Week 1 Video part 1 of Concepts of cross sectional anatomy Flashcards
Planes of sectional anatomy
Image orientation
Patient always opposite
CT Computed Tomography
Axial one image (CAT scan)- singularly
Helical (spiral scan)- volume
CT Scanner
CT Scan Helical
Circular x-ray and patient moves through gantry. faster , hold breath once.
Not as clear compared to axial. Not as shape
CT window/level changes
to the anatomical structures. changes how see. can black out areas. color level
is called windowing.
CT can use oral and IV contrast Enhancement
oral for stomach and intestine and IV for vascular. To help
visualualize structures better.
CT plane
Can change plane to see coronal/sagital instead of just axial. Give the ability to see above and below. Can also change to an oblique plane. This is the benefit of an helical scan
CT 3D Reconstruction
Setup to look at all three planes.
CT 3D Reconstruction
Image Acquisition
Matrix, Pixel, Voxel
Image Acquisition matrix
higher rows and column will create higher resolution in image but at a price of media storage space (data)
Voxel
A voxel is a measurement of volume in a structure that is to be imaged. Each voxel represents a defined volume, and can be localized by coordinates on a three-dimensional grid. Both CT and MRI scanners image a slab of tissue and describe it in a two-dimensional image on the computer screen.
Pixel
Pixel: Two dimensional picture element that makes up the matrix. Each pixel represents a CT number and is the building block of the matrix and image. Prospective data: An image automatically reconstructed from the scan data.
Matrix
A CT scan image matrix is a square arrangement of pixels, or picture elements, in columns and rows. The size of the matrix can range from 256 x 256 to 1024 x 1024 pixels, but the most common size is 512 x 512, which is made up of 262,144 pixels
Image quality Spatial Resolution
Larger the matrix the better the spacial resolution. Higher detail then. Small structure can provide a better image. Low resolution may not be able to see well
Image quality Noise
Not real information. Electric noise created by electronic interferance. Voltage irregularities. A replacement part like metal in a person can cause streak artifacts.
Image quality Distortion
unusual anatomy can be cause by a person moving, cough, moved foot during imaging. this will cause a distortion.
Image quality filters
smoothing- can reduce voxel by averaging hense will smooth image. used on soft tissue.
edge enancement- to improve visibilty to increase edge sharpness.
Image quality Partial volume averaging
Partial volume ave- slice thickness . voxel with anatomy in two voxel containing???
AI answer- Partial volume averaging (PVA) is a CT artifact that occurs when different tissues with different absorption values are in the same CT voxel. This results in beam attenuation that is proportional to the average value of the tissues
Image quality Artifacts
Streak, motion, beam-hardening, ring, bloom, metallic
Image analysis ROI (region of interest)
x-ray photon intensity is a hounsfield unit which helps identify bone which would have a high number at 1000. Water is standard which is 0. Air is -1000
Hounsfield unit (HU)
A Hounsfield unit (HU), also known as a CT unit, is a quantitative measurement of radio density used by radiologists to interpret computed tomography (CT) images
Fat will have a low HU.
Examples of HU values for different types of tissue:
Air: –1,000 HU
Water: 0 HU
Bone: 1,000 HU
soft tissue = 400
Grey matter: +37 to +45 HU
Lung: –700 to –600 HU
Silver foreign objects: +17,000 HU
Image analysis pitch
Pitch is the rotation speed of the x-ray aournd the person in relation to the table speed through the gantry.
