normal ultrasound week 2

Artifacts

Structure or feature on an ultrasound image that does not correspond to the actual anatomy being imaged

Artifacts in sonography may:

Misrepresent the size, shape, or location of anatomy

Display brightness that may not correspond to the actual reflectivity of the tissue reflecting the sound

Fail to display structures that are really there

Display structures that are not really there

Causes of artifacts

Improper equipment settings/technique

Interaction of sound with tissue

Physics assumptions built into design of ultrasound equipment

What does the ultrasound machine assume?

Sound travels in a straight line down the beam axis

Echoes originate from structures along beam axis

amplitudes of returning echoes directly correspond to the Echogenic nature of the structure producing the echo

The distance to reflectors corresponds to the round trip travel time of 13 microseconds/cm of depth

Propagation artifacts

Result of the way sound passes through tissue

Result of the way beam is constructed (equipment)

Result of how the sound interacts with the tissue (sound tissue artifact)

Slice thickness artifact (section thickness or partial volume artifact)

Loss of lateral or axial resolution results in blurring of image (two structures blended to be displayed as one)

Fix slice thickness artifact

Increase frequency

Focusing improves lateral resolution

Elevation resolution/slice thickness results in?

Appearance of echoes within and otherwise anechoic structure, like a blood vessel or cyst

Fix by changing beam position or focusing

Speckle artifact

Combination of constructive and destructive interference between scattered sound waves results in light and dark spots we see in tissue like the liver

Reverberation

Sound tissue artifact

Occurs when echoes “bounce” between the transducer and a strong reflector

Or bouncing between two strong reflectors

Types of reverberation

Comet tail

Ring down

Resonance

Mirror image

Fix reverberation

Changing transducer position, rolling patient, different frequency

Mirror image artifact caused by

Caused by sound interaction with large, curved reflector like the diaphragm and pleura

Mirror image artifact

Object anterior to the large reflector is interrogated by multiple scan lines of sound

Part of the sound energy that strikes the object is reflected back to the transducer, causing an accurate depiction of the object

Part of the energy reverberates through the object down to the large reflector (diaphragm) and is then belatedly reflected back to the transducer, resulting in additional depiction

Mirror image artifact also called?

Multi path reflection

Comet tail artifact

Result of multiple internal reflections within a small, highly reflective structure

Large difference in acoustic impedance between reflector and surrounding tissue causes a series of short path reverberations

Usually seen in anechoic or Hypoechoic areas, seen as short very Echogenic trail of bands posterior to reflection

Resonance (ring-down)

Occurs when sound strikes a gas bubble and causes it to expand and contract (vibrate)

Gas bubble acts as transmitter of ultrasound, leading to strong echoes behind bubble

No banding seen

Refraction

Bending of sound beam causes a reflector to be displaced laterally on the image and leads to distortion of size and shape

Occurs at boundaries where tissues involved have different propagation speeds and beam strikes boundary at an angle

Misregistration

Part of refraction, sound tissue artifact

object not displayed on the image ar its true location. Size and shape may be distorted

Defocusing

Part of refraction, sound tissue artifact

Loss of resolution die to disturbance of the sound beam structure

Leads to edge shadowing

Fix misregistration

Change transducer position

Fix defocusing

Using compound imaging or changing transducer position

Often recognized for what it is

Ghost image

Type of refraction

Sound tissue artifact

See duplicates of structures posterior to the rectus muscle

Fix ghost image

Moving transducer to different angle

Sometimes eliminate by using more or less probe pressure

Side lobes

Off-axis lobes of energy are created outside the main ultrasound beam, resulting in artificial display of echoes along the mean beam path

Equipment artifact

Fix side lobes

Changing transducer position

Adjusting focus

Grating lobes

Type of side lobe berated by the way that elements are spaced in an array transducer

Usually greater intensity than typical side lobes

Cumulative effect of multiple elements

Equipment artifact

Fix grating lobes

Moving transducer

Adjusting focus

Propagation speed error

When sound travels through tissue at a different speed from the 1540m/s assumed

What happens when sound travels through faster than assumed

Object displayed more superficial

What happens when sound travels slower than assumed

Object displayed deeper

Range ambiguity artifact

Ultrasound machine assumes that all echoes received are generated by the most recent transmitted pulse

If an object that generates an echo lies beyond the depth that can be displayed with a given PRF, it may but displayed more anteriorly in the image

Happens because echoes not received until after next transmitted pulse

The maximum depth accurately displayed is related to what

The pulse repetition frequency (PRF)

Fix range ambiguity artifact

Decrease PRF

Dirty shadow

Sound tissue artifact

When sound strikes strong interface and reverberates, creating blurry echoes that obscure anatomy

Fix dirty shadow

Compressing tissue displaces gas or rolling patient to different position

Sharp shadow

Sound tissue artifact

When sound strikes a very strong interface like bone, mineral salts, or Metal, that prevents transmission of the sound beam through object

Fix sharp shadow

Changing transducer position to see tissue posterior to object

Often used as diagnostic sign

Posterior enhancement

When sound passes through substance that doesn’t attenuate the beam so that stringer sound waves hit the tissue posterior to the structure

Fix posterior enhancement

Adjusting TGCs to reduce amplification of echoes posterior to low attenuator

Also used as diagnostic tool

Noise

Technique artifact

Caused by setting gain too high

See echoes in structures that should be anechoice

Fix noise

Decrease overall gain or TGCs

Banding

Technique artifacts

Caused by tightly focused transducer causing more intense beam in central portion of image while divergent in near and far fields (not common with current tech) -fix by changing probes

Also caused by inaccurate TGC setting (more common with current tech) -fix by adjusting TGC

Breathing artifact

Motion artifact

Blurring of images caused by organs moving as patient breathes

Also happens when picking up probe as freezing an image

Fix breathing artifact

Having patient hold breath

Use cine loop to go back

Edge shadowing artifact

Result of the refraction of the ultrasound beam along the edge of a curved structure that results in a decrease in the intensity of the ultrasound beam posterior to the curved edge

Information required for all exams

Patient name and identifier (dob)

Type of exam

Reason for exam

Ordering physician

Sonographer

Date of exam

Labeling info needed

Scan plane

Patient position (if not indicated, assume supine)

Area of interest

Specific transducer position in relation to a body surface landmark may be required

How specific does labeling need to be?

Specific enough another sonographer could come in and duplicate the image

Why do patients need to be NPO for 8 hours before abdominal exam

Minimized bowel gas to allow maximum visualization of organs

Ensures gallbladder not contracted

SSALT

Size: measure in 3 planes

Shape: ovoid, round, tubular, well defined, irregular

Acoustic properties: Echogenic, Hypoechoic, etc

Location: head of pancreas, long left liver, etc

Through transmission: posterior enhancement, posterior shadowing, no change

Depth

Center area of interest

Focus

Place at area of interest

For large organs, place posterior portion of AOI

Gain settings

Use liver as baseline, should be even medium gray

Adjust dynamic range to achieve appropriate contrast for AOI

Ultrasound advantages

No radiation exposure

Portable imaging modalities