CR to DR – Optimizing Image Quality and Dose

Bruce Apgar B.S.

George Curley R.T.

Agfa Healthcare Inc.

Greenville, SC

What is DR? Mobile Radiography:

What is DR? Retrofit DR Panels:

Floor mounted

Ceiling mounted

R/F rooms

What is DR? In Room Systems:

Benefits:

• Workflow Improvement / Automation

• Dose Reduction

• Improved Image Quality

Radiology Today: Radiology Today July 2014

Benefits:

• Cost coming down

• “Need for speed”

• Detector sharing

Radiology Today: Radiology Today April 2012

Why the Move from CR to DR?

Workflow Improvements:

Loma Linda University Medical Center Case Study

• DR Retrofit conversion from distributed multi-plate CR

Outcomes:

• Streamlined workflow & time savings

• 8.16 seconds less time per exam (portable chest, bone

surveys)

• More patients per day / year

• 100% FTE gain

• Rapid ROI

Why the Move from CR to DR?

Best Practices, ASRT Advisory Council 2012:

• Background

• Dose / ALARA

• Social Marketing and Safety Initiatives

• ACR Guidelines before getting to the scope of the white paper

ASRT HCIAC:

ASRT White Paper

Making the Move from CR to DR…

Challenges: Minimizing Patient Dose with Pediatric DR

– Equipment variation

– Technique guides not always provided

– Large detectors (AED target area)

– Artifacts from pediatric positioning devices may be more easily seen

– Repeat/Reject Analysis implementation critical

ASRT Directed Reading: Radiation Safety

Compliance; Radiologic Technology,

volume 87 - number 5 May/June 2016:

page 522

Making the Move from CR to DR…

DR: Image Capture Technologies

Electronic control

Triggers the switching diodes

X-ray scintillator screen or charge collector

Converts x-rays to light

or to electric charges

TFT array

Collects charges from the upper

layer

Switching diodes

Connects each pixel to readout device

in

out

Analog-to digital

conversionMultiplexer

Readout the electronic signal

*Lança L., Silva A. (2013) Digital Imaging Systems for Plain Radiography, New York: Springer

DR Panel Technology*

1. Absorption of X-rays in the phosphor screen

2. X-ray is converted into visible light

3. Photo diodes read light signal and generates charges

4. Signals are amplified, digitized, processed and archived

5. Soft Copy display or hardcopy optional

Image Capture Technologies

Image Quality ImprovementRequires Improved Phosphor Technology

Calcium Tungstate for Film

Barium Fluoride Bromide (BaFlBr) for CR

Gadolinium Oxysulfide (GOS) for DR

High Efficiency Needle PhosphorsTraditional Powder Phosphors

Cesium Iodide (CsI) for DR

Cesium Bromide (CBr) for CR

The thickness of CR BaFlBr powder phosphor layer is limited to less than 300 µm, because of light

scattering. This thickness limits the X-ray absorption.

Due to the low light scattering of CsI a thicker phosphor layer can be used without jeopardizing the

sharpness of the imaging system. Higher X-ray absorption is possible with DR detectors using CsI

needle crystalline phosphors. This results in lower dose and better image quality.

Phosphor Technology

CR- BaFlBr DR- CsI

70 kVp 10 mAs70 kVp 10 mAs

CR DR

70 kVp 10 mAs

Image Quality Improvement

Image Quality Improvement and Lower Dose

70 kVp 10 mAs 70 kVp 5 mAs

CR DR

DR Cesium Iodide (CsI) Phosphors*

• Significantly reduce internal light scatter

• Improve image sharpness

• Enable thicker phosphor layers

• Improve X-ray absorption

• Reduce Dose ~ 2 X

• Reduce scatter sensitivity

* When compared to BaFlBr CR phosphor plates

Image Processing Technology

Image Processing Technology

14 µGy 55 µGy 225 µGy

Image processing can improve usable diagnostic

information at lower dose

Standard Processing 14 µGy Multi Scale

Neonatal Processing

Image Processing Can Reduce Image Noise

Standard Processing Noise Reduction Technology

Proper Image Processing Should:

• Provide consistent performance • For patient body habitus & age: Neonatal, Pediatric, Adult, Bariatric • Over a wide range of exposure factors

• Increase productivity, not create more work• Little or no post processing should be needed • Should require few window / level adjustments, electronic masking, manual ROI selection

• Should not create artifacts

• Should be dose tolerant & low dose friendly

• Be easy to configure and set up • Work well out of the box• Provide simple understandable adjustment settings• Not complex parameters requiring imaging specialists for set up

Anti-Scatter Grids for DR “Key Factors”

• Grid Ratio

• Bucky factor: amount by which the exposure has to be adapted

• Grid Positioning • Angle and Distance

• Stationary vs. Reciprocating

• Line Rate (frequency) in lines/cm or lines/inch

• Grid line direction

• Focus vs. parallel

Grid Performance

Factors

• Very important clinically

• Very important clinically

• Very important clinically

• Critical

• Critical

• Critical

• Least important to digital

How it will Impact Digital

Image Quality:

Purpose:

Identifies repeating patterns caused by grid/panel interference and removes them

Result:

Improved viewing conditions

Grid Line Suppression Algorithms

DR Grid Recommendations*

* With Agfa Grid Line Suppression Software - GLS10% variation In

grid specification

Panel Type DX-D 30 / 35 C DX- D 40 C DX-D 45 C CR

Plate

Resolution 125 micron 139 micron 124 micron 100-150 micron

32 lines / cm

80 lines / inch

36 lines / cm

90 lines/ inch

40 lines / cm

103 lines / inch

50 lines / cm

132 lines / inch

70 lines / cm

178 lines / inch

80 lines / cm

215 lines / inch

Poor Results

Not Recommended

Poor Results

Not Recommended

Poor Results

Not Recommended

Better Results

Recommended for Use

Better Results

Recommended for Use

Better Results

Recommended for Use

Better Results

Recommended for Use

Better Results

Recommended for Use

Good Results

Acceptable for Use

Good Results

Acceptable for Use

Good Results

Acceptable for Use

Poor Results

Not Recommended

Best Results

Recommended for Use

Best Results

Recommended for Use

Best Results

Recommended for Use

Best Results

Recommended for Use

Poor Results

Not Recommended

Poor Results

Not Recommended

Poor Results

Not Recommended

Poor Results

Not Recommended

Poor Results

Not Recommended

Poor Results

Not Recommended

Poor Results

Not Recommended

Good Results

Acceptable for Use

Tube / collimator angle

- 20 degrees

Grid Angle -5 degrees

Grid

Incorrect Grid Alignment = Poor Image Quality

Angle of tube collimator is not the same as the grid/panel Tube/collimator is not parallel to the grid

• Most “portable” stationary grids are the same size as the cassette being used

• Grid lines are often oriented along the long dimension

• May also be oriented along the short dimension (usually called “decubitus” grids)

• Grids in tables and upright buckys are usually 17 – 20 inch “square” grids

Typical grid line orientation “Decubitus” grid orientationSquare table or upright

bucky grid

Tube Collimator and Grid are NOT Parallel (6:1)

High Scatter Poor Lung and Spine Detail

Grid

Proper Grid Alignment = Good Image Quality

Angle of tube the same as the grid/panel

Tube collimator parallel to the grid

Tube Collimator and Grid ARE Parallel (6:1)

Low Scatter Improved Lung and Spine Detail

Tube Collimator and Grid are not parallel

High Scatter Poor Lung and Spine Detail

“Decubitus” grid orientation

Angled positioning but Good Lung and Spine Detail

Tube / collimator angle

- 20 degrees

Grid Angle -5 degrees

Grid

Incorrect Alignment = Poor Image Quality

Angle of tube collimator is not the same as the grid/panel Tube collimator is not parallel to Grid

Tube / collimator angle

- 20 degrees

Grid Angle -5 degrees

Grid

Angled Tube = Good Image Quality

Angle of tube collimator is off but it is centered A “Decubitus Grid” was used

“Decubitus” grid orientation

Grid Positioning and Orientation

• Most “portable” stationary grids are the same size as the panel being used

• Grid lines are often oriented along the long dimension

• May also be oriented along the short dimension (usually called “decubitus” grids) these good for landscape chests

• Grids in tables and upright buckys are usually 17 – 20 inch “square” grids

Typical grid line orientation“Decubitus” grid orientation Square table or upright

bucky grid

“Non-Grid”, Scatter Suppression Software

• Product Types • Agfa MUSICA Chest +

• Fuji Virtual Grid

• Philips Skyflow

• Other ?

• How does it work ? • Reduces the need for a grid using advanced image processing

• Scatter radiation is low frequency in an image

• Scatter Suppression Software reduces the visualization of low frequencies while enhancing medium to high frequencies

Low Frequency Scatter Contribution

Scatter Suppression Software extracts low frequency scatter

information while enhancing relevant clinic information

Insert Non Grid Beside Chest Image

GenRad Soft

Non Grid Chest with Standard Processing

Low Frequency Scatter Contribution

Scatter Suppression Software extracts low frequency scatter

information while enhancing relevant clinic information

Insert Non Grid Beside Chest Image

GenRad Soft

Non Grid Chest with Scatter Suppression

Software

Scatter Suppression Software can improve lung field detail without

the use of an anti-scatter grid

Chest Phantom with 6:1 Grid

MUSICA 2 GenRad Soft Chest Processing

100 kVp 3.2 mAs

Chest Phantom no Grid

MUSICA 3 Chest + Processing

100 kVp 1.6 mAs

flipped for comparison

* When compared to non grid exposures , grid exposures may require up to 50% higher exposure depending on conditions

Scatter Suppression Software may also be used with a Grid to give the

best overall results but requires proper positioning at a higher dose*

Chest Phantom with 6:1 Grid

MUSICA 2 GenRad Soft Chest Processing

100 kVp 3.2 mAs

Chest Phantom with 6:1 Grid

MUSICA 3 Chest Processing

100 kVp 3.2 mAsflipped for comparison

MUSICA 2 GenRad Soft Processing

Non Grid

Clinical Examples

MUSICA 3 + Chest Processing

Non Grid

Can Image Processing Software Eliminate the Need for a Grid with DR?

• It Depends• On the application

• Mobile or In room

• On the Patient Size• Pediatric, Normal, Obese

• On the workflow requirements• Grid and Panel Weight

• On the examination criteria • Image Quality

• Dose

• “Non-grid” image processing is another option in the toolbox that should be considered and used when appropriate to improve image quality and reduce dose.

Managing Exposure and Dose to Optimize Image Quality

5 mAs 10 mAs 20 mAs

1/2 ref dose ref dose 2x ref dose

Dynamic Range: Film

Dynamic Range: CR

2.5 mAs 10 mAs 160 mAs

Dynamic Range: DR

1/4 ref dose ref dose 4x ref dose

2.5 mAs 10 mAs 40 mAs

Managing Exposure and Dose to Optimize Image Quality

70 kVp 160 mAs 70 kVp 160 mAs

CR DR

• Better image quality at lower dose • DR images can be higher in contrast and sharpness

• DR panels (CsI) require less exposure to achieve equal to or better image quality

• Significantly less Exposure Latitude with DR• CR Exposure Range -4x to +16 x mAs

• DR Exposure Range ± 4x mAs

• Image Saturation can occur with DR !!!! Data is not recoverable !!!

• With DR Accurate exposure is key (similar to film)

CR vs DR Image Quality and Dose

To maintain proper exposure

One Uniform Standard required for measuring exposure

!!!!Exposure in

µGyFuji Canon Agfa Carestream

IEC

Exposure

Index *

2.5 710 30 1.96 1451 250

5 355 60 2.26 1751 500

10 177 120 2.56 2051 1000

20 89 240 2.86 2351 2000

*Flatfield RQA5 beam quality

Managing Exposure and Dose to Optimize Image Quality

• A standard way to measure the exposure to a digital detector • Developed by IEC - International Electrotechnical Commission

• IEC 62494-1 “Exposure index of digital X-ray imaging systems”

• Standard Calibration Condition – RQA-5

• Designed to monitor exposure consistency within an exam type

• Consists of three values • Exposure Index – EI

• Target Exposure Index - TEI

• Deviation Index - DI

• In a perfect situation the DI would be zero (0)

A Better Approach; Exposure Index (IEC 62494-1)

DI =10 * Log TEI[ EI_ ] 500500_[DI =10 * Log ] = 0

Actual

Exposure

Index

Target

Exposure

Index

Deviation

Index

Exposure

Factor

%

Change

1300 500 4 2.6 160%

1000 500 3 2 100%

800 500 2 1.6 60%

630 500 1 1.26 26%

500 500 0 1 0%

400 500 -1 0.8 -20%

300 500 -2 0.6 -40%

250 500 -3 0.5 -50%

200 500 -4 0.4 -60%

Target Exposure Index and Deviation Index

“On Target” Exposure

EI = TEI

DI = 0

60 kVp 1 mAs

. Exposure Monitoring Software

1. Color Coded Exposure Bar

2. Exposure Index Performance Table

60 kVp 1.75 mAs

Green

within range

Overexposed within range Less

than + or - 2X exposure

Less than + or – 3.0 DI

The dose bar is an indication to see how far the applied Exposure Index

(Detector exposure) is away from the reference exposure (Target Exposure

Index) identified for this exposure.

Overexposed outside of range

Greater than 2X exposure

Greater than 3.0 DI

The bar gives a relative indication of the exposure to the plate and it is a good

measure of the variation of exposure to the plate within a given exam type, but it

is not an absolute dose measurement value.

60 kVp 2.88 mAs

Yellow Slightly

Overexposed

60 kVp 4.75 mAs

Overexposed far

outside of range.

Greater than 4X exposure

Greater than 6.0 DI

Red Significantly

Overexposed

Underexposed far

outside of range.

Less than 1/4X exposure

Less than - 6.0 DI

60 kVp 0.23 mAs

Red Significantly

Underexposed

Automatic ROI Selection

Deviation Index in range

EI 264

DI -0.6

TEI 300

Region of Interest ROI Selection Affects Exposure Index

Manual ROI Selection of appropriate

region for examination

Deviation Index in range

EI 375

DI 1.0

TEI 300

Region of Interest ROI Selection Affects Exposure Index

Manual ROI Selection of incorrect

region for examination

Deviation Index out of range

EI 64DI -6.7

TEI 300

Region of Interest ROI Selection Affects Exposure Index

Region of Interest ROI Selection Affects Exposure Index

Manual ROI Selection of

incorrect region for examination

ROI outside of clinical region

Deviation Index out of range

EI 1924

DI 8.1

TEI 300

Ongoing Exposure - Trend Analysis

Dose Monitoring

DICOM Mapping of EI, TEI, DI

The DICOM committee defined tags:

• EI : (0018,1411)

• TEI : (0018,1412)

• DI : (0018,1413)

• “DAP” Dose Area Product: (0018,115E)

Proper X-Ray Collimation for

region of interest

If the X-ray collimation is done correctly the area of

interest should be detected automatically and minimal

manual cropping should be required

Proper X-Ray Collimation is Key to Dose and Image Quality with DR

Proper Automatic image Collimation

(black borders) for region of interest

No Manual Collimation Required

Collimation Issues

Original Plate size 24 x 30 cm

X-Ray Collimated area size 20 x 28 cm (77%)

Region of interest size only 16 x 15 cm (33%)

Automatic collimation with black borders applied based on X-Ray collimation

The technologist does additional manual

collimation (cropping) at the workstation

The Radiologist may be unaware of the actual

patient exposure – quantity and anatomically

If the X-ray collimation is correct, minimal

manual cropping should need to be done

The actual region of interest size is 16 x 15 cm (33%)

Repeat Rates are Changing with DR

1. Panel Technology and Phosphor Type - Can reduce dose 50% or more

2. Proper Image Processing - Can significantly reduce dose and improve image quality

3. Proper Grid selection and position – Will greatly influence image quality

a. Grid lines per inch

b. Grid position and distance

c. Non Grid Scatter Suppression software - Is an option to improve workflow and dose

4. Repeat Rates with DR are increasing

a. Repeats for positioning are increasing because it is so easy to repeat

CR to DR – Optimizing Image Quality and Dose

5. Proper Technique Selection is more important than ever

a. DR Dynamic Range is much less than CR

b. DR images can be saturated (image recovery is not possible)

c. The IEC Exposure Index can be used to monitor and control exposure

6. X-ray Collimation

a. Influences scatter, image processing and overall image quality

b. Improper Electronic collimation or masking reduces image quality and increasesdose

CR to DR – Optimizing Image Quality and Dose