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					     Technological Innovations
          over the years
         and their impact
       on Nuclear Imaging

       Shantanu Ganguly
Regional Radiation Medicine Centre
         VECC,KOLKATA
                   Nuclear Imaging
• A type of EMISSION IMAGING
• Radiopharmaceutical (Radioisotope+ Compound)
  depending on target organ >administered to patient >
  accumulates in target organ>Gamma Radiation emitted
  from organ > detected by external detector>image of
  organ created

• Single Photon Emitting Radioisotope:[ Gamma Camera]
  Tc-99m, I-131, I-123, Tl-201, Ga-67, In-111
• Positron Emitting Radioisotope:[ PET Camera]
  F-18, C-11, N-13, O-15, Rb-82
 Static Imaging (Structure): Bone, Thyroid, Liver, Brain
 Dynamic Imaging( Function): Renal dynamic, Hepatobiliary,
                           Cardiac GBP and MPI
GAMMA CAMERA (ANGER CAMERA)
PET   CAMERA




BGO DETECTOR RINGS
  Improvements in Gamma Camera Performance

   All-digital cameras
  exhibit much better performance parameters:
• Intrinsic Spatial resolution:<4.5mm (~10mm)
• Intrinsic Uniformity :<4.0% (~10%)
• Intrinsic Count rate Performance: Max.>300K cps (<50K cps)
  - Makes Cardiac First Pass Studies possible
  Data Acquisition Matrix size:
• 128x128 SPECT & Dynamic (64x64)
• Up to 512x512 Static (256x256)
• Up to 5.0 zoom acquisition available (2.0 zoom)
• Larger matrix and higher acquisition zoom ensures
  better image details
• WINDOWS based acquisition and processing software-
  More convenient to use
                     DISPLAY
Color Display
• 64 level gray scales> 256 shades color scale
• Subtle differences in count can be identified
• Very low activity distinguished from zero
  activity
• Film printing > Paper printing [ mostly color]
Cine Mode Display
• In MUGA, Myocardial Perfusion studies mostly
• Visual assessment of cardiac wall motion
• Identification of patient motion and artifact
               ECG Gated Imaging

• Used in Equilibrium Radionuclide Ventriculography
  and Gated Myocardial Perfusion SPECT Imaging
• ECG input synchronized to computer so that the R-
  wave triggers acquisition of data (Physiological
  Gating)
• Each R-R interval divided into 24 equal frames.
• Individual frames grouped with identical time frames
  of subsequent beats
• After several hundred beats, a series of single
  composite images representing a single cardiac
  cycle with enough counts is created
• Provision for Aberrant Beat Rejection during
  acquisition
GATED IMAGING -12-FRAME
          Whole Body Mode Imaging
• Mostly used for Imaging the entire bony skeleton
  to detect Metastases
• Large Rectangular Detectors[40 cm.x50+cm.]
• Dual Detector Camera [Simultaneous Anterior and
  Posterior images]
• Infra-red sensors mounted on detectors for body
  contouring
Advantages:
• Short scanning time: Patient comfort
• More patient turnover
• Entire skeleton seen at a time: Better scan
  interpretation
WHOLE BODY MODE SKELETAL IMAGING
        Parametric images in GBP

Based on Fourier Transformation of Time-activity
  curves
Phase Image:
• Shows synchrony or asynchrony of cardiac wall motion
• Ventricles one phase, Atria 180 degrees apart
• Conduction defect, scar, aneurysm-out of phase
Amplitude Image:
• Shows extent of cardiac wall contraction
• Normally, high values of contraction across both
  ventricles
• Decreased or Absent contraction (Scars)-
   reduced/absent amplitude
                 Why SPECT?

• Planar Nuclear Imaging produces 2-D Projection
  of 3-D Radionuclide Distribution inside the body or
  individual organ
• Planar imaging unable to provide information in the
  depth of a large organ
• Attenuation by overlying tissue
• Activity from overlying and underlying tissues
• Shape and disposition of some organs( Heart,
  Brain etc.)
• Hence, Sectional Images are Essential
              Why SPECT?- Contd.
                             Detector
Rays
from
                               Gamma Rays
Overlying
Organ                          Attenuation +
                               Scatter in overlying
                               organ

                                    Lesion of Interest


Organ                            Body Contour
of interest
                 Rays from
                 Underlying Organ
Advantages of SPECT over Planar imaging
• Improved contrast and easier interpretation
• Overlapping organ Tissue below and above
  slice of interest is eliminated
• 3-D representation of the organ is created
• The counts in a given pixel represents the
  counts in an actual volume of tissue
• Images can be reconstructed at different and
  arbitrary angles-
  Transversal, Sagittal , Coronal, and Oblique
  slices
             SPECT Procedure

• Rotating gantry with Gamma Camera Heads
• Dual Heads preferred to Single Head
• More counts collected in same time period
• Total study time short :
  Routine use feasible
• Step and Shoot mode
• H-and L-modes
• Triple Head and Cylindrical (Annular Head)
  cameras- for Brain only
H-MODE    L-MODE
          CARDIAC
GENERAL
              SPECT Reconstruction

Older Method : Filtered Back projection (FBP)
Newer method: Iterative Reconstruction
• A model of System degradations,
  like Attenuation, Scatter, and Camera System
   Characteristics included in parameters (not available in
   FBP)
• Back projection and Re projection repeated (iterated)
   repeatedly, till there is minimal difference between original
   measured and calculated data
• Results are far better than FBP method
 Introduction of more powerful computers has made routine
   use of Iterative Reconstruction techniques possible
               Time-Of-Flight PET
• Difference in arrival times of annihilation photons
  helps to pinpoint the exact annihilation point
• TOF information used to constraint back-projection
  to exact region of origin of event
• Results in better signal-to-noise ratio in reconstructed
   image
• Made possible by faster detector crystals
  (BaF2 ,LSO) and faster electronics
• Current TOF can detect a difference in arrival times of
   ~0.3 nanosecond, resulting in TOF resolution~5 cm.
           2-D and 3-D imaging in PET

2-D imaging (old):
 Detector rings separated by septa, intended to reduce scatter
• Also reduces true counts, decreasing camera sensitivity
3-D imaging (current):
 No septa between detector rings (volume imaging)
• Allows detection of true coincidence events that occur in
   different detectors on different rings
• Increases sensitivity by 5-to 10-fold or more
 3-D imaging made feasible by:
• Faster detector crystals and better electronics, which
 leads to better temporal and energy resolutions-
  can eliminate scatter
3-D ACQUISITION IN PET IMAGING
            Fusion Imaging-
         SPECT-CT and PET-CT
• Single instrument that can acquire both SPECT
  or PET and CT data in immediate sequence with
  unchanged patient position
 Benefits of Fusion Imaging:
• Attenuation Correction
• Precise anatomical localization of a lesion seen
  on SPECT/PET image
 Since 2008,PET/MRI scanners have started
 operating
ALL IN ONE SYSTEM: hybrid imaging
      Clinical benefits of SPECT-CT

• Adds anatomical information to nuclear studies
• Improves specificity of nuclear studies
  -Reduces the differential diagnosis
• Exact anatomical location identified by CT is often
   the key to proper diagnosis of a lesion visualized on
   nuclear image
• Improves nuclear image quality via Attenuation
   Correction
• SPECT-CT finds application in imaging of most
   organs: Bones, Cardiac, Tumors, Thyroid, Infection,
   Brain, Lungs etc.
► solitary bone metastasis   0941661 15/3/06
PET-CT CAMERA
                  PET-CT imaging-
               Attenuation Correction
• Improvement over older Transmission Data from
  Radioactive line sources
 CT data used for PET attenuation correction
Advantages:
• Quality and Spatial resolution of CT data far superior
  to conventional transmission data
• Whole body CT scan acquired in<1min. with latest
   spiral CT scanner, compared to >20 min.
   for transmission scan
• CT source does not decay and need replacement
        Clinical Benefits of PET-CT
• Mainly useful in Oncology-
  Breast, Esophageal, Melanoma, Lymphoma, Lung,
  Colorectal, Head and Neck, Ovarian, Brain
Applications:
• Identifies presence and precise location of cancer
• Determines full extent of disease, helping Staging of
  cancer

• Can assess response to Chemotherapy by assessing the
  size and activity of lesion
• Can guide Surgery or Radiotherapy treatment planning
• Can distinguish residual/recurrent disease from scar or
  necrotic tissue following Surgery or Radiotherapy
        BENEFITS OF NETWORKING

• Separate acquisition and processing workstations
  connected by LAN
 Simultaneous acquisition of study and processing of earlier
  studies
 More powerful and versatile processing software
• Multiple Gamma Camera Acquisition Stations connected
  by LAN to one processing workstation
• Processing workstation at Gamma Camera connected by
  LAN to workstation at NM physician’s chamber
 Viewing images on screen
 Processing by NM physician

 INTERNET:TELENUCLEAR MEDICINE

				
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posted:8/25/2011
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