Introduction To Thoracic (Cardiac & Respiratory) Imaging Flashcards
What is the commonest modality used to image the thorax? Why?
CXR
Can see lung + cardiac pathology
Useful quick primary screen that is relatively cheap
What other modality’s can be used to image the thorax? Why?
CT: see multiple thoracic structures
CTPA: pulmonary angiography e.g. in embolism
US: pleural pathology
Why would you not use MRI as a first choice to image the thorax?
Expensive, takes time + is unpleasant for patients
What is MRI used mainly for in terms of imaging the thorax?
Cardiac investigation
How do X-rays work?
X-ray generator produces X-ray beams which come out of point source projector + spread out going through the patient + into the detector/film
How directions can thorax X-rays be done in? How do you achieve this?
PA: X-ray source anterior to patient, detector posterior
AP: X-ray source posterior to patient, detector anterior
What direction are most thoracic films taken in? Why?
PA
Want the heart to appear life size so it must be as near to detector as possible
How should thoracic images be read in a systematic way?
- Demographics (ID, DOB + name)
- RIP (rotation, inspiration + penetration)
- ADCDE (airway, breathing, cardiac, diaphragm + everything else)
How can you assess the rotation of a patient on an X-ray?
Sternal head of clavicle + spinous processes in midline of vertebrae (tear drops) - see if spinous processes equidistant from collar bone joint + if so, the patient is head on
How can you assess the inspiration of a patient on an X-ray?
You want to be able to see ribs 5-7 anteriorly
Start counting from the 2 dark ovals at the lung apex (rib 1) + follow their curvature
How can you assess the penetration of an X-ray?
You want to be able to see the vertebral column outline + invertebral discs behind the heart
What will the trachea look like on an X-ray?
Midline (should be lined up with spinous processes) mostly below the clavicle
Appears dark as air is in it whilst surrounding tissue is white due to sot tissue, fat + blood etc.
Should be able to trace it down to R + L bronchus at rib 2 where it bifurcates
What should the diaphragm look like on an X-ray?
Dome shaped on both sides
Why do the back of the ribs on an X-ray appear whiter than the front?
Because the front is cartilage
What is penetration?
How well the X-ray has been absorbed by the structures i.e. how well you can visualize them
Why should you not rely on the heart as a marker for the direction the patient is facing?
In conditions such as dextrocardio, the heart is on the right, so this will confuse the image
What in the airways do you want to mainly look at on X-ray?
Tracheal position
What do you want to look for in a X-ray in terms of breathing + cardiac structures?
Breathing: hilum + lung fields
Cardiac: cardiothoracic ratio
What should the hilum of the lung look like on X-ray?
Hilar point is V-shaped where bronchi start to divide
Appears whiter than surrounding lung tissue as its denser due to vessels + bronchi
If the lung hilum is not visible due to a larger white structure in the way, what may this be? Why might a patient have this?
Mediastinal lymphadenopathy
Tumour may have metastasized to the lymph nodes in the mediastinum
If a patient has mediastinal lymphadenopathy, what clinical picture may they present with?
Dysphagia Stridor in breathing (due to tracheal compression) Hoarse voice (due to RLN compression)
What should normal lung fields look like on an X-ray?
White lines should project to edge of thoracic cage meeting outer perimeter due to blood supply + tracheobronchial tree
What are the 4 different zones examined on X-ray of the lungs?
- Apical: above clavicle
- Upper: below clavicle + above lung hilum/cardiac shadow
- Middle: level with lung hilum
- Lower: below hilum + including costodiaphragmatic recess
What should the costodiaphragmatic recess look like on X-ray?
V-shaped black groove in lower zone of lungs
What is a lower zone opacity?
Costodiaphragmatic recess whiter in colour having lost its shape indicating fluid build-up here
Why do you take X-rays on inspiration?
As costodiaphragmatic recess lined by parietal pleura + lungs travel into these when you take a deep breath in as diaphragm contracts dropping down opening up these V-shaped grooves for the lungs to slide into
How can you tell if opacity is fluid?
Fluid line i.e. meniscus affected by gravity
Why can pleural effusions occur on 1 side of the lung?
Because pleura are not continuous from the left to the right lung
What is the Mach effect?
Optical illusion where the edges of darker objects adjacent to lighter ones appear lighter (vice versa) - can trick you into thinking there is a shadow on an X-ray
What marking can you use for the horizontal lung fissure of the right lung?
Costal cartilage of rib 4
What marking can you use for the middle lobe of the right lung?
Wedge-shaped structure just below the costal cartilage of rib 4
Why can you not see the whole of the inferior lobes on X-ray?
A lot of it extends round the back of the other lobes (will become visible if it becomes white due to pathology)
Why would you want to be able to know where the different lung lobes are on X-ray?
So you know where pathology is occurring e.g. can just get a middle lobar pneumonia where just this lobe shows opacity
What type of scan was utilised before CT scans? Why is this no longer used?
Radio-opaque high MW substance injected into tracheobronchial tree enhancing contrast
Substance was oily so after patients got infections/inflammation - no longer used as CT has superseded it
What are the smallest functional segments of the lung?
Bronchopulmonary segments (further subdivision of lobes)
What might you see in an X-ray if bronchopulmonary segments are pathologically affected?
Gravity dependent regions due to postural gravity drainage so fluid may collect when a patient is laying down
What is an atelectasis? What can cause it?
Collapse of lung
Blockage of segmental or lobar bronchus
What is a silhouette?
Structures that cast a shadow e.g. heart
If the lung fields appear blacker, what is the problem?
Pneumothorax
In order, what are the common causes of pleural effusion?
- CHF (transudate)
- Pneumonia (exudate)
- Cancer (exudate)
- Pulmonary embolus (transudate/exudate)
- Viral disease (exudate)
- CAB surgery (exudate)
- Cirrhosis with ascites (transudate)
What is the difference between transudate and exudate fluid in a pleural effusion?
Transudate is fluid pushed through the capillary due to high pressure within the capillary. Exudate is fluid that leaks around the cells of the capillaries caused by inflammation
Why is the diaphragm slightly higher up on the right?
Liver
You need to take the X-ray along with the ___ __ to make a diagnosis.
Clinical picture
What will you see in an X-ray of a COPD patient?
Hyperinflated thorax
Flattened diaphragm
Increased Hilar shadow
Perhaps bullae
How can you quantify the size of the heart on an X-ray?
A normal sized heart on a PA X-ray should be 50% or < of the cardio-thoracic width on inspiration at rest
Measured by cardiac width/thorax width
What should the aorta look like on X-ray?
Hockey stick/candy cane as it curls up, around + down
If the aorta appears enlarged, what might the problem be?
Aortic aneurysm
What should the pulmonary trunk look like on X-ray?
Grey T-shaped shadow showing the PA going to the L lung
What is the problem called if there is black space below the diaphragm?
Pneumoperitoneum
What other form of scan may be used to view the pulmonary trunk?
Artery angiogram
What other organs, not in the thorax, may show up on thoracic X-rays?
Abdominal organs
How are axial CT images viewed?
As if you are looking up the feet of a patient lying in their bed
Why can you view internal structures in the lung clearly on a CT scan?
Can change black + white points
When viewing the heart on a coronary CT, what must you be aware of to help orientate yourself?
Most of LV is round the back along with LA (will be lower on scan)
RV + RA round the front (will be higher on scan)
