week 1- terminology Flashcards
what are the key components of SFOV
- Information that will be reconstructed and available to see
- Anatomy should be positioned in the isocentre
- Anatomy outside SFOV cannot be displayed
what anatomy requires a small SFOV
head
spine
orthopaedic
what anatomy requires a large sfov
chest, abdo, pelvis
what factors influence slice thickness
beam collimation and detector array configuration
what is automatic tube current modulation
- Automatically adjusts mA during scan in accordance with tissue density
what is longitudinal tube current modulation
- Allows for variable mA in accordance to the body part you are scanning (calculates average mA)
- Uses information from one or two view localisers
why is patient centring important?
- Patient positioned above or below isocentre can affect calculation of attenuation and impact implementation of AEC
- Patient mispositioning to the left or right of isocentre will result in one side of the body receiving more radiation dose than the other
what are the differences between a pitch >1 and a pitch <1 and which is better
> 1
- Decreased dose, faster scan time, lower quality MPR/3D reformats, bigger the gap, lower the quality
<1
- Increased dose, slow scan time, improves MPR/ 3D reformats, more overlap better the quality, therefore this is superior
what are the two types of image reconstruction
filtered back projection
Iterative reconstruction
what are HU
Every pixel is assigned a HU based on location and attenuation; each slice has a scan matrix (commonly 512-1024)
what is volume imaging?
Reconstruct images into slices (axial, coronal, sagittal)
Each slice has a thickness and scan matrix (usually 512 or 1024)
Stack slices together to create a volume of data/ image information
Thinner slice thickness = greater resolution; increased noise, overlap in acquisition, improves quality of MPR’s
what are reconstruction filters/ algorithms used for?
- Used to enhance features of certain structures; sharpen or smooth edges of reconstructed image
- Smooth filters decrease noise (soft tissue)
- Edge enhancement filter sharpens edges (bone and lung)
define thickness and interval
- Thickness = how we acquire the data (thickness of image)
- Interval = the gap between each of the slices that occur (how far apart the images are)
- Used when scanning axially or reformatting images for viewing
what is window width and window levels?
different WW and WL highlight areas of anatomy to better differentiate structures within the image
what is metal artefact reduction
-Beam hardening artefacts caused by metallic implants, reduce effect by applying MAR, IR algorithm
what is the post-processing technique, multiplanar reformations
- We take all the axial information we have acquired and are now reconstructing it into coronal and sagittal planes
- Used to demonstrate anatomy and pathology from different planes to that of scan
- Viewed as an average of HU
- Maximum Intensity Projection (MIP), commonly used in CTA; uses the highest HU and creates an average based on that
what are 6 examples of post-processing techniques
MPRs averages density MPR oblique MPR curved MPR 2D MPR MIPS MinIP
what are 5 types of 3D image processing
SSD volume rendering 3D MIP vessel tracking virtual reality navigation
define hypodense pathology
less dense
if an abnormality is less dense than the reference structure
define isodense pathology
the same density
if an abnormality is the same density as the reference structure
define hyperdense pathology
more dense
if an abnormality is bright (white) on CT
define abdominal aortic aneurysm (AAA) pathology
a ballooning out of a segment of artery caused by disease or weakness in the vessel wall that occurs in the portion of the aorta that runs through the abdomen
define ascites pathology
a condition in which fluid accumulates in the abdomen and causes swelling
define bronchiectasis pathology
a dilation of the bronchi, often caused by infection
