Biomedical Engineering Reference
In-Depth Information
spatial resolution employed in this study, 3D-TRICKS may be the method of
choice.
3.4.14 Autocorrected MRA for Motion-Induced Artifacts
This technique was used to investigate the efficacy of a retrospective adap-
tive motion correction technique known as autocorrection for reducing
motion-induced artifacts in high-resolution three-dimensional time-of-flight MR
angiography of the circle of Willis [14]. Gradient-recalled echo three-dimensional
time-of-flight MR angiography sequence was used for MRA of the circle of Willis.
Each volunteer was asked to rotate approximately 2
◦
after completion of one
third and one half of the acquisition in the axial, sagittal, and oblique planes (45
◦
to the axial and sagittal planes). A single static data set was also acquired for
each volunteer. Unprocessed and autocorrected maximum-intensity-projection
images were reviewed as blinded image pairs by six radiologists and were com-
pared on a five-point image quality scale. Mean improvement in image quality
after autocorrection was 1.4 (
p
<
0
.
0001), 1.1 (
p
<
0
.
0001), and 0.2 (
p
=
0
.
003)
observer points (maximum value 2.0), respectively, for examinations corrupted
by motion in the axial, oblique, and sagittal planes. All three axes had statisti-
cally significant improvement in image quality compared with the uncorrected
images. Autocorrection can reduce artifacts in motion-corrupted MR angiogra-
phy of the circle of Willis without distorting motion-free examinations.
3.4.15 Multiphase Contrast-Enhanced Magnetic
Resonance Angiography
A fast pulse sequence with spiral in-plane readout and conventional 3D partition
encoding was reported for multiphase contrast-enhanced magnetic resonance
angiography (CE-MRA) of the renal vasculature and compared to a standard
multiphase 3D CE-MRA with FLASH readout [15]. An isotropic in-plane spa-
tial resolution of 1
.
4
×
1
.
4mm
2
over 2
.
0
×
1
.
4mm
2
could be achieved with a
high temporal resolution. The theoretical gain of spatial resolution by using the
spiral pulse sequence and the performance in the presence of turbulent flow
was evaluated in phantom measurements. A deblurring technique corrected the
spiral raw data. Thereby, the off-resonance frequencies were determined by
