Transcript Diagnostic Imaging Agents

Diagnostic Imaging Agents
by Broox Boze
Southern Methodist University
What is Diagnostic Imaging?

A field of medicine used in determining
physiology, managing disease, and locating
abnormalities in the body.
Diagnostic Techniques

X-Ray Imaging
 CAT or CT Scans
 Ultrasound Imaging
 Magnetic Resonance Imaging
 Scintigraphy (Radionucleotides)
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
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


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
OH· + OH· v H2O2
H· + OH· v H2O
OH· + H2O2 v HO2· + H2O
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

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

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) -------------> 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
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
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
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

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
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
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/technetium99 system where molybdenum is obtained as a
fission product of uranium
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

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
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
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
To Sum It All Up…