Diagnostic Imaging Agents

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Diagnostic Imaging Agents

• by Broox Boze
• Southern Methodist University

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What is Diagnostic Imaging?

• A field of medicine used in determining
  physiology, managing disease, and locating
  abnormalities in the body.

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Diagnostic Techniques

• X-Ray Imaging
• CAT or CT Scans
• Ultrasound Imaging
• Magnetic Resonance Imaging
• Scintigraphy (Radionucleotides)

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Where did it all begin?

• President Garfield was shot and lived for weeks
  with a bullet somewhere in his body
• Alexander Graham Bell though he could develop a
  sound induction device which would trigger when
  it came in contact with an item of different
  density

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X-Ray Imaging

• Was the first Great Discovery in the field of
  diagnostic imaging
• Wilhelm Roentgen was working with light rays of
  higher density and shorter wavelength than the
  light filling this room
• He discovered that a piece of aluminum foil
  coated in barium platinocyanide showed
  luminescent properties and began to investigate
• After months of playing with various objects
  and determining density he discovered that
  placing his hand between the light source and
  film resulted in the image of his skeleton

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• The benefits of x-rays far out weigh the
  potential risks
• X-rays cause atoms to lose electrons through
  bombardment with photons
• Radiolysis cause the formation of the free
  radicals HO. and H.
• Free radicals form hydrogen peroxide and HO2
  which are damaging to DNA, stop replication, and
  result in cell death

H H v H2
H OH v H2O OH OH v H2O2
OH H2O2 v HO2 H2O
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CAT or CT Scans

• Essentially an x-ray technique
• Produces more detailed images of internal organs
  that traditional x-rays
• Used in diagnosing muscle and bone disorders,
  locating blood clots, detecting internal
  bleeding, monitoring diseases such as cancer

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• To enhance imaging patients are given laxatives,
  enemas, or suppositories.
• Agents serving to increase contrast by weakening
  or blocking x-ray transmission include
• Barium (Ba)
• Barium Sulphate (BaSO4)
• Iodine (I)
• Gastrograffin
• These agents all work in the same way but vary in
  function by how they are administered

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• Intravenous Agents
• Are usually iodine based
• Eliminated from the body extremely quickly
• Travel through the blood vessels, brain, spine,
  liver, and kidney
• Oral Agents
• Most common are Barium Sulphate and Gastrograffin
  administered in a milk shake type formula
• BaCl2 (aq)    (NH4)2SO4 (s)  -------------gt
   BaSO4 (s)    2NH4Cl (aq)
• Rectal Agents
• Used in imaging the lower gastrointestinal tract
  including the large intestine
• Not the most comfortable method and can cause
  constipation, itching, and swelling

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Ultrasound Imaging

• The most underdeveloped of the 5 areas
• Used in imaging solid or water filled organs,
  including the liver, spleen, kidney, heart, blood
  vessels, and bladder
• Performed with a handheld device and is easily
  portable to patients
• No Contrast Agents are used on a regular basis
  but the use of microbubbles has potential
• The biggest problem is preventing breakdown in
  the heart and lungs
• A biodegradable shell of polybutyl-2
  cyanoacrylate has been shown to work in some
  cases

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Magnetic Resonance Imaging

• Newest and fastest growing field
• Focuses on smaller and more selective areas than
  x-rays or CT scans
• Three important parameters determining image
  viability
• Water Content (proton density)
• Blood Flow
• Relaxation Time

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MRI Contrast Agents

• Contrast Agents are usually paramagnetic metal
  systems which function by altering hydrogen
  nuclei of water protons
• Are classified as T1 or T2 agents
• Four Types of Magnetic Fields
• Diamagnetic agents are useful in gastrointestinal
  imaging
• Superparamagnetic and Ferromagnetic agents which
  have a net magnetic dipole larger than the sum of
  unpaired electrons. Dephasing of protons
  shortens T2
• Paramagnetic agents include oxygen, nitroxides,
  and ions of the metals Fe, Mg, Gd, and Dy, all of
  which have unpaired electrons and result in
  positive enhancement

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• Toxicity of paramagnetic agents can be reduced by
  gadolinium chelates
• Gd-DTPA was the first IV MRI agent approved
• The nonionic forms (Gd-DTPA-BMA and
  Gd-DOTA) quickly followed
• These agents differed in charge and number of
  gadolinium complexes
  which increased
  stability and altered
  viscosity

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Scintigraphy

• The only imaging technique entirely dependant on
  contrast agents
• Radionucleotides are drugs that contain some
  radioactive element. They are typically small
  organic molecules, such as peptides, but can also
  be macromolecules such as antibodies.
• All the radionucleotides used in diagnostic
  imaging are artificially produced in a cyclotron
  or radioisotope generator

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Technetium (Tc-99m)

• Technetium pharmaceuticals are metal-electron
  donor complexes
• Tc is an electron deficient metal and therefore
  interacts with electronegative groups
• Produced using the molybdenum-99/technetium-99
  system where molybdenum is obtained as a fission
  product of uranium

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Iodine

• used in imaging blood vessels and solid organs
• The original Iodine contrast agents had
  triiodinated benzoic acid salts that dissociated
  in water to give 3 iodides for every 2 molecules
  of water in solution
• Drugs include diatrizoate and iothalamate
• Newer agents have a higher ratio of iodine which
  improves its function

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• Low osmolar contrast agents can be used in
  smaller doses and are much safer than the
  previous drugs
• These drugs are 20 times the cost of high osmolar
  contrast agents

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Indium

• Indium-111 is used in brain studies
• Most stable in acid solutions below ph 3.5
• Functions by binding to somatostatin receptors
  throughout the body

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Fluorine

• Fluorine-18 decays to oxygen-18 by electron
  capture and then aids imaging by emitting gamma
  rays.
• Fluorodeoxyglucose is used in PET Scans along
  with Carbon-11, Oxygen-15, and Nitrogen-13

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To Sum It All Up