Imaging in Research by CtFBO4G

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									 Imaging in Research

    Gail Stevenson, DVM
           Radiology
Center for Gamma Ray Imaging
              Introduction
• In vivo molecular imaging in small animals
  is the bridge between in vitro data and
  translation to clinical application
• Multiple longitudinal images provide more
  reliable information and reduce animal
  numbers needed.
• No one imaging method is ideal for all
  studies.
               Cost vs. Value
•   Cost of animal
•   Cost of technician time
•   Cost of radiotracers
•   Cost of machine time
•   Value of your time
•   Value of your results
Biomedical Imaging: The Big Picture
                                       Imaging
                 Biomedicalmodels of human disease
         is mostly about mouse and rat



Normal        Myocardial Infarct          Myocardial Infarct        Normal




    Clinical Images of Humans             Laboratory Images of Rat Models



                         SPECT 99mTc-Sestamibi
                        Myocardial Perfusion Scans
                   Convergence
Biology/Medicine        Technology         Imaging Science
Physiology            Materials Science     Modeling
Genomics              Detection Physics     Reconstruction
Proteomics            Electronics           Optimization
Cellular              Computing             Estimation
  Biochemistry              Power            Techniques
Immunology            Mechanics             Calibration
 Mouse models         Instrumentation        Methodology



               An interdisciplinary endeavor!
       Principal Biomedical Imaging
                 Modalities
  • Magnetic Resonance Imaging (MRI)
  • Ultrasound (2D and 3D)
  • Optical Imaging
      – Microscopy
      – Fluorescence Imaging
      – Bioluminescence Imaging
      – Coherence Tomography (OCT)
  • X-ray Computed Tomography (CT)
  • Single Photon Emission Computed Tomography (SPECT)
  • Positron Emission Tomography (PET)


Research universities, are investing in multimodality laboratories that provide
their basic scientists with access to most if not all of these techniques.
          One (or a few) Camera Design
                     Options



• Stationary camera(s)                   Stationary mouse
• Mouse rotates about vertical axis      Camera rotates about horizontal axis
• Pros:                                  Pros:
                                             Mouse in normal position
    – Simplest arrangement               Cons:
• Cons:                                      High precision motion required with
    – Abnormal position for mouse            possibly heavy camera(s)
                                             PSF probably needs to be modeled
    – Measured or modeled PSF must
      be rotated during reconstruction
• Anatomical
• Functional
 Molecular Imaging Components
• Requires the administration of an image-altering
  substance known as the contrast agent
• Contrast agent must be able to bind or activate
• 3 components
   – Molecular target expressed within animal
   – Reporter which enables detection of the contrast agent
     by an imaging modality
   – Targeting ligand which enables the contrast agent to
     bind to the molecular target
     Exogenous Contrast: The Tracer
               Principle
                    Basis for molecular imaging




 George Charles de Hevesy
       (1885 – 1966)
1943 Nobel Prize in Chemistry


             Molecular target becomes a signal source (photon pairs)
 Label             Tracer should not affect target or organism
  Ligand
        Computer Tomography

• Various tissue types absorb X-rays differently as
  they pass through the body
• High anatomical resolution
• Probes are iodine or barium-based and are needed
  for molecular capabilities
• Probes increase radiation damage
• Increasing the duration of exposure increases
  sensitivity and spatial resolution.
• Both these later factors limit repeat imaging due to
  radiation dose.
              FaCT: Adaptive CT
On-board
Computer


Electronics                           Static
                                  Counterweight

    X-ray
   Source                           Dynamic
                                  Counterweight

Translating
                                   Detector
   Beam
FaCT Sample Projections




Low-Mag   Mid-Mag   Hi-Mag
       Optical Imaging

– Employs light emission (photons). Two
  main forms: fluorescence or
  bioluminescense.
– Can employ bioluminescence probes, near-
  infrared fluorochromes, and red fluorescent
  proteins.
– Works primarily for structures near the
  surface.
Optical Imaging with the Window
            Chamber




   Attached to a dorsal skin fold. Cover slip replaces
   one section of skin. Creates a ~2-D environment for
   implanted tumors.
           Fluorescence

• visible light excites the area and a camera or
  fluorescent microscope detects it.
• Does not require administration of a substrate, so no
  tail vein injections.
• Fluorescence Molecular Tomography (FMT)
  employs a continuous pulse light and multiple
  detectors resulting in a 3-D image.
          Optical pH Imaging of an Invasive
                       Tumor
              SNARF-1
          Ch.3             Ch.2




                                                               Calibrated ratio provides
      A fluorescent tracer, SNARF-1,                           image of local pH, showing
      has a pH-dependent spectral                              highly acidic tumor
      response.
                                       Separate fluorescence   microenvironment
                                       images

Courtesy of A.F. Gmitro,
 S. Moore, R. Gatenby
             Bioluminescense
• Light emission does not require excitations of a reporter.
• Light originates from a substrate reaction which releases
  photons.
• Commonly transfect with one of the luciferase family (usually
  from firefly). And luciferase protein can catalyze reaction.
• Give the animal D-luciferin by IV or IP injection at saturating
  levels for the luciferase reaction
• Detects lower limits of light
• Ten-fold decrease for every centimeter of tissue depth
• Catalytic reaction is time and enzyme-dependent so window
  for optimum image capture (usually image within 15 minutes
  for up to 60 minutes)
• Images are generally overlaid black and white photos of the
  mouse taken at the same time to determine location.
               Ultrasound
• Formed by interaction of sound with subject
• Transducer produces acoustic energy
• Acoustic energy is attenuated and reflected
  by structures
• Impedence appears brighter (cysts are dark)
• Instantaneous results
• No radiation
       Magnetic Resonance Imaging
                  MRI
• A large magnet generates a field around the
  subject. This causes hydrogen atoms to align
  themselves in water (dipole). Coils around the
  animal generate a temporary radio frequency pulse
  that can change the alignment of the dipoles.When
  the pulse stops, the dipoles relax to normal. The
  parameters are different for different tissues.
• Modified techniques extend the capability.
  Gadolinium can be a nonspecific probe, or can
  become a targeted probe when labeled.
       MRI Advantages and Disadvantages

•No ionizing radiation                        •Expensive to purchase, install, and operate,
                                              requires technological expertise
•Non-invasive, does not require a
contrast agent (although agents are           •Low sensitivity in many applications, can be
used to improve contrast and sensitivity      improved with appropriate contrast agents
in some cases)
                                              •Requires cooperation of patients (patients must
•MRI is very flexible, can produce an         remain very still), can require sedation
amazing variety of images for different
applications                                  •Limited space inside magnet, claustrophobia and
                                              obesity can be problematic
•MRI can produce ‘slice’ images of
arbitrary orientation without moving          •Pacemakers and metallic (especially ferrous)
the patient or machine                        implants need special consideration and can
                                              prevent scanning
•Excellent for obtaining contrast in ‘soft’
tissues (not as good with bones,              •Magnetic field requires special safety precautions,
cartilage, etc.)                              potential for disaster if a large piece of metal gets
                                              too close (iron O2 tanks)
HARDWARE I


             BIOSPEC 4.7 Tesla
                 (Avance)
                     -40 cm gradient coil system (S116)
                            (15 gauss/cm)
HARDWARE II

              AMX400 WB 9.3 Tesla

                        40 mm gradient coil system
                             (100 gauss/cm)
                               Dual/single tune inserts




                                   Micro 2.5
  Biological Magnetic Resonance
  at the University of Arizona


Facility:
1.5 T whole body MRI scanner
4.7 T MRI/MRS scanner
7.0 T MRI/MRS scanner (summer 2007)
9.4 T MRI/MRS system
11.7 T NMR spectrometer
Un-anesthetized acclimated, operant
    conditioned SCID mouse

        chocolate milk delivery system
                EMBRYOS IN SITU (9.3 Tesla)



- 150 mm isotropic
  resolution
- 3D RARE
  (T2 weighted)
         Alzheimers Disease, Fixed brains




APP/PS1 model of Alzheimer’s Disease                     Control mouse

Dark spots in grey matter of APP/PS1 mouse are likely deposits of amyloid plaques   32
 Positron Emission Tomography
              PET
• PET isotopes emit beta + radiation (positrons);
  each positron undergoes an annihilation reaction
  with an electron which results in the generation of
  two photons (high energy) that are detected and
  converted into visible light.
• Isotopes last from minutes to days (18F=110
  minutes)
• 18FDG (18-fluorodeoxyglucose) is well-known.
  Accumulates where there is glucose uptake.
• Probes are in nanomolar concentrations so little
  interference with biological processes.
               Useful Radioisotopes
      Designation   Main Emission   Half-life   Chemistry
       18F            positron      2 hrs
PET




      15O             positron      2 min
      11C             positron      20 min
      64Cu            positron       12.7 hr
     Single Photon Emission Computed
          Tomography (SPECT)

• Differs from PET as isotopes are direct
  gamma emitters in a single direction.
• Typical isotopes are 123 Iodine
  99mTechnetium.

• Isotopes have a longer half-life than most
  PET isotopes, making it easier to do studies.
  Half-life of technetium is 6 hours.
              CGRI SPECT Systems


FastSPECT I                                   SPECT/CT

                                SemiSPECT
                 FastSPECT II


Spot Imager
                                                 M3R




                 LumiSPECT        FaCT      Adaptive System
 ModCam
                Some Useful Radioisotopes
        Designation     Main Emission   Half-life   Chemistry
        99mTc          140 keV Gamma     6 hrs
         123I          159 keV Gamma    13 hrs
         125I          ∼30 keV X        60 days
SPECT




         131I          364 keV Gamma     8 days
        111In     171 & 245 keV Gamma   3 days
        133Xe           81 keV Gamma     5 days
        67Ga           185 keV Gamma     3 days
        201Tl           77 keV X        3 days
        Anesthesia
Anesthetics affect experiments
Experiments affect anesthetics
Evolution of Mouse Imaging Holders

Supine + Anesthesia       Prone + Awake

                      Opaque Nose Cone




                            Electric Heater


   Original Method     Current Imaging Method
Multi-Camera Multi-Resolution System



                                                           Five 1-mm pinholes


                                                           Nine 0.25-mm pinholes

 Table-top four-camera SPECT system with
   interchangeable apertures
 Test bed to address the question: for a given task
   and ensemble of objects, what is best
   configuration?
           Hesterman et al., Med. Phys. 34(3), 987-993, 2007.
Prototype Adaptive Imaging System




     • Interleaved stages to permit independent motion of camera and
       aperture assembly relative to object
     • Aperture enclosure contains microstage system for selecting
       pinhole from array of sizes

              Freed et al, Med. Phys. 35(5), 1912-1925, 2008.
                          FastSPECT II →
Key Features:              AdaptiSPECT • Listmode data
• 16 cameras in 2                            acquisition architecture
rings of 8 with
adjustable radial                            • Full dynamic imaging
position                                     capability for periodic
                                             and non-periodic
• 5 axis robotic stage                       processes
for calibration and
imaging subject                              • Gigabit data link for
positioning                                  compute-intensive
                                             processing on PS3
• Exchangeable                               cluster
cylindrical imaging
apertures for choice of                      • Raw data rate: 50
magnification/field-of-                      Gigabits/sec
view
    FastSPECT II Imaging-
     Configuration Space

                     18X Magnification

             Resolution                  Sensitivity


                                                                       FS II




                                                       Magnification
                          Field of View

3X Magnification
AdaptiSPECT




 • Adjustable aperture
 • Motorized cameras
AdaptiSPECT




 • Adjustable aperture
 • Motorized cameras
AdaptiSPECT




 • Adjustable aperture
 • Motorized cameras
AdaptiSPECT Aperture



• Six aperture selections
     – Three center of FOV to pinhole distances
     – Two pinhole selections at each distance
         Single pinholes
         Quincunx pinholes
                   Motivations
• Study planning
      – ensure tissue of interest is in field of view
• Localization
      – provide anatomical framework that supports interpretation
        of functional image
• Complementary information
      – use second modality to show different process
• Quantitation
      • provide information for scatter and absorption correction to
        permit derivation of absolute tracer concentration, for
        example
                   Motivations
• Expand the parameter space
      – extend spatial and temporal resolution
      – enhance detection sensitivity
      – improve signal to noise ratio
• Integrate strengths/eliminate weaknesses
• Provide information for adaptation
      – use a first modality to guide parameters of second modality


• More information → better diagnoses
• Better information → better science
      Gene Transfer to Ovarian Tumors
                               Ring of infected cells
                                 on tumor surface
        Kidney       6 mm



            11 mm




                                                    Gut

Collaboration with Kurt Zinn
Univ. of Alabama Birmingham
          SPECT Study of Multi-drug
                Resistance
•   Multi-drug resistance is a trait of many malignant tumors
•   A result of over expression of a gene (MDR-1) that codes for p-
    glycoprotein 170 – a transport channel that ejects cationic, lipophilic
    substances (like many cytotoxins) from within the cell
•   One cause of chemotherapy failure




                                                         Lipophilic cationic
                                                              targets




Z. Liu et al.
                             Hypothesis
•   SPECT imaging with cationic, lipophilic radiotracers should reveal the
    action of the efflux pump:
     –   Time/activity curves should differ for drug sensitive versus drug resistant
         tumor lines
•   Model
     –   SCID mice carrying human breast cancer tumors
•   Instrument
     –   FastSPECT 24 camera dynamic imager
•   Tracers
     –   99mTc-sestamibi

     –   99mTc-tetrofosmin

     –   99mTc-Q12
           Dynamic Images of 99mTc-
             sestamibi in MCF7/S



Time in
minutes




          Tumor line does not have multidrug resistance trait
Dynamic Images of 99mTc-sestamibi in
           MCF7/D40



Time in
minutes




          Tumor line has multidrug resistance trait
 Follow-on Study: Modulation of p-
           Glycoprotein
Evaluate whether imaging could detect inhibition of multidrug
resistance by a proposed agent: PSC833

Repeat the imaging experiments:
                MCF7/S with and without PSC833 2 hours earlier
                MCF7/D40 with and without PSC833 2 hours
   earlier
FASTSPECT dynamic images over 30 min
Tumor time-activity curves from ROI analysis.
Dynamic Imaging of 99mTc-sestamibi in
     MCF7/D40 with PSC833




 Time in
 minutes
Reproducibility & Computing Solutions
• Optical position sensor
  based on Hamamatsu PS-
  photodiode: 25 µm.




• PS3 cluster with ~40
  machines, fast network, and
  Luca Caucci
                   Contrast
• Endogenous
   – Basic property of tissue
   – Examples:
       Linear attenuation coefficient in CT
       Proton density in MRI


• Exogenous
   – Introduced via contrast agent
   – Examples:
       Radiopharmaceutical in SPECT or PET
       Fluorescent tag in bioluminescence
              Contrast - CT
• Endogenous
   – Linear attenuation coefficient - electron density
       Tissue density
       Average atomic number


• Exogenous
   – Introduced via contrast agent with high z element
   – Examples:
       Iohexol (Omnipaque)
       Barium sulfate
             Contrast - PET
• Endogenous
   – None


• Exogenous
   – Introduced via contrast agent with positron emitter
   – Examples:
       18F-FDG
       82Rb-chloride (Cardiogen-82)
         Contrast - SPECT
• Endogenous
   – None


• Exogenous
   – Introduced via contrast agent with gamma-ray emitter
   – Examples:
       99mTc-sestamibi
       99mTc-methylenediphosphonate (MDP)
              Contrast - MRI
• Endogenous
   –   Proton Density
   –   Relaxation times (T1, T2, T2*)
   –   Chemical shift
   –   Diffusion/water motion


• Exogenous
   – Introduced via paramagnetic contrast agent
   – Examples:
       Gd3+-DTPA (Magnevist)
       Superparamagnetic iron oxide nanoparticles
           Contrast – Optical
• Endogenous
   –   Index of refraction
   –   Density
   –   Chemical/spectral
   –   Scatter/dimensional


• Exogenous
   – Introduced via fluorescent/bioluminescent molecules
   – May involve gene insertion/modification
   – Examples:
       Luciferin
       Green fluorescent protein
       Nanoparticles
     Contrast – Ultrasound
• Endogenous
   – Interfaces between tissue with different speeds of sound
   – Motion
   – Scatter/dimensional features


• Exogenous
   – Introduced via microbubbles
   – May be targeted or untargeted depending on bubble surface
     chemistry
   – Examples:
       Albumin shell with octafluoropropane gas core (Optison)
       Lipid/galactose shell with air core (Levovist)
    Single Modality Comparisons



   CT        ♦♦♦   ♦♦♦    ♦♦♦       ♦     ♦      ♦

   MRI       ♦♦    ♦♦♦    ♦♦♦       ♦♦♦   ♦♦    N/A

 Optical     ♦♦♦    ♦    ♦          ♦♦♦   ♦♦♦   N/A
                              ♦♦♦
  PET        ♦♦♦   ♦♦♦       ♦♦     ♦♦♦   ♦♦♦   ♦♦

             ♦♦♦   ♦♦♦   ♦♦         ♦♦♦   ♦♦    ♦♦♦
 SPECT                      ♦♦♦
Ultrasound    ♦     ♦     ♦♦♦        ♦    ♦♦    N/A
     Single Modality Weaknesses
             Acceptable x-ray dose limits spatial resolution and sensitivity, low
       CT    endogenous contrast for soft tissues
             Limited sensitivity to molecular targets, contrast related to pathology
      MRI    via their effect on relaxation parameters Long acquisition time..
             Rapid loss of resolution with depth due to strong interaction with
   Optical   tissue, hard to do tomography
             Limited resolution due to positron range; affected by scatter.and
     PET     attenuation (correctable_ Cyclotron must be nearby.. Radiation.
             Low collection efficiency due to collimators or pinholes, affected by
   SPECT     scatter and attenuation (neither easily corrected) Radiation

Ultrasound   Contact with specimen required, whole body scanning difficult
Modality Sensitivity and Resolution




     Meikle et al., Phys. Med. Biol. 50 (2005) R45-R61
Stewardship
                        Conclusions
• Biomedical imaging is a very exciting area of work

• Lots of opportunities for improvements in systems – it all starts with
  detectors

• Optical arrangements need to be able to adapt to imaging subjects and
  objectives

								
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