Imaging Flashcards
what is image registration
process of spatially aligning two images together
what info does CT provide?
great anatomical detail, enhanced with contrast
what info does RNI provide
great physiological info, but poor anatomical info, so is used alongside other modalities
what is the role of imaging
that the target volume is being treated
what info does MRI provide
greater anatomical details, enhanced with contrast, with an increased use
what info does ultrasound provide
great anatomical detail for soft tissues
why are images gathered
to avoid errors
- systematic = QA program
- random = imaging, QA programme and education
why is registration important
- follow up studies
- inflammatory disease diagnosis
- RT planning
- neurological disorders
- RT portal film comparison with ref image
why is registration important
- follow up studies
- inflammatory disease diagnosis
- RT planning
- neurological disorders
- RT portal film comparison with ref image
what is a random error
a deviation which can vary in direction and magnitude for each delivered fraction. these are not inherent within the process, normally only occur once
<2mm
what is a systematic error
an error which is introduced at the beginning of treatment and carried throughout the whole treatment. The deviation occurs in the same direction and is of similar magnitude for each fraction throughout the treatment course.
<5mm
what is a pixel
2D space
what is a voxel
3D space
what are fiducial markers
markers which are found internally or outside the treatment couch, which act as a reference point. They are used in image registration
what is localisation
location of where it is in reference with other body parts. it can act as a reference marker outside the body
what position is the same as the treatment position
CT position
what are some equipment adaptations
- couch is flat and not dish shaped
- treatment position, otherwise it could lead to geographical miss
- accessory equipment must attach directly to the couch accurately
what is a simulator
it is similar to the treatment couch, which is isocentrically mounted, but it doesn’t visualise soft tissue, all tissue looks the same
what is the ideal equipment
- treatment position
- anatomical + functional info
- minimal/no radiation dose
- localisation and position of where the tumour is active
- good image quality
- information of x-ray absorption
why are radio-opaque markers used
they are inserted in the body, which help with the alignment so that the patient is in the same position
what is contrast
it is the state of being strikingly different from something else in juxtaposition or close association. There is a difference in density
bone = white, air = black, soft tissue = grey
what is the density of darker images
greater density
what energy is used in electrons
MeV
what is a reference image
a selected standard image used against all online images, MV images are taken prior treatment
what is geographical miss
it is when the beam placement is wrong, so the target is missed and normal tissue is treatment
what is a radiation map
it is a representation of a patients internal anatomy, in which the map interacts with the recording system converting to light. As more light reaches the system, the more blackening occurs
how is detailed controlled
by the number of pixels, each pixel represents a ‘colour’ (a shade of grey which is matched with the number of IE which it holds)
what does magnification do to an image
stretches the pixels
what is CR
Computed radiography
- x-ray images are captured on a cassette which contain a phobostimuble phosphor imaging plate
- the x-ray is trapped and the image is extracted from the IP through a laser and then digitised
what is DRR
Direct Digital Radiograph
- contains a conversion layer and an electronic readout layer, x-rays are converted into light and then electrical charges. Its transmitted out of the detector using algorithms to produce an image
why is a Kodak film useful
at high dose ranges within relative dosimetry
what are the two ways of creating images
passive: reflects a fluorescent light through the crystals projecting an image, it has a time lag so there is a low viewing angle and reduced brightness
active: uses a LED containing brighter lights, superior contrast and resolution with angles similar to TV monitors
what happens to the crystals
they can shape allowing a variable amount of light through
do darker regions have more or less absorption
more
what does a HL7 ensure
that textual info is encoded in a way that only other computers can decode and decipher strings of text
what 5 RT objects has a DICOM specified
- RT image: DRR, portal + simulator images
- RT plan: contains geometric and dosimetric data for external beam and brachytherapy
- RTSS: anatomical info
- RT dose: dose data
- RT treatment record: data from sessions and records
why are digital images useful
they allow for extraction of info or correct original data. The grey values are represented in the DRR panel when the image is generated - system fidelity
what is a method needed for:
- directing radiation through the body
- recording the radiation patterns
- converting the patterns accurately
- radiation into light - an image
what are artefacts
a structure which doesn’t directly correlate with the actual tissue
what are the causes of artefacts
- acoustic properties of tissue
- improper operation of equipment
- malfunctioning or faulty equipment
where are artefacts common
- reverberation
- resolution
- posterior acoustic shadow
- posterior cystic enhancement
- mirror image
- edge artefact
