Tech Help

HOW TO MAXIMIZE X-RAY TUBE LIFE

* MINIMIZE FILAMENT BOOST -("PREP") TIME - This is especially important at high mA stations. Preparation time will usually exceed actual exposure time. High filament currents shorten filament life and can lead to unstable operation as evaporated tungsten is deposited on the glass envelope.

* USE LOWER TUBE CURRENT (mA) - The high filament currents required to produce high mA values shorten filament life and can lead to unstable operation as evaporated tungsten is deposited on the glass envelope.

* FOLLOW RATING CHARTS AND ANODE HEATING/COOLING CURVES - Operation beyond published rating can lead to premature focal track wear or damage. Excessive heat transfer through the rotor stem can lead to bearing failure or to a slow running condition that will cause melts on the focal track. 

* LIMIT OPERATION TO 80% OF MAXIMUM SINGLE EXPOSURE RATINGS - Although higher power levels are both possible and permitted, this reduction will assure long focal track life. Also, the reduction in radiation output associated with a roughened focal track will be minimized.

* DO NOT EXCEED ANODE THERMAL CAPACITY OR DISSIPATION RATE - The greatest danger is heat flow into the bearing structure, as discussed before. Overheating can even cause some target types to "flatten out" during high speed rotation causing the target angle to decrease. In addition, there is some risk that gasses will be emitted from the various metals within the tube if the temperature reached is appreciably higher than that used during the "outgassing" stage of manufacture and high voltage instability can result.

 

 *DO NOT MAKE HIGH MA EXPOSURES ON A COLD TARGET - Uneven expansion caused by thermal stress can result in a cracked target. Do not assume that a "thermally relieved" target design provides absolute protection. Always follow the recommended warm-up procedure. The procedure may need to be repeated between patients if the "idle" time is long enough in addition to that performed at the beginning of the work day. 

* AVOID LONG SPOT-FILM HOLDOVERS - Most systems are designed to allow a high speed "holdover" period of up to 25 seconds between spot-films before the rotor brake/reboost cycle can occur. Sometimes the filament temperature remains at the exposure value during this period, resulting in excessive filament evaporation. 

* LIMIT ROTOR START/STOP OPERATIONS- Rotor start/stop operations especially to/from high speed (180 Hz) generate considerable heat in the stator windings, which can lead to stator damage in extreme cases. Generally there should be a minimum of 30 to 40 seconds between starts. Tubes equipped with a heat exchanger will be less sensitive to this potential problem because oil circulation will help prevent hot spots within the housing. 

Note: Good work practices can significantly prolong tube life. These recommendations should be followed whenever possible.