Digital Techniques for Myocardial Perfusion SPECT Dr. Muhammad Ayub Diplomate Certification Board of Nuclear Cardiology Diplomate 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 Display• Camera Heads PHA – Collimator x y – Scintillation Crystal Lead Shield – Photo multiplier tubes Pulse Processing Electronics – PHA – ADC PMTs Crystal Collimator
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 stepStep and shoot acquisition
Theory of Back Projection 1 0 22.5 Imaging a point source 45 • Rotating camera headPoint • Step and shoot at 8source 67.5 angles over 180 90 • Only photons to camera face are detected • Planar ‘projection’ 180 acquisition at each step
Back Projection of 4 Ray Sums Camera angle x 0° 22.5° Depth in 45° transaxial slice 67.5° Transaxial Plane
Filtering• Pre filtering• 3D Post Filtering• Types – Low pass – Metz – Wiener – Band
Types of Filters Used Magnitude•Ramp filter –Always applied –Removes star-burst effect (good!) –Amplifies high frequency noise (bad!) Frequency•Smoothing filter 1.0 –E.g. Hanning or Butterworth –Smooths image (removes noise 0.0 generated by ramp filter)
The Iterative Loop Flow chart of a loop in iterative process• 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.
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 translationtable may produce pseudocontouring: the false perception of an edgewhen none, in fact, is present. An image thatshows a linear transition from maximal to minimal counts is shownusing 3 different color tables. The steady transition of the image isshown most faithfully by the gray scale.