image quality in cardiac angiography

International Atomic Energy AgencyIAEA

Image Quality in Cardiac Image Quality in Cardiac AngiographyAngiography

L 8

Lecture 8: Image Quality in Cardiac Angiography 2Radiation Protection in Cardiology IAEAIAEA

Are these statements “True” or “False”?Are these statements “True” or “False”?

1. Image quality of coronary angiography is commonly measured objectively using well-defined objective criteria.

2. Recommended acquisition frame rate for coronary angiography in adult is 30 fps.


Educational ObjectivesEducational Objectives

1. Components of image quality

2. Determinants of cardiac angiographic image quality

3. How to assess image quality of cardiac angiographic images?

4. Some Quality Criteria for assessing cardiac angiographic images


Is this coronary angiography of good quality?Is this coronary angiography of good quality?

[ video clip]


Quality of cardiac imagesQuality of cardiac images

• Background cardiac cine-angiographic images should allow the

cardiologist to evaluate the anatomic (and sometimes functional) details which are relevant for clinical decision making

• Variables technical performance of the imaging systempatient cooperationangiographic technique


An angiography series consists of multiple still images in quick succession


Quality of each still imagecontributes to overall quality

of the whole angiography series



• Background cardiac cine-

angiographic images should allow the cardiologist to evaluate the anatomic (and sometimes functional) details which are relevant for clinical decision making



• Image (“photographic”) quality sharpness contrast noise

• “Content” foreshortening? overlap? delineate the lesion? composition enough information?

• Is this acquisition run long enough to give adequate information(“tell the story”)?

• Is the acquisition run too long?• Are there “wasted/unnecessary” frames?

[ video clip]

cine


• What do you think about this picture?

Too many extra things that make it difficult to know where emphasis should lie.

Content and composition


Lesson:

Include only the area of interest when taking photography coronary angiogram

Content and composition


3 main quality parameters for still image3 main quality parameters for still image

• Sharpness

• Contrast

• Noise

• Contrast – “to detect the object”• Sharpness / spatial resolution – “to characterize the

object”• Noise – “uneven brightness graininess of image”


Focal Point UnsharpnessFocal Point Unsharpness


Fluoroscopic pulsing X rays are produced during a small portion of the video frame time. The narrower the pulse width, the sharper the image. ( “Faster

shutter speed” in camera )


Medical Imaging is the Process of Converting Tissue Characteristics into a Visual Image (shades of gray or colour)


Imaging with X ray

• Image = “shadow”• Relies on various

degree of “lucency” or opacity

• Requires point source

• 3D object --> 2 D image (projection)


ContrastContrast

• Contrast difference

• An object within the body will be visible in an image only if it has sufficient physical contrast relative to surrounding tissue.

• Contrast of an image difference in• shades of gray• light intensities• colours


Increasing Contrast Sensitivity Increases Image Contrast and the Visibility of Objects in the Body


Contrast SensitivityContrast Sensitivity

• relates to the system's ability to translate physical object contrast into image contrast.

• characteristics of the imaging method, and the variables of the particular imaging system

Lecture 8: Image Quality in Cardiac Angiography 21Radiation Protection in Cardiology IAEAIAEAEffect of Contrast Sensitivity on Object Visibility


Lossy compression


““Lossy” compression Lossy” compression loss of details loss of details

1:801:501:1


Factors Affecting Angiographic Image Factors Affecting Angiographic Image ContrastContrast

• Subject contrast• Vessel size• X ray kV (lower contrast at > 75 kV)

• Scatter• Patient thickness along beam• X ray beam area (FOV and collimation)

• Image intensifier veiling glare

• Digital image processing


Dose vs. NoiseDose vs. Noise

2 µR per frame 15 µR per frame 24 µR per frame


Relationship between Image Quality and DoseRelationship between Image Quality and Dose

• Detection is limited by NOISE.

• Acceptable noise depends on TASK.

• Noise 1 / • Acceptable dose

level depends on TASK

DOSE


Image QualityImage Quality

• 3 parameters are interdependent.• Aim usable image, not a perfect image. image contrast low kVp large patient

exposure dose kVp patient dose; image contrast receptor input dose patient exposure; image

noise• Optimal compromise set of exposure parameters that

preserve diagnostic quality image contrast at an acceptable image noise level while minimizing patient dose


Effect of X ray Beam Penetration on Contrast, Body Penetration, and Dose


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Beam energy: In general, every X ray system produces a range of energies

Low energy X rays: high image contrast but high skin dose

Middle energy X rays: high contrast for iodine and moderate skin dose

High energy X rays: poor contrast and low skin dose


Beam energy: The goal is to shape the beam energy spectrum for the best contrast at the lowest dose. An improved spectrum with 0.2 mm Copper filtration is depicted by the dashes:

Middle energy x rays are retained for best compromise on image quality and dose

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Low-contrast high energy x rays are reduced by lower kVp

Filtration reduces poorly penetrating low energy x rays


Scatter and Veiling Glare depend on FOVScatter and Veiling Glare depend on FOV


RadiationDose

ImageQuality


Is there difference in Quality of Is there difference in Quality of Coronary Angiographic Coronary Angiographic

Images?Images?


No. of technical deficiencies 153 49.6%

No. of reference segments 32 11.4%

Inadequate separation from background 35 11.4%

Inadequate lesion/vessel separation 67 22%

Inadequate opacification flow 48 15.6%

Inadequate opacification technique 68 22%

Inadequate radiographic procedure 10 3.2%

Totally inadequate 7 2.3%

Epicardial vessel not injected 5 1.6%

N %

Types of technical deficiencies in 308 Types of technical deficiencies in 308 cineangiogramscineangiograms (Leape, Am Heart J 2000;139:106-13)(Leape, Am Heart J 2000;139:106-13)

Percentage of inadequate studies by Percentage of inadequate studies by different hospitals different hospitals (Leape, Am Heart J 2000;139:106-13)(Leape, Am Heart J 2000;139:106-13)

In 12/29 hosp. 50% of studies had deficencies

6 of these are teching hosp.


Country DAP (Gy×cm2) FT (min) No. of frames

median mean median mean median mean

Greece 38.6 46.7 5.5 7.1 1620 960

Spain 27.8 39.4 6.4 9.4 903 1596

Italy 28.2 33.5 3.0 4.2 570 610

England 28.2 33.5 3.0 4.2 570 610

Ireland 33.3 37.5 3.2 4.4 580 585

Finland 39.6 52.7 4.1 4.8 417 803

mean fluoroscopy time, frame number and dose-area product (DAP) in some European centers during coronary angiography

Neofotistou, ER 2003+ 41% + 113%

+ 288%


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Dublin % Leuven % Athens % Madrid %

LEFT-CR (+,+)

LEFT-CAU (+,-)

RIGHT-CR (-,+)

RIGHT-CAU (-,-)

projections’ distribution

11.5

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15.4

13.812.4

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Udine Dublin Leuven Greece Treviso Spain

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mean number of series DIMOND 3 data

1000.4

1045.1

982.4

950.0

960.0970.0

980.0

990.01000.0

1010.0

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1050.0

Dublin Greece Spain

SIID

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focus-detector mean distances


Imaging Assessment StrategyImaging Assessment Strategy


Image assessment strategyImage assessment strategy

• Observer-based Observations• traditional method for field analysis, QC

• “subjective”

• not sensitive to small difference in image quality

• Physics-based measurement• traditionally performed by vendors

• “objective”

• not usually performed under realistic clinical conditions


Based on measurement of some physical parameters• system transfer factor K

• spatial resolution (MTF, modulation transfer function)

• detective quantum efficiency (DQE)

• noise

They are rather complex and rarely applied to daily practice

Quality evaluation of angiographic imagesQuality evaluation of angiographic images Method 1Method 1: Objective, physics-based measurements.: Objective, physics-based measurements.


test objects or phantoms• they are able to simulate the same radiation

conditions as the part of the body

• they describe behaviour of radiology equipment in specific operating condition

evaluation of clinical images • allow evaluation of the overall performance including

patient’s collaboration and technique

Quality evaluation of angiographic imagesQuality evaluation of angiographic images

Method 2Method 2: Subjective methods: Subjective methods


test objects


Line Pair Test ObjectsLine Pair Test Objects

1 Megapixel Digital Cine film


ACC Expert Consensus Document on Radiation Safety ACC Expert Consensus Document on Radiation Safety in the Practice of Cardiologyin the Practice of Cardiology

JACC Vol. 31, No. 4, March 15, 1998:892-913 JACC Vol. 31, No. 4, March 15, 1998:892-913 • risks of radiation exposure to medical professionals

in many aspects of cardiology, including catheterization, electrophysiology, and nuclear cardiology.

• Background on radiation physics and biology, as well as recommendations to reduce radiation exposure and provide for operator safety during pregnancy or when pregnancy is planned.

• Emphasis is placed on the ALARA principle, and includes recommendations for training and discussion of shielding options and monitoring badges


American College of Cardiology Training Statement on Recommendations American College of Cardiology Training Statement on Recommendations for the Structure of an Optimal Adult Interventional Cardiology Training for the Structure of an Optimal Adult Interventional Cardiology Training

ProgramProgram JACC 1999; 34:2141-7JACC 1999; 34:2141-7

• Training in radiology imaging and radiation safety

• Principles of X-ray imaging, quantitative coronary arteriography, operation of cineflurographic X-ray equipment, operation of digital video imaging systems, radiation biology and radiation protection


Evaluation of Clinical Coronary Evaluation of Clinical Coronary Angiographic ImagesAngiographic Images


Scientific societies implemented guidelines to guarantee

adequate level of quality and performance of invasive

cardiology

• training of operators

• quantitative standards to maintain the expertise in coronary

angiography or angioplasty

• quality-assurance programme

Pepine, J Am Coll Cardiol 1995;25:14–6

Miller, Can J Cardiol 1996;12:470–2

Cowley, Cathet Cardiovasc Diagn 1993;30:1–4

Heupler, Cathet Cardiovasc Diagn 1993;30:191–200

Scanlon, J Am Coll Cardiol 1999;33:1756–824

Quality in invasive cardiology and scientific Quality in invasive cardiology and scientific societiessocieties


the specific problem of achieving and maintaining

high-quality standards in angiographic imaging

• responsibility of cardiac catheterization laboratory directors

• involves periodic cine-angiograms review

• lesion quantification (QCA, calipers)

precise criteria have never been stated for coronary procedures

Quality of cardiac images and scientific Quality of cardiac images and scientific societiessocieties


Development of Quality Criteria in EuropeDevelopment of Quality Criteria in Europe

1995-1996: GISE Società Italiana di Cardiologia Invasiva and AIFM Associazione Italiana di Fisica Biomedica

1996–2003: European Concerted Action DIMOND Cardiology Group (Digital Imaging: Measures for Optimizing Radiological INformation Content and Dose)

contracts FI 4P-0042DG12-WSMN, FIGM-CT-2000-00061-DIMOND

http://www.dimond3.org/


DIMOND I, II, III & SENTINEL Projects DIMOND I, II, III & SENTINEL Projects (Europe)(Europe)

• For more information, please refer to website: http:// www.DIMOND3.org

• Also see supplementary section


Diagnostic requirementsDiagnostic requirementsadapted from EUR 16260 ENadapted from EUR 16260 EN

Image criteria

In most cases specify important anatomical structures that should be visible on an image to aid accurate diagnosis. Some of these criteria depend fundamentally on correct positioning and cooperation of the patient or good angiographic technique, whereas others reflect technical performance of the imaging system

Important image detailsProvide quantitative information on the minimum sizes at which important anatomical details should become visible on the image. Some of these anatomical details may be pathological.


Is this coronary angiography of good quality?Is this coronary angiography of good quality?

[ video clip]


Component 1: Clinical criteria are defined as important anatomical features that should be visible; the level of visualisation is as follows visualization: characteristic features are detectable, but details are not fully

reproduced (features just visible)

reproduction: details of anatomical structures are visible, but not necessarily clearly defined (details emerging)

visually sharp reproduction: anatomical details are clearly defined (details clear)

Component 2: Technical criteria help to asses the technical quality of the procedure

features not necessarily impair the clinical information content (panning, arms position, etc.)

Component 3: Aspects of an optimized angiographic technique aim to have optimized radiological technique

DIMONDDIMOND:: definition of terms definition of terms


Component 1: Clinical criteria are defined as important anatomical features that should be visible; the level of visualization is as follows

visualization: characteristic features are detectable, but details are not fully reproduced (features just visible)

reproduction: details of anatomical structures are visible, but not necessarily clearly defined (details emerging)

visually sharp reproduction: anatomical details are clearly defined (details clear)

Component 2: Technical criteria help to asses the technical quality of the procedure

features not necessarily impair the clinical information content (panning, arms position, etc.)

Component 3: Aspects of an optimised angiographic technique set of technical information

aimed to have optimized radiological technique

DIMONDDIMOND:: definition of termsdefinition of terms


Level 1: Visualization: characteristic features are detectable, but details are not fully reproduced (features just visible)

[ video clip]


Level 2: reproduction: details of anatomical structures are visible, but not necessarily clearly defined (details emerging)

[ video clip]


Level 3: visually sharp reproduction: anatomical details are clearly defined (details clear)

[ video clip]


1) Simultaneous and full opacification of the vessel lumen at least until the first flow-limiting lesion (in general ~ 90-95% by visual estimation)

2) Performed at full inspiration if necessary to avoid diaphragm superimposition or to change anatomic relationship (in apnoea in any case)

3) Arms should be raised clear of the angiographic field

4) Panning should be limited. If necessary, pan in steps rather than continuously, or make subsequent cine runs to record remote structures

5) When clinical criteria 1-4 have been fulfilled, avoid extra projections (mainly LAO semi-axial)

22ndnd Component Component: : Technical criteriaTechnical criteria


Diaphragm

[still]

Lecture 8: Image Quality in Cardiac Angiography 63Radiation Protection in Cardiology IAEAIAEA[ video clip]

What is technically suboptimal about this cine What is technically suboptimal about this cine run?run?


33rdrd component component: : Aspects of an optimised Aspects of an optimised angiographic techniqueangiographic technique

1) Use of the wedge filter on bright peripheral areas

2) 2-3 sequences (except for difficult anatomic details)

3) 12.5-15 frames/s (25-30 only if heart rate exceeds 90-100

bpm or in paediatric patients)

4) 60 images per sequence (series) on average (12.5-15 fr/s)

except if collaterals have to be imaged or in case of slow

flow


proper filtering

improper filtering

[still]


Collateral

98 frames

[ video clip]


DIMOND Scoring SystemDIMOND Scoring System

• Attempt to objectively evaluate, using a scoring system, quality of coronary angiography with pre-specified criteria.

• An example of this scoring can be found in supplementary slides

• For more info, http://www.DIMOND3.org

• DIMOND survey showed inter-lab and inter-country variability in image quality, radiation dose etc


Image quality is not always guaranteed in coronary angiography

A great variability is found in common practice among different

operators and radiological exposure varies considerably

Image quality assessment plays a pivotal role in the optimization of

angiographic procedures

Optimization implies a continuous process of research and audit which

should involve

scientific societies

individual operators

cooperation of all professionals in the cath. lab.

Closing remarksClosing remarks


Revision Questions: “True” or “False”?Revision Questions: “True” or “False”?

1. Typically a good coronary angiography sequence/series consists of at least 90 frames.

2. DIMOND criteria were established in Europe to objectively evaluate the image quality of coronary angiography.


Revision Questions: “True” or “False”?Revision Questions: “True” or “False”?

3. The more X ray photons reaching the image receptor, the more contrast is achieved in the image.


Thank YouThank You


Supplementary SlidesSupplementary Slides


The method of image quality evaluation based on DIMOND Quality Criteria


Clinical criteria for RCA projections based on Clinical criteria for RCA projections based on operator’s choiceoperator’s choice

1. Visually sharp reproduction of the origin, proximal, mid (especially the crux region) and distal portion in at least two orthogonal views, with minimal foreshortening and overlap

2. Visually sharp reproduction of side branches 1.5 mm in at least two orthogonal views, with minimal foreshortening and overlap. The origin should be seen in at least one projection

3. Visually sharp reproduction of lesions in vessels 1.5 mm in at least two orthogonal views, with minimal foreshortening and overlap

4. Visualization of collateral circulation when present


Example of quality score calculation (QS) for RCA

[ video clip]


[ video clip]


sum of scores = 91 (actual score)

maximum theoretical score = 96

QS = actual score/theoretical score %

= 65/88x100 = 94%

Example of QS calculation for RCA


total score (mean and std. dev.)total score (mean and std. dev.)15 angio, 65 readings, 3 european centers15 angio, 65 readings, 3 european centers

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Linear (med)

% within pts variability = 0.08

Lin’s coeff = .76 (CI .67-.84)

AJC, 1999 (abs)


total score (mean and std dev.)total score (mean and std dev.)30 angio, 160 readings, 6 european centers30 angio, 160 readings, 6 european centers

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good (33 readings) (mean SD)

acceptable (28 readings) (mean SD)

P

total score 96 4 93 9 0,11

total scores compared to subjective opinion “good” and “acceptable”

two cases lacking


problems related to subjective evaluation of images ……


What is subjective opinion?What is subjective opinion?

good I get all the information needed to treat the patient and I

like this examination

acceptable

I get all the information needed to treat the patient but I don’t like very much this examination

unacceptable

I don’t get all the information needed to treat the patient and I don’t like this examination at all


RemarksRemarks

The method based on Quality Criteria applies to cardiac angiography

Reproducibility is goodMeasure of clinical acceptability seems

improved in comparison to subjective opinionThe method allows a systematic and

standardized analysis of the imagesSpecific training not requested (but it may

improve agreement)

image quality in cardiac angiography

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