Aim/Introduction: 15O-water PET/CT is the gold standard for noninvasive measurements of tissue blood fow and can potentially
play a future role in the diagnosis and treatment of peripheral artery
disease. In the current study, we aimed to measure the variation of
normal resting blood fow in lower leg muscles between individuals
(healthy subjects) as well as between repeated measurements in
the same individual. Materials and Methods: We have enrolled
7/10 planned healthy subjects who underwent two identical
15O-water PET/CT scans of the lower legs, separated by a 5-minute
break. During the break, subjects were taken out of the scanner and
asked to take a few steps. After additional 5 minutes of resting in a
supine position, they completed the second scan. In both scans,
a standardized intravenous injection of 400 MBq 15O-H2O was
followed by a 6-minute dynamic PET acquisition. In low-dose CT
images, we defned volumes of interest (VOIs) in diferent lower leg
muscles (gastrocnemius(GAS), soleus(SOL), tibialis anterior(TA), and
peroneus longus(PL)) of each subject. As the PET scan was acquired
immediately after the CT, VOIs could be transferred directly to the
PET images for quantitative measurements of 15O-H2O uptake,
and time-activity curves were extracted. Kinetic analysis was
performed using in-house developed software. K1 (ml/100ml/min)
was estimated using a single-tissue compartment model. Results:
Resting K1 values ranged from 0.16-0.73 ml/100ml/min (median
0.26,IQR:0.21-0.33). At muscle level, variation was observed in
the muscle groups, with median K1 values of 0.32(GAS), 0.24(PL),
0.37(SOL), and 0.25(TA) ml/100ml/min in the frst scan. Repeated
measurements of 15O-water PET/CT perfusion in lower extremities
showed a strong correlation of K1 values (slope:1.02,intercept:-
0.03,r=0.90) and the blood input function did not change between
the repeated scans (correlation for AUC: r=0.97 with no signifcant
bias). Bland-Altman analysis revealed both negative and positive
proportional bias at an individual level in 3/6 scans, suggesting that
perfusion changed between the scans. Conclusion: Normal resting
blood fow in four muscle groups of the lower leg ranged from 0.16-
0.73 ml/100ml/min in healthy individuals. The largest variation was
seen between individuals, whereas a smaller variation was seen
between muscle groups. Repeated measurement of resting blood
fow yielded a strong overall correlation of K1. When utilizing resting
blood fow of the lower extremities for vascular disease evaluation
(e.g. diabetes) or treatment response evaluation, inter-patient
variation in blood fow, as well as intra-patient variation induced
by the small diferences in resting conditions, must be taken into
account