MRI Annual Physics Tests - Beyond the Ba · 2005. 7. 21. · Title: MRI Annual Physics Tests - Beyond the Ba Author: Carl Created Date: 7/21/2005 10:09:15 AM
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MRI Annual Physics Tests - Beyond Just the Scans & Measurements July 21, 2005
Carl R. Keener, Ph.D. 1
MR Accreditation Program Quality ControlBeyond Just the Scans and Measurements
u ACR T1 series on ACR phantomu 1 operator (physicist)
SNR vs MRAP LCD
0
10
20
30
40
0 50 100 150 200 250 300 350 400
SNR
LC
D
u @ 1.5T:
u mean = 35.4, SD = 2.7, n = 35
MRI Annual Physics Tests - Beyond Just the Scans & Measurements July 21, 2005
Carl R. Keener, Ph.D. 7
low contrast detectability / SNR
u LCD & SNR correlate closelyu 1 scanner, 1 surveyu tracked within survey
7828site T2
21139ACR T2
18238site T1
29739ACR T1
SNRLCDseries
low contrast detectability / SNR
u LCD & SNRu tracked within surveyu tracked between surveys
u why did LCD & SNR drop in 2002?u QC scores for slice 8 = 10,10, 10, 10, 10, 10, etc.u 2002 physicist score for slice 8 = 4
SNRLCD
80
30
68
111
2002
76
220
333
2001
GRE
815site T2
2727ACR T2
site T1
2936ACR T1
20022001series
low contrast detectability / daily QC
u SNR was 50-60% lower on phantomu SNR had not dropped on other coils
u why did LCD & SNR drop in 2002?u technologist was scoring slice 11 instead of slice 8
• slice 11 score = 10; slice 8 score = 4
slice 8 slice 9 slice 10 slice 11
1.5T
low contrast detectability / SNR
u head coil was defective
u ↑↑ numbers after coil correctedu site QC program correctedu LCD & SNR stable following corrections
80
147
223
306
2004
21
32
39
40
2004
SNRLCD
80
30
68
111
2002
78
182
211
297
2003
28
38
39
39
2003
76
220
333
2001
GRE
815site T2
2727ACR T2
site T1
2936ACR T1
20022001series
coils
u same coilu consistent from year to
year• SNR• ghosting• uniformity
u different coilsu are they comparable?
u ghostingu from coil or gradient?
coils – year to year
u is coil performingsimilar to previousyear?
u same setup,phantom,techniques
• photos 23594.3%0.11%1/30/2004
23993.9%0.08%2/1/2005
25194.9%0.02%12/20/2002
12993.6%0.58%9/27/2001
12793.9%0.02%8/7/2000
18993.6%1.03%10/21/1999
SNRuniformityghostingdate
MRI Annual Physics Tests - Beyond Just the Scans & Measurements July 21, 2005
Carl R. Keener, Ph.D. 8
comparing coils
u similar coils on samescanner
u same phantom• head SNR sphere
u same techniques• SE, TR=500, TE=20, 20 cm FOV,
256x128, 15.6 kHz
u measured max signal &noise
old shouldercoil
new shouldercoil
coil
771.88144
10402.312402
maxSNRnoisemax
signal
ghosting – comparing coils
"When troubleshooting the ghosting, concentrate on the head coil as itmay be the source of the problem. There is also noticeable ghosting onthe CTL spine coil. All other coils have minimal ghosting or none atall."
noticeableCTL
noneShoulder
noneSmall joint
0.04 %NVA
0.35 %Wrist
0.06 %Volume neck
0.11 %Quad knee
1.03 %Head
0.20 %Body
GhostingCoil
???
ghosting – most coils
u ghosting on most coilsu problem in scanner, not
coils
u alternate phase-encoding direction todeterminemalfunctioning gradient
u documentation
RF shielding
u image quality problemsu random lines from RF
noise
u increased image noise
u simple check withportable radio
u check doors
u check ceiling
RF shielding
u new scanner with grainy imagesu ACR T1 LCD = 30
• vs. 35.4 +/- 2.7 average
u ACR T1 SNR = 163• vs. 251 +/- 47 average
u radio signal strong throughoutroom
• slightly audible with door closed
u conclusion:u RF shielding was compromised
during install
magnetic fringe field
u 5 gauss line must beposted
u pacemakers
u actively shieldedmagnets
u 5 gauss line inside scanroom or very close
u unshielded magnetsu 5 gauss line ~ 30 feet
away• outside scan room• outside building
MRI Annual Physics Tests - Beyond Just the Scans & Measurements July 21, 2005
Carl R. Keener, Ph.D. 9
magnetic fringe field
u are signs appropriate?u has scanner been changed?u gauss meter
conclusions
u communicationu have there been
changes?….problems?
u comparisonu baselines from
previous surveysu measurements from
similar scannersu manufacturer's specsu QC values
u combine test resultsu creativity
u additional tests andmeasurements
u homogeneityu center frequency / QCu ACR phantom testsu coil testsu non-phantom tests
MR Accreditation Program Quality ControlBeyond Just the Scans and Measurements