Chapter 21: Quality Assurance

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1

Quality Assurance

routine, periodic evaluation of an ultrasound system to quarantee optimal images.

2

Four requirements for a quality assuance program are:

1. assessment of system componenets
2. repairs
3. preventiative maintenance
4. record keeping

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Goals of Quality assurance

proper operation of equipment
detect gradual changes
minimize downtime
reduce non-diagnostic exams
reduce repeat scans

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AIUM 100 mm Test Object

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fluid filled tank containing stainles steel pins or plastic strings

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What properties of the AIUM 100 mm Test object makes a good evaluation test

the speed of sound is identical to that of soft tissue.

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One draw back of the AIUM 100 mm Test object

it does not have the same attenuation properties of soft tissue so grayscale can not be evaluated.

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What does the AIUM 100 mm Test object evaluate?

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Axial Resolution

Lateral Resolution

Electronic caliper accuracy

Dead zone

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How is Axial Resolution evaluated?

when the pins in the test object are parallel to the sound beam's main axis.

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How is Lateral Resolution evaluated?

when the pins in the test object are perpendicular to the sound beam's main axis.

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How is Electronic caliper accuracy evaluated?

by comparing the distances between reflections on the display with the actual distances in the test object.

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How is Dead zone evaluated?

by scanning the pins located as the top of the test object, very close to the transducer.

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Tissue Equivalent Phantom

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has ultrasonic features imilar to soft tissue.

speed of sound
attenuation
scattering characteristics
echogenicity

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How is grayscale evaluatied with the Tissue Equivalent Phantom?

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it contains small scatterers that resemble soft tissue. Structures that mimic hollow cysts and solid masses are imbedded in the phantom.

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Doppler Phantom

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device of choice for evaluating doppler systems.

moddern doppler phantoms include a circulation pump which propels fluid through vessels embedded in a tissue equivalent phantom.

older versions have vibrating strings and moving belts

15

What does a Doppler Phantom evaluates?

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pulsed mode
continuous wave mode
color mode
power mode

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Slice Thickness Phantom

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assesses the slice thickness and its effects upon image accuracy.

contains a diffuse scattering plane at an angle to the incident sound beam,

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Minimum Sensitivity evaluation

assesses the weakest echo signal that is accurately displayed.- low level echos in the far field

setting the TGC flat, then increasing gain from the minimum value to the gain when a deep rod in the test object is displayed.

the setting should not vary from on routine evaluation to the next.

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Normal Sensitivity

all the pins, solid masses and cystic structures in the test phantom are displayed.

Ouput power, TGC, and amplification are adjusted to establish normal sensitivity.

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Maximum Sensitivity

evaluated with the the output power and amplification of the system set to maximum practical level

the setting should not vary from on routine evaluation to the next.

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Dead Zone

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the region close to the transducer where images are inacurate. It extends from the transducer to the shallowest depth from which meaningful reflections appear.

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How is the dead zone evaluted

with the shallowest pins in the test object

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Higher frequency transducers will have a thinner or thicker dead zones?

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thinner

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WHat does an increasingly deeper dead zone indicate?

cracked crystal
detached backing material
longer pulse duration

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Registration Accuracy

the ability of the sytem to place reflects in proper positions from different orientations

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Depth Calibration

Range Accuracy

describes the system's accuracy in placing reflectors at correct depths

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Horizontal Calibration

describes the system's accuracy in placing reflectors at position perpendicular to the sound beam

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