quantitative assessment of cardiac left ventricular parameters using mri scanners … ·...
TRANSCRIPT
Quantitative Assessment of Cardiac Left
Ventricular Parameters using MRI Scanners from
Two Different Vendors – Implications for Multi-
centre Studies
Gandy SJ1,3, Waugh SA1, Nicholas RS1, Simpson H2,
Milne W3, Brunton T3, Houston JG3
1Medical Physics, 2School of Medicine, 3Clinical RadiologyNHS Tayside,
Ninewells Hospital,Dundee DD1 9SY
UNITED KINGDOM
Cardiac MR - Basic Protocol
• Patient in scanner – cardiac RF coil
• ECG gating – removes cardiac motion artefacts
• Breath holding – removes respiratory motion artefacts
Simpson’s Rule
Base
Apex
• Use 4ch and 2ch images to plan SA stack
• Acquire SA stack from base to apex of left ventricle
• Post-processing - select endo- and epicardial borders
• Compute structural and functional parameters
• Measure endo- and epicardial borders at end diastole & end systole
Quantitative Measures in CMR
• EDV = End diastolic volume (vol inside red contours at ED), ml
• ESV = End systolic volume (vol inside red contours at ES), ml
• EF = Ejection fraction ((EDV-ESV)/EDV)*100, %
• SV = Stroke volume (EDV – ESV), ml
• CO = Cardiac output (EDV – ESV) * heart rate, ml/min
• LVM = Left ventricular mass (at ED), grams
ED ES
Hardware & Software Variations• Type of scanner, gradients, RF coil architecture
• Steady state sequences - TrueFISP, bFFE, FIESTA
• TR, TE, FA, resolution parameters, filters
• ECG gating mechanisms
Siemens Philips GE
32 channel RF coils for cardiac MRI
Data Acquisition Variations• Scanner operator – same or different?
• Positioning of ECG leads – good ECG trace?
• Prepared to repeat scans if ECG triggering difficulties?
• Prepared to repeat scans if poor breath holding by patient?
• Scan to scan variations due to re-positioning - unavoidable
• Patient compliance – motionless? 1 or 2 slices per breath-hold?
Post-processing Variations• Type of software used (Argus or Mass) – edge detection
• Identification of base/apex slices, & end diastole/systole phases
• Inclusion or exclusion of papillary muscles
• Viewing monitor settings (contrast, window/level, luminance)
• Intra/inter-observer variation
• Single time-points
• Different time-points
• Different scanners
Objective of the Work
• Examine healthy volunteers using scanners from different vendors in order to gain understanding of the various sources oferror that may influence similar ‘multi-centre’ investigations
Specific Targets – Intra- and Inter-observer Variation
• Datasets acquired at a single time point
• Datasets from two different time points, same scanner
• Datasets from two different time points, different scanners
• Example: LVM, wish to detect changes - 5-10%
Subjects and Imaging
• 15 consenting healthy volunteers (9M 6F, age range 23-45 years, mean 31 yr)
• Short-axis CMR images - acquired twice on two separate visits at the same centre using a 1.5T Avanto (Siemens), and once at a different centre using a 1.5T Signa Excite (GE)
• Images acquired at similar time of day (17:00-18:00) on separate occasions within a two month period (3 time-points – TP1, TP2, TP3)
• Mean time for completed scan visits for each patient = 22 days
Siemens Magnetom
Avanto - SCANNER ‘A’
GE Signa Excite –
SCANNER ‘B’
Phantom Validation
• LV anthropomorphic phantom (Data Spectrum Co, USA) filled with Gd-doped water and imaged on both scanners using same parameters & analysis methods as for volunteer imaging
• Outer chamber ‘myocardium’ = 233ml. Measured as 224ml (Siemens) and 220ml (GE). Inter-scanner measurement CoV = 1.2%
• Inner chamber ‘blood’ = 52ml. Measured as 54ml (Siemens) and 52 ml (GE). Inter-scanner measurement CoV = 1.8%
Phantom and simulated short-axis images
Short-Axis Image Acquisitions
MR Imaging using Scanner A (twice per volunteer on separate occasions)
• Sequence & coils: 2D ECG-G BH segmented TrueFISP CINE, body matrix and spine matrix RF coils
• Short-axis images of the LV acquired (atrio-ventricular ring to the apex)
• Imaging parameters: TR 2.5-2.8ms, TE 1.2ms, FA 60o. 1-2 slices/BH, GRAPPA x2, 192 & 256 resolution, 350mm FOV, ST 6mm & 4mm gap
MR Imaging using Scanner B (once per volunteer)
• Sequence & coils: 2D ECG-G BH segmented FIESTA CINE, 8ch torso-pelvis array RF coil
• Imaging parameters: TR 3.4ms, TE 1.5ms, FA 45o, 1 slice/BH, other parameters identical
Example Short-Axis Images
TP1
Scanner A
TP2
Scanner A
TP1
Scanner B
TP1
Scanner A
TP2
Scanner A
TP1
Scanner B
END DIASTOLE
END SYSTOLE
END DIASTOLE
END SYSTOLE
41 days
39 days
Segmentation Methods - ARGUS
ED ES
(v VA60C) MMWP MR PhysicistsED/ES phasesBasal slicesPapillary muscles
Segmentation Methods – MASS A+
ED ES
(v 5.1), Adv. Workstation MR PhysicistsED/ES phasesBasal slicesPapillary muscles
150 Segmentations
Observer 1 Observer 1 Observer 2Siemens Avanto
Siemens Avanto
GE Signa
Observer 1
Observer 1
i
• RMS Coefficient of variation (CoV) values for EF and LVM, calculated
as RMSD/mean, where RMSD = (Σ ((x2-x1)2/n))0.5)
• (i) Intra- & (ii) inter-observer, single imaging TP, single scanner
• (iii) Intra- & (iv) inter-observer, different imaging TP’s, same scanner
• (v) Intra- & (vi) inter-observer, different imaging TP’s, different scanners
• One-way ANOVA (95% CL) - significant differences between the means of the EF and LVM parameters (SPSS version 14.0)
iiiii
ivv
vi
Results – EF and LV Mass
• Mean EF (n=15) range – 65.9% to 67.9% - typical of normal range
• Standard deviation (n=9 patients) ranged from 5.5% to 7.0%
• Mean LVM (n=15) range – 95.3g to 114.4g (lower end normal range)
• Standard deviation (n=9 patients) ranged from 19.5g to 23.8g
Scanner & Observer Segmentation
Time-point number 192 resolution 256 resolution 192 resolution 256 resolution
A (TP1) Obs1 1 67.2 +/- 6.8 66.0 +/- 6.1 96.8 +/- 21.7 100.3 +/- 23.5
A (TP1) Obs1 2 67.1 +/- 6.1 66.9 +/- 6.7 97.3 +/- 22.3 99.7 +/- 22.6
A (TP1) Obs2 1 67.9 +/- 6.7 65.9 +/- 7.0 109.3 +/- 22.3 114.4 +/- 19.8
A (TP2) Obs1 1 67.8 +/- 6.4 67.2 +/- 7.0 95.3 +/- 19.5 101.1 +/- 21.1
B (TP3) Obs1 1 66.3 +/- 5.8 67.8 +/- 5.5 96.5 +/- 21.9 97.0 +/- 23.8
Mean EF (%) Mean LVM (g)
Tendency for obs1 to measure LVM lower thanobs 2, but means not significantly different
Intra- and Inter-observer Variation
For EF, CoV rises as different observers and scanners are incorporatedFor LVM, clear increase in CoV between intra- and inter-observer measures
Analysis Code Timepoint Scanner Observer EF LVM
(i) Same Same Same 2.15 4.12
(ii) Different Same Same 5.51 5.20
(iii) Different Different Same 5.78 8.25
(iv) Same Same Different 3.60 13.43
(v) Different Same Different 4.29 15.94
(vi) Different Different Different 6.13 13.74
RMS CoV (%)
Bland Altman Analysis Example
Reproducibility for LVM (single time-point, same scanner)
LV
M d
iffe
rence (
g)
Mean LVM (g)
-10
-5
0
5
10
15
20
25
30
50 70 90 110 130 150
LV
M d
iffe
rence (
g)
Mean LVM (g)
-10
-5
0
5
10
15
20
25
30
50 70 90 110 130 150
Intra-observer data Inter-observer dataIntra-observer data Inter-observer data
Summary -1
• EF and LVM ranges similar to other published work (LVM at low end), but are MRI ‘normal ranges’ influenced by larger LVM echo data?
• EF: reproducible - for single or multiple observers, or for data acquired at different time points on same or different scanners
• LVM: dependent upon whether single or multiple observers make the measurement - low-contrast boundary at the epicardial border?
• 192x192 data better reproducibility than 256x256 data, superior SNR?
• Suitable endpoints for longitudinal monitoring and response to therapy as part of multi-centre patient investigations
• But number of observers should be carefully considered in conjunction with the anticipated size of any clinical effect that one may wish to demonstrate
HNVPMILVHCHF
Card
iac P
hase
Clinical Condition
ED
ES
FIGURE 1
Healthy
Normal
Volunteers
Post
Myocardial
Infarct
Left
Ventricular
Hypertrophy
Chronic
Heart
Failure
Card
iac P
hase
Clinical Condition
ED
ES
Different Clinical Conditions
EF & LVM - Clinical Conditions
• Lowest EF and highest LVM in CHF group
• LVM elevated in LVH and PMI, but not significant
• EF lowered in PMI group - resulting from the recent infarct
• Biggest variability in PMI group – heterogeneity of cohort
Parameter CHF LVH PMI HNV
LV Ejection Fraction, EF (%) 30.4 +/-6.4 72.7 +/- 7.5 53.0 +/- 13.9 67.0 +/- 5.2
LVM at End Diastole (g) 143 +/- 29 122 +/- 22 124 +/- 27 107 +/- 19
Magnitude Data
Reproducibility – Clinical Conditions
0
2
4
6
8
10
12
EF
LV Mass
RM
S C
oV
(%
)
CHF LVH PMI HNV
5.7
7.8
5.2
4.1
11.9
1.9
4.8
2.3
Bland Altman – Clinical Conditions
-20
-15
-10
-5
0
5
10
15
20
25
50 70 90 110 130 150 170 190
Diffe
ren
ce
(g
)
Mean LVM at ED (g)
Mean Versus Difference of Two LVM Measurements
CHF
PMI
LVH
HNV
Summary - 2
• Intra-observer reproducibility varies for different clinical conditions
• Should be considered carefully if the measures are to be used inclinical multi-centre studies
Acknowledgments & References
Acknowledgments
• Tayside Institute for Cardiovascular Research
• MRI staff at NHS Tayside
• SINAPSE
Example References of Interest
• Alfakih K et al. JMRI 2003; 17: 323-329
• Hudsmith LE et al. JMRI 2006; 24: 312-318
• Malayeri AA et al. JMRI 2008; 28: 60-66
• Lyne JC, Pennell DJ. Coron. Art. Dis. 2005; 16: 337-343
For Further Information