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« Discours de la Méthode »
(Descartes)
« Discours de la Méthode »
(Descartes)
Practical method for the interpretation of frontal and
lateral chest radiographs
Practical method for the interpretation of frontal and
lateral chest radiographs
Martina MartinsMartina Martins
Charles PerrotCharles Perrot
Nigel HowarthNigel Howarth
Department of RadiologyDepartment of Community Medicine
Geneva University Hospitals
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• Chest radiography is the most Chest radiography is the most frequently performed frequently performed examination in hospitals and examination in hospitals and private practices.private practices.
(1)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• 150 million x-rays/year in the US150 million x-rays/year in the US
(1,2)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
Everyone thought, rather naively, Everyone thought, rather naively, that :that :
Introduction to the “discours de la méthode”
Introduction to the “discours de la méthode”
• If a lesion is present in the lungs, it will show up on the x-ray,
(1,2,3)
• If a lesion shows up on the x-ray, it will be detected by the physician,• If the lesion is detected by the physician, it will be correctly interpreted, and• If the lesion is interpreted correctly, the right diagnosis will be made.
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
Large scale studies, spanning over 20 years, have shown that :
• 20 to 30% of radiographs considered as NORMAL are in fact PATHOLOGICAL (= FALSE NEGATIVESFALSE NEGATIVES)
• And 1 to 20% of radiographs considered as PATHOLOGICAL are in fact NORMAL (= FALSE POSITIVESFALSE POSITIVES)
(1,3)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
The perception of pulmonary lesions is influenced by numerous and complex
factors.
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
To SEESEE
is to look look and learnlearn
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
TO LOOKTO LOOK
is first and foremost a question is first and foremost a question of attention !of attention !
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
PARIS IN THE THE SPRING
Did you notice that Did you notice that « the » « the »
is written twice?is written twice?
Sapira JD. The art and science of Bedside diagnosis
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
There are two interfaces involved in radiography:
• The technical interface : enormous progress has been achieved over the past few years, leading to considerable improvements in the quality of radiological imaging. This interface is well standardised and reproducible.
(4,5,6)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• The human interface : widely minimised in the past, it is now attracting growing interest.
(4,5,6)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• How does the human eye look at images?
• How does the human eye see images?
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
(9,10)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• Cones and rodsCones and rods are two types of cells found in the retinaretina.
• Cones Cones are used for visual discrimination and colour perception. They are present in the maculamacula, the centre of visual acuity.
• At the centre of the macula is the foveafovea which contains only cones = area of most acute vision.
(9,10)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• RodsRods are found mostly in the extra-macular areas of the retina and work best under dim light.
• The extra-macular retina serves night vision and visual orientation.
• The peripheral retina helps us avoid obstacles whilst moving around in the dark.
(9,10)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• Visual scanningVisual scanning is a complex action.
• Eye movement recordings in a person reading a chest x-ray show that central vision, also known as foveal vision, proceeds from one point to anotherfrom one point to another, in saccadessaccades interspersed with fixationsfixations.
(9,10)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• The central foveal zone subtends an angle of about 2 degrees when looking at an object 1 meter away. This means that the area seen by the fovea is no more than 2.2 cm in diameter.
IMPORTANT:
• A small pulmonary nodule is best detected by foveal vision.
(9,10,32)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
( cones)( cones)
(rods)(rods)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• In practice, an x-ray is read in 30 seconds, which leaves enough time for approximately 80 to 120 fixations80 to 120 fixations..
Visual analysis by a neophyteVisual analysis by a neophyte
A neophyte A neophyte just looks at just looks at the central the central area then area then
focuses with focuses with worry on the worry on the
stomach stomach bubble! bubble!
Visual analysis by a non-specialistVisual analysis by a non-specialist
A physician with A physician with no radiology no radiology
training does not training does not look at the look at the
peripheral, extra-peripheral, extra-thoracic and sub -thoracic and sub -
diaphragmatic diaphragmatic areas.areas.
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• A standard radiograph measures 35 x 43cm, a surface which can be filled with approximately 300 circles of 2.2 cm. Therefore, some 300 foveal fixations300 foveal fixations are necessary to cover the whole x-ray when standing at a distance of 1 meter.
• Conclusion:Large sections of the thorax are not « scanned » by the area of most acute vision, the fovea!!!
(9,10)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• When viewing a standard radiograph with a reducing lens, the area shown is four times smaller (17.5 x 21.5 cm), and therefore requires only 70 foveal fixations70 foveal fixations.
(8,9,10)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
(9,10,32)
Cortical integration and perception
6 "F"6 "F"
• Most people say 3 "F" when in fact there are 6.
• The brain tends to see the "F" of the word "OF" as a "V"
How many "Fs" do you see in this sentence?
FINISHED FILES ARE THE RE-
SULT OF YEARS OF SCIENTIF-
IC STUDY COMBINED WITH
THE EXPERIENCE OF YEARS
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
Cortical integration is affected by all sorts of factors.
For instance, when reading a chest radiograph:
• The mention of « hemoptysis » is associated with more false positives.
• The mention of« dyspnea » is associated with more false negatives.
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• « Seeing » Seeing » is based on the information content of the object
• « Perceiving » Perceiving » on the information content of the observer
Most of us see but few perceive !Most of us see but few perceive !
(13,14)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
• An unstructured gaze produces no results (e.g. the watch you look at dozens of times a day!)
(13,14)
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
Hide your watch and draw it.• Colour and shape of the face?• Arab or roman numerals?• Shape of the hands?• Where is the brand name?• Where is the date?
Look at your watch: how many mistakes have you made?
Answer : Many Many And yet… it is the object most frequently looked at
during the day!!!
Sapira JD. The art and science of Bedside diagnosis
Introduction to the « discours de la méthode »
Introduction to the « discours de la méthode »
An examination methodology is essential to a structured structured gaze.
This methodology is…
(11,13)
« Le Discours de la
Méthode »
« Le Discours de la
Méthode »
« Discours de la méthode » « Discours de la méthode »
This methodology is designed to help you:• Focus on a maximum of areas.• Improve your visual acuity on the required
radiological fields by increasing the number of fixations.
(11)
« Discours de la méthode » « Discours de la méthode »
• The following basic rules are designed to improve the image perception:
« Discours de la méthode »« Discours de la méthode »
« WISDOM BEGINS BY TURNING « WISDOM BEGINS BY TURNING OFF THE LIGHTS »OFF THE LIGHTS » says says His HolinessHis Holiness Tenzin GyatsoTenzin Gyatso..
““THIS APPLIES TO RADIOGRAPH THIS APPLIES TO RADIOGRAPH READING AS WELL!!!”READING AS WELL!!!”
says your humble servantsays your humble servant
(14th. Dalai Lama)
« Discours de la méthode »« Discours de la méthode »
• Vary the viewing distances (using convergent and divergent lenses if necessary).
« Discours de la méthode »« Discours de la méthode »
To SEESEE
is to look look and learnlearn
« Discours de la méthode »« Discours de la méthode »
TO LEARNLEARN
TO LEARNTO LEARN
What you don’t know you don’t see !!!
(Benjamin Felson)
Famous radiologist
TO LEARN TO LEARN
• Ignorance leads to non detection or minimisation.• The viewer must learn a whole set of radiological
signssigns. • The viewer must learn the radiological
vocabularyvocabulary.• The viewer must learn to communicate his
findings in an appropriate, clear and committed way (activeactive expression is better than passive!)passive!)
(15,33)
« Discours de la Méthode » « Discours de la Méthode »
• A CartesianCartesian mind is an analyticalanalytical mind: mind: it breaks down a complex matter into several units simpler to analyse.
• Then comes the rationalrational stage, which produces conclusions and practical solutions based on the analysis.
(11,15)
« Discours de la Méthode » « Discours de la Méthode »
TO SEE is :
« to LOOK and LEARN »
Analytical breakdown
Application of the « Discours de la Méthode »
In short
(11)
There are There are 3 fatal errors3 fatal errors responsible for the high rate responsible for the high rate of false negatives in chest radiography of false negatives in chest radiography
interpretation:interpretation:
Error in Error in detectingdetecting the lesion: the area in question has not the lesion: the area in question has not been « scanned ».been « scanned ».
Error in Error in recognisingrecognising the lesion: it has been detected but not the lesion: it has been detected but not identified.identified.
Error of Error of judgementjudgement: the lesion has been detected but is : the lesion has been detected but is considered as irrelevant.considered as irrelevant.
Don’t worry: Don’t worry: fatal errors exist fatal errors exist in golf as well!!!in golf as well!!!
(15)
« Discours de la Méthode »« Discours de la Méthode »
«I THINK THEREFORE I AM»«I THINK THEREFORE I AM»said Descartessaid Descartes
whichwhich translatestranslates in radiologyin radiology asas«I SEE THEREFORE I AM»«I SEE THEREFORE I AM»
(11)
« Discours de la Méthode »« Discours de la Méthode »
This methodology will This methodology will save you from:save you from:
• Radiological loungingRadiological lounging• Unproductive beatitudeUnproductive beatitude• Hasty diagnosesHasty diagnoses• Dogged fixation on « irrelevance »Dogged fixation on « irrelevance »
