Biomedical Engineering Reference
In-Depth Information
Figure 3.30:
FFEP MRA.
minimizing the imaginary part of the data in image space. The correction algo-
rithm reduced image blurring substantially in all MRA phases (see Fig. 3.30).
The image quality of the spiral CE-MRA pulse sequence was comparable to
that of the FLASH CE-MRA with increased spatial resolution and a reduced
contrast-to-noise ratio. Additionally, artifacts specific to spiral MRI could be
observed that had no impact on the assessment of the renal arteries.
3.4.16 High-Resolution MRA with Phase/Frequency
Flow Compensation
A newly developed pulse sequence 3D TOF-VTE was tested on clinical MRI
systems, by performing scans of the cervical carotid artery and intracranial
carotid artery at the carotid siphon. It required very long echo delay times (TE).
Variable TE (VTE) was implemented into flow-compensated 3D TOF to minimize
the effective TE and reduce the flow-related signal void. The k-space of the
3D TOF was divided into segment groups ranging from two to 32 segments
with different TE. The TE were minimized and the flow-compensation gradient
lobes were calculated to null the total first moment at the peak of the echo for
each segment [16]. Possible artifacts and off-resonance effects were evaluated,
with respect to the number of TE segments, using the point spread function
