2005 Proceedings - ASNR

Thursday
Paper 366 Starting at 10:24 AM, Ending at 10:32 AM
Comparison of High-Resolution 3D Flash Contrast-
Enhanced MR Angiography Using Parallel Acquisition
Techniques to Conventional 3D Time-of-Flight MR
Angiography in Carotid Artery Stenosis
Sunenshine, P. J. · Pramanik, B. · Law, E. M. · Hecht, E. M.
New York University Medical Center
New York, NY
PURPOSE
Three-dimensional (3D) time-of-flight (TOF) MR angiography
(MRA) is a well established high-resolution noninvasive
way to assess carotid artery stenosis. Although accurate, this
method is prone to artifacts as a result of long acquisition
times and saturation effects. Contrast-enhanced MRA techniques
have become increasingly popular to counter the saturation
effects of slow flow and decrease acquisition times.
However, spatial resolution of contrast-enhanced MRA is
relatively low compared to conventional 3D TOF imaging.
With the advent of parallel acquisition techniques and multichannel
neck coils, spatial resolution can be increased significantly
without sacrificing temporal resolution. The purpose
of this study is to compare conventional 3D TOF MRA
and 3D FLASH contrast-enhanced MRA with parallel imaging
to determine if parallel imaging can be used to improve
the spatial resolution of dynamic contrast-enhanced MRA to
that comparable with conventional 3D TOF MRA.
MATERIALS & METHODS
Prospectively, four consecutive patients presenting for
carotid MRA underwent 3D TOF MRA and 3D contrastenhanced
MRA with parallel acquisition techniques (GRAP-
PA, acceleration factor 3) at 1.5 T using a 4-channel phasedarray
neck coil and a multiple-channel head coil.
Conventional 3D imaging was performed using a voxel size
of 0.7 x 0.5 x 0.9 mm, a 288 x 384 matrix, and an acquisition
time of 6:21 minutes. Dynamic contrast-enhanced MRA
with parallel imaging was performed using a 3D FLASH
sequence using a voxel size of 0.8 x 0.8 x 0.8, a 384 x 512
matrix, and an acquisition time of 24 seconds following
intravenous injection of gadolinium (0.2 mmol/kg) and a 20
cc saline bolus via power injector. Timing was determined
using a time-resolved echo-sharing angiographic technique
(TREAT) using a 3 cc contrast bolus and 20 cc saline flush.
Quantitative assessment was performed by calculating signal-to-noise
ratio (SNR) and contrast-to-noise ratios (CNR)
in the distal common carotid artery for each MRA sequence.
Qualitative assessment was performed by two neuroradiologists
blinded to the imaging method used. Subjective assessment
of image quality, noise, degree of stenosis using the
NASCET criteria, and degree of confidence in diagnosis was
performed using a 4-point scale (1 = excellent, 4 = nondiagnostic).
RESULTS
Signal-to-noise ratio and CNR were both increased with contrast-enhanced
MRA as shown in the table. Qualitative
parameters such as overall quality was better in the contrastenhanced
MRA sequences. Image quality of the contrastenhanced
MRA was rated the same or higher on all patients
when compared with conventional noncontrast-enhanced 3D
TOF imaging.
198
TABLE 1 3D TOF vs CE MRA with Parallel Imaging
NC 3D TOF 3D CE MRA P-value
SNR 106.6 139.4 p ≤ 0.75
CNR 81.7 121.9 p ≤ 0.5
Overall Quality 2.2 1.9 p ≤ 0.5
*Note: Average overall quality on a scale of 1-4; (1 = excellent,
2 = more than adequate for diagnosis, 3 = adequate for
diagnosis, 4 = nondiagnostic).
CONCLUSION
Although not statistically significant in this preliminary
small group of patients, dynamic contrast-enhanced MRA
using parallel imaging to achieve comparable spatial resolution
demonstrated an overall trend of increased signal to
noise and better overall quality of image when compared to
conventional 3D TOF imaging.
KEY WORDS: MR angiography, carotid, parallel
Paper 367 Starting at 10:32 AM, Ending at 10:40 AM
Utility of CT Angiography with Virtual Angioscopy versus
Doppler Ultrasound in the Examination of the
Stented Carotid Artery
Orbach, D. B. · Pramanik, B. · Lee, J. · Maldonado, T. · Riles,
T. · Grossman, R. I.
New York University Medical Center
New York, NY
PURPOSE
Doppler ultrasound (DU) is the imaging modality most commonly
used for follow up after placement of carotid artery
stents. However, many studies have reported a not insignificant
incidence of false-positive DU reports of intrastent
stenosis, likely due to distortion of the ultrasound beam by
the stent material. We developed a methodology for accurately
assessing carotid stents using a multidetector CT to
perform CT angiography (CTA) and virtual angioscopy.
MATERIALS & METHODS
We measured luminal stent diameter in a cohort of six
patients who recently had undergone carotid stenting and in
whom we had CTA, intraoperative digital subtraction
angiograms (DSA), and DU, all performed within 1 month.
Additionally, we generated virtual angioscopic endoluminal
views inside the stents in order to assess the surface morphology
of the endoluminal aspect of the stent. The patients
returned for 6-month follow up, at which time their DU
results were compared again with the CTA and virtual
angioscopy. Our methodology for performing the CTA, as
previously described, involved a specialized reconstruction
kernel and optimized transparency and color tables for the
virtual angioscopy.
RESULTS
In two cases, the first post-stent DU reported a moderate
stenosis, while the DSA and CTA showed the stents to be
patent. In cases in which there was true restenosis requiring
repeat angioplasty, all three modalities were likely to give an
accurate depiction. However, only CTA with virtual
angioscopy allowed for visualization of the morphology of
the stenotic lesion. In a case with restenosis requiring repeat