[Music] hello everyone this is the first video in a series on interpreting chest x-rays my goal of this series is to be able to take people who literally know nothing about chest x-rays and teach them everything they'll need to know while taking care of patients regardless of specific Health Care profession with the one except of a radiologist if any of you happen to be a future radiologist I think these videos will still provide a good very early foundation for you but I suspect you'll want to track down a more robust resource the course will have 10 videos here's the structure lesson one that is this video will cover the fundamentals of how an x-ray is taken and the physics involved please don't let the word physics scare you away it's really basic and includes some pretty pictures lesson two will introduce a systematic approach to chess x-ray interpretation and demonstrate how x-ray Shadows relate to normal chest Anatomy lesson three will discuss how one assesses the technical quality of the film lessons 4 through 8 will then each cover a subset of chest pathology that can be assessed with x-ray these will include plenty of examples of common abnormalities lesson n will discuss how to assess the placement of lines and tubes as well as how to identify devices and findings consequent from prior surgeries such as artificial heart valves finally lesson 10 will be a self assessment where unknown chest films are displayed alongside a brief clinical vignette and after a chance for you to pause the video and study the films on your own I'll review them as I implied a moment ago by the end of these 10it lessons you should be able to identify the overwhelming majority of abnormalities visible on a conventional chest xray the learning objectives of this video lesson one are first to be familiar with the basic physics and method of obtaining chest x-rays and to be familiar with the basic chest X-ray views that is the PA lateral and AP views along with the EKG the chest x-ray is one of the most common diagnostic tests in medicine that does not involve drawing blood there are many indications for getting a chest x-ray they include evaluation of symptoms which can be shortness of breath chest pain cough hemoptisis fever or unexplained weight loss evaluation of signs picked up on a physical exam such as hypoxemia or an abnormal pulmonary exam evaluation of the placement of central lines nasogastric tubes and endotracheal tubes screening for a pneumothorax which is air in the plural space after lung biopsy central line placement and pacemaker placement finally a relatively specific indication is evaluation of suspected pacemaker lead fracture there are a few situations you'll notice are not listed here for example routine chest x-rays prior to surgery in the overwhelming majority of patients are of no benefit and should be avoided also inappropriate are routine screening chest x-rays for lung cancer and smokers Al so there may be benefit in screening chest CT scans but that's a discussion for another day so how does a chest x-ray actually work we need a source of x-rays which themselves are a form of electromagnetic radiation x-rays are carried by photons just like visible light but have higher frequencies and thus higher energies so they penetrate tissue much better unfortunately these high energy photons can cause DNA damage leading to cancer which is why x-ray exposure should be generally be limited to detect the presence of x-rays we'll need something called appropriately enough a detector for the first 100 Years of x-rays in medicine the detector was a photographic plate or film I'll add a sheet of unexposed X-ray film here now however most hospitals have replaced these with digital detectors which allow for real-time viewing as well as improve post exposure digital manipulation finally of course we'll need a patient to stand in between the source and the detector this patient is in the typical position for a chest x-ray she's facing away from the source hands on her hips and chest against the detector the reason to put her hands on her hips is essentially to keep the arms from obscuring the view of the thorax the reason she is standing in a way that intuitively seems backwards will be discussed in lesson five now we have our source our detector and our patient so we'll turn on the X-ray for a very brief predetermined length of time and x-rays that is high energy photons will shoot out of the source some of these will pass right through the patient some will be absorbed by the interposed organs and tissues and some will be scattered for the purpose of examining the X-ray film it's actually the pattern of photons that are blocked which are of Interest as these create the Shadows of the internal organs so what are the factors that determine how many photons pass through a particular spot on a patient to reach the detector in other words the factors which determine Shadow brightness there are essentially three the first is the density of the interposed tissue technically this depends not just on the literal density as mass per unit volume but also independently on the atomic mass of the particles in the interposed tissue let me show you some examples so here is our table and on it I'll place an empty glass jar the jar is filled just with some air on the far side of the jar is our photographic film notice that it starts off white the X-ray source is then brought in we fire some X-rays at the jar which of course aren't in the visible spectrum like this might suggest as the x-rays are traveling across the table the ones that either pass around the jar or through the jar interact with the film here's what's left any part of the film where many x-rays struck has turned black parts of the film where no x-rays struck have remained White and the parts of the film where a modest amount of X-ray struck show various Shades of Gray since air has a very low density x-rays easily pass through the jar and thus the jar appears empty on the film note that the metal lid has blocked nearly all of the x-rays which has left a sharply demarcated rectangular patch of white unexposed film here's some more examples next we can take a jar of water and do the exact same thing expose it briefly to x-rays which also exposes the film behind it in this case water is denser than air so it blocks more X-rays and therefore the jars contents now appear gray on the film it's important to realize that even if the fluid in the jar is completely 100% transparent it will still block X-rays and therefore look gray the fraction of X-rays of substance blocks has absolutely nothing to do with its color or degree of translucency within the visible light spectrum and now for a more interesting test subject what happens when x-rays strike a skull you can see that the resulting image is lighter than the jar of water but not Pure White like the image formed from the Jar's metal cap in summary there is a spectrum of radio densities into which different materials fall those that allow most x-rays through are called radiolucent and appear black or near black on x-ray those that block most x-rays are called radioopaque and appear white for medical x-rays there are essentially four classes of material air which is the most radiolucent next is fluid and soft tissue then bone and finally metal the next factor which determines Shadow brightness is the thickness of the structure being x-rayed if we take a single relatively thin glass of water and expose it to x-rays most will pass through resulting in a very dark image on the film If instead of one glass of water we line up two glasses in a row and shoot x-rays through both twice as many will be blocked the resulting image will therefore be more gray because the specific part of the film corresponding to the the shadow of the glasses have been relatively less exposed finally if we shoot x-rays through three glasses of water the image of the glass will be brighter still in summary the thicker the structure the brighter it will appear on the X-ray film the third and last factor is the duration of exposure for the X-ray interpreter this factor is only relevant when trying to understand a technical error in image acquisition imagine we have two glasses of water again and I'm going to give these a very short or brief x-ray exposure during that brief amount of time few x-rays have an opportunity to pass through the water so the film where the glass's shadow was cast is relatively underexposed and thus it's relatively bright if I use a medium exposure the film behind the glass will receive more X-rays and thus the glass appears a little darker finally if I use a very long exposure even though the glasses of water are in the way there's enough time for many x-rays to pass through so the glasses appear fairly dark on the film The Bottom Line short exposures lead to images that are too bright and long exposures lead to images that are too dark this is the opposite of what most people initially expect because intuitively we assume that all film starts off black and turns white after exposure to light but remember x-ray film is the opposite let's return to our patient who has been patiently waiting for us in the radiology department and let's fire some X-rays at her you can see that some pass through some get absorbed and a few even get scattered around the room the result is an image formed on the photographic film of the Shadows cast by the various structures in the patient's chest and here is that result from the pattern of white black and gray we can infer things about those chest structures for one this area here because it is generally relatively dark it must correspond to an airfill structure a lung this area here which is a medium gray in brightness must correspond to a structure composed of either fluid and or soft tissue in this case the heart since the layout of the human body is amazingly consistent from person to person each major line and shape on this x-ray corresponds with a known and identifiable anatomic part I'll review these parts in lesson two but before then there are two quick practical things to point out first it may have happened so fast that you did not notice it but when I removed the film from the detector stand I flipped it around horizontally the consequence of this is that the left side of the film as we are looking at it actually corresponds to the right side of the patient and vice versa this puts the X-ray in the same orientation as if we were standing in front of the patient and looking directly at him or her if that seems a little weird right now it will probably feel intuitive after examining just a dozen or so examples the second practical thing to mention is the idea of chest X-ray views in Radiology the term View view refers to the orientation of the person relative to the beam of X-rays at this point there are three views to know the first view is the most important and the one you've already been shown it's called the PA view which stands for posterior to anterior meaning the x-rays entered the body squarely in the back and exited squarely out of the front in most cases the pi view will automatically be accompanied by the lateral view as the term implies the lateral view is the two-dimensional projection of the patient's internal structures as seen from the side the pi view should be distinguished from another situation common in the hospital where patients may be physically unable to stand due to weakness confusion surgical wounds or invasive tubes in that circumstance when the patient is in a hospital bed a portable x-ray Source will be wheeled into the patient's room an x-ray film will be placed into a metal tray and slid behind the patient's back and the x-rays will be passed through the patient front to back this is forly known as the AP view though more commonly known as a portable chest x-ray AP films are inferior in quality to PA films for a number of reasons some of which will be discussed in lesson three and some in lesson 5 that concludes this introduction to chest x-rays if you found it helpful please remember to like or share it the next video will discuss a systematic approach to interpretation as well as normal chest x-ray Anatomy