Carl R. Keener, Ph.D., DABMP, DABR … · transmitter gain/attenuation - Siemens Symphony ... ACR MRI QC program

MARP, Inc.

ACR MRI QC Program July 2009

Carl R. Keener, Ph.D., DABMP, [email protected]

MARP &Medical Radiation Physics, Inc.

MARP, Inc.

ACR MRI QC program

technologist’s roledaily/weekly QC tests• performing• action limits

physicist’s rolesetting up QC program• baselines• review

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"

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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weekly (formerly daily)• phantom setup• central frequency• transmitter gain



annual:• physicist (or MRI scientist)

performance evaluation

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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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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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adjustable • alignment• centering ??• attached to ACR phantom

~ $700

3rd party holdersdesigned for ACR phantomdesigned for specific head coilsreproducible

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computer paper holderadjust # sheets for correct heightmarked for proper alignmentwedges for correct levelkeep phantom from moving

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replacing manufacturer phantom holder with home-made

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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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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.

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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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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transmitter gain/attenuation - GE

• displayed on screen following pre-scan

• AX (Hz)• TG

• also available post-scan in image browser

• “text page"- "series page"

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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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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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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transmitter gain/attenuation - Toshiba

• "acquisition window"• center frequency (MHz)• RF level

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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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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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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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baselines - example

1.5 T short borefrequency

• SD = 316 Hz• ± 100 Hz not OK• ± 700 Hz better

transmitter• SD = 14• ± 27 OK


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baselines - example

0.2 T openfrequency

• SD = 1961 Hz• ± 100 Hz not OK• ± 3800 Hz better

transmitter• SD = 3.5• ± 7 OK


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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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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.

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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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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daily• phantom setup• central frequency• transmitter gain





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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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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.

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.

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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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

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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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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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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setting up QC program -documentation

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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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QC program - setup aids

ACR manual

notes on QC sheet

film "cheat sheet"

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QC program - establishing baselines

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baselines - example

1.5 Tfrequency

• SD = 48.1 Hz• ± 100 Hz OK

transmitter• SD = 6.3 V• ± 13 V OK


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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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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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QC review

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QC review

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MARP, Inc.

visual checklist

weeklypatient bed transportalignment lightsRF room integrityemergency cartsignsmonitors

problems should be corrected

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

MARP, Inc.

ACR MRI QC Program July 2009

Carl R. Keener, Ph.D., DABMP, [email protected]

MARP &Medical Radiation Physics, Inc.

Documents

Carl R. Keener, Ph.D., DABMP, DABR … · transmitter gain/attenuation - Siemens Symphony ... ACR MRI QC program