THE TUFFEST STUFF CT REGISTRY REVIEW SEMINAR · components do not experience the shock or stress of...

THE TUFFEST STUFF CT REGISTRY REVIEW SOLUTION

PHYSICS and INSTRUMENTATION

CT SYSTEM PRINCIPLES, OPERATION and COMPONENTS

SECTION 1 PRESENTATION D

EPISODE 4

The Modern COOLIDGE X-ray Tube

• CT X-RAY TUBE FUNCTION• CONVERT ELECTRICAL E TO ELECTROMAGNETIC E

• THE EM SPECTRUM family member characteristics• NO MASS

• NO ELECTRICAL CHARGE

• TRAVEL AT THE SPEED OF LIGHT (c)

EPISODE 4 THE TUFFEST STUFF CT REGISTRY REVIEW SEMINAR SOLUTION

2

High E =short wavelength & high frequency

Vs.Low E =

Long wavelength & low frequency

FOUR MAJOR COMPONENTS + 2

1.The CATHODE

2.The ANODE

3.The ENVELOPE

4.The VACUUM

5.The EXIT WINDOW or TUBE PORT

6.The ROTOR/STATOR


3


Four major components +2:

1.The CATHODE1.The negative electrical terminal

2.Components1.Focus cup- maintains the electron

cloud associated with Thermionic Emission

2.Dual filaments where Thermionic Emission takes place


4


Four major components +2:1.Dual filaments where

Thermionic Emission takes place1.Thermions change to Projectile

electrons when kVp is applied

2.Filaments are made from Tungsten

1.CT Small FSS = 0.5 – 0.6 mm Effective focus

2.CT Large FSS = 1.0 – 1.2 mm Effective focus


5


Four major components + 2:

2. The ANODE1.The positive electrical

terminal2.Components

1.Large rotating disk, aka, the “Target”-Tungsten + rhenium alloy

1.focal track

2.Focal spot- source of X-ray production


6

3.The target stema. Molybdenum


• UPGRADED ANODE CHARACTERISTICS:• 200 mm or more diameter target

• Thick graphite backing

• High temperature rotor bearings

• 5X increase in anode heat capacity

• DECREASED TUBE MASS = FASTER SCAN TIMES

• GROUNDED ANODE INNOVATION• Eliminates arcing risk

• Improved cooling


7

TARGETThe Modern COOLIDGE X-ray Tube

• THE THIRD & FOURTH MAJOR COMPONENTS:• THE METAL ENVELOPE

• THE VACUUM


8


4. The Rotor/Stator

a.Copper windingsb.Stainless steel bearings


9


5. The EXIT WINDOW or TUBE PORT

1. Made of low Z material to avoid filtration

1.Beryllium

6. ROTOR BEARINGS

1. overheating takes them out-of-round


10


• The other HU!

• HEAT UNITS are derived from the Joule• The thermal E that an x-ray tube must be able to

support & dissipate

• MODERN MDCT• X-ray tube coupled to a single phase high frequency

generator• Voltage ripple is less than 1%

• HU = mA x exposure time in seconds x kVp x 1.41


11


• Heat capacity• Up to 8 MHU

• How much is that?

• HU = mA x S x kVp x 1.41

• Heat dissipation capability• 2,000 kHu/minute

• Ever have to wait before going onto the next exam?

• MODERN MDCT- a positive note• MDCT Systems have the potential to cause decreased

heat load because more slices are acquired per tube rotation in the Z axis


12


•Relative to the future of MDCT and HU calculations• Increased scan power•More acquisitions per tube rotation in the Z axis

• Shorter rotation times• Shorter cool down times• Smaller focal spots


13


The Modern COOLIDGE X-ray TubeFundamentals of X-ray Production

• The “two stage” exposure• Stage 1- READY THE TUBE

• While the Rotor spins the Target, ultimately reaching 10,000 rpm,

• THERMIONIC EMISSION occurs: the selected filament glows incandescent boiling off electrons (called thermions) in a quantity consistent with the mA selected• Focus cup function: maintain the SPACE CHARGE


14

• The “two stage” exposure• Stage 2

• The circuit is completed and electrical pressure is applied to the electrical terminals• Electrical pressure = kVp

selected


15


• The “two stage” exposure: X-RAY PRODUCTION• Stage 2- CLOSE THE SWITCH

• THERMIONS gathered at the filament according to the mA selected

• Selection & Application of kVp- close the switch

• THERMIONS in motion = Projectile Electrons

• PROJECTILE ELECTRONS bombard the focal spot on the focal track of the anode

• Bremstrahlung & Characteristic are the two ionizing radiation production processes that occur


16


•What happens when mA is selected?• mA selection programs the quantity of electricity to

be applied to the filament consistent with the mA selected• Programming mA determines the quantity of

THERMIONIC EMISSION that is to occur during Stage 1, tube ready


17


• What happens when kVp is selected?• kVp selection programs the voltage from the

autotransformer that will be boosted to kilovolts by the High Tension Transformer

• During Stage 2, with the circuit closed, kVp is the electrical pressure that will cause the kinetic movement of the thermions to bombard the Focal Spot of the Target. Thermions in motion are called Projectile Electrons.


18



19

• The two major x-ray production processes• #1 BREMSTRAHLUNG

• AKA, “BREMS, “BRAKING”, “GENERAL”, “WHITE”

• The “CONTINUOUS” X-ray production process


20


• BREMSTRAHLUNG• Occurs when Projectile electrons at the focal spot of

the focal track are slowed or stopped by Tungsten target atoms &/or atomic force fields

• The Kinetic E “lost” by the Projectile electrons bombarding the target is transformed to electromagnetic E, that is, X-RAY, X-RAY PHOTONS, PHOTONS OR QUANTA


21


* The two major x-ray production processes

* #2 CHARACTERISTIC RADIATION PRODUCTION

* MACHINATIONS are similar to Photoelectric effect

* The “DISCRETE” X-ray production process


22


• CHARACTERISTIC RADIATION PRODUCTION

Occurrence:

* Tungsten target & 69.5 kev

* Projectile electrons interact with a TUNGSTEN target atom resulting in the ejection of a k-shell electron

* Characteristic cascade results in the production of SECONDARY RADIATION


23


• MODERN MDCT• At 100 kVp, approximately 70% of the

beam is Bremstrahlung while 30% is Characteristic

• However, the most common radiation produced in the X-ray production process is HEAT or Thermal E!


24


THE MODERN CT GENERATOR

• SINGLE PHASE, HIGH FREQUENCY• LESS THAN 1% VOLTAGE RIPPLE

• Heat Units = mA x S x kVp x 1.41


25

• If 100 kVp were selected, due to < 1%

voltage ripple, 99%+ of projectile

electrons would bombard the target

with energies from 99 to 100 kVp.

• Calculate the Heat Units generated given the following factors:• 400 mA• 8 Second exposure time• 120 kVp• Single phase, high frequency generator (1.41 multiplication

factor)

• 400 x 8 x 120 x 1.41 = 541,440 HU


26


•Why TUNGSTEN?1.Target material is primarily

Tungsten alloyed with a small amount of Rhenium

2.Filaments are made of Tungsten1. Z = 74 2. Melting point is 3422 degrees C

or 6191 degrees F3. Electrical conductor


27


• CT X-ray Tube Warm-up Procedure• Always according to manufacturers recommendations

• Warm-up period before optimal system operation, including:• System boot-up

• Operating system boot-up

• X-ray tube warm-up

• Detector calibration

• Stabilization of displays

• Special CT considerations• Daily air calibration

• X-ray tube warm-up procedure built into the System boot-up procedureEPISODE 4 THE TUFFEST STUFF CT REGISTRY REVIEW

SEMINAR SOLUTION28


•WARM-UP PROCEDURES• OBJECTIVE: To assure that the ANODE & other

components do not experience the shock or stress of a sudden, excessive heat load

• FREQUENCY: Daily. Also when the unit has remained idle for 2+ hours


29


•WARM-UP PROCEDURE• STEPS: Follow manufacturer’s recommendations

or, as follows:• Turn system on & perform warm-up with room

empty of personnel and door closed• Use large focal spot with a set technique of 100 mA,

70 kVp and 2 seconds


30


•WARM-UP PROCEDURE•CORRECTIVE ACTION: consult service engineer if an

unusual event or noise is noted• Corrective actions must be completed within 30 days,

documented and records kept of each corrective service or action for at least 2 years.


31


Things to study…

1. The conversion of electrical E to EM E is the specific function of which important CT Imaging Chain component?

2. Name the four principle parts of the x-ray tube.

a.

b.

c.

d.

3. Now write an important detail about each component above.


Things to study…

4. What material is commonly used for the tube port and why?

5. What is the function of the rotor/stator? How about the rotor bearings? Did you know that the rotor/stator operates on the basis of electromagnetic induction?

6. What is remarkable about CT tube filaments and focal spots?

7. The other HU! And while we are at it……what about Z?


Things to study…

8. Can you solve a heat unit problem?

mA x time x kVp x 1.41 = _____ HU

9. What is significant about the impact of the Beam Shaping Filter combined with the Single Phase High Frequency Generator?

10. What happens during stage 1 of the exposure sequence?

11. What happens during stage 2 of the exposure sequence?


Things to study…12. What is important about mA selection? kVp selection?

13. Between Bremstrahlung & Characteristic, which one is an ionization event?

14. List an important function of each of the following x-ray circuit components:

a. Autotransformerb. High Tension Transformerc. Filament Transformerd. System of rectificatione. Pre-reading kVp meter


THE TUFFEST STUFF CT REGISTRY REVIEW SEMINAR · components do not experience the shock or stress of...

Documents

Transcript of THE TUFFEST STUFF CT REGISTRY REVIEW SEMINAR · components do not experience the shock or stress of...