Computed Tomography- Lecture One Flashcards
What is the most significant development in radiology in the past 40 years?
Computed Tomography
Do MRI and Ultrasound use x-ray to produce image?
No
How does the x-ray tube move for computed tomography?
It spins around the patient
When does tomography trace back to?
1920’s
How does tomography “cut” the body?
For a specific layer or section of the body
What is axial tomography?
The images parallel to the long axis of the body
What is a transverse image or one perpendicular to the long axis of the body?
The x-ray tube moves across the image
How is conventional tomography and computed tomography different?
Conventional uses axial tomography (parallel to the long axis of the body)
Computed uses transverse image
(One perpendicular to the axis of the body)
Who laid down the roots of tomography in terms of mathematics? And when?
Radon; 1917
What did Godrey Hounsfield conclude from his investigational work with pattern recognition and reconstruction techniques by using computers? And when?
He found that when an x-ray beam passed through a body from all directions and measurements were made of all of these transmissions, information about the internal structures of the body can be obtained
1967
When was CT developed by Godrey Hounsfield?
1969
What was the EMI scanner used for?
To CT brains only
Who did Hounsfield share the Nobel Prize in Medicine and Physiology with?
Alan Cormack of Tufts University.
How did Cormack contribute to win the Nobel Prize?
He worked out the mathematical solutions to problems in CT
How many major design advancements has CT been through since 1970?
Five
What did each major design advancement improve?
Scan time and resolution or image quality
Scan times have been reduced from _____ to ______
5 minutes to 50 ms
What did the first scanner use?
a very tightly collimated pencil beam
How many degrees did the 1st generation CT scanner rotate?
180 degrees
How many degrees would the 1st generation CT scanner rotation per image?
1 degree
How long would it take for one image from the 1st generation CT scanner to process?
5 minutes
How many detectors did the 1st generation CT scanner have?
1 detector
How many degrees would the 2nd generation CT scanner rotate?
180 degrees
Why was there more scatter radiation from the 2nd generation CT scanner?
It used fan beam collimation
How many detectors did the 2nd generation CT scanner have?
5 to 30 detectors
How many degrees would the 2nd generation CT scanner rotate per image?
10 degrees per translation & 18 per scan
Which had a faster scan time the 1st or 2nd generation CT scanner?
2nd
How much would the 3rd generation CT scanner rotate?
360 degrees
What kind of beam was used in the 3rd generation CT scanner?
A fan shaped beam of 30-60 degrees for full coverage
How did the 3rd generation CT scanner have constant Source to detector distance?
Due to curvilinear detector array
What happens if one detector fails in a 3rd generation CT scanner?
A ring appears
Will a radiologist read a scan if there is a ring artifact?
NO
What is the scan time for the 3rd generation CT scanner?
1 sec
What does the 3rd generation have compared to the 1st and 2nd?
Superior reconstruction and resolution
Why didn’t the 4ht generation Ct scanners last long?
-Cost of the detectors
-Too much scatter given off
How many detectors are used in the 4th generation CT scanner?
As many as 8000 detectors
What is the scan time for the 4th generation CT scanner?
1 sec
What was eliminated from the 4th generation compared to previous scanner and how?
The ring artifact because it uses auto-detector calibration
What kind of beam does the 4th generation CT scanner use?
Fan beam; high radiation dose compared to earlier scanners
How does the 4th generation take an image?
The tube rotates around the stationary ring of detectors
What was the 5the generation specifically used for?
Cardiac
What does the 5th generation allow?
For continuous rotation of the tube for spiral CT
What did the Heartscan by Imatron use?
An electron beam instead of x-ray tube and 50ms scan times
What does spiral CT allow for?
Continuous or even overlapping data acquisition
What would happen as the tube spins in the 5th generation?
the table would move
Spiral Ct was made possible by what?
Slipring technology
How did the slipring change CT?
It allowed the tube to continuously rotate 360 degrees versus previously without it, it needed to stop after each rotation with conventional CT
How many detectors are used in Spiral CT?
As many as 14,600, each 1.25mm wide
What does the large amount of detectors in Spiral CT allow?
Allows multiple slices to be made with one scan and move tissue volume to be imaged
What are benefits of Spiral CT?
-Less motion artifacts
-Improve lesion detection because the reconstructed image can be at arbitrary intervals
-Reduced partial volume because of overlapping reconstruction intervals
-Reduced scan time
-Advances in computer processing allows for multi-planar reconstruction and even 3D reconstruction
What are basic CT scanner components?
-Gantry includes the pedestal or table, tube, collimators, detectors, and high voltage generator
-Mechanical supports
-Operators Console
-Computers
How many steps does the formation of CT images by a CT scanner involve and what are they?
3 steps
1- Date Acquisition
2- Image reconstruction
3- Image Display
What is Data acquisition?
Refers to the collection of x-ray transmission measurements from the patients
What are components of data acquisition?
-Generator, Gantry, and patient table
What are power ratings for the high-frequency generator?
Typically from 30 to 60 kilowatts
