3308965 PVCF painful vertebral compression fractures 1 3308961 PVCF partial volume correction factor 1 3308964 PVCF Pathologic vertebral compression fractures 1 3308962 PVCF perivascular collagen fraction 1 3308963 PVCF prophylactic VCF use 1 3308966 PVCF PV curve using the constant flow method on the ventilator 1