Biomedical Engineering Reference
In-Depth Information
This technique visualized the left main, the right coronary artery up to segment 3,
the LAD up to segment 8, and the RCX with segments 11 and 13. The average
signal-to-noise value at the level of the right coronary artery was 11
.
4
±
5
.
0, at the
level of the left coronary artery 12
.
3
±
4
.
5 with an in-place resolution of 0
.
63
×
0
.
63 mm
2
. This resulted in a too low signal-to-noise ratio so that an adequate
assessment of coronary arteries was no longer possible. 3D-MR coronary angiog-
raphy using the navigator technique is limited by the low signal-to-noise ratio.
3.4.6 Navigator Echo and Cine Gradient-Echo Technique
This technique was used to evaluate coronary artery stents with MR [6]. For
both sequences the low-signal artifact was used to localize the stent, whereas
the flow-related high signal before and distal to the stent was considered as
a potency sign. All the stents were recognized as signal void with GE, and all
but one with NE. Positive EET, with a stent on the left anterior descending
coronary artery, presented low signal distal to the stent at both MR sequences.
These suggested the dysfunction stenosis at conventional coronary angiography
(CCA). Two sequential stents on the right coronary artery presented lack of
signal distal to the stents at both MR sequences. It suggested occlusion (97%
stenosis at CCA). However, negative EET, MR high signal before and distal to
the stent suggested patency at both sequences. MR seems to be a safe and
promising technique for noninvasive evaluation of coronary stents.
3.4.7 MR Phase-Contrast Doppler Flow Quantification
Determination of blood flow volume is useful in assessing ischemic cerebrovas-
cular disease. Blood flow volume measurement was evaluated by three noninva-
sive imaging techniques, namely color velocity imaging quantification, spectral
Doppler imaging quantification, and MR phase-contrast flow quantification, to
see how well the flow values determined by each technique agreed with one
another [7]. Flow volume quantification was tested experimentally using a flow
simulator and three techniques. These techniques evaluated the vertebral and in-
ternal carotid arteries of patients with history of cerebral ischemia. In the flow
simulation study, the flow values in each technique were compared with the
phantom flow using Wilcoxon's signed rank test. Flow volumes were measured
by color velocity imaging quantification. MR phase-contrast flow quantification
