Biomedical Engineering Reference
In-Depth Information
hydrogen; T1 and T2 are the longitudinal and transverse relaxation
times of that signal which varies between tissue types. Therefore,
various contrasts can be generated by selecting speciic values of
T1 and T2. When T2 is emphasized, water is a high signal, making
the image whiter. When T1 is emphasized, water is a low signal and
the pictures becomes darker, fat becomes a high signal. Bone tissue
becomes a low signal in any case. Based on this property tissue
characteristics and the blood vessel area can be differentiated from
surrounding tissue in MRI.
Figure 3.5 is three-dimensional image of the blood vessel
obtained by setting the threshold processing to 177 on the MRI
image taken with emphasis on the T2 signal. The bone area can be
completely separated compared with CT, and only the brain blood
vessel area can be extracted as conirmed from this igure. Like this,
MRI has an excellent merit in the parting of the blood vessel area and
the bone tissue. However, it is a disadvantage that the resolution and
the image registration speed are low compared with CT. Therefore,
it is appropriate to limit its use for cases where the blood vessel is
adjacent to the bone tissue.
a)
b)
Figure 3.5
Reconstruction of three-dimensional vascular structure based
on individual image obtained by MRI modality: (a) Extracted
vessel area by threshold application. (b) Reconstructed three-
dimensional structure.
3.4
Additional Vascular Shape Modification
By using CAD software, it becomes possible to make modiications
on vascular shapes that are reconstructed based on angiographies
Search WWH ::
Custom Search