SA Imaging Flashcards
What does overexposure and underexposure look like on x rays?
Overexposure = black (digital imaging will correct this) Underexposure = white (grainy with digital imaging)
What happens if too high mAs with digital imaging?
Main concern is noise
Increasing mAs -> less noise
Too high mAs -> more scatter, less contrast
What if part of an x ray is sharp, but another part is blurred?
Likely movement artefact
So increase sedation and check exposure time
What is a grid for x rays used for?
Removes most scatter
Less radiation will reach the film so need to increase exposure to compensate
Bucky = a grid which vibrates to blur our grid lines
What is object-film length of x rays and how does it affect the image?
= Distance between the plate and the centre of interest
Shorter = more accurate the size of the image (think of a shadow when close or far away from a light)
E.g. lateral pelvis - ill wings will be superimposed if aligned correctly, but upper most will always appear larger as further from plate
Is DV or VD better to assess lung lobes on x ray?
VD - particularly for accessory lobe as heart and lungs fall away from sternum (but do get ventral mediastinal reflection)
When is a VD X-ray contraindicated?
Dyspneic or stressed animals
How to determine if a DV/VD X-ray is straight?
Spine and sternum should be superimposed
Dorsal spinous processes should be straight
Axial rotation if not
How to assess positioning of a lateral xray?
Costochondral junctions should be at same level
How to determine if a lateral xray was taken at maximal inspiration?
Diaphragm should cross dorsally at T13-L1
How to tell if a lateral x ray is left or right lateral?
Left lateral
- diaphragm crura intersect (Y shape)
- caudal vena cava (ST opacity) passes into first crura from caudal cardiac silhouette?
Right lateral - diaphragm crura parallel, caudal vena cava passes through first crura and into second?
Where to assess the size of the pulmonary artery and vein on a DV/VD xray? And cranial lobe vessels on laterals?
DV pulmonary vessels: Where cross 9th rib
Lateral, cranial lobe vessels: width compared to proximal third of 4th rib
Why should you do both lateral xray views if looking for pulmonary nodules?
Dependent side will be deflated so will get effacement of nodules on that side so will only see if do other view (e.g. see right sided nodules better on left lateral)
What does dorsal elevation of the trachea on lateral x rays suggest? What does straightening of the caudal border of the cardiac silhouette suggest?
Dorsal elevation of trachea: LV enlargement
Straightening of caudal border: LA enlargement
What may you see on radiography with a pleural effusion?
Pleural fissure lines (fluid between separated lung lobes)
Lung retraction from thoracic wall
Mediastinal shift (away from effusion)
Effacement of cardiac silhouette/diaphragm
What may you see with a pneumothorax on radiography?
Air outside lungs - no lung detail, very radiolucent
Retraction of lunds
May have dorsal displacement of cardiac silhouette
What are the 4 lung patterns on radiography and how do they look different?
Alveolar:
- air bronchograms
- effacement
- lobar sign (where one lobe is an increased ST opacity than another so can see the contrast between 2 lobes)
Bronchial:
- doughnuts and tramlines away from perihilar area (thickened bronchi - irregular, thick)
- bronchiectasis
- bronchial wall mineralisation
- peribronchial cuffing
Interstitial:
- hazy, mesh like
- increased ST opacity but no effacement of vessels etc
Vascular:
- widened vessels
- vessels not tapering off towards periphery
What to do to investigate a bronchial pattern?
Bronchoscopy and BAL
What could <3mm ST opacities be on radiography?
Can't be ST masses as would be too small to be seen Ddx: - osteomata - end on vessels - superimposed military structures
Ddx for increased lung opacity and where would they be distributed?
Bronchopneumonia and aspiration pneumonia - cranioventral
Cardiogenic oedema - perihilar in dogs
Non cardiogenic pulmonary oedema - caudodorsal
Atelectasis
Contusions
Ddx for a bronchial pattern?
Chronic bronchitis
Eosinophilic bronchopneumopathy
When is mediastinal shift seen?
Away from effusions, masses etc
Towards atelectasis
Ddx for mediastinal thickening (increased ST opacity) on x rays?
Lymphoma Thymoma Cyst LN enlargement Abscess Granuloma
How wide is a normal mediastinum?
<2x thoracic vertebral body width (wider in brachycephalics and fat dogs)
Where would a cranioventral mediastinal mass be located on a DV x ray?
Towards the left side because mediastinum normally deviates to the left in caudal thorax
What do pulmonary masses look like on radiography?
May have air bronchogram within it
Usually look different on left and right laterals
Soft tissue mass ddx on x rays?
CHANG Cyst Haematoma Abscess Neoplasia Granuloma
How to determine if a lateral abdominal x ray is a left or right lateral?
R lateral: - gas in fundus - duodenum and pylorus superimposed on eachother L lateral: - gas in pylorus
What should a normal liver look like on x ray?
Should be within costal arch
Sharp caudoventral border
Look at gastric axis
What should a normal spleen look like on x ray?
Semicircular shaped area of head (where attached to stomach dorsally, curved over on itself)
Tail is ventral, caudal to liver
What does it suggest if there is gas inside a mass on x ray?
Intestinal tumour
What could it be if mineral opacity in the stomach on x ray?
Barium study
Cat litter
Ddx for ascites?
FIP Lymphoma Pericardial effusion -> cardiac tamponade -> ascites R-CHF Peritonitis Etc
How to differentiate between GDV and pyloric outflow obstruction on x ray?
GDV: gas opacity
Pyloric outflow obstruction: ST/fluid opacity
Appearance of GDV on x ray?
- Can’t follow oesophagus into stomach
- Fundus distended and displaced ventrally (should be craniodorsal)
- Body caudodorsal to fundus
- Pylorus displaced to craniodorsal position
- Mass effect pushing intestines caudally
- Spleen may be enlarged
- Boxing glove/smurf head
- On VD: fundus displaced to right (on left normally), body on right going towards pylorus
Causes of megaoesophagus?
Idiopathic PRAA (cranial portion widened only) Myaesthenia gravis Aerophagia (mild e.g. if been panting lots) GDV Addison's Oesophagitis Artefact in sedated patients
Ddx for septic peritonitis?
Perforated mass
FB
Pyometra
How to assess x rays for hip dysplasia? What is a morgan line? What is the Norberg angle?
50% of femoral head should be within acetabulum - place dot in centre of head, should be medial to dorsal acetabular rim
Morgan line on neck of femur = mineralisation at border of joint capsule (sign of joint instability)
Norberg angle:
- place dot in centre of both femoral heads
- draw line between dots and a line from each dot to cranial (effective) acetabular rim
- angle should be >105 degrees if good hips
How do osteosarcomas appear on x rays?
Monostotic Radiolucency due to lysis Periosteal reaction Cortical destruction Expansile
Ddx for aggressive bone lesions on x ray?
Bone tumour or osteomyelitis
Ddx for stifle effusion?
Cruciate disease +/- meniscal tear
Septic arthritis (usually post-trauma or post-op)
Synovial cell tumour (would see destruction of tissue and aggressive changes)
Osteochondrosis
IMPA
Haemoarthrosis
What do you see on x ray with OC of tarsus?
Widened joint space between tibia and talus due to loss of medial ridge of trochlea of talus
Can get fragment migration into DDFT
What may otitis media look like on x ray?
Thickened wall of tympanic bulla (bone opacity)
ST opacity in bulla lumen (fluid)
Anatomy of tympanic bulla in dogs compared to cats?
Dogs - not divided, smaller
Cats - divided into dorsolateral compartment and ventromedial compartment, larger
How to assess spinal x rays?
Positioning - facets should be superimposed
Centring - important to centre on area of interest (as geometric distortion of vertebrae at either end)
Compare each vertebra to the two either side of it - should look similar
Assess vertebral canal diameter, foramen (horses head), articular processes
What would you expect on thoracic radiography with a cat in left sided CHF?
Pleural effusion
Pericardial effusion
Perihilar pulmonary oedema
What would you expect on thoracic radiography with a dog in left or right CHF?
L-CHF: pulmonary oedema
R-CHF: pleural effusion
What suggests overall cardiomegaly on lateral radiographs?
VHS >10
>60% of thorax taken up by heart
Centring and collimation for lateral thorax radiograph?
Centre: caudal border of scapula/mid thorax
Collimation: include thoracic inlet cranially, last rib caudally
Centring and collimation for VD/DV thorax radiograph?
Centre: sternum/spine and caudal border of scapula
Collimation: include thoracic inlet cranially, last rib caudally
Is DV or VD better for abdominal organs?
VD as organs spread out so less cramped
Centring and collimation of lateral/VD abdomen radiograph?
Centre: last rib (1cm caudal to last rib in cats)
Collimation: just cranial to xiphisternum and include greater trochanter caudally (include intrapelvic area in males if want to assess urethra)
Centring and collimation of mediolateral shoulder radiograph?
Centre: caudal and slightly proximal to greater tubercle
Collimation: include distal 1/2 of scapula and proximal 1/3 of humerus
Centring and collimation of caudocranial shoulder radiograph? How to check positioning?
Centre: midway between greater tubercle and acromion process
Collimation: include distal 1/2 of scapula and proximal 1/3 of humerus
Rotate patient slightly towards opposite limb
Palpate olecranon - should be pointing upwards
Centring and collimation of a mediolateral elbow radiograph?
Centre: medial condyle
Collimation: include distal 1/3 of humerus and proximal 1/3 of radius/ulna
Centring and collimation of a craniocaudal elbow radiograph?
Centre: midway between medial and lateral condyle
Collimation: include distal 1/3 of humerus and proximal 1/3 of radius/ulna
Centring and collimation for mediolateral and dorospalmar radiographs of the carpus?
Centre: accessory carpal
Collimation: include distal 1/3 of radius and ulna
Centring and collimation for lateral pelvis radiograph?
Centre: slightly cranial to greater trochanter
Collimation: to include proximal 1/3 of femur, wing of ilium cranial/dorsal and ischiadic tuberosity caudally
Centring and collimation for VD pelvis?
Centre: for hip scoring/BVA, the stifles must be included so centre on midline just caudal to greater trochanters
Collimation: include wings of ilium cranially and stifles caudally
Centring and collimation for mediolateral stifle radiograph?
Centre: cranial and distal to medial femoral condyle
Collimation: include distal 1/3 of femur and proximal 1/3 of tibia
Centring and collimation for CrCd and CdCr stifle radiograph?
CdCr better as closer to plate
Centre: midway between and distal to medial and lateral femoral condyles
Collimation: include distal 1/3 of femur and proximal 1/3 of tibia
How does US work?
Transducer head contains piezoelectric crystals
Electric current applied -> crystals vibrate and produce ultrasound waves -> transmitted through patient -> reflected back from tissue -> turned into electrical signal and processed
What is US acoustic impedance? How does it vary for gas, fluid, muscles, ST, fat and bone?
Acoustic impedance = product of tissue’s physical density and velocity of sound within the tissue
Gas: very low acoustic impedance
Fluid, ST, muscle, fat: all have a similar acoustic impedance
Bone: very high acoustic impedance
Therefore, US not good at producing images next to bone/gas as they have a big difference of impedance compared to other tissues so acts as boundary (bone has black shadow, gas has white shadow)
What are large curvilinear, linear and micro convex US transducers appropriate to use for? Frequency?
Large curvilinear: - low frequency - suitable for looking deep into tissues Small micro convex: - mid frequency - suitable for mid depth into tissues - smaller so good for scanning un between ribs and under ribs Linear: - high frequency - suitable for superficial regions e.g. testes, thyroid, musculoskeletal, cat abdomens
How do frequency and resolution and depth relate to each other with US?
Higher frequency = better resolution = reduced penetration
So have to reduce the frequency to image deeper tissues
What are B gain and TGC on an US machine?
B gain: alters the overall brightness
Time gain compensation (TGC): signal strength is reduced with depth due to attenuation, so TGC control used to suppress echoes close to the transducer and increase echoes from deeper regions to compensate for attenuation
What is the focal zone on an US machine used for?
Want to position the narrowest part of the beam (focal zone) at the depth of interest for good resolution
What frame rate is needed to keep up with cardiac valve movement on US?
50hz (50 images/second)
What is acoustic shadowing on US?
US beam unable to pass through an object (too dense or contains gas)
So less signal is received distal to the object -> shadow
Dark acoustic shadow = dense object
Hyperechoic acoustic shadow = gas object (e.g. loop of gas filled intestine - rays of sunshine)
What is reverberation on US?
Occurs when high intensity returning echoes hit the transducer and are reflected back into the patient a second time and so on
Appear as equally spaced parallel lines, becoming weaker with depth
What is acoustic enhancement on US?
Opposite of acoustic shadowing
Occurs deep to regions of low attenuation
E.g. a fluid filled cyst, or the bladder
Very low attenuation through the liquid, so stronger echoes from tissue deep to this = bright
How would a hypo echoic solid mass and a cyst appear differently on US?
Both hypo echoic but:
Solid mass: distal shadowing
Cyst: acoustic enhancement below it
What is the doppler effect on US? How is it used?
Occurs when US is reflected from moving blood cells
If blood flows towards the transducer, the returning echoes have a higher frequency than was transmitted (positive doppler shift)
If blood flows away from the transducer, the returning echoes have a lower frequency than was transmitted (negative doppler shift)
To be reliable, need transducer beam as parallel to flow as possible
Red = flow towards transducer
Blue = flow away from transducer
Brighter = faster flow
What would a thrombus look like with colour doppler on US?
Thrombus would be static with no colour doppler
Make sure not just perpendicular to blood flow
How echoic is the spleen on US compared to the liver?
Hyperechoic compared to liver
How echoic is the kidney on US?
Hypoechoic/anechoic medulla
Good corticomedullary definition
Hyperechoic pelvis
What does CKD look like on US?
Medullar hyperechoic with hyperechoic speckles
Loss of corticomedullary definition
Which parts of the intestine are anechoic/hyperechoic on US? What if muscular layer is thickened? What if mucosa has grey stripes or spots?
Mucosa and muscularis: anechoic
Submucosa and serosa: thin, hyperechoic
If muscularis layer thickened and becoming equal to mucosa: indicates IBD or infiltrative neoplasia (most often seen in cats)
If mucosa becomes greyer (grey stripes or spots): indicates enteritis or infiltrative neoplasia – check if grey dots go by changing the gain as may be artefactual
