SA Imaging Flashcards
Define collimation
Restriction of the beam size to the area under investigation. Good collimation limits scatter
Define exposure
Amount of radiation used to generate the image
Under= too white
Over= too black
How is a radiograph generated?
Electromagnetic radiation (x-rays) are produced by electrons colliding with a tungsten anode A beam of x-rays is directed through the anatomy of interest to a digital plate The beam is attenuated to varying extents by the tissues it passes through -> image on plate
Give the 5 opacities seen on a radiograph
Air (black; most radiolucent) Fat Soft tissue/fluid Bone (mineral) Metal (white; most radiopaque)
What does opacity of a tissue depend on?
Tissue’s atomic number and physical density
How can you differentiate between fluid and soft tissue on a radiograph?
Contrast
How are you able to see margins of organs in the abdomen on a radiograph?
Surrounding fat
How do you assess a radiograph?
Identify species and view Is it correctly labelled? Is it correctly positioned? Is the centre of the image the area of interest? Is it collimated correctly? Is the exposure adequate?
What is ‘mass effect’?
The effects of a growing mass that results in secondary pathological effects by pushing on or displacing surrounding tissue
How do cat skulls differ from dog skulls
Greater doming on the frontal and nasal bones
Smaller frontal sinuses (may be absent in Persians)
More complete bony orbits
Wider skulls due to wider zygomatic arches
What is ‘mediastinal shift’?
Deviation of the mediastinal structures towards one side of the chest cavity
Causes: volume expansion on one side of the thorax, volume loss on one side of the thorax, mediastinal masses, vertebral/chest wall abnormalities
What is the normal thickness of the following structures: Stomach wall Small and large bowel Duodenum Jejunum Large intestine
Stomach wall: 3-5mm Small and large bowel: 2-3mm Duodenum: 3-4mm Jejunum: 2-3mm Large intestine: <1.5mm
What is the difference between atelectasis and consolidation?
Atelectasis: collapse of one or more areas of lung
Consolidation: swelling and hardening of lung tissue due to the presence of fluid in the alveoli and smaller airways
When is atelectasis seen?
After surgery- air sacs collapse as a side effect of anaesthesia.
May also be caused by obstruction of airways (mucus plug/ FB/ tumour)
Pneumothorax
Pleural effusion
When is lung consolidation seen?
Pneumonia
Pulmonary oedema
Neoplasia
How do you classify a fracture on a radiograph?
Open/closed
Which bone/s?
Position: articular/epiphyseal/growth plate/diaphyseal
Fracture line: transverse/oblique/spiral/comminuted/segmental
Degree of displacement
Reconstructable?
What is border effacement?
Borders of an organ are lost due to loss of normal contrasting opacity
What is an air bronchogram?
Black bronchi ('trees') within surrounding white alveoli (filled with fluid or inflammatory exudates)
Seen with alveolar patternsWhat can cause osteophytes to form in the stifle joint?
Rupture of the cranial cruciate ligament
What is spondylosis deformans?
Bony spurs along the bottom, sides and upper aspects of the vertebrae of the spinal column
Response to ageing/ injury/ trauma
What is osteochondritis dessicans?
Disturbance of normal endochondral ossification
Often due to disruption in blood supply to the bone
Results in excess cartilage at the site -> abnormally thick, weaker regions of cartilage -> cartilage flap
Which dog breeds are most affected by Ostechondritis dessicans?
Large breed dogs eg Great Danes, Labradors, Rottweilers
What is an ‘alveolar pattern’ and when does it occur?
What are the radiographic signs?
Occurs when air in alveoli is replaced by fluid or cells, or not replaced at all (atelectasis)
Radiographic signs:
-White fluid opacity, varying from faint or fluffy, to solid, complete opacification
-Border effacement
-Lobar sign (only one lobe is affected)
-Air bronchogram (black bronchi against surrounding white alveoli)
-Effaced vessels
What is a ‘lobar sign’?
Only one lung lobe affected by an alveolar pattern
How do you differentiate between a DV and VD thoracic radiograph?
VD: diaphragm is flat with ‘Mickey Mouse’ ears
DV: diaphragm is rounded. Heart appears rounder and is displaced into left hemithorax. Fundus visible on the left of the radiograph
How could you tell if a thoracic radiograph is right or left lateral?
Right lateral:
- Can’t see caudal vena cava reaching the 2nd crus of the diaphragm
- 2 crura of diaphragm run parallel to each other
- Gas accumulation in fundus of stomach (will be in pylorus on LHS)
Which position should you place the patient in if you want to radiograph a mass on the left lung?
Right lateral
Will be harder to see in left lateral as the left lung will be collapsed
How big should a normal heart be on a radiograph?
2.5-3.5 intercostal spaces wide, 2/3 the height of the thorax
Why should you always take DV views before laterals?
To prevent mediastinal shift
Which is the best radiographic view for evaluating the cardiac silhouette and caudal pulmonary vessels?
DV
What would you think if you saw mineralisation in the adrenal glands in cats and dogs?
Cats: normal
Dogs: suspect adenocarcinoma
What are the Rontgen signs when looking at a radiograph?
Size Shape inc margins Number Opacity Location/position Margination
Why is it hard to differentiate between abdominal organs on a radiograph?
Fluid in abdomen -> border effacement
What is a ‘bucky’?
Used when radiographing thicker things (>10cm), has a grid on to reduce scatter
When taking a lateral radiograph of the abdomen, what should you centre on?
Where should you collimate?
How should you position the legs?
Centre on last rib
Collimate from just cranial to xiphisternum, to greater trochanter
Extend FLs cranially and secure with sandbags/rope ties
Extend HLs caudally and secure with sandbags/rope ties
Place foam pad between FLs and HLs so they are parallel to one another
Check sternum to spine height-should be level. If not, place a foam wedge under the sternum or spine to correct (not under ventrla abdomen as can alter how the abdominal contents lies)
When taking a lateral radiograph of the thorax, what should you centre on?
Where should you collimate?
How should you position the legs?
Centre on mid thorax/caudal border of scapula for cats and small dogs
Centre on mid thorax/caudal to caudal border of scapula for larger dogs
Collimate to include the thoracic inlet cranially, and the last rib caudally
Extend FLs cranially and secure with sandbags/rope ties
Extend HLs caudally and secure with sandbags/rope ties
Place foam pad between FLs and HLs so they are parallel with each other
Check sternum to spine height, should be level- if not, place foam pad under sternum or spine
How do you position for a VD thoracic radiograph?
What do you centre on?
How should you collimate?
Dorsal recumbency, supported by foam wedges/sandbags
Extend FLs cranially and secure with rope ties
HLs can remain neutral
Check for axial rotation
Centre on sternum/caudal border of scapula for cats and small dogs (caudal to caudal border in larger patients)
Collimation: include thoracic inlet cranially and last rib caudally
How do you position for a DV thoracic radiograph?
What do you centre on?
How should you collimate?
Sternal recumbency
Place head on foam pad
Place sandbag over neck
Partially extend FLs cranially
Palpate spine to ensure it’s straight, scapulae should be equal height
Centre on spine/caudal border of scapula for cats and small dogs (caudal to caudal border for larger patients)
Collimation: include thoracic inlet cranially and last rib caudally
How are veins positioned on a radiograph?
Ventral and central
Give some differentials for free gas in the abdomen on a radiograph
GI perforation eg ulcer, sepsis (gas produced by bateria)
How big should a kidney be on a radiograph?
<2.5 x length of L2 on VD/DV
Why may a kidney be enlarged on a radiograph?
Acute renal injury, hydronephrosis (eg obstruction, congenital), polycystic kidneys, neoplasia (lymphoma if bilateral, carcinoma if unilateral), peri-renal pseudocyst
Give a differential for seeing a small kidney on a radiograph
CKD
What do you see with a bronchial pattern on a radiograph?
Why does it occur?
Caused by thickening and increased prominence of bronchial walls, usually secondary to chronic inflammation.
Radiographic changes:
-Bronchial walls are visible further out in the periphery compared to normal
-‘Tram lines’ (thickened bronchi seen longitudinally as parallel radiopaque lines)
-End-on bronchi (‘donuts’)
What is penumbra?
Edge shadowing seen on radiographs
When would you use high and low frequency US probes?
High frequency: superficial structures
Low frequency: deeper structures
How do you differentiate between the liver and spleen on US?
Liver is hypo-echoic (more black) compared to spleen
How do you differentiate between hepatic and portal vessels on US?
Portal vessels have white borders (like ‘portholes’), hepatic vessels do not
What may you see in a normal bladder of a cat on US?
Floating speckles of sediment or fat
The trachea naturally runs on which side of the body?
Right
How wide should the mediastinum be on a radiograph?
No more than 2 x width of thoracic vertebrae
If wide with a soft tissue opacity -> mediastinal mass
Give some common diseases associated with an alveolar pattern
Pneumonia Pulmonary oedema (eg L-CHF) Haemorrhage Atelectasis Neoplasia
What is an ‘interstitial pattern’ and when does it occur?
What are the radiographic signs?
Occurs when there is thickening, fluid or cellular infiltrate into the interstitial space
Radiographic signs:
-Overall increase in hazy, linear opacities
-Vasculature is ‘smudged’ but still visible
Give some causes of an interstitial pattern on a radiograph
Geriatric fibrosis (benign, 'old age' change) Interstitial pulmonary oedema Haemorrhage Interstitial pneumonia Pulmonary fibrosis Neoplasia
Give some causes of a bronchial pattern on a radiograph
Chronic bronchitis
Feline asthma
Bronchiectasis (irreversible dilation of bronchi due to very chronic inflammation)
Pulmonary infiltrates with eosinophilia (severe hypersensitivity reaction)
When are ‘vascular patterns’ seen on a radiograph?
Where are the vessels visible on lateral and DV/VD views?
Present when pulmonary arteries and/or veins increase in prominence.
Causes: heartworm, L-CHF, left-to-right shunt (PDA, VSD)
Lateral: vessels seen best in cranial lobes
DV/VD: vessels seen best in caudal lobes
Which lung lobes does aspiration pneumonia tend to affect?
Cranial and right middle
Give some causes of megaoesophagus
Hyperthyroid Myasthenia gravis Addisons Idiopathic Lead toxicity Mechanical obstruction Stricture
When do growth plates close in cats and dogs?
Dogs: 18 months in large/giant breeds,10-12 months in other breeds
Cats: begins at 4 months, usually complete by 7-9 months
What do the red and blue colours represent when using Doppler with US?
Red: blood flowing towards the probe
Blue: blood flowing away from the probe
(vessel must be running at an angle to the probe therefore angle the probe at least 60 degrees to the vessel)
What size needle should you use for US-guided FNA?
22G, 1.5” needle
When might you use aspiration when taking an US-guided FNA?
Lymph nodes, poorly exfoliative masses
What should the thickness of the bladder wall be on US?
2-3mm
Where would transitional cell carcinomas be located within the bladder?
Bladder neck
How do nasal turbinates differ in appearance from ethmoturbinates?
Nasal turbinates are very linear, whereas ethmoturbinates are more tortuous
How does the tympanic bulla differ between cats and dogs?
Cats: have a septum when separates them into 2 compartments
Why may you see dorsal displacement of the trachea on a radiograph?
LA enlargement
Why may you see ventral displacement of the trachea on a radiograph?
Megaoesophagus
What might you suspect if you see thickening of the gallbladder wall on US?
Start of cholestasis
How does the location of gas within the stomach vary with radiographic positioning?
RL: gas is located within the body and fundus
LL: gas is located within the pyloric antrum
VD: gas is located within the centre of the stomach
DV: gas is located mainly at the body and fundus, with a small amount at the pyloric antrum
How thick should the stomach wall be on US?
3-5mm
Is mucosa and muscularis hypo- or hyper-echoic on US?
What about submucosa and serosa?
Mucosa and muscularis: hypoechoic (more black)
Submucosa and serosa: hyperechoic (more white)
What is the normal diameter of the intestines on a radiograph in cats and dogs?
Dogs: <1.6 x depth of L5
Cats: 12mm
What is functional ileus?
How does it look on a radiograph?
Absent peristalsis with no mechanical obstruction
Appears as uniform intestinal dilation, mostly filled with gas
What should the diameter of the colon be on a radiograph?
<1.5 x length of L7
How thick should the wall of the large intestine be on US in dogs and cats?
Dogs: 2-3mm
Cats: 1.5-2mm
How would you identify megacolon on a radiograph?
Partial/generalised enlargement of the colon
Large amount of faecal material is usually present in affected areas
Give some causes of megacolon
Idiopathic
Neurologic disease
Chronic constipation
Chronic inflammation
Give some differentials for pneumoperitoneum (free gas in the peritoneal space)
Penetrating trauma
Rupture of a hollow viscus
Iatrogenic (eg secondary to laparotomy)
Are lymph nodes visible radiographically?
NO, unless enlarged or mineralized
How do we assess liver size on a radiograph?
By evaluating position of gastric axis on a lateral radiograph (normal= somewhere between parallel to ribs and perpendicular to spine)
How would we identify hepatomegaly on a radiograph?
Anticlockwise rotation of the gastric axis
Rounded liver margins
Give some differentials for hepatomegaly on a radiograph
Endocrine disease Hepatic lipidosis (cats) Neoplasia Venous congestion Inflammatory/infectious Severe nodular hyperplasia
How would we identify microhepatica (small liver) on a radiograph?
Clockwise rotation of the gastric axis
Decreased distance between stomach and diaphragm
What would we suspect as a cause of microhepatica on a radiograph?
Vascular shunt
Chronic inflammation
How would we identify splenomegaly on a radiograph?
Thickened, rounded, blunted margins
Dorsal and caudal displacement of the jejunum
Give some differentials for splenomegaly on a radiograph
Inflammation/infection Hyperplasia Congestion Neoplasia GA/sedation (ACP/Thio)
How might we see an adrenal mass on a radiograph?
Soft tissue/partially mineralised mass craniomedial to a kidney
May displace kidneys ventrolaterally if large enough
How would you identify benign prostatic hypertrophy on a radiograph?
Symmetric enlargement with smooth, well-defined margins
Cranial displacement of the bladder
Dorsal displacement of the rectum
How would you identify prostatitis on a radiograph?
Symmetrical/asymmetrical prostatomegaly
Often ill-defined margins
When may you see mineralisation of the prostate?
Neoplasia
