Exhibit Hall | Forum 2
Purpose: To measure the relaxivity of ferumoxytol (Feraheme) on a 0.35T MR-guided radiation therapy (MRgRT) system and to evaluate the feasibility of using ferumoxytol for MRI signal enhancement.
Methods: We prepared ferumoxytol phantoms at various concentrations (0.0, 0.16, 0.31, 0.63, 1.26, and 2.52mM) by diluting stock ferumoxytol in normal saline and imaging the phantoms using a 0.35T MRgRT system. To determine the r1 and r2 relaxivity, 2D inversion-recovery turbo spin echo (TSE) images (inversion times (TI):0-1000ms) and 2D TSE images (echo times (TE):6-100ms) were acquired at room temperature. T1 and T2 maps were generated from a voxel-wise exponential fit of the observed signal intensity over the range of TI and TE times. Mean R1 (1/T1) and R2 (1/T2) were measured for each ferumoxytol dilution. r1 and r2 relaxivity were computed via a linear regression between the observed R1 or R2 relaxation rate with contrast concentration. To evaluate the effect of ferumoxytol concentration on signal enhancement, high resolution (1mm) 2D T1-weighted (T1w) TSE, T1w spoiled gradient echo (SGE), and balanced steady state free precession (bSSFP) acquisitions were performed. Mean signal intensity for phantom was measured and normalized by the saline-only phantom. Coefficient of variations (CoV) of the mean signal intensity was calculated.
Results: At 0.35T, r1 and r2 of ferumoxytol were 33.1mM⁻¹/s⁻¹ (r-squared=0.98) and 85.0mM⁻¹/s⁻¹ (r-squared=0.99) at room temperature. For T1w TSE and SGE acquisitions, signal intensity peaked at 0.16 mM with a signal enhancement of 5.81 and 5.68. For the bSSFP, the signal plateaued between 0.16-1.26 mM with a signal enhancement of 2. The average CoV for TSE, SGE, and bSSFP were 19%, 9%, and 5%.
Conclusion: At low concentrations (0.16-1.26mM), ferumoxytol provides a 2-6-fold signal enhancement (relative to 0mM) on a 0.35T MRgRT system. Its r1 relaxivity may be exploited to improve vascular imaging for vessel sparing radiotherapy.
Funding Support, Disclosures, and Conflict of Interest: Dr. Yang received honoraria and consulting fees from ViewRay.
MRI, Contrast Agent, Vascular Imaging
IM/TH- MRI in Radiation Therapy: Development (new technology and techniques)