(2nd) 2

known combinations of waves

This allows the beam to be "shaped" by using

reflection

The most important single interaction process for purposes of generating an ultrasound image is

specular reflection

Best reflection occurs from a smooth surface and is called

ACOUSTIC IMPEDANCE

The ratio of the pressure over an imaginary surface in a sound wave to the rate of particle flow across the surface.

• Angle of incidence

• Acoustic Impedance

• Width of the tissue boundary

• Angle of tissue boundary

Reflection depends on:

• Z=pc

• Z = acoustic impedance

• p = density

• c = velocity / speed of sound

fundamental properties of matter:

0.0004

Air ACOUSTIC IMPEDANCE

1.38

Fat ACOUSTIC IMPEDANCE

1.54

WATER (50°c) ACOUSTIC IMPEDANCE

1.58

Brain ACOUSTIC IMPEDANCE

1.61

Blood ACOUSTIC IMPEDANCE

1.62

Kidney ACOUSTIC IMPEDANCE

1.65

Liver ACOUSTIC IMPEDANCE

1.70

Muscle ACOUSTIC IMPEDANCE

7.8

Skull (bone) ACOUSTIC IMPEDANCE

330

Air speed (m/s)

600

Lung speed (m/s)

1450

Fat speed (m/s)

1480

Water speed (m/s)

1540

Soft tissue average speed (m/s)

1600

Muscle speed (m/s)

4080

Bone speed (m/s)

0.0004 × 10(6 sa babaw)

Air Z (rayls)

0.18 × 10(6)

Lung Z (rayls)

1.34 × 10(6)

Fat Z (rayls)

1.48 × 10(6)

Water Z (rayls)

1.62 × 10(6)

Soft tissue average Z (rayls)

1.71 × 10(6)

Muscle Z (rayls)

7.8 × 10(6)

Bone Z (rayls)

ANGLE OF INCIDENCE

The amount of reflection is determined by the angle between the sound beam and reflecting surface

Perpendicular Reflection

Incident beam is perpendicular to the tissue boundary

T=1-R*100

Percentage of beam transmitted is given by

Percentage of beam transmitted

T=

Specular Reflection

Incident angle is equal to the transmitted angle

"noisy" background

The loss in energy results in a

displayed

If the signal-to-noise ratio is good then a clear picture will be

blurry picture

A poor signal-to-noise ratio results in a

• R= (Z2-Z1/Z2+Z1)2*100

• R = Percentage of beam reflected

• Z1 = Acoustic impedance of medium 1

• Z2 = Acoustic impedance of medium 2

Percentage of beam reflected is given:

• Transducer Frequency

• Acoustic Impedance

• Acoustic Impedance Mismatch

factors that affect attenuation are:

- constructive interference

- destructive interference

two extremes of interference:

ultrasound transducer

is a critical device used in medical imaging to both emit and receive ultrasound waves for diagnostic purposes.

emit and receive ultrasound waves

An ultrasound transducer is a critical device used ni medical imaging to both __ for diagnostic purposes.

PIEZOELECTRIC EFFECT

is the ability of certain materials (like crystals) to generate electric charges when mechanical stress is applied to them.

CONVERT ELECTRICAL ENERGY INTO MECHANICAL VIBRATIONS (emitting ultrasound waves)

In ultrasound transducers, piezoelectric crystals

electrical signals (receiving echoes)

In ultrasound transducers, mechanical vibrations into

• Lead Zirconate titanate (PZT)

• Poly Vinylidene Difluoride (PVDF)

PIEZOELECTRIC CRYSTALS:

Lead Zirconate titanate (PZT) and Poly Vinylidene Difuoride (PVDF)

These crystals are responsible for converting electrical signals into mechanical vibrations and vice versa, forming the basis of ultrasound emission and reception.

matching layer

often made of a resin-based material, helps to optimize sound wave transmission between the transducer and the patient's skin by reducing impedance mismatch.

optimize sound wave transmission

A matching layer, often made of a resin-based material, helps to _ between the transducer and the patient's skin by reducing impedance mismatch.

Endocavitary probes

provide the opportunity to perform internal examinations of the patient. Therefore, they are designed to fit specific body orifices.