Problematic MARAN NMR Measurements

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Problematic MARAN NMR Measurements

• Arjun Kurup, Michael Rauschhuber, Neeraj Rohilla
• March 26, 2008

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Problematic NMR Measurements

• CPMG measurements at varying half-echo spacing, t
• Measurements with H2O, undoped
• Three types of problems
• Shape of decay at specific t
• Dependent on small increments of t, P180, O1
• Decrease in T2 with increasing t
• Noise channel remnants after rotation of data

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Shape of Decay at Specific t (1)

• t near 4ms
• Increments of 50ms
• Broad range of problematic values
• 3.75mslttlt4.4ms
• Non-monotonic behavior common

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Shape of Decay at Specific t (2)

• t near 2ms
• Increments of 25ms
• Narrower range of problematic values
• 2.000mslttlt2.175ms
• Non-exponential behavior visible, but no
  non-monotonic behavior

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Decrease in T2 with increasing t

• T2 deceases sharply for short t
• T2 almost constant for tgt8-10ms
• Exponential time domain decays

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Resultant relaxation time distributions
t 2 ms
t 4 ms
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Example Behavior at t4 and t2ms
Water
t 4 ms
Seen only with Temco vessel, grad amp on
Water
t 2 ms
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CPMG polar plot
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(except small anomaly at TE0.4ms)
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Evaluation in terms of sampling frequency
Electrical lines possibly not the source of
oscillatory errors
Data for 50mm dia. sample of water
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T2 varies with Echo Spacing DI Water
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(No Transcript)
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T2 varies with Echo Spacing Yates D Core
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Problematic MARAN NMR Measurements with un-doped
bulk DI water
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Typical T2 measurement on Maran
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After Sampling and Averaging
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T2 Distribution
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Problematic T2 Measurement
Oscillations in the signals at early
times Different patterns of Noise
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After Sampling and Averaging
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T2 Distribution
Two peaks observed of undoped bulk DI water
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Noise for some problematic sets
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Noise for some problematic sets
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Observations

• At certain values of echo spacing, we obtain
  bi-modal distribution for a bulk sample
• The drift in O1, p90 and p180 results in shifting
  of problematic value of the echo spacing
• The problematic measurements are reproducible at
  any given day for the settings of the earlier day
  (corresponding to problematic measurements)

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Interplay of echo spacing, p180 and O1
O1 O1problem 10 Hz
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Interplay of echo spacing, p180 and O1
p180 p180problem 10ns
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Observations

• The problematic measurements are due to some
  combination of echo spacing, p180 and Offset O1.
• Sometimes changing O1 by 10 Hz results in a
  unimodal distribution
• Sometimes changing p180 by 10 ns results in a
  unimodal distribution
• Sometimes changing echo spacing by 10 ns
  results in a unimodal distribution