3/31/2011...3/31/2011 1 Teaching Radiographic Technique in a Digital Imaging Paradigm Dawn Couch Moore, M.M.Sc., RT(R) Assistant Professor and Director Emory University Medical Imaging

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Teaching Radiographic Technique

in a

Digital Imaging Paradigm

Dawn Couch Moore, M.M.Sc., RT(R)

Assistant Professor and Director

Emory University

Medical Imaging Program

Objectives

1. Discuss the historical development of digital imaging.

2. Review digital image receptor characteristics.

3. Identify methodologies suitable for teaching radiographic technique with digital imaging systems.

Emory University

• Medical Imaging Program

– BMSc degree (2005)

– 1 + 3 design

• 8 semesters

– Major

• Diagnostic Radiography

– Minor Tracks

• CT, MRI, IR, Ed., Adm.

Historical Development

• Film

– Glass Base (1895)

– Cellulose nitrate base (1917)

– Cellulose triacetate (1923)

– Polyester (1960)

• Screens

– Zinc cadmium sulfide

– Calcium tungstate

– Rare earth phosphors (1974)

Carlton & Adler, 2006


• Image Intensifier (1948)

• CT (1973)

• MRI (1973)



• Computed Radiography

(CR)

– 1984

– Photostimulable

Phosphor (PSP)Carlton & Adler, 2006

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• Direct Radiography (DR)

– 1996

– Direct Detectors

– Indirect Detectors


Instructional Methodologies

• Traditional

– Lecture-based

• Active Learning

– Group Activities

– Case-based

– Problem-based

Instructional Methodologies

• Lecture

– Teacher centered

• Active learning

– Learner centered

Image Acquisition

(Conventional FS Radiography)

• X-ray source

• Film/ screen combination

• Processor

• Fileroom

• Reading room

Bushong, 2004

Film-Screen Image Quality

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Cummings, 2009

Film-Screen Image Evaluation

• Density

– Too light → repeat

– Too dark → hot light?

• Pertinent anatomy demonstrated

• mAs controls image density

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• Contrast

– Adequate penetration

– Acceptable grayscale

• kVp controls image contrast

60 kVp

100 kVp



• Recorded detail

– Sharp edges

– Boney trabeculae visible

– Motion



• Distortion

– Size

– Shape

– Understand „normal‟


Teaching Methodologies

• What teaching methodologies did you use with

film-screen systems?

Digital Radiography

Digital Radiography

CR-

Photostimulable

Phosphor

(Cassette-based/

Phosphor-based)

Direct DR-

a-Se/ TFT

(Cassette-less)

Indirect DR-

CsI, a-Si/ TFT

(Cassette-less)

Image Acquisition(Cassette/Phosphor-based Systems)

• X-ray source

• Detector

• Plate Reader

• Monitor

• Reading room(PACS)

http://www.medical.philips.com/main/products/xray/assets/images/rad/digitalradiography/rad_pcrintrophoto.jpg

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Cassette/Phosphor-based Image

Acquisition

Three components

– Cassette

• Holds plate

– Photostimulable phosphor imaging plate

• Latent image formation

– Plate reader

• Manifestation of the latent image

Imaging Plate

• Photostimulable

phosphor

– PSP

• Imaging plate

– IPCarlton & Adler, 2006

Imaging Plate

• Photostimulable

Phosphors

– Materials that store

information when

exposed to one

stimulus (x-rays) and

release the information

when exposed to

another (laser light)

Imaging Plate

• Phosphor K-edge attenuation

– Best between 35 – 50 keV

• 35 keV: average energy of 80 kVp beam

– More exposure needed if applied kVp is

outside of this range

* More sensitive to scatter than FS systems

Image Acquisition

(Cassette-less System)

• X-ray source

• Detector

• Monitor

• Reading room (PACS)

Bushong, 2006

Image Acquisition

(Cassette-less System)

• Types of Sensors (Image Receptors)

– Indirect Image Receptors

• Flat Panel

• CCD

– Direct Image Receptors Carlton & Adler, 2006

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DR Image Receptor Comparison

• Indirect IR

– X-rays →Light (phosphor) →Electrical Charge

• Direct IR

– X-rays → Electrical Charge (photoconductor)

Teaching Ideas

• Lecture

• Written Assignment

– Compare the structure of a FS receptor to a

CR receptor.

– Describe the steps in latent image production

using FS, a PSP and a DR receptor.

Teaching Ideas

• Labs

1. Expose a conventional screen and a PSP in a dark

radiographic room. Describe the results.

2. Expose a medium-sized anatomical phantom (knee)

at a low kVp, low mAs level (50 kVp; 5 mAs) using a

PSP. Take additional exposures, increasing the

mAs each time and monitoring the exposure

indicator. Evaluate the required mAs to achieve an

acceptable EI. Repeat at 60 and 70 kVp levels.

Teaching Ideas

• Case-based Learning

– Provide students with a FS cassette and a CR

cassette

– As a group, the students should explore the IR

systems. This would require:

• Acquisition of critical knowledge

• Problem-solving proficiency

• Self-directed learning strategies

• Team participation skills

Digital Image Quality

• Goals remain the same as FS

– Provide optimal diagnostic information

– Demonstrate pertinent anatomy

– Optimal brightness (density)

– Optimal contrast

– Optimal recorded detail

– Acceptable distortion

29 30

Cummings, 2009

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ARRT, 2011


• Dynamic Range

– The exposure range

over which the system

can respond

– Digital receptors have

a much wider dynamic

range than FS Frank & Ballinger,2003

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• Dynamic Range and Latitude

– Latitude: The range of exposures that allows a quality image to be captured.

– Because of digital image processing there is a false impression of wide latitude

• Film screen: +50% to -30%*

• Cassette-based (CR): + 200% to -50%*

• Will give similar brightness, but…33


www.sprawls.org


• > 50% underexposed

– Noisy, mottled image

• 3X overexposure

– Contrast degradation (↑ scatter)

– ALARA violation

– Potential loss of adjustment at PACS

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Cassette-based Exposure

Indicators

• Fuji, Philips, Konica

– S number (Sensitivity number)

• 1.0 mR S=200

• 10 mR S=20

• 0.1 mR S=2000

– Inverse, Linear relationship

• Carestream (Kodak)

– EI (Exposure Index)

• 1.0 mR EI=2000

• 2.0 mR EI=2300

• 0.5 mR EI-1700

– Direct, Logrithmic relationship

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Teaching Ideas

• Lecture

• Written Assignments

• Lab

• Problem-based Learning

Digital Image Processing

1. Latent Image Creation (@ receptor)

2. Image Readout (to computer)

3. Image Processing

4. Advanced Post-processing

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39

www.sprawls.org


• Exam selection

determines:

– Automatic

Rescaling

• Brightness

(Density)

– Look-up Tables

• Contrast

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www.sprawls.org


• Automatic Rescaling

– Mapping grayscale to “values of interest”

• Provides images that have uniform display

brightness over wide exposure range

– Controls Image Brightness (density)

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Automatic Rescaling

4 mAs 8 mAs 16 mAs


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Image ProcessingNot Possible with Conventional Imaging

4 mAs 8 mAs 16 mAs

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• Contrast Enhancement

– Look-up Tables (LUT)

– Windowing

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www.sprawls.org

Look-up Table

• Converts the original

pixel value to another

value to enhance

image contrast

• Look-up Tables are

specific to exam type

– Chest, Abdomen, etc.

45

www.sprawls.org

Look-up Table

46www.sprawls.org

Look-up Table

47www.sprawls.org

Look-up Table

48www.sprawls.org

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• Image Brightness (Density)

– Controlled by Automatic Rescaling

– Not by mAs

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2 mAs 10 mAs 20 mAs

Image Source:James Barba MA, R.T.(R)

Clinical Assistant ProfessorDivision of Radiologic Science

Department of Allied Health SciencesUNC-Chapel Hill School of Medicine


• Image Contrast

– Controlled by Look-up Table

– Not by kVp

75 kVp 95 kVp 130 kVp

Image Source:James Barba MA, R.T.(R)

Clinical Assistant ProfessorDivision of Radiologic Science

Department of Allied Health SciencesUNC-Chapel Hill School of Medicine

Teaching Ideas

• Lecture

• Written Assignments

• Lab

• Problem-based Learning

Technical Considerations

• Digital receptor systems are exposure driven

– Provide optimal exposure to the image receptor

• High SNR

• Optimal exposure (kVp and mAs)

– Maximize the signal

• Minimize the „noise‟

– Control scatter

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• kVp and mAs selection

• Anatomical part determines selection

• Use higher kVp than used for film-screen (+15-20)

– Decreased mAs results in lower patient dose

– Captures more anatomical data

High subject

contrast, high kVp

Moderate subject

contrast, moderate

kVp

Low subject

contrast, low kVp

Chest x-rays Adult extremities Pediatric extremities

Contrast studies Abdominal studies

Prosthetic devices Pelvis and hip

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• To maximize resolution and minimize distortion:

• Use smallest focal spot size practical

• Follow accepted standards for positioning,

centering, etc.

• Use largest practical SID

• Use smallest practical OID

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• Optimal kVp range for adults: 60-120

• >120 kVp ~ decreased absorption efficiency

• Optimal kVp range for peds (<100 lbs.): 50-90

• Fuji CR do not use < 55 kVp

• Use standard rules (15%, 30%, etc.) to adjust technique

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Image A = Correct exposureImage B ~ 60% Underexposed - objectionable mottle

A B

Image Source: Lauren Noble, Ed.D., R.T.(R)Clinical Assistant ProfessorDivision of Radiologic ScienceDepartment of Allied Health SciencesUNC Chapel Hill School of Medicine

• ↑ kVp and ↓mAs can result in:

• Low signal (mottle)

• Increased scatter production (noise)

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Technical Considerations• Grid selection

– Parallel FS imaging

• Critical for scatter (noise) control

• Increased grid ratio → increased

mAs

• Avoid “moiré” effect

– generally 150 LPI or higher

Image Source:James Barba MA, R.T.(R)Clinical Assistant ProfessorDivision of Radiologic ScienceDepartment of Allied Health SciencesUNC-Chapel Hill School of Medicine

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• Collimation

• Collimation recognition critical in CR

– Symmetrical

– Sharp, well-defined borders

• Cassette-based systems use automatic exposure field edge

detection (eliminates signals from outside collimated field)

• Scatter and off-focus radiation contribute to rescaling errors

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Rescaling error due to improper collimationResults in faulty application of Pattern Recognizer

for Irradiated Exposure Field (PRIEF)

Proper collimation, proper rescaling


• Collimation

• Cassette/ phosphor based systems

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• Collimation (cassette/phosphor based systems)

Collimation “OK” Collimation NOT “OK”Image Source:James Barba MA, R.T.(R)Clinical Assistant ProfessorDivision of Radiologic ScienceDepartment of Allied Health SciencesUNC-Chapel Hill School of Medicine

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• Centering

Non-centered single fieldSingle collimation margin

Non-centered, singlesided collimationHistogram includedthe low intensity off-focusradiation


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• IR size (Cassette/ phosphor based systems)

• Use smallest practical IR size

• Use consistent orientation of IR

• Ensures consistent and comparable display


Navicular on 18 by 24

Navicular on 24 by 30

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Image Evaluation

• Similar to film-screen

evaluation

• Check for:

– Proper positioning

– Proper centering

– Proper collimation

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Image Evaluation

• To evaluate for proper technical factors:

• Check for penetration of the part

• Brightness

• Contrast

• Exposure index

• Noise


Teaching Ideas

• Integrate concepts throughout the curriculum

– Introduction Course

– Radiation Safety Course

– Physics and Equipment Courses

– Radiographic Technique Courses

– Procedures Courses

– Image Processing Course

– Clinical Education Courses

Teaching Ideas

• Teaching Methodologies

– Concepts

• Lecture

• Independent Research

• Discussion

– Technique and Equipment

• Lab Assignments

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Teaching Ideas

• Teaching Methodologies

– Clinical Education Courses

• Practical Experience

• Checklists

• Competency Evaluations

• Image Evaluation

– S #; EI; LGM

– Mottle evaluation

– Brightness/ contrast evaluation

– Cropping vs collimation

Contact Information

Dawn Couch Moore, M.M.Sc, RT(R)

Emory University

PO Box 25901

Atlanta, GA 30322

404-727-3200

[email protected]

Documents

3/31/2011...3/31/2011 1 Teaching Radiographic Technique in a Digital Imaging Paradigm Dawn Couch Moore, M.M.Sc., RT(R) Assistant Professor and Director Emory University Medical Imaging