Diagnostic Imaging Flashcards
what are the main types of diagnostic imaging?
- CXR &CT
- MRI
- Ultrasound
- nuclear medicine imaging
CXR & CT
what do solid tissues appear as on imaging?
white (absorb radiation)
CXR & CT
what appears as dark?
air filled spaces which dont absorb radiation
what does an MRI use?
magnets and radiofrequency pulses
what does an US use?
high frequency sound waves, reflected from tissues
what happens in nuclear medicine imaging?
radioactive medication is injected, inhaled or swallowed, then picked up with a gamma camera
is a chest x-ray non-invasive?
yes
is a chest xray common?
yes
is a CXR low or high radiation?
low (vs CT)
what is a CXR used for?
- diagnosis of conditions
- pre-operative assessment
- to check correct position of medical therapies involving lines/tubes (e.g. IV, ICC)
- to assess effectiveness of therapies
limitations of a CXR
- 2D view of a complex 3D structure
- therefore, requires multiple CXR views to visualise structures adequately
how is the CXR always viewed?
as if the patient is facing you (i.e. their left is your right)
what happens if the patient has the left chest wall on the cassette?
- diminishes effect of heart magnification
- demonstrates better anatomical detail of the heart
when is an AP CXR taken?
when the patient is unable to stand/ go to the radiology department
- may be taken sitting / supine
order of how to read a CXR?
- technical details e.g. name, AP/PA
- quality of film
- extra-thoracic structures e.g. UL girdle, soft tissues, abdominal structures
- thoracic cage e.g. bones, diaphragm
- intra-thoracic structures e.g. mediastinum (trachea, heart, hilum), lung fields
- attachments / foreign structures
IMAGE QUALITY
What should the medial ends of the clavicle be for you to know the patient isnt rotated?
equidistant from the spinous processes
IMAGE QUALITY
what should the film be taken on?
full inspiration
what ribs intersect the diaphragm (anteriorly)
5-6 (one rib lower on the left)
what ribs intersect the mid diaphragm posteriorly?
9-10 (one rib lower on the left)
how can you tell if CXR = over or under exposed?
IV disc should be just visible through heart shadow
underexposed CXR characteristics?
- whiter
- unable to see IV disc spaces behind heart
- may ‘over-interpret’ opacities
overexposed CXR chracteristics?
- blacker
- loss of lung markings
- may ‘miss’ abnormalities
what UL girdle things can you see on CXR?
- clavicle height
- scapular outlines (white arrows, on AP view)
what soft tissues can you see on CXR?
- muscles / adipose tissue
- breast shadow
what features lie below the diaphragm on a CXR?
air, gastric bubble
THORACIC CAGE
what features of the spine can you se on CXR?
curvatures e.g. scoliosis/ kyphosis, rotation, fractures
THORACIC CAGE
what rib features do you look for on CXR?
- shape anteriorly & post
- crowding / increased rib spaces
- fractures
THORACIC CAGE
what do you look for in diaphragm
- shapes, outline/ borders, position, angles
diaphragm features in CXR
- should be clearly defined
- domed shape
- costophrenic & cardiophrenic angles (clear & acute)
- right hemi diaphragm (2xm higher than left)
- raised : paralysed (SCI/phrenic nerve), LL atelectasis/ collapse, low lung volumes / poor inspiratory effort
- lowered: hyperinflation (gas trapped in lungs), gas in the pleural space (pneumothorax)
INTRA-THORACIC STRUCTURES (MEDIASTINUM)
Trachea features
- midline
- bifuractes into L&R main bronchi at the carina, approx T5-7 vertebral level
INTRA-THORACIC STRUCTURES (MEDIASTINUM)
Hilar region features
- contains pulmonary arteries / veins, bronchi, lymph nodes
- size
- position (L should be higher than R)
INTRA-THORACIC STRUCTURES (MEDIASTINUM)
Major vessels features
- aortic arch
- vena cava
INTRA-THORACIC STRUCTURES (MEDIASTINUM)
Heart features
- position = 1/3 on right, 2/3 on left
- size & shape = heart should be <50% internal diameter of the chest cavity (larger heart size may be cardiomegaly)
- borders = clearly defined, loss of left heart border could mean issue in lingula, loss of right heart border could mean issue in RML
- heart chambers = RA, RV, LA, LV
how should the lung fields look?
mostly dark with thin white lung markings throughout
where do the lung markings extend to?
edges near thoracic cage
density of lung fields
L=R
when is there extra shadowing/ opacity? which pathologies?
- pneumonia/ consolidation (patchy opacity)
- atelectasis / collapse
- cancer / tumour (rounded opacity)
how do CT’s work?
X-rays are processed by a computer to form tomographic (slices) images and a 3D picture
what are the 3 main types of CT?
- standard method
- CTPA (CT pulmonary angiography)
- high res CT
Standard Method Chest CT
- contrast used to highlight mediastinal structures
- entire thorax imaged
- slices = 5-10 mm thick
CTPA
- looking for blood flow abnormalities, such as pulmonary embolus
- use a contrast
high res CT
- very thin (1mm) axial sections
- only 10-20 mm taken
- no contrast used
- used in ILD suspencted & bronchectasis (highlights narrow walls & thick mucous plugging)
advantages of chest CT
- 3D images
- greater diagnostic accuracy and localisation of pathology
- better at imaging small airways, mediastinum, pleura, and lung parenchyma than CXR
- CTPA is gold standard for diagnosing PE
disadvantages of chest CT
- cost
- access
- radiation dose is much higher than XR
- CT scan contrast agents can worsen vulnerable kidneys
- minor movement artefact
what is a silhouette sign?
- the loss of a silhouette/ clear defined border
how does a silhouette sign occur?
if an area of lung becomes collapsed/ consolidated it becomes denser (more white), as there is less air there
what does the loss of the L heart border indicate issues with?
lingula
what does the loss of the R heart border indicate issues with?
RML
what does the loss of the diaphragm border indicate issues with?
lower lobe
air bronchogram definition
air-filled bronchi (dark) are made visible by the opacification of the surrounding alveoli (white)
air bronchogram pathophysiology
caused by pathologic alveolar process in which something other than air fills the alveoli e.g. pus, blood, fluid, ARDS, pulmonary oedema
what is atelectasis/ lung-collapse a result of?
loss of air in a lung / part of the lung with subsequent volume loss & increased density
features of atelectasis/ lung volume
- opacity (due to loss of air)
- smaller lung due to loss of air in the lung overall
- structures can shift towards an area of lung collapse
- e.g. diaphragm moves up, mediastinum moves towards the side of loss of volume, rib cage moves towards mediastinum - +/- silhouette sign depending which part of lung is affected
- +/- air bronchogram
what is consolidation?
alveoli filled with fluid, usually indicating pneumonia
features of consolidation on CXR:
Opacity (whiteness)
* Lung is ‘solid’ because air spaces are filled with fluid
* Opacity may be “anatomically” delineated (lobar
pneumonia) or “patchy” (bronchopneumonia)
– No loss of volume
± silhouette sign depending which part of lung is affected
± air bronchogram
consolidation vs collapse
- collapse = structures are shifted towards the area of collapse
hyperinflation
increased lung volumes e.g. TLC
Features of hyperinflation on CXR
Increased lucency (blackness)
* Lung contains more air
* Loss of lung tissue (less lung markings)
Increased volume
* Low, flat diaphragm (loss of dome)
* Obtuse (less acute) costo and cardiophrenic angles
* Increased rib spaces
* Posterior ribs more horizontal
Elongated heart & media stinum structures
± bullae (thin walled air filled spaces within the lung)
what are bullae
numerous thin-walled,
air-containing structures
that represent the walls
of numerous bullae
(white arrows).
acute pulmonary oedema pathophysiology
fluid accumulation in the extra-vascular spaces of the lung (i.e. interstitium &/or alveoli)
acute pulmonary oedema aetiology (causes)
- cardiogenic (e.g. left heart failure)
- non-cardiogenic (e.g. sepsis, drowning, ARDS)
features of acute Pulmonary Oedema on CXR
Increased opacity (diffuse, bilateral, “batwing”)
± septal lines (Kerley B lines)
± cardiomegaly (where heart failure is the cause)
± pleural effusions
Pleural effusion definition
fluid in the pleural space
features of PEff on CXR
– Increased opacity
– Blunting of the costophrenic angle/s (meniscus)
– May be unilateral or bilateral depending on cause
– Characteristic ovoid/elliptical appearance on lateral view
± features of the causal condition (eg heart failure, Ca)
Pneumothorax definition
air in the pleural space (between visceral and parietal pleura)
Features of pneumothorax on CXR
– Area of increased lucency (blackness)
– Absence of lung markings
– Lung edge visible (of visceral pleura)
– Usually accumulates non-dependently; apical on upright
CXR if small pneumothorax
± other features (eg # ribs, subcutaneous emphysema)
what is a tension pneumothorax?
progressive build-up of air within the pleural space
what is a tension pneumothrax usually due to?
a lung laceration which allows air to escape into the pleural space but not to return
is a tension Pneum life threatening? if so, why?
yes - requires urgent decompression
what does a tension pneum result in?
shift of structures away
from side of pneumothorax (>1/3 of hemithoracic volume or shift of mediastinum)
subcutaneous emphysema definiton?
air in the subcutaneous tissues (skin & muscle layers)
features of subcutaneous emphysema on the CXR
areas on increased lucency (blackness) in extrathoracic soft tissue +/- other features (e.g. #ribs, pneumothorax)
what is a lung abscess?
A localized collection of pus within the lung that leads to formation of a cavity, usually with a thick wall.
what is a malignant mesothelioma?
an aggressive malignant tumour of the mesothelium, mostly arising from the pleura
what is a malignant mesothelioma the most common of?
primary pleural neoplasm
CXR mesothelioma
pleural opacity which encases & contracts the affected hemithorax
+/- pleural effusion
key points to note with infants CXR
- Different chest wall shape
- Horizontal ribs
- Proportionally larger heart
