kVp and Contrast

[@vrl9037]

By setting a high kVp, we need to use a low mAs, reducing patient dose. By setting a low kVp, we need to use a higher mAs, increasing patient dose.

[@brookebeck3367]

Really helped me understand the gap between high kVp = low contrast; low kVp = high contrast. I didn't follow from kVp = speed of electrons to final image. Now I see that the speed affects penetrating power i.e. HOW MUCH XRAYS ARE STOPPED/ABSORBED BY PATIENT vs xrays able to get to plate/film/sensor and that is the way contrast is changed.

[@brookebeck3367]

more kVp = faster speed e- = more penetrating power of xray = more interactions to occur = more (smaller) changes in energy of photon at plate/film/sensor = more shades of gray = low/long-scale contrast ?

[@RockTheRegistry]

@@brookebeck3367 This is super close, but it's not speed. kVp increases the wave frequency. Speed is a constant for the electromagnetic spectrum.

[@عزالدينالشيخسليمان]

man I couldn't find better explanation, thanks a lot

[@RockTheRegistry]

Thank you!!

[@عزالدينالشيخسليمان]

​@@RockTheRegistry I would like to ask, suppose if I'm not intersted in the contract of the image, rather I want to make soft tissue as clear as possible in the image, is that achieved by rising the kVp ? and does that have anything to do with compton effect ?

[@RockTheRegistry]

Good question! The answer depends on what is meant by "making the soft tissue as clear as possible." Generally, soft tissue techniques require a decrease in kVp without change in mAs. Mammography is a good example. If you want to just see bones (ie see clear through the soft tissue), then the best thing to increase is the mAs (not kVp). You are correct that increasing kVp impacts contrast in part through increasing compton scatter.

[@عزالدينالشيخسليمان]

@@RockTheRegistry got it, thanks man really appreciate that ^_^

[@RockTheRegistry]

Hey, I think you might enjoy a book I've recommended to my students. It's called Time, Distance, and Shielding. It's a medical thriller with an x-ray tech as the hero. It’s a fun read, and it has a lot of stuff in it about patient care. Here's a link to the book on Amazon: www.amazon.com/dp/B088867YHK

[@renukasahoo3022]

A really good conceptualised explanation. Thank you

[@RockTheRegistry]

Glad it was helpful!

[@mzmolly4898]

Best explanation I've heard so far. Thank you!!!

[@chad969]

Hi Benjamin, I came across a confusing quiz answer on the ARRT prep site Corectec. I would really appreciate it if you could clarify this as I don't know who else to ask. The quiz question says: _The scapula image you just took at 10 mAs and 60 kVp was underpenetrated. How could you adjust your technique?_ I thought the right answer would be 5 mAs at 70 kVp, since that would result in more penetration of the part without doubling the exposure. But according to Corectec, the right answer is 10 mAs at 70 kVp. I don't understand why that's the right answer. When an anatomical part is underpenetrated, why is it not sufficient to increase the kVp by 15% and cut the mAs in half? Isn't there a risk of overexposure by keeping mAs constant while increasing kVp by 15%?

[@RockTheRegistry]

Great question. The Corectec answer is right. 5 mAs at 70 kVp would maintain exposure. You need to increased penetration. So increase kVp and keep mAs the same.

[@chad969]

@@RockTheRegistry I see. Thank you for the reply

[@RED-ZONE11]

Hello, how are you? I have a question, please, what are the materials that x-rays cannot penetrate

[@techguyofficialchannel]

Amazing Explanation, Keep it up 👍👍

[@gavin4981]

Getting it like it was

[@SharkRockstar]

Does increasing intensity of x-ray increase contrast?

[@RockTheRegistry]

Intensity (mAs) is unrelated to subject contrast. Only penetrability (kVp) influences subject contrast. As kVp increases, subject contrast decreases.

[@SharkRockstar]

@@RockTheRegistry God bless💗

[@lastbar7853]

@Shruti Shrivastav i believe it has to do with attenuation due to part thickness. So you would increase the mAs for a thicker part of the body, because the ray has to go through more tissue.

[@deepthiraosonitha]

How to calculate the radiation dose of x-ray images?

[@RockTheRegistry]

Dose to what? Dose is a fairly complex concept.

[@swagatikapanda7683]

My baby had x ray hip and pelvic.. I only know that kv is 40 and ma 400..image is very good.. How can I know mas is high Or low for baby?

[@RockTheRegistry]

Does it give you an exposure indicator or a deviation index? What about the mAs?

[@swagatikapanda7683]

@@RockTheRegistry I don't know about mas. Only know about kv..

[@RockTheRegistry]

@@swagatikapanda7683 If you're trying to determine the dose, this isn't enough information. But, it sounds like the technique was a good technique. The dose is most likely "as low as reasonably achievable."

[@swagatikapanda7683]

@@RockTheRegistry the mas was 10,40kv , 400ma and mas was 10.is it ok for baby?

[@RockTheRegistry]

@@swagatikapanda7683 Yes, that is a perfect pediatric hip/pelvis technique.

[@deepthiraosonitha]

Which technique can be used to reduce the radiation dose of the x-ray images?

[@RockTheRegistry]

Increase kVp and decrease mAs. That's the basics. There's at least fifty different ways to reduce patient dose in diagnostic x-ray.

[@deepthiraosonitha]

thank you for your reply. But I want to reduce the dose from an x-ray image dataset obtained after ct scan or performing an x-ray not while performing the x-ray or ct scan.

[@RockTheRegistry]

@@deepthiraosonitha The only dose is that given while performing the x-ray or CT exam. There is no dose associated with images afterward.

[@deepthiraosonitha]

@@RockTheRegistry ok Thank you for your reply. Can I get to you if I have any doubts in the future regarding this?

[@RockTheRegistry]

@@deepthiraosonitha Sure thing.

[@guychi-chifly950]

Simple question, is the NanoX arc legit enough to be reasonably equivalent to conventional x-rays?

[@RockTheRegistry]

Great question! NanoX offers an interesting cold cathode tube design that is more compact and - potentially - cheaper to manufacture and operate than rotating anode tubes. I have yet to find information on the actual x-ray production spectrum, but the radiographs demonstrated at RSNA 2020 def look like radiographs taken with conventional tubes.

[@guychi-chifly950]

@@RockTheRegistry thank you friend. Great day to you.

[@ZacharyYoung-h4r]

Jacobs Crest

[@no-de3lg]

What is contrast i don’t understand why image 3 better than 1 ans why there is some dark area inside the bone

[@RockTheRegistry]

Contrast is the ability to see a difference between two adjacent structures.

[@cancelation648]

These three images not good example to explain contrast relative to radiography dose . They look with nice degree of contrast. anther thing the soft tissue 5th finger 😂 so long than normal

[@love-sw7ow]

My baby had chest xray ( 2 PA views 62 kvp and 3 mas and 1 lateral view 65 kvp and 3 mas ) ..is it safe for the child, is it according to pediatric dose? How much is the radiation dose? How much is the future cancer risk ? Please reply...thanks

[@RockTheRegistry]

Hi, yes. This sounds like a good pediatric technique.

[@love-sw7ow]

@@RockTheRegistry please can you tell me the radiation dose my child recieved from kvp and mas...any guess about the dose????...

[@RockTheRegistry]

@@love-sw7ow Dose calculations do not work that way... the easiest way to consider it is in relation to natural background radiation. In general chest x-rays are equivalent to 2 weeks of natural background radiation.

[@niluothman8604]

Q1: why low KVp = high does ??? cuz i know low KVp =low energy and low intenstiy = low does. Q2: why image 3 is better than image 1 ? thanx alot!

[@user-xm6cl4jz5o]

low kvp mean the photons have less energy, less penetrating power, so it gets attenuated as it travels thru tissue. It's more likely to be absorbed by soft tissue, instead of passing through and reaching the image receptor. so that contributes to absorbed dose

[@visitingstatue69]

Low kVp = high mAs generally. Even though the X-ray photons have lower energy, the amount of X-ray photons increases (mAs).

[@cherryroseabalon3856]

Is it safe to have a 29 mAs to a 62 kVp in chest x-ray?

[@RockTheRegistry]

Safe? No amount of ionizing radiation is considered safe. If you're asking whether that's a good technique for a chest x-ray exam, the answer is NO! That's more like a KUB technique.

[@PhoebeHunt-e9v]

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