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Jul 12
2010
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Chest radiography is the most frequently performed diagnostic examination in the public hospitals and private practices.
Almost 150 million chest X-rays are performed every year in US.
This practice is based on a very simple misbelief and everyone thinks rather naively that :
- 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.
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)
The perception of pulmonary lesions is influenced by numerous and complex factors.
To SEE is to look and learn.
Did you notice that “the” is written twice?
To LOOK is first and foremost a question of attention !
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.
- The human interface: widely minimised in the past, it is now attracting growing interest.
What we must know and understand is :
- How does the human eye look at images?
- How does the human eye see images?
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 center of visual acuity.
At the center of the macula is the fovea which contains only cones = area of most acute vision.
Visual 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 another, in cascades interspersed with fixations.
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.
From this we can easily conclude that - Large sections of the thorax are NOT “scanned” by the area of most acute vision, the fovea!!!
In practice, an x-ray is read in 30 seconds, which leaves enough time for approximately 80 to 120 fixations.
A neophyte just looks at the central area then focuses with worry on the stomach bubble!
A physician with NO radiology training does not look at the peripheral, extra-thoracic and sub-diaphragmatic areas.
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.
“Seeing” is based on the information content of the object and “Perceiving” on the information content of the observer.
Most of us see but few perceive!
An unstructured gaze produces no results (e.g. the watch you look at dozens of times a day!)
An examination methodology is essential to a structured gaze.
Often we are left speechless and confused when put up with an X-ray. So it helps if we follow a methodology to approach the x-ray film.
An easy way to read a chest X-ray is :
STEP 1:
STEP 2:
STEP 3:
STEP 4:
This methodology helps to:
- Focus on a maximum of areas.
- Improve your visual acuity on the required radiological fields by increasing the number of fixations.
What you don’t know you don’t see !!! (Benjamin Felson)
Pnemonics to remember as to how should we go about reading a chest x-ray is :
Are There Some More Patients
- Abdomen
- Thorax
- Silhouette
- Mediastinum
- Parenchyma
OR
American Thoracic Society of Mighty Pneumologists
OR
All These Students Must Persevere
A Cartesian mind 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.
In short :
“I Think Therefore I Am” said Descartes
which translates in radiology as :
Average user rating from: 3 user(s)
Reviewed by Dr. Prakash Vohra September 29, 2010
Reviewed by Anuj Mishra September 15, 2010
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Keshav Kulkarni
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... Without doubt, CXR remain an enigma for radiologists and clinicians. Clinicians want to see their clinical diagnosis in CXRs. It is essentially a job of radiologist to see the unseen. For example, if a clinician is suspecting sarcoid, the hila invariably look bulky in most of the cases. Pulmonologist rarelu looks at the mediastinum. Casualty department are usually obscessed with pneumothorax. The problem with radiologists is enormous amount of workload and the speed at which we have to report CXR. I know many of the radiologists report 70-80 X-rays in 3.5 hours, and at least half of them are CXRs. We do get biased, based on clinical information, previous reports, who is referring, from where the referral is coming from (specialist or general practictioner or casualty or ITU), so on and so forth. Well written article. Good discussion with great learning points for all. It would have been nice if you had given the references in the end of the blog. |
Anuj Mishra
said:
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... Many thanks for your kind appreciation, Dr. Keshav. This article is primarily what I have learnt in medical school and what I have gained in my daily practice. The authors' of the quotes have been mentioned alongwith. Thanks again.  |
Dr. Sridhar V
said:
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... Thank you Dr.Anuj for yet another teaching blog article, helpful to both the beginner and the experienced. Mnemonic are the best way to remember the sequences to be followed.And One can develop his or her own Mnemonics and no surprise there are so many Mnemonics for the same topic. I think interpreting the Chest x ray films many times appear very simple and equally at times very tough Sometimes interpreting the chest x ray films reminds me of the 'MIRAGE PHENOMENON' simply because we start imagining the shadows..in other words...I am seeing something which may not be what i am thinking....even it may not be there ! In certain situations interpretation of chest x ray films is extremely difficult and intimidating even for the experienced radiologist. No surprise then, that thoracic surgeons,chest physicians and general physicians,cardiologists,cardiac surgeons... however confident they are in interpreting chest x rays ....from their heart always wish to have a second look into the Radiologists report. |
Alok Varshney
said:
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... Wow, Dr. Anuj, really great article. Kudos and thanks.. The art of interpreting radiographs, be it chest or any other body part, seems to be getting lost. A radiology resident or a practitioner has so much to learn about more advanced and certainly more lucrative imaging modalities that interpretation of a plain radiograph is getting a short shift. Even in big radiology depratments, reporting X-rays is often relegated to the junior most member of the team. In the era of dying general-radiology, who will have the time to read a radiograph ? Should a resident/ radiologist invest time to learn this dying art ? |
Dr. Sridhar V
said:
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... Thank you Dr.Alok for calling spade a spade. There can not be any disagreement about what you stated. Now a days x rays machines are dumped into 1.Orthopedics dept.( radiologist is not interested in learning trauma radiology neither it is taught in the post graduation training), 2.into Chest departments ( interpreting chest x rays is a waste of time since you have mastered higher imaging modalities and invariably recommend either ct or mri...then keep enough energy to learn higher modalities rather than chest x ray interpretation) 3.In corporate hospitals , both juniors and seniors are dumped into plain x ray reporting as a punishment.How can one create interest in learning the art of x-ray reading ? Forget about plain x ray interpretation even the Great Ultrasound which all radiologists claim their domain ...losing charm among youngistan radiologists. Why ? How much time you think left for General Radiology to take its last breath ? |
Dr. Anuj Mishra
said:
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... I agree with you Drs. Alok and Sridhar. The 'art' of radiograph interpretation is indeed getting lost. And sadly this field is being completely taken over by 'neophytes'. Hence, the need of refreshing our knowledge and gaining expertise in this field. I think you have yourself answered your questions. We must impart the knowledge and skills to our junior colleagues and teach them the 'tips & tricks' for interpreting plain radiographs so that they can distinguish themselves in multispeciality teamwork. We must refine our skills in basic radiology to keep us ahead of our clinical colleagues. If my plain chest radiograph interpretation is wrong and misguided, none of my physician friends would trust my CT or MR reports too. This is very important to build one's professional credibility, I feel. |
Dr. Muneesh Sharma
said:
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... Nice Discussion, Actually nobody should expect to do random assessment of any image, it must be structured and organized..for all modalities. What i want to add is that the present change we see is a natural process...like Ducatis replacing BSA-SLRs.. What has happened is that with rampant use of CT (read as replacing X rays and USG as a screening exam) it is but consequent for loss of interest in the less informative screening tools (though practically they may be better for the patient in terms of radiation and cost) especially among the freshers... U see we dont want to huff puff uphill on the BSA when u could vroom on the ducati....lol Wrong.. maybe.. but definitely the normal human psychology... |
Anuj Mishra
said:
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... of course dr. muneesh.......this is human psychology. But what I wanted to convey is the importance of structured methodology for interpreting chest radiographs and , as you have truly remarked, can be extrapolated to all imaging modalities i.e.USG, CT or MRI. One can encounter ultrasonologists misreporting the location of renal lesions as upper pole or lower pole due to paucity of sonographic anatomy knowledge. Likewise, for CT and MRI too, a structured methodology is indeed important to avoid errors. |
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