My Slide Presentation in Journal Club Thanks Author for Good Medical Research

1. Quantitative Analysis of
Myocardial Perfusion SPECT
Anatomically Guided by Coregistered
64-Slice Coronary CT Angiography
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

2. Coronary CT Myocardial perfusion
angiography (CTA) SPECT (MPS)
• precise localization • detect and estimate
and classification of severity of ischemia
coronary artery
plaques + depiction of
coronary anatomy
• 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

3. Previous studies
• Need interactive alignment
• Complicate protocol
• Reduce clinical usability

4. Aim 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

5. MATERIALS AND METHODS

6. Patient 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

7. 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)

8. Patient Characteristics

9. 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

10. 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

11. CTA Image Evaluation
• 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.

12. ICA Image Acquisition and 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

13. • Left main stenosis > 50% was
considered as significant for the
LAD and LCX territories
• If present the
ramus intermedius
-> assigned to the
LCX territory.

14. Angiographic Characteristics of Data (n = 35)

15. MPS Protocol
• 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

16. MPS image processing

18. MPS image processing
static MPS images in end-diastolic (ED) phase
to match the diastolic cardiac phase of coronary CTA

19. MPS image processing

20. 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

21. MPS image processing

22. 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

23. MPS image processing

24. 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 with
the 3D LV MPS surfaces
– with color-coded perfusion information
– and with a coregistered volume-rendered segmented 3D
coronary tree

25. • 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

27. MPS image processing
•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

28. QMPS

29. RESULTS

30. • 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

31. • 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

32. • unenhanced CT calcium score ; average
was 942 + 1,530 (range, 0–7,781)
– Heavy calcification (score > 500) in 15/33

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

34. • TID ; 1.15 + 0.14 (range, 0.96–1.4)
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%)

35. Registration 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

36. • 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

37. Accuracy of Automated Alignment
of SPECT and Coronary CTA
for Translations and Rotations

38. CTA
MPS
fused unregistered MPS and CTA
after automated volume registration

39. Contour 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%.

40. Combined Performance for CAD Detection
Areas Under ROC Curves for Detection of CAD
(>70% Luminal Stenosis) in Individual Vessels

41. ROC curves for disease detection in
individual vessels by partial TPD per vessel
LAD LCX RCA
• Stand-alone MPS (blue)
• CTA-guided MPS (pink)
• * CTA-guided MPS significantly different from stand-alone MPS

42. MPS LAD LCX RAD
Sensitivity % 67 67 67
Specificity % 50 83 60
CTA-guided MPS LAD LCX RAD
Sensitivity % 76 75 87
Specificity % 71 100 85*
* P = 0.025

43. Number of lesions correctly identified
corresponding to > 70% stenosis on ICA
LAD LCX RAD
CTA guided MPS 17/21 9/12 13/15
CTA alone 17/21 6/12 10/15
Quantitative MPS alone 14/21 8/12 10/15
After apply CTA or
CTA-guided MPS
positive criteria 19/21 10/12 13/15

44. 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

45. • A. valve plane is
determined
incorrectly
• B. after MPS
contour
adjustment
revealing RCA
defect.
• ICA confirmed
RCA stenosis
>70%

46. CTA : nonsignificant,
<50% proximal RCA lesion
and significant LAD lesion

47. 3% defect in typical RCA territory
defect between LAD and LCX
CTA-MPS coregister → Need for contour adjustment → Quantification

48. 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

49. DISCUSSION

50. • 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

51. • 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 coregistered
coronary CTA anatomy
– → the quantitative results can be reassigned
to the correct territories
– → improved diagnostic performance,
especially for LCX and RCA lesions

52. • Combined visual analysis
– size and the severity of the stenosis increase accuracy
– 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

53. • 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

54. • 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

55. • 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

56. Bias 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
CTA-guided QMPS
• helpful in RCA and LCX territories
• but did not significantly improve LAD disease detection
• impact of basal contour adjustment on MPS

57. Radiation 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.

58. Limitations
• 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

59. • 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.

60. CONCLUSION
• 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.

61. Thank You
Left main LCX
Ramus int.
RCA
LAD