Xray, Xray Production, Xray Tubes And Xray Generators

Question 1

reduction in the x-ray beam intensity toward the anode side of the x-ray field caused by the greater attenuation of x-rays directed toward the anode side of the field by the anode itself. The ______ is less prominent with a longer source-to-image distance (SID).

Answer 1

heel effect

Question 2

Results from electrons that scatter from the anode, and are re-accelerated back to the anode, outside of the focal spot area. These electrons cause low-intensity x-ray emission over the entire face of the anode, as shown in Figure 6-18,
increasing patient exposure, causing geometric blurring, reducing image contrast, and increasing random noise.

Answer 2

Off-focal radiation

Question 3

The x-ray tube insert

Answer 3

cathode, anode, rotor assembly, and support structures sealed in a glass or metal enclosure under a high vacuum

Question 4

“getter” circuit

Answer 4

used to trap gas in the

insert and to maintain the vacuum

Question 5

Mammography tubes use ____ in the port to minimize absorption of the low-energy x-rays used in mammography

Answer 5

beryllium (Z = 4)

Question 6

has a focusing cup that is electrically isolated from the cathode
filament and maintained at a more negative voltage
-Turning off ___ allows the tube current to flow and x-rays to be produced.
- requires approximately −4,000 V applied to the focusing cup with respect to the filament
to switch the x-ray tube current off (see Fig. 6-10).
- used in applications such as pulsed fluoroscopy and cine-angiography, where rapid x-ray
pulsing is necessary.
- more expensive

Answer 6

grid-biased tube

Question 7

Mammography tubes are designed to provide the ____ necessary to
produce optimal mammographic images. As explained in Chapter 8, the main differences between a dedicated mammography tube and a conventional x-ray tube are the
target materials (—), the output port (____
versus glass or metal insert material), the _____ effective focal spot sizes (typically
_____ sizes), and the use of __

Answer 7

• low-energy x-rays
• molybdenum, rhodium, and tungsten
• beryllium
• smaller, 0.3 and 0.10 mm nominal focal spot
• grounded anodes

Question 8

Mammography tubes are designed to provide the ____ necessary to
produce optimal mammographic images. As explained in Chapter 8, the main differences between a dedicated mammography tube and a conventional x-ray tube are the
target materials (—), the output port (____
versus glass or metal insert material), the _____ effective focal spot sizes (typically
0.3 and 0.1 mm nominal focal spot sizes), and the use of __

Answer 8

• low-energy x-rays
• molybdenum, rhodium, and tungsten
• beryllium
• smaller, 0.3 and 0.1
• grounded anodes

Question 9

Major tube components are the

Answer 9

cathode, anode, rotor/stator, glass

or metal envelope, tube port, cable sockets, and tube housing

Question 10

x-ray tube voltage is set to values from

Answer 10

40 to 150 kV for diagnostic imaging, and 25

to 40 kV for mammography

Question 11

For continuous fluoroscopy, the
tube current is relatively low, from —-, and for projection radiography, the
tube current is set from —- in conjunction with short exposure times
(typically less than 100 ms). (In pulsed fluoroscopy, the tube current is commonly
delivered in short pulses instead of being continuous; the average tube current is
typically in the range of —

Answer 11

1 to 5 mA
50 to 1,200 mA
10 to 50 mA

Question 12

When energized, the filament circuit heats the filament through electrical resistance, and the process of — releases electrons from the filament
surface at a rate determined by the filament current and corresponding filament
temperature. Heat generated by resistance to electron flow in the filament raises the
temperature to a point where electrons can leave the surface

Answer 12

thermionic emission

Question 13

As a large voltage is applied between the cathode and anode in the correct polarity,
electrons are accelerated into a tight distribution and travel to the anode, striking a
small area called the —

Answer 13

focal spot

Question 14

focal spot dimensions are determined

by the 1 and 2

Answer 14

length of the filament in one direction

the width of electron distribution
in the perpendicular direction.

Question 15

The — is a metal target electrode that is maintained at a large positive potential
difference relative to the cathode.

Answer 15

anode

Question 16

— is the most
widely used anode material because of its high melting point and high atomic number.
can handle substantial heat deposition without cracking or
pitting of its surface. An alloy of 10% — and 90% provides added
resistance to surface damage. Tungsten provides greater bremsstrahlung production
than elements with lower atomic numbers (Equation 6-1).

—-abd —- are used as anode materials
in mammographic x-ray tubes. These materials provide useful characteristic x-rays
for breast imaging (see Table 6-2).

Answer 16

Tungsten (W, Z = 74)
Rhenium and tungsten

Molybdenum (Mo, Z = 42) and rhodium (Rh, Z = 45)