Purpose: MRI/A is useful for disease detection and surveillance in large vessel vasculitis such as Takayasu's Arteritis (TA). TA is pathologically indistinguishable from Giant Cell Arteritis (GCA) but the utility of MRI for superficial temporal artery (STA) assessment is unproven. This study assesses MR imaging of the normal STA by; 1. Determining the optimal imaging sequences 2. Evaluating the reproducibility in measuring the vessel wall, luminal diameter, flow and peak velocity.
Methods and Materials: 5 healthy volunteers have MRI of the STA on 3 separate visits using a 1.5T MR system (General Electric, Wisconsin) with a TMJ surface coil, FOV= 12mm and these sequences; 1. Axial and sagittal-oblique DIR + FS-flip 90°, TE 77ms, TR 2.2s, 3mm/0, 512 x 256, 2 NEX 2. Axial Fast Cine Phase Contrast (FCPC)- flip 20°, TE 5.1ms, TR 10.9ms, 2/0mm, 256 x 128, 1 NEX. 3. Axial and sagittal-oblique T1 FSE FS- flip 90°, TE 19ms, TR 0.7s, 3/0.5mm, 512 x 256, 2 NEX. Soft copy interpretation is performed on an eFilm workstation v1.7 (eFilm-Merge, Toronto, Ontario), vessel analysis on an Advantage Windows Workstation (General Electric) using dedicated software (CV Flow and Functool). The following are documented; a. visualization of the STA and branches b. vessel wall caliber and luminal diameter c. blood flow and peak velocity. Repeated (x3) measurements are made independently by 2 radiologists (NP, EK) blinded to the subject's details and results. Reproducibility assessment of intra / inter-observer measurements is performed.
Results: In progress All of the MRI examinations (15) have been performed. The STA and branches are seen in exquisite detail on all studies. The anatomy is best seen on DIR acquisitions; wall measurements from the axial sequence and branch anatomy on the sagittal-oblique sequence. The intimate relationship between the STA and vein is best demonstrated on the axial FCPC from which reproducible measurements of the flow and peak velocities are calculated. There is within subject variation in flow measurements between the 3 MRI studies, representing changes in cerebral vasoconstriction. The intra-observer (NP) caliber measurements are within a range of 0.1mm.
Conclusion: Reproducible anatomical and physiological data from the normal STA and its branches is obtained in 30-40 minutes with clinically available software. This study is a platform for a prospective trial of MRI/A on patients with Temporal Arteritis to evaluate whether the changes seen in TA are seen in GCA. If so, MRI/A could be a useful guide for temporal artery biopsy and disease surveillance.
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