ULTRASOUND

Question 1

To understand how an image on the screen of an ultrasound system is produced, it is necessary to examine the features of a __ and the __ that it creates and receives.

Answer 1

transducer; ultrasound beams

Question 2

A transducer consists of many __ elements that convert electrical energy into __ and vice versa.

Answer 2

piezoelectric ; sound energy

Question 3

Ultrasound, in the form of a __, propagates from the surface of the transducer into soft tissue

Answer 3

pulsed beam

Question 4

__ are absorbed in part by tissue but are also reflected back to the transducer where they are detected.

Answer 4

Sound waves

Question 5

are able to process many pulsed beams instantly and thus create real-time images for diagnostic use.

Answer 5

Ultrasound scanners

Question 6

The ability of an ultrasound system to distinguish between two points at a particular depth in tissue, that is to say, __ and __ , is determined predominantly by the transducer.

Answer 6

axial resolution ; lateral resolution

Question 7

(also called longitudinal) resolution is the minimum distance that can be differentiated between two reflectors located parallel to the direction of ultrasound beam.

Answer 7

AXIAL RESOLUTION

Question 8

Mathematically, it is equal to half the spatial pulse length. Axial resolution is high when the spatial pulse length is ___.

Answer 8

short

Question 9

is the product of the number of cycles in a pulse of ultrasound and the wavelength

Answer 9

Spatial pulse length

Question 10

Most pulses consist of __ cycles, the number of which is determined by damping of piezoelectric elements after __ : high damping reduces the ___ in a pulse and hence shortens spatial pulse length

Answer 10

two or three ; excitation; number of cycles

Question 11

is determined by the operating frequency of the transducer; transducers of high frequency have thin piezoelectric elements that generate pulses of short wavelength (Fig. 1B). The __ is equal to twice the thickness of the elements in the transducer.

Answer 11

wavelength of a pulse

Question 12

These potentially desirable characteristics, that is to say, damping and high frequency, have the following problems related to attenuation.

Answer 12

(i) Excessive damping is associated with loss of amplitude and hence low-intensity ultrasound (Fig. 1B).
(ii) High-frequency pulses are attenuated well in soft tissue which means that they may not be reflected back sufficiently from deep structures, for detection by the transducer.

Question 13

Attenuation is expressed __ and is determined by both the __ and ___ from the transducer.

Answer 13

decibels; frequency of ultrasound and depth of the reflector

Question 14

At a particular frequency, increasing attenuation at longer depths from the transducer is minimized by progressive amplification of the power of the reflected pulses. This process is called__ and is expressed as a ___, in decibels, similar to attenuation.

Answer 14

‘Time Gain Compensation’ ; logarithmic ratio of power

Question 15

with respect to an image containing pulses of ultrasound scanned across a plane of tissue, is the minimum distance that can be distinguished between two reflectors located perpendicular to the direction of the ultrasound beam.

Answer 15

LATERAL RESOLUTION

Question 16

Lateral resolution is __when the width of the beam of ultrasound is __.

Answer 16

high; narrow.

Question 17

The width of the beam and hence lateral resolution varies with distance from the transducer, that is to say:
(i)At the transducer, beam width is approximately equal to the width of the transducer.
(ii) Then, the beam converges to its narrowest width which is half the width of the transducer, at a perpendicular distance from the transducer called the ___ (Fig. 2A). The region of space subtended by the beam is called the ___
(iii) At a distance greater than the near-zone length, that is to say in the __, the beam diverges such that it becomes the width of the transducer, when the distance from the transducer to the reflector is twice the near-zone length. Here, lateral resolution ___.

Answer 17

near-zone length; near zone (Fresnel’s zone); far zone(Fraunhofer’s zone); decreases

Question 18

Lateral resolution is high when near-zone length is __

Answer 18

long

Question 19

Factors that increase near- zone length include:

Answer 19

(i) short wavelength;
(ii) high frequency of transducer, comprising thin piezoelectric elements with high damping (frequency and wavelength are inversely related);
(iii) large aperture (wide element width).

Question 20

When low-frequency transducers are utilized, lateral resolution __: in this situation, near-zone length is short which means that structures beyond the near zone are scanned by a __

Answer 20

deteriorates; divergent beam

Question 21

Four different modes of ultrasound are used in medical imaging

Answer 21

A-mode
B-mode
M-mode
Doppler mode

Question 22

__ are (called grating lobes) surrounding the main beam from a multi-element transducer may cause artifact and reduce lateral resolution. Grating lobes may be minimized by driving the elements at variable voltages in a process called a __

Answer 22

extraneous beams ; podization.

Question 23

is the simplest type of ultrasound. A single transducer scans a line through the body with the echoes plotted on screen as a function of depth.

Answer 23

A-mode

Question 24

Therapeutic ultrasound aimed at a specific tumor or calculus is also __, to allow for pinpoint accurate focus of the destructive wave energy.

Answer 24

A-mode

Question 25

is used to principally to measure the depth of interfaces and their separation accurately.

Answer 25

A-mode imaging

Question 26

For A-mode ultrasound, echoes appear on cathode ray tube as a __

Answer 26

series of blips.

Question 27

In B-mode ultrasound, a ___ simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen.

Answer 27

linear array of transducers

Question 28

the intensity of the echo is represented by a bright dot on the CRT.

Answer 28

B-mode imaging

Question 29

Depending upon the transducer design, B-mode images will be formatted as __

Answer 29

rectangular or sector views

Question 30

a rapid sequence of B-mode scans whose images follow each other in sequence on screen enables doctors to see and measure range of__, as the organ boundaries that produce reflections move relative to the probe.

Answer 30

M-mode; motion

Question 31

This mode makes use of the __ in measuring and visualizing blood flow. Sonography can be enhanced with __, which employ the __ to assess whether structures (usually blood) are moving towards or away from the probe, and its relative velocity.

Answer 31

Doppler mode; Doppler effect; Doppler measurements

Question 32

It refers to the changes in frequency resulting from a moving sound source.

Answer 32

Doppler Effect

Question 33

Objects moving toward the detector reflect sound that has a ___. The __ in frequency is associated with a __ in wavelength.

Answer 33

higher frequency; increase; reduction

Question 34

Objects moving away from the detector reflect sound that has a __. The __ in frequency is associated with an __ in wavelength.

Answer 34

lower frequency; reduction; increase

Question 35

Real time imaging is possible because of the development of the __ and the __.

Answer 35

digital scan converter and the microprocessor

Question 36

Real time imaging is to diagnostic ultrasound as fluoroscopy is to x-ray imaging - both are called __

Answer 36

dynamic imaging

Question 37

TYPES OF REALTIME IMAGERS

Answer 37

Mechanical array
Annular array
Linear array
Curvilinear array
Phased array

Question 38

STRAIGHT LINEAR ARRAY

Answer 38

• breast
• carotid
• muscles
• penis
• testis

Question 39

CURVED LINEAR ARRAY

Answer 39

• obstetrics

Question 40

SECTOR SCANNER -

Answer 40

• abdomen
• cardiology
• gynecology
• neonatal