digital techniques for myocardial perfusion spect
DESCRIPTION
SPECT Techniques for data acquisition, processing and display in Nuclear CardiologyTRANSCRIPT
Digital Techniques for Myocardial Perfusion SPECT
Dr. Muhammad AyubDiplomate Certification Board of Nuclear CardiologyDiplomate Certification Board of Cardiovascular CT
Punjab Institute of Cardiology, Lahore
SINGLEPHOTONEMISSIONCOMPUTEDTOMOGRAPHY
A Modern SPECT Gamma Camera
SPECT Equipment
• Camera– Single Detector– Multi detector
• Analog to digital converter• Computer interface
– Data storage– Data processing– Display
Gamma Camera• Gantry• Camera Heads
– Collimator– Scintillation
Crystal– Photo multiplier
tubes– PHA– ADC Crystal
PMTs
Lead Shield
Pulse Processing Electronics
Collimator
PHAx y
Display
Cardiac SPECT Acquisition
• Gamma camera with 1 or 2 heads (90 ° angle)
• 180° rotation• 32 steps (16 per head
if 2)• Planar projection
acquisition at each step
Step and shoot acquisition
Workstation
• Types– Unix Workstations– PCs, Macs
• Storage• Memory• Graphics• Software
PHA
Tomographic Acquisition
• Matrix• Angular Range• Angular Steps• Time per Step• Gated Vs non gated acquisition• Continuous Vs Step and Shoot
acquisition
Tomographic Acquisition
• Matrix– 64 x 64 Standard– 128 x 128
Tomographic Acquisition
• Angular Range– 180 degrees– 360 degrees
215 LPO
RAO
135
Tomographic Acquisition
Angular Steps – 3 degrees Recommended for Tc Studies– 6 degrees Recommended for Tl Studies– 12 degrees Not Recommended
Image Acquisition
• Orbit– Circular Standard– Non-circular Optional
Tomographic AcquisitionGated SPECT
Technical Considerations
• QC– Energy– Uniformity– Linearity– COR
Problems
• Motion Artifacts• COR defects• Soft tissue attenuation• Foreign Objects
Image Processing
• Filtered Back projection• Filtering• Iterative Reconstruction• Corrections
– Attenuation Correction– Scatter Correction
Theory of Back Projection 1
Imaging a point source• Rotating camera head• Step and shoot at 8
angles over 180°• Only photons to
camera face are detected
• Planar ‘projection’ acquisition at each step
0°22.5 °
45°
67.5°
90°
180°
Point source
45°
67.5°
22.5°0°
Back Projection of 4 Ray Sums
Camera anglex
Depth in transaxial slice
Transaxial Plane
Filtering
• Pre filtering• 3D Post Filtering• Types
– Low pass– Metz– Wiener– Band
Types of Filters Used
• Smoothing filter–E.g. Hanning or Butterworth–Smooths image (removes noise
generated by ramp filter)
1.0
0.0
Frequency
Magnitude• Ramp filter –Always applied–Removes star-burst effect (good!)–Amplifies high frequency noise (bad!)
Pre filtration
3 D Post FilterLow pass Filter
Metz Filter
Wiener Filter
Band Pass Filter
Filter Example: Butterworth
Filtered Raw image
Butterworth [Cutoff = 0.3 Order =5]
Filter Reconstructed slice
Too smooth!
Filter Example: Butterworth
Butterworth [Cutoff = 0.5 Order =5]
Filter Filtered Raw image
Reconstructed slice
Good quality
Image Reconstruction
• Short Axis• Vertical Long Slices• Horizontal Long Slices• Slice Thickness
Transverse Reconstruction
• Initial estimate – e.g. uniform object• Compare forward projection to real projections• Perform several iterations:
– Each time, alter original transverse estimate until pseudo-projections converge with real ones.
The Iterative Loop
Flow chart of a loop in iterative process
Copyright ©2008 American College of Cardiology Foundation. Restrictions may apply.
Sharir, T. et al. J Am Coll Cardiol Img 2008;1:156-163
New MethodsWIDE BEAM RECONSTUCTION
Oblique Reformatting
Image Display
• Cardiac Stress Rest Display Format• Colored and Black & White Display• 3D display• Cine Display• Animation
The use of different colors (as opposed to intensities) in a translation table may produce pseudocontouring: the false perception of an edge when none, in fact, is present. An image thatshows a linear transition from maximal to minimal counts is shown using 3 different color tables. The steady transition of the image is shown most faithfully by the gray scale.
Visual scoring1
0
4
2
4
4
1
2
2
3
4
4
100%
70
50
30
10
0
4 normal 100 - 70%
3 mild 70 - 50%
2 moderate 50 - 30%
1 severe 30 - 10%
0 absent 10 - 0%
Score
Normal Scan
3D Display
Quantitative Display
• Bulls Eye Reconstruction– Cequal– PTQ map
• Quantitative Gated SPECT Display
PTQ Map
3 : no uptake ; defect3 : no uptake ; defect2 : severely decreased uptake2 : severely decreased uptake1 : slightly decreased uptake1 : slightly decreased uptake0 : normal uptake0 : normal uptake
Segmental analysisSegmental analysis
A four-point grading system
A four-point grading system
apicalapical basalbasal
V-long axisV-long axisshort-axisshort-axis
1717
1818
1919
2020
22
3344
11
5566
7788
1111
99
1010
12121313
1414
1515
1616
Quantitative Gated SPECT
QGS
Thank You