Transcript QUALITY ASSURANCE & ACR ACCREDITATION

QUALITY ASSURANCE
&
ACR ACCREDITATION
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WHY ACR ?
Images property of Yu Liu PhD
WHY ACR ?
Images property of Yu Liu PhD
IMAGE QUALITY
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Diagnostic Accuracy
Signal to Noise (SNR)
Contrast to Noise (CNR)
Spatial Resolution
Absence of Artifacts
SNR- Is the relationship between MR signal and background
noise.
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Signal- Is the processing of induced voltage (Faraday’s Law of
Induction) in a receiver coil after excitation.
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The voltage is dependent on the strength of the magnet (NMV) used for
induction.
Signal is not the only factor contributing to the quality of the
image. Noise is refer as unavoidable background signals
By evaluating SNR we can assess the overall quality of the MR
Signal
Images property of e-MRI.org
CONTRAST to NOISE RATIO
(CNR)
CNR: Also refers as Contrast Resolution ,is the ability to
distinguish between differences in intensity in an
image. CNR is influence by the SNR and spatial
resolution in the MR image.
CONTRAST to NOISE (CNR)
CNR : Is the ability to distinguished between two adjacent structures or tissue
Matrix (In-Plane)
192 x 256
224 x 320
CONTRAST to NOISE (CNR)
CNR : Is the ability to distinguished between two adjacent structures or tissue
Slice Thickness
5mm
1.5mm
IMAGE QUALITY
SNR/Spatial Resolution & Absence of Artifacts
Scanner Performance
ACR (Q/A)
The MRI Accreditation Program evaluates the qualifications
of personnel, the quality control program, MR safety policies
and image quality specific to MRI.
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Quaterly Preventive Maintenance
Weekly Technologist Phantom
– Phantom Scans
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Annual Testing by a Physicist
– Phantom Scans
– Coil Testing
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Re- Accreditation by the ACR
– Every three years
ACR MRI ACCREDITATION
Getting Started:
• Get the Team Together
– Radiologist (Medical Director MRI)
– Chief Technologist (Clinical Imaging)
– MR Physicist (Scanner Testing)
• Buy ACR Phantom (JM Specialty Part – San Diego,CA)
• Weekly Technologist Phantom (3-6 months ACR
recommends)
• Scanner Testing by a Physicist (Annual/Initial)
• Apply online for ACR Accreditation (Select Module desire)
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Survey Agreement (Site)
Six Modules (Brain,Spine,Msk,Body,Vascular,Cardiac )
45 days to complete your submission and return it to ACR
Could go back 6 months to provide clinical images.
ACR PHANTOM
Level Phantom Correctly
Images property of Chen Lin PhD
ACR PHANTOM
ACR WEEKLY PROTOCOL :
• Sag Scout
• Ax T1 SE
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TR 500
TE 20
FOV 25
Matrix 256 x 256
Slices 11
Slice Thickness 5mm
Gap 5mm
ACR PHANTOM
CENTER FREQUENCY:
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Set to the resonance frequency of water protons
Depends on Main Magnetic Field (1.5T vs. 3T)
Affects fat saturations
Severity off resonance artifacts
ACR recommended criteria < +/- 1.5ppm different between weekly test.
Possible Causes of Failures :
• Phantom not Isocenter
• Magnet Drift
ACR PHANTOM
TRANSMITTER GAIN:
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RF power required to achived certain flip angles
Depends on RF Coils,Phantom,and Pulse Sequence
Should remain constant
Severity off resonance artifacts
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Possible Causes of Failures :
• Defective RF Transmitter Coil
• RF Amplifier
ACR PHANTOM
ACR Sequence Positioning:
ACR PHANTOM
Geometric Accuracy: Related to image distortion
190 mm
148 mm
Images property of Chen Lin PhD
ACR PHANTOM
Geometric Accuracy: Related to image distortion
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Possible Causes of Failures
• Phantom not level appropriate
• Gradient Non Linearity
• Eddy Currents
ACR recommended criteria +/- 2mm in all directions
ACR PHANTOM
SPATIAL RESOLUTION:
• Ability to detect differences between small structures
• Depends on Pixel/Voxel size (FOV/Matrix)
ACR PHANTOM
Spatial Resolution:
ACR recommended criteria
<= 1.0mm
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Possible Causes of Failures
• Poor SNR
• Bad Receiver Coil
• Eddy Currents
• Gradient Calibration
1.1 mm
1.0mm
0.9mm
ACR PHANTOM
Low Contrast Detectability (LCD):
• Ability to detect objects with subtle differences in signal intensity
Possible Causes of Failures
• Poor SNR
• Inaccurate slice positioning
• Artifacts
ACR PHANTOM
Additional Testing:
• Image uniformity
• Slice Thickness
• Ghosting/Artifacts
ACR PHANTOM
Artifacts:
Zipper/RF Leak
ACR ACCREDITATION
Clinical Modules:
Images property of Chen Lin PhD
ACR ACCREDITATION
Clinical Images Evaluations :
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Pulse Sequence
Image Contrast
Anatomical Coverage
Imaging Planes
Spatial Resolution (Pixel & Voxel size)
Artifacts
ID Exam
ACR ACCREDITATION
Tips & Suggestions
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All clinical images must be done in patients (No
Volunteer).
Include all identification required (Patient &
Parameters).
DICOM images with a viewer.
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Except Cardiac and Phantom DICOM only
Record True Matrix,not Reconstructed Matrix (Pixel
size).
Check for Artifacts prior to submission .
Present best cases,no motion on images.
Submit all required sequences,include localizers.
ACR ACCREDITATION
Be Aware :
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Spine Axial GRE T2*/TSE at 3T,CSF must be bright(no
flow artifact)
MRCP include entire Biliary Tree Anatomy (Best when
using 3D rather 2D MRCP)
Liver MRI ,use flouro technique to acquired true
arterial phase.
CE-MRA,no venous contamination (Neck Carotid)
Cardiac MRI ,Viability exam myocardium fully
saturated (Scar visible)
Considered using Dixon for In/Out Phase at 3T
Forms fill them out correctly(take your time)
ACR ACCREDITATION
Breast Accreditation: Facilities performing breast
MRI must have the capacity to perform
mammographic correlation, directed breast
ultrasound, and MRI-guided intervention, or create
a referral arrangement with a cooperating facility
that could provide these services.
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Radiologists – Requirement of Breast MRI read in the last 36 months
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Facilities must use the Breast Imaging Reporting and Data System (BIRADS®)7 final assessment codes and terminology for reporting and
tracking outcomes.
Technologists – Requirement of 50 MRI Breast examination prior 24
months.
ACR ACCREDITATION
Breast Accreditation:
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Facility must submit 1 case with a known, enhancing, biopsyproven carcinoma clearly visible in the breast parenchyma.
No Masectomy cases
Pulse Sequences
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T2W/Bright Fluid
T1W (Pre,Arterial,Delay) - Bilateral
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Slice Thickness < 3mm(No Gap),In Plane Resolution/Pixel Size < 1.0
ACR ACCREDITATION
Summary:
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ACR Q/A Phantom needs to be done weekly
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Yearly Evaluation (PhD)
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Compares year to year scanner performance
ACR Accreditation
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Check scanner image quality
Done every three years ,includes clinical images and phantoms.
Why ACR ?
Is all about image quality!!!!!!