Maximizing Contrast-to-Noise Ratio in Ultra-High Resolution Peripheral MR Angiography Using a Blood Pool Agent and Parallel Imaging


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Abstract

Purpose:To determine sequence parameters that maximize vascular contrast-to-noise (CNR) for ultra-high resolution equilibrium phase (EP) peripheral imaging for the blood pool agent (BPA) Vasovist.Materials and Methods:A model for maximizing CNR in EP MR angiography (MRA) is presented. Tissue relaxation times, coil geometry (g)-factors, and clinical imaging requirements (voxel volume and scan time) were determined from human studies. Using these known values, parameters for TR, TE, bandwidth, flip angle (FA), and sensitivity encoding (SENSE) factor that maximized CNR were derived from the model. CNR was enhanced by using reduction in scan time gained from parallel imaging to increase TR and minimize bandwidth. A total of 10 patients were imaged using model-derived EP CE-MRA parameters.Results:The model closely predicted experimental CNR data measured in two clinical studies (r2 = 0.85) and demonstrated an increase in CNR by a factor of 2.3 when subjects were imaged using optimal sequence parameters (P < 0.001). Thigh and calf data were acquired with voxel volumes on the order of 0.2 mm3 using a SENSE factor of 4.Conclusion:Recommended imaging parameters for a 12-channel and 18-channel peripheral vascular coil at two doses of Vasovist (0.03 mmol/kg and 0.05 mmol/kg) are presented.

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