Faculty Collaboration Database

Magnetization transfer or spin-lock? An investigation of off-resonance saturation pulse imaging with varying frequency offsets. AJNR Am J Neuroradiol 1996 May;17(5):805-19

Date

05/01/1996

Pubmed ID

8733952

Pubmed Central ID

PMC8337510

Scopus ID

2-s2.0-0029983511 (requires institutional sign-in at Scopus site)   59 Citations

Abstract

PURPOSE: To characterize near-resonance saturation pulse MR imaging on a 1.5-T scanner in order to gain insight into underlying mechanisms that alter tissue contrast and to optimize the technique for neuroimaging.

METHODS: Off-resonance saturation pulses were applied to T1-weighted, spin-density-weighted, and T2-weighted sequences at frequency offsets ranging from 50 Hz to 20,000 Hz down field from water resonance. Suppression ratios were determined at each offset for phantom materials (MnCl2 solution, gadopentetate dimeglumine, corn oil, water, and agar), normal brain structures, and a variety of brain lesions.

RESULTS: Signal suppression of MnCl2 on T1-weighted images occurred at offsets of less than 2000 Hz even though no macromolecules were present in the solution. Only those phantom materials and tissues with short or intermediate T1 relaxation times and relatively large T1/T2 ratios were sensitive to changing frequency offsets. Suppression of brain increased from approximately 20% at 2000 Hz offset to approximately 45% when the offset was reduced to 300 Hz. In human subjects, the net effect of reducing the frequency offset was to increase T2 contrast on T1-weighted, spin-density-weighted, and T2-weighted images. Distilled water and contrast material did not suppress except at very low offsets ( < 300 Hz). A frequency offset of 300 Hz was optimal for maximizing conspicuity between most contrast-enhancing lesions and adjacent brain while preserving anatomic detail.

CONCLUSION: Suppression of MnCl2 indicates that magnetization transfer is not the sole mechanism of contrast in near-resonance saturation MR imaging. Spin-lock excitation can reasonably explain the behavior of the phantom solutions and the increase in T2 contrast of tissues achieved as the frequency offset is decreased from 2000 Hz to 300 Hz. Below 300 Hz, saturation is presumably caused by spin-tip effects. With our pulse design, an offset of 300 Hz is optimal for many routine clinical imaging examinations.

Author List

Ulmer JL, Mathews VP, Hamilton CA, Elster AD, Moran PR

Author

Vincent Mathews MD Chair, Professor in the Radiology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Adult
Agar
Brain
Brain Diseases
Brain Neoplasms
Cerebrovascular Disorders
Chlorides
Contrast Media
Corn Oil
Drug Combinations
Electron Spin Resonance Spectroscopy
Female
Gadolinium
Gadolinium DTPA
Humans
Image Enhancement
Macromolecular Substances
Magnetic Resonance Imaging
Male
Manganese Compounds
Meglumine
Middle Aged
Organometallic Compounds
Pentetic Acid
Phantoms, Imaging
Water