SPI module 1 정리 - ③

* Continous wave / Pulsed wave

Continous wave = CW	Pulsed wave = PW
is continously transmiiting and receiving sound	transmit in a series of short pulses
must have two crystal.	same crystal used for both transmission and reception.
uniform  amplitude and frequency.	is used in all imaging US sound system except CW Doppler.
Duty factor = 1	Duty factor < 1

 

 

---

 

* PRF : Pulse Repetition Frequency

 - the number of US pulses

 - unit : Hz / typically 5KHz 

 - limited by the depth of field

 

* PRP : Pulse Repetition Period

 - unit : ms

 

PRP = 1/PRF

 

★ depth ↑ ? PRF ↓ PRP ↑

 

 

* PD : Pulse Duration

 - number of cycles × period

 

* Duty Factor

 - the ratio of sound on time

 -  b . 0~1

 - PF = PD / PRP

 

 

 

* SPL : Spatial Pulse Length

 - unit : mm

 - number of cycle × wavelength 

 - axial resolution α 1/SPL

 - axial resolution = SPL/2

---

* Decibel unit

 - "Relative sclae"

 - logarithmic scale

 

 - decibel equation for intensity or power : dB= 10 log (ratio)

 - decibel equation for amplitude : dB= 20 log (ratio)

 

because, Intensity α Power α Amplitude^2

 

Intensity or power increased by a factor of 2 = 3dB

amplitude increased by a factor of 2 = 6dB

 

because, log 2 = 0.30

 

---

* attenuation

 - weakens both the pulse and the echo

 - always implies a loss of energy (amplitude, intensity, power)

 

* 3 mechanism of attenuation

1. Absorption : heat
2. Reflection : large, smooth interface
3. Scattering : small, irregular interface

 

* frequency α attenuation α 1/ penetration 

 

 

* Attenuation Coefficient

 - in soft tissue : 0.5 dB/cm/ MHz

 

ex) 8MHz, 10cm...

0.5dB/cm/MHz * 10cm * 8MHz = 40dB