Ultrasound Etc

Question 1

Unit of acoustic impedance

Answer 1

Rayl (Ry)

Question 2

Acoustic impedance (Z) equation

Answer 2

Acoustic impedance (Z) = Medium density (p) x Ultrasound velocity in medium (v)

Question 3

Wave equation

Answer 3

Velocity (v) {m/s-1}= Frequency (f) {Hz} x Wavelength (lamda) {metres}

Question 4

High frequency waves

Answer 4

-Shorter wavelengths
-Higher interaction with materials and so it loses energy (attenuation)

Question 5

What are higher frequency waves used for

Answer 5

To detect smaller features inside the body

Question 6

Attenuation of ultrasound

Answer 6

I=I0e^-mewx
-I=Intensity (Watts, Joules)
-I0=original intensity
-mew=attenuation coefficient
-x=distance travelled

Question 7

B scans

Answer 7

-Brightness scan
-Gives 2D image based on A scan information
-Built up from many A scans

Question 8

A scan

Answer 8

-Amplitude scan
-Gives numeric information

Question 9

Doppler effect

Answer 9

The artificial modification in apparent wavelength due to relative motion between source and observer

Question 10

Key bits in discharging tube

Answer 10

-Cathode
-Evacuated chamber
-Vaccum
-Bevel anode with tungsten target
-Voltage
-Electron beam
-Protective lead shield

Question 11

Cathode in discharging tube

Answer 11

Gives out electrons which are attracted to anode

Question 12

Evacuated chamber

Answer 12

The air is removed to prevent collisions (energy loss) between electrons and air molecules

Question 13

High voltage

Answer 13

To give electrons enough energy to leave the cathode

Question 14

Bevel anode

Answer 14

Forces x-rays to exit the evacuated envelope

Question 15

Electron beam

Answer 15

High energy electrons, energised off the cathode, accelerated across potential difference gap & strike tungsten target with high kinetic energy

Question 16

What is the potential difference between electrodes

Answer 16

Approximately 150kV

Question 17

What happens in x-ray (discharge tube)

Answer 17

Electrons are accelerated via high voltage from the cathode and pass through the potential difference gap, strike the bevel anode and slow down. The energy loss is converted to x-rays

Question 18

What else increases as kinetic energy does?

Answer 18

Speed squared.

^KE=^ (speed)^2

Question 19

What are continuous x-rays also called?

Answer 19

Bremsstrahlung x-ray photons/Braking x-rays

Question 20

Ultrasound frequency range

Answer 20

Medical 2-18 MHz
US is anything above 20kHz

Question 21

Transducer

Answer 21

A device which converts one form of energy into another

Question 22

How piezoelectric crystals act as transducers

Answer 22

Convert pressure to energy, due to net zero charge the crystals are not pushed. This is due to single + charge of silicon balancing two - charge in oxygen at the back. When crystal pushed, the force pushes the ions together, causing a difference in charge, which generates an electric charge.

Question 23

Mineral with piezoelectric properties?

Answer 23

Quartz crustal

Question 24

Acoustic matching

Answer 24

Increases the transmission of ultrasound waves via a coupling agent (gel) due to air

Question 25

Acoustic impedance of air

Answer 25

4.29x10^2

Question 26

Acoustic insulator

Answer 26

Prevents interference from external sources (e.g. Someone speaking)

Question 27

Plastic nose

Answer 27

Barrier between patient and instrument

Question 28

Backing block/damper

Answer 28

Prevents returning signal resonating in the probe as it blurs image

Question 29

Power cable

Answer 29

Alternate current with high frequency at 1-20MHz

Question 30

Electrodes

Answer 30

Take Alt current and transit it to the crystal and also take the signal from the reflected pulse and transit to the cable

Question 31

Acoustic impedance

Answer 31

How much the US wave is slowed down in a medium

Question 32

Characteristic radiation

Answer 32

Bremstrahlung. Caused by electrons being ejected and another dropping down energy level. Only few discrete transitions thag can result in a characteristic peak

Question 33

Why the reflection coefficient (alpha) is unitless?

Answer 33

The units cancel each other out?

Question 34

Continuous/Bremsstrahlung

Answer 34

Energised electrons hit atoms in tungsten anode and are slowed down. Each electron interacts different with target nuclei so attenuation varies in continuum

Question 35

X-ray beam
Intensity

Answer 35

Controlled by the electron beam current given in the machine. More current means more electrons per second so more x-ray photons. A higher current results in higher beam intensity, decreasing image production time

Question 36

Alpha and Kbeta

Answer 36

Produced by electrons transitioning from one energy level to another

Question 37

X-ray beam photon

Answer 37

Controlled by voltage. High voltage produces high energy photons with shorter wavelengths and high frequency. Lower voltage produces low energy photons with longer wavelengths and lower frequency.

Question 38

How frequency affects ultrasound

Answer 38

Low frequency gives clearer image but low level of penetration
High frequency ultrasound are not as penetrating as they get attenuated more

Question 39

Characteristic spectra

Answer 39

Peaks appear at high voltage when accelerated electrons collide with tungsten target atom’s electrons in orbitals and knows them out of their energy levels. As they move down energy levels, characteristic spectrum is emitted

Question 40

Kalpha

Answer 40

Quantum 2 to 1

Question 41

Kbeta

Answer 41

Quantum 3 to 1

Question 42

Tungsten target

Answer 42

High melt point and high atomic number to increase positive charge, collisions and x-rays

Question 43

Why acoustic matching?

Answer 43

Greater difference in acoustic impedance of tissues causes more reflection