5 short answer questions--GENERAL PHYSICS/POSITIONING LECTURE NOTES---20 POINTS Flashcards
General Positioning/Physics Notes
The following are some general characteristic about X-rays:
- X-rays are highly penetrating and invisible
- They are electrically and magnetically ________
- They are ________,(one beam contains many energy levels)
- Produce only a MINIMAL amount of HEAT while passing through matter
- They travel in a ______ ______and diverge from their source
- Travel at the SPEED OF LIGHT
- CANNOT be focused by a LENS
- They cause certain crystals to emit energy as the form of visible light
- They affect photographic film
- Produce _______ _______ upon contact with matter.
- Can cause CHEMICAL and BIOLOGICAL changes
- Can ionize matter
neutral
polyenergetic
straight line
scatter radiation
General Positioning/Physics Notes
X-RAY PRODUCTION –X-rays are produced in a vacuum
tube. The vacuum serves to prevent
___________ in the tube that would burnout the filament
prematurely. This vacuum also prevents ___ _____ from interacting with the electrons.
oxidation
air molecules
General Positioning/Physics Notes
CATHODE:
The cathode is the ______ side of the X-ray tube and has two primary parts: a FILAMENT and a FOCUSING cup.
negative
General Positioning/Physics Notes
FILAMENT:
The filament is a coil of wire similar to that in a kitchen toaster except much smaller. It is made of tungsten because of its high melting point. When a current flows through the filament it heats up to a point to where electrons are emitted. This is called _____ _______
There are usually 2 filaments, which produce 2 focal spot sizes.
1—Small focal spot size=50 and 100 mA
2—Large focal spot size=100 mA and larger
FOCUSING CUP:
Negatively charged cup that focuses the electron beam. Without it, the beam would scatter all over the inside of the ______
thermionic emission.
tube.
General Positioning/Physics Notes
ANODE:
The anode (photo on right) is the ______ side of the
x-ray tube. This is where the X-rays are produced.
The anode can be ___________ or rotating. Most
general purpose X-ray tubes have the ________-anode
type because this allows the beam to interact with a
larger area, which helps INCREASE the heat capacity.
After the rotor switch is activated (the first button),
1-2 seconds are needed to allow the rotor to
accelerate to its designed RPM of 3,000 to 10,000.
At this point a clicking sound or ____ will signal you to push the exposure switch.
positive
stationary
rotating
light
General Positioning/Physics Notes
The _____ is the area of the anode struck by the electrons from the CATHODE. When the electrons
from the cathode strike the _____ on the ANODE the swift deceleration of the electron causes an Xray to be emitted.
______ ______= The actual area on the target from
which X-rays are emitted.
______ ______ ______: The area on the target that is
hit by the electron beam and dispersed.
target/ target
Focal spot:
ACTUAL focal spot
General Positioning/Physics Notes
_____ ______ _______: The area projected onto
the patient. The smaller the effective focal
spot, the smaller the _________, the better the
detail.
________: The portion of the X-ray beam that
consists of the image.
Effective Focal Spot
penumbra
Umbra
General Positioning/Physics Notes
_______________ = Represents the
lighter, hazy area at the edge of the image. It
is caused by rays originating at various points
on the focal spot and passing tangentially to
the edge of a structured detail in an object.
Penumbra
General Positioning/Physics Notes
- -The SIZE of the focal spot is controlled by the SIZE of the _________.
- -The SMALLER the focal spot the BETTER the _______.
- -The SMALLER the focal spot the HIGHER the concentration of ______..
- -A HIGH concentration of HEAT for a period of time will eventually overload and melt the target.
filament
detail
heat
General Positioning/Physics Notes
kVp dictates the quality or “_______” of the X-ray beam.
kVp has a direct and exponential relationship to _____ AND _________ respectively. When the kVp is increased by ___%, this has the same effect on the density as DOUBLING the mAs. It also directly controls ______
hardness
scatter and density
15%
contrast.
General Positioning/Physics Notes
Contrast:
This is the difference in density between the light and dark areas; it can also be defined as the different shades of gray. It functions to make detail more ______.
HIGH contrast = is lots of black and whites
LOW contrast = is many shades of grey.
LOW kVp: Short scale of contrast High contrast film Brightness in tones is greater and more abrupt EX.\_\_\_\_\_\_\_\_\_\_\_ views (60 kVp)
HIGH KVP: Long scale of contrast Low contrast film Transition between tones is more gradual Increase scatter EX \_\_\_\_\_ views (120 kVp)
visible
Extremity
Chest
General Positioning/Physics Notes
_________– controls the AMOUNT of current passing through the filament thereby controlling the
AMOUNT of electrons that will “_____” off. This in turn will determine the number of X-ray photons
that will be emitted. The amount of X-rays is referred to as the quantity.
The amount of _____ emitted for a period of TIME. When the mAs is doubled the density on the film doubles (to a point) and when the mAs is decreased by 1/2, the density is cut in half. The ________OR _________ of the film refers to mAs.
Milliamperes
“boil”
X-rays
exposure or blackness
General Positioning/Physics Notes
RADIOGRAPHIC QUALITY
This is the accuracy in which the anatomical structure is represented on the radiograph. It is governed by four variables.
1) . ________ (overall blackness)
2) . _________ (differences between densities)
3) . _________ (sharpness of the image)
4) . __________ (misrepresentation of true size/shape of the object)
Density
Contrast
Detail
Distortion
General Positioning/Physics Notes
ASSESSING RADIOGRAPHIC QUALITY
OVER-Exposed: A too _____ film.
- -Keep KVP constant
- DECREASE the MAS (usually by 1/2)
UNDER Exposed: A too _____ film.
- Keep kVp constant
- INCREASE the mAs (2X’s to double the density)
dark
light
General Positioning/Physics Notes
FILM DETAIL/DEFINITION
This is affected by three primary factors, all of which affect the size of the penumbra.
*****Remember that it is desirable to have a
________ penumbra.
1) . Focal Spot Size: The SMALLER the focal spot size the SMALLER the size of the penumbra.
2) . FFD: The ________ the Focal Film Distance the SMALLER the penumbra.
3) . OFD: The SHORTER the Object Film DISTANCE, the smaller the Penumbra.
SMALL
longer
General Positioning/Physics Notes
GRIDS
Invented in 1913 by Gustave Bucky
(therefore a grid is sometimes referred to as a “Bucky”).
—It consists of lead strips imbedded in a ________
material.
—The function of the grid is to absorb the
________ __________produced in the patient.
—This will, then, _______ film fog.
— Film fog REDUCES the CONTRAST on the film and REDUCES the ____________.
radiolucent
scatter radiation
reduce
definition
General Positioning/Physics Notes
Grid Ratio:
The ratio of the height of the lead strips to the
space between the strips. High ratio grids
require more exposure to the patient. Common
ratios are ______ AND ______
Grid Frequency:
The number of lead strips per inch. Typically
range from 60-103/inch. The HIGHER the number
the more _______ the Bucky is, but MORE of the
X-ray beam is absorbed. To maintain the same
density the exposure must be _________ and
GREATER EXPOSURE results for the patient.
8:1 and 10:1.
efficient
increased
General Positioning/Physics Notes
Grid Radius or Grid focus:
The proper FFD that a grid will operate, typically a range like _____” + _______”. If a distance is used that
is out of the range of a grid, grid cut-off will result. This is when the grid absorbs the PRIMARY beam and leaves _______ ________ on the film.
40”-72”
white lines
General Positioning/Physics Notes
Rare Earth Screens:
These are the screens used in the radiology department at LACC WHC. They are more efficient in converting X-rays into light than REGULAR screens thus further REDUCING the EXPOSURE to the patient. Rare Earth screens operate about TWICE as fast as regular screens. This speed difference is one of the reasons that the correction factors are different for different _______. Because of the chemical composition of the rare earth crystals, a kVp above ____ is usually used.
The goal of the radiographer is to see at least __
sides of collimation on each film taken. The
ideal film will have the collimation “_____” the
image.
cassettes.
60
3
frame
General Positioning/Physics Notes
RULE FOR FFD AND ANGULATION
Whenever the tube is angulated, for every 5 degrees of angulation starting after 15 degrees, you decrease the FFD by ONE INCH. Remember that when measuring the body part, always measure with the __________!
PATIENT INSTRUCTIONS
1). _________ - For anatomy BELOW the diaphragm.
2). _________ - For anatomy ABOVE the diaphragm.
3–Patients with bandages, or splints should NOT be forced to remove them.
4. Place proper shielding on patient.
***_______ ________ are the #1 cause of repeated examinations!
angulation.
Expiration
Inspiration
Darkroom errors
General Positioning/Physics Notes
DARKROOM PROCEDURES
Errors in darkroom procedure are a common cause of retakes. A retake means that the patient received a dose of ionizing radiation without diagnostic benefit. There is NO MINIMUM dose of radiation that is known to be safe. Therefore, RETAKE examinations are to be AVOIDED.
Following the protocol listed below will help to minimize the possibility of having to retake a film. After an exposure is taken:
1. Enter the darkroom with the cassette containing the exposed film.
2. Make sure that the safelight, processor and exhaust fan are all TURNED ON.
3. Unless a special lightproof rotating door is present, CLOSE AND LOCK the door behind you
(so no one can open the door from the outside while you have undeveloped film out).
4. Remove the exposed film from the cassette.
5. Flash the __________ ________ on to the film.
6. Place the film on the processor input tray, straight and even with an edge (to avoid FEED JAMS).
7. OPEN the film storage bin and REFILL the cassette with unexposed film, then immediately CLOSE the bin. Even a “_____” light will eventually expose film, so the bin should remain open for the shortest possible amount of time. Also note that watch dials, pager or ________________ and luminescent objects (like little glowey skeletons from cereal box offers) will expose film also.
8. WAIT for the film to be fully taken into the processor before exiting (usually signaled by a BUZZ OR BEEP).
9. Exit the darkroom and close the door after you.
10. Put the refilled cassette back in the storage area, ready for the next patient.
Points worthy of emphasis:
— If there is any light other than the safelight on in the darkroom, or if the door is open, even just a crack;
DO NOT OPEN THE FILM BIN!!!!
— An important task to perform in the darkroom is to _____ _____ _______
patient identification
safe
cell phone lights
refill the cassette.
