Biomedical Engineering Reference
In-Depth Information
Helical CT:
Helical (spiral) was announced by Kalender in 1990 [3].
Helical CT continuously irradiates X-rays. This method collects the
projection data while the table on which the patient lies slides through
the slipping ring, at the same time the X-ray emitter continuously
rotates in this ring. It is called helical CT, because the tracks of an X-ray
beam draw spiral. This method allows (1) drastically shortening the
imaging time, (2) reconstructing slice image of arbitrary position,
(3) displaying three-dimensional information and MRP (multi-
planar reconstruction).
Multi-slice CT:
Multi-slice CT (MSCT), which has a multi-row
detector, appeared in 1999. Technical improvements, such as
high-speed scanning and reduction of slicing pitch, were made by
the MSCT detector. As a result, it realized (1) drastic reduction of
scanning time, (2) sagittal section imaging, (3) isotropic voxels, (4)
high-resolution 3D image and (5) improvement of time resolution.
Moreover, since the drastic reduction of scanning period widens the
imaging range, it becomes possible to obtain sagittal section image
that has the same resolution as the axial section image, by adopting
isotropic voxel. Consequently, it becomes possible to reduce the
partial volume effect (PVE) that originated in the slice interval. The
resolution of CT has improved up to about 0.2
mm (about several
millimeters in CT) by the appearance of MSCT.
Magnetic Resonance Imaging:
The clinical application of MRI
started in the 1980s. An excellent image can be obtained now
because it is possible to obtain a strong and steady magnetic ield
by the development of super-conductivity and permanent magnet
modality and because of the advancement of image reconstruction
method. MRI has the following features:
(1) Arbitrary section image is attainable including sagittal/
coronal direction.
(2) No X-ray irradiation.
(3) Excellent tissue resolution (easy separation of vascular
region).
(4) Relationship between vasculature and disease can be
recognized since the vasculature is detected as signal area.
On the other hand, the disadvantages of MRI are
(1) Low spatial resolution
(2) Long imaging period
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