Image quality, digital technology and radiation protection

Kenneth L. Bontrager

John P. Lampignano

Image Quality, Digital Technology, Image Quality, Digital Technology, and Radiation Protectionand Radiation Protection

Image Quality FactorsImage Quality Factors——Film-Screen Film-Screen SystemsSystems

1. Density1. Density

2. Contrast2. Contrast

3. Resolution3. Resolution

4. Distortion4. Distortion

Exposure Factors (Technique)Exposure Factors (Technique)

1.1. Kilovoltage (kV)Kilovoltage (kV)

2.2. Milliamperage Milliamperage (mA)(mA)

3.3. Exposure time Exposure time

(seconds)(seconds)

–– mAs mAs (milliampere- (milliampere- seconds)seconds)

DensityDensity

Amount of blacknessAmount of blackness

Controlling factors:Controlling factors:

–– mAs (mA × time)mAs (mA × time)

–– kVkV

Influencing factors:Influencing factors:

–– Source image receptor distance (SID)Source image receptor distance (SID)

–– Screen and IR speedScreen and IR speed

Density Change RuleDensity Change Rule

15% change in kV15% change in kV

(similar to doubling mAs)(similar to doubling mAs)

Examples:Examples:

80 kV 80 kV .15 = 12 kV .15 = 12 kV

60 kV 60 kV .15 = 9 kV .15 = 9 kV

Density Change RulesDensity Change Rules

Density adjustment rule:Density adjustment rule: 25% to 30% increase in mAs (minimum change)25% to 30% increase in mAs (minimum change)Density repeat rule:Density repeat rule: Doubling mAs (to correct density on repeats)Doubling mAs (to correct density on repeats)

Anode Heel EffectAnode Heel Effect

More intense under More intense under cathodecathode

Increase withIncrease with

–– Small focal spotSmall focal spot

–– Shorter SIDShorter SID

–– Larger IR sizeLarger IR size ApplicationApplication

–– Thicker parts at Thicker parts at cathodecathode

Compensating Filters

Compensating filters filter out a portion of the primary beam toward the thin or less dense part of the body that is being imaged.

Types of compensating filters include the following: Wedge filter Trough Boomerang

Compensating Filters

Wedge filter Boomerang filter

Benefits of Compensating Filter

Radiographic ContrastRadiographic Contrast

Differences (variation) Differences (variation) in densityin density

Controlling factorControlling factor——kVkV

High vs. Low ContrastHigh vs. Low Contrast High contrast:High contrast:

–– Short scaleShort scale

–– 50 kV (800 mAs)50 kV (800 mAs)

Low contrast:Low contrast:

–– Long scaleLong scale

–– 110 kV (20 mAs)110 kV (20 mAs)

Off-Center Grid Cutoff

Off-Level Grid Cutoff

Off-Focus Grid Cutoff

Upside-Down Grid Cutoff

Resolution (Definition)Resolution (Definition)

Recorded sharpness of structuresRecorded sharpness of structures

Lack of definition is blur or unsharpness.Lack of definition is blur or unsharpness.

Motion is greatest deterrent (two types).Motion is greatest deterrent (two types).

MotionMotion

Voluntary motion (breathing)Voluntary motion (breathing) Involuntary motion (peristalsis) Involuntary motion (peristalsis)

Image Quality Summary ChartImage Quality Summary Chart

1. Small focal spot1. Small focal spot——Use small focal spot Use small focal spot whenever possible to improve detail.whenever possible to improve detail.

2. Shorter exposure time2. Shorter exposure time——Use shortest exposure Use shortest exposure time possible to control voluntary and time possible to control voluntary and involuntary motion.involuntary motion.

3. Film-screen speed3. Film-screen speed——Use faster film-screen Use faster film-screen speed to control voluntary and involuntary speed to control voluntary and involuntary motion.motion.

4. SID4. SID——Use longer SID to improve detail.Use longer SID to improve detail.

5. OID5. OID——Use shorter OID to improve detail.Use shorter OID to improve detail.

Focal Spot SizeFocal Spot Size

Distortion (Magnification)Distortion (Magnification)

Misrepresentation Misrepresentation of object size or of object size or shapeshape

X-ray beam X-ray beam divergencedivergence

DistortionDistortion

Controlling factorsControlling factors SID (source image SID (source image

receptor distance)receptor distance) OIDOID Object IR alignmentObject IR alignment CR alignmentCR alignment

Controlling factorsControlling factors SIDSID OID (object image OID (object image

receptor distance)receptor distance)

Controlling factorsControlling factors SIDSID OIDOID Object IR Object IR

alignmentalignment

Digits parallelDigits parallel——joint openjoint open Digits not parallelDigits not parallel——joints not openjoints not open

Controlling factorsControlling factors SIDSID OIDOID Object IR Object IR

alignmentalignment CR alignmentCR alignment

CR Alignment

CR parallel to joint CR not parallel to joint

Quiz Me

Which of the following is NOT a quality factor for film-based radiography?

A. Density

B. Focal spot size

C. Contrast

D. Distortion

E. Resolution

Quiz Me

The primary controlling factor for density is

A. mAs

C. SID

D. OID

Quiz Me

When the anode heel rule is applied, the thicker aspect of the anatomy should be placed under the cathode end of the x-ray tube.

A. True

B. False

Quiz Me

Which of the following is not a type of compensating filter?

A. Wedge

B. Boomerang

C. Slotted

D. Trough

Quiz Me

What is the primary controlling factor for radiographic contrast?

A. mAs

C. SID

D. Focal spot size

Quiz Me

What type of grid cutoff will occur if a shorter SID is used than what is specified for a particular grid?

A. Off-center

B. Off-level

C. Off-focus

D. Off-distance

Image Quality in Digital RadiographyImage Quality in Digital Radiography

Processing digital image Exposure controls—kV, mAs, and time

Image Quality in Digital RadiographyImage Quality in Digital Radiography

BrightnessBrightness ContrastContrast ResolutionResolution DistortionDistortion Exposure indexExposure index NoiseNoise

BrightnessBrightness

AP shoulder—high brightness AP shoulder—less brightness

Intensity of light representing individual pixels in image

ContrastContrastDifferences in brightness Differences in brightness between light and dark between light and dark areas of imageareas of image

AP shoulder—higher contrast AP shoulder—lower contrast

ResolutionResolution

Controlling factors:Controlling factors: Acquisition pixel sizeAcquisition pixel size

– – Inherent to the digital imaging detectorInherent to the digital imaging detector Display matrixDisplay matrix

– – DDependent on capabilities of the display ependent on capabilities of the display monitormonitor

Recorded Sharpness of Structures on Image

Controlling factors:Controlling factors: SIDSID OIDOID CR alignmentCR alignment

Misrepresentation of Object Size or Shape

Exposure Index Exposure Index (referred to by some manufacturers as sensitivity (referred to by some manufacturers as sensitivity

“S” numbers)“S” numbers)

A numeric value that is representative of the A numeric value that is representative of the exposure the image receptor receivedexposure the image receptor received May be inversely or directly proportional to May be inversely or directly proportional to radiation striking the image receptorradiation striking the image receptor Key in verifying optimal digital image is obtained Key in verifying optimal digital image is obtained with least dose to patientwith least dose to patient

Exposure IndexExposure Index

Dependent on the intensity of the radiation Dependent on the intensity of the radiation striking the detector, which is the effect ofstriking the detector, which is the effect of

–– mAsmAs

–– kVkV

–– Total detector area irradiatedTotal detector area irradiated

–– Objects exposed (air, metal implants, Objects exposed (air, metal implants, patient anatomy)patient anatomy)

Low exposure index (high “S” number)—Underexposed

Acceptable exposure index

High exposure index (low “S” number) Acceptable exposure index

NoiseNoise

Random disturbance that obscures image Random disturbance that obscures image clarityclarity

High signal-to-noise ratio (SNR) is High signal-to-noise ratio (SNR) is desirable.desirable.

Low signal-to-noise ratio (SNR) is Low signal-to-noise ratio (SNR) is undesirable.undesirable.

Acceptable SNR (good image quality)

Low SNR (poor image quality)

Post-processingPost-processing

Changing or enhancing the electronic image to Changing or enhancing the electronic image to improve diagnostic qualityimprove diagnostic quality Algorithms applied to improve diagnostic Algorithms applied to improve diagnostic quality of imagequality of image Post-processing cannot improve low SNR Post-processing cannot improve low SNR image.image.

Post-processing OptionsPost-processing Options

WindowingWindowing SmoothingSmoothing MagnificationMagnification Edge enhancementEdge enhancement SubtractionSubtraction Image reversalImage reversal AnnotationAnnotation

Chest without any post-processing Chest with image reversal

Nonsubtracted AP shoulder Subtracted and magnified shoulder angiogram

Quiz Me

Highly complex mathematical formulas are called

A. Binary codes

B. Exposure indices

C. Equalization filters

D. Algorithms

Quiz Me

The intensity of light that represents the individual pixels in the digital image on the monitor is the definition for

A. Brightness

B. Contrast

C. Density

D. Noise

Quiz Me

Random disturbance that obscures or reduces clarity is the definition for

A. Noise

B. Resolution

C. SNR

D. Distortion

Quiz Me

A low SNR digital image can be enhanced through post-processing techniques.

A. True

B. False

Applications of Digital TechnologyApplications of Digital Technology

Computed tomography (CT), one of the first Computed tomography (CT), one of the first applications of computers in radiographyapplications of computers in radiography

Computed Radiography (CR)Computed Radiography (CR)

Image Plate Reader/Processor and Image Plate Reader/Processor and WorkstationWorkstation

Why is it important to collimate and use lead Why is it important to collimate and use lead blockers with CR?blockers with CR?

Direct Digital Radiography (DR)Direct Digital Radiography (DR)

DR Chest Imaging SystemDR Chest Imaging System

DR Mammography UnitDR Mammography Unit

Steps of Image Production ComparisonSteps of Image Production Comparison

Film-screen Computed radiography (CR)

Direct digital radiography (DR)

PACS NetworkPACS Network

Provide Definitions for the Following Provide Definitions for the Following Digital-Related Acronyms:Digital-Related Acronyms:

PACSPACS RISRIS HISHIS HL7HL7 DICOMDICOM IPIP IRIR SNRSNR

ReviewReview

What is the difference between “window level” What is the difference between “window level” and “window width”?and “window width”?

What is the difference between “density” and What is the difference between “density” and “brightness”?“brightness”?

Define the term “noise.”Define the term “noise.”

Radiation ProtectionRadiation Protection

PatientPatient Fellow workersFellow workers SelfSelf

Units of RadiationUnits of Radiation

Roentgen (R) Roentgen (R)

used for measurements in airused for measurements in air

Rad (radiation absorbed dose) Rad (radiation absorbed dose)

used for patient dose purposesused for patient dose purposes

Rem (radiation equivalent man) Rem (radiation equivalent man)

used for worker protection purposesused for worker protection purposes

Units of RadiationUnits of Radiation(traditional and SI units)(traditional and SI units)

TraditionalTraditional SI UnitsSI Units

RoentgenRoentgen Coulombs/kg of airCoulombs/kg of air

RadRad Gray (Gy)Gray (Gy)

RemRem Sievert (Sv)Sievert (Sv)

Dose-Limiting RecommendationsDose-Limiting RecommendationsReplaced MPD (maximum permissible dose) in 1994Replaced MPD (maximum permissible dose) in 1994

Occupationally exposed workersOccupationally exposed workers

Annual: 5 rem (50 mSv) per year (ED)Annual: 5 rem (50 mSv) per year (ED)

Cumulative: 1 rem (10 mSv) times years of Cumulative: 1 rem (10 mSv) times years of ageage

General populationGeneral population

–– .1 rem (1 mSv) per year.1 rem (1 mSv) per year

Pregnant TechnologistsPregnant Technologists

What is the dose limit for a pregnant What is the dose limit for a pregnant technologist per month?technologist per month?

What is it for the entire gestational period?What is it for the entire gestational period?

Personnel MonitoringPersonnel Monitoring Film badgeFilm badge TLD TLD

(thermoluminescent (thermoluminescent dosimeter)dosimeter)

OSL (optically OSL (optically stimulated stimulated luminescence) luminescence)

*Worn at waist or *Worn at waist or chest level chest level or or on collar during on collar during fluoroscopyfluoroscopy

*Consult RSO.*Consult RSO.

ALARA PrinciplesALARA Principles

1.1. Always wear a Always wear a personnel monitor.personnel monitor.

2.2. Radiology personnel Radiology personnel should not restrain should not restrain patients.patients.

3.3. Sound radiographic Sound radiographic exposure factorsexposure factors

4.4. Cardinal rules of Cardinal rules of radiation protection:radiation protection:–– TimeTime–– DistanceDistance–– ShieldingShielding Mobile fluoroscopy or C-arm

Fluoroscopy exposure patterns (without tower drape shields in place)Fluoroscopy exposure patterns (without tower drape shields in place)

Worker Protection During FluoroscopyWorker Protection During Fluoroscopy

Fluoroscopy exposure patterns (with tower drape shields in place)

Fluoroscopy Safety PracticesFluoroscopy Safety Practices

Bucky slot coverBucky slot cover Lead drapeLead drape .5 mm lead apron.5 mm lead apron Exposure limit: Exposure limit:

10 R/min10 R/min

Thyroid shield with protective apron

Patient ProtectionPatient Protection

1.1. Minimum repeat radiographsMinimum repeat radiographs–– Clear instructionsClear instructions–– Positioning and exposure factorsPositioning and exposure factors

Radiation Protection PracticesRadiation Protection Practices

1.1. Minimum repeat radiographsMinimum repeat radiographs

2.2. Correct filtrationCorrect filtration

–– Inherent and addedInherent and added

–– 2.5 mm Al total2.5 mm Al total

Close four-sided collimation: One of the best Close four-sided collimation: One of the best ways of reducing patient exposure! ways of reducing patient exposure! (Remember divergence of x-ray beam.)(Remember divergence of x-ray beam.)

Radiation Protection PracticesRadiation Protection Practices

1.1. Minimum repeat Minimum repeat radiographsradiographs

2.2. Correct filtrationCorrect filtration3.3. Accurate collimationAccurate collimation

Types of collimatorsTypes of collimators

–– Manual typeManual type–– Positive-beam limitation Positive-beam limitation

(PBL)(PBL)

2.2. Correct filtrationCorrect filtration

3.3. Accurate collimationAccurate collimation

4.4. Specific area shieldingSpecific area shielding

–– Shadow shieldsShadow shields

–– Contact shieldsContact shields

Vinyl-covered lead shield

Gonadal contact shieldsGonadal contact shields

–– 1 mm lead equivalent1 mm lead equivalent

–– Reduces dose 50% to Reduces dose 50% to 90%90%

2.2. Correct filtrationCorrect filtration3.3. Accurate collimationAccurate collimation4.4. Specific area shieldingSpecific area shielding5.5. Protection for Protection for

pregnanciespregnancies

Quiz Me

The SI unit equivalent for Rad is

A. Coulombs/kg of air

B. Gray

C. Sievert

D. Curie

Quiz Me

What is the annual dose limit for a technologist per year?

A. 5 mSv

B. 15 mSv

C. 50 mSv

D. 500 mSv

Quiz Me

What minimum lead thickness or equivalency must a protective apron possess when worn for a fluoroscopy procedure?

A. .5 mm Pb/Eq

B. 1.0 mm Pb/Eq

C. 1.5 mm Pb/Eq

D. 2.5 mm Pb/Eq

Quiz Me

What is the most effective way to reduce patient dose?

A. Use of high kV

B. Increase in added filtration in x-ray tube

C. Use of gonadal shielding

D. Close four-sided collimation

Image Quality, Digital Technology, and Image Quality, Digital Technology, and Radiation ProtectionRadiation Protection

-- The End The End --

Chapter 2

Image quality, digital technology and radiation protection

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