Quantification of myocardial beta-adrenoceptor density (B-max) is of intere
st in cardiac diseases in which altered function of the sympathetic nervous
system is thought to play a pathophysiological role. PET provides an unriv
aled means of taking regional measurements of cardiac microcirculatory func
tion, tissue metabolism and autonomic nervous system activity. Measurements
in small regional areas may be biased because of increased noise levels. T
his study examined the parametric polar map approach for the regional quant
ification of B-max. Methods: Dynamic PE-T with parametric polar map imaging
was performed in 10 healthy volunteers and 4 patients with hypertrophic ca
rdiomyopathy using (S)-[C-11]-(4-(3-tertiarybutylamino-2-hydroxypropoxy)-be
nzidimazole-2)-on hydrochloride (CGP)-12177 and a double-injection protocol
. Time-activity curves were corrected for partial volume, spill-over and wa
ll motion effects. The mean B-max of the left ventricle was calculated in t
wo ways. First, the average time-activity curve of all segments, having the
highest achievable signal-to-noise ratio, was used to calculate B-max(mTAC
) (the myocardial beta-adrenoceptor density of the left ventricle calculate
d using the average time-activity curve). The bias in B-max(mTAC) introduce
d by noise is minimal. Second, an estimate of whole-heart receptor density
was calculated using the polar map method by averaging the values of B-max
obtained for 576 individual segments. In these calculations, three differen
t filters (3 x 5, 3 x 9 and 3 x 13 segments) were used to smooth the time-a
ctivity curves before calculating B-max. Mean values of whole-left-ventricu
lar receptor density obtained by averaging regional values using the differ
ent filters (B-max(PMF1/2/3)) were compared with B-max(mTAC) to assess bias
introduced by the polar map approach. Segments with a calculated B-max out
side the range 0.1-50 pmol/g were considered unreliable and were excluded f
rom the analysis. Results: The differences between the two methods of calcu
lating B-max were small (7.8%, 4.8% and 3.2%, with the three filters, respe
ctively). Reliable results were obtained in >95% of the segments and in 9 v
olunteers and all 4 patients. Conclusion: When using PET for the quantifica
tion of beta-adrenoceptor density, the regional variation in B-max can be r
eliably assessed using the parametric polar map approach.