Image RECONSTRUCTION & PROCESSING Flashcards
During a CT scan, numerous measurements of the transmission of X-rays through a patient are acquired at many angles
This is the basis for _____
reconstruction of the CT image.
are taken from a large number of angles and backprojected (d) yielding a strongly blurred image
Transmission profiles
Mathematics shows that simple backprojection is not
sufficient for accurate image reconstruction in CT..
Instead a ___ must be used ⚫It is the standard for image reconstruction in CT.
filtered backprojection
Solves number of simultaneous equations
Algebraic reconstruction
(statistical) reconstructions are sometimes used
• These are routinely used in nuclear medicine. • They are becoming available for commercial CT scanners
Iterative
Potential benefits of iterative reconstructions ⚫ the removal of streak artefacts (particularly when fewer projectionangles are used) ⚫ better performance in ____
low-dose CT acquisitions
is the most frequently applied
technique for CT reconstruction
Filtered backprojection
3 domains in filterrd backprojection
Object, Radon & Fourier space
The three domains associated with the technique of filtered backprojection are
a) __ (linear attenuation values).
b) ____ (projection values recorded under many angles) this domain is also referred to as sinogram space where Cartesian coordinate are used).
c) _____
which can be derived from object space by a 2D Fourier transform.
Object space
Radon space
Fourier space
theorem states that the 1D Fourier transform of the projection profile yields an angulated line in (Cartesian) Fourier space at the angle of the projection
Fourier slice
A 2D Radon transform
converts the object
space into __
space.
Radon
The creation of 2D Radon
space is carried out during a CT
scan: projections are recorded
and they are stored as ___
in 2D Radon space
raw data
Multi-slice or multi-row scanners enabled *
Thinner slicesLonger scan volumesFaster scan volumes
A typical acquisition with a single detector row scanner covered __mm.
5
Techniques for reconstruction include*
Simple backprojection
*Algebraic reconstruction
*Iterative reconstruction
*Filtered back projection
The 2D image space is defined as ƒ(x,y), where __ are the cartesian coordinates in image space.
(x,y)
One 1D projection of the 2D image space with equidistant
and parallel rays yields one line in Radon space
• expressed as the projection p(t,θ),
where _ is the distance from
the projected x-ray to the
iso-center and
θ is the ____
t
projection angle
2D Fourier space is sometimes
also referred to as ___
k-space
A reconstruction can thus, at least theoretically, be achieved by first a construction of the ___
F(u,v) by many1D Fourier transforms of the projection
profiles measured under many projection angles, and subsequently a 2D inverse Fourier transform of the 2D fourier space to the 2D image space.
2D Fourier space
