Powerpoint Flashcards
Ct detectors are called?
Does what?
Solid state detectors
- turns photons into lights
Voxel profile
Contents in the profile
Any Ct acquisition can be reconstructed with one or more reconstruction filters( bone, soft tissue)?
True
Data can be classified as(4)
Measurement data
Raw data
Convoluted data
Image data
Measurement data
Arise from detectors and are subject to preprocessing to correct the measurement data before the image algorithmn is applied
Raw data
The result of pre- processed scan data subject to the reconstruction algorithmn
Convolved data
Image reconstruction used by current Ct scanners is filtered back projection
Raw data is first filtered with mathematical filter or kernel. Process is called convolution technique which improves image quality by removing blur
Most popular reconstruction algorithmn
Filtered back projection
Kernel
Mathematical filter
Image data
Reconstructed data are convolved data that have been back projected into the image matrix to create Ct images displayed on a monitor
Image quality Ct
General image quality can be described by several,key performance parameters. High contrast, low contrast, spatial resolution, temporal resolution
Determining factors image quality
Artifacts
Contrast resolution
Linearity
Noise
Spatial resolution
Artifacts
- are?
- arise (4)?
Distortion or error in an image that is unrelated to the subject being scanned. It can degrade image quality , affect the perceptibility of detail.
Arise from number sources :
- inappropriate selection of protocol
- reconstruction process
- problems relating to equipment( malfunctions)
- fundamental limitations to physics
Ct # 40
Blood
Ct # 1000
Air
Streak artifacts
Caused by errors of isolated Channels or views and enhanced by the convolution process and manifested into lines during the back projection
Why streaks?
Improper sampling data Partial volume averaging Patient motion Metal Beam hardening Noise Spiral/ helical scanning Mechanical failure
Shading artifact
Often appear near objects of high densities and can be caused by beam hardening , partial volume, averaging, spiral/ helical scanning , scatter, off focal radiation and incomplete projections
Why shading artifact
Partial volume averaging Beam hardening Spiral/ helical scanning Scatter radiation Off focal radiation Incomplete projections
Ring and bands artifacts
Produced when the projection readings of single channel or group of channels consistently deviate from the truth . It can be result of a defective detector cells or das channels, deficiencies in system calibration or suboptimal image generation
Why ring and band artifact?
Bad detector channels in 3rd gen Ct scanners
Patient based artifacts
Motion artifact
Transient interruption of contrast
Motion artifact
Decrease scan time , increase interscan delay
Transient interruption of contrast
Use of filters ( algorithmns)