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Abstract
Purpose
To evaluate the degree of image distortion caused by orthodontic devices during a intracranial magnetic resonance angiography (MRA), and to determine the effectiveness of the 3 dimensional phase-contrast (3D PC).
Materials and Methods
Subjects were divided into group A (n = 20) wearing a home-made orthodontic device, and group B (n = 10) with an actual orthodontic device. A 3.0T MR scanner was used, applying 3D time-of-flight (TOF) and 3D PC. Two board-certified radiologists evaluated images independently based on a four point scale classifying segments of the circle of Willis. Magnetic susceptibility variations and contrast-to-noise ratio (CNR) on maximum intensity projection images were measured.
Results
In group A, scores of the 3D TOF and 3D PC were 2.84 ± 0.1 vs. 2.88 ± 0.1 (before) and 1.8 ± 0.4 vs 2.83 ± 0.1 (after wearing device), respectively. In group B, the scores of 3D TOF and 3D PC were 1.86 ± 0.43 and 2.81 ± 0.15 (p = 0.005), respectively. Magnetic susceptibility variations showed meaningful results after wearing the device (p = 0.0001). CNRs of the 3D PC before and after wearing device were 142.9 ± 6.6 vs. 140.8 ± 7.2 (p = 0.7507), respectively. In the 3D TOF, CNRs were 324.8 ± 25.4 vs. 466.3 ± 41.7 (p = 0.0001).
Figures and Tables
Fig. 1
Photograph of home-made orthodontic device model in group A (A) and patient wearing therapeutic orthodontic device in group B (B).
Fig. 2
Three dimensional time of flight magnetic resonance angiographys in control (group A) before (top images) and after wearing the orthodontic device (bottom images). Maximal intensity projection images of various directions without wearing the device show well delineation of distal cerebral arteries. However, after wearing the device, there are multiple arteries with signal loss and poor margination.
Note.-S-I = superior-inferior direction, R-L = right-left direction, A-P = anterior-posterior direction
Fig. 3
Three dimensional phase contrast magnetic resonance angiographys in control (group A) before (top images) and after wearing the orthodontic device (bottom images). All maximal intensity projection images show well marginated cerebral arteries regardless of wearing the device. Venous flows are detected in both transverse and sigmoid sinuses.
Note.-S-I = superior-inferior direction, R-L = right-left direction, A-P = anterior-posterior direction
Fig. 4
Distribution of scoring ratio in controls (group A). Scoring ratios (percentage) measured from 3D TOF method show significant difference between group before wearing device and group after wearing device. In 3D PC method, there are no differences of scoring ratios in two groups. 'Inhance 3D velocity' is MRA means 3D PC technique.
Note.-MRA = magnetic resonance angiography, PC = phase contrast, TOF = time of flight, 3D = 3 dimensional
Fig. 5
Distribution of scoring ratio in patients (group B). In patients wearing actual orthodontic devices, Difference of scoring ratios between group with 3D TOF method (average 68%) and group with 3D PC method (average 94%) is significant. 'Inhance 3D velocity' means MRA using 3D PC technique.
Note.-MRA = magnetic resonance angiography, PC = phase contrast, TOF = time of flight, 3D = 3 dimensional
Fig. 6
Comparison of 3D PC MRAs by variable velocity encoding (VENC) values (25 cm/sec in A, 35 cm/sec in B, 45 cm/sec in C). MRAs scanned by 25 and 35 cm/sec VENC values show multifocal signal losses mimicking stenosis or slow flow in cerebral arteries (arrows). However, these phenomena disappear in C (45 cm/sec VENC value).
Note.-3D PC MRA = 3 dimensional phase contrast magnetic resonance angiography
Table 2
The Results of 3D TOF MRA and Inhance 3D Velocity MRA Interpretations Based on Four Point (0-3) Scoring for Vessels Visibility in Controls (group A)
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