The reliable quantification of myocardial blood flow (MBF)
with MRI, necessitates the correction of errors in arterial input
function (AIF) caused by the T1 saturation effect. The aim of this study
was to compare MBF determined by a traditional dual bolus method
against a modified dual bolus approach and to evaluate both methods
against PET in a porcine model of myocardial ischemia.

Local
myocardial ischemia was induced in five pigs, which were subsequently
examined with contrast enhanced MRI (gadoteric acid) and PET (O-15
water). In the determination of MBF, the initial high
concentration AIF was corrected using the ratio of low and high contrast
AIF areas, normalized according to the corresponding heart rates. MBF
was determined from the MRI, during stress and at rest, using the dual
bolus and the modified dual bolus methods in 24 segments of the
myocardium (total of 240 segments, five pigs in stress and rest). Due to
image artifacts and technical problems 53% of the segments had to be
rejected from further analyses. These two estimates were later compared
against respective rest and stress PET-based MBF measurements.

Values of MBF were determined for 112/240 regions. Correlations for MBF between the modified dual bolus method and PET was r_s = 0.84, and between the traditional dual bolus method and PET r_s = 0.79.
The intraclass correlation was very good (ICC = 0.85) between the
modified dual bolus method and PET, but poor between the traditional
dual bolus method and PET (ICC = 0.07).

The
modified dual bolus method showed a better agreement with PET than the
traditional dual bolus method. The modified dual bolus method was found
to be more reliable than the traditional dual bolus method, especially
when there was variation in the heart rate. However, the difference
between the MBF values estimated with either of the two MRI-based
dual-bolus methods and those estimated with the gold-standard PET
method were statistically significant.