Diagnostic X-Ray Production

heat dissapation is —-% heat/—-% x-rays

99, 1

what are the 4 x-ray generator settings

1. voltage

2. current

3. time

4. resistance

what are the units for voltage

V

define voltage

the speed with which the electrons in the electric current transfer energy along the circuit.

what are the units for high voltage

kV

high voltage produces (3) x-rays

1. short-wavelength

2. high frequency

3. highly penetrating

current is also known as

amerage

what is the unit for current

upper case ‘i’

define current

to measure the electric current that activates the x-ray tube.

the x-ray unit consists of a closed circuit with 5 main criteria:

1. It must have enough power to eventually produce x-rays.

2. It must have selections where the power can be increased or decreased as necessary.

3. The electric current must travel in the same direction through the x-ray tube.

4. There must be a way to produce free electrons with enough energy to produce x-rays.

5. There must be an efficient way to dissipate the heat that results in the interaction of the photons and the anode.

circuit breakers acts as a

fuse

how do circuit breakers act as fuses

If the voltage or current is set too high, or if a component malfunctions, the circuit breaker will cut the power to the unit

define fuse

safety devices that will mechanically interrupt the flow of electricity if a problem arises that would overheat the circuit

define ground wire

Redirects current flow of excess electrons if circuit is broken

what color is the ground wire usually

green

operating console is aka

generator

voltage controls

penetrating power

current controls (2)

1. number of photons

2. density of image

power (WATT) equation

Power (WATT) = voltage (V) X Current (A)

purpose of line voltage compensator

Stabilizes incoming power line

define direct current

Source of power near the end user

define Alternating Current

One positive pulse and then one matching negative pulse

how many cycles are in alternating current

120 cycles/sec

define transformers

Transformers step up (increase) the power at one end of the journey and then step down (decrease) the power at the destination

define rectifiers

Allow current to keep moving in one direction within x-ray unit

What is the problem with single-phase circuits

The problem that arose was the long exposure time due to the low power of these units and the loss of power as the voltage dropped during the exposure with the completion of each pulse

what are 3-phase circuits used for

large animal chest and abdominals

why is 3-phase circuits used for large animal

high milliamperes (mA) combined with short times (seconds) are necessary to image large-animal chests and abdomen

what are the 3 kinds of circuits

1. single-phase

2. three-phase

3. high-frequency

what are the 3 components of the x-ray unit

1. High-voltage transformer / high-tension transformer

2. X-ray generator

3. X-ray tube

define High-voltage transformer / high-tension transformer

It is connected to the hospital power lines and uses the power supplied to the hospital by the outside power lines.

define X-ray generator

receives its power from the highvoltage transformer and sends it through the circuit to the rectifiers and then to the x-ray tube

define x-ray tube

it is here that the x-rays are produced

what is in the x-ray tube (7)

1. Cathode

2. anode

3. Near vacuum

4. Power must enter thru the cathode

5. Heat will exit through stem of the anode

6. Stem is mounted on ball bearings which are coated in light oil

7. Every x-ray tube is shielded with a metal covering, which restricts most off-focus radiation from exiting the tube other than at the tube port.

the x-ray tube process to produce x-rays (5)

1. the exposure switch is closed

2. the electrons are drawn across to the anode by electromagnetic force

3. they are stopped very suddenly by the density of the metal of the anode.

4. They react immediately by losing speed

5. converting the forward motion to energy, which results in heat and x-rays (99% heat and 1% x-rays).

define thermionic emission

emission due to heating

define thermionic emission related to cathodes

When this coil is heated by electricity, it produces a cloud of electrons

why is tungsten used in the cathode

can withstand very high temperatures without melting.

why is the focusing cup slightly negative

to focus the electrons that are boiled off the cathode filaments

why does the focusing cup have beveled edges

are designed to focus on very small areas of the anode.

define Space charge effect

The cloud of electrons that is produced as the electrons are boiled off

what are the 2 types of anodes

1. rotating

2. stationary

purpose of rotating anode

invented to dissipate heat on one spot

purpose of stationary anode

used in lower kV units

The intensity of the radiation is greater on the —- side

cathode

The thicker end of the animal should be placed on the —- side

cathode

why is The thicker end of the animal should be placed on the cathode side

to take advantage of the greater amount of radiation at that end

define line focus principle

describes how the electrons interact with the anode and change direction

If the angle of the anode is less than 15 degrees from the vertical, the resulting x-ray beam will be —, and the image will have —- resolution

narrow, higher

If the angle is greater than 15 degrees, the beam will be —-, resulting in … on the very small focal spot and decreasing the “bloom” effect on the focal spot.

wider, less heat focused

define Focal spot bloom

The images will lose resolution as the focal spot enlarges

define Bremsstrahlung interactions

the incoming electron avoids hitting a tungsten electron but travels very close to its nucleus

define Characteristic interactions

occur when an incoming electron interacts with an electron from the inner shell of the tungsten atom

heat unit equation

kV × mA × Seconds × Number of exposures = Heat units