Fig. 1.

MRI/MRS detection of CK energy flux in the human heart. Shown are cardiac MRI and ³¹P spectra from FAST studies of a normal subject acquired at rest (a and b) and during dobutamine stress (c), and of a 37-year-old patient with NYHA class III heart failure at rest (d and e). Horizontal white lines in images denote the source of the spectra in the anterior myocardium. The white box shows the detector coil location. Arrows on the spectra identify the frequency of the saturating irradiation tuned to the γ-ATP resonance (spectra on right) and in a symmetric control location, relative to PCr (spectra on left). With γ-ATP saturated, the PCr resonance decreases (oblique lines) in direct proportion to the forward CK flux because the saturated γ-ATP signal is unable to contribute to the PCr signal by the reverse reaction: the greater the flux the greater the decrease. Dobutamine stress had a dramatic 2-fold effect on cardiac workload (rate-pressure product), but did not dramatically alter CK flux in the heart (b and c). At rest, the flux in the patient is lower (e). In each study, four such ³¹P data sets are acquired with saturation and two different flip angles (20); then a ³¹P and a ¹H data set are acquired without saturation to measure concentrations (10, 11, 22). The spectral scale is chemical shift in ppm.