Medical Imaging Flashcards
significance of the AP vs PA view
AP view can show cardiomegaly even though there isn’t any
why does AP view enlarge the heart
it is farther away from the plate which magnifies the x-ray; you want things to be closer to the plate to be more accurate
digital subtraction angiography
subtracts the images you want to see; images become black
- ex: hernia picture
- angiography of the brachial artery
downside of DSA
invasive procedure; artery must be entered percutaneously
MR angiogram
shows all of the vessels; pumped intravenously
hounsfield scale
defines the different grey scales in imaging
the number on the hounsfield scale set to middle gray is referred to as
the window level
the range of the grey scale mapped on the hounsfield scale is called the
window width
advantages of CT
gray scale can be manipulated on viewing screen; good resolution; widely available and cheaper than MRI; quick
disadvantages of CT
ionizing radiation; renal function needs to be evaluated; reaction to iodide
T1
measure of time taken for spinning protons to realign with the external magnetic field
- fluid appears dark
T2
measure of time taken for spinning protons to lose phase coherence among nuclei spinning perpendicular to main field
- fluid appears light
advantages of MRI
no ionizing radiation; better soft tissue contrast than CT; versatile
disadvantages of MRI
longer time for sequences; more expensive, images cannot be manipulated on viewing screen; cannot do if patients have certain metals in body
