Quantitative Analysis of
         Myocardial Perfusion SPECT

  Anatomically Guided by Coregistered
   64-Slice Coronary C...
Coronary CT                 Myocardial perfusion
  angiography (CTA)               SPECT (MPS)

• precise localization    ...
Previous studies




• Need interactive alignment
• Complicate protocol

• Reduce clinical usability
Aim of the study
• To develop tool for rapid automatic
  – Coregistration
  – Visualization
  – Combined quantification
  ...
MATERIALS AND METHODS
Patient Selection
• Between October 2005 and May 2007
• Retrospectively 40 consecutive patients
  – who underwent myocardi...
The imaging indications
• post–myocardial infarction (3 cases)
• post–percutaneous coronary intervention risk stratificati...
Patient Characteristics
CT Image Acquisition


                        Unenhanced CT scan


                  CT coronary calcium scores


       ...
Coronary CTA Image Reconstruction


Raw CTA data → retrospectively gated reconstruction
    performed at 40%-80% of the R-...
CTA Image Evaluation

• A coronary CTA reader
   – with experienced >300 coronary CTA interpretations
   – Unaware of MPS ...
ICA Image Acquisition and Evaluation

• Standard technique of intensive coronary
  angiography
• Evaluate by interventiona...
• Left main stenosis > 50% was
  considered as significant for the
  LAD and LCX territories

• If present the
ramus inter...
Angiographic Characteristics of Data (n = 35)
MPS Protocol

• Standard protocol
   – 1- or 2-d protocols
   – dual-isotope (thallium–technetium) protocol

• MPS acquisi...
MPS image processing
MPS image processing

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




Validation of Automatic Registration (error analysis)
manual alignment parameters (3 translations...
MPS image processing
MPS image processing
                 2-dimensional/3D textures

 Segmented CTA voxel maps → rendered in 3D within QPS
and...
MPS image processing
CTA-Guided MPS Contour
              and Territory Adjustment

• Fused coronary CTA and MPS images were evaluated
  with o...
• Adjust vascular territories segment by
  segment
  – based on a 17-segment American Heart
    Association model
  – usin...
MPS image processing


•perfusion-defect performed individually for
each vessel, 17 segments vascular territory

•total pe...
QMPS
RESULTS
• Of 35 cases with all 3 scans (CTA, MPS,
  and ICA) available
  – 20 patients underwent CTA after MPS
  – 15 underwent MP...
• In cases underwent MPS after CTA
  – 7 had at least 1 nondiagnostic major coronary
    segment on CTA
  – 4 had maximal ...
• 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
   –...
• TID ; 1.15 + 0.14 (range, 0.96–1.4)

                     MPS findings
• Visually ;
   –   normal              in 3 case...
Registration Algorithm
• Speed of automated registration = 1–2 s per study

• The automatic volume registration of motion-...
• All 3 failed cases were women with small hearts
  – (motion-frozen stress diastolic volumes, 29–52 mL on MPS)


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




MPS




fused unregistered MPS and CTA




after automated volume registration
Contour and Territory Adjustments
• Adjust
   – MPS vascular region definitions 17 studies
   – LV contours (valve plane l...
Combined Performance for CAD Detection


  Areas Under ROC Curves for Detection of CAD
  (>70% Luminal Stenosis) in Indivi...
ROC curves for disease detection in
individual vessels by partial TPD per vessel

       LAD                     LCX      ...
MPS         LAD   LCX     RAD

 Sensitivity %   67    67       67

 Specificity %   50    83       60




CTA-guided MPS  ...
Number of lesions correctly identified
     corresponding to > 70% stenosis on ICA


                         LAD     LCX ...
CTA-guided MPS agreed with angiography in
• 4/9 discordant cases for LAD
• 4/5 discordant cases for LCX
• 3/6 discordant c...
•   A. valve plane is
    determined
    incorrectly

•   B. after MPS
    contour
    adjustment
    revealing RCA
    de...
CTA : nonsignificant,
<50% proximal RCA lesion
 and significant LAD lesion
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% RC...
DISCUSSION
• Software image fusion of coronary CTA and MPS from
  separate or hybrid scanners has been proposed before

• Previous st...
• MPS contours (mitral valve plane position)
  – can be adjusted on the basis of the CTA
    anatomic volume data
     • M...
• Combined visual analysis
   – size and the severity of the stenosis        increase accuracy
   – presence of artifacts
...
• MPS + unenhanced CT registration from hybrid
  scanners
  – for attenuation correction
  – are already in an approximate...
• Summed MPS + coronary CTA
  – lead to mismatches in the size of the ventricle


• Motion-frozen MPS + coronary CTA
  – m...
• Hybrid MPS–coronary CTA or PET–coronary CTA

• Not used routinely in cardiac imaging
   – because of the difficulty in p...
Bias in our study population

• patients with
   – frequent occurrences of equivocal results from the initial test
   – si...
Radiation dose
Mean estimated radiation dose
• CT (CTA and coronary calcium scoring scan) ~ 19.7 mSv
• dual isotope stress...
Limitations
• This study : fully automated quantitative analysis and
  automated image registration

• But the contour def...
• Retrospective study
• Biased population
  – high prevalence of equivocal results on the initial
    imaging test
  – cli...
CONCLUSION
• Software coregistration of coronary CTA
  and MPS images obtained on separate
  scanners can be acquired rapi...
Thank You
      Left main   LCX
                         Ramus int.
RCA

                        LAD
Myocardial Perfusion SPECT coregistered Coronary CTA
Myocardial Perfusion SPECT coregistered Coronary CTA
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Myocardial Perfusion SPECT coregistered Coronary CTA

  1. 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. 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. 3. Previous studies • Need interactive alignment • Complicate protocol • Reduce clinical usability
  4. 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. 5. MATERIALS AND METHODS
  6. 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. 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. 8. Patient Characteristics
  9. 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. 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. 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. 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. 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. 14. Angiographic Characteristics of Data (n = 35)
  15. 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. 16. MPS image processing
  17. 17. MPS image processing static MPS images in end-diastolic (ED) phase to match the diastolic cardiac phase of coronary CTA
  18. 18. MPS image processing
  19. 19. 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
  20. 20. MPS image processing
  21. 21. 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
  22. 22. MPS image processing
  23. 23. 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
  24. 24. • 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
  25. 25. 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
  26. 26. QMPS
  27. 27. RESULTS
  28. 28. • 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
  29. 29. • 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
  30. 30. • unenhanced CT calcium score ; average was 942 + 1,530 (range, 0–7,781) – Heavy calcification (score > 500) in 15/33
  31. 31. • 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
  32. 32. • 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%)
  33. 33. 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
  34. 34. • 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
  35. 35. Accuracy of Automated Alignment of SPECT and Coronary CTA for Translations and Rotations
  36. 36. CTA MPS fused unregistered MPS and CTA after automated volume registration
  37. 37. 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%.
  38. 38. Combined Performance for CAD Detection Areas Under ROC Curves for Detection of CAD (>70% Luminal Stenosis) in Individual Vessels
  39. 39. 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
  40. 40. 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
  41. 41. 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
  42. 42. 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
  43. 43. • A. valve plane is determined incorrectly • B. after MPS contour adjustment revealing RCA defect. • ICA confirmed RCA stenosis >70%
  44. 44. CTA : nonsignificant, <50% proximal RCA lesion and significant LAD lesion
  45. 45. 3% defect in typical RCA territory defect between LAD and LCX CTA-MPS coregister → Need for contour adjustment → Quantification
  46. 46. 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
  47. 47. DISCUSSION
  48. 48. • 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
  49. 49. • 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
  50. 50. • 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
  51. 51. • 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
  52. 52. • 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
  53. 53. • 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
  54. 54. 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
  55. 55. 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.
  56. 56. 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
  57. 57. • 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.
  58. 58. 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.
  59. 59. Thank You Left main LCX Ramus int. RCA LAD

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