carl r. keener, ph.d., dabmp, dabr … · transmitter gain/attenuation - siemens symphony ... acr...
TRANSCRIPT
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MARP, Inc.
ACR MRI QC Program July 2009
Carl R. Keener, Ph.D., DABMP, [email protected]
MARP &Medical Radiation Physics, Inc.
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MARP, Inc.
ACR MRI QC program
technologist’s roledaily/weekly QC tests• performing• action limits
physicist’s rolesetting up QC program• baselines• review
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MARP, Inc.
ACR MRAP QC requirements
2004 MRI QC Manual• QC program required in
August 2002• QC data required for
reaccreditation in July 2005
• QC data required for all new applications
weekly tests (originally daily):
• central frequency• transmitter gain
/attenuation• geometric accuracy• spatial resolution• low-contrast detectablilty• image artifact assessment
weekly:• laser film QC• visual checklist
annual:• medical physicist / MR
scientist* performance evaluation
* in this talk , "medical physicist" will be used instead of "qualified medical physicist/MR scientist"
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MARP, Inc.
NoseChin
ACR MRI phantom
J.M. Specialty Parts11689-Q Sorrento Valley RoadSan Diego, CA 92121(858) 794-7200
$1050previously $730
delivery6-8 weeks without MRAP number2-3 weeks with MRAP numberorder without MRAP, then call to add MRAP
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MARP, Inc.
ACR MRAP QC requirements
weekly (formerly daily)• phantom setup• central frequency• transmitter gain
/attenuation• geometric accuracy• spatial resolution• low-contrast detectablilty• image artifact assessment
weekly:• laser film QC• visual checklist
annual:• physicist (or MRI scientist)
performance evaluation
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MARP, Inc.
setup of ACR phantom
accurate, reproducible, easyphysicist assists with initial setup
centered in coil & magnet
APSILR
levelnot rotatednot tilted
view on localizer
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MARP, Inc.
setup of ACR phantom
available on site• designed for manufacturer's
phantoms• not designed for ACR phantom
imperfect alignment• not centered in head coil• may / may not be reproducible
manufacturer-supplied holders
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MARP, Inc.
setup of ACR phantom
adjustable • alignment• centering ??• attached to ACR phantom
~ $700
3rd party holdersdesigned for ACR phantomdesigned for specific head coilsreproducible
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MARP, Inc.
setup of ACR phantom
computer paper holderadjust # sheets for correct heightmarked for proper alignmentwedges for correct levelkeep phantom from moving
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MARP, Inc.
setup of ACR phantom
replacing manufacturer phantom holder with home-made
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MARP, Inc.
setup of ACR phantom – 8 channel head coils
alignment will not be perfectcenter of phantom may not be in center of coil
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MARP, Inc.
daily QC scans
same 2 scans dailysagittal localizer
• 25 cm FOV, 256x256, 20 mm slice, 1 NEX
• SE, TR=200 ms, TE = 20 ms
ACR T1 sequence:• 11 slices prescribed from sagittal localizer• 25 cm FOV, 256x256, 5 mm slice, 5 mm gap,
1 NEX• SE, TR=500 ms, TE = 20 ms
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MARP, Inc.
ACR MRAP QC requirements
weekly (formerly daily)• phantom setup• central frequency• transmitter gain
/attenuation• geometric accuracy• spatial resolution• low-contrast detectablilty• image artifact assessment
weekly:• laser film QC• visual checklist
annual:• physicist (or MRI scientist)
performance evaluation
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MARP, Inc.
center frequency
center frequency slowly declines must be measured and recorded dailyconsole has built in protocol for determining center frequency
00 B⋅= γω
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MARP, Inc.
transmitter gain/attenuation
reflects power system needs to optimize pulse sequence following prescan• depends on phantom, coil,
hardware performance, etc.• remains stable over time if
nothing in protocol or hardware has changed
terminology & units vary with vendor, system & software
90º
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MARP, Inc.
transmitter gain/attenuation - GE
• displayed on screen following pre-scan
• AX (Hz)• TG
• also available post-scan in image browser
• “text page"- "series page"
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MARP, Inc.
transmitter gain/attenuation - Siemens Symphony
• “system" - "adjustments" – check “confirm freq adjustment“• window pops up during prescan• frequency (MHz)
• Ref. amplitude 1H (V)• valid on for most recent scan
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MARP, Inc.
transmitter gain/attenuation - Philips
• located in separate window accessible after scan• "System performance" " tools" " parameters"
• SP_proton_freq (Hz)• SP_act _ RF _drive_scale
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MARP, Inc.
transmitter gain/attenuation - Hitachi
located in separate window accessible after scan• “Diagnostics“ “Frequency Log Display”
• Freq (Hz)• Tune & Gain• H1 (RF Gain)
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MARP, Inc.
transmitter gain/attenuation - Toshiba
• "acquisition window"• center frequency (MHz)• RF level
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MARP, Inc.
center frequency actions limits
1.5 T1.5 ppm = 96 Hz20 day average
• ± 100 Hz
0.3 T1.5 ppm = 19 Hz
• most low-field open systems vary more than this
20 day average• ± 2-3 SD
ACR QC manual suggests 1.5 ppm
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MARP, Inc.
transmitter gain/attenuation
physicist / MR scientist establishes action limits:
~ 20 day averageno ACR specifications± 2-3 SD • rounded
will change if coil is tuned
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MARP, Inc.
baselines - example
1.5 Tfrequency
• SD = 48.1 Hz• ± 100 Hz OK
transmitter• SD = 6.3• ± 13 OK
LCD• mean = 8.4• baseline > 5• slice 8
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MARP, Inc.
baselines - example
1.5 T short borefrequency
• SD = 316 Hz• ± 100 Hz not OK• ± 700 Hz better
transmitter• SD = 14• ± 27 OK
LCD• mean = 8.2• baseline > 5• slice 8
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MARP, Inc.
baselines - example
0.2 T openfrequency
• SD = 1961 Hz• ± 100 Hz not OK• ± 3800 Hz better
transmitter• SD = 3.5• ± 7 OK
LCD• mean = 8.1• baseline > 5• slice 11
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MARP, Inc.
ACR MRAP QC requirements
weekly (formerly daily)• phantom setup• central frequency• transmitter gain
/attenuation• geometric accuracy• spatial resolution• low-contrast detectablilty• image artifact assessment
weekly:• laser film QC• visual checklist
annual:• physicist (or MRI scientist)
performance evaluation
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MARP, Inc.
geometric accuracy
sagittal localizer & ACR axial T1 slice 5specific window & level:
window/level must be set separately for localizer & axial T1• record levels for daily use
window as narrow as possibleset level where ½ of water is dark (mean)set window width = mean value & window level = ½ mean value
example
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MARP, Inc.
geometric accuracy
slice 5 of ACR axial T1• horizontal & vertical (x & y)• 190 mm• different W/L than localizer
action limits• ± 2 mm
sagittal localizer• top-bottom (z)• 148 mm
action limits• ± 2 mm
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MARP, Inc.
ACR MRAP QC requirements
weekly (formerly daily)• phantom setup• central frequency• transmitter gain
/attenuation• geometric accuracy• spatial resolution• low-contrast detectablilty• image artifact assessment
weekly:• laser film QC• visual checklist
annual:• physicist (or MRI scientist)
performance evaluation
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MARP, Inc.
high-contrast spatial resolution
slice 1 of ACR axial T1.3 sets of holes
• 1.1 mm, 1.0 mm, 0.9 mm
magnify , adjust window / levelobserve UL holes
• all 4 holes in a single row must be distinguishable
repeat for LR array (columns)
UL
LR
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MARP, Inc.
high-contrast spatial resolution
action level:any detectable changeACR performance criteria: 1.0 mm
• on many units 0.9 mm is visible• set appropriate action level
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MARP, Inc.
ACR MRAP QC requirements
daily• phantom setup• central frequency• transmitter gain
/attenuation• geometric accuracy• spatial resolution• low-contrast detectablilty• image artifact assessment
weekly:• laser film QC• visual checklist
annual:• physicist (or MRI scientist)
performance evaluation
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MARP, Inc.
low-contrast object detectability
4 slices with low-contrast holesslices 8-11
• decreasing contrast levels (11→ 8)
10 spokes per slice• 3 holes per spoke• decreasing size (clockwise)
count complete spokesall 3 disks must be discernible
• more apparent than background
end with last complete spokefor phantom review:
• all slices are counted
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MARP, Inc.
low-contrast detectability - daily QC
checked for one slice onlydetermine slice at threshold of detectability
• low-field → slice 11• high field → slice 8 (or 9)
count fully visible spokesaction limit:
reduction of > 3 spokesrepeat
• phantom may be tilted
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MARP, Inc.
ACR MRAP QC requirements
weekly (formerly daily)• phantom setup• central frequency• transmitter gain
/attenuation• geometric accuracy• spatial resolution• low-contrast detectablilty• image artifact assessment
weekly:• laser film QC• visual checklist
annual:• physicist (or MRI scientist)
performance evaluation
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MARP, Inc.
artifact evaluation
observe daily phantom images
window / levelcheck for:• distortion?• ghosts in phantom or background?• streaks?• bright or dark spots?• new features?• inappropriate blurring or truncation
artifacts?
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MARP, Inc.
ACR MRAP QC requirements
weekly (formerly daily)• phantom setup• central frequency• transmitter gain
/attenuation• geometric accuracy• spatial resolution• low-contrast detectablilty• image artifact assessment
weekly:• laser film QC• visual checklist
annual:• physicist (or MRI scientist)
performance evaluation
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MARP, Inc.
laser film QC - setup
verify monitor calibrationview SMPTE pattern on console (default W/L)• verify gray levels
• 0 / 5 % patch• 95 / 100 % patch• consistent gray-level
changes
• film 6 on 1• 4 on 1 if necessary
• measure OD • 0% patch• 10% patch• 40% patch• 90% patch
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MARP, Inc.
laser film QC - weekly
view SMPTE pattern on console (default W/L)• verify gray levels
• 0 / 5 % patch• 95 / 100 % patch• consistent gray-level
changes
• film 6 on 1• 4 on 1 if necessary
• measure & plot OD • 0% patch• 10% patch• 40% patch• 90% patch
• check film for artifacts & resolution
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MARP, Inc.
laser film QC
plot dataaction limits:
SMPTE Patch OD Control limit
0 2.45 ± 0.15
10% 2.10 ± 0.15
40% 1.15 ± 0.15
90% 0.30 ± 0.08
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MARP, Inc.
laser film QC - additional setup requirement
print SMPTE pattern from laser printer• measure OD
• 0% patch• 10% patch• 40% patch• 90% patch
• save for troubleshooting
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MARP, Inc.
setting up QC program
make certain scanner is at peak performance
acceptance testPM and reviewannual test
• & corrective action if needed
demonstrate QC tests to technologist~20 days measurementsestablish baselines
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MARP, Inc.
setting up QC program -documentation
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MARP, Inc.
QC program -initial documentation
center frequency parameter (4.)transmission gain parameter (5.)distances (6. - 8.)
• orientations• sagittal window & level• axial window & level
resolution• UL orientation (9.)• LR orientaion (10.)
low-contrast slice (11.)
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MARP, Inc.
QC program - setup aids
ACR manual
notes on QC sheet
film "cheat sheet"
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MARP, Inc.
QC program - establishing baselines
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MARP, Inc.
baselines - example
1.5 Tfrequency
• SD = 48.1 Hz• ± 100 Hz OK
transmitter• SD = 6.3 V• ± 13 V OK
LCD• mean = 8.4• baseline > 5• slice 8
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MARP, Inc.
QC program - establishing baselines
action levels• ACR specified• ± 2 standard deviations?• how often will site be out of
limits?• what will site do when it is
out of limits?• sent (faxed or emailed) to site
~20 days of data• sent (faxed) to physicist
done correctly?baseline
• mean
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MARP, Inc.
QC program - review
QC must be reviewed by medical physicist / MR scientist at least annually
• is QC performed regularly?• at least weekly
• is it correct?• are problems / changes
noted?• is corrective action taken?
documentation:• signature on form• may be reviewed more
frequently
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MARP, Inc.
QC review
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MARP, Inc.
QC review
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MARP, Inc.
ACR MRAP QC requirements
weekly (formerly daily)• phantom setup• central frequency• transmitter gain
/attenuation• geometric accuracy• spatial resolution• low-contrast detectablilty• image artifact assessment
weekly:• laser film QC• visual checklist
annual:• physicist (or MRI scientist)
performance evaluation
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MARP, Inc.
visual checklist
weeklypatient bed transportalignment lightsRF room integrityemergency cartsignsmonitors
problems should be corrected
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MARP, Inc.
ACR MRI QC program
setup up by medical physicist / MR scientistperformed by technologist
daily preferredweekly acceptable if OK with physicist~ 10 minutes per day
baselines & action limitsestablished by ACR and/or physicist / MR scientistrepeat test when outside limits
corrective action when neededdocumentation
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MARP, Inc.
ACR MRI QC Program July 2009
Carl R. Keener, Ph.D., DABMP, [email protected]
MARP &Medical Radiation Physics, Inc.