Biomedical Engineering Reference
In-Depth Information
agreed with the phantom flow simulation within the tested range, and spec-
tral Doppler imaging quantification values were significantly overestimated. In
patients, a large variation in the blood flow volume was obtained between each
technique. Blood flow volume measurements determined by the three nonin-
vasive imaging techniques on the same vessel can differ widely, and spectral
Doppler imaging quantification consistently overestimated the flow volume.
Color velocity imaging quantification or MR phase-contrast flow quantification
can be used for clinical follow-up investigations in the future.
3.4.8 Breath-Hold Contrast Enhanced MRA
The purpose of this technique was to evaluate the effect of breathing on image
quality of the aortic arch and carotid vessels during contrast-enhanced MR an-
giography. It showed that high-resolution breath-hold contrast-enhanced MR an-
giography combined with a timing-bolus technique can produce high-quality im-
ages of the entire carotid circulation [8]. High-resolution contrast-enhanced MR
angiography on a 1.5-T Siemens imager was used for coronal three-dimensional
gradient-echo sequence (TR/TE, 4.36/1.64; flip angle, 25
◦
) with asymmetric k-
space acquisition. The 136
×
512 matrix yielded voxel sizes of 1
.
33
×
0
.
64
×
1
.
0
mm
3
. A timing-bolus acquisition, orientated in the coronal plane to include the
aortic arch, was obtained initially during free-breathing. Twenty milliliters of
gadopenetate dimeglumine was injected at 2 mL/sec. Unenhanced and enhanced
3D volumes were recorded. A subtracted 3D set was calculated and subjected to
a maximum-intensity-projection algorithm. Half of the patients held their breath
during angiography and the other half did not. Aortic arch motion was measured
on the timing-bolus acquisition as the distance moved by a single pixel in both
the
x
and
y
directions. Two observers assessed MIP MR images independently
and vessel sharpness was scored on a scale of 1-5. Sharpness was also assessed
quantitatively by generating a signal intensity profile across the aortic arch ves-
sel wall and calculating the average of the upward slope and downward slope
at full-width half maximum. Visualization of carotid branch vessels was scored
on a scale of 0-5, and venous contamination was scored on a scale of 0-3. Aver-
age in-plane aortic arch movement was 10.3 mm in the
x
direction and 8.7 mm
in the
y
direction. Quantitative and qualitative sharpness of the aortic arch and
great vessel origins was better (
p
<
0
.
05) during breath-holding than during non-
breath-holding. No difference in the sharpness of the carotid vessels was noted
