Development and validation of a short 31P cardiac magnetic resonance spectroscopy protocol
Journal of Cardiovascular Magnetic Resonance volume 12, Article number: P123 (2010)
Cardiac 31P-MRS is the only non-invasive in vivo technique for the determination of cardiac high energy phosphate metabolism. Changes in cardiac phosphocreatine to adenosine triphosphate ratios (PCr/ATP) occur in common cardiac pathologies and have diagnostic, prognostic and therapeutic utility. However, long acquisition times (20 minutes or more, depending on heart rate) required to achieve sufficient signal to noise ratios for reliable interpretation have limited the clinical utility of 31P-MRS studies in patients with severe cardiac disease.
We have developed an 8 minute 31P-MRS protocol and demonstrate the validity of this 'short' acquisition by comparison with a 'long' (at least 20 minutes) method of published reproducibility (Tyler, NMR Biomed:2008).
To design a robust, 'short' cardiac 31P-magnetic resonance spectroscopy (31P- MRS) protocol which facilitates acquisition within a clinically acceptable timeframe.
This 'short' protocol essentially incorporates a larger voxel (93 mls compared to 39 mls for 'long' protocol) but eliminates extra myocardial contamination by:
• active suppression of chest wall muscle and liver signals,
• raw data acquisition weighted to reduce contamination arising from outside the nominal voxel.
The accuracy of the data and its interpretation is improved by:
• optimised radio frequency (RF) pulse,
• flip angle calibration (at voxel of interest) used during post-processing to calculate and correct for subject variation to coil loading.
• calibrated signal enhancement (Nuclear Overhauser Enhancement (NOE)),
• rapid repetition time (with calibrated saturation correction).
22 healthy volunteers (age 42 ± 16.5; 13 males, 9 females), were scanned (3 T Siemens Trio) with both the 'long' and 'short' acquisitions.
Acquisition parameters for both protocols are summarised and compared in Table 1.
There was no difference of derived PCr/ATP ratios for both methods ('short' 1.83 ± 0.32; 'long' 1.78 ± 0.27). Bland-Altman analysis demonstrates excellent agreement between the two methods (Figure 1) confirming equivalence for clinical purposes. Figure 2 shows an example of spectra acquired from one subject, using both methods.
We have developed a novel 'short' cardiac 31P-MRS protocol of high data quality. This protocol allows cardiac spectroscopy to be measured in patients who are often intolerant of long acquisition times, such as those with severe cardiac disease and children. Hence this work provides a useful tool for the routine clinical assessment of cardiac 31P-MRS.
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Dass, S., Cochlin, L.E., Holloway, C.J. et al. Development and validation of a short 31P cardiac magnetic resonance spectroscopy protocol. J Cardiovasc Magn Reson 12 (Suppl 1), P123 (2010). https://doi.org/10.1186/1532-429X-12-S1-P123