Diagnostic Imaging Flashcards
How are X-rays produced?
By the interaction of fast moving electrons with a metal target. Used in radiography.
How are gamma rays produced?
Gamma rays are produced by decay of radioactive elements and are used in nuclear medicine/scintigraphy.
How do x-ray machines vary?
In specifications of exposures, anode type, focal spot and filtration.
What is the relationship between current, temperature and number of electrons produced?
The higher the filament current = the higher the temperature = the greater the number of electrons produced
In an x-ray machine, what is the typical potential difference between electrodes?
50-100,000 V
What is the anode made of and why?
Anode is the target and is made of solid tungsten, as it has a high atomic number (74) and so a melting point of 3380 C.
How is the energy of an x-ray determined?
Maximum energy of an x-ray emitted = kV applied across the tube. The spectrum of energies in the beam are less than this. (Peaks on a spectrum due to the properties of tungsten).
What produces x-rays and in what proportion?
The interaction between the electrons and the anode produced heat (99%) and X-rays (1%)
How does kV affect the x-rays produced?
Higher potential difference = faster electrons will travel between electrodes = more kinetic energy at anode = x-rays are higher energy
What is the typical kV of the resultant x-rays?
40-120kV
How does kV need to be altered for different parts of the body?
Thicker parts of the body = increase kV needed
What is the relationship between kV and exposure?
An increase of 10kV approximately doubles the exposure
How does mA affect exposure?
Doubling the mA approximately doubles the exposure
What is the typical mA in x-ray machines?
Typically mA is 20-60mA in a portable and 1000mA in a fixed machine
How does mA differ for different parts of the body?
Higher for thicker parts of the body
What is the effect of time of exposure on resultant x-rays?
Increasing the time of exposure results in an increase in the number of X-rays produced
What do time and mA govern?
Quantity of x-rays produced
How is exposure affected by distance?
Distance affecting exposure via the inverse square law: the exposure is inversely proportional to the square of the distance from the x-ray tube. It is important to keep the distance between the x-ray tube and the x-ray cassette constant.
What are the 3 interaction of electrons with matter?
X-ray photons pass through unchanged
X-ray photons are absorbed
X-ray photons are scattered
What are the 3 factors affecting x-ray absorption?
Atomic number
Physical density
Thickness of tissues
What is the relationship of absorption factors with radio-opacity?
Greater thickness/ Higher Z/ Greater density = increased absorption = more radio-opaque
What are the 5 opacities detected?
Gas = black
Fat = dark grey
Soft tissues = grey
Bone = white
Metal = bright white
Can soft tissues be differentiated on radiographs?
No. The only thing that will change how they look is thickness. Only fat and soft tissues can be distinguished.
What is CR and DR?
Different image receptor: storage phosphor cassette CR or flat panel detector DR.
What is input pixel intensity?
The amount of radiation reaching the receptor.
What is the risk of overexposure?
Overexposure will still have a good image but may subject patient to more and more radiation and scatter radiation to staff.
What are the advantages of digital radiography?
- Decreased costs
- Reduced repeat rate so saves time and decreased radiation dose
- Improved images
- Easy easily stored and sent
- Portable – instant images in ‘field’
- Good for seeing soft tissues
What are the disadvantages of digital radiography?
- Set up costs
- Viewing images limited by availability of computers
- Specific artefacts
- Ensuring adequate back up files
Define contrast.
The difference in density between 2 adjacent areas on a radiograph
Define subject contrast.
Range of radiographic densities within an animal, that depends on a tissue’s atomic number, density, thickness.
How does kV affect contrast?
Higher kV results in an overall rise in x-ray penetration through all tissues = lower contrast
How do abdominal and thoracic radiographs differ and why?
Abdominal uses lower kV, as there is less inherent subject contrast.
How does scattered radiation affect contrast?
Causes overall blackening of the film and reducing contrast.
How can scatter be reduced?
Using grids in thicker areas
Collimation reduces size of primary beam
What is the consequence of using grids to reduce scatter?
A proportion of the primary beam is also removed by the grid, leading to an increase in the exposure required.
What is a grid factor?
- Multiple of mAs, typically 2-6, needed when using grid compared to same exposure without grid
- Depends on grid ratio
- Higher grid ratio = more primary beam is removed = higher grid factor
When does grid cut off happen?
Due to upside down focused grid.
What does collimation do?
- Reduces the production of scattered radiation, which improves image quality
- Reduces exposure to staff and patient
What is sharpness affected by?
Movement blur, focal spot size, distance from the film to focal spot and the distance from the object to the film.
Why does a smaller focal spot create a sharper image?
Smaller penumbra/blurring around the edge due to lines continuing to diverge after the object
What is FFD and its affect on sharpness?
Focal film distance. Typically between machine and table. Smaller FFD leads to larger penumbra and therefore less sharpness.
What is OFD and its affect on sharpness?
Object film distance. Typically between image and detector. Larger OFD leads to larger penumbra and therefore less sharpness.
What is magnification the result of?
Result of a diverging beam, more they spread out, the more magnified the image is
How is magnification calculated?
Magnification = FFD ÷ (FFD – OFD)
How is magnification reduced?
Using a longer FFD and a smaller OFD
When does distortion occur?
When the object is not parallel to the film and is increased by poor positioning.
What does Uberschwinger/rebound artifact look like?
Blank ring/radiolucent halo. If artefact, halo continues into soft tissues and does not stop at bone.
Where does Uberschwinger/rebound artifact occur?
- Occurs whenever there is a large density difference between adjacent objects
- Most commonly seen around orthopaedic implants
- Arises due to excessive edge enhancement of the image
What does Uberschwinger/rebound artifact indicate?
Important to recognise this artefact as it can mimic implant loosening
Why may a ghost image occur?
Incomplete erasure of a CR plate before use or if a CR plate is exposed to light.
What does the Moire artefact look like?
Bands seen across the image in CR systems
Why does Moire artefact occur?
Results of interference/mismatch between the frequency of the laser reader and the number of lines per cm in the grid.
How is the Moire artefact solved?
Turn grid 90˚ or use higher frequency grid
Why are even small doses of radiation dangerous?
Doses are cumulative
Which cells are most susceptible to ionising radiation?
Rapidly dividing cells - bone marrow, ovary/testes, skin, GI tract, embryo
What are the effects of ionising radiation?
Inflammation
Slowed cell growth
Necrosis
Potential malignant change due to DNA damage
Genetic mutation
Name the methods of protection against ionising radiation.
Space/distance
Barriers
Protective clothing
Time
What are the parameters of a controlled area?
Area where the radiation dose mat exceed 7.5uSv*/hour. Effectively 2m around a vertical beam.
What is the legal radiation dose of the general public?
1mSv
What is the legal radiation dose of trainees 16-18y?
6mSv
What is the legal radiation dose of occupational 18+y?
20mSv
What are the advantages of MRI?
- Good anatomical detail
- No ionising radiation.
- Imaging inaccessible areas (particularly brain and spinal cord)
- Accurate assessment of extent of spread of a lesion
What are the disadvantages of MRI?
- Not widely available
- Expensive - equipment, installation, maintenance and the time taken (every sequence/plane takes extra time).
- GA.
- No metallic objects around
What are the uses of CT scans?
- Detailed anatomical reconstructions
- Inaccessible areas
- Scanning time shorter than with MRI
- Availability increasing
- Avoids superimposition
- More sensitive than radiographs for detection of changes to the nasal turbinates and bullae and to pulmonary metastases
- Lymph nodes visible
What does 3D CT reconstruction allow?
- 3D printing of bones is possible from CT data
- Facilitates surgical planning and practising before going into surgery
What are the disadvantages of CT?
- Not widely available in practice
- More expensive than radiography
- Slower scan time than an X-ray
- Uses ionising radiation so higher patient doses than radiography
- Repeated CT scans are likely to have a very high dose of radiation
Which radioisotope is commonly used in scintigraphy?
Technetium-99, with energy around 140kV
What are the main veterinary uses of scintigraphy?
- Look for skeletal injury in horses, especially in difficult radiography areas – spine, pelvis.
- Used in large and small animals where it is difficult to localise the source of lameness.
- Look for ectopic thyroid tissue is hyperthyroid cats.
What are the advantages of scintigraphy?
- Increasingly available in larger equine centres, less so in small animal practices.
- The uptake of the bound isotope depends on metabolism and not just anatomy, so element of functional assessment.
What are the disadvantages of scintigraphy?
- Ionising radiation
- Patient remains radioactive for some time afterwards
- Patient care – minimise contact time
- Disposal considerations – bedding, faeces
- Poor anatomical detail
- Additional legislation by environmental agency apply
What is the half life of technetium?
6 hours so patient remains radioactive for 48 hours after
What type of waves do ultrasounds use?
High frequency sound waves, typically 5-10MHz in 1ms pulses
How are sound waves different to x-rays?
Need a materials to travel through (velocity depends on material)
How are sound waves for ultrasounds produced?
Piezoelectric effect – through a crystal
How long are the sound waves typically sent out by transducers?
Typically 3 wavelengths. 1.5mm in 1us (important for resolution). Production of ultrasound 1% of the time and receiving ultrasound 99% of the time.
What is the equation for acoustic impedance?
Acoustic impedance = density of tissue x speed of sound in tissue
What does acoustic impedance affect?
Proportion reflected
What is spectrum (mirror) reflection?
Beam hits large smooth surface. Air creates bright line, as air reflects. If perpendicular, strong reflection.
What is non-specular reflection?
Beam hits small structures. Re-radiation in all directions – weak echoes. Gives texture to organs on ultrasounds
What are the different display modes for ultrasounds?
A mode/amplitude - few clinical indications, only ultrasounding the eye)
B mode/brightness
M mode/motion - cardiology
How does B mode work?
Images a slice through the patient. Brightness depends on signal amplitude. See movement in real time
How does M mode work?
B-mode image used to position a single line. Switch to M mode for this graphical display. Movement of points along fixed line followed. Can be linked to ECG
What are the advantages of ultrasound examination?
- Can be done conscious or with light sedation
- Relatively quick (longer if you want to look at everything in the abdomen)
- Non-invasive
- Safe
- Real time information (cardiac function, peristalsis)
What is the purpose of surgical spirit in ultrasounds?
Cleans the skin but may damage the transducer
What is the purpose of acoustic gel in ultrasounds?
Gets rid of air between transducer and skin
What are 3 types of ultrasound transducer?
Phased array – steered electronically. Easy to manipulate. Good for cardiac work. Fan shaped image.
Linear array – multiple elements/crystals in a line and triggered in groups. Good for superficial structures.
Microconvex/convex – elements arranged in a curve.
What is the relationship between transducer frequency and wavelength?
As frequency increases, wavelength decreases
Better resolution if wavelength and therefore pulse length is smaller
What is the frequency of sound used for a good image resolution in an ultrasound?
(High) 7.5-18+ Hz
What is attenuation and its relationship to transducer frequency?
Attenuation is proportional to frequency – so sound does not penetrate so far into the body, absorbed quicker by tissues.
What is higher frequency ultrasounding used for?
7.5-18MHz: superficial structures in larger animals, such as the eye, tendons. All structures in smaller animals. High resolution
What is lower frequency ultrasounding used for?
2.5-5MHz: deeper structures, such as liver large dogs. Larger animals, such as equine abdomen. Poorer resolution
What are the ultrasonographic terms?
Hyperechoic/echogenic – bright on image, such as liver parenchyma
Hypoechoic – all tissues that fall in the middle.
Anechoic/echolucent – black on image (no density change), such as fluid
List the common ultrasound artefacts.
Acoustic enhancement
Acoustic shadowing
Reverberation
Mirror image
What is acoustic enhancement?
Low attenuating structures so increased echogenicity seen distal to fluid-filled structures (bladder and cysts).
More sound remains deep to these structures compared to surrounding tissue, so returning echoes are stronger.
Useful to differentiate cysts from hyperechoic solid masses
What is acoustic shadowing?
Hypo to anechoic area below structure that is highly attenuating
What is clean and dirty acoustic shadowing?
Soft tissue to bone has 30% reflection. Clean shadow, most of remaining sound absorbed.
Soft tissue to gas has 99% reflection. Dirty shadow due to reflection/reverberation.
What is reverberation?
Spurious echoes due to internal reflectors in path of sound – gas interfaces. Gives multiple echoes back to transducer from one pulse – only first echo is correctly positioned
What is mirror image artefact?
Occurs at highly reflective interfaces, typically the diaphragm-lung interface. For each of these subsequent echoes, the distance and therefore time to the transducer is increased producing a mirror image of the liver deep to the diaphragm.
What are the disadvantages of ultrasound?
- Clipping usually needed
- Some experience needed to interpret real time procedure – no record to fall back on
- Gas and fat hinder interpretation
- Many findings are non-specific – tissue sampling needed
What is Doppler shift?
When the sound waves hit small moving targets, such as RBCs, the frequency of the reflected sound is slightly different from the frequency of incident sound.
How can doppler shift be used?
Show blood flow with ultrasound - direction, velocity, laminar, turbulent.
Or colour superimposed onto 2d image in colour flow doppler.
List the radiology Roentgen signs?
- Size
- Shape
- Position
- Opacity
- Margination
- Number
Why may shape vary?
- 1 part of a composite structure may change, such as a cardiac chamber
- Abnormal tissue may be present, such as neoplasia, abscess, cyst, periosteal new bone
- Structure itself may distort, such as collapsing trachea
What is a change in position indicative of?
Change in another organ
What causes opacity to increase?
- Excess of fluid or soft tissue
- Deposition of bone or calcium
- Foreign body
What causes opacity to decrease?
- Abnormal gas accumulation
- Loss of normal tissue
What can occur in soft tissues that can change opacity?
Enough calcium deposited will change opacity
Either due to damaged tissue/dystrophic or hypercalcaemia (secondary to neoplasia)/metastatic
How do tissues appear on ultrasounds?
Fluid – black/anechoic
Fat – white/echogenic
Soft tissues – variable
What causes echogenicity to increase?
Fat, glycogen, collagen, crystalline material
What causes echogenicity to decrease?
Oedema
Which abdominal organs are least to most echogenic?
From least to most echogenic – kidney > liver > spleen
What are the normal findings of the liver on ulatrsounds?
- Course but even echotexture
- Individual lobes not usually seen
- Hepatic veins – anechoic
- Portal veins – echoic walls
What are the normal findings of the gall bladder in ultrasounds?
- Anechoic, pear shaped structure
- Lies to the right of midline
- Between quadrate and right medial lobes (dog) or 2 parts right medial lobe (cat)
- Feline gall bladder may occasionally be duplicated/bilobed
Can the intrahepatic biliary tree be seen on an ultrasound?
Not usually seen in normal animals, only seen once enlarged
What are the normal findings of the bile duct on ultrasounds?
- Usually seen at least partially
- Anechoic tube
What are the normal findings of the spleen on ultrasounds?
The spleen has a finer echotexture than the liver. Smooth well defined echogenic capsule. Anechoic vessels converge at the hilum.
What are the normal findings of the parenchyma on ultrasounds?
Parenchyma is more echogenic and of a finer echotexture than the liver.
What are the normal findings of the stomach and small intestinal walls on ultrasounds?
5 layered – mucosal surface, mucosal layer (black on ultrasound), submucosal layer (white), muscularis and serosa.
When can the stomach rugal folds be seen on ultrasounds?
- Rugal folds evident, especially when stomach is empty
- Tend to flatten/become less obvious when the stomach is distended
What are the normal findings of the small intestine on ultrasounds?
Can identify duodenum and ileum from their location and adjacent structures – stomach and caecum/colon. Cannot follow jejunum from start to finish in most animals.
What is the appearance of the colon on ultrasounds?
Shadowing content
What is the normal findings of the renal cortex on ultrasounds?
Homogenous structure. Usually hypoechoic compared to liver and spleen. Cats can be more echogenic due to fat deposition.
What are the normal findings of the renal medulla on ultrasounds?
Hypoechoic to anechoic. Separated into sections by echogenic pelvic diverticula and interlobar vessels.
What are the normal findings of the renal sinus on ultrasounds?
Echogenic due to peripelvic fat. Pelvis is not usually seen unless dilated.
What are the normal findings of the bladder on ultrasounds?
- May be indented by a full colon
- Wall appears as echogenic double line – inner line is mucosal interface and outer line is the interface between the bladder wall and surrounding tissue
- Muscle layers appear as thin hypoechoic line between the echogenic lines
Contrast radiography and ultrasonography on what you can see with each.
Radiography: can see fat and air. cannot see fluid/soft tissue
Ultrasonography: cannot see fat and air. Can see fluid/soft tissue
What are the radiographic factors affecting imaging acquisition?
- Positioning
- Collimation
- Inadequate number of projections
- Miscellaneous error with technique
- Inadequate inflation (thorax)
How do you tell which side the body is raised in a radiograph?
Side that lies higher lies more perpendicular to the beam and so appears larger.
What can lying an animal on its side cause?
Will collapse its lungs, lungs need to be inflated to make it easier to assess. Put dog in sternal for both lings to be reasonably well inflated.
What is the consequence of collimation being too wide?
Increased scatter production, less accurate depiction of anatomy
What is the consequence of collimation being too tight?
May cut off anatomical area of interest
What is the issue and solution to a radiograph tat is grainy with streaky lines?
Want to change the grid, which will affect the exposure. Grid is not centred enough and is causing to be underexposed.
How do exposure factors change when a grid is used?
Increase mAs – takes out more scatter and some primary beam due to grid so we need more electrons.
Why do we use thyroid protectors?
Thyroid has one of the highest risk and susceptibility to radiation
What is pulmonary osteomata and how are they identified on a radoiograph?
Mineralisation within the lung, which is a normal aging change. They are very radiopaque and not very circular.
How is pleural fluid shown on a radiograph?
Fluid obscures cardiac border and edges of lung lobes are elevated form the sternum
What must occur for thoracic radiographs?
Lungs must be inflated
What are the indications of thoracic radiographs?
- Assessment of cardiac failure
- Characterisation of lung disease
- Detection of metastases
- Work-up of cases where coughing/dyspnoea, heart murmur, trauma, regurgitation, collapse/cyanosis
- Pre-anaesthetic check/other screening
Name the 4 standard views of thoracic radiographs.
Dorsoventral
Ventrodorsal
Right lateral
Left lateral
Distinguish when dorsoventral and ventrodorsal views of thoracic radiographs are used.
DV – take first, avoids atelectasis, preferable for heart, dyspnoeic animals
VD – lungs, small pleural effusion, avoid is dyspnoeic
Describe lateral thoracic radiographs.
- Lowest (dependent) crus is most cranial
- Caudal vena cava passes through right side, so seen to cross the cranial aspect of diaphragm on left lateral view
- Gastric fundus with/without gas is further cranial on left lateral view
What is useful in assessing the stage of the respiratory cycle in thoracic radiographs?
The position radiographs
Describe the appearance of a lateral thoracic radiograph during expiration.
- Upright and in contact with or overlapping the cardiac silhouette
- Consider for detection of bullae, to confirm tracheal collapse
- Detection of ‘air trapping’ for detection of a small pneumothorax
Describe the appearance of lateral thoracic radiographs during inspiration.
Caudally clopping with minimal or no contact between cardiac silhouette and diaphragm. Usually best
What exposure is used during thoracic radiographs?
High kV technique helps to keep exposure time low, with/without a grid
How is diaphragmatic rupture identified from thoracic radiographs?
Abdominal viscera in the thorax and/or the absence of abdominal organs from their normal position in the abdomen
What can you check the vertebrae, sternum and ribs for in thoracic radiographs?
- Alignment of vertebral bodies and of sternebrae
- Rib lesions
- Costal cartilages may mineralise at a young age, and can look very patchy and irregular
Describe the appearance of rib fractures on thoracic radiographs.
- Recent rib fractures have clearly defined edges, with no sign of bone proliferation or mineralised callus
- May be associated subcutaneous emphysema
- Healed fractures have smooth bony callus at the site of the original fracture
What is a pleural line on thoracic radiographs?
- Pleural reflections between lung lobes as thin lines
- If aligned with x-ray beam, called pleural line
- Of no clinical significance
- Only gets significant if it gets significantly thicker (fibrosis) or fluid dissecting between the lung lobes
What should the width of the cranial mediastinum be in small animals on thoracic radiographs?
Not greater than 2x width of spine on DV in dog (can be wider normally in fat animals/brachiocephalic breeds) or 1x width of spine on DV in cat
What is cranial mediastinal reflection on thoracic radiographs?
Seen due to asymmetry of the lung lobes. Less air due to only the tip of 1 lung lobe and then behind it 2 lung lobes so more air and more radiolucency.
What is pneumothorax?
Free air in the pleural space by external or internal trauma but air can accumulate between lung lobes and between the lungs and chest walls. Causes the heart to appear to be lifted form the sternum on the lateral view.
What occurs in moderate to severe pneumothorax?
The caudal lung margins also become separated from the spine dorsally with/without the diaphragm caudally
Why may pneumomediastinum occur?
- Leak into the mediastinum from a perforation of the cervical/thoracic oesophagus or trachea
- Arise due to rupture of small airways near the hilus of the lung
What are structures outlined in pneumomediastium?
- The outer wall of the trachea
- The major blood vessels in the cranial mediastinum – cranial vena cava and aortic branches
- The base of the heart
- The azygos vein
What can be done about pneumomediastinum?
Can’t do anything about but the important question is about how the gas got there
What is the appearance of pleural fluid on thoracic radiographs?
- Leads to a soft tissue opacity within the thorax, which obscures the outlines of adjacent soft tissue structures
- On the lateral view, fluid is seen ventrally, with the partially collapsed lung lobes lying dorsally
- Lung lobe edges often rounded or scalloped
- The caudo-dorsal lung margins may also retract from the spine
- On DV, lung margins are retracted from the thoracic wall
- Reduced margination of cardiac silhouette
How do thoracic masses appear on thoracic radiographs?
- Usually soft tissue opacity – occasionally contain mineralisation or gas
- May displace or obscure normal structures
- May be obscured by pleural fluid if present
What is the appearance of cranial mediastinal masses on thoracic radiographs?
- Widening of the cranial mediastinal
- Caudal displacement of the tips of the cranial lung lobes – normally inflated lungs should reach the 1st rib
- May lead to elevation of the trachea or caudal displacement of the carina and heart
What is the normal appearance of the trachea on thoracic radiographs?
- Should be air filled, of an even diameter and have a smooth internal surface
- Some normal variation in its course, influenced mainly by the position of the head and neck
- The bifurcation (or carina) should be at the 4th or 5th intercostal space
- Mineralisation of the tracheal rings is normal
What does under-inflation of the lungs cause on thoracic radiographs?
Increase in pulmonary opacity
How do end on blood vessels appear on thoracic radiographs?
End on blood vessels looks more radio-opaque compared to equivalent long blood vessels as they are going through more soft tissue.
Name the 3 lung patterns.
Bronchial
Alveolar
Interstitial
What is the appearance of bronchial lung pattern in thoracic radiographs?
- Commonly visible in the hilar region
- More prominent with age
- Increase due to calcification of the walls, thickening of the walls, or peri-bronchial infiltration
- Bronchial pattern = there is still air but walls get thicker
Do bronchi taper?
If they stay wide in the periphery, which are prominent, indication for pathology
What are the causes of bronchial change?
- Chronic lower airway disease – bacterial, viral, parasitic, allergic
- Cushing’s disease
- Age
What is the appearance of alveolar lung pattern on thoracic radiographs?
- Fluffy or hazy patches which may coalesce
- Soft tissue margins obscured in affected areas
- And bronchi are the only bits now containing air and so appear black.
- Radiolucent airways remain visible – air bronchograms
What causes air bronchograms?
With progression, all the alveoli become flooded/collapsed leaving the radiolucent airways highlighted against a background of soft tissue opacity
What are the causes of alveolar filling?
Pulmonary oedema
Haemorrhage
Pneumonia
Neoplasia
What is interstitial lung pattern?
- Nodules are not reliably seen if they are less than 4-5mm diameter
- Take right LPs to see left lung best and left lateral projections to see right lung best
What is the appearance of unstructured interstitial pattern?
- Increased opacity of lung
- Blurring of vessel margins
- Artefactually on expiratory or under-exposed film
- Mimicked by incidental aging change/obesity
- Infiltration of the supporting lung tissue with fluid, cells or fibrous tissue
- Partially obscures the normal broncho-vascular markings
What are the differential diagnoses of unstructured interstitial lung pattern?
Oedema
Pneumonia
Haemorrhage
Pulmonary fibrosis
Diffuse neoplasia
Pneumocystis carinii pneumonia
Viral pneumonia
What are the vascular markings that should be clearly seen on well inflated radiographs?
- Main pulmonary artery/vein for each lung lobe
- Lateral projections – see cranial lobar vessels
- DV/VD projections – see caudal lobar vessels
- Veins lie ventral and central to their respective artery/bronchus
- The diameter of the caudal lobar pulmonary vessels should not be greater than the width of the 9th rib where they cross
- The cranial lobar vessels are compared to the proximal 1/3 of the 4th rib
Why may there be alterations in vessel size on thoracic radiographs?
- Left-sided congestive heart failure – enlarged pulmonary veins
- Dirofilariasis – enlarged, tortuous pulmonary arteries
- Left-to-right shunts – both arteries and veins large
- Hypovolaemia, Addison’s disease – vessels small
What should the size of the heart be on thoracic radiographs?
- The heart should be 2-2.5 intercostal space wide ion the cat and 2.5-3.5 intercostal spaces wide in the dog
- The height of the heart should be 2/3-3/4 that of the thoracic cavity
- On the DV projection, the heart should be about two-thirds the width of the thoracic cavity
What is the vertebral heart scores of cats and dogs?
Dogs is 8.5-10.6
Less frequently used in cats, range 7-8
Where do the cardiac chambers lie on thoracic radiographs?
R chambers lie more cranial than L chambers
What is left cardiac enlargement?
- Elevation/compression of caudal lobar bronchus
- Straight caudal border
- Increased length of heart
- Rounding of left ventricular border
- Apex may be displaced to right
- Enlarged left auricular
How may left cardiac enlargement be acquired?
Dilated cardiomyopathy
Mitral valve insufficiency (endocarditis)
How may left cardiac enlargement be congenital?
Patent ductus arteriosus
Ventricular septal defect
Mitral dysplasia
Aortic stenosis
What is right cardiac enlargement?
- Wide heart
- Apex may lift from sternum
- Rounding of the right side and relatively straight left sided, giving a reverse D shape
How may right cardiac enlargement be acquired?
Tricuspid insufficiency
Pulmonary hypertension
Dirofilarias
How may right cardiac enlargement be congenital?
Pulmonic stenosis
Tricuspid dysplasia
Tetralogy of Fallot
Ventricular Septal Defect
What is generalised cardiomegaly?
Signs of both left and right sided enlargement, wide and tall heart
How does pericardial disease appear on thoracic radiographs?
- Rounded, globular heart
- Sharp margin
- Uniform opacity
What is PPDH?
Peritoneo-pericardial diaphragmatic hernia - congenital communication between peritoneal and pericardial cavities
