« Discours de la Méthode » (Descartes)

1. « Discours de la Méthode »(Descartes)

2. Practical method for the interpretation of frontal and lateral chest radiographs Martina Martins Charles Perrot Nigel Howarth Department of Radiology Department of Community Medicine Geneva University Hospitals

3. Introduction to the « discours de la méthode » • Chest radiography is the most frequently performed examination in hospitals and private practices. (1)

4. Introduction to the « discours de la méthode» • 150 million x-rays/year in the US (1,2)

5. Introduction to the « discours de la méthode » Everyone thought, rather naively, that :

6. Introduction to the “discours de la méthode” • If a lesion is present in the lungs, it will show up on the x-ray, • 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. (1,2,3)

7. 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 NEGATIVES) • And 1 to 20% of radiographs considered as PATHOLOGICAL are in fact NORMAL (= FALSE POSITIVES) (1,3)

8. Introduction to the « discours de la méthode » The perception of pulmonary lesions is influenced by numerous and complex factors.

9. Introduction to the « discours de la méthode » To SEE is to look and learn

10. Introduction to the « discours de la méthode » TO LOOK is first and foremost a question of attention !

11. Introduction to the « discours de la méthode » Did you notice that « the » is written twice? PARIS IN THE THE SPRING Sapira JD. The art and science of Bedside diagnosis

12. 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)

13. Introduction to the « discours de la méthode » • The human interface : widely minimised in the past, it is now attracting growing interest. (4,5,6)

14. Introduction to the « discours de la méthode » • How does the human eye look at images? • How does the human eye see images?

15. Introduction to the « discours de la méthode » (9,10)

16. Introduction to the « discours de la méthode » • Cones and rods are two types of cells found in the retina. • Cones are used for visual discrimination and colour perception. They are present in the macula, the centre of visual acuity. • At the centre of the macula is the fovea which contains only cones = area of most acute vision. (9,10)

17. Introduction to the « discours de la méthode » • Rodsare 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)

18. Introduction to the « discours de la méthode » • Visual scanningis 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 another, insaccadesinterspersed with fixations. (9,10)

19. 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)

20. Introduction to the « discours de la méthode » ( cones) (rods)

21. 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 fixations.

22. Visual analysis by a neophyte A neophyte just looks at the central area then focuses with worry on the stomach bubble!

23. Visual analysis by a non-specialist A physician with no radiology training does not look at the peripheral, extra-thoracic and sub -diaphragmatic areas.

24. 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 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)

25. 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 fixations. (8,9,10)

26. Introduction to the « discours de la méthode » Cortical integration and perception (9,10,32)

27. 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" FINISHED FILES ARE THE RE- SULT OF YEARS OF SCIENTIF- IC STUDY COMBINED WITH THE EXPERIENCE OF YEARS How many "Fs" do you see in this sentence?

28. 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.

29. Introduction to the « discours de la méthode » • « Seeing » is based on the information content of the object • « Perceiving » on the information content of the observer Most of us see but few perceive ! (13,14)

30. Introduction to the « discours de la méthode » • An unstructuredgaze produces no results (e.g. the watch you look at dozens of times a day!) (13,14)

31. 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 And yet… it is the object most frequently looked at during the day!!! Sapira JD. The art and science of Bedside diagnosis

32. Introduction to the « discours de la méthode » An examination methodology is essential to a structured gaze. This methodology is… (11,13)

33. « Le Discours de la Méthode »

34. « 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)

35. « Discours de la méthode » • The following basic rules are designed to improve the image perception:

36. « Discours de la méthode » « WISDOM BEGINS BY TURNING OFF THE LIGHTS » says His HolinessTenzin Gyatso. (14th. Dalai Lama) “THIS APPLIES TO RADIOGRAPH READING AS WELL!!!” says your humble servant

37. « Discours de la méthode » • Vary the viewing distances (using convergent and divergent lenses if necessary).

38. « Discours de la méthode » To SEE is to look and learn

39. « Discours de la méthode » TO LEARN

40. TO LEARN What you don’t know you don’t see !!! (Benjamin Felson) Famous radiologist

41. TO LEARN • Ignorance leads to non detection or minimisation. • The viewer must learn a whole set of radiological signs. • The viewer must learn the radiological vocabulary. • The viewer must learn to communicate his findings in an appropriate, clear and committed way (active expression is better than passive!) (15,33)

42. « Discours de la Méthode » • A Cartesianmind is an analytical mind: it breaks down a complex matter into several units simpler to analyse. • Then comes the rational stage, which produces conclusions and practical solutions based on the analysis. (11,15)

43. « Discours de la Méthode » In short TO SEE is : « to LOOK and LEARN » Analytical breakdown Application of the « Discours de la Méthode »  (11)

44. There are 3 fatal errors responsible for the high rate of false negatives in chest radiography interpretation: Don’t worry: fatal errors exist in golf as well!!! Error in detecting the lesion: the area in question has not been « scanned ». Error in recognising the lesion: it has been detected but not identified. Error of judgement: the lesion has been detected but is considered as irrelevant. (15)

45. « Discours de la Méthode » «I THINK THEREFORE I AM» said Descartes whichtranslatesin radiologyas «I SEE THEREFORE I AM» (11)

46. « Discours de la Méthode » This methodology will save you from: • Radiological lounging • Unproductive beatitude • Hasty diagnoses • Dogged fixation on « irrelevance  »