1. 354 Chapt. 6 X-ray Tube TWO Primary components – cathode and anode Tube must be supported: Ceiling/floor mounted/C-arm, etc. – SID’s – Detents (center and SID’s) – Over ride timer for AEC

2. Protective tube housing X-rays are produced “isotropically” (in all directions) – tube housing allows only those directed at the “window” to escape Leakage radiation = less than 100 mR/hr at 1 m in any direction other than the window

3. Filament (thoriated tungsten) 3410 F degree melting point Tungsten wire – usually 1-2 cm long and 2mm in diameter Dual filament (equals dual target size) Thermionic emission Electron cloud (space charge affect) NEGATIVELY charged focusing cup NEGATIVE charged side of x-ray tube

4. Anode Most are rotating discs to give MORE surface area for heat dissipation 3400-10,000 rpm rotation Angled to give LARGER actual BUT SMALLER effective F.S. Composite – Tungsten/rhenium Support arm assembly assists to rid anode of heat and is made of molybdnium/rhenium, tungsten and copper

5. Brems/Breaking Radiation

6. Characteristic Radiation

7. Other anode attributes Line-focus principle – actual/effective focal spot Heel effect Angles (smaller anode angle = LARGER heel effect More penetrating beam on CATHODE side due to heel effect

8. Line-focus principle/heel effect

9. “HEAT” enemy #1! Tube warm up is required if ONE hour or more has lapsed since the last exposure – CHECK PRIOR TO PLACING PATIENT IN THE ROOM/ON THE TABLE! PRIMARY reason for tube failure!

10. Tube rating charts Variable kVp/fixed mAs – not too practical as kVp is driven by atomic mass density or the patient or contrast agent Variable mAs/fixed OPTIMUM kVp = most practical as atomic mass number is the “driving force” of kVp and mAs = the amount of radiation produced to make the OD

11. Tube rating chart

12. Cooling Chart

13. Tube Cooling Processes