IVC2 - CT Fundamentals Flashcards
(19 cards)
What is windowing as it applied to the fundamentals of CT?
Windowing is the process why which a specific range of shades of grey are displayed on a CT
Every tissue has a hounsfield unit, by windowing you alter the contrast of the imaging by selecting which hounsfield units should be included within the display
What is the housefield unit of pure water?
0 HU
What is the hounsfield unit of air?
-1000 HU (black)
What is the hounsfield unit of bone (approximately)?
+1000 HU (white)
What is the hounsfield unit of brain (approximately)?
30 HU
What is the hounsfield unit of white matter of the brain?
25 HU
What is the hounsfield unit of grey matter of the brain?
35 HU
What is the hounsfield unit of CSF?
0 HU
In practice may actually be closer to 5
What is the hounsfield unit of hemorrhage?
40-100 HU
What should dictate where you place your window center when reviewing a CT?
Choose you window center to be approximately at the level of the tissue of interest
Example: window center of 600 for bone
What should dictate what you window width is set to when reviewing a CT?
Determines how narrow a focus you would like from the center
Tissues with inherently very little difference in HU will need a small window width to highly those differences (e.g. brain)
Whereas tissues with inherently very large variations in HU will need a wider window width in order to capture the full spectrum of variation (e.g. bone)
The below setting for window center and window width would be best for highlighting what type of tissue?
WC = 600
WW = 2400
Bone
High window center, wide window width
The HU range would be -600 to 1800
The below setting for window center and window width would be best for highlighting what type of tissue?
WC = 50
WW = 350
Soft tissues
Low window center (around the HU of soft tissue), small window width to highlight smaller variations in HU
The HU range would be -125 to 225
The below setting for window center and window width would be best for highlighting what type of tissue?
WC = -600
WW = 1600
Lung
Negative window center moves the center towards HU of air and wide window width allows it to pick up a greater range of structures
The HU range would be -1400 and 200
Based on the below window center and window width, what would be the range of HU that would be displayed? What would be the color of tissues with HU above or below this range?
WC = 50
WW = 300
HU range -100 and 200
Below -100 HU would be black
Above 200 HU would be white
What window setting is best for evaluating contrast media on a CT?
A soft tissue window as this window highlights more subtle differences
What is the window type of this CT image?
Bone window
Note the greying out of the soft tissues, and the nice bone detail
What is the window type of this CT image?
Bone window
Note the greying out of the soft tissue and the nice bone detail
What is the window type of this CT image?
Soft tissue window
Note the whiting out of the bone, and the high degree of contrast between the soft tissues
