Biomedical Engineering Reference
In-Depth Information
all the possible velocities in the vessels. This concept is also used in Doppler
sonography. The sequence uses the gradient reversal. Reversed gradient sup-
presses the signal from stationary tissue but does not affect phase angle of the
flowing tissue. It also corrects magnetic field inhomogeneity and zero phase
determination.
3.2 Techniques and Principles of Magnetic
Resonance Angiography
There are two main methods of acquiring angiographic images. We shall de-
scribe them from the point of view of intravascular flow imaging. Later, we shall
describe recent refinements and modifications in the angiography methods.
TOF MRA
PC MRA
Each technique can be performed using 2D-FT. Thus, there are mainly four
different methods:
1. 2D-TOF MRA
2. 2D-PC MRA
3. 3D-TOF MRA
4. 3D-PC MRA.
Each of these techniques is advantageous to a different type of clinical applica-
tion.
Before discussing these techniques, let us understand the basic physical
principles of flow inside the vessel which is the fundamental principle of an-
giography. This information is important for MR instrument physicists in day to
day practice.
3.2.1 TOF MRA
This approach is based on flow-related enhancement in which 2D or 3D GRE
techniques are applied (see Fig. 3.6). Usually, FC (flow compensation) is used
perpendicular to the lumen of the vessel. So, it relies primarily on flow-related
