fail safe: mr. sano
first, for fluoro c-arms, there is sorta a dead man switch like in mobile x-ray but not really... but, obviously, if you take your finger foot of the switch pedal you no longer emit.
also, there is an audible tone and visual light when emitting, and each of these are different between normal dose and high dose (boost) settings.
there also exists a manual over-ride "shut off" switch to turn the entire apparatus off.
there are exposure rates which appear on the monitor in mobile c-arm fluoroscopy...
there is an alarm which you must turn off in order to quiet it, at every 5 minute mark. this, doesn't mean you can no long image the patient... its just serves to let people know 5 minutes elapsed.
some, if not all of these things are required by regulations.
again, the annual/biannual physics acceptance tests help optimal operation of the device so that patients are not being over-radiated...
as well as, annual preventative maintenance by field engineers...
c-arms default to "automatic brightness control" meaning the maching knows how much exposure is necessary and adjusts your "power" accordingly... this id done by knowing how much is being emitted and how much is being received (or thusly, how much is being attenuated)... of course the operate can over-ride this in order to reduce dose if necessary... or adjust as necessary...
you can also collimate the beam... via lead shutters in order to form the beam and radiated as little area as possible, for instance, a super c-arm has an field of view of 23 cm in normal magnification mode (i.e., no magnification)... the geometries are set that the opening from the housing unit/x-ray tube are such that it (the opening) is only big enough to meet that max radius (23 cm)... however, you can use octagonal lead shutters which are radio-opaque and thus heavily lead lined in order to reduce the area, buy remember if you halve the perimeter you decrease area irradiated by a power of four... this use of the shutters is called collimation and the proper term is collimate... afterall, you only want to see your region of interest... there also exist semi-transparent lung leaves shutters... which you can also use at the same time. with some large body types (habitus) you may need to leave the shutters open though just so you get as much photons to the image receptor as possible, since the larger one is the hard it is to get photons through them without being attenuated.
you gotta remember, when talking fluoro, we are all in there in the moment... it is a "surgical/interventional tool." it is a scope.
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the testing, both physics-wise and field engineer-wise are also performed on CT scanners.
regarding CT scanners, they are calibrated way more frequently with 'phantoms' i.e., dummies...
there some or some CT going forward which will adjust exposure factors, i.e., your penetrating "power," imaging technique to meet the subject/patient requirement durig what is called a scout scan... this is mentioned in the article i posted on CT scanners from M MAHESH... this will serve as sort of an "automatic brightness control" feature in the realm of CT scanners...
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everything is multi-faceted...
