Session 6 Vascular Studies

Question 1

Main disadvantage of ultrasound in general?

Answer 1

highly operator dependent

Question 2

What does a duplex scanner do? (duplex ultrasonography)

Answer 2

does 2 things:

• grey-scale (brightness mode)= visualise architecture of a body part, atheromatous plaque can be directly visualised in blood vessel.
• colour flow imaging- doppler ultrasound, visualise flow or movement of a structure

Question 3

how does sound travel?

Answer 3

as a longitudinal wave, as sound is a pressure wave and when an object vibrates, it creates a mechanical
disturbance in the medium in which it is
directly adjacent to (usually air.) The medium then carries the disturbance in the form of oscillating and propagating pressure waves.
Sound travels at different velocities in different
mediums.
Air molecules compressed and stretched in order to allow wave propagation

Question 4

what quality of sound is relied upon in ultrasound to produce an image?

Answer 4

reflections and echoes in path of beam, so sound goes back to transducer

Question 5

frequency of ultrasound?

Answer 5

> 3 million Hz, so greater than our threshold for hearing

Question 6

how does an ultrasound investigation work?

Answer 6

100s of piezoelectric crystals along face of transducer. When an electric current is applied to these crystals, they change shape rapidly. The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward, with electrical to acoustic energy conversion. Conversely, when sound or pressure waves hit the crystals, they emit electrical currents. Therefore, the same crystals can be used to send and receive sound waves.

Question 7

basis of B mode (brightness) imaging?

Answer 7

2D image produced from linear array of transducers simultaneously scanning a plane through the body. Specular reflection occurs at large interfaces e.g. atheromatous plaque, scattering occurs at rough surfaces and small structures- smaller than wavelength of US beam. Resistance to ultrasound passage= acoustic impedence. Adjacent US beams formed across transducer face.

Question 8

how can distance from a reflector to transducer be measured?

Answer 8

as know speed of US in tissue, and can measure how quickly echoes return, so D=VxT

Question 9

how does impedence mis-match in B mode imaging affect reflection?

Answer 9

higher impedence mismatch, means a bigger difference in resitance to US passage between 2 adjacent materials, and this causes a stronger reflection from boundary e.g. plaque appears white, and blood black

Question 10

colour on B mode imaging display if high intensity reflection?

Answer 10

white e.g. plaque

Question 11

what is attenuation?

Answer 11

gradual loss of energy of US beam as it passes through deeper structures

Question 12

problem of high-frequency transducer?

Answer 12

doesn’t penetrate as far into body, so would be useful at looking at superficial structures

Question 13

advantage of high-frequency transducer?

Answer 13

good resolution

Question 14

disadvantage of wide shaped transducer?

Answer 14

poorer resolution, but may be used for aortic aneurysms to be able to look at whole area of aneurysm

Question 15

advantage of low-frequency transducer?

Answer 15

can penetrate more into body, so look at deeper structures

Question 16

what do colours mean of Doppler colour flow imaging?

Answer 16

brighter hue= faster velocity

red= flow towards transducer, blue= flow away from

Question 17

How can arterial stenoses be graded?

Answer 17

Using doppler indices: velocity increases across a stenosis, so more narrowing, higher velocity of blood flow, which is visible as a brighter hue on colour Doppler US

Question 18

advantages of duplex scanning compared to CT scanning?

Answer 18

non-invasive, portable, low cost, can repeat, no radiation, real time

Question 19

limitations of duplex scanning compared to CT scanning?

Answer 19

very operator dependent, so operator error

poorer resolution when looking at deeper structures

Question 20

limitations of Ankle brachial pressure index? (continuous wave doppler)

Answer 20

contraindicated if calcification of arteries e.g. in diabetes mellitus as less or incompressible arteries, will produce falsely elevated ankle pressure, so giving false -ves

Question 21

lower blood pressure in leg compared to arm is indicator of what?

Answer 21

peripheral vascular disease

Question 22

how is ankle BP index calculated?

Answer 22

Highest Ankle Systolic Pressure /

Brachial Systolic Pressure

Question 23

clinical applications of doppler ultrasound?

Answer 23

carotid stenoses
AAA
ankle brachial pressure index
peripheral assessments- DVT, varicose veins
transcranial doppler

Question 24

process of ankle brachial pressure index measurement?

Answer 24

Use a Doppler and a sphygmomanometer
Measure dorsalis pedis and posterior tibial pulses
Compare pressure to brachial
Calculation: Ankle systolic/brachial systolic
Less than 1 – abnormal
The smaller the value the worse the disease
Greater than 1 - normal

Question 25

usefulness of a flat/linear probe and a set probe?

Answer 25

Flat/linear
•	High frequency
•	Higher resolution
•	Poor penetration
Set
•	Lower frequency
•	Lower resolution
•	Greater penetration

Question 26

how to tackle loss of signal from deeper structures?

Answer 26

Deeper structures
Produce a weaker signal
Could lead to an unbalanced image
But can use Gain controls
 Boost the intensity of returning signal
 Intensity is the same regardless of depth of tissues
• Balances images

Question 27

Doppler effect: when sound approaches an object, how is the frequency?

Answer 27

it is higher

Question 28

what does a continous wave doppler achieve?

Answer 28

picks up all vessels- arteries and veins, at the same time

Question 29

function of duplex scanning in looking at stenoses?

Answer 29

Identify position of blockage
Extent and severity of disease
      Better than angiogram
•	Cheaper
•	No radiation
•	Less invasive

Question 30

how can varicose veins be sealed?

Answer 30

laser tment

Question 31

what will veins not do if DVT?

Answer 31

won’t collapse if clot present