Biomedical Engineering Reference
In-Depth Information
Figure 3.24: The figure represents the method of reformatting of TOF-MRA im-
ages by MIP. The technique generates the 3D images of blood vessels with blood
motion. Larger flip angle at given TR show loss of magnetization and generate
the different 3D appearance of vasculature (shown on right panel at bottom).
3D imaging in which volume imaging is performed over an imaging slab. Signal
losses might be significant from one end of the slab to the other end of the slab.
3.2.7 Multislice GRE Techniques
These techniques use longer decrease in repetition time TR. As a result, the
saturation effects lead to signal loss with the use of larger flip angles. This
approach using longer decrease in TR improves the SNR. Other ways are also
used to decrease saturation effects. Common use of paramagnetic contrast agent
such as gadolinium chelate causes spin-lattice relaxation time (T1) shortening
of blood (see Fig. 3.25). Consequently, the T1 recovery (from short T1 to normal
T1 values) is faster with less saturation effects. In routine, multiple overlapping
thin-slab acquisition (MOTSA) tilt optimized nonsaturated excitation (TONE)
are also promising techniques to reduce saturation effects.
