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contains carbon double bonded to an oxygen, single bonded to another oxygen and has a negative charge at the pH of the body
interactions between electrons of atoms that hold the atoms together in a stable group; line drawn between atoms indicates a bond: H-O-H
involuntary constriction of the bronchial tubes usually resulting from an immune system reaction to a foreign particle or molecule
substance composed of two or more elements combined in definite rations that give the substance specific properties
factors of a patient's history or present status that indicate that a medical procedure should not be performed or that a medication should not be given
nitrogen-containing waste products of metabolism excreted by the kidney's filtration system; high blood plasma levels indicate poor filtration by the kidney
compound formed by bonding of two identical simpler molecules. Ioxaglate - composed of two connected benzene hexagons.
long chains of carbon atoms linked to each other and to hydrogen atoms; at one end of the chain is an acid group that contains two oxygen atoms and a hydrogen atom arranged in a particuar way
formation of flaky masses resulting from precipitation or coming out of a suspension or solution
molecular susbstance containing anamine group; causes bronchial constriction and a decrease in blood pressure
common chemical group, part of the water molecule, containing one atom of hydrogen and one atom of oxygen; carries a negative charge (anion) when not a part of a molecule
simple molecule of a compound of relatively low molecular weight- most ionic iodine contrast media are monomers.
measurement of the number of particles (molecules or ions or cations) that can crowd out water molecules in a measure mass (kilogram) of water
movement of water from an area of high concentration to an area of low concentration through a semipermeable membrane such as blood vessell walls and cell membranes
relative acidity or basicity (alkalinity) of a solution; pH below 7.0 is acidic and has more hydrogen cations than hydroxyl anions, wheres a pH above 7.) is alkaline and has more hydroxyl anions than hydrogen cations
pharmaceutical compound that is attached to a radioisotope. Not a contrast agent. It's a radionuclide attached to a pharmaceutical that has a specific biodistribution in the human body. Can be gas, liquid, or solid. Depends on administration and sensitivity as well as specificity of the pharmaceutical in the body as it is taken up. The radioisotope is imaged using a gamma camera that sees where the radiopharmaceutical is in the body and forms an image. Prime example: renal imaging whereby the rp is taken up by the kidneys, metabolized into urine and collected in the bladder. If pt has a kidney stone, the stone would show up while performing the study.
inadequate blood flow within the body with resulting loss of oxygen and therefore energy. Osmotic effects further reducing body cell volume.
uniform mixture of 2 or more substances composed of molecule-sized particles that do not react together chemically
nonuniform mixture of 2 or more substances, one of which is composed of larger-than-molecule-size particles that have a tendency to cluster together
awakened the medical profession to realize that diseases of the GI tract could be studied by watching the movement of radiopaque media through the tract.
basic chemical structures from which both ionic and nonionic water-soluble iodine contrast media originate
Purpose of contrast media
to enhance the density differences within the area of interest to improve visualization of the anatomic detail
Factors that affect the degree of radiographic density differences
absorption characteristics of the tissues that comprise the anatomic part, technical factors used, characteristics of the IR, automatic image processing and the use of contrast media agents.
diagnostic agents instilled into body orifices or injected into vascular system, joints and ducts to enhance subject contrast in anatomic areas where low subject contrast exists. Depends on ataomic # of the element used and concentration of atoms of the element per volume of the medium.
Negative/radiolucent contrast agents
decrease attenuation of the x-ray been and produce areas of increased density (dark areas). Radiolucent. Low atomic numbers
positive/radiopaque contrast agents
incrase the attenuation of the x-ray beam and produce areas of decreased density on the radiograph (light areas). Radiopaque. High atomic numbers.
specialty contrast agents
MRI - gadolinium diethylenetriaminepenta-acetic acide (gadolinium-DTPA). Metallic and magnetic agent that wil after signal intensity.
sonography - contrast agents are gas-filled bubbles that affect sound wave to enhance ultrasound contrast.
negative contrast media properties
Low-atomic number gas (air) or gas-producing tablets, crystals or soda water (carbon dioxide). Because cells absorb O2 quickly, the gas is rarely used alone as a contrast agent.
Specific procedures: laryngopharyngography - upper respiratory structures contain air naturally.
Adverse reactions: minimal. Air can cause emboli that lodge in blood vessells causing pain and loss of O2.
positive contrast media properties
Barium - high atomic # of 56. Radiopaque. Inert powder of crystals use for examining digestive system. BaSO4. Compound. not soluble in water, must be shaken or mixed into a suspension. Can flocculate. Sodium carbonate or sodium citrate are used to prevent flocculation. (suspending agents)
Barium sulfate suspension
most be concentrated enough so that x-rays are absorbed and coat the lining of organs.
Small intestine studies
oral formulations of barium sulfate and methylcellulose (nondigestible starch) designed to give a see-through effect to diagnose lesions
Lower GI studies
barium sulfate with cold tap water to reduce colon irritation and aid pt in holding the enema. Reduces spasm and cramping. Warm water could be used for maximal pt comfot.
problem that can occur when the colon absorbs excess fluid and sends it to the circulatory system. 2 tsp of salt per L of H2O in enema preparation reduces the risk. Water from a cleansing enema and barium enema can be shifted from the colon into the circulatory system, increasing blood volume. Fluid overload is pulmonary edema, seizures, coma and death. Observe pt for changes in mental status, apathy, drowsiness - indicators of onset of hypervoleumia. Sedative premedication is contraindicated for lower GI exams for this reason.
Barium sulfate can be a problem to pts with pre-existing disease or status. If performation of the digestive tract, body does not absorb barium sulfate naturally and it could enter the peritoneal or pelvic cavity and cause peritonitis and must be surgically removed. Use a water-soluble iodine contrast agent instead.
BaSO4 can result in perforation of the colon. Pt history must be taken:
Age - ability to communicate, here and follow directions
Diverticulitis or ulcerative colitis - Increased risk of colon performation caused by loss of tissue tone, difficult in holding an enema, risk of colon perforation
Long-term steroid therapy - risk of colon perforation
Colon biopsy within previous 2 weeks - lower GI series contraindicated
Pregnancy - Inform radiologist before proceeding with exam
Mental retardation, confusion or dizziness - increased risk of aspiration during upper GI series
Recent onset of constipation or diarrhea - increased risk of colon perforation or tumor rupture
Nausea and voming - increased risk of aspiration during upper GI series.
Adverse reactions to BaSO4 suspensions
These suspensions transit the colon. BaSO4 residue within the colon can dry and cause an obstruction. Major symptom is constipation.
A complication with lower GI: perforation of the colon with extravasation into the abdom. cavity. - barium peritonitis
diverticulitis and ulcerative colitis - diseases that result in inflammation and degradation of the colon tissues.
toxic megacolon - should not have lower GI procedures - serious complication of ulcerative colitis resuts in a dilated colon that can rupture.
Recent biopsy of the colon - contraindication to a lower GI series until the area heals.
vaginal rupture - rare - due to misplacement of the catheter.
diverticulitis and ulcerative colitis
diseases that result in inflammation and degradation of the colon tissues.
should not have lower GI procedures - serious complication of ulcerative colitis resuts in a dilated colon that can rupture.
should not undergo upper GI exams because swallowing reflect is diminished, increasing risk of aspiration of BaSO4 suspension with resultant barium pneumonia.
ionic contrast media
One particle has a negative charge (anion) and one has a positive charge (cation). Higher osmolality media because of their osmotic effects. Disassociates into 2 molecular particles in water or blood plasma. Anion and cation. When plasma water is displaced by contrast particles, water from body cells moves into the vascular system. Can result in hypervolemia and blood vessel dilatation, producing pain and discomfort. BP may decrease due to vessel dilatation or may increase due to hypervolemia and effects of hormones in the kidneys.
ionic iodine contrast media
Atomic number of 53, relatively radiopaque. The anion is associated with a 6-carbon bonded hexagon called benzene. Most ionic iodine contrast media are higher-osmolality contrast media. Most adverse reactions are related to osmolality having an increased # of particles in solution, which pulls water toward them.
increased number of particles in solution, such as blood plasma, which pull water toward them. When
nonionic iodine contast media
molecules do not dissociate into anions and cations. Lower-osmolality contrast media.
2 benzene hexagons - called a dimer. Carries 6 iodine atoms per molecule. Dimers are large molecules, so osmotic effects are low. They are viscous.
Lower-osmolaltiy contrast media
more hydrophilic - do not dissociate into anions and cations. Also less likely to be reactive with the cells that can trigger allergic effects.
minor - hives
nausea, vmoniting - caused by a release of histamine from certain cells in the lungs, stomach and lining of blood vessels. Premedication with steroids and antihistamines can reduce or eliminate allergice effects.
high-osmolality contrast media can cause arteries of kidneys to expand as a result of the osmotic effect. Pts with renal disease or diabetes and older pts are at increased risk for complications.
Blood urea nitrogen (BUN) and creatinine
levels indicate that the patient may have renal disease as is a good indicator for possible contrast media-induced renal effects.
increased BP, bradycardia, tachycardia. Sickle cell pts - media may cause cells to sickle.
Hypertension drugs may increase risk for anaphylactoid reactions.
Calcium-channel blockers - risk for heart block and abrupt decrease in BP
Metformin - for noninsulin dependent diabetes. Should be discontinued 48 hours before iodine contrast media.
Considerations for use of nonionic contrast media
Decreased osmolality, less painful injections during angiography. Kidney toxicity has not been reduced. BUN and creatinine levels included in pt history are important. Nonionic cost 2x or 3x more than ionic. Use for:
Patients with histories of adverse reactions to contrast media, excluding sensation of heat/flushing
Pt with history of asthma or allergies
pt. with known cardiac problems
pt with generalized severe debilitating conditions
pt who will undergo helical CT procedures
Pts with diabetes mellitus, renal disease or elevated creatinine levels, or sickle cell disease.
Oil-based Iodine contrast media
Made from fatty acids in plants and animals. An ethyl group changes fatty acids into esters. Then iodine is added = iodinated ethyl esters of fatty acids. Insoluble in water and do not flow easily - viscous. Store in dark, cool area. Should be pale yellow or amber. Plastic syringes cannot be used because toxic substances can dissolve into the media. Main disadvantage: persist in the body because they are insoluble in water.
Specific procedures for oil-based iodine contrast media
Infrequent. Use for bronchography, dacryocystography, sialography,and lymphography. Myelography used to be but no uses nonionic contrast media.
Adverse reactions to oil-based media
Mostly, it's the procedure that is associated with adverse reactions. Infrequent allergic effects.
Positron emission tomography - positron, aka antimatter, cannot exist long when in contact with a negative electron. PET takes advantage of this. Positron emitters are formed in a cyclotron and often have very short half-lives.
Primary concern when working with short-lived unsealed radiation sources
contamination on pts, personnel, floors, tables or imaging equipment that might be misconstrued as part of the image produced. Increased radiation exposure to personnel and patients. Nuclear medicine personnel recap needles on a syringe whereas all other medical personnel do not.
Rad tech responsibilities
Be able to identify signs and symptoms of adverse reactions and adequate knowledge of how to treat them.
Prevention of contrast media reactions
depends on obtaining a thorough pt history that can indicate contrast media contraindications or increased likelihood of adverse reactions; pt preprocedural preparations and instructions to include adequate hydration and appropriate premedication when indicated; and adequate knowledge in the treatment and use of emergency equipment in cases of adver reactions.
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