Radiography & Ultrasound of Normal Thorax Flashcards
what are the views that can be used to assess the thorax
- right lateral
- left lateral
- dorsoventral
- ventrodorsal
what needs to be ensured in DV and VD views
the sternum should be in midline with the thoracic vertebrae
incorrect positioning can interfere with image quality
what is the convention of lateral views
head to left
vertebral column to top
what is convention for DV and VD views
head to top
left of patient to right of viewer
what are the two standard views used for assessment of the lungfields
- right lateral
- ventrodorsal
identify the lungfields
identify the lungfields
identify these structures
a. lobar artery
b. main bronchi
v. lobar vein
how far does the ultrasound beam penetrate
as far as outer pleural surface of the lung
what does ultrasound of normal lung show
which is visualized as a hyperechoic interface with distal acoustic shadowing that is filled in with regular lines of reveberation artefact (A lines)
this hyperechoic interface is smooth and can be seen to move with respiration
when can ultrasound be used
Ultrasound can only be used to visualise other structures in the thoracic cavity if they are in contact with the parietal pleura or there is an acoustic window through which the beam can pass to reach them. If there is any air present between the parietal pleura and the structure, either within the lung or free within the thoracic cavity then the structure will not be visible.
what structures can be assessed in the rest of the thorax using radiograph
trachea (gas filled)
what occurs during expiration
- heart looks bigger
- heart and diaphragm appear to touch or overlap
- accentuated bronchovascular pattern
what occurs during inspiration to thoracic radiographs
- lungfields appear larger
- appear more lucent
what is the effect of positioning
- the crura of the diaphragm appear to be parallel with each other in right lateral views but in left lateral views they appear to diverge producing an inverted “Y” shape. The abdominal contents push the lower crus in a cranial direction which means that in right lateral views it is the right crus of the diaphragm that is located most cranially but in left lateral views it is the left crus.
- The caudal vena cava runs through the right crus of the diaphragm therefore is seen to merge with the cranial crus on right lateral views but on left lateral views it passes the cranially located left crus to merge with the caudally located right crus.
- The heart is fixed at the base and mobile at the apex which in a standing dog sits slightly to the left of midline. In right lateral recumbency, the apex of the heart falls towards the right side of midline under gravity but is tethered by the pericardial ligament. This results in a more oval shape or egg shape to the cardiac shadow and the presence of an increased area of contact with the sternum.
- In left lateral recumbency, the heart apex falls to the left of midline and is not tethered therefore falls into a more upright position. This results in a smaller more rounded outline and the apex may be displaced slightly dorsally from the sternum
- Hypostasis and collapse of the lower lung due to the weight of the mediastinal contents and compensatory hyperinflation of the uppermost lung means that in right lateral views, lesions in the left lung will be better visualised and in left lateral recumbency the right lung will be better visualised.
- On dorsoventral views with the dog in sternal recumbency, the heart maintains its normal upright position in the thorax and therefore produces an oval shape in these views.
- In ventrodorsal views with the animal in dorsal recumbency, the apex of the heart falls away from the sternum and so the cardiac shadow appears longer and narrower than DV views.
- In DV views, the weight of the liver in the abdomen pushes the cupola of the diaphragm cranially so it appears as a single smooth bulge. In VD views the two crura are seen overlying the cupola producing a three humped appearance.
