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.