CT Imaging for the PA Flashcards
What is a CT?
Computed Tomography
Used gantry with rotating xray beam and multiple detectors in various arrays along with sophisticated computer algorithms to process the data
What does a CT scan produce?
large number of 2D, slicelike images each of which are millimeters in diameter
What are the two major types of CT?
Helical
Conventional, Axial, Step and Shoot CT
What is a conventional, axial, Step and shoot CT used for?
high-resolution scanning of lungs, coronary artery calcium scoring, and prospective ECG-triggered coronary CT angiography
What are the principal components of a CT machine?
xray tube
diametrically opposed array of detectors
What does collimation determine?
thickness of a section
What is the standard chest collimation for mediastinum?
2.5 mm
What is the standard chest collimation for lung parenchyma?
1.25 mm
What is narrow collimation?
1 to 1.25 mm
What is narrow collimation used for?
CT pulmonary angiography
high resolution CT scanning of the lung parenchyma
imaging of small pulmonary nodules
What is wide collimation?
2.5 mm
What is wide collimation used for?
heavy patients to decrease the quantum noise at the cost of decreased spatial resolution
What is a CT image composed of?
matrix of thousands of tiny squares called pixels which are computer assigned a Hounsfield Number
What is the Hounsfield number?
a measure of how much of the xray beam is absorbed by the tissues at each point in the scan
What is the Hounsfield number of air?
-1000HU
What is the Hounsfield number of fat?
-40 to -100 HU
What is the Hounsfield number of water?
0 HU
What is the Hounsfield number of soft tissue?
20 to 100 HU
What is the Hounsfield number of bone?
400-600 HU
What is the Hounsfield number of metal?
> 1000 HU
What are the characteristics of Denser substances on a CT?
absorb more xrays
have high CT numbers
demonstrate increased attenuation
displayed as whiter densities on CT scans
What are the characteristics of less dense substances?
absorb fewer xrays
have low CT numbers
said to demonstrate decreased attenuation
displayed as blacker densities on CT scans
What is attenuation?
the chemical make up of the material; determined by how many xrays make it through the patient to hit the detector and what the image looks like
stopping of xrays
What can a CT image do after it has been taken?
the image can be post processed to optimize visibility
What type of imaging is a CT image?
structural; represents a moment in time