CT image interpretation Flashcards
What are the 3 anatomical planes?
Axial, coronal , sagittal
When is Volume rendering used?
Bone injury
Soft tissue stab injury
Vascular injury
Facial trauma
What are Hounsfield units?
Image data represents a distribution of values
Values are assigned to a CT number
These are scaled to hounsfeild units
values of water and air fixed
Definition of Hounsfield unit
The Hounsfield unit (HU) scale is a linear transformation of the original linear attenuation coefficient measurement into one in which the radiodensity of distilled water at standard pressure and temperature (STP) is defined as zero Hounsfield units (HU), while the radiodensity of air at STP is defined as -1000 HU
What is the HU value for water?
0
What is the HU and colour of value for air?
Black - 1000 Hu
What is the Hu value and appearance of bone?
White + 1000
How many grey levels are CT numbers displayed as?
256 or 2^8
What is the approximate window level and width for soft tissues?
350 width
50 level
narrow window as most tissues are similar density so we need narrow to distinguish different organs
What is the approximate window level for Lung
Width = 1500
level = -600
Can have a wider width as large contrast between lung and surrounding tissues
What is the approximate window level for bone?
Width = 2500
Level = 500
What is the approximate window level for brain?
Width = 80
level = 40
very narrow window to distinguish white and grey matter apart
What are 4 main types of contrast?
Inherent, IV, Oral, rectal
What is inherent contrast?
naturally occurring eg:
Air in lings, kidney stones or fat surrounding organs
What is contrast media?
A substance we add to highlight any abnormalities with the imaging procedure
it has a different atomic number and density to the surrounding tissue
