The Dual-Angle Method for Fast, Sensitive T1 Measurement in Vivo with Low-Angle Adiabatic Pulses
✍ Scribed by P.A. Bottomley; R. Ouwerkerk
- Book ID
- 102972438
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 656 KB
- Volume
- 104
- Category
- Article
- ISSN
- 1064-1866
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✦ Synopsis
A new method for measuring (T_{1}) based on a measurement of the ratio, (R), of the steady-state partially saturated NMR signals acquired at two fixed low flip angles (\left(<90^{\circ}\right)) and a single sequence-repetition period, (T_{\mathrm{R}}), is presented. The flip angles are chosen to optimize both the signal-to-noise ratio per unit time relative to the best possible Ernst-angle performance and the sensitivity with which a measurement of (R) can resolve differences in (T_{1}). A flip-angle pair at or around (\left(60^{\circ}, 15^{\circ}\right)) yields (70-79 %) of the maximum achievable Ernst-angle signal-to-noise ratio and a near-linear dependence of (R) on (T_{\mathrm{R}} / T_{\text {, with }}) wradient of about (2: 1) over the range (0.1 \leqslant T_{\mathrm{R}} / T_{1} \leqslant 1). Errors in flip-angle and excitation-field (\left(B_{1}\right)) inhomogeneity result in roughly proportionate errors in the apparent (T_{1}). The method is best implemented with adiabatic low-angle pulses such as (B_{1})-independent rotation (BIR-4) or BIR-4 phase-cycled (BIRP) pulses, which permit measurements with surface coils. Experimental validation was obtained at (2 \mathrm{~T}) by comparison of unlocalized inversionrecovery and dual-angle proton (\left({ }^{1} \mathrm{H}\right)) and phosphorus (\left({ }^{31} \mathrm{P}\right)) measurements from vials containing doped water with (0.04 \leqslant) (T_{1} \leqslant 2.8 \mathrm{~s}) and from the metabolites in the calf muscles of eight human volunteers. Calf muscle values of (6 \pm 0.5 \mathrm{~s}) for phosphocreatine and around (3.7 \pm 0.8 \mathrm{~s}) for the adenosine triphosphates (ATP) were in good agreement with inversion-recovery (T_{1}) values and values from the literature. Use of the dual-angle method accelerated (T_{1}) measurement time by about fivefold over inversion recovery. The dual-angle method was implemented in a onedimensional localized surface-coil ({ }^{31} \mathrm{P}) spectroscopy sequence, producing consistent (T_{1}) measurements from phantoms, the calf muscle, and the human liver. ({ }^{31} \mathrm{P} T_{1}) values of (\mathrm{ATP}) in the livers of six volunteers were about (0.5 \pm 0.1) to (0.6 \pm 0.2 \mathrm{~s}) : the total exam times were about 35 minutes per subject. The method is ideally suited to low-sensitivity and/or low-concentration moieties, such as in ({ }^{31} \mathrm{P}) NMR in vivo, where study-time limitations are critical, and for rapid 'H (T_{1}) imaging. (1994 Academic Press, Inc.