliseconds or seconds Determined by: sound source Adjustability: not by operator Typical Value: 0.3 - 2.0 µs Sonographic pulse = usually 2 - 3 cycles long Doppler pulses = typically 5 - 30 cycles long Shorter pulses improve image quality Direct relationship between PD & n ⟡ If # of cycles ⇈ ⟡ If Period ⇈ ⤏ PD ⇈ ⤏ PD ⇈ ➔ Remember: inverse relationship between period & frequency ⟡ PD = n x [1/frequency] OR n/frequency ⟡ If frequency ⇈ ⤏ period [T] ⇊ ⤏ PD ⇊ Spatial Pulse Length [SPL] ➔ Definition: length of pulse from front to end ➔ Wavelength [distance of one cycle] ∗ # of cycles in pulse [n] ➔ ➔ ➔ ➔ ➔ Formula: SPL [mm] = n ∗ 𝝺 [mm] Unit: any unit of distance [mm] Determined by: sound source & medium Adjustability: not by operator Typical value: 0.1 - 1.0 mm ➔ Shorter pulses improve image quality ➔ Direct relationship between SPL & n ➔ Direct relationship between SPL & 𝝺 ⟡ If # of cycles ⇈ ⟡ If 𝝺 ⇈ ⤏ SPL ⇈ ⤏ SPL ⇈ ➔ Remember: inverse relationship between 𝝺 & f ⟡ SPL = n [c/f] OR [nc/f] ⟡ If frequency ⇈ ⤏ 𝝺 ⇊ ⤏ SPL ⇊ Pulse Repetition Period [PRP] ➔ ➔ ➔ ➔ ➔ Definition: time from start of one pulse to start of next pulse --- has no relation c̅ period Formula: PRP = 1/PRF Unit: any unit of time [ms] Determined by: sound source Adjustability: yes - by changing imaging depth ⤏ ⟡ shallow depth short PRP/deeper ➔ Typical value: 100 µs - 1 ms ⤏ longer PRP ➔ Directly related to depth of view [max distance into body that US system images] ⤏ PRP ⇈ ⟡ If depth of view ⇊ ⤏ PRP ⇊ ⟡ If depth of view ⇈ ➔ Two components of PRP: ✶ Transmit time [pulse duration] ✶ Receive time ➷ Operator can’t ▵ PD [transmit time] ➷ Depth of view ▵’s receiving time Pulse Repetition Frequency [PRF] ➔ ➔ ➔ ➔ ➔ Definition: # of pulses occurring in a second --- has no relation c̅ frequency Formula: PRF = 1/PRP Unit: Hz or per second Determined by: sound source Adjustability: yes - by changing imaging depth ⟡ shallow depth ⤏ high PRF/deeper ⤏ lower PRF ➔ Typical value: 1,000 - 10,000 hertz ➔ Inversely related to depth of view [max distance into body that US system images] ⤏ PRF ⇊ ⟡ If depth of view ⇊ ⤏ PRF ⇈ ⟡ If depth of view ⇈ ➔ PRF & PRP = inverse relationship ⤏ PRF ⇊ ⟡ If PRP ⇊ ⤏ PRF ⇈ ⟡ If PRP ⇈ ➔ Use complementary units c̅ PRP & PRF Duty Factor [DF] ➔ ➔ ➔ ➔ ➔ Definition: fraction of time or percentage that pulsed US = “on” Formula: DF = PD µs / PRP µs Unit: it’s a fraction so it’s unitless Determined by: sound source Adjustability: yes - by changing imaging depth ⟡ shallow depth ⤏ high DF/deeper ⤏ low DF ➔ Typical value: 0.002 - 0.005 OR 0.2% - 0.5% in pulsed US ➔ Inversely related to depth of view [max distance into body that US system images] ⤏ PRP ⇈ ⤏ DF ⇊ ⟡ If depth of view ⇊ ⤏ PRP ⇊ ⤏ DF ⇈ ⟡ If depth of view ⇈ ➔ Note: PD can’t be ▵ by operator ➔ PRF & PRP = inverse relationship ⤏ PRP ⇊ ⤏ DF ⇈ ⟡ If PRF ⇊ ⤏ PRP ⇈ ⤏ DF ⇊ ⟡ If PRF ⇈ ➔ DF = unit less ➔ Maximum value = 1 or 100% ➔ Minimum value = 0 or 0% Formulas ➙ PD [µs] = n ∗ T [µs] ➙ SPL [mm] = n ∗𝝺 [mm] ➙ PRP = 1/PRF ➙ PRF = 1/PRP ➙ DF = PD [µs] / PRP [µs] ✘ PRP, PRF & DF = can ▵ by changing depth of view ✘ PRP = unrelated to period ✘ PRF = unrelated to frequency