myocardial perfusion spect coregistered coronary cta
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Quantitative Analysis of Quantitative Analysis of
Myocardial PerfusionMyocardial Perfusion SPECTSPECT
Anatomically Guided by CoregisteredAnatomically Guided by Coregistered
6464--Slice Coronary CTSlice Coronary CT AngiographyAngiography
Piotr J. Slomka et al.
Departments of Imaging and Medicine,Cedars-Sinai Medical Center
J Nucl Med, Oct 2009
Resident : Apichaya Claimon
Advisor : Rujaporn Chanachai
Coronary CT
angiography (CTA)
• precise localization
and classification of
coronary artery
plaques + depiction of
coronary anatomy
• detect and estimate
severity of ischemia
Myocardial perfusion
SPECT (MPS)
• Inconclusive results obtained by 1 of the tests ->
sequential testing by both modalities
• Visual analysis of fused MPS and coronary CTA images
-> improve the diagnostic value
• Manual tools for the purpose of combined visual analysis
have been developed
Previous studies
• Need interactive alignment
• Complicate protocol
• Reduce clinical usability
Aim of the studyAim of the study
• To develop tool for rapid automatic
– Coregistration
– Visualization
– Combined quantification
Between coronary CTA and MPS ; obtained from stand-
alone scanners in different scanning sessions
• To showed that coregistered MPS–CTA data
can be used to improve quantitative MPS
analysis
MATERIALS AND METHODSMATERIALS AND METHODS
Patient SelectionPatient Selection
• Between October 2005 and May 2007
• Retrospectively 40 consecutive patients – who underwent myocardial MPS, CTA, and invasive coronary angiography (ICA) within a 90-d period
• 2 patients excluded ; the relevant imaging data could not be retrieved
• 22 patients ; evaluation of symptoms – either chest pain or dyspnea; 8 had prior MI
• 16 patients ; asymptomatic
The imaging indications
• post–myocardial infarction (3 cases)
• post–percutaneous coronary intervention risk stratification (3 cases)
• risk stratification without prior event (10 cases)
• 3 patients excluded ; because of CABG surgery
The remaining 35 patients
• 5 cases, CTA and MPS were performed on the same day
• 20 cases, CTA was performed after MPS – (range, 1–49 d; median, 9 d)
• 10 cases, MPS was performed after CTA– (range, 1–73 d; median, 13 d)
Patient CharacteristicsPatient Characteristics
CT Image Acquisition
Unenhanced CT scan
CT coronary calcium scores
Coronary CTA
Electrocardiogram (ECG)-gated during a 9- to 12-s breath hold
ECG-based dose modulation 40%-80% of the cardiac cycle ; to limit radiation dose
Coronary CTA Image Reconstruction
Raw CTA data → retrospectively gated reconstruction
performed at 40%-80% of the R-R interval
Extract coronary arterial trees using vendors’ software
Transferred to a Windows workstation
for MPS–CTA fusion
• A coronary CTA reader – with experienced >300 coronary CTA interpretations
– Unaware of MPS and ICA results
• Evaluate coronary segments > 1.5 mm in diameter
• Evaluate for the presence and degree of stenosis.
• Any stenosis narrowing the luminal diameter by > 50% or > 70% was recorded.
• If a segment could not be assessed because of artifacts, no stenosis was recorded.
CTA Image Evaluation
• Standard technique of intensive coronary
angiography
• Evaluate by interventional cardiologist, unaware
of coronary CTA and MPS results
• By visual inspection
• Whether luminal diameter
narrowing > 50% or > 70%
was present
ICA Image Acquisition and Evaluation
• Left main stenosis > 50% was
considered as significant for the
LAD and LCX territories
• If present the
ramus intermedius
-> assigned to the
LCX territory.
Angiographic Characteristics of Data (n = 35)
• Standard protocol– 1- or 2-d protocols
– dual-isotope (thallium–technetium) protocol
• MPS acquisitions ; 64 projections, 45o RAO to 45o LPO
• Stress scan ; exercise, adenosine injection, or adenosine–walk protocol
• No attenuation or scatter correction
• Reconstruct gated images to original transverse orientation – with filtered backprojection and a Butterworth filter
MPS Protocol
MPS image processing
MPS image processing
static MPS images in end-diastolic (ED) phase
to match the diastolic cardiac phase of coronary CTA
MPS image processing
MPS image processing
Validation of Automatic Registration (error analysis)
manual alignment parameters (3 translations and 3 rotations)
Visual alignment was performed without knowledge of the automatic results
MPS image processing
MPS image processing
2-dimensional/3D textures
Segmented CTA voxel maps → rendered in 3D within QPS
and within the same coordinates as the epicardial 3D surface
display with overlaid MPS function and perfusion
MPS image processing
CTA-Guided MPS Contour
and Territory Adjustment
• Fused coronary CTA and MPS images were evaluated with overlaid contours in multiplanar orientations
• If discrepancies between the MPS and CTA valve plane position -> manually adjust the contour
• Overlaid the default vascular territory boundaries withthe 3D LV MPS surfaces– with color-coded perfusion information
– and with a coregistered volume-rendered segmented 3D coronary tree
• Adjust vascular territories segment by segment
– based on a 17-segment American Heart Association model
– using anatomic information provided by the coronary CTA
• If adjusted MPS contours or vascular territories -> repeat QMPS analysis
•perfusion-defect performed individually for
each vessel, 17 segments vascular territory
•total perfusion deficit (TPD) of territory ->
automated quantification in each vessel
•threshold of 2%
•record QMPS before and after adjustments
MPS image processing
QMPSQMPS
RESULTSRESULTS
• Of 35 cases with all 3 scans (CTA, MPS,
and ICA) available
– 20 patients underwent CTA after MPS
– 15 underwent MPS after CTA
• In cases performed CTA after MPS
– 11 had equivocal reversible defects on visual
evaluation of MPS
– 9 done CTA because MPS were discordant
with clinical or suspected multivessel disease
• In cases underwent MPS after CTA
– 7 had at least 1 nondiagnostic major coronary
segment on CTA
– 4 had maximal luminal stenosis in the LAD
estimated at 50% and considered of
borderline significance
– 4 patients done for assess hypoperfusion
• unenhanced CT calcium score ; average
was 942 + 1,530 (range, 0–7,781)
– Heavy calcification (score > 500) in 15/33
• 10 cases ; motion artifacts on CTA
• Interpretation difficulties ; 9 cases
• Significant CT disease ; 27/35, with – 6 LCX lesions
– 11 RCA lesions
– 21 LAD lesions
– 2 left main lesions
• MPS ejection fractions – 57.4% + 14% (range, 32%-83%) on stress
– 57.2% + 14 (range, 25%-83%) on rest
• TID ; 1.15 + 0.14 (range, 0.96–1.4)
MPS findings MPS findings
• Visually ;– normal in 3 cases
– probably normal in 3 cases
– borderline in 6 cases
– probably abnormal in 1 case
– abnormal in 22 cases
• Quantitatively; total perfusion deficit (TPD) was – 16.5% + 12.7% on stress (range, 0%-44%)
– 5.6% + 8.1% on rest (range, 0%-25%)
Registration AlgorithmRegistration Algorithm
• Speed of automated registration = 1–2 s per study
• The automatic volume registration of motion-frozen MPS with CTA was successful in – 33/35 stress
– 34/35 rest studies
as assessed qualitatively
with an overall success rate of 96%
• In 1 patient, registration fail for both stress and rest– because of the unusually high blood-pool contrast intensity
on coronary CTA
– inadequate matching of assigned blood-pool contrast with the actual CT value in the blood-pool region
• All 3 failed cases were women with small hearts – (motion-frozen stress diastolic volumes, 29–52 mL on MPS)
• These results were easily corrected by
interactive alignment.
• No significant differences
– between errors in different directions
– or between studies from 2 different systems
Accuracy of Automated Alignment Accuracy of Automated Alignment
of SPECT and Coronary CTA of SPECT and Coronary CTA
for Translations and Rotationsfor Translations and Rotations
CTA
MPS
fused unregistered MPS and CTA
after automated volume registration
Contour and Territory AdjustmentsContour and Territory Adjustments
• Adjust– MPS vascular region definitions 17 studies
– LV contours (valve plane location) 11 studies
• Use coregistered coronary CTA images as a guide
• The territory adjustment – modified perfusion results for a specific vessel
– but not the overall perfusion deficit per study
– and did not change the global perfusion measure per study
• The MPS contour adjustment – modified overall TPD in 7 of 35 (20%) of the cases
• by more than 2%.
Areas Under ROC Curves for Detection of CAD
(>70% Luminal Stenosis) in Individual Vessels
Combined Performance for CAD DetectionCombined Performance for CAD Detection
ROC curves for disease detection in
individual vessels by partial TPD per vessel
• Stand-alone MPS (blue)
• CTA-guided MPS (pink)• * CTA-guided MPS significantly different from stand-alone MPS
LAD LCX RCA
608350Specificity %
676767Sensitivity %Sensitivity %
RADLCXLADMPS
85*10071Specificity %
877576Sensitivity %Sensitivity %
RADLCXLADCTA-guided MPS
* P = 0.025
Number of lesions correctly identifiedNumber of lesions correctly identified
corresponding to corresponding to >> 70% 70% stenosisstenosis on ICAon ICA
13/1510/1219/21
After apply CTA or
CTA-guided MPS
positive criteria
10/158/1214/21Quantitative MPS alone
10/156/1217/21CTA alone
13/159/1217/21CTA guided MPS
RADLCXLAD
CTA-guided MPS agreed with angiography in
• 4/9 discordant cases for LAD
• 4/5 discordant cases for LCX
• 3/6 discordant cases for RCA
• A. valve plane is determined incorrectly
• B. after MPS contour adjustment revealing RCA defect.
• ICA confirmed RCA stenosis>70%
CTA : nonsignificant,
<50% proximal RCA lesion
and significant LAD lesion
CTA-MPS coregister→ Need for contour adjustment → Quantification
3% defect in typical RCA territory
defect between LAD and LCX
LAD
• Adjust coronary territory on the basis of superimposed CTA coronary tree
• ICA revealed
– 50% - 69% RCA lesion
– 90% LAD lesion
• CTA-guided analysis → additional RCA lesion in MPS
DISCUSSIONDISCUSSION
• Software image fusion of coronary CTA and MPS from separate or hybrid scanners has been proposed before
• Previous study of MPS-CCTA fusion required manual alignment
• This study propose fully automatic registration of coregistered CTA and motion-frozen MPS data obtained on stand-alone scanners
• CT-guided adjustment of contours and territories on MPS after image coregistration
• accurate
• success rate 96%
• in as short as 1–2 s
• increases the diagnostic performance (area under the ROC curves) for the detection of CAD
• MPS contours (mitral valve plane position)
– can be adjusted on the basis of the CTA anatomic volume data• MPS contour verification
• MPS vascular territories
– can be modified on the basis of coregisteredcoronary CTA anatomy
–→ the quantitative results can be reassigned
to the correct territories
–→ improved diagnostic performance,
especially for LCX and RCA lesions
• Combined visual analysis – size and the severity of the stenosis
– presence of artifacts
• When stand-alone CTA or MPS is insufficient to diagnose or localize CAD → CTA-guided MPS
quantification have important role
• 3D coronary artery reconstructed from ICA + MPS surface– RCA, left main a. can positioned away from myocardium
– misregistration due to brach omission during vv extraction
increase accuracy
• MPS + unenhanced CT registration from hybrid
scanners
– for attenuation correction
– are already in an approximate alignment and only
small correction is required
• MRI + MPS
– motion on MRI -> presegment MRI heart -> register
with MPS
– cannot applied in this study : only 1 phase of CTA
available
• Multiphase not available for prospective gated CTA
• Summed MPS + coronary CTA
– lead to mismatches in the size of the ventricle
• Motion-frozen MPS + coronary CTA
– motion-frozen perfusion image = ED phase
– myocardial dimensions and wall thickness = ED
– better suited for fusion with coronary CTA
• typically reconstructed in 70%-80% phase
– for visualization of the coronary lesions
• Hybrid MPS–coronary CTA or PET–coronary CTA
• Not used routinely in cardiac imaging – because of the difficulty in predicting a priori which patients would
benefit from such combined examination
• even if MPS–CTA scans are obtained on a hybrid scanner, software coregistration is still required – because of mismatches in the respiratory phases
• Sequential approach is often applied in clinical practice– additional scans (CTA or MPS) performed only if the results of the
initial modality are equivocal
– minimization of the cost and radiation dose
– software registration can reliably bring MPS and CTA data into appropriate alignment
Bias in our study populationBias in our study population
• patients with – frequent occurrences of equivocal results from the initial test
– significant discrepancy between initial test interpretation and clinical suspicion
• in such difficult cases, CTA–MPS image fusion and subsequent quantitative analysis can be helpful
CTACTA--guided QMPSguided QMPS
• helpful in RCA and LCX territories
• but did not significantly improve LAD disease detection
• impact of basal contour adjustment on MPS
Radiation doseRadiation dose
Mean estimated radiation dose
• CT (CTA and coronary calcium scoring scan) ~ 19.7 mSv
• dual isotope stress–rest MPS scans ~ 24 mSv
Significantly reduced coronary CTA radiation dose by
• acquiring with prospective ECG gating ~ 2–5.8 mSv
• patient-specific algorithm to select the optimal dose-lowering combination for retrospectively gated acquisitions ~ 8 mSv
• changed standard MPS protocol to 99mTc-sestamibi for both stress and rest ~ 10 mSv
• Thus, it is possible to perform a combined CTA and MPS study with the total dose less than 20 mSv, even with CTA retrospective gating.
LimitationsLimitations
• This study : fully automated quantitative analysis and automated image registration
• But the contour definitions and vascular territory were manually guided by the coregistered CTA anatomy– this adjustment can be automated in the future if perform CTA
automatic segmentation
• The success of registration depends on successful MPS contour determination– If the contours are incorrectly determined, causing the LV shape
to be grossly distorted -> fail automatic registration
• Retrospective study
• Biased population– high prevalence of equivocal results on the initial imaging test
– clinical conditions that led to performance of ICA, MPS, and CTA
• Most of the general MPS population will not significantly benefit from CTA-mediated contour and territory adjustments of MPS.
• But these minor population represent cases in which the CTA-guided MPS quantification could be clinically useful.
CONCLUSIONCONCLUSION
• Software coregistration of coronary CTA
and MPS images obtained on separate
scanners can be acquired rapidly and
automatically
• allowing CTA-guided contour and vascular
territory adjustment on MPS for improved
quantitative MPS analysis.
Thank YouThank YouLeft main LCX
LAD
RCA
Ramus int.
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