In  medical CT, Which algorithm has better motion suppression...

In  medical CT, Which algorithm has better motion suppression capability: the half-scan or the underscan? Justify your answer. Q 7-22 from below attachment. Information regarding question is provided in same attachment.

Chapter 7
Image Artifacts: Appearances,
Causes, and Corrections
7.1 What Is an Image Artifact?
Chapter 3 provided a representative flow diagram for the image generation
process and stated that the preprocessing and postprocessing steps used to
overcome nonideal data collection often outweigh, in terms of the number
of operations, “ textbook ” tomographic reconstruction. In other words, a
significant portion of the computation associated with CT image generation
is related to the reduction or elimination of image artifacts. This chapter
provides a broad overview of the causes of some artifacts and presents
solutions to avoid or correct them whenever appropriate.
The definition of an image artifact is not as clearly defined as one might
expect. Theoretically, an image artifact can be defined as any discrepancy
between the reconstructed values in an image and the true attenuation
coefficients of the object. Although this definition is broad enough to cover
nearly all types of nonideal images, it has little practical value since nearly
every image produced by a CT scanner contains an artifact by this definition.
In fact, most pixels in a CT image are artifacts in some shape or form. In
practice, we have to limit our discussion to the discrepancies that are clinically
significant or relevant as judged by the radiologists. We want to examine only
the discrepancies that impact the radiologists ’ performance.
Compared to conventional radiography, CT systems are inherently more
prone to artifacts. Recall the discussion in Chapter 3 that explained how a CT
image is generated with a larger number of projections (about 1000). In a
typical CT system, each projection contains roughly 1000 separate measure-
ments. (In the case of a multislice CT scanner, which will be discussed in
Chapter 10, the number of measurements in a single projection can easily be
quadrupled.) As a result, nearly 10
6
independent readings or measurements
are used to form an image. Because the nature of the backprojection process is
to map a point in a projection to a straight line in an image, an error in the
projection reading is no longer localized, as is the case for conventional
245
Downloaded From: http://ebooks.spiedigitallibrary.org/ on 09/16/2016 Terms of Use: http://spiedigitallibrary.org/ss/termsofuse.aspx