This educational resource provides an overview of how to identify structures within the human thorax on a radiograph. It discusses how dense tissues like bones appear brighter on radiographs since they absorb more x-rays, while less dense tissues like lungs appear darker. The document then labels key bones, organs and other structures visible on a chest x-ray, including the ribs, heart, lungs, trachea and intercostal muscles.

1. Educational Resource Transcript
Radiographs are images that are produced by X-rays
This non-invasive imaging modality allows us to visualise internal bodily structures
In this educational resource I will be talking you through how to identify different structures
within the human thorax and then at the end you will have the opportunity to label a black
image on your own to consolidate your learning.
PA chest x-ray, picture was taken posterior to anteriorly
The patients front would have been in contact with the detector board
Although bones are more noticeable and clearer structures to identify on a radiograph,
some organs can also be visualized
Using this radiograph of a thorax, I am going to demonstrate and label organs and bones as
well as some muscle attachments
Before adding labels, this image is great for showing the how different tissues appear after
undergoing an x-ray
As density of tissue increases, x-ray absorption increases and the brighter these structures
appear on a radiograph and vice versa
So less dense materials appear darker as less x-rays have been absorbed
Therefore, on this radiograph dense bones, such as the ribs and vertebral column, appear
white as the calcium absorbs the x-rays
We can also visibly see the lungs in this image as we know the ribs are air filled and
therefore appear black due to air’s lack of density
Now let’s go on to labelling some structures and anatomy
First, we can see the trachea and the left and right main bronchi forming the airways
Next, as mentioned earlier, we can identify the lungs
The horizontal and oblique fissures separating the lobes of the right lung
And the singular oblique fissure of the left lung
Notice the inferior boarder of the right lung appears higher than the left as the liver would
occupy more space moving from the thorax to the abdomen
Next, we can identify the heart as a central structure
Notice the light grey colour of the cardiac muscles and tissue as its denser than air, but less
dense than bone
An orientation indicator is how the left ventricle is seen protruding and occupy more space
in the left side of the thoracic cavity
Roughly we can also identify the right ventricle as well as the left and right atria
Another key feature of the heart is the aortic arch as shown
We can also identify the inferior and superior vena cava, entering the right-hand side of the
heart

2. Now we’ll focus on the skeleton of the thorax
Indicated here are the clavicles or more colloquially known as the ‘collar bones’, which are
positioned anteriorly
Here all 12 pair of ribs have been labelled
Ribs 1-7 are called true ribs as they articulate directly with the sternum via costal cartilage
Ribs 8-10 are known as false ribs as they have an indirect connection with the sternum and
are attached via the costal arch
And ribs 11 and 12 are called floating ribs as they lack any connection with the sternum
We can also slightly see the shape of the scapula's or ‘shoulder blades’ and their articulation
with the left and right humeral heads forming the shoulder joint
Lastly, by defining the ribs making it clearer, we can draw on the attachments of the 3 layers
of intercostal muscles
The deepest layer are the innermost intercostal muscles and their fibres run in a vertical
direction between each rib, hence ‘inter’ meaning between , ‘costal’ meaning ribs
The next, more superficial layer to the innermost are the internal intercostal muscles.
These muscle fibres run obliquely backwards and downwards from the sternum to the angle
of the rib
And finally, drawn in yellow, the most superficial layer consist of the external intercostal
muscles which run obliquely forwards and downwards
Now with the knowledge you’ve just learned try to label this image yourself
Particularly keeping in mind, the density of tissues and therefore the colour structures will
appear on this radiograph