Brain MR imaging at ultra-low radiofrequency power

Subhendra N. Sarkar, David C. Alsop, Ananth J. Madhuranthakam, Reed F. Busse, Philip M. Robson, Neil M. Rofsky, David B. Hackney

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Purpose: To explore the lower limits for radiofrequency (RF) power- induced specific absorption rate (SAR) achievable at 1.5 T for brain magnetic resonance (MR) imaging without loss of tissue signal or contrast present in high-SAR clinical imaging in order to create a potentially viable MR method at ultra-low RF power to image tissues containing implanted devices. Materials and Methods: An institutional review board-approved HIPAA-compliant prospective MR study design was used, with written informed consent from all subjects prior to MR sessions. Seven healthy subjects were imaged prospectively at 1.5 T with ultra-low-SAR optimized three-dimensional (3D) fast spin-echo (FSE) and fl uid-attenuated inversion-recovery (FLAIR) T2-weighted sequences and an ultra-low-SAR 3D spoiled gradient-recalled acquisition in the steady state T1-weighted sequence. Corresponding high-SAR twodimensional (2D) clinical sequences were also performed. In addition to qualitative comparisons, absolute signal-tonoise ratios (SNRs) and contrast-to-noise ratios (CNRs) for multicoil, parallel imaging acquisitions were generated by using a Monte Carlo method for quantitative comparisonbetween ultra-low-SAR and high-SAR results. Results: There were minor to moderate differences in the absolute tissue SNR and CNR values and in qualitative appearance of brain images obtained by using ultra-low-SAR and high-SAR techniques. High-SAR 2D T2-weighted imaging produced slightly higher SNR, while ultra-low-SAR 3D technique not only produced higher SNR for T1-weighted and FLAIR images but also higher CNRs for all three sequences for most of the brain tissues. Conclusion: The 3D techniques adopted here led to a decrease in the absorbed RF power by two orders of magnitude at 1.5 T, and still the image quality was preserved within clinically acceptable imaging times.

Original languageEnglish (US)
Pages (from-to)550-557
Number of pages8
Issue number2
StatePublished - May 2011

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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