Focal Spot Size: Explained! (Fine vs Broad Focus)

[@curiousminds513]

Keep making videos man, I learn something every time i watch them, thanks for explaining the focal spot size. 👍🏻

[@derakhshanahmad5767]

Sorry I have question 🙋‍♀️, and it’s not about this subject,it’s about cassette , we are use the blue cassette with blue screen. And use green cassette with green screen , I want to know what the difference between them ? Till now I am working I don’t find any difference between green and blue cassette.or maybe i wasn’t sense it

[@SahandHooshmand]

I’m not entirely sure what you mean by blue or green screen cassettes 🤔 I’m assuming this is not related to digital image receptors?

[@derakhshanahmad5767]

@@SahandHooshmand kzbin.info/www/bejne/Z5nWY6imf5afe7Msi=XOQ_4msyW0i7mFa- I talk about this..?

[@JunkieMonkey321]

This used to confuse me to no end. One thing I'm wondering is: is it true that the broad focus is also used in situations where a short exposure time is beneficial, like for a PA thorax because of the heart and the so they don't have to hold their breath for quite as long? Does that factor into the decision-making, or is it just the fact that you can get a larger ROI as well as not needing the extra spatial resolution around the smaller anatomy? Thanks in advance

[@SahandHooshmand]

Hello! So I believe for something like a CXR, because the total mAs is so low (whatever the mA and s combination is), e.g. anything from about 3-9 mAs, it should be fine to use the fine focus setting, but I will check this myself on the machine and will get back to you. The fine or broad focus setting doesn't affect the ROI by the way, you can still collimate for the same amount on either setting, it just changes the effective focal spot size which therefore can affect the penumbra (resolution of the image). Hope that helps! If something isn't clear, do let me know

[@JunkieMonkey321]

@@SahandHooshmand That makes more sense regarding the ROI/penumbra. That's probably what always tripped me up. No need to check the mAs stuff as I haven't gotten far enough in my education for the answer to really mean much. I'm only finishing up my 2nd semester here in a couple of weeks, so anything to do with parameters is still a bit abstract and hasn't really found a place in my brain yet, only on the page :D But thanks for the offer, and thanks for clearing up the focal spot confusion for me!

[@EndIess]

A larger focal spot can dissipate heat more efficiently, as electrons interact with a larger area of the anode. Therefore, for a high X-ray tube current, low exposure time shot, the larger focal spot would be more suitable. However this would depend on the system being used. Nowadays the system will automatically switch to the large focal spot where necessary as it can calculate whether or not the heat generated from that shot exceeds the cooling capability on the small focus. Something to look out for when a small focus is absolutely necessary as it doesnt generally notify you of the focal spot size change.