Chapter 22 Flashcards
Quality assurance
The routine, periodic evaluation of an ultrasound system to guarantee optimal image quality.
Time interval for QA
Time interval depends on clinical circumstances but must be done routinely.
Is QA a medical and legal necessity for every imaging facility
Yes
Assessment of system components include
Repairs,
Preventative maintenance,
Record keeping
Who is responsible for QA
Sonographers
Goals of Quality
Assurance
Guarantee proper orientation of the system,
Detect gradual changes, Minimize downtime,
Reduce the number of non-diagnostic exams,
Reduce the number of repeat scans
Methods for Quality
Assurance
Test under known, defined conditions.
Use constant instrument settings,
Use a phantom with measureable characteristics,
Image in an identical environment
completely unbiased, factual, repeatable, able to be counted.
Objective
Objective is
The same, even when obtained by different people
influenced by an individuals experiences or beliefs, cannot be verified using concrete facts or figures, affected by opinion.
Subjective
Varies from person to person
Subjective
Quality Assurance should be based on
Objective standards
Devices for Quality
Assurance
Tissue equivalent phantom, Doppler phantom, beam profile/ slice thickness phantom
Tissue Equivalent Phantom: ultrasonic features are similar to
Soft tissue
Tissue Equivalent Phantom is used to evaluate
characteristics such as gray scale and tissue texture
Tissue equivalent phantom contains
Small scatterers that act like soft tissue
With _ phantoms nylon may be embedded into the phantom to produce reflections at strategic locations
Tissue equivalent
With _ phantoms structures that mimic hollow cysts and solid masses are also embedded into the phantom
Tissue equivalent
Tissue Equivalent
Phantom
Simulate tissue properties, allowing assessment of:
Detail resolution, Contrast resolution, Penetration,
Dynamic range, Time-gain compensation
Doppler Phantom
• Assess the characteristics of
All Doppler modalities •Pulsed wave
•Continuous wave
•Color
•Power
Doppler phantom includes a _ which propels fluid through vessels embedded in a tissue equivalent phantom.
Circulation pump
What does a circulation pump do?
propels fluid through vessels embedded in a tissue equivalent phantom.
Other Doppler phantoms contain _
vibrating strings or moving belts.
Doppler test objects and flow phantoms enable the evaluation of:
Spectral speed calibration, Gate location,
Penetration of spectral and color Doppler instruments
Slice Thickness
Phantom
assesses the
slice thickness and its effect upon image quality
_ Contains a diffuse scattering plane that is at an angle to the incident sound beam.
Slice thickness phantom
Slice thickness phantom contains
a diffuse scattering plane that is at an angle to the incident sound beam.
Slice thickness phantom: medium mimics _
Soft tissue
Slice thickness phantom measures
The beam geometry perpendicular to the imaging plane
the ability of a system to display low-level
echoes.
Sensitivity
Normal sensitivity
settings at which all the pins, solid masses, and cystic structures in the test phantom are accurately displayed.
Normal sensitivity: _, _ , and _ are adjusted to establish normal sensitivity
Output power, TGC, and amplification
evaluated with the output power and amplification of the system set to the maximum practical levels.
Maximum sensitivity
the region close to the transducer where
images are inaccurate. Extends from the transducer to the shallowest depth from which meaningful reflections appear.
Dead zone
Dead zone
the region close to the transducer where
images are inaccurate. Extends from the transducer to the shallowest depth from which meaningful reflections appear.
Should info from the dead zone be used in a diagnostic setting?
No
Dead zone results from
transducer ringing and the time it takes the system to switch from the transmit to the receive mode.
Dead zone is assessed with
the shallowest series of pins in a test object.
Dead zone: _ depth at which uniform tissue texture appears in a tissue equivalent phantom
Shallowest
Higher frequency transducers have a _ dead zone than lower frequency transducers
Thinner
_ positioned between the transducer and the patient allows accurate imaging of important superficial structures.
Stand-off or gel pad
An increasingly deeper dead zone may indicate a
cracked crystal, detached backing material, or a longer pulse duration.
The ability of the system to place reflections in proper positions while imaging from different orientations.
Registration accuracy
Registration accuracy
The ability of the system to place reflections in proper positions while imaging from different orientations.
describes the system’s accuracy in placing reflectors at correct depths located parallel to the sound beam.
Range accuracy
Range accuracy
describes the system’s accuracy in placing reflectors at correct depths located parallel to the sound beam.
Range accuracy aka
Vertical depth calibration
Range accuracy: Differences between the ultrasound scan and actual pin location may be caused by
system malfunction or the speed of sound in the phantom is different than 1,540 m/s.
the system’s ability to place echoes in their correct position when the reflectors are perpendicular to the sound beam.
Horizontal calibration
Horizontal calibration
the system’s ability to place echoes in their correct position when the reflectors are perpendicular to the sound beam.
digital calipers should be checked in both vertical and horizontal directions periodically.
Distance Measurement Accuracy
Distance Measurement Accuracy
digital calipers should be checked in both vertical and horizontal directions periodically.
The _ is the depth at which the intensity is the highest and the beam is the narrowest
Focus
_ zone surrounds the focus
Focal
Lateral resolution is _ in the focal zone because
Excellent,
The beam is narrow
The focus of phased array transducers must be
Carefully evaluated
Axial resolution is evaluated by
scanning sets of successively closer spaced pins within the phantom.
Axial resolution: pins are _ to the sound beam
Parallel
The smallest distance at which two pins positioned parallel to the sound beam are displayed as two distinct echoes.
Axial resolution
The minimum distance at which two side-by-side pins are displayed as two distinct images.
Lateral resolution
Lateral resolution: Another method is to measure _. This approximates _
the width of reflections on the display that are created by point targets in the phantom.
Beam diameter at that depth
Uniformity describes
the system’s ability to display similar reflectors in the phantom with echoes of equal brightness. With proper TGC, identical reflectors should have the same appearance on the monitor, regardless of depth.
Compensation Operation or Uniformity: The system should
accurately display hollow structures as anechoic and solid structures as hyperechoic
