ECSE-4963 Introduction to Subsurface Sensing and Imaging Systems

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ECSE-4963Introduction to Subsurface Sensing and
Imaging Systems

• Lecture 23 Molecular Imaging
• Kai Thomenius1 Badri Roysam2
• 1Chief Technologist, Imaging Technologies,
• General Electric Global Research Center
• 2Professor, Rensselaer Polytechnic Institute

Center for Sub-Surface Imaging Sensing
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Recap

• Last time we discussed
• MRI coil designs
• Gradient
• RF
• Phased Array
• Image quality in MRI
• Different modes of MRI imaging
• fMRI or functional MRI
• MRA
• Brief history of work done at GEs Global
  Research
• Today
• Introduction to Molecular Imaging

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What is Molecular Imaging?

• Molecular imaging (MI) is
• the remote sensing of cellular processes at the
  molecular level in vivo.
• So far, this has involved animals, typically
  mice, but humans are the longer term target.
• This remote sensing is being done with
• Conventional or modified imaging methods (e.g.
  MRI, PET scanners, optical methods)
• Exogenous agents (called probes) which interact
  with the cellular processes
• Except for nuclear medicine and PET, the focus
  today is on technique development on experimental
  animals

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What is Molecular Imaging?

• Current increase in interest due to
• Recent marriage of imaging techniques with
  molecular biology.
• Expansion of MI to a variety of modalities.
• Advances in several key scientific disciplines
  germane to specific and sensitive imaging, e.g.
  human genome project nanotechnology.
• Molecular Imaging has the potential of changing
  imaging landscape dramatically.

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Vision for Molecular Imaging
If successful, the following will be true

• a life-threatening disease is detected before
  symptoms appear
• therapeutic drugs are seen hitting their target,
  instantaneously
• therapeutic efficacy is measured in hours instead
  of months
• life saving drugs tailored to your genetic
  make-up and disease variant get to market years
  faster than possible today.

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Molecular Imaging

• Rationale
• Changes at cellular level occur well before
  anatomic changes
• Hence promise of earlier diagnosis.
• Functional changes may occur as much as a decade
  before anatomical changes.
• Redefinition of diseases such as cancer
• from
• organ system-based diseases
• to
• aberrations in molecular structure function
  traceable to the genetic (DNA) level.

Breast Carcinoma
We may be able toidentify genetic
pre-disposition to a disease.
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Big PicturePassive Molecular Imaging Systems
Processor
Detector(s)
Output
Surface
Molecule(s) of Interest
Background Molecule(s)
Detector(s)
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Big PictureActive Molecular Imaging Systems
Probing Transducer(s)
Processor
Detector(s)
Output
Surface
Influence Field
Molecule(s) of Interest
Modulation Field
Background Molecule(s)
Detector(s)
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Big PicturePassive/Active Molecular Imaging
With Contrast Agent
Probing Transducer(s)
Processor
Detector(s)
Output
Surface
Influence Field
Molecule(s) of Interest
Molecule-specific Contrast Agent
Modulation Field
Background Molecule(s)
Detector(s)
Role of the contrast agent is two-fold 1. Give
a stronger substance-specific contrast 2.
Enable use of existing modalities
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Background Animal Cell

• Cell Membrane
• Encloses cell, allows selected substances to pass
  through, has huge surface area, but little
  volume, very important site of biochemical
  activity
• Nucleus
• Holds DNA
• RNA is transcribed here
• Nucleolus
• Part of the nucleus where ribosomes are formed
• RNA is translated to proteins in ribosomes
• ER Endoplasmic reticulum
• A pathway to transport materials to specific
  places, instead of floating freely in cytoplasm
• Rough ER has lots of ribosomes sticking to it

Energy Producers
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Animal Cell

• Lysosome
• digests waste materials and food within the cell
  using enzymes
• Golgi Complex
• modifies molecules and packages them into small
  membrane bound sacs called vesicles. These sacs
  are targeted at various locations in the cell and
  even to its exterior
• Mitochondria
• The major energy production center
• Has its own DNA

• Chloroplasts
• Does photosynthesis in plant cells
• like mitochondria in many ways

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Key Molecules in a Cell

• DNA
• De-oxy ribonucleic acid
• RNA
• Ribonucleic acid
• Proteins
• 90 of a cell is water
• 50 of whats left is proteins

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Chromosomes

• A chromosome is formed from a single DNA
  molecule.
• Ploidy the number of sets of chromosomes an
  individual has
• A chromosomal DNA molecule contains three
  specific nucleotide sequences which are required
  for replication
• a DNA replication origin
• a centromere to attach the DNA to the mitotic
  spindle
• a telomere located at each end of the linear
  chromosome.

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De-oxy Ribonucleic Acid (DNA)

• Chemical method for long-term information
  storage. Like all information storage devices,
• It can encode information using pattern of base
  pairs
• The information can be read
• The molecule is stable secure over millions of
  years.
• Famous double-helix structure.
• Structural Constraints
• A pairs with T only
• G pairs with C only
• Length measured in terms of base pairs
• The human haploid genome contains 3,000,000,000
  DNA pairs.

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DNA Replication

• On any given rung, if you know one letter, you
  also know the other.
• Because of this property, DNA can replicate
  itself.
• First, it "unzips" down the middle. This leaves
  half-rungs exposed. Then A, C, G, and T chemicals
  float over and re-build a complete ladder.
• Errors in this process are rare, but do happen
• Called mutations
• Mutagens increase/cause mutations
• Ultraviolet light, nitrous acid,
• Cell kills itself if DNA is damaged too much
• Called apoptosis

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Ribonucleic Acid (RNA)

• Single-stranded, unlike DNA
• The role of RNA is three-fold
• a structural molecule,
• an information transfer molecule,
• information decoding molecule

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Genes

• A piece of DNA that includes all the code for a
  specific protein, as well as the code for when
  the protein is made
• Humans have about 30,000 genes
• A gene occupies a specific place, on a chromosome
  and is always found in the same chromosome in all
  persons.
• A gene expresses itself by making proteins by a
  two-stage process
• Transcription stage a particular enzyme
  recognizes the sequence of base pairs for a
  gene (a part called the promoter), and moving
  along the gene, makes a copy in the form of an
  RNA molecule.
• The messenger RNA is translated to a protein in a
  ribosome

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Proteins

• Truly the physical basis of life
• Every function of cell depends on them
• They are polymers constructed from one or more
  unbranched chains of amino acids
• Amino acids are the 20 building blocks of
  proteins, each coded for by a specific 3
  base-pair codon on the DNA.
• A typical protein contains 200-300 amino acids
  but some are much smaller (the smallest are often
  called peptides)

http//users.rcn.com/jkimball.ma.ultranet/BiologyP
ages/P/Proteins.html
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Molecular Imaging

• Practical Goals
• To image gene delivery expression
• MI identifies specific gene products
  intracellular processes
• To understand cellular processes in their intact
  microenvironments
• To develop new imaging technologies to realize
  such goals
• To facilitate new drug development and methods
  for therapeutic monitoring, and
• To promote an interdisciplinary approach to
  biomedical imaging issues.

Most of these goals involve action at the
cellular level.
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Top Ten Terms in Molecular Genetics(what you
must know to survive at a pharmacogenetics
cocktail party)

• 10. Gene specific sequence of nucleotide bases
  that carries information for constructing
  proteins exons are the regions that actually
  encode for the protein
• 9. Chromosome one of the 24 distinct,
  physically separate microscopic units of DNA that
  comprise the genome
• 8. Genetics the study of the patterns of
  inheritance of specific traits
• 7. Genomics the study of an organisms entire
  complement of genetic material and its function
• 6. Proteomics the study of an organisms entire
  protein material, its structure and
  function

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Top Ten Terms in Molecular Genetics

• 5. Amino acids the 20 building blocks of
  proteins, each coded for by a specific 3
  base-pair codon.
• 4. Allele one of the two copies of a specific
  gene
• 3. Polymorphism a gene that varies between
  individual members of the population in more than
  1 of the population. Most commonly, these are
  single nucleotide variations (SNPs).
• 2. Transcription the synthesis of an RNA copy
  from a sequence of DNA the first step in gene
  expression.
• 1. Translation the synthesis of proteins from
  mRNA and amino acids

2a. Gene Expression Formation of a protein
from a DNA sequence
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Two More Terms

• Angiogenesis
• growth of new blood vessels on demand, e.g. to
  sustain or establish tumor growth.
• Occurs both in health and in disease.

• Desirable angiogenesis
• Restores blood flow after injuries
• Placenta growth
• Undesirable angiogenesis
• Tumor growth
• Macular degeneration
• Angiogenesis MI
• Can we image formation of new blood vessels?
• Can we image reduction in angiogenesis?

http//www.angio.org/understanding/understanding.h
tml
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3D Imaging of Tumor Microvasculature
Normal
Multi-photon Microscope
Abnormal
Injected contrast agent
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Two More Terms

• Apoptosis
• Programmed cell death
• Destruction cells by an organized plan
• Why should cells commit suicide?
• Resorption of the tadpole tail at the time of its
  metamorphosis into a frog
• Formation of the fingers and toes of the fetus
  requires the removal, by apoptosis, of the tissue
  between them.
• Sloughing off of the inner lining of the uterus
  (the endometrium) at the start of menstruation.
• Apoptosis MI
• Apoptosis occurs in response to certain drugs,
  e.g. chemotherapy agents.
• Can we image the onset of this process and
  thereby determine the utility of the therapy?

http//users.rcn.com/jkimball.ma.ultranet/BiologyP
ages/A/Apoptosis.html
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Nuclear Medicine-based MI Example

• Apomate is a kit (Tc-99m) based probe specific
  for apoptosis.
• In apoptosis, an intracellular chemical, PS, can
  be translocated to the extracellular membrane
• Apomate has strong affinity to PS will attach
  to it.
• Nuclear medicine imagers are great at Tc-99m
  imaging
• Proposed Uses
• Apoptosis occurs in response to radio- or
  chemotherapy agents.
• Taxol effect.
• Apoptosis occurs in infarcted tissues.
• First clinical trials to assess utility of
  chemotherapy.
• Currently in Phase II clinical trials.

Apomate, product of North American Scientific,
Inc.
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Molecular Imaging

• Key enablers
• Highly specific imaging probes (i.e. MI agents
  injected into a lab animal to study cellular
  processes).
• Suitable amplification strategies for signal
  starved modalities such as MR
• More sensitive imaging methods
• Imaging Probes
• probes can be single-stranded DNA or RNA
  molecules of specific base sequence.
• Must clear from all irrelevant sites within the
  time frame of an imaging study.
• Must traverse physiologic barriers to get to
  their target sites of action.

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Gene Expression DNA to mRNA to Protein
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Fluorescence in-situ Hybridization (FISH)
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• FISH Imaging of Immediate Early Gene Arc
• (Quick Acting)

• Nuclear FISH Signal 2 15 min
• Cytoplasmic FISH Signal 20 60 min

Double labeling showing Arc (green) zif268
(red) foci
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Design for a MRI Probe

• Yet some more new terminology
• Ligand Part of the MI probe that is target
  specific, i.e. has special affinity to a site on
  a cell.
• Moiety specific chemical component of a probe
• Key components of probe
• Targeting ligand
• Attachment of the ligand to the receptor site
  releases enzymes
• These enzymes activate contrast agent
• Polymer based backbone for signal amplification
• Enzyme (or pH) activatable contrast capability

http//www.science.uwaterloo.ca/course_notes/biolo
gy/biol473/lecture7.pdf
(Patents Pending)
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Optical Imaging MI

• Optical Imaging is gaining popularity rapidly in
  MI.
• Various imaging methods
• Fluorescence
• Bioluminescence
• Absorption
• Diffuse optical tomography
• Confocal imaging
• Multi-photon imaging
• Almost all of these are limited to small animals.
• Translation to imaging of humans will be a
  challenge.

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Two Views on SSI Modalities MI

• Top chart
• Pomper, Acad Rad. 81141
• Bottom
• Weissleder, Radiology 216 331
• Nuclear very strong on metabolic molecular
  stuff
• Optical imaging may be the up and coming modality.

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Targeted Agent for Ultrasound

• Work by Wickline Lanza at Wash. U.
• Nanoparticle agent
• About 250 nm in diameter.
• Targeting a three-step process
• Antibody attached to clot
• Avidin attaches to the antibody
• Contrast agent attaches to avidin.
• Successful ultrasound images of fibrin have been
  made

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Intravascular study w. u/s agent

• Pig carotid arteries were overstretched w.
  balloon catheters.
• Damage introduced to observe healing process.
• Tissue factor is a glycoprotein that initiates
  healing process.
• Arteries were imaged w. tissue factor targeted
  agent and control agent.
• Enhancement due to targeted agent is obvious.

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Therapy Agents

• Thrombus-targeted agent, MRX-408
• Agent small white bubbles, IV injection
• Contains ligands which bind to platelets in clot.
• Agents make clots more visible
• Ultrasound can be used to destroy agent via
  cavitation
• Helps in dissolving clot
• Drug delivery
• Therapeutic microbubbles circulate
• They are selectively destroyed by ultrasound when
  passing through pathology.

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Summary

• Molecular Imaging has tremendous potential.
• MI is the result from a tight coupling of biology
  subsurface imaging technologies.
• Pursuit of activities in this area will require a
  good grounding in cell biology, biochemistry.
• PET, nuclear will be most likely the first
  modalities esp. in human imaging.
• Optical imaging, MRI are receiving much attention
  in animal studies.
• There is a very exciting potential for a
  fundamental change in diagnostic therapeutic
  medicine.

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Homework Lecture 20

• All the examples of molecular imaging dealt with
  medical applications.
• Propose a non-medical application of molecular
  imaging, i.e. an imaging situation where
• an external agent is introduced
• that agent alters the imaged site
• that alteration is imaged by an SSI probe.

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Instructor Contact Information

• Badri Roysam
• Professor of Electrical, Computer, Systems
  Engineering
• Office JEC 7010
• Rensselaer Polytechnic Institute
• 110, 8th Street, Troy, New York 12180
• Phone [phone]
• Fax [phone]
• Email roysam_at_ecse.rpi.edu
• Website http//www.rpi.edu/roysab
• NetMeeting ID (for off-campus students)
  128.113.61.80
• Secretary Laraine Michaelides (michal_at_rpi.edu),
  518-276-8525

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Instructor Contact Information

• Kai E Thomenius
• Chief Technologist, Ultrasound Biomedical
• Office KW-C300A
• GE Global Research
• Imaging Technologies
• Niskayuna, New York 12309
• Phone [phone]
• Fax [phone]
• Email thomeniu_at_crd.ge.com, thomenius_at_ecse.rpi.edu
  
• Secretary Laraine Michaelides (michal_at_rpi.edu),
  518-276-8525

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Ultrasound and Molecular Imaging

• Possible Collaborators
• Sam Wickline Washington U. in St. Louis
• Nanoparticle based targeted agent
  (perfluorocarbon emulsion)
• Michael Sherar U. of Toronto
• Detection of rate of apoptosis efficacy of
  chemotherapy
• Evan Unger CEO of ImaRx Prof. _at_ U. of Arizona
• Numerous agents, drug delivery, gene transfection
• Katherine Ferrara U. of California at Davis
• Broad program on molecular imaging, GEMS interest

Microbubble w. DNA payload (ImaRx)