Water excitation: a possible pitfall in cerebral time-of-flight angiography.
OBJECTIVE
Time-of-flight MR angiography (TOF MRA), with its advantage of high spatial resolution, is widely used for visualization of intracranial arteries. Fat signal intensity from bone marrow can interfere with vessel signal intensity, especially in maximum intensity projection reconstructions. Use of a technique such as fat saturation or water excitation can reduce this signal intensity.


METHODS
Ten volunteers were included in this study. TOF MRA was performed by using spoiled gradient echo sequences on a 1.5-T MR unit either with or without water excitation. Water excitation was performed by using a binomial excitation pulse pair, with a null in the excitation profile at the fat frequency to obtain fat suppression. Two blinded neuroradiologists then judged the images. Additional studies by using a phantom with a flow of about 2 mL/s were performed under the same conditions. Image quality obtained with and that without water excitation was graded as similar by both neuroradiologists.


RESULTS
As the main finding, the sequences by using water excitation revealed an important pitfall: apparent carotid artery stenosis was detected in 4/10 and occlusions in 1/10 cases. Use of a flow phantom could reveal the same pitfall. Intracranial vessel disease was excluded in all volunteers by using Doppler sonography.


CONCLUSIONS
The type of water excitation tested here can induce significant artifacts in cerebral TOF MRA. These artifacts can be misinterpreted as carotid artery stenosis or even occlusion, whereas the benefit brought by water excitation with respect to fat suppression is less significant.
Gizewski
Elke R
ER
Departments of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany.
Ladd
Mark E
ME
Paul
Andrena
A
Wanke
Isabel
I
Göricke
Sophie
S
Forsting
Michael
M
D000328:Adult; D016477:Artifacts; D016893:Carotid Stenosis / Q000175:diagnosis*; D002533:Cerebral Angiography / Q000295:instrumentation*; D002539:Cerebral Arterial Diseases / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007089:Image Enhancement; D018810:Magnetic Resonance Angiography / Q000295:instrumentation*; D008297:Male; D019047:Phantoms, Imaging; D012984:Software; D013113:Spin Labels; D017585:Ultrasonography, Doppler, Transcranial; D014867:Water
D013113:Spin Labels; D014867:Water