M Part I Flashcards
A precise step to be performed in a specific order to solve a problem
Basis for most computer programming
Algorithm
A mathematical method of creating missing data
Interpolation
Two types of data
Raw data
Image data
-have assigned value
-includes all measurements detailed from the detector array
-requires more storage space
Raw data
The reconstruction that is automatically produced during scanning
Prospective Reconstruction
The process of generating new image after scanning
Retrospective Reconstruction
Image data is also known as [..]
Reconstructed Data
Convolved data that have been back-projected into the image matrix to create CT images displayed on a monitor
Various digital filters are available to suppress noise and improved data
Image data
Factors that affect attenuation
Atomic no.
POI thickness
Energy of x-ray
Those which result once the computer has processed the raw data
One HU is assigned to each pixel
Image Data
IF ONLY IMAGE DATA IS AVAILABLE, DATA MANIPULATION IS [..]
LIMITED
Reconstruction that can make slices thinner/thicker using raw data
Retrospective Reconstruction
The part of the beam that falls one irection
Ray
The detector senses each arriving ray and measures how much of the beam has been attenuated
Ray Sum
A complete set of ray sums
View
The system accounts for attenuation properties of each ray sum and correlates it to the position of the ray
Attenuation profile
Reconstruction Algorithms (3)
Back Projection
Filtered Back Projection
Adaptive Statistical Iterative Reconstruction
Other names for Back Projecion
Summation Method/Linear Superposition Method
PROCESS of Back projection
Ray sum data acquired from each projection
Projected back onto the matrix
PROBLEM of Back Projection
- Low spatial resolution
- Bluming and produces star pattern artifact
Introduced to address the star pattern artifact
Filtered Back Projection
Process of applying a filter function to an attenuation profile
Convolution/Kernel Elements
Used in filtered back projection of reduce statistical noise
Fouler Theory
FILTER FUNCTIONS CAN ONLY BE APPLIED TO [..]
RAW DATA
Starts with an assumption and compares this assumption with measured values, makes corrections to bring the two in agreement
Adaptive Statistical Iterative Reconstruction
Used in an iterative manner to extract additional image clarity and suppress noise
Statistical noise profiles
[adv] Adaptive Statistical Iterative Reconstruction
Improved image quality
Reduced image noise
[importance] image display
Diff brightness- see pathologies in different configurations
Patients couch inserted then rotate (in-out)
Step and Shoot Scanning (1980s)
Continuous patient couch moving in while gantry rotates
Spiral/Helical CT Scanning
Used and defined as table distance travelled in one 360 deg rotation divided by beam collimation
Pitch
Refers to table movement (speed) in going in the gantry
Table feed per rotation
Pitch [formula]
Table feed per rotation/section width
[pitch] distance is enough
Can adjust to rotation of X-ray tube
Pitch I
X-ray beam are contiguous for adjacent rotations
P = 1.0
X-ray beams are not contiguous for adjacent rotations [gaps in x-ray helix]
P>1.0
There is x-ray beam overlap
P<1.0
Getting data from same structure more than once
Oversampling
[disadv,adv] oversampling
Disadv: Increase pt dose
Adv: Increase image quality due to increase SNR
Oversampling application
Facial bones
Paranasal bones - frontal, sphenoidal, ethmoidal, maxillary
[adv,disadv] Of undersampling
Disadv. Lower pt does
Adv. decreased image quality due to decreased SNR, more artifact
Undersampling application
Trauma
CT angiography (contrast quickly flushed
Measure of the range of the CT number the image contains
Window Width (WW)
ALL VALUES HIGHER THAN SELECTED VALUES WILL APPEAR [..]
WHITE
ALL VALUES SELECTED LOWER THAN THE SELECTED VALUES WITHH APPEAR [..]
BLACK
Term for increasing window width
Widening the width
Selects which Hounsfield values are displayed as shades of gray
(Center of WW)
Roughly same value as tissue of interest
Window Level
Manipulation of the window width and level to optimize contrast
Windowing
COMPUTER CAN ASSIGN OVER [..] HU
2000
COMPUTER CAN DISPLAY [..] SHADES OF GRAY
256
NAKD EYE CAN ONLY DISTINGUISH ROUGHLY LESS THAN [..] SHADES OF GRY
40
Best used in areas of acute differing values [lungs, air and vessels is side by side]
Wide window width
excellent when examining areas of similar attenuation [soft tissue]
Narrow Window Width
WW UL AND LL FORMULA
UL = WL + (WW/2)
LL = WL - (WW/2)
Helpful in reporting size of abnormality
Essential for placement of biopsy needle or drainage apparatus
Distance Measurement
Used to make original image appear larger to see relevant data
Clarify margins of abnormality
Image Magnification
Graphical display showing how frequently a range of CT no occurs within an area
Histogram
Allows more than one image to be displayed in a single frame
Multiple image display