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copy deck
- What is a CT composed of?
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- xray tube
- gantry
- a detector array
- patient bed
- How does the CT work?
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- narrow fan shaped beam of xrays passes through the patient to get cross sectional images as the patient moves through the gantry in small increments or continuously
- If the patient moves through the gantry at small increments it is called what?
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a axial scan
- If the patient moves through the gantry continuously what type of scan is it?
- - helical scan
- What does a CT have in common with an xray?
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- the absorption of xrays by tissues of different density
- low density tissues appear black and high density tissues appear grey or white. - How are the images of a CT analyzed?
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- the density is given a number and coverted to a pixel
- each pixal number describes the amount of attenuation of the xray beem and is called hounsfield units - What are hounsfield units in CT?
- - the pixal mesurement for the amount of attenuation the xray beam produces from the patient
- The principles of xray are the same as CT what are they related to interpretation?
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- number
- position
- size
- shape
- margination
- density
- hounsfield units
- What does window width mean in CT?
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- the range of greys displayed from white to black
- narrow window for soft tissue and contrast scans - What is the advantage of CT from radiography or ultrasonography?
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- lack or superimpostiion
- superb anatomic detail
- great contrast - What is MRI based on?
- - the precession of the hydrogen proton induced by a magnetic field
- What are the two types of magnets in an MRI?
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- a permanent which is mad of iron and ceramic
- superconductive made of electromagnets
- What is the magnetic field strength of an MRI measured in?
- - Gauss and Tesla
- What are the 3 gradient coils corresponding to in the MRI?
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- the three orthogonal planes
- transverse
-sagittal
-dorsal - What is a faraday cage?
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- a room with little metallic mesh
- intercepting incoming radiowaves. - What happens when radiofrequency energy is applied to the patient?
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- when applied to the protons it causes the hydrogen to spin causing more protons to spin in an antiparallel state and brings them all in phase with each other.
- What happens with the RF transmission is turned off in an MRI?
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- the absorbed FR energy is reetasmitted as signal called proton density
- some begin to slow down called diphase or T2 relation
- the protons that were in antiparralle spin are then returned to normal called T1 relaxation - What is the pulse sequence of an MRI?
- - the sequence and timing of the RF pulses and the gradient applications required to produce the image.
- What are the three types of pulse sequence?
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- gradient echo - GRE
- Fast spin echo - FSE
- inversion recovery - IR - What is a gradient echo, GRE?
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- where there is a gradient to forcibly dephase spins then reverses to produce an echo
- quicker scan but more artefacts - What is a fast spin echo, FSE?
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- first uses a 90 degree spin then a 180 degree spin to cause the protons to rephase or refocus
- gives re-growth of the signal and less susceptible to artfacts - What is an inversion recovery IR?
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- start with 180 deree inversion pulse then relaation or recover, then standard spin echo sequence.
- it allows for eliminating signal from fat or fluid
- good for orthopaedics or CNS diseases. - What are the disadvantages to using MRI from another imaging tool?
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- time
- cost
- What are the advantages for using MRI from another imaging tool?
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- does not use ionizing radiation
- best contrast resolution
- best tissue discrimination
- great detail without contrast - What does air and bone look like on an MRI?
- - always dark
- What does fat look like on an MRI?
- - always bright
- What does fluid look like on an MRI?
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T1- dark
T2 bright - What does the brain look like on an MRI?
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- T1- white matter brighter than gray
- T2- grey matter brighter than white - Why is collimation important?
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- minimizes amount of scattered radiation
- enhances image
- minimizes the volume of tissue that is irradiated. - What are the characteristics of tissue that influence xray?
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- thickness
- density
- atomic number - How does fat look in comparision to soft tissue on an xray?
- - fat is radiolucent compaired to soft tissue so it appears darker on an xray
- What is osteoarthosis? How does it look on an xray
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- osteoarthritis, degenerative joint disease
- increased intracapsular soft tissue opacity
- formation of periarticular spurs
- increase in subchodral bone opacity
- remodeling of subchondral bone. - How can aggressive lesions on xrays be evaluated?
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- ew bone production
- bone loss or destruction
- cortical changes
- rate which changes take place - Where do primary bone tumors usually form in a bone?
- - metaphyseal region
- Where do metastatic neoplastic or fungal lesion usually form in bones?
- - multiple sites apposed to a primary tumor that is a single site
- Which lateral recumbency is perferable for examination of a cardiac shadow?
- - right since the phrenicopericardial ligament inhibits movement of the cardia apex
- Which is the best view of the heart?
- DV view
- Which is the best view on an xray of the lungs?
- - vd
- Where should the beam be centered in thoracic radiographs?
- 5th ics at the level the caudal border of the scapula
- What is an air bronchogram?
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where the alveolar is inflitrated and the air filled bronchial structures can be seen as dark branching tapering strips on a white background
- What are tramlines?
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- thickening or increased opacity of the bronchial walls that produce a linear pattern
- can be incidental in older dogs and cats - Does an interstitial pattern produce brochograms
- no
- What does the mediastinum contain?
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- trachea
- esophagus
- great vessels
- heart
-LN
- lymphatic structures
- What does the cranial medisastinum contain?
- - cranial to the heart
- What does the middle mediastinum contain?
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- heart with pericardium
- great vessels
- mainstem bronchi - What does the caudal mediastinum conatin?
- - everything caudal to the heart
- What is a treacheal stripe?
- - when gas is in the esophagus it highlights the ventral wall of the esophagus and the dorsal wall of the trachea is as a single thick soft tissue line called the tracheal stripe