Ultrasound Physics

Front 1

Hyperechoic

Back 1

Portions of an image that are brighter than surrounding tissues, or tissues that appear brighter than normal

Front 2

Hypoechoic

Back 2

Portions of an image that are not as bright as surrounding tissues, or tissues that appear less bright than normal.

Front 3

Anechoic

Back 3

Without echoes, echo free, black means fluid.

Front 4

Isoechoic

Back 4

Describes structures with equal echo brightness.

Front 5

Homongeneous

Back 5

A portion of tissue or a structure that has similar echo characterstics throughout.

Front 6

Hetrogenous

Back 6

Displaying a variety of different echo charatersitic within the tissue

Front 7

Artifacts

Errors in Imaging

Back 7

Not Real
Missing reflectors
improper brightness
Improper shape
Improper size
Improper position

Front 8

The casuses of artifacts

Back 8

-Violation of assumptions (acoustic artifacts)
-Equipment malfunction or design
-physics of ultrasound
-Interpreter error (anatomic pitfalls)
-Operator error

Front 9

6 basic assumptions of imaging systems

Back 9

1. Sound travels in a straight line

2. Sound travels directly to a reflector and back to the transducer

3. Sound travels exactly 1,540 meters/second

4. Reflections arise from the structures positioned along the beams main axis (side lobe and grating lobe)

5.Intensity of the reflections is related to the scatering characterstics of the tissue (shadowing and enhancement)

6. The imaging plane is extremely thin

Front 10

Reverberations

Back 10

Multiple eches appearing on the display as a result of US bouncing between two reflectors.
1. Multiple
2. Equally spaced
3. parallel to the sound beam
4. Deeper and along a straight line

Assumption # 1 Sound travels in a straight line

Front 11

Comet tail or ring down

Back 11

Appears as a solid line directed downward, merged reverberation.
1. Single, solid hyperechoic line
2.Long echo
3. Parallel to sound beam
4. A reverb with the 'space' squezzed out.

Hint when you have two strong reflectors there is a high differenc in the propagation speeds.
Assumption # 1 sound travels in a straight line

Front 12

Shadowing

Back 12

On occasions the US beam is unable to pass through a structure has a higher than usual attenuation.
1. shadow same as backround color
2.A result of too much attenuation
3. Abscence of true anatomy on scan
4.Parallel to the sound beam
Assumption # 5 Intensity of the reflections is related to the scattering characteristics of the tissue.

Front 13

Edge Shadow

Back 13

Reflector at the edge of a circular structure can also create an artifact. This is called SHADOWING BY REFRATION OR EDGE SHADOW.
1. Hypoechoic, background color
2. Due to beam spreading
3. Absence of true anatomy on scan
4. Parallel to the sound beam
Assumption #5 Intensity of the reflections is related to the scattering charateristics of the tissue

Front 14

Enhancement

Back 14

Occurs when the medium through which the sound travels has a lower attenuation rate than soft tissue.

Causes: Low attenuation
High focusing
1. Foreground color (brighter echoes)
2. Results from too little attenuation
3. Parallel to the sound beam
4. Beneath the structure with reduced attenuation

Assumption #5 Intensity of the reflections is related to the scattering charateristics of the tissue.

Front 15

Focal Enhancement or
Banding

Back 15

Another form of enhancement within the forcal zone. This results from the increase in beam intensity found within the focal zone of a sound beam
1. Hyperechoic when compared to tissues above the beneath the enhanced region.

2. A bright stripe within the focal zone (side to side band)

Caused by Hyper focusing

Assumption # 5 Intensity of the reflections is related to the scattering charateristics of the tissues,

Front 16

Mirror Image

Back 16

Sound may bounce off a strong reflector, called a mirror, in its path and be redirected.

1. Second copy of a reflector (duplicates) (extra reflections on the scan)

2. Artifact (A) located deeper than the true reflector (R)

3. Mirror lies on the straight line between the artifact and transducer

4. True reflector and artifact are equal distances from mirror.
Assumption #2 Sound travels directly to a reflector and back to the transducer.

Front 17

Propagation speed errors

Back 17

If the media through which the US travels doesn't propagate at 1.54 km/s then the assumed relationship between time and distance is invalid.

This results in:
1. Correct number of reflections on scan
2. Improper depths

Speed errors appear as a step off, split or cut

Assumption #3 Sound travels exactly 1,540 meters/second

Front 18

Synonyms for propagation
speed errors....

Back 18

1. Range error artifact

2. Range ambiguity artifact

Front 19

When the propagation speed is greater than 1,540 m/s The reflector speed will be placed too....

Back 19

shallow on the display

Front 20

When the propagation speed is less than soft tissue's the reflector will be placed too....

Back 20

deep on the display

Front 21

Refraction

Back 21

SOund changes direction when it strikes a boundary:
1. Obliquely
2. When the media has different propagation speeds.

-Duplicate picture of the true reflector
-Duplicate pictures are placed side by side of the true anatomic structure.

Assumption #1 Sound travels in a straight line

Front 22

Refraction artifact degrades what resolution?

Back 22

It degrades the lateral resolution.

Front 23

Mirror and refraction are both reflector artifacts the difference in the two is?

Back 23

Mirror is deeper

Refraction has the duplicate side by side

Front 24

Side lobes and Grating lobes

Back 24

Extra acoustic energy may be transmitted in directions other than the beam's main axis.

1. Duplicate image of reflector (too much information on a scan)

2. Side by side with the true reflector

Assumption #4 Reflections arise from the structures positioned along the beam's main axis

Front 25

Side Lobes

Back 25

Mechanical or single crystal transducer create side lobes

Echoes appearing on the sides of the beam

Front 26

Grating lobes

Back 26

Arrays create grating lobes

Front 27

Subdicing the grating
lobe artifact....

Back 27

Grating lobe artifact can be reduced or cured by dividing each element into even smaller miniature pieces this is called subdicing.

Front 28

Apodization

Back 28

Grating lobes are further reduced by exciting the subdiced elements with different voltages. Subelembets closer to the center of the sound beam are excited with the higher voltages, while the outermost sublelements, further away from the center, are excited with lower voltages. This is called apodization.

Front 29

Lobe artifact degrades which resolution?

Back 29

Degrades lateral resolution

Front 30

Slice Thickness

Back 30

Ultrasound beams have measurable thickness. However we asume that the imaging plane is razor thin. Occurs when beam has a greater width or size than the reflector.
Therefore the reflections produced by structures above or below the ideal imaging plane appears in the image. This may act to fill in hollow structures such as cysts.

Assumption #6 The imaging plane is extremly thin.

1. True reflector located outside of the idealized imaging plane appear on the image.

This artifact is cured with the 1 1/2 dimentional array transducer

Front 31

Cross Talk

Back 31

Found only in DOPPLER!

Special form of mirror image where the doppler spectrum appears above and below the basline.

True unidirectional flow appears bidirectional, flow that should appear only on one side of the basline, incorrectly appears on both sides

Assumption # 2 Sound travels directly to a reflector and back to the transducer

Front 32

There are two causes of cross talk they are....

Back 32

1. Doppler reciever gain is set too high.

2.Incident angle near 90 degrees when flow is at focus

Front 33

What is the assumption # for slice thickness?

Back 33

Assumption #6 The imaging plane is extremely thin

Front 34

What is the assumption # for comet tail or ring down?

Back 34

assumption #1 Sound travels in a straight line

Front 35

What is the assumption # for reverberations?

Back 35

Assumption #1 Sound travels in a straight line

Front 36

What is the assumption # for shadowing and edge shadowing?

Back 36

Assumption # 5 Intensity of the reflections is related to the scattering characteristics of the tissues (shadowing and enhancement)

Front 37

What is the assumption # for Enhancement

Back 37

Assumption #5 Intensity of the reflections is related to the scattering charateristics of the tissue (relates to shadowing and enhancement)

Front 38

What is the assumption # for forcal enhancement or Banding?

Back 38

Assumption # 5 Intensity of the reflections is related to the scattering charateristics of the tissue (shadowing and enhancement)

Front 39

What is the assumption # for Mirror image?

Back 39

Assumption # 2 Sound travels directly to a reflector and back to the transducer.

Front 40

What is the assumption # for propagation speed errors?

Back 40

Assumption # 3 Sound travels exactly 1, 540 meters/ second

Front 41

What is the assumption # for refraction?

Back 41

Assumption # 1 sound travels in a straight line

Front 42

What is the assumption # for side lobes and grating lobes?

Back 42

Assumption # 4 Reflections arise from structures positioned alon the beam's main axis

Front 43

What is the assumption # for cross talk?

Back 43

Assumption # 2 Sound travels directly to the reflector and back to the transducer.