X-rays Flashcards
Define radiation:
Transmission of energy through space.
What kinds of rays are involved with medical radiation?
X-rays and gamma rays
Why is it called “ionizing” radiation?
Has enough energy to knock electrons loose, creating ion atoms or molecules.
Which end of the spectrum has shorter wavelength?
Gamma rays, X-rays, and upper region of ultraviolet spectrum.
Which rays have higher energy?
Higher frequencies (ultraviolet and up) have more energy.
Where does radiation come from in nature?
Cosmic rays, terrestrial radiation from Earth deposits, and radon.
Where do we get most of the radiation we get in our lives?
Medical radiation is most of our exposure.
What are other sources of man-made radiation?
Nuke power, research, industrial sources, certain consumer items.
What are some units of measure for radiation? (7 examples)
Bequerels, curies, roentgens, rads, grays, rems, sieverts
How much exposure is maximum?
5,000 mrems annually
What kinds of harm can excess exposure cause?
Skin burns, radiation sickness, higher cancer risk, genetic damage
What does “ALARA” stand for?
As Low As Reasonably Achievable
Use the mimimum possible/ necessary
What are the three factors that control the amount of exposure to radiation?
Time, distance, protection (shielding)
What is the inverse square law?
Dosage is reduced with the square of the distance (i.e., big reduction in dosage with modest increase of distance: twice as far away from source means 1/4 the intensity).
This is because the energy from a point source is distributed more widely over a 2-dimensional area at each point of distance…
What on earth is a Crookes tube?
Glass container, partial vacuum, cathode and anode, cathode rays (electrons) generated by voltage.
Who used one to discover X-rays?
Wilhelm Roentgen
Who invented the fluoroscope?
Thomas Edison
What on earth is a Snook transformer?
Who knows. Works with Coolidge’s tube to produce X-rays.
In the X-ray tube, what component emits the electrons?
Cathode emits electrons.
What component is hit by the electrons?
The electrons hit the anode (or target).
When the electrons hit the anode, what happens to the energy?
Most energy is lost as heat, but some electrons release energy as photons: X-rays.
What is a C-arm?
X-ray unit used in cath lab (and portable version elsewhere sometimes).
Why that shape of the C-arm?
X-ray emitter is underneath, sensing device is above patient.
C shape facilitates rotating around patient for different projections.
How is an X-ray image produced?
Differences in tissue density hold back or allow to pass the X-ray energy; this is registered on film (not any more) or digital sensing plate.
What kind of tissue causes light vs. dark areas on the image?
Dense, calcified structures (bone, etc) hold back X-rays;
Soft tissue allows it to pass.
What kind of absorption occurs?
Photoelectric absorption
What does “opacification” mean?
Making opaque: holding back the X-rays.
How accurate are visual assessments of coronary angiograms?
Only sort of accurate.
When estimating stenosis, how much variation is there among interpreters?
20% or more variation in estimates of stenosis among interpreters.
What are typical categories (ranges) of coronary artery stenosis?
50% or less. 50-75%. 75-95%. Total occlusion.
Stenosis of which coronary artery is especially dicey during angiography?
Left main; any obstruction compromises LV acutely.
What quantitative measure is provided by the ventriculogram?
EJ: ejection fraction.
Qualitative assessment: wall motion.
What complications can result from LV gram? (5 examples given)
Arrhythmia (including asystole), staining, embolism, reaction to contrast, transient hypo-tension.
Why on earth would you want to use a septal occluder?
Septal occluders close septal defects (openings).
What are some other man-made objects that might show up on a chest X-ray?
New valves (annular rings), pacemakers and or defibrillators, sternal wires, LVAD (left-ventricular assist device), catheters
What are a couple of disorders?
Pneumothorax, calcification (arteries, etc.).
What characterizes the appearance on X-ray of a myxoma?
It has a highly vascular appearance (blush).
What distinguishes fluoroscopy from standard X-ray imaging?
Fluoroscopy is in real time.
How does fluoroscopy image quality compare to acquisition mode image quality?
Fluoroscopy image quality is not as good.
How does X-ray dosage with fluoroscopy compare to acquisition mode?
X-ray dosage with fluoroscopy is not as high.
What is “acquisition mode”?
Higher-intensity X-rays, reducing noise and obtaining higher resolution.
What does the image-intensifier do?
Image intensifier converts X-rays to visible light.
What are the components (including the patient) of the fluoroscopy imaging chain?
X-ray generator. X-ray tube. Collimator. Filtration. Table. Patient. Grid. Image intensifier. Optical coupling. Video camera. Monitor.
