Blood - chapter 1

Question 1

What does the strength of signal received by the transducer depend on?

Answer 1

The backscattering of ultrasound by blood and the attenuation of ultrasound by tissue.

Question 2

What is the approximate difference in echo strength between blood and tissue?

Answer 2

43dB

Question 3

How can you reduce the speckle pattern of blood within the lumen?

Answer 3

Decrease the dynamic range

Question 4

Why do reverberation artefacts occur of vessel walls inside the lumen?

Answer 4

Vessel walls are strong specular reflectors

Question 5

What is the relative backscatter of blood?

Answer 5

76.9 x 10-6 cm-1Sr-1

Question 6

Why is a high doppler angle sometimes used?

Answer 6

In deep structures, penetration into the lumen is best when the transducer is closer to perpendicular

Question 7

What component of blood is responsible for backscattering?

Answer 7

RBCs

Question 8

What is the percentage volume of whole blood occupied by RBCs known as?

Answer 8

Haematocrit

Question 9

What is a typical haematocrit %?

Answer 9

45% in men, 42% in women

Question 10

What is Rayleigh Scattering?

Answer 10

The scattering of sound in all directions by particles much smaller than its wavelength

Question 11

What does echo signal strength depend on?

Answer 11

The size and number of scatterers - very strong dependence on scatterer size

Question 12

What happens as haematocrit increases > 10%?

Answer 12

There are enough RBCs to form groups of cells that act as single scatterers

Question 13

What happens at physiological haematocrit levels?

Answer 13

There are so many RBCs present, they can no longer be considered individually

Question 14

What are the 3 situations when the echogenicity of blood is increased?

Answer 14

1. Stationary blood - Rouleaux
2. Turbulent flow - plasma and RBCs pulled apart
3. Thrombus