Tube current modulation is a feature of modern CT scanners to alter the strength of the beam by modulating the current of the x-ray tube depending on the signal to noise ratio. The purpose of tube current modulation is to maintain a near constant signal to noise ratio in the image across different areas of the body with varying thicknesses in order to avoid excessive radiation doses whilst maintaining image quality.
Why are X rays bad?
Why are x rays bad. Ionizing radiation is a form of radiation that has enough energy to potentially cause damage to DNA. Risks from exposure to ionizing radiation include: a small increase in the possibility that a person exposed to X-rays will develop cancer later in life. 1 Is it bad to have a lot of X-rays?
What is X-ray tube voltage?
The x-ray tube voltage is set to values from 40 to 150 kV for diagnostic imaging, and 25 to 49 kV for mammography, depending on the type of imaging exam and anatomy being imaged.
Are X rays dangerous?
Since X-rays are passed through the body, they may pose a risk to our health because of exposure to radiation. MRI scans work by using a magnetic field and radio waves which help in producing images of the internal structure of the body.
How to read an X-ray?
We have a couple of clues to help you make an interpretation:
- Use symmetry when you can. Compare both sides, legs, or whatever else that might be useful.
- Pull your face away from the screen and scan the whole x-ray before you jump into the details.
- After you have scanned the whole radiograph look very closely for subtle changes.
Which current is used in x-ray tube?
To operate, a DC voltage of a few kilovolts to as much as 100 kV was applied between the anodes and the cathode, usually generated by an induction coil, or for larger tubes, an electrostatic machine.
Are X-ray tubes AC or DC?
DC X-Ray. AC x-ray machines use an alternating current to drive the tube head to produce x-rays. This is usually the same 120v AC supply that powers our home; the voltage alternates from +60 to -60 volts, giving 120v of potential across two wires.
What happens when x-ray tube cathode current is increased?
The increase in x-ray tube voltage increases the amount of radiation coming out of the x-ray tube, as well as the average photon energy (i.e., increased penetration).
What does an x-ray tube do?
The x-ray tube serves the function of creating x-ray photons from electric energy supplied by the x-ray generator. The process of creating the x-ray beam is very inefficient, with only 1% of the electric energy converted to x-ray photons and the remaining 99% converted to heat in the x-ray tube assembly.
What is xray tube voltage?
The power supply for X-ray tubes is a cathode-grounded high-voltage power supply, with tube voltages ranging from 50 kV to 80 kV and power from 50 W to 4 kW.
What converts AC to DC in the xray?
Rectifiers ensure that electrons flow in only one direction through the x-ray tube by converting alternating current (AC) into direct current (DC).
How does tube current affect the spectrum?
As the tube current (mA) increases, the number of incoming electrons striking target increases. In addition the number of X-ray photons produced in both Bremsstrahlung and characteristic x-ray portions of x-ray spectrum is altered.
Why do we increase kVp?
Increasing the kVp increases the penetrating power of the radiation and increases the exposure to the image receptor. For film-screen IRs, kVp has a direct relationship with density; however, the effect of the kVp on density is not equal throughout the range of kVp (low, middle, and high).
Is kV and kVp the same?
Most modern X-ray generators apply a constant potential across the X-ray tube; in such systems, the kVp and the steady-state kV are identical. kVp controls the property called "radiographic contrast" of an X-ray image (the ratio of transmitted radiation through regions of different thickness or density).
Why do we need DC for x-ray tube?
A DC X-ray machine uses direct electric current to power the X-ray tube head. These constant potential (DC) machines, neither change direction nor the intensity making it a steady supply of power. This facilitates production of smooth and consistent X-rays.
What are the two components of xray tube?
The x-ray tube contains two principal elements: filament (also acts as cathode): boils off electrons by thermionic emission. target (also acts as anode): electrons strike to produce x-rays.
How X-ray tube works step by step?
1:323:30How does X Ray Work (X-Ray Production) - YouTubeYouTubeStart of suggested clipEnd of suggested clipIs decelerating the electrons these highly energetic electrons slam into the anode of the x-ray tubeMoreIs decelerating the electrons these highly energetic electrons slam into the anode of the x-ray tube and in the process of decelerating. They actually release their energy as heat.
What will occur when Kilovoltage is increased?
An increase in kVp extends and intensifies the x-ray emission spectrum, such that the maximal and average/effective energies are higher and the photon number/intensity is higher.
What change is noticed in cathode ray tube when the anode voltage is increased?
As the anode voltage is increased, the electrons get accelerated at faster rate which results in increase in the kinetic energy (or velocity) of the electrons.
What happens when voltage is increased during electrolysis?
Hence, when voltage is increased during electrolysis, the rate of the reaction increases.
What happens when cathode rays are subjected to a strong electric field?
When cathode rays are subjected to an electrical field, these get deflected towards the positively charge plate i.e. Anode. We know that a positively charged body would attract only a negatively charged body, therefore the particles of cathode rays carry negative charge.
What is an X-ray tube?
X-ray tube. From Wikipedia, the free encyclopedia. Jump to navigation Jump to search. An X-ray tube is a vacuum tube that converts electrical input power into X-rays. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation.
What is the power source of an X-ray tube?
A high voltage power source, for example 30 to 150 kilovolts (kV), called the tube voltage, is connected across cathode and anode to accelerate the electrons. The X-ray spectrum depends on the anode material and the accelerating voltage.
How are electrons produced in a coolidge tube?
In the Coolidge tube, the electrons are produced by thermionic effect from a tungsten filament heated by an electric current. The filament is the cathode of the tube. The high voltage potential is between the cathode and the anode, the electrons are thus accelerated, and then hit the anode.
Why are Crookes tubes unreliable?
Crookes tubes were unreliable. As time passed, the residual air would be absorbed by the walls of the tube, reducing the pressure. This increased the voltage across the tube, generating 'harder' X-rays, until eventually the tube stopped working. To prevent this, 'softener' devices were used (see picture).
What is the best vacuum for X-ray generator?
The Coolidge tube, also called hot cathode tube, is the most widely used. It works with a very good quality vacuum (about 10 −4 Pa, or 10 −6 Torr). Until the late 1980s, X-ray generators were merely high-voltage, AC to DC variable power supplies.
What happens to tungsten in X-rays?
Over time, tungsten will be deposited from the target onto the interior surface of the tube, including the glass surface. This will slowly darken the tube and was thought to degrade the quality of the X-ray beam.
How much power does a coolidge tube have?
The power of a Coolidge tube usually ranges from 0.1 to 18 kW .
What is the function of an x-ray tube?
An x-ray tube functions as a specific energy converter, receiving electrical energy and converting it into two other forms of energy: x-radiation (1%) and heat (99%).
What are the components of an x-ray tube?
The x-ray tube contains two principal elements: Additional components include: The filament/cathode and target/anode are contained in the envelope, which provides vacuum, support and electrical insulation. The envelope is most often made from glass, although some tubes contain envelopes formed from ceramic or even metal.
How does a generator work in x-rays?
The energy used for this process is provided from a generator, connected by an electrical circuit connected to the x-ray tube. The generator also needs to convert the mains supplied alternating current (AC), into direct current (DC), as needed by the x-ray tube. The reason for this is to ensure a constant unidirectional flow of electrons from the positive charged cathode to negatively charged anode.
How is x-radiation controlled?
The quality and the quantity of the x-radiation are controlled by adjusting the electrical parameters ( kV – tube voltage (potential difference applied across the tube), mA – tube current (flows through the tube) and exposure time, usually a fraction of a second.
When was x-ray tube invented?
Wilhelm Roentgen discovered x-rays using a Crookes tube in 1895. Until the invention of the Coolidge tube in 1913, all x-ray tubes were based on the Crookes or cold cathode gas tube technology. From the late 1910s onwards there was a rapid replacement of gas tubes by the far more effective Coolidge tubes.
What is the filament in an electrical tube made of?
The filament/cathode and target/anode are contained in the envelope, which provides vacuum, support and electrical insulation. The envelope is most often made from glass, although some tubes contain envelopes formed from ceramic or even metal.
What type of tube was discovered after Roentgen?
NB: This article is about the modern vacuum tube. For the first twenty years after Roentgen's discovery, all tubes were of the gas type.
What is the purpose of an x-ray tube?
The x-ray tube provides an environment to produce bremsstrahlung and characteristic x-rays. Major tube components include the cathode, anode, rotor/stator, glass or metal envelope, tube port, cable sockets, and tube housing, illustrated in Figure 6-6. An actual x-ray tube showing the x-ray tube insert and a cut-away of the housing is shown in Figure 6-7. The x-ray generator (Section 6.3) supplies the power and permits selection of x-ray tube voltage, tube current, and exposure time. The x-ray tube voltageis set to values from 40 to 150 kV for diagnostic imaging, and 25 to 49 kV for mammography, depending on the type of imaging exam and anatomy being imaged. The x-ray tube current, measured in milliamperes (mA), represents the number of electrons per second flowing from the cathode to the anode, where 1 mA = 6.24 × 1015electrons/s. For projection radiography, the tube current typically ranges from 100 to 1,000 mA with exposure times less than 100 ms for most examinations. The kV, mA, and exposure time are the three major selectable parameters on the x-ray generator control panel that determine the x-ray beam characteristics. Often, the product of the tube current and exposure time is considered as one entity, the mAs (milliampere-second). These parameters are discussed further in the following sections.
How fast does an xray tube rotate?
Before an exposure, the stator/rotor induction motor is energized to spin the anode, and after a short delay, rotation speeds of 3,000 to 3,600 (low speed) or 9,000 to 10,000 (high speed) revolutions per minute (rpm) are achieved. X-ray tube-generator systems for general radiography are designed such that the x-ray tube voltage is applied only when the anode is at full speed, causing a short delay (1 to 2 seconds [s]) prior to x-ray exposure when the button is pushed by the technologist.
How does a rotating anode work?
Rotating anodes allow higher x-ray output by spreading the heat over a larger area as the anode surface rotates relative to the electron beam. The rotating anode is designed as a beveled disk mounted on a rotorassembly supported by bearings in the x-ray tube insert for radiographic x-ray tubes (Fig. 6-13). In many x-ray tube anodes for radiography and fluoroscopy applications, the bulk of the material is molybdenum, with a tungsten target blended with 3% to 10% of rhenium to enhance ductility of ˜0.5 mm thickness sintered onto the focal track area. The rotor consists of copper bars arranged around a cylindrical iron shell. A donut-shaped statordevice, comprised of electromagnet coils, surrounds the rotor and is mounted outside of the
What is the K-value of a X-ray?
Characteristic K x-rays are produced onlywhen the electrons impinging on the target exceedthe binding energy of a K-shell electron (KBE). X-ray tube potentials must therefore be greater than 69.5 kV for W (KBE= 69.5 keV), 20.0 kV for Mo (KBE= 20.0 keV), and 23.2 kV for Rh (KBE= 23.2 keV) for characteristic x-rays to be produced on these targets. As the x-ray tube voltage increases, the ratio of characteristic to bremsstrahlung x-ray energy fluence also increases. For example, at 80 kV, approximately 5% of the total x-ray energy fluence for a tungsten anode is composed of characteristic radiation, increasing to about 10% at 100 kV. Figure 6-5illustrates a bremsstrahlung plus characteristic radiation spectrum.
How does a filament circuit work?
When energized, the filament circuit is activated to pass current with a potential difference of about 10 V through the filament. Electrical resistance heats the filament to a temperature determined by the amplitude of the current (3 to 7 amperes [A]), resulting in a release of electrons from the filament surface by a process called thermionic emission. A static electron cloud “space charge” is formed around the
What is the energy of a characteristic x-ray?
In addition to the continuous bremsstrahlung x-ray spectrum, discrete x-ray energy peaks called “characteristic radiation” are present, with x-ray energies depending on the elemental composition of the anode and the applied x-ray tube voltage. Electrons in an atom are distributed in orbital “shells” and have specific electron binding energies to maintain equilibrium. The innermost shell is designated the K shell and has the highest electron binding energy, followed by the L, M, and N shells, with progressively less binding energy. Table 6-1lists the common anode target materials and the binding energies of the K, L, and M electron shells that are “characteristic” of the element. When the kinetic energy of an incident electron exceeds the binding energy of an electron shell in a target atom, an interaction can eject an electron from its shell, creating a vacancy. As discussed in Chapter 2, an outer shell electron with less binding energy immediately transitions to fill the vacancy, and a characteristic x-ray is emitted with an energy equal to the difference in the electron binding energies of the two shells (Fig. 6-4).
How are x-rays produced?
X-rays are produced when highly energetic electrons interact with matter, converting some or all of their kinetic energy into electromagnetic radiation. The x-ray tube insert contains an electron source, a vacuum environment, and a target electrode; an external power source provides high voltage (potential difference) to accelerate the electrons. The x-ray tube insert is mounted within a tube housing, which includes a metal enclosure; protective radiation shielding; x-ray beam filters for shaping the x-ray spectrum; and collimators, which define the size and shape of the x-ray field. The x-ray generator supplies the tube potential to accelerate the electrons, a filament circuit to control tube current, and an exposure timer. These components work in concert to produce a beam of x-ray photons with controlled fluence (number of incident photons per unit area), energy fluence (energy weighted number of photons per unit area), and a well-collimated trajectory. In terms of nomenclature used in this chapter, the fluence and energy fluence are scalar radiometric quantities. The term exposure is a dosimetric quantity describing the amount of charge in coulombs (C) released in a known mass of air (unit of C/kg) and is expressed in terms of the energy fluence and energy absorption integrated over energy. The exposure rate is the increment of exposure in a time interval (unit of C/kg/s).
What is an X-ray tube?
The x ray tube is a energy converter which converts electrical energy into X ray radiation and heat. The following are the components of the x ray tube.
What is the window of an X-ray tube made of?
The x ray tube window is usually made up of beryllium which allows X rays to pass through and has sufficient strength to hold the vacuum required for x ray tube to operate.
How are X-rays similar to visible light?
X rays are almost similar to visible lights. But the only difference is that they have different wavelengths. We can see visible light of higher wavelength, but we cannot see the X ray beams with lower wavelength and high energy. The frequency of X rays is 1020 Hz and wavelength ranges from 10 Picometres to 10 Nanometres.
Why is the output of X-rays decreasing?
Decreased output of X ray beams due to scattering of X ray beams and more absorption of X ray beams by anode target itself.
What is the purpose of an anode in an X-ray tube?
Rotating anode is used mostly. Anode has two main functions, one is it convert electric energy into X ray radiation and to dissipate the heat created in the process.
Why do gases in X-ray tubes damage the electric circuit?
The presence of gases in the X ray tube would allow electric current to flow through the tube freely instead of flowing only in the electron beam. Thus, inferring in the X ray production and damages the electric circuit.
Why is X-ray equipment important?
The x ray machine produces the images of inside of our body in black and white. Therefore it is important for every healthcare professional to know in detail about x ray machine.
What happens to the tube current after increasing the voltage?
After increasing tube voltage: Tube current: Increasing the tube current can increase the number of electrons that shoot the anode target, so that more photons penetrate the object and reach the flat panel detector. Usually we also use the milliamp number (mA) of the tube current to indirectly express the intensity of X-rays.
What happens when you increase the voltage of a tube?
Tube voltage: Increasing tube voltage produces photon with higher frequencies and shorter wavelengths, that is, the energy of photons is higher , which allows photons to penetrate objects with higher density and thickness.
What is the hardness of X-rays?
Let me introduce a concept here, called X-ray hardness, which refers to the penetration ability of X-rays, which depends on the energy of photons, that is, the wavelength of X-rays, and has nothing to do with the number of photons. Therefore, the hardness of the X-ray is related to the tube voltage and has nothing to do with the tube current.
Is the hardness of an X-ray a tube current?
Therefore, the hardness of the X-ray is related to the tube voltage and has nothing to do with the tube current. The higher the tube voltage, the harder the X-rays are. The hardness of X-rays is usually expressed in kilovolts (kV) of tube voltage. Before increasing tube voltage:
What is an X-ray tube?from en.wikipedia.org
X-ray tube. From Wikipedia, the free encyclopedia. Jump to navigation Jump to search. An X-ray tube is a vacuum tube that converts electrical input power into X-rays. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation.
What is the power source of an X-ray tube?from en.wikipedia.org
A high voltage power source, for example 30 to 150 kilovolts (kV), called the tube voltage, is connected across cathode and anode to accelerate the electrons. The X-ray spectrum depends on the anode material and the accelerating voltage.
What is the anode on a Crookes X-ray tube?from en.wikipedia.org
Crookes tube (cold cathode tube) Crookes X-ray tube from early 1900s. The cathode is on the right, the anode is in the center with attached heat sink at left. The electrode at the 10 o'clock position is the anticathode. The device at top is a 'softener' used to regulate the gas pressure.
How are electrons produced in a coolidge tube?from en.wikipedia.org
In the Coolidge tube, the electrons are produced by thermionic effect from a tungsten filament heated by an electric current. The filament is the cathode of the tube. The high voltage potential is between the cathode and the anode, the electrons are thus accelerated, and then hit the anode.
What are the two types of microfocus X-ray tubes?from en.wikipedia.org
There are two basic types of microfocus X-ray tubes: solid-anode tubes and metal-jet-anode tubes. Solid-anode microfocus X-ray tubes are in principle very similar to the Coolidge tube, but with the important distinction that care has been taken to be able to focus the electron beam into a very small spot on the anode.
What are the two types of tubes?from en.wikipedia.org
There are two designs: end-window tubes and side-window tubes. End window tubes usually have "transmission target" which is thin enough to allow X-rays to pass through the target (X-rays are emitted in the same direction as the electrons are moving.) In one common type of end-window tube, the filament is around the anode ("annular" or ring-shaped), the electrons have a curved path (half of a toroid).
What is the best vacuum for X-ray generator?from en.wikipedia.org
The Coolidge tube, also called hot cathode tube, is the most widely used. It works with a very good quality vacuum (about 10 −4 Pa, or 10 −6 Torr). Until the late 1980s, X-ray generators were merely high-voltage, AC to DC variable power supplies.
Overview
Physics
As with any vacuum tube, there is a cathode, which emits electrons into the vacuum and an anode to collect the electrons, thus establishing a flow of electrical current, known as the beam, through the tube. A high voltage power source, for example 30 to 150 kilovolts (kV), called the tube voltage, is connected across cathode and anode to accelerate the electrons. The X-ray spectrum dep…
History
X-ray tubes evolved from experimental Crookes tubes with which X-rays were first discovered on November 8, 1895, by the German physicist Wilhelm Conrad Röntgen. These first generation cold cathode or Crookes X-ray tubes were used until the 1920s. The Crookes tube was improved by William Coolidge in 1913. The Coolidge tube, also called hot cathode tube, is the most widely used. It works with a very good quality vacuum (about 10 Pa, or 10 Torr).
Types
Crookes tubes generated the electrons needed to create X-rays by ionization of the residual air in the tube, instead of a heated filament, so they were partially but not completely evacuated. They consisted of a glass bulb with around 10 to 5×10 atmospheric pressure of air (0.1 to 0.005 Pa). They had an aluminum cathode plate at one end of the tube, and a platinum anode target at the other end. The a…
Hazards of X-ray production from vacuum tubes
Any vacuum tube operating at several thousand volts or more can produce X-rays as an unwanted byproduct, raising safety issues. The higher the voltage, the more penetrating the resulting radiation and the more the hazard. CRT displays, once common in color televisions and computer displays, operate at 3-40 kilovolts depending on size, making them the main concern among household …
See also
• Electron beam tomography
• Coronary angiography
• Synchrotron radiation
• X-ray fluorescence
• X-ray generator
Patents
• Coolidge, U.S. Patent 1,211,092, "X-ray tube"
• Langmuir, U.S. Patent 1,251,388, "Method of and apparatus for controlling X-ray tubes
• Coolidge, U.S. Patent 1,917,099, "X-ray tube"
• Coolidge, U.S. Patent 1,946,312, "X-ray tube"
External links
• X-ray Tube - A Radiograph of an X-ray Tube
• The Cathode Ray Tube site
• NY State Society of Radiologic Sciences
• Collection of X-ray tubes by Grzegorz Jezierski of Poland