Ultrasound Physics & Mathematics ( Concept of Operations )( Part 2)

Ultrasound Imaging

Ultrasound is a mechanical, longitudinal wave with a frequency exceeding the Upper limit of human hearing, which is 20,000 Hz or 20 kHz[more than this is not hearable to humans ]

Medical Ultrasound

1-Imaging ( 1-12MHz (>40MHz in specialized applications))

2-Therapy ( 100kHz-1MHz )

Ultrasound Imaging

Ultrasound imaging is a way of using sound waves to look inside the human body(pets also) , High-frequency sound is transmitted into the body, usually in very short pulses , Returning echoes are analyzed to create an images

Basic Imaging Principle[pulse echo method]

Ultrasound transducer produces “pulses” of ultrasound waves , These waves travel within the body and interact with various tissues , The reflected waves return to the transducer and are processed by the ultrasound machine

An image which represents these reflections is formed on the monitor Selection is done using relays. One time it will act as transmitter, Another time as receiver

This technique is called as. Pulse Echo method

**************************************************************

Generation and detection of Ultrasound Wave

piezoelectric effect Generation and detection is taking place inside the ultrasound probe(or transducer ), Probe contain one or more quartz crystals called piezoelectric crystals.When an electric current is applied to these crystals, they change shape rapidly and produce ultrasound , These waves are entered inside the body and some parts are return back(echos) , Detection is also taking place on the same crystal, it convert echos again into electrical signals

The pulse repetition frequency (PRF )in Ultrasound

The pulse repetition frequency (PRF) is the number of pulses of a repeating signal in a specific time unit, normally measured in pulses per second , Because of the ultrasound images are Captured in real time, they can show the structure and movement of the body's internal organs as well as blood flowing through blood vessels

Ultrasounds are used for imaging many of the body parts

Heart and blood vessels - Liver - gall bladder -Spleen - pancreas - Kidney - bladder - uterusOveries and unborn child(foetus) in pregnant patients - Eyes - Thyroid and parathyroid glands - carotid artery- Scrotum -brain in infants -Hip infants

Doppler in Ultrasound

Used to evaluate and quantify blood flow , Flow is in motion relative to the transducer , Doppler produces an audible signal as well as a graphical representation of

flow = Spectral Waveform

The Doppler Effect

Apparent change in received frequency due to a relative motion between a sound source and sound receiver

Sound TOWARD receiver = frequency increases

Sound AWAY from receiver = frequency decreases

****************************************

Types of Doppler

1-Pulsed Wave (PW)

Produces short bursts/pulses of sound , Uses the same crystals to send and receive the signal , This follows the same pulse-echo technique used in 2D image formation

2-Continuous Wave (CW)

Uses different crystals to send and receive the signal , One crystal constantly sends a sound wave of a single frequency, the other constantly receives the reflected signal

****************************************

Different Modes

1-A Mode Scan

Echoes returning from the body are displayed as signals on an oscilloscope , Baseline represents time or distance , Upward deflections represents spikes depicting the acoustic interfaces.

2- B Mode Scan

Real-time gray scale B mode display , 2-D Display of Ultra sound , Multiple ultrasound pulses are sent as a series of successive scan lines building a 2-D representation of echoes.

Signals of great intensity is represented as white Absence of signal is shown as black. Intermediate intensity signals appears as shades of grey

3-M Mode Scan

Display moving structure along single line in the ultrasound beam , Single beam can be used to produce M mode. Mainly used in Echocardiography Helps in assessing rates and monitor with , help of high sampling frequency.

4- Color Doppler Mode

This mode help to analyze the blood flow in the vascular system and organs , Usually known as color Doppler , The blood flow in vein and arteries are distinguished by blue and red colors. Towards the probe the flow will be indicated as Red , Away from probe flow is indicated as Blue.

5- Pulse wave Doppler

Here the signals are transmitted and received in form of fixed duration pulses. This mode also found use of Doppler Effect principle , Output will be in spectral as well as in audio format

6- Continuous wave Doppler

Used in Echocardiography procedures , A technique in which the transducer emits and receives the ultrasound beam continuously.Two dedicated transducer elements are there. Enable the measurements high velocity blood flow in vessels.

7- Harmonic Imaging

New mode of ultrasound imaging , In which the fundamental frequency of returning echoes is suppressed and signals of harmonic frequency are received, processed and displayed. Abbreviated form is HI The image quality will be high and image will be smoother than other modes.