Images comparing analog and digital exposures

Understanding Radiology Exposure Indicators

Reading Time: 5 minutes read

Knowing how number is used is key to controlling exposure.

Imaging in a radiology film environment is much like playing Goldilocks and the Three Bears. You take your image, hold it up to the viewbox and say: “This image is too light”; “This image is too dark”; or, “This image is just right!” If you underexpose your image, it will be too light, and if you overexpose the image, it will be too dark (See figure 1). The density and contrast of the image on film is controlled by the kV, mAs and other exposure factors.

However, with digital imaging devices, brightness and contrast are no longer linked to exposure factors. Digital systems produce images with consistent density and contrast regardless of the exposure factors (See figure 2). So how does a radiographer know if a digital image is over- or under-exposed?

The potential for gross overexposure is one issue we encounter when a radiology department or clinic changes to a digital image receptor. The reason for this increased risk is that we’ve lost the visual connection between the exposure and an image’s appearance. That’s why it’s so important for the radiographer to understand how to read and utilize the exposure indicators.

Read the related blog on Diagnostic Reference Levels.

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).

The exposure index allows the radiographer to match the exposure to the desired speed class of operation. The speed class is set in a given department by consulting with an interpreting radiologist. The radiologist’s feedback on sample images helps determine the level of image noise he or she can accept. It’s important to note that, as speed class increases, so does the amount of image noise. Once an acceptable noise level is established, a radiographer can identify the speed class of operation for the imaging system and the corresponding technique charts. It’s the responsibility of the radiographer to select a technique that provides enough exposure to reduce the amount of noise while also adhering to ALARA standards.

Images comparing analog and digital exposures

The exposure index is indirectly proportional to the speed class of operation. If you’re using the Carestream Exposure Index values, for every 300-exposure-index increase, the speed class is reduced by half. In other words, if the exposure index increases from 1400 to 1700, the speed class is reduced from a 400-speed class to a 200-speed class. The Carestream EI is not necessarily unique to the receptor type. However, CR systems typically operate at a lower speed class than DR systems.

IEC Exposure Index is international standard

Remember that each radiology imaging manufacturer has its own method of providing exposure indicators. This can be confusing to radiographers who have multiple vendors within their facility. Fortunately, there is a standard for exposure index for digital X-ray imaging systems. Developed concurrently by the International Electrotechnical Commission (IEC) and the American Association of Physicists in Medicine (AAPM), in cooperation with digital radiography system manufacturers, the index has been implemented as an international standard. It’s known as the IEC exposure index. Carestream systems are configurable for the user to display the Carestream EI, the IEC EI, or both.

visit carestream.com for more information
Learn how we can help you with your challenges in medical imaging.

The IEC exposure index is unique to the receptor type being used and to the exam performed. Three default Target Exposure Index (TEI) values are preloaded into the system. The three values represent the default Target EI for bucky, non-bucky and pediatric exams.

Once the operating speed class is determined, the key operator can adjust the Target EIs to correspond to the recommendations made by the facility’s physicist. After an exposure, the IEC EI will display, followed by the deviation index (DI) in parentheses. The deviation index quantifies the difference between the actual EI and the Target EI, and this feedback allows the radiographer to track and adjust his or her exposures. When the actual EI is equal to the Target EI, the DI will equal 0. A positive or negative DI indicates the amount of exposure greater or lesser than the target EI. It does not necessarily mean that an image needs to be

repeated. If the deviation is greater than +3, the exposure index displays in red to indicate a high/low exposure that might need further review.

The DI chart below outlines how to use the deviation index. In the example above, the DI was calculated as 1.06. In the chart you’ll see that a DI of 1 means the resulting exposure was ~26% higher than the Target EI. The initial DI was 1.06, so we can estimate that we are slightly higher, perhaps closer to 30%. Although it might be a good image, it is merely an indicator to the radiographer that he/she might be able to reduce the exposure factors the next time a particular exam is performed- reducing the dose to the patient while still acquiring an acceptable image.

Index
Martin Pesce

Martin Pesce, RT, is Clinical Development Manager at Carestream

COMMENTS

  • reply

    Mary Seib

    good read

  • reply

    DIONYSIOS TRYFONAS

    Dear sir ,
    I am a veterinary surgeon (Southest poin of continental Greece , KALAMATA) , not specialist in radiography. I use a kodak POC 140. How i can find the carestream exposure index (for small animals) and how i can use it , to develop the x-rays <>.

    • reply

      Hello, here is our local representative in Greece who should be able to help you.
      Phone: 30 211 200 6200
      Carestream Healthgr@Carestream Health.com
      Fax: 30 210 6668 375

      Carestream Health Hellas
      Anthousas Av.
      Anthousa 15349
      Attica-Greece

      • reply

        Monica Quintero

        Can you please email me at monica.qd@live.com
        I’m currently writing a power point on how to lower dose, keeping ALARA, in the digital era.
        Can you help me?
        thanks,
        monica
        also, if anyone had further questions, Can I give your information to contact you???

  • reply

    noor

    hello
    I would like to know the value of EI in your X-ray digital radiography for each section on the body

    • reply

      Hello, I emailed you a document that should answer your questions. Thank you for reading Everything Rad!

      • reply

        Agboje Azuka

        Hello,
        I would like to know the value of EI in your X-ray digital radiography for each section on the body.

      • reply

        Sarra. Xray

        Hi,
        Could you please send me the same information

      • reply

        Cast

        Hi I use the Kodak Carestream Point-of-Care CR 140 system and I would like to know the value of EI in your X-ray digital radiography for each section on the body.

    • reply

      Raymalee Frank

      Good afternoon-

      Could you please send me this information for as well? I would like to know the EI for each section of the body.
      Thank you.

      • reply

        Hello, I sent them to your email address. Thank you for reading Everything Rad!

        • reply

          Brett Temme

          I would like to know the EI range for carestream equipment.

          • Hello, I sent it to your email address. Thank you for reading Everything Rad!

          • Fais

            Hello, I would like to know the EI range for carestream equipment too and about red or other color indicator in carestream EI.

          • Hello, I sent them to your gmail address. Thank you for reading Everything Rad!

        • reply

          Christina juel

          Hi there
          I would also like to
          Know the El value for each section of the body please

        • reply

          Sarra. Xray

          Hi,
          Could you please send me the same information

        • reply

          STEPHEN MCNULTY

          Hello,

          Could I also receive the EI values for Carestream?

          Thank you.

  • reply

    Xray

    Hello,
    Can u send me the value of exposure in your X-ray CR/digital radiography for each section on the body?
    Thanks,

    • reply

      Greetings, Without further detail of the specifics of your location, equipment and local processes, I would like to recommend that you utilize Best Practices of the ASRT (American Society of Radiologic Technologists) https://www.asrt.org/docs/default-source/publications/whitepapers/asrt12_bstpracdigradwhp_final.pdf or refer to their general site: https://www.asrt.org

      If you are still interested in more information, if you can kindly provide your name, facility name, city, country and phone number – we can have a Carestream representative follow-up to understand your specific requirements. Or you can complete the Contact Us from found here: https://www.carestream.com/en/us/medical/contact-us/publiccontactform
      Thank you!

    • reply

      Ramses

      Can I also get a copy of this please

      • reply

        Hello, I sent the attachment to your email address. Thank you for reading Everything Rad!

        • reply

          J Milham

          I need an exposure list for the carestream/vieworks setup. They are in ranges of 300-500 from what I’ve seen. I’m not sure what optimal is for this system.

          • Hello, I sent them to your email address. I hope they are useful to you.

    • reply

      Ellie

      Can I also get the EI range for all body parts?

  • reply

    Gijs

    Dear Sir, Madam,

    I am currently trying to implement the EI/DI at our radiology department. I have set a target EI for thorax images using a very life-like, anthropomorphic thorax phantom in collaboration with our radiologists. I now however would like to know how I can set target EIs for the other body parts/views. Can you help me with that?

    Kind regards,
    Gijs

    • reply

      Hello Gijs, the procedure for creating target EIs is a function that is performed by a medical physicist. We suggest that you contact your physicist. He/she should be able to help you. Thank you for reading Everything Rad!

  • reply

    hazlina

    HI, HELLO

    I would like to know the value of EI in your X-ray digital radiography for each section on the body for lower and maximum value of EI

    thanks

    • reply

      Hello, we are happy to help but this is difficult to answer as a comment. Could you please send me your email address and/or phone # so that we can get in touch with you? You can post your contact information here, or you can send it to me at socialmedia@carestream.com It will be private that way. Thank you

  • reply

    Gabriel

    Hello I’d like a reference EI for the carestream drx ascend model Toshiba E7252X how would I go about acquiring it?

    • reply

      Hello Gabriel, the EI range is dependent upon the detector type (GOS or CsI) and not the system type (Evolution, Ascend, etc.). It is also dependent upon the speed class that you are using.
      I will send you via email a document that shows the EI ranges for each detector type and the speed classes. (I can’t include an attachment in this comments’ field.) Thank you for reading Everything Rad!

      • reply

        STEPHEN MCNULTY

        Hello,

        Could I also receive the EI values for Carestream?

        Thank you.

          • siti munirah

            hello, could I also get the same info about EI values for carestream for all body parts too? hope u can email it to me at sitimunirah178@gmail.com

  • reply

    Ben Oakes

    Multiple exposure measures confuse radiologists and technologists. Exposure values may not be reported in. PACS 0xc0000185 , Just Cannot access data for analysis. I know, however, would like to know how I can set a target for the other body parts?

    • reply

      Hello, I’m afraid I do not understand your reference to “multiple exposures measures” and how it relates to your Toshiba system.
      But I can provide these instructions for setting target values. I hope this is helpful.

      I. Log in the system as Key Operator
      II. From the main menu, select Key Operator Functions
      III. Select System Configuration
      IV. Select View Configuration
      V. Select the radio button that includes “target index”
      VI. Select the body part you wish to change from the list of views
      VII. Highlight the Target Index by touching it on the screen
      VIII. Enter the new target index that your physicist has calculated
      IX. Select “Save Changes”
      X. Repeat as needed for each additional body part being sure to save your changes before exiting the page,
      XI. Select “Main Menu” button when finished
      XII. Log out to exit as key operator.

  • reply

    Sherri

    Hello Sir, I am currently pursuing Radiography in school and would like to know how to utilize the 15% rule of KVp and mAs to diffrent IR types ie. PPS,FPD and Film. Also Thankyou for explaining the need for SI values as well as DI values. Honestly, I now fully understand.

    • reply

      Hello, in general, an increase of 15 percent in kV approximately doubles the exposure. This is true regardless of the receptor type, but the visual effects on the receptor type will be different.

      The 15% rule is used extensively when utilizing film. That is how you adjusted your density. Anything less than 15% and you would see no change in density on the film. As a student, I use to laugh every time a radiographer told me to “go up 2 kV”, because anything less than 15% has no physical change on density.

      In the CR/DR world where density is controlled electronically, you will see no physical change to the density on the image being displayed. However, what you will see is a change to your exposure index and the amount of noise in the image. If you are decreasing 15%, your density will remain the same, but the amount of noise in the image will increase and your EI will decrease and vice versa. I hope that answers your question and good luck with your radiography education!

      • reply

        Sherri

        Thankyou so much, well explained!

  • reply

    Nasrullah khan

    Hello, Sir
    Can u send me the value of exposure in your X-ray CR/digital radiography for each section on the body?
    Thanks,

    • reply

      Hello, I need to ask our clinical application specialist for this. He is traveling abroad so it might be some time before I have an answer for you.

  • reply

    Gretchen Koontz

    We have a Carestream 7500 that was installed in mid ’09. I have noticed lately that the exposure indicators for a few exams are not in the 1500 – 1800 range that we were given as acceptable originally for our x-ray unit. For example: Tibia-Fibula – AP 1940, AP 2004, Lat 1981, Lat 2209 (images were a little dark).

  • reply

    sudibyo

    May i question
    If overexposure, and index exposure high, why the image in komputer is blank/white, see in computer monitor (or light view) ?

  • reply

    Walter Errickson

    I have just been given a Kodak Point of Care CR140 system after using DR for years. I am trying to find the EI numbers for various body parts. After reading the above article and the reference article “standard for exposure index ” it appears to me that these numbers must be given to me by my company’s medical physicist. Is this the case or can you provide me with a standard range for this system?

    • reply

      Hi Walter. Thank you for reading our article and for your question. Please follow this link to find the appropriate contact in your region who will be able to answer this question for you. https://www.carestream.com/en/us/medical/contact-us/world-wide-contacts

      Thanks and have a great day!

    • reply

      Hello Walter, you are correct that this is usually provided by your medical physicist. In addition, I sent a document with EI values for our receptors to your gmail address. I hope this is useful to you.

  • reply

    Amanda Douglass

    DXR Revolution

    What are the EI recommendation for all body body parts for this machine? Thank you for your time!

    • reply

      Hello Amanda, I sent the document with the information you requested to your gmail. Thank you for reading Everything Rad!

  • reply

    Chris Hernes

    DRX Revolution
    What are the EI recommendation for all body body parts for this machine?

    DRX Evolution
    What are the EI recommendation for all body body parts for this machine?

    Thank you for your time!

    • reply

      Hello Chris, I sent the document to your email address. Thank you for reading the blog!

      • reply

        Cori

        Hi CareStream! Is there any way you could send me a copy of this information as well? Thank you so much!

        • reply

          Hello Cori, I emailed them to your email address. Thank you for your interest!

  • reply

    Raman Rana

    DRX Revolution
    Can you please provide me the EI recommendation for all body body parts for this machine?

    Also, can you please forward any other white papers too that could help me understand the mathematical formula/calculation Carestream is using to come up with these EI values?

    • reply

      Hello, thank you for your interest. I sent our EIs to your gmail address. Thank you for reading Everything Rad!

  • reply

    Johnny

    DRX Revolution
    What are the EI recommendation for all body body parts for this machine?

    DRX Evolution
    What are the EI recommendation for all body body parts for this machine?

    Thank you for your time!

    • reply

      Hello Johnny, I sent them to your gmail account. Thank you for reading Everything Rad!

  • reply

    Hana Beta

    Dear Sir,

    I have a question. How does CR Carestream systems calculate the exposure index before using? or exposure index of an images without radiation exposure such as for acceptance testing? In pattern algorithm, the exposure index just 22-30 values.

    Thank you for helping.

    • reply

      Hello, I sent our EI document to your gmail address. Thank you for reading Everything Rad.

  • reply

    Christina juel

    I would like to know the El value of each body part too

  • reply

    S. N

    Hello

    I would really appreciate If i could receive the EI Value of Each body parts for CR / DRX.

    Thanks

    • reply

      Hello, I sent them to your email address. Thank you for reading Everything Rad!

      • reply

        S. N

        Hello

        Thank you for sending the Exposure index chart to me, However it only says extremities and Chest.

        This doesn’t clearly say the EI Values, Please explain Speed Vs. EI Value.

        I would really appreciate If i could receive the EI Value of Each body parts for CR / DRX.

        Thanks

  • reply

    Brian Tunell

    Two comments about this blog;

    1: The quality of film based X-ray’s were also dependent on the developer chemistry, and temperature, not just the techniques.

    2: There was a time before EI, that the Technologist was capable of determining whether their film was diagnostic or not. Thirty-eight years later, I’m seeing students coming through our department that are unable to tell a good X-ray from a bad one, unless they have an EI to reference. To know a good film from a bad one is a lost art, and I’m afraid the EI is at the heart of this.

  • reply

    Salomon Ramirez

    Hello,

    I would like to know the EI value for each body part for CR/DRX.

    Thank you.

    • reply

      Hello, I sent our EIs to your email address. Thank you for reading Everything Rad.

  • reply

    David

    Hi there

    Is it possible to get a range of exposure index values for each body part. What we should ideally be within?

  • reply

    David

    Hi there

    Is it possible to get a range of exposure index values for each body part that we should be within?

    • reply

      Hello David, I sent them to your gmail address. Thank you for reading Everything Rad!

  • reply

    S. N

    Hello

    Thank you for sending the Exposure index chart to me, However it only says extremities and Chest.

    This doesn’t clearly say the EI Values, Please explain Speed Vs. EI Value.

    I would really appreciate If i could receive the EI Value of Each body parts for CR / DRX.

    Thanks

  • reply

    anna kolisa

    hello can I get exposure index range chart for carestream and for portable carestream range we should be within?

  • reply

    ana k

    Is it possible to get a range of exposure index values for each body part that we should be within?

    • reply

      Hello Ana, I sent it to your yahoo email address. Thank you for reading Everything Rad!

  • reply

    Bill

    Maybe a little late to the game, but how does one determine the adjustment in technique if -3 and +3 are the lower and upper limits? Sadly I’ve seen larger errors than those DIs reflect.

    • reply

      Hello, please call our support team at +1-800-328-2910. They will be able to answer your question.
      Thank you for reading Everything Rad.

  • reply

    Christer Strom

    Hello,

    Is it possible to get a range of exposure index values for each body part? We are going to implement the IEC standard in Sweden.

    Sincerely

    Christer

    • reply

      Hello Christer, I sent the EIs to your email address. I hope you find them useful.

  • reply

    Lucky-Fiakpa Ochuko

    Good read. Please i would like to know the EI range for all body parts

  • reply

    Melissa Ellis

    May I please get a copy of the Exposure Index values for each body part?
    Thank you kindly!

    • reply

      Hello Melissa, I sent them to your email address. I hope they are helpful.

  • reply

    juliana leoh

    Good evening sir-

    Could you please send me this information for as well? I would like to know the EI for each section of the body.
    Thank you.

  • reply

    Lucky-Fiakpa Ochuko

    Can i get the EI range for all body parts

  • reply

    Lucky-Fiakpa Ochuko

    Can i get EI range for all body parts

  • reply

    Tessa Hunter

    May I please get a copy of the Exposure Index recommendations for each part of the body?

    • reply

      Hello Tessa, I sent them to your ConeHealth email address.

  • reply

    je joong kim

    hello, Can I get an e-mail about ECF ???

    ti is caretream DRX revolution, ACE and ECF part.

    • reply

      Hello, I am sorry but I do not understand your question. Can you explain it further? Thank you

  • reply

    Alena

    Hi, is any way to find out how actually EI is generated? I am a physicist and we are trying to find out how let’s say EI of 2000 is created and what it is depend. Thanks.

    • reply

      Hello, good question! I am trying to find the right resource in Carestream to answer your question. I’ll be in touch.

    • reply

      Hello Alena, I emailed 2 documents to you that I hope will be useful to you.

  • reply

    Sophia Page

    nice information.

  • reply

    kishor

    Hi There I am radiography student and would like to get the exposure index chart if there is any for carestream radiography machines for different parts of the body.

  • reply

    Kishor

    Hi There i am a medical imaging student and would like to get the exposure index chart if there is one for carestream radiography machine for different parts of the body.

    • reply

      Hello, I sent them to you canberra email address. I hope you find them useful.

      • reply

        The email will not go through; it comes back as undeliverable. Do you have another email address I can send it to?

  • reply

    Jessie

    Hello, I would like to know the EI range for carestream equipment (DRX-Plus 3543C)
    Thank you!

    • reply

      Hello Jessie, I sent them to your email address. I hope you find them useful.

  • reply

    Steven

    My radiology department is using your DR system for more than 7 year. Recently we tried to make a long exposure time (around 3s) for imaging the PA oblique view for sternum. But we found the detector seem cannot accepted ( the error message “Detector cannot be used fir extended exposures until a successful Dark calibration is performed ”
    Actually what does this mean?
    Is it we can still using a longer exposure time after the Dark Calibration?
    Or is there a limitation for the exposure time for your detectors?
    Many thanks!

    • reply

      Hello, this means that the detector needs calibration before it can be used for a long exposure. The daily dark, which is an automatic calibration, is failing. Typically this is corrected by performing a full calibration of the detector. Once this is complete, you should be able to perform exposures of up to 3.2 seconds. Our service department can help you do this. You can find a service representative in your area here. https://www.carestream.com/en/us/services-and-support

      • reply

        Luis

        Hello, I am having the same issue that Steven has. I did the full calibration but It keeps asking me for dark calibration. What should I do in this case?
        Thank You!

  • reply

    Christy

    Hello! Our hospital is currently doing a study on EI for our chest x-rays. May I know how are the EI values generated and what are those values dependent on? Does every carestream machine come calibrated to a certain guideline when purchased? Could I have a copy of the EI recommendations for each part of the body as well? Thank You!

  • reply

    Ellie

    Can I get the EI range for all body parts?

  • reply

    Ellie

    I would like to know the exposure index for each part of the body. My facility uses the care stream image suite software. Thanks.

  • reply

    Luke

    Can I also get a copy of this please

  • reply

    Ahmad

    hello , I work in hospital as a Rad Tec, and newly they brought a carestream ascend plane Xray device, but i have a problem that I don’t know the optimum exposure factors to use for body parts for patients , so I’m asking if there a chart or index to get the right numbers for ideal kVp and mAs to use.

  • reply

    Lutfan

    hello, I work as a radiographer in Indonesia, I’m currently doing a study to make a chart of exposure factors based on EIs. Could I have a copy of the EI recommendations for each part of the body?

  • reply

    Daniel

    Hello, I’m a medical physicist working in an institution with majority of rad units from Carestream (Revolution, Evolution Plus, Ascend). We are working on target EI optimization to better guide our techs on exposure and image quality control. Can I also get the document of Carestream recommended EI values and the rationales behind it? Also, if you have any documents about AEC calibration and detector target dose it would be great. Thank you.

  • reply

    Bonnie

    Hi, I would like to know the EI range for carestream equipment (DRX-Revolution)
    Thanks!

  • reply

    Mary Hagemeier

    What are the EI numbers for the DRX Revolution Carestream Portable?

  • reply

    Nadhirah

    hello, may I also get a copy of the EI range for different part of the body? thank you

POST A COMMENT

This site uses Akismet to reduce spam. Learn how your comment data is processed.