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What is a CT composed of?
- xray tube
- gantry
- a detector array
- patient bed

How does the CT work?
- 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?
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?
- 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?
- 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?
- number
- position
- size
- shape
- margination
- density
- hounsfield units

What does window width mean in CT?
- 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?
- 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?
- 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?
- the three orthogonal planes
- transverse

What is a faraday cage?
- a room with little metallic mesh
- intercepting incoming radiowaves.
What happens when radiofrequency energy is applied to the patient?
- 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?
- 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?
- gradient echo - GRE
- Fast spin echo - FSE
- inversion recovery - IR

What is a gradient echo, GRE?
- 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?
- 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?
- 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?
- time
- cost

What are the advantages for using MRI from another imaging tool?
- 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?
T1- dark
T2 bright
What does the brain look like on an MRI?
- T1- white matter brighter than gray
- T2- grey matter brighter than white
Why is collimation important?
- minimizes amount of scattered radiation
- enhances image
- minimizes the volume of tissue that is irradiated.

What are the characteristics of tissue that influence xray?
- 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
- 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?
- 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?
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?
- 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
What does the mediastinum contain?
- trachea
- esophagus
- great vessels
- heart
- lymphatic structures

What does the cranial medisastinum contain?
- cranial to the heart
What does the middle mediastinum contain?
- 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

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