Frequency offset dependence of adiabatic rotating frame relaxation rate constants: Relevance to MRS investigations of metabolite dynamics in vivo

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Abstract

In this work, we investigated the frequency-offset dependence of the rotating frame longitudinal (R ) and transverse (R ) relaxation rate constants when using hyperbolic-secant adiabatic full passage pulses or continuous-wave spin-lock irradiation. Phantom and in vivo measurements were performed to validate theoretical predictions of the dominant relaxation mechanisms existing during adiabatic full passage pulses when using different settings of the frequency offset relative to the carrier. In addition, adiabatic R and R values of total creatine and N-acetylaspartate were measured in vivo from the human brain at 4 T. When the continuous-wave pulse power was limited to safe specific absorption rates for humans, simulations revealed a strong dependence of R and R values on the frequency offset for both dipolar interactions and anisochronous exchange mechanisms. By contrast, theoretical and experimental results showed adiabatic R and R values to be practically invariant within the large subregion of the bandwidth of the hyperbolic-secant pulse where complete inversion was achieved. However, adiabatic R and R values of the methyl protons of total creatine (at 3.03ppm) were almost doubled when compared with those of the methyl protons of N-acetylaspartate (at 2.01ppm) in spite of the fact that these resonances were in the flat region of the inversion band of the adiabatic full passage pulses. We conclude that differences in adiabatic R and R values of human brain metabolites are not a result of their chemical shifts, but instead reflect differences in dynamics.

Original languageEnglish (US)
Pages (from-to)807-814
Number of pages8
JournalNMR in Biomedicine
Volume24
Issue number7
DOIs
StatePublished - Aug 1 2011

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Creatine
Metabolites
Protons
Rate constants
Brain
Spin waves
Chemical shift
Irradiation
Bandwidth
N-acetylaspartate

Keywords

  • Adiabatic pulse
  • Ethanol
  • Exchange and dipolar relaxation
  • Glycerol
  • Human brain metabolites
  • In vivo
  • Rotating frame
  • Transverse and longitudinal relaxations

Cite this

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title = "Frequency offset dependence of adiabatic rotating frame relaxation rate constants: Relevance to MRS investigations of metabolite dynamics in vivo",
abstract = "In this work, we investigated the frequency-offset dependence of the rotating frame longitudinal (R 1ρ) and transverse (R 2ρ) relaxation rate constants when using hyperbolic-secant adiabatic full passage pulses or continuous-wave spin-lock irradiation. Phantom and in vivo measurements were performed to validate theoretical predictions of the dominant relaxation mechanisms existing during adiabatic full passage pulses when using different settings of the frequency offset relative to the carrier. In addition, adiabatic R 1ρ and R 2ρ values of total creatine and N-acetylaspartate were measured in vivo from the human brain at 4 T. When the continuous-wave pulse power was limited to safe specific absorption rates for humans, simulations revealed a strong dependence of R 1ρ and R 2ρ values on the frequency offset for both dipolar interactions and anisochronous exchange mechanisms. By contrast, theoretical and experimental results showed adiabatic R 1ρ and R 2ρ values to be practically invariant within the large subregion of the bandwidth of the hyperbolic-secant pulse where complete inversion was achieved. However, adiabatic R 1ρ and R 2ρ values of the methyl protons of total creatine (at 3.03ppm) were almost doubled when compared with those of the methyl protons of N-acetylaspartate (at 2.01ppm) in spite of the fact that these resonances were in the flat region of the inversion band of the adiabatic full passage pulses. We conclude that differences in adiabatic R 1ρ and R 2ρ values of human brain metabolites are not a result of their chemical shifts, but instead reflect differences in dynamics.",
keywords = "Adiabatic pulse, Ethanol, Exchange and dipolar relaxation, Glycerol, Human brain metabolites, In vivo, Rotating frame, Transverse and longitudinal relaxations",
author = "Silvia Mangia and Timo Liimatainen and Michael Garwood and Ivan Tkac and Pierre-Gilles Henry and Deelchand, {Dinesh K} and Shalom Michaeli",
year = "2011",
month = "8",
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doi = "10.1002/nbm.1626",
language = "English (US)",
volume = "24",
pages = "807--814",
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TY - JOUR

T1 - Frequency offset dependence of adiabatic rotating frame relaxation rate constants

T2 - Relevance to MRS investigations of metabolite dynamics in vivo

AU - Mangia, Silvia

AU - Liimatainen, Timo

AU - Garwood, Michael

AU - Tkac, Ivan

AU - Henry, Pierre-Gilles

AU - Deelchand, Dinesh K

AU - Michaeli, Shalom

PY - 2011/8/1

Y1 - 2011/8/1

N2 - In this work, we investigated the frequency-offset dependence of the rotating frame longitudinal (R 1ρ) and transverse (R 2ρ) relaxation rate constants when using hyperbolic-secant adiabatic full passage pulses or continuous-wave spin-lock irradiation. Phantom and in vivo measurements were performed to validate theoretical predictions of the dominant relaxation mechanisms existing during adiabatic full passage pulses when using different settings of the frequency offset relative to the carrier. In addition, adiabatic R 1ρ and R 2ρ values of total creatine and N-acetylaspartate were measured in vivo from the human brain at 4 T. When the continuous-wave pulse power was limited to safe specific absorption rates for humans, simulations revealed a strong dependence of R 1ρ and R 2ρ values on the frequency offset for both dipolar interactions and anisochronous exchange mechanisms. By contrast, theoretical and experimental results showed adiabatic R 1ρ and R 2ρ values to be practically invariant within the large subregion of the bandwidth of the hyperbolic-secant pulse where complete inversion was achieved. However, adiabatic R 1ρ and R 2ρ values of the methyl protons of total creatine (at 3.03ppm) were almost doubled when compared with those of the methyl protons of N-acetylaspartate (at 2.01ppm) in spite of the fact that these resonances were in the flat region of the inversion band of the adiabatic full passage pulses. We conclude that differences in adiabatic R 1ρ and R 2ρ values of human brain metabolites are not a result of their chemical shifts, but instead reflect differences in dynamics.

AB - In this work, we investigated the frequency-offset dependence of the rotating frame longitudinal (R 1ρ) and transverse (R 2ρ) relaxation rate constants when using hyperbolic-secant adiabatic full passage pulses or continuous-wave spin-lock irradiation. Phantom and in vivo measurements were performed to validate theoretical predictions of the dominant relaxation mechanisms existing during adiabatic full passage pulses when using different settings of the frequency offset relative to the carrier. In addition, adiabatic R 1ρ and R 2ρ values of total creatine and N-acetylaspartate were measured in vivo from the human brain at 4 T. When the continuous-wave pulse power was limited to safe specific absorption rates for humans, simulations revealed a strong dependence of R 1ρ and R 2ρ values on the frequency offset for both dipolar interactions and anisochronous exchange mechanisms. By contrast, theoretical and experimental results showed adiabatic R 1ρ and R 2ρ values to be practically invariant within the large subregion of the bandwidth of the hyperbolic-secant pulse where complete inversion was achieved. However, adiabatic R 1ρ and R 2ρ values of the methyl protons of total creatine (at 3.03ppm) were almost doubled when compared with those of the methyl protons of N-acetylaspartate (at 2.01ppm) in spite of the fact that these resonances were in the flat region of the inversion band of the adiabatic full passage pulses. We conclude that differences in adiabatic R 1ρ and R 2ρ values of human brain metabolites are not a result of their chemical shifts, but instead reflect differences in dynamics.

KW - Adiabatic pulse

KW - Ethanol

KW - Exchange and dipolar relaxation

KW - Glycerol

KW - Human brain metabolites

KW - In vivo

KW - Rotating frame

KW - Transverse and longitudinal relaxations

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U2 - 10.1002/nbm.1626

DO - 10.1002/nbm.1626

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C2 - 21264976

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VL - 24

SP - 807

EP - 814

JO - NMR in Biomedicine

JF - NMR in Biomedicine

SN - 0952-3480

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