DETECTOR EXPOSURE INDICATOR IN GE X-RAY SYSTEMS

Transcription

1 DETECTOR EXPOSURE INDICATOR IN GE X-RAY SYSTEMS Prepared by Sung Jeon, GE Healthcare Abstract: Detector exposure indicator (DEI) is a feature that provides visual information for detector exposure in digital X-ray images The lack of visual/quantitative information in digital X-ray images led several X-ray system manufacturers to develop DEI feature on their systems over the last few years However, different DEI calculation methods and reports by different vendors often caused confusion to the users In recent years, efforts for DEI standardization have been driven by the medical physics and radiology communities In response to standardization efforts, the IEC developed and published the standard IEC In this whitepaper, we discuss the DEI feature in GE X-ray systems using the terminologies defined in IEC This whitepaper is intended to provide essential information of the DEI feature in GE X-ray systems for typical users as well as DEI design details for advanced users/physicists 1 Background 11 Introduction The direct connection between the level of detector exposure and optical density is well established in film-screen radiography However, that is not the case in processed digital images because of dynamic detector range and automatic image processing that optimizes image display (Figure 1) Over- or under-exposure is not easily detectable in digital imaging Lack of visual cue for over-exposure is more problematic: the radiographer tends to attempt to achieve noiseless images in order to satisfy the radiologist, and this tendency could lead to unnecessary increases in patient exposure This is well known as Dose Creep To help address such behaviors, system manufacturers have provided ways for the users to read and understand detector exposure information Underexposure Optimal Overexposure Figure 1: Exposure level is easy to detect in Film Radiography (top row) while it is difficult to detect in Digital Radiography (bottom row) 12 DEI standardization Over the past few years, different manufacturers, including GE Healthcare, have come up with their own methods for calculating and displaying detector exposure indicator/index (DEI) This has been a source of confusion among the end users With facilities having multi-vendor equipment, it became a challenge to interpret among the DEI values of different vendors and to have effective Quality Control (QC) or Quality Assurance (QA) in place To address such diversities, the radiology community acted on harmonizing detector exposure indicator in the past few years: The International Electrotechnical Commission (IEC) published the standard in 2008 [1] The American Association of Physicist in Medicine (AAPM) published the report based on the efforts driven by Task Group 116 in 2009 [2] ImageGently stakeholders agreed to adopt the IEC standard in 2010 [3] Film Digital Data subject to change without notice 1

2 In response to standardization efforts, GE Healthcare introduced a new design for DEI starting from the products released in year 2011 (eg Precision* 500D/ Proteus* WDR1 Upgrade, Optima* XR220amx, and Discovery* XR656) The new design is intended to provide detector entrance exposure information as defined in IEC This whitepaper describes the DEI feature in GE Healthcare x-ray systems Section 2 contains basic information about the DEI feature, including the user interface, available operation options and guidelines for the users Section 3 includes details about DEI design and algorithm, which may be of interest to advanced users or physicists Note that all references to DEI in the current paper refer to the new DEI design observed in GE Healthcare x-ray systems introduced since 2011, unless stated otherwise 2 DEI Typical Usage 21 Basic components DEI design in GE X-ray systems provides detector entrance exposure values in terminologies as defined in IEC [1] The following definitions of main DEI components are excerpted from IEC Exposure Index (EI) Measure of the detector response to radiation in the relevant image region of an image acquired with a digital X-ray imaging system Target Exposure Index ( ) Expected value of the exposure index when exposing the X-ray image receptor properly Deviation Index (DI) Number quantifying the deviation of the actual exposure index from a target exposure index 22 Interpretation of DEI values EI allows the operator to judge if an image was taken at a detector exposure level suitable for the intended level of image quality EI is proportional to the detector entrance exposure: If the entrance exposure is increased, EI value is increased The value of EI divided by 100 is comparable to detector entrance dose measurement in the unit of µgy at calibration conditions DI is a relative indicator showing how far EI deviates from with the base 10 logarithmic scale A scaling factor of 10 is applied to calculate DI number When EI is close to, DI becomes close to 0 When EI is 25% higher than, DI becomes 1 In other words, DI = 1 means that detector entrance exposure for the image is 25% larger than the expected exposure index for the selected anatomy and view DI becomes -1 when EI is 20% lower than Similarly, DI becomes 3 when EI is 100% higher than, and it becomes -3 when EI is 50% lower than 23 Displaying DI values on GE Healthcare X-Ray Systems The DI result for each exposure is displayed with a graphical bar indicator as shown in Figure 2, and both EI and DI are displayed in the annotation as well By default, DI ranges and limits for GE X-ray systems are set as following: If -3 <= DI <=2: Display Optimal Range text message with green color in the bar indicator Figure 2: Color Coded DI calculation result, DI limits, and text messages are displayed for each acquired image and reprocessed image The user has an option for not displaying DI information at all or displaying numerical DI result only If -3 > DI >=-5 or 2 < DI<= 4: Display Acceptable Range text message with yellow color in the bar indicator If DI <-5 or DI> 4: Display Out of desired range text message with orange color in the bar indicator The same DI ranges and limits are applied to all digital images IEC does not specify requirements for displaying DI range and limit AAPM Task Group 116 recommends 5 ranges with 4 limits in their report, which is similar to the values used in GE X-ray systems, but their initial recommendation was tighter than GE s default range and limit setting [2] Data subject to change without notice 2

3 25 Adjusting DEI feature on GE X-ray systems is designed to allow the user to set values independently for different combinations of anatomy, view, and patient size (Adult/Pediatric) For each anatomy, view, and patient size, there are two values: Factory and Custom as shown in Figure 4 The Custom is the used for DI calculation and is the adjusted value based upon Factory and Adjustment factor At installation, Custom value equals the Factory value Changing the Adjustment by 10 adjusts the Custom by 1 Renard step For a fixed exposure, mas increase of 1 Renard step increases the mas by approximately 25% Figure 3: The limits and text messages are configurable in the user preference (Preference 6 DI 6 DI Control Limits) GE X-ray systems also provide an option to change the limits and the corresponding messages in the user preference (Figure 3) 24 DEI export/dicom The DI export option, which can be found in Preferences 6 DI 6 DI Export Logs, allows the user with the ability to retrieve DEI information onto a CD or USB flash drive in the form of a CSV file The exported CSV file lists DEI information with acquisition time and date, relevant X-ray techniques, selected anatomy/view/patient size for past exposures It can be useful to analyze trends of X-ray techniques and the corresponding DEI values for different patient anatomy/view/size The information in this file also may be useful to adjust values For each acquired image and processed image, the different DEI values are also stored in the DICOM tags The table below lists the details DICOM Tags Description 0011,1036 Median (Anatomy) Count 0011,1037 DEI limit values 0018,1411 Exposure Index 0018,1412 (Compensated) Target Exposure Index 0018,1413 Deviation Index 0011, 106D Uncompensated Detector Sensitivity 0011,1034 Compensated Detector Exposure 0018,6000 Compensated Detector Sensitivity Figure 4: values are listed in Preferences 6 DI 6 DI-Preferences For each anatomy/ view/patient size, Factory Target EI is a reference, and Custom Target EI, which is equal to Factory Target EI by default, can be modified by changing the Target EI Adjustment factor In the example above, indicated by the square box, the Adjustment was set to (-2) for Abdomen/antero posterior/pediatric, making Custom approximately 2 Renard steps lower than the Factory for Abdomen/antero posterior/pediatric exposures 26 Steps for customizing DEI Users should not rely on the DI result alone in order to determine appropriate X-ray techniques It is also suggested not to modify Custom as a first mitigation step when DI value deviates from the desired range based on one or two exams The tradeoff of IQ and dose should be the dominant factor to determine appropriate and proper X-ray technique based on each site s preference Advanced users and physicists who understand DEI and the IQ/ Dose tradeoff should be involved in making Custom modification decisions Below are general guidelines for adjusting X-ray techniques and/or when necessary Table 1: Relevant DICOM tags for the DEI feature Data subject to change without notice 3

4 Step 1: Confirm that detector calibrations were recently completed by the local field engineer Poor or out of date calibration results can adversely impact EI and DI accuracy Step 2: Make sure that imaging conditions are appropriate and do not deviate from the nominal For example, check following factors when EI/DI values are unusual Collimation and shuttering Unusual body habitus Presence of prosthetics Shielding material in the imaging region of interest AEC functionality and patient positioning relative to enabled ion chamber cells 27 Impact of re-shuttering on EI/DI EI/DI are calculated immediately after image acquisition and after every instance of image reprocessing After a reshuttering operation, EI/DI recalculation is essential to account for any change in the relevant image region (Figure 5) If re-shuttering the image changes the extent of anatomical content in shuttered region of image, then the value of interest used in the DEI algorithm could also change, thus affecting the EI/DI values Users should note that the new EI/DI values are generated only after the image reprocessing operation is fully complete, which happens only when the user selects the image reprocess button after adjusting the shutter position Step 3: If image quality and/or patient entrance dose are within user s expectation, but DI is beyond desired range for the selected exposure techniques, consider the following: When DI is higher than 0, increase Adjustment in order to set the Custom higher than the Factory When DI is lower than 0, decrease Adjustment in order to set the Custom lower than Factory It s not advisable to make a change based on only a few results When DI consistently deviates from default, the users may consider modifying Custom Step 4: If image quality and/or patient entrance dose do not meet the expectation: When assessing image quality, always ensure that Window Width/Window Level (WW/WL) is set correctly Adjust kvp, mas, and/or speed in AEC mode if necessary to achieve desired image quality and patient entrance dose If DI is still out of range although image quality is acceptable, customize as described in Step 3 Depending on the system type, patient entrance dose or DAP is available from direct DAP meter reading or Dose/DAP calculation based on the x-ray techniques Figure 5: (1) Processed image after data acquisition and (2) Re-processed image after manual shuttering Both of them share identical raw data EI and DI values were changed because manual shuttering changed the median anatomy count Note: the date and time and institution name on these two images are blocked 28 Benefits of the DEI feature Some benefits and practical usages of DEI information are listed below DEI features provides appropriate detector exposure level in clinical imaging, which is not easily detectable in digital radiographic images In Fixed mode, EI/DI values can be monitored to minimize the tendency to increase exposure over time (prevent dose creep ) In AEC mode, variation in EI/DI values can be monitored as indicators of patient and ion chamber positioning or collimation problems DEI feature enables technologists to monitor patient-specific detector exposure levels and to maintain consistent IQ with minimum dose Data subject to change without notice 4

5 Recent studies and investigations performed by different research groups [4-8,] have strengthened the case that DEI can be a useful tool for QA/QC in X-ray digital images 29 Summary DEI is designed to provide detector entrance exposure information in digital radiography where under- or over-exposure is not obvious from the digital image due to the wide dynamic range of the digital detector and automatic image processing Harmonized DEI terminologies found in recent GE X-ray systems would help reduce the potential confusion for utilizing DEI information DEI is different from and cannot replace patient entrance dose, which is provided by the DAP meter or Dose/DAP calculation in GE Healthcare systems The relationship between patient entrance dose and detector entrance dose depends on many variables including patient thickness, kv, collimation, etc X-ray beam quality is different before and after passing through the patient and thereby DEI doesn t directly convey dose to the patient EI is proportional to detector entrance exposure, and EI divided by 100 reflects detector entrance dose in the unit of µgy at calibration conditions DI is to calculate the deviation of EI from DI is a metric for understanding appropriateness of the exposure for each anatomy/view/patient size It s important to understand that EI or DI is not the indicator for image quality Appropriateness of the exposure based on DI number comes with the assumption that is properly set for each anatomy/view/patient size although the default may not be optimized Each site may consider adjusting if DI is consistently not in desired ranges despite acceptable image quality Recent studies by different research groups have also discussed the challenges and the importance of optimization [3-5] 3 DEI design details for advanced users/physicists 31 Algorithm overview Following factors impacts on DEI calculation: X-ray techniques including filter/grid status Collimation and Electronic Shuttering Raw data (image) Detector calibration results Anatomy segmentation performance Pre-defined scaling factors addressing X-ray technique variation compared to the calibration (near-rqa5) condition The figure below illustrates DEI calculation workflow, which is executed for each exposure Figure 6: DEI calculation workflow diagram Values in bold are recorded in the DICOM tags as listed in Table 1 32 Raw Image/Raw data in GE X-ray systems DEI calculation is always done using the original data, not the processed data Per IEC , data type definitions are as following [1]: Raw data pixel values read directly after the analogue-digital-conversion from the digital X-ray imaging device without any software corrections Original data Raw data to which the allowed corrections are applied Allowed corrections include bad pixel corrections, flat-field correction (gain and offset corrections), and geometrical distortion correction Data subject to change without notice 5

6 In GE documents (eg service manual, operator manual), the terminology raw data is in fact referring to the original data defined in IEC In this document, raw and original data are not differentiated, and both of them refer to original data defined in IEC Details for Exposure Index (EI) According to IEC , EI is related to the value of interest V: (1) (2) Figure 7: (1) Anthropomorphic phantom image and (2) Output of anatomy segmentation algorithm The black area in the subsampled image is considered as the relevant anatomic image region for DEI calculation EI=C 0 g(v) where C 0 =100µGy -1 and g(v) is an equipment-specific inverse calibration function The value of interest is defined as the central tendency of the original data in the relevant image region [1] The inverse calibration function in GE Healthcare systems is proportional to the median image count in the raw data, the value of interest V, and inversely proportional to the uncompensated detector sensitivity (counts/µgy) Hence, the above equation is implemented as following on the GE Healthcare system EI=100 [µgy -1 ] Median Count [counts] counts Detector sensitivity µgy The original data comes from the image read from the digital detector after bad pixel, offset, and gain correction and is available to the user The relevant image region in GE Healthcare systems is defined as the anatomic region under all clinical conditions The anatomic region is identified from image processing by removing the collimator blades and the areas of raw radiation An example of anatomic region identification is shown in Figure 7 The detector calibration procedure determines the value of conversion factor (CF, electrons/x-ray photon,) which is used to calculate the detector sensitivity value Hence, proper detector CF calibration is vital in order to achieve accurate EI values As the count in the raw data is linear to the amount of exposure, EI shows direct linear relationship with Air Kerma measurement At calibration conditions, the relationship between EI/100 and measured dose in the unit of µgy is one-to-one Figure 8 demonstrates the relationship between Air Kerma measurement and EI In the test, EI accuracy was below the specified accuracy limit (20%) in IEC at calibration conditions Figure 8: Calculated EI vs Direct Detector Air Kerma measurement Detector Air Kerma was measured at the center of the detector position using a dosimeter (RadCal 9010 with 6 cc probe) (1) Linear relationship is apparent between EI and Detector Air Kerma measurement (2) The error is calculated using the formula 100*(Air Kerma EI/100)/ Air Kerma, and it is done for different mas The errors are below the accuracy limit (20%) specified in IEC The measurement was done in Discovery XR656 Digital Cassette mode with 20 mmal phantom, SID = 100 cm, No Copper filter, No Grid, 80 kvp, 41cmx41cm collimator opening, and DI technical mode Note that the result in Figure 8 was obtained with DI Technical Mode with 20 mmal flat field phantom in the X-ray beam and fully open collimation FOV EI in clinical conditions does not necessarily equal the detector entrance dose due to differences in beam hardening and scattering It is important to set the detector Air Kerma measurement condition equal to the detector EI measurement condition when evaluating EI performance eg (1) Position of the dosimeter probe should be at the center of the image plane, (2) The dosimeter probe should be located at Data subject to change without notice 6

7 the same source-to-image distance (SID) compared to the detector: otherwise, the distance ratio adjustment (R-squared correction) may also be considered if the probe cannot be placed at the detector position, (3) Attenuation, scattering and backscattering condition for dose measurement should be set equivalent to those for the detector, and (4) The acceptance angle of the dosimeter probe should be similar to the one for the detector Proper collimation is an essential step to help minimize - dose to patient, and it also helps identifying the relevant image region properly Incorrect collimation may lead to improper anatomy segmentation, and it may result in biased EI and DI 34 Details for Target Exposure Index At system installation, Custom is equal to Factory These default values were determined empirically based on statistical data analysis of median count values for different anatomy and view combinations in a fixed radiographic system During the design phase, the data used for setting in most cases were acquired with in AEC mode Each anatomy has different values, because expected median count values and contrast are different for each anatomy For example, for chest AP/PA is different from that for abdomen because the radiographic contrast in the anatomical area of the chest image is different from that of abdomen The contrast is important because the location of the ion chambers used for AEC is in the lung area, but a large fraction of the image has lower signal (Spine, heart, diaphragm) The Factory should not be considered as the gold standard target value in all circumstance for following reasons: (1) Factory does not address variability in system usage or patient size/position because limited data were used for the analysis (2) Although the system lets the user set different depending on patient size, Factory values for pediatric mode are currently equal to those for adult mode Since the exposure level for pediatric is generally lower than the one for the adult, for pediatric should ideally be lower than for adult (3) Factory values for the mobile system (Optima XR220amx) were derived from those for the fixed system while the factory X-ray technique setting for each anatomy and view are not same between the mobile and the fixed system GE Healthcare continues to collect clinical feedback and perform ongoing experimental analysis to monitor and to evaluate the performance of the DEI feature This ongoing effort will be continually used to provide improved Factory for the users 35 Details for Deviation Index DI in GE X-ray systems is defined as the following: where (Compensated ) is based on Custom shown in Figure 4 and accounts for kvp, Cu filter, grid, and receptor difference between actual exposure and the condition when setting the default and Custom can be different depending on X-ray techniques being used is saved in DICOM header as described in Table 1 and the DI Export log file The relationship between and can be expressed as the following Film equivalent speeds other than 400 will impact Details for the speed factor are discussed in the next two sections kvp, Grid, Cu filter, and receptor changes compared to the condition for default also impact Their contributions were predetermined and stored in look-up tables based on laboratory tests with different thickness of a PMMA (Poly Methyl MethAcrylate) phantom, also known as Plexiglas, at different kvp 36 Speed setting for X-ray systems Speed should be used and understood differently between Film and CR/DR This section provides clarification on the use of Speed on digital radiography systems Speed for Film Speed is a characteristic of the film/screen system and is inversely proportional to the exposure to the film/screen required to reach a specific optical density In AEC mode, exposure to the film/screen is controlled by the system based on clinical protocols In non-aec mode, a clinically relevant exposure for each application (based on anatomy/view) requires the correct film/screen combination to be selected Data subject to change without notice 7

8 Speed for Digital Systems On a digital system, equivalent film speed is NOT related to specific image brightness Post image processing algorithms determine brightness and contrast values for display Speed in digital X-Ray is not determined by the sensitivity of the digital detector In AEC mode, exposure to the detector is controlled by the system based on clinical protocols Different clinical protocols are required to meet different imaging needs Speed is considered a metric for the exposure and is included in each clinical protocol High Speed: pediatric application requiring low dose Low Speed: higher signal-to-noise ratio, higher dose imaging applications In non-aec mode, a clinically relevant exposure for each application (based on anatomy and view) is determined by the specific X-ray techniques in protocols not by the speed 37 Impact of speed change on DI calculation The amount of exposure is controlled by the equivalent film speed setting in AEC mode while it is manually controlled by ma and exposure time in Fixed exposure technique In both AEC and Fixed mode, equivalent film speed is used as a factor adjusting the expected exposure level The DI calculation result will be different between AEC and Fixed mode depending on the speed setting because speed change does not contribute to exposure change in Fixed mode In AEC mode: When the speed is increased, EI becomes lower as the amount of exposure decreases, and is scaled down inversely proportional to speed As a result, the calculated DI is constant When the speed is decreased, EI becomes higher as the amount of exposure increases, and is scaled up inversely proportional to speed As a result, the calculated DI is constant In Fixed exposure mode: When the speed is increased, EI doesn t change, but is scaled down inversely proportional to speed As a result, the calculated DI increases for the same fixed exposure When the speed is decreased, EI doesn t change, but is scaled up inversely proportional to speed As a result, the calculated DI decreases for the same fixed exposure 38 DEI (DI) Technical Mode DEI (DI) Technical Mode option is provided in DI preferences (a checkbox shown in Figure 4) Once it is enabled, the anatomic segmentation step is disabled, and the region of interest (ROI) used is the central rectangular region (512x512 pixels Median count is obtained from the fixed ROI A central ROI is also used for the CF calibration CF calibration impacts the detector sensitivity and thereby EI/DI calculation result The technical mode can be useful for evaluating DEI performance since it will help eliminate the potential variability introduced by the anatomy segmentation, but it shouldn t be used for regular clinical exposures for the same reason 39 Compensated Detector Exposure (CDExp) CDExp is not defined in IEC It has been used to display detector exposure information in the previous DEI feature and is carried forward into the new DEI feature To calculate CDExp, the median count in the identified anatomy is converted to exposure in μgy based on the compensated detector sensitivity, which is the adjusted value of uncompensated detector sensitivity based on receptor type, kvp, Grid, and Cu filtration changes Unlike EI, CDExp reports detector entrance exposure in simulated clinical conditions In order to simulate patient attenuation, a set of Plexiglas has been used as attenuation material resulting in a different X-ray spectral attenuation than RQA5 beam condition However, a set of Plexiglas still cannot account for expected variations in actual patient thicknesses and body compositions Depending on patient size and type, CDExp may over- or underestimate detector entrance exposure CDExp, Although the units of CDExp are Gray, it should not be considered as an absolute detector entrance exposure but as another indicator for the detector exposure Data subject to change without notice 8

9 To demonstrate the difference between EI and CDExp, test results are presented in Table 2 EI represents Detector Air Kerma at the calibration condition whereas CDExp closely represents detector Air Kerma at the simulated clinical imaging condition In the table below, actual detector Air Kerma is close to reported EI/100 with 20 mm Al plate (GE flat-field phantom) Air Kerma is close to CDExp with Plexiglas Depending on the systems calibration status and measurement setup, the test results will vary It s important to understand that EI relates to Air Kerma at a hard beam (near RQA5) condition realized with a 20 mm Al plate, and CDExp relates to Air Kerma at a soft beam condition realized with a set of Plexiglas X-ray technique 20 mm Al Plate 475 inches Plexiglas kv mas EI CDExp [µgy] Air Kerma [µgy] EI CDExp [µgy] Air Kerma [µgy] Table 2: Comparison among Air Kerma, EI, and CDExp The test was done in Digital Cassette mode without grid Note: As more manufacturers follow the IEC standard for expressing detector entrance exposure and as more customers interpret detector entrance exposure using EI/DI from the IEC standard, CDExp won t play a significant role for delivering detector exposure information In some instances, the customers are confused for understanding detector exposure information in the context of CDExp along with EI/DI Therefore, to minimize such confusion and to simplify DEI information, DEI feature on future systems may not include CDExp on the image display CDExp value will continue to be available in DICOM headers and the DI log export file 310 Difference with previous DEI design for the users who are familiar with previous DEI design Prior to introducing new DEI design, GEHC X-ray systems released earlier than year 2010 (eg Definium 5000, Definium 6000, Definium 8000, Discovery XR650, Optima XR640, Definium AMX 700) displayed three DEI values characterizing detector entrance exposure Uncompensated Detector Exposure (UDExp): Median count value in the anatomy converted to exposure in μgy based on the detector sensitivity in counts/μgy at 80 kvp, no Cu filtration And no grid It includes a factor to correct to a Soft Beam condition Detector Exposure Index (DEI): The raw count value in the segmented anatomy divided by the expected count value for the given acquisition parameters (Speed setting, kvp, Cu, Grid) The expected count value is specific for certain thickness of Plexiglas (eg 5 inches for 80 kvp) Ideal DEI (index) ranges vary depending on anatomy/view Compensated Detector Exposure (CDExp): Same definition with new DEI design UDExp in prior DEI design is replaced by EI in new DEI design The difference is that UDExp characterizes detector entrance exposure in soft beam condition (5 inches of Plexiglas) whereas EI characterizes detector entrance exposure in hard beam condition (calibration condition) In addition, the unit for UDExp is μgy while EI is unitless and equal to 100 times μgy Detector exposure index (displayed as DEI on the monitor) in previous DEI design is replaced by DI in the new DEI design Detector exposure index is the ratio of measured count divided by the expected median count Expected median count is derived at specific conditions (different thickness of Plexiglas for different kvp) while raw median count is calculated for each clinical exposure Therefore, optimal detector exposure index for each anatomy is different while the optimal DI is fixed To understand the optimal detector exposure in the context of detector exposure index, the user must know the reference ranges for detector exposure index, which were predetermined based on empirical data and can be configured by users For example, the factory default detector exposure index range for chest PA is set to and the one for Abdomen is set to The chart below summarizes the difference between Detector exposure index in the previous design and DI in new design Data subject to change without notice 9

10 Property Detector exposure index in old design DI in new design Expected Count or (denominator in index or DI calculation) per Anatomy/View Optimal outcome (score) per Anatomy/View Fixed Dependent Varies and configurable Independent Limit (range) per Anatomy/View Varies and configurable Constant Number of ranges 3 5 Linearity with dose Linear Log with the base 10 Table 3: Comparison between DEI (Index) in previous design and DI in the new design Data subject to change without notice 10

11 4 References: 1 Medical electrical equipment Exposure Index of digital X-ray imaging systems Part 1: Definitions and requirements for general radiography, IEC Ed S Jeff Shepard et al, An Exposure Indicator for digital radiography: AAPM Task Group 116 (Executive Summary), Med Phys 36(7), July 2009, p Quentin Moore et al, Image Gently: using Exposure Indicators To Improve Pediatric Digital Radiography, Radio Tech, 84(1), Sep/ Oct 2012, p Menglong Zhang et al, Dose optimization for different medical imaging tasks from exposure index, exposure control factor, and mas in Digital Radiography, Health Physics, 103(3), Sep 2012, p J Anthony Seibert et al, The standardized exposure index for digital radiography: an opportunity for optimization of radiation dose to the pediatric population, Pediatr Radiol, 841, 2011, p Steven Don et al, New Exposure Indicators for Digital Radiography Simplified for Radiologists and Technologists, AJR, 199, Dec 2012, p H Warren-Forward et al, An assessment of exposure indices in computed radiography for the posterior-anterior chest and the lateral lumbar spine, The British Journal of Radiology, 80, Jan 2007, p ML Butler et al, Are exposure index values consistent in clinical practice? A multi-manufacturer investigation, Radiation Protection Dosimetry, 2010, p1-4 General Electric Company reserves the right to make changes in specifications and features shown herein, or discontinue any products described at any time without notice or obligation Please contact your GE representative for the most current information 2014 General Electric Company-All rights reserved GE and GE Monogram are trademarks of General Electric Company *Trademarks of General Electric Company GE Healthcare, a division of General Electric Company GE Healthcare Chalfont StGiles, Buckinghamshire, UK gehealthcarecom JB18925US