What is the unit of measurement in this X-Ray?

[Gary_T2018]

Hi I hope I'm not posting under the wrong forum but I'm pretty sure this is physics related.

If you go to have an X-ray, in the film there will be information detailing the dosage you just received. However I encountered a rather unusual one like this:

70kV 100mAs 100mS -- dGycm² El_s:300

As far as dGycm² goes, the figure following it should well below 1, most likely 0.2 or something, yet it has 300.

What IS that? The X-Ray wasn't done in the US.

My apologies again if it has been posted under the wrong subforum.

 

[davenn]

70kV 100mAs 100mS -- dGycm2 El_s:300

I'm assuming that 100 mS should really be 100 mSv ?? as in 100 milliSieverts ?

or maybe it really is 100mS = milli Seconds ?? as in dosage (exposure) time

I don't know what 100 mAs is ?


100 mSv = 1 dGy

@ZapperZ help please


Dave

 

[Asymptotic]

mA is current in milliamps applied for 100 milliseconds? At 70 kV, this is 700 joule (watt-seconds).

dGycm2 El_s:300

decigray⋅cm²?

Found this ... Understanding Radiology Exposure Indicators

 

[Gary_T2018]

mA is current in milliamps applied for 100 milliseconds? At 70 kV, this is 700 joule (watt-seconds).

decigray⋅cm²?

Found this ... Understanding Radiology Exposure Indicators

What is El_s then? If 300 is Gycm2 then it's nothing much better than a gass chamber.

 

[Gary_T2018]

I'm assuming that 100 mS should really be 100 mSv ?? as in 100 milliSieverts ?

Most likely miliseconds. 100mSv is enough to cause someone symptoms.

or maybe it really is 100mS = milli Seconds ?? as in dosage (exposure) time

Then how do you really calculate the effective dosage?

 

[davenn]

decigray⋅cm2?

that's the easy part haha deciGrey per cm²
1 dGy = 1 deciGrey is 1/10 of a Grey = 100 mSv = 10 Rad (10,000 milliRad)

Yeah, I have no idea what "EL_s" is either haven't found a link

hence why I called on ZapperZ for help in the thread


Dave

 

[davenn]

Most likely miliseconds. 100mSv is enough to cause someone symptoms.
Then how do you really calculate the effective dosage?

From
https://www.translatorscafe.com/uni...n-absorbed-dose/18-25/milligray-millisievert/

Effective Dose
The units above are used for radiation that is uniformly absorbed by the tissue, usually in a localized area. They help determine how much radiation affects a particular organ. To calculate the effect on the entire body when only some part of the body is absorbing radiation, an effective radiation dose is used. This unit is needed because the increase in the risk of cancer is different for different organs, even if the amount of radiation absorbed is the same.

Effective dose calculations account for that by multiplying the absorbed radiation by the coefficient of the seriousness of the impact of radiation on each type of tissue or organ. When determining values of coefficient for different organs, researchers weighed not only the overall cancer risk but also the duration and quality of life of the patient, once cancer is contracted.

Effective dose is also measured in sieverts. It is important to understand when reading about radiation measured in sieverts, whether the source refers to the effective dose, or the radiation dose equivalent. It is likely that when sieverts are mentioned in mass media in the general context of talking about radioactivity-related accidents and disasters, the source is referring to the radiation dose equivalent. Often there is not enough information about which body tissues are affected or may be affected by the radioactive contamination, therefore it is not possible to talk about the effective dose.

 

[Gary_T2018]

Also the 700 Joule makes it sound even scarier. I mean if we are talking about 700J per kilogram it's effectively death ray.
700J per gram sounds like a neutron bomb.

 

[sophiecentaur]

In general, I have found that Medics are a lot less fussy about their units than you might expect. They often rely on 'local rules' to specify doses in general - in the same way that they launch into acronyms and groups of capital letters for diseases and symptoms . I think the 'excuse' for this is the historical attitude that kept information away from their patients.
It surprises me that there are relatively few disasters resulting from this habit of shorthand terminology.

 

[Gary_T2018]

In general, I have found that Medics are a lot less fussy about their units than you might expect. They often rely on 'local rules' to specify doses in general - in the same way that they launch into acronyms and groups of capital letters for diseases and symptoms . I think the 'excuse' for this is the historical attitude that kept information away from their patients.
It surprises me that there are relatively few disasters resulting from this habit of shorthand terminology.

Ok then. Now, another question: how long after a large dose of exposure to gamma radiation should you able to observe abnormalities in white cell quantities?

 

[Asymptotic]

What is El_s then? If 300 is Gycm2 then it's nothing much better than a gass chamber.

From the Understanding Radiology Exposure Indicators article,

On digital imaging systems, an exposure indicator provides useful feedback to the radiographer about exposures delivered to the image receptor (ASRT, 2010). An over- or under-exposed image will deliver an incorrect exposure indicator; whereas a correct exposure will provide a corresponding exposure indicator. The indicator is a vendor-specific value that provides the radiographer with an indication of the accuracy of their exposure settings for a specific image (ASRT, 2010). The exposure indicator has as many different names as there are vendors in the market. The names include S-number, REG, IgM, ExI and Exposure Index.

Carestream’s computed radiography (CR) and digital radiography (DR) systems both reference their exposure indicator as the exposure index or EI. After an exposure is made, the resulting image appears on the monitor and displays a number in the Exposure Index field. The number is a representation of the average pixel value for the image in a predefined Region of Interest (ROI).

EI_s:300 would fit with it being such an exposure indicator.

70kV 100mAs 100mS -- dGycm2 El_s:300

I'm wondering whether the '--' symbols preceding 'dGycm2' indicate this field wasn't enumerated.

 

[sophiecentaur]

Ok then. Now, another question: how long after a large dose of exposure to gamma radiation should you able to observe abnormalities in white cell quantities?

Surely you can find that from Google. Radiation effects on the human body are such a favourite topic.
The total dose is not the only factor. Several years ago I was given Radiotherapy and the 50Gy total dose was given in less than 3Gy lots spread over many weeks on the grounds that the body can deal better with it than the cancer cells can, over a long period of time. I don't know how that relates to white cell population but I was not aware of any blood test for white cell levels.

 

[Gary_T2018]

From the Understanding Radiology Exposure Indicators article,



EI_s:300 would fit with it being such an exposure indicator.

Well thanks! That's some major progress made! At least I know 300 isn't 300 dGy.

Now, if only it can be figured out how much mSv of radiation were absorbed in taking that shot of digital X-ray...

 

[Gary_T2018]

Surely you can find that from Google. Radiation effects on the human body are such a favourite topic.
The total dose is not the only factor. Several years ago I was given Radiotherapy and the 50Gy total dose was given in less than 3Gy lots spread over many weeks on the grounds that the body can deal better with it than the cancer cells can, over a long period of time. I don't know how that relates to white cell population but I was not aware of any blood test for white cell levels.

Wow. How did it go? Was the tumor eliminated?

 

[sophiecentaur]

Wow. How did it go? Was the tumor eliminated?

Seems to be OK so far - thanks for asking. The surgery was about six years ago and no signs since all the treatment all ended. The Radiotherapy procedure and equipment was very interesting for me (the opportunistic Physicist). They use splines to form an aperture for the beam to fit the appropriate area and use three different radial directions for the beam to reduce damage to surrounding tissue. The beam uses a linear accelerator as an energy source for an electron beam which hits a target and produces the X rays (also interesting). It's very high precision stuff (they work to about a mm) and I lay totally motionless during the exposure to help the beam avoid nearby important bits. Nearly seven weeks of commuting up to London for it was far more knackering than the treatment itself, I think. So far so good!

 

[sophiecentaur]

As far as dGycm2 goes,

Looking at the units of that:
A Gray is one J of Energy per kg. I'm not sure what the meaning of one Gy times 1cm₂ could be indicating.
Perhaps, if the density is in gm/cm³ then XGycm² = X J cm/ρ
If ρ is 1 (reasonable) then the thickness of the tissue that a 1cm² beam passes through will dissipate X Joules of energy per cm as it passes through. I guess that's reasonable because the thicker the tissue being imaged, the less dose does the body get from a given beam power and area. Obvs, a good Xray image will use just enough radiation to register the most dense tissue of interest.
It seems a funny approach to units though. What do you think?

 

[PSRB191921]

Hi,
Gy.cm2 is a dose per fluence unit (D/phi)

For example for k Gy.cm2 and for a parallel beam with a radius r the fluence rate is N/(pi.r.r) and the dose rate in Gray per second is k.N/(pi.r.r) (N the particles flux in s-1)

 

[sophiecentaur]

Hi,
Gy.cm2 is a dose per fluence unit (D/phi)

For example for k Gy.cm2 and for a parallel beam with a radius r the fluence rate is N/(pi.r.r) and the dose rate in Gray per second is k.N/(pi.r.r) (N the particles flux in s-1)

That has confused me a bit, I'm afraid.
The basic Definition of 1Gy is in terms of Energy per kg and that is how it seems to be defined everywhere I look. Using a derivative of the Gy is not an intuitive thing to do and it must be for a pretty subtle reason. The thing of interest if you want to assess potential damage must surely (once you have eliminated frequency variation etc.) still be the Gy. I can see how a source can be calibrated in terms of Power Flux or Flux density, which gives the Energy involved when the time is specified. That is independent of the mass of the receiving piece of body.
Gy includes the mass of tissue.
I have been looking athttp://www.npl.co.uk/upload/pdf/20101117_irmf_bailey.pdf which has helped a bit and it sort of suggests to me that the way doses are specified could usefully be looked at again. But I guess that it would all make perfectly reasonable sense to someone in the business.

 

[gleem]

Since the dose which is specified by the energy deposited in tissue per unit mass does not really provide a risk estimate from a radiation exposure due to the fact that the amount to tissue receiving the dose must be taken into account it has become fashionable in the last decade or so to specify the dose area product (DAP) for a given film. This number is automatically calculated by the machine based on the collimator setting, the tube current, the time of exposure, and the KVP used. The larger the dose and or area exposed the greater the risk. The maximum area for a film is about 1000 cm² . For 70 kVp (3 phase unit) the dose rate is about 0.06 mGy/mAs.. For 100mAs you get 6mGy or 0.06dGy. I am not familiar with the term EL_s (European?) in conjunction with DAP and for this exposure the 300 cannot be the DAP. If the DAP were cGycm² then it would be reasonable.

 

[Gary_T2018]

Seems to be OK so far - thanks for asking.

Hey no problem.

So 6 years and you haven't developed anything malignant due to radio-therapy? That's really interesting, I am under the impression that one spine x-ray which blasts you with 2 mSv worth of X-ray dooms you for life. I'm really worried.

Anyway, glad to know you are OK!

 

[Gary_T2018]

Looking at the units of that:
A Gray is one J of Energy per kg. I'm not sure what the meaning of one Gy times 1cm₂ could be indicating.
Perhaps, if the density is in gm/cm³ then XGycm² = X J cm/ρ
If ρ is 1 (reasonable) then the thickness of the tissue that a 1cm² beam passes through will dissipate X Joules of energy per cm as it passes through. I guess that's reasonable because the thicker the tissue being imaged, the less dose does the body get from a given beam power and area. Obvs, a good Xray image will use just enough radiation to register the most dense tissue of interest.
It seems a funny approach to units though. What do you think?

I haven't the foggiest idea, that's why I'm here asking those who might have the technical side of the knowledge.

 

[Gary_T2018]

For 70 kVp (3 phase unit) the dose rate is about 0.06 mGy/mAs.. For 100mAs you get 6mGy or 0.06dGy. I am not familiar with the term EL_s

0.06dGy equals 6 mSv. For a lumbar spine X-ray it is way too high. Heck for a CT that is way too high.

 

[Gary_T2018]

If the DAP were cGycm2 then it would be reasonable.

In terms us laymen could understand, the radiation does for this 1 shot/view, in mSv, would be??

 

[Gary_T2018]

For 70 kVp (3 phase unit) the dose rate is about 0.06 mGy/mAs.. For 100mAs you get 6mGy or 0.06dGy.

Hi, thanks a lot for the information. Can you explain with a bit more detail how it is calculated? Technical documents are also appreciated :)

 

[Gary_T2018]

Hello folks, thanks for the help so far but I am able to determine that "El_s" should actually be "EI_s", no idea what the "s" at the end stands for still but am pretty sure that "l" should infact, be "i", so it's most likely exposure index, as Asymptotic had suggested

 

[sophiecentaur]

So 6 years and you haven't developed anything malignant due to radio-therapy?

The lesser of the two evils is, so I believe, very much the lesser. For old gimmers, the extended life expectancy due to the treatment is way more than the risk of the treatment producing other kinds of tumor and shortening life. Using 'conformal' radiation makes a big difference to local collateral damage because the beam is quite extreme and other organs could fry (as indeed they used to in the old days). The effect of RT is fairly extreme - so bad that follow up surgery is pretty well impossible due to scar tissue and distortions.
So compared with RT, investigative imaging needs to use much much lower doses to keep it as non-invasive as possible. My introduction of RT into the conversation was more to justify my interest in dosage specification.
I talked with the Oncologist at the time and he confirmed that, for a given dose (in Gy), the total Energy is proportional to the beam size. (amount of tissue that's actually irradiated) so, to calculate the risk of further ill effects, the total energy would need to be taken into consideration. In my case, the RT was post op so it was only the margins of the original tumour that needed radiation - meaning probably quite a bit less total energy was involved. That term "fluence' is important.

 

[gleem]

I cannot answer all your question right now but for now,

I am under the impression that one spine x-ray which blasts you with 2 mSv worth of X-ray dooms you for life. I'm really worried.

Keep in mind that most people get yearly unavoidable radiation doses from natural background fro 2 to 3 mSv depending on location. Background radiation is not considered significant source of exposure and the risk associated with this is for an individual is negligible compared to all other risks we are subject to. I'll get back to you with more info.

 

[gleem]

That's really interesting, I am under the impression that one spine x-ray which blasts you with 2 mSv worth of X-ray dooms you for life. I'm really worried.

The 3mSv you stated for a dose for a lumbar spine might not be the dose you think it is. Typically you would want to state an average or effective dose to the irradiated field. The 3mSv is quite high for an effective dose. One these day should expect less than 1mSv as an effective dose. The exposure is determined by how much radiation is needed by the imaging device i.e., film or these days electronic digital imaging receptors. The skin dose at the entrance of the beam will be quite high and the dose will decrease about exponentially through the body. The dose will depend significantly on thickness of the body part and the kVp used depending about kVP².. Of course it depends linearly on the mA and time. of the exposure. Also there is a dependence on the machine age and power source.

A word of warning about estimated doses for exams, they are estimates sometimes on survey made over decades with large contributions from old technology. Even today you may have significant variations of doses from institution to institution. In the US most hospitals have a medical physicist as consultants or on staff that can attest to the dose from various units.

The bottom line for most people is if an Xray exam is indicated for the determination of a specific diagnosis then the risk/ benefit is a no-brainer don't worry. Xray exam should not be taken on an asymptomatic person, no benefit usually. One of the links of cancer to radiation exposure was back in the 1930's or so patients where treated for various non cancerous conditions using fluoroscopy which resulted in exposure in the neighborhood of 1 Gy, and a number of cancers where produced.

If the DAP were cGycm2 then it would be reasonable.

Something is missing here sorry. I meant to say if the DAP were 60dSvcm2 that would be reasonable. BUT I made an error in choosing the 0.06mGy/mAs for the output by selecting the wrong data. For a real xray machines it is more like 0.20mGy/mAs at 70 kVp AND that is the dose to air at a specified distance (say 60cm) not the dose to the patient . That make the 300 dSvcm² very reasonable. How do you relate DAP to the effective dose to the patient? Well the DAP measures the energy in the form of radiation that is being outputted by the machine. Since almost all of it is absorbed by the patient then the DAP will be a reasonable surrogate for the effective dose to the patient.

In terms us laymen could understand, the radiation does for this 1 shot/view, in mSv, would be??

There are two standard views a lateral ( xray tube from the side) and anterior-posterior xray tube above a supine patient. The doses are a bit different but around 1 mSv. again with significant variation for hospital to hospital. depending on the machine and image receptor used.

 

[Gary_T2018]

I cannot answer all your question right now but for now,


Keep in mind that most people get yearly unavoidable radiation doses from natural background fro 2 to 3 mSv depending on location. Background radiation is not considered significant source of exposure and the risk associated with this is for an individual is negligible compared to all other risks we are subject to. I'll get back to you with more info.

Thank you once again for the reply.

I understand that, but xray blast you with that dose in under perhaps 1 second, while "naturally occurring" radiation does that over a course of 356 days. I don't believe they are comparable?

 

[Gary_T2018]

There are two standard views a lateral ( xray tube from the side) and anterior-posterior xray tube above a supine patient. The doses are a bit different but around 1 mSv. again with significant variation for hospital to hospital. depending on the machine and image receptor used.

So 4 view, 1 front, 1 side, 2 45 degrees view puts the approx. dose at around 2mSv?

Combined with 1 front 1 side lumbar earlier roughly 20 days ago, the total dose is expected to be 3 mSv I suppose?

How dangerous is that? Am I expected to develop some form of cancer in the next 10 or 20 years?

That's really awful, rotten news! I'm still kind of young...

 

[gleem]

I understand that, but xray blast you with that dose in under perhaps 1 second, while "naturally occurring" radiation does that over a course of 356 days. I don't believe they are comparable?

That is correct but the data linking radiation exposure to cancer is from high dose exposures over short intervals. It is believed doses over short periods overwhelm the repair mechanism. Smaller doses over the same interval may not do so since the damage is much smaller i.e.damage is proportional to dose.

The repair mechanism for large doses may be complete in as little as six hours.

How dangerous is that? Am I expected to develop some form of cancer in the next 10 or 20 years?

Still negligible compared to all other risks that we face in our daily lives. Estimates for cancer incidence is based on large exposure with significant uncertainty The working assumption has been for many decades that the risk of cancer is linearly related to dose even down to the smallest doses meaning that all exposure carries some risk. However there is not real data that supports this assumption and that it is believed based on animal studies that there is a threshold for cancer induction below which radiation exposure does not produce cancers. Current estimates say that this dose might be as large as 100 mSv/yr. The problem is more psychological/political in backtracking the dose limits until there is irrefutable human data. Human data that does exist on radiation workers generally has shown that over a lifetime there is no statistically significant difference in life expectancy compare to comparable work with no radiation exposure. So lacking good data the general philosophy regarding radiation exposure will probably remain "keep radiation exposure to a minimum".and only when there is a benefit.

 

[sophiecentaur]

How dangerous is that? Am I expected to develop some form of cancer in the next 10 or 20 years?

Way back, when X rays were first used, you would have been justified in worrying. When I was a kid, they had X Ray machines in shoe shops which showed on a green screen your foot bones and the outline of your shoes. And that was mainly to 'keep children's feet healthy!' I was told that hospital radiography departments used to use massive doses for imaging fractures. As films got more sensitive, many were reluctant to back off the dose. It would have been the operators who suffered more in the long run, despite sometimes standing behind a lead screen during the exposure. Things have improved in the light of lots of reputable statistics.
This link shows that the existence of a low level of natural radiation may actually stimulate repair mechanisms, with the minimum risk being when there is actually some degree of exposure.

 

[Gary_T2018]

The repair mechanism for large doses may be complete in as little as six hours.

Thank you for your reply! I do not know of your academic background but forgive me for my zero understanding in medical science if I bore/upset you! I really have no deliberate intention to do that I'm having a major existential? mid-life crisis at this moment so any help would be great!

Do you have any literature that I can read on "6 hours"? That certainly makes me feel better.

Also according to my non-existent knowledge in medicine, aren't some "repairs" done "erroneously" in that they leave the double-helix "mis-assembled"? In which case they will keep replicating over and over and turn into cancer cells? I'm really worried...

Still negligible compared to all other risks that we face in our daily lives. Estimates for cancer incidence is based on large exposure with significant uncertainty

OK I have 2 questions on that:

1, can you help put that into perspective? What risks are greater than my taking xrays too often? For example?

2, What is the estimated risk of cancer for 3mSv of xray exposure? Assuming that's the dose?

And last but not least:

I understand that the 50mSv threshold put by the US CDC( or IAEA? I'm sorry I forgot) was based on studies on Hiroshima and Nagasaki survivors, so surely high energy gamma rays are more destructive than less energetic xrays right?

My sincere apologies once again if I bore you. I need as much data as I can get even though I don't know very well what to deal with probabilities.

 

[Gary_T2018]

Way back, when X rays were first used, you would have been justified in worrying. When I was a kid, they had X Ray machines in shoe shops which showed on a green screen your foot bones and the outline of your shoes. And that was mainly to 'keep children's feet healthy!' I was told that hospital radiography departments used to use massive doses for imaging fractures. As films got more sensitive, many were reluctant to back off the dose. It would have been the operators who suffered more in the long run, despite sometimes standing behind a lead screen during the exposure. Things have improved in the light of lots of reputable statistics.
This link shows that the existence of a low level of natural radiation may actually stimulate repair mechanisms, with the minimum risk being when there is actually some degree of exposure.

Thanks! I got a feeling that you are at least 70 years of age?

What happened to all those xray technicians?

Also this may sound silly but do you know of someone who had taken CT scan(which surely includes dosage much larger) in their 20s or 30s yet alive and well for many decades without developing anything malignant?

 

[berkeman]

Thank you for your reply! I do not know of your academic background

Many of us post our background in our Profile page. Just click on a user's Avatar and select Profile Page. You will see why @gleem is able to be so helpful in threads like this.