Total Patient Exams
Total Patient Exams is simply the sum of individual cases performed with the X-ray tube.
It does not include info on the length of the exams or how much energy they required.
Hence, it is the most uncertain way to determine the tube use and CT tube life expectancy.
Therefore, it is rarely used, and is mostly given when no other info is available.
This method of measuring CT tube count tells you how many exposures the tube has performed.
However, it does not include how much energy has been used during these exposures.
From clicks, you can calculate the amount of time the tube has been used, based on gantry rotation speed.
This term is most commonly used by Toshiba, now Canon Medical.
This is a meaure of the duration of the tube exposures, so how much time has the tube been used for. Hereby, it is a more accurate measure than the ones described above.
However, this does not indicate how much effect/heat ran through the tube either.
This is the measure of tube counts that we see most often and it is popular among most manufacturers, like Philips, GE, Siemens, and Toshiba.
Milliampere Seconds (mAs) provides you with information on both, the duration of the exposures and on how much power has run through the tube.
Hereby, it is the most accurate measure of X-ray tube count and is mainly found on GE CT scanners.
Predicting lifetimes of X-ray tubes is very difficult. But on average a 7 MHU tube will last more than 150 million mAs, and a 4 MHU tube will last approximately 70-100 million mAs.