title: Quantitative cardiac 31P spectroscopy at 3 Tesla using adiabatic pulses.
abstract: Cardiac phosphorus magnetic resonance spectroscopy (MRS) with surface coils promises better quantification at 3 Tesla (T) from improved signal-to-noise ratios and spectral resolution compared with 1.5 T. However, Bloch equation and field analyses at 3T show that for efficient quantitative MRS protocols using small-angle adiabatic (BIR4/BIRP) pulses the excitation-field is limited by radiofrequency (RF) power requirements and power deposition. When BIR4/BIRP pulse duration is increased to reduce power levels, T2-decay can introduce flip-angle dependent errors in the steady-state magnetization, causing errors in saturation corrections for metabolite quantification and in T1s measured by varying the flip-angle. A new dual-repetition-time (2TR) T1 method using frequency-sign-cycled adiabatic-half-passage pulses is introduced to alleviate power requirements, and avoid the problem related to T2 relaxation during the RF pulse. The 2TR method is validated against inversion-recovery in phantoms using a practical transmit/receive coil set designed for phosphorus MRS of the heart at depths of 9-10 cm with 4 kW of pulse power. The T1s of phosphocreatine (PCr) and adenosine triphosphate (gamma-ATP) in the calf-muscle (n=9) at 3 T are 6.8+/-0.3 s and 5.4+/-0.6 s, respectively. For heart (n=10) the values are 5.8+/-0.5 s (PCr) and 3.1+/-0.6 s (gamma-ATP). The 2TR protocol measurements agreed with those obtained by conventional methods to within 10%.
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
authors.forename: AbdEl-Monem
authors.initials: AM
authors.lastname: El-Sharkawy
authors.forename: Michael
authors.initials: M
authors.lastname: Schär
authors.forename: Ronald
authors.initials: R
authors.lastname: Ouwerkerk
authors.forename: Robert G
authors.initials: RG
authors.lastname: Weiss
authors.forename: Paul A
authors.initials: PA
authors.lastname: Bottomley
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis*; D000328:Adult; D000465:Algorithms; D005260:Female; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010725:Phosphocreatine / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis; D012815:Signal Processing, Computer-Assisted
chemical_list: D010725:Phosphocreatine; D010758:Phosphorus; D000255:Adenosine Triphosphate