(b) Brain tissue has a density of 1 . 04 × 10 3 kg m - 3 and ultrasound travels at 1 . 58 × 10 3 m s - 1 through it. Calculate the acoustic impedance of brain tissue.

Given, ρ = 1 . 04 × 10 3 k g m - 3 c = 1 . 58 × 10 3 m / s Acoustic impedance of brain tissue is given by Z = ρ c = 1 . 04 × 10 3 × 1 . 58 × 10 3 = 1 . 64 × 10 6 m 2 s - 1

Determine the fraction of the intensity of an ultrasound beam that is reflected when a beam is incident normally on a boundary between water and fat. (Use values from Table ) Material Density / kg m - 3 Speed of sound / ms - 1 Acoustic impedane / 10 6 kgm - 2 s - 1 Lead zirconate titanate 7650 3790 29 . 0 Quartz 2650 5700 15 . 1 Polyvinylidese diflouride 1780 2360 4 . 20

Fraction of intensity is given by I r I o = ( Z 2 - Z 1 ) 2 ( Z 2 + Z 1 ) 2 = ( 1 . 34 - 1 . 50 ) 2 ( 1 . 34 + 1 . 50 ) 2 = 3 . 2 × 10 - 3

For ultrasound of frequency 3 . 5 MHz , the acoustic impedance of muscle is 1 . 78 × 10 6 kg m - 2 s - 1 , and that of soft tissue is 1 . 63 × 10 6 kg m - 2 s - 1 . Calculate the percentage of the incident ultrasound reflected at a muscle-soft tissue boundary.

The percentage of the incident ultrasound reflected at a muscle soft tissue boundary is I r I o = ( Z 2 - Z 1 ) 2 ( Z 2 + Z 1 ) 2 = ( 1 . 78 - 1 . 63 ) 2 ( 1 . 78 + 1 . 68 ) 2 = 0 . 0019 = 0 . 19 %

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The reflection of ultrasound allows the image to be generated by the ultrasound machine.

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Important Questions on Medical Imaging

EASY

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

SONAR is an application of acoustics.

HARD

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

(b) Brain tissue has a density of

1.04 \times 10^{3} kg m^{- 3}

and ultrasound travels at

1.58 \times 10^{3} m s^{- 1}

through it. Calculate the acoustic impedance of brain tissue.

HARD

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

Determine the fraction of the intensity of an ultrasound beam that is reflected when a beam is incident normally on a boundary between water and fat. (Use values from Table )

Material	$Density / {kg m}^{- 3}$	$Speed of sound / {ms}^{- 1}$	$Acoustic impedane / 10^{6} {kgm}^{- 2} s^{- 1}$
Lead zirconate titanate	$7650$	$3790$	$29.0$
Quartz	$2650$	$5700$	$15.1$
Polyvinylidese diflouride	$1780$	$2360$	$4.20$

MEDIUM

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

What do you mean by the acoustics of buildings? Suggest four steps that can be taken, while constructing buildings, to avoid the problems which may occur due to multiple reflection of the sound.

EASY

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

What are the Essential and Important Differences between A-Scan and B scan ?

HARD

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

(c) This is the trace formed on the screen of an oscilloscope when ultrasound is reflected from the front and rear surfaces of the head of a foetus. The time-base of the oscilloscope is set at $10 μ {siv}^{- 1}$ .

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(ii) Calculate the diameter of the head of the foetus.

HARD

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

Piezo-electric crystals have many applications other than in ultrasound scanning. For example, they are used in:

(d) the auto-focus mechanism of some cameras (to move the lens back and forth).

MEDIUM

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

Represent the union of two sets by Venn diagram for each of the following.

$X = {x | x$ is a prime number between $80$ and $100}$

$Y = {y | y$ is an odd number between $90$ and $100}$

HARD

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

Define the threshold of hearing.

HARD

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

Calculate the acoustic impedance of muscle tissue. (Density

= 1075 kg m^{- 3};

speed of sound

= 1590 m s^{- 1}

EASY

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

State any two application of acoustics

MEDIUM

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

B-scan is considered the _____ scan.

HARD

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

For ultrasound of frequency

3.5 MHz

, the acoustic impedance of muscle is

1.78 \times 10^{6} kg m^{- 2} s^{- 1}

, and that of soft tissue is

1.63 \times 10^{6} kg m^{- 2} s^{- 1}

.
Calculate the percentage of the incident ultrasound reflected at a muscle-soft tissue boundary.

EASY

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

The branch of physics which deals with the study of production, transmissions and reception of sound is called?

HARD

Physics>Modern Physics>Medical Imaging>Ultrasound Scanning

The ultrasound image shown in Figure clearly shows the baby's skin and some bones. Explain why these show up clearly while softer organs inside its body do not.

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