Diagnostic Imaging

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  • Created by: LBCW0502
  • Created on: 04-02-20 10:47
What is diagnostic imaging?
A field of medicine used in determining physiology, managing disease, and locating abnormalities in the body
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What are the diagnostic techniques?
X-Ray Imaging. CAT or CT Scans. Ultrasound Imaging. Magnetic Resonance Imaging. Scintigraphy (Radionucleotides). Different chemistry, different safety profiles, different regulations
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What is the issue with the use of these diagnostic techniques
Use of ionising radiation. X-ray imaging - exposure results in damage to DNA. Radionucleotides – decay/decompose, don’t want radiopharmaceuticals to remain in the body (need a short half-life for safety purposes) – not used all the time (safety)
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How are agents for diagnostic techniques developed?
Agents developed in the same way as therapeutics (same kinetics, ROA, formulation) but must only be diagnostic/no therapeutic effect (inert), increase contrast between healthy tissue and diseased tissue (consider specificity for drug delivery)
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Describe features of X-ray imaging (1)
Discovery - working with light rays of higher density and shorter wavelength than the light filling this room, discovered that a piece of aluminum foil coated in barium platinocyanide showed luminescent properties and began to investigate
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Describe features of X-ray imaging (2)
Determined that placing a hand between the light source and film resulted in the image of his skeleton
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Describe features of X-ray imaging (3)
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.
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Describe features of X-ray imaging (4)
Free radicals form hydrogen peroxide and HO2· which are damaging to DNA, stop replication, and result in cell death
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Describe features of CAT or CT scans (1)
Essentially an x-ray technique. Produces more detailed images of internal organs than 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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Describe features of CAT or CT scans (2)
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, (Diatrizoic acid, I)
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Describe features of CAT or CT scans (3)
These agents all work in the same way but vary in function by how they are administered
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Describe features of CAT or CT scans (4)
Intravenous Agents - are usually iodine based, eliminated from the body extremely quickly, travel through the blood vessels, brain, spine, liver, and kidney
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Describe features of CAT or CT scans (5)
Oral agents - most common are Barium Sulphate and Gastrograffin administered in a milk shake type formula (reaction equation)
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Describe features of CAT or CT scans (6)
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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Describe features of ultrasound imaging (1)
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
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Describe features of ultrasound imaging (2)
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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Describe features of ultrasound imaging (3)
Microbubbles – composed of lipid bilayers, but contain inert gas (e.g. SF60 gas), gas interacts with ultrasound to make the image clearer, microbubbles could burst in lungs (so designed to be very short-lived, 2 minutes)
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Describe features of magnetic resonance imaging
Derived from NMR. 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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Describe features of MRI contrast agents (1)
Contrast agents are usually paramagnetic metal systems which function by altering hydrogen nuclei of water protons. Are classified as T1 or T2 agents
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Describe features of MRI contrast agents (2)
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
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Describe features of MRI contrast agents (3)
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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Describe features of MRI contrast agents (4)
Toxicity of paramagnetic agents can be reduced by gadolinium chelates. Gd-DTPA - first IV MRI agent approved. The nonionic forms (Gd-DTPA-BMA and Gd-DOTA) quickly followed
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Describe features of MRI contrast agents (5)
These agents differed in charge and number of gadolinium complexes which increased stability and altered viscosity
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Describe features of scintigraphy (1)
The only imaging technique entirely depending 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
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Describe features of scintigraphy (2)
All the radionucleotides used in diagnostic imaging are artificially produced in a cyclotron or radioisotope generator
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Describe features of iodine (1)
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.
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Describe features of iodine (2)
Newer agents have a higher ratio of iodine which improves its function
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Describe features of 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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Describe features of 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. Monitor increase uptake of glucose by certain tumours
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What is a radionuclide? (1)
A radionuclide is an atom with unstable nucleus, available to be imparted either to a new radiation particle within the nucleus, or to an atomic electron . The radionuclide, undergoes radioactive decay, and emit gamma rays and/or subatomic particles.
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What is a radionuclide? (2)
These particles form the ionizing radiation. Radionuclides may occur naturally, or artificially produced.
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State features of the energy spectrum
Energy emitted from a source is generally referred to as radiation. Examples include heat or light from the sun, microwaves from an oven, X rays from an X-ray tube, and gamma rays from radioactive elements
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State features of particular radiation
Particulate radiation, consisting of atomic or subatomic particles (electrons, protons, etc.) which carry energy in the form of kinetic energy or mass in motion.
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State features of EM radiation (1)
Energy is carried by oscillating electrical and magnetic fields traveling through space at the speed of light.
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State features of EM radiation (2)
Alpha particles and beta particles are considered directly ionizing because they carry a charge and can, therefore, interact directly with atomic electrons through coulombic forces
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State features of EM radiation (3)
The neutron is an indirectly ionizing particle, because it does not carry an electrical charge. Ionization is caused by charged particles, which are produced during collisions with atomic nuclei.
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State features of EM radiation (4)
The third type of ionizing radiation includes gamma and X rays, which are electromagnetic, indirectly ionizing radiation.
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What are isotopes?
Atoms with the same number of protons, different number of neutrons. An isotope may be defined as one or two or more forms of the same element having the same atomic number (Z), differing mass numbers (A), and the same chemical properties
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What is the activity of a radioisotope?
The activity of a radioisotope is simply a measure of how many atoms undergo radioactive decay per a unit of time. (Slide - units, diagram)
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What are the sources of radionuclides? (1)
Natural. Nuclear Reactors Fission products – 131I, 99Mo/99mTc. Particle accelerators. Cyclotron for positron emitters. Generator systems 99Mo/99mTc generator system
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What are the sources of radionuclides? (2)
99m-Tc – most abundantly used radionuclide (6 hours half-life, patients not in danger of radionuclide activity in the body).Estimate decay rate – relate to radioactive signal. Parent decreased, daughter increases. Mo/Tc generator
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Outline the principle of operation for the Mo/Tc generator
Column with adsorbent (alumina Al2O3). Parent nuclide loaded as 99MoO42-. Daughter forms by decay (not chemical). Daughter chemical form 99mTcO4-. Elute daughter as Na pertechnetate with 0.9% NaCl solution
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Describe features of radiopharmaceuticals (1)
Used in the diagnosis and treatment of disease. Diagnosis: gamma emitters, brain, lung, liver, kidney, heart, tumours
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Describe features of radiopharmaceuticals (2)
Images of biodistribution of radioactivity are diagnostic. E.g. thyroid scans with 131I, 99mTc labelled microspheres: lung, 99mTc-Phosphate for bone imaging 81Kr inert gas for lung imaging
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Describe features of radiopharmaceuticals (3)
Therapy: alpha and beta emitters. Thyroid cancer, bone cancer, localised radiation intended to kill cells. Imaging with gamma camera e.g. 18-F FDG normal biodistribution
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Give examples of commercial radipharmaceuticals (1)
Na 32-P (therapy for haemoproliferative disease). 51-Cr edetate (glomerular filtration rate determinations). 67-Ga citrate (soft tissue tumour imaging). 111-Sr chloride (palliation of bone pain in metastatic bone disease)
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Give examples of commercial radipharmaceuticals (2)
111 in oxine (white cell labelling). 111 in penetrate (CSF imaging). 123-I iodohippurate (functional renal imaging). Na 131-I iodide (diagnosis/therapy of thyroid disease). 210-TI thallous chloride (heart imaging)
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Card 2

Front

What are the diagnostic techniques?

Back

X-Ray Imaging. CAT or CT Scans. Ultrasound Imaging. Magnetic Resonance Imaging. Scintigraphy (Radionucleotides). Different chemistry, different safety profiles, different regulations

Card 3

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What is the issue with the use of these diagnostic techniques

Back

Preview of the front of card 3

Card 4

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How are agents for diagnostic techniques developed?

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Card 5

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Describe features of X-ray imaging (1)

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