Midterm I Flashcards
Roentgen noticed a glow from a barium platinocyanide plate while working with a __________ tube.
Crookes
Who discovered x-rays in 1895?
Wilhelm C. Roentgen
T or F: The barium plate continued to glow when surrounded by an opaque black paper
True
Roentgen “accidentally” discovered________effect.
Photographic
Roentgen noticed that the Crookes tube emitted an energy that is not________ but instead is _________.
Light; X-Rays
T or F: Roentgen ID’d all characteristics of x-rays including biological effect.
False, all but the biological effects
Thomas Edison discovered ________ and experimented with over 1800 flourescent matierals for use in x-ray imaging.
Flouroscope
George Eastman developed photographic plates and invented _______ for photography and radiography.
Film
Who developed the x-ray grid?
Bucky
Law of Conservation of Energy -Newton is:
Energy can be neither created nor destroyed, but it can change form.
What kind of wave radiation are energies that change the field they pass through?
Electromagnetic (EM) Wave Radiation
Name of the form of a repeating wave pattern that field changes occur?
Sine Wave (sinusoidal form)
Visible light and X-rays are what kind of energy?
Electromagnetic Energy
_________Radiation can remove an electron from it’s orbit, has a wavelength < or = 1nm, and x-rays are a form.
Ionizing
What is a particle model used to depict the nature of EM energy?
Quantum Theory
What is the smallest unit of EM energy?
Photon
What is Quanta?
groups or “bundles” of photons (singular is quantum)
What’s the smallest unit (“particle”) of a quantum?
Photon
How is an x-ray photon visualized?
- 2 perpendicular sine waves
- traveling in a straight line & at speed of light
What is a form of energy associated with many naturally occurring phenomena, such as EM radiation, and has a recurring wave form?
Sine waves
Sine wave characteristics?
Amplitude, Wavelength, Frequency, Velocity
Distance from crest to valley is?
Amplitude
Crest to crest distance of a sine wave?
Wavelength
Number of crests (or valleys) that pass a fixed point per unit time?
Frequency
Wavelength x Frequency = ?
Velocity (EM velocity = 3x10^10 cm/sec)
Do sine wave with shorter wavelengths have more or less energy?
More energy (shorter wavelengths = higher frequency)
Do x-rays increase penetration with a shorter or longer wavelength?
Shorter
Characteristics of x-rays:
*travel in straight line at speed of light
*diverge into space until absorbed
*cause types of crystals to flouresce
*photographic effect
*human senses can’t detect
*mass and density of matter create differential penetration of x-rays
*lens cannot refract
*produce biological effects
*
Primary Radiation
x-ray beam that leaves the tube and is unattenuated (except by air); direction and location are predictable and controllable
Secondary/Scatter Radiation
Radiation created/scattered by interaction with matter and primary x-ray beam, travels in all directions, difficult to control, Primary beam energy > secondary beam energy.
Radiation that creates a pattern of differential absorption remaining from primary beam after it’s been attenuated by matter and creates a film image?
Remnant Radiation
Electricity: Direct current?
Constant power source and the current from from neg (-) to pos (+).
Electricity: alternating current?
power source alternates between positive and negative at regular intervals.
What is the difference in electrical potential (polarity) between 2 locations in a circuit that is measured in Volts (V), Kilovolts (kV), Kiolovolts peak (kVp)?
Electromotive Force (EMF), causing electric charges to flow thru the circuit
Describe Kilovolts
Voltage measured at the peak of the electrical cycle in an X-ray tube cirucuit
Current is the flow of electrical charges in the circuit. What units is used to measure the current?
- Coulombs
- Amperes (A or amp)
- Milliamperes (mA): 1mA = 0.001A
What represents the total quantity of electrical charges
Coulombs
What represents the rate of flow of electrical charges?
Amperes (coulombs/second)
What is the Electrical supply to:
- Household
- X-ray tube circuit
Household: 120V or 30 amps
X-ray tube circuit: 120,000V or 0.3 amps; 120 kVp or 300 mA
4 requirements for the production of X-rays:
- Vacuum
- Source of electrons
- Target for the electrons
- High potential difference b/t source and target
Electron source for x-ray production is:
Tungsten filament, heated by electric current
Thermionic Emission is:
Heated tungsten -> electrons in tungsten atom orbits spin faster -> electrons move farther from nucleus -> electrons are flung out of atom -> electrons form “electron cloud” or space charge -> charge creates electron source for X-Ray
Tungsten filament’s space charge move to the ________ target, forming an __________.
Tungsten; “electron stream”
How is the Tungsten target positioned?
Slanted and located at the opposite end of the tube from the tungsten filament.
The positive end of the tube is called the _________ and the negative end of the tube is the _________.
Anode; Cathode
The anode is associated with the ________ and the cathode is associated with the __________.
Target; Filament
When the electrons strike the Tungsten target how much energy is converted to heat vs. x-rays?
99 +% into heat AND a tiny amount into X-rays.
The fast-moving electrons heading at the target has ________ energy from that convert to heat and x-ray when stopped by target.
Kinetic
The majority of x-ray beam consists of _________ ; which is a result of the sudden halt of electron stream at target, as kinetic energy converts to other forms of energy.
Bremsstrahlung (braking rays)
Characteristic Radiation is formed where?
Within the Target Atom as a result of interaction with electron stream.
When an orbital electron moves from 1 energy level (shell) to another, the difference in binding energy of the 2 shells is emitted as an x-ray photon called _________.
Characteristic Radiation
Why is radiation coined Characteristic Radiation?
Because the x-ray photon always has the same wavelength and is “characteristic” of the target element.
The difference in binding energy b/t the 2 shells is always the same
Purpose of X-ray Tube Housing?
- protects tube
- absorbs radiation
- provides mounting for tube attachments (ie. collimator)
Requirements of x-ray production
- Vaccuum
- Free electrons
- Target
- High voltage (high potential diff b/t source and target)
2 types of interactions form the primary beam:
- Bremsstrahlung (heterogenous)
* Characteristic (unique wavelength specific to target material)
What would happen without a Focusing Cup at the Cathode?
Electron stream would spread beyond the target area.
Negatively charged focusing cup _______ electrons, focusing them on small ________ ______.
Repels; target area (“focal spot”)
Most modern general purpose tubes are “_____ ______.”
Dual Focus
Dual Focus tubes have 6 important components?
- 2 x filaments
- 2 x focusing cups
- 2 x concentric focal spots
Filaments and focal spots are selected in association with mA settings and mA circuits. What is an example?
25-150 mA use small filament and small focal spot.
vs.
200 mA and above use large filament and large focal spot.
Composition of Anode:
- Tungsten target imbedded in molybdenum disc
* Mass of copper (conducts heat from target)
2 characteristics of Anode?
- Angulation: target face is beveled at 10-20 degree slant
* 2 concentric focal spots: 1 large & 1 small
Actual focal spot vs. Effective focal spot
Actual = measurement of focal spot ON target surface
Effective = measurement of vertical projection
Tubes that have 2 concentric focal spots, 1 large and 1 small, are called?
Dual Focus tubes
Actual Focal spot size affects tube _____ ______ and ______ size is Better.
Heat Capacity; BIGGER
Effective Focal Spot size affects ______ ______ and ______ size is better.
Image sharpness; Smaller
Line Focus Principle:
- size of Effective focal spot determines image sharpness
- target Angle determine relative size of effective focal spot
- Steeper angle of target creates a greater difference b/t actual and effective focal spot sizes.
Anode Angulation determines maximum ______ ______ and the steeper the angle results in a ________ effective focal spot.
Field Size; Smaller
Steeper the Target Angle ________ differential between Actual and Effective focal spots AND results in a ________ Effective Focal Spot.
Increases; Smaller
What anode angulation (degree) is needed to cover a 14” x17” distance from the source?
12 degrees
Where are x-rays formed?
a. within Target Material
b. within Cathode Filament
c. Between a and b
a. Target Material
T or F: Anode Heel Effect is caused by an uneven absorption of the primary beam at the sloping target.
True - and results in variation in radiation intensity
The “heel” of the sloping target absorbs the most of the primary beam causing the radiation at the “heel” to be _________ intense.
Less
Radiation intensity is _________ toward the cathode end of the Targets slope.
Greater
The Anode Heel Effect is important in AP Thoracic spine. Why?
The greatest X-ray intensity needs to go through the thickest part of the body, which we know is at the cathode end of the field.
Anode Heel Effect: The thinner part (head) is placed at ______ side (“cathode facing”) and the thicker (chest) is placed at _______ side.
Anode; Cathode
To control rate of flow of electrons across the tube the ______units are set to heat up the filament, therefore controlling rate of ________production.
mA; X-Ray (Radiation exposure is proportional to mA)
Exposure Time is controlled by a _______ in x-ray circuit, therefore controlling duration of exposure and _______of x-rays produced.
Timer; Quantity (Radiation exposure is proportional to exposure time)
mA x ? = mAs (total quantity of electricity involved in exposure)
time
What is controlled to increase speed of electrons and kinetic energy and shorter wavelength?
Kilovoltage (kVp); control power source
What does 99+% of x-ray tube energy convert into?
Heat
What are 4 effects of overheating the tube?
- Anode degradation -> unsharp image
- Extra gas from hot components -> erratic exposures
- Heavy exposure -> crack anode
- Break tubes, compromises tube/oil seal -> destroys tube
What features of the tube design are helping to minimize overheating tube?
- Rotating anode on circumferential focal spot
- Material used (tungsten, molybdenum, & graphite)
- Copper conducts heat away from Tungsten
- Control Circuits (mA, kVp, time)
Common Sense when taking x-ray, pertaining to the tube?
- Tube needs 10-30 seconds to cool after each exposure
- If tube is hot to touch then don’t use until tube has cooled
- Allow cold tube to warm-up
- Safe large exposures: use tube rating chart to determine
- Don’t hold Rotor Switch down for long time
- Don’t use tube when rotor bearings are heard
What are 4 points unique about Tube Rating Charts?
- Indicate maximum safe settings
- Specific chart to each tube design
- Use when creating a technique chart
- Check when using Large Exposure
Estimate the tube load with the info below:
exposure = 400 mA, 1/10 sec, 85 kVp
Max. safe exposure = 400 mA, 3/10 sec, 85 kVp
mA x time = mAs
Exposure: mAs = 40
Max. safe exp: mAs = 120
Therefore Tube Load: 40/120 = 33 1/3%
Why is this equation used:
mA x Time x kVp x 1.45 = HU
To make a cooling chart when evaluating a series of exposures with little time in between
The process of causing alternating current flow in 1 direction only?
Rectification (“To Make Right”)
When the nature of the X-ray tube prevents current from flowing from anode to cathode during 1/2 the electrical cycle it’s called?
Self-Rectification
When diodes placed within the circuit to “back-up” self-rectification this is called?
Half-wave Rectification (same prevention of back-flow of current)
When 4 diodes in a circuit are used to redirect current during the whole cycle allowing x-ray production during the entire electrical cycle it’s called?
Full-Wave Rectification
Full-Wave Rectification decreases exposure time to ________ that required by self- or half-rectified x-ray machine.
Half
What are some benefits to a Three-phase and High Frequency Generation?
- more constant power supply and efficient voltage source
- the rectified current is a ripple with no real low points
- produces near-constant voltage waveform
What accessory on the tube controls the Radiation Field?
Collimator
What are 3 types of Collimators?
- Manual - adjust to each field dimension
- Automatic - Sensors in film tray determine film size and adjust collimator.
- Semi-automatic - manually adjusted, but exposure is locked out unless field size is smaller than film size
Legal Requirements for Collimators?
- Rectangular collimator with independent adjustment of each dimension
- Must indicate field dimensions
- Must have light that delineates field accurately within 2% of SID & indicates center of field
- Field cannot be larger than film (only collimate clinical interest)
What wavelength gets filtered out of the primary beam and why?
- Long wavelength (attenuates low energy photons)
* It doesn’t have sufficient energy to penetrate the patient, lowers radiation does significantly
Units filtration is measured?
millimeters of aluminum (mm. Al equiv.)
Types of accumulated Filtration of the primary beam(p. 13)?
- Inherent - by glass of the tube envelope; 0.5 mm. Al equiv.
- Added - Aluminum plates (1.0 mm. Al) & Collimator parts (mirror, face plate; 1.0 mm. Al)
All machines capable of operating above 70 kVp are required to have at least ____ mm Al equiv. total filtration permanently installed.
2.5
Filtration changes:
a. dose of radiation
b. exposure requirements
c. image quality
a. - decreases dose to ~1/4 the unfiltered dose
Which of the following will make the radiograph darker:
a. Increased mA
b. Increased exposure time
c. Both a & b
d. neither
c.
Exposure is directly proportional to milliamperage (mA) and Quantity of exposure is directly proportional to __________.
Time
Higher mA increases heat load of tube – greater total load is possible with _______mA settings.
Lower
Unit used to indicate the total quantity of x-rays in an exposure?
Milliampere-seconds (mAs)
What is the primary controller of radiographic density:
a. mA
b. time
c. mAs
c. mAs
What units of voltage is the primary controller of the speed of electrons from cathode to target?
Kilovoltage (kVp)
kVp is not directly proportional to exposure, but kVp does directly affect radiographic _________.
Contrast
High kVp produces a _______contrast image and Low kVp produces a ________contrast image.
Low; High
kVp is the primary controller of radiographic __________.
Contrast
Two functions of kVp are?
- Penetration of beam
* Radiographic scale of contrast
The distance between the tube target and imaging receptor?
Source-Image Distance (SID)
The Inverse Square Law says the intensity of the radiation is ______ proportional to the square of the _______. Therefore, when SID 80 inches (vs. 40 inches) the field size is 4X as large, and the x-ray intensity is 4X less.
inversely; distance
I1 D2^2
— = —
I2 D1^2
What’s I2 at 80” if the intensity is 1 at 40”
Intensity of I2 = 1/4
Since distance (SID) affects radiation intensity and mAs affects radiation intensity, then an increase in SID may need to _______ mAs to compensate for distance.
increase
mAs Distance rule = constant exposure is maintained when changing the distance by varying the mAs in direct proportion to the _______ of the distance.
SQUARE
mAs1 D1^2
—— = ——
mAs2 D2^2
mAs1 D1^2
—— = ——
mAs2 D2^2
D2^2 =72” ; D1^2=40 ; mAs1=10 ; mAs2 = ?
mAs2 = 32.4
Radiographic Density is affects the visibility (over-all blackness/density) of detail of exposure, which is directly controlled by________ and indirectly controlled by _______ & _______.
mAs; kVp & SID
What is the difference in radiographic density between adjacent portions of the image?
Contrast
What is the Contrast primarily controlled by?
kilovoltage (kVp)
High kVp creates a _________contrast and Low kVp creates _______contrast.
low (many shades of gray) ; high (few shades of gray more black/white)
Films looking for bone problems try to use ________contrast, films looking at soft tissues (lung fields) try to use ________contrast.
High; Low
What is the name of a step-wedge made of aluminum that estimates the # of shades of gray in film?
Penetrometer
The desired scale of contrast is influenced by the range of differences in the intensity of the x-ray beam exiting the body, which is known as the _______ ________.
Subject contrast
The Abdomen has a _______subject contrast due to the similar tissue densities of the tissue, and needs a _____kVp. The Chest has________subject contrast due to the wide varying tissue densities, and needs a _______kVp.
low and high; high and low
General, unwanted exposure to the film is referred to as_________ and ________contrast (hint: longer scale of contrast).
Fog; decrease
What is the difference between the actual subject and it the radiographic image?
Distortion
Magnification caused by any combo of short SID &/or large OID is?
Size distortion
What is the unequal magnification of image due to the part being imaged not being parallel to the image or the beam not being perpendicular to the image (or both)?
Shape distortion (i.e. scaphoid image)
When OID is larger therefore ________Magnification and Distortion.
Increases
Decrease the SID _______Magnification and Distortion. To correct for a large OID _________SID.
Increase; Decrease
2 things that cause shape distortion?
- object not parallel/aligned to image receptor (IR)
2. X-ray tube and IR are not aligned
When trying to maximize the detail/sharpness of the radiograph what are 3 important factors?
- Focal Spot Size (FSS)
- Object-image distance (OID)
- Source-image distance (SID)
When the FSS is reduced to the size of a point does it increase or decrease penumbra? Why?
Decreases, because the x-ray beam is produced in less areas of the anode target decreasing the divergence of photons.
What changes (increase or decrease) in OID and SID will decrease the penumbra?
decrease OID and increase SID
What does P.A.C.S. stand for?
Picture Archiving and Communication System
What is hardware and software for managing digital images with computed and/or digital radiography?
PACS
