title: Validation of pixel-wise parametric mapping of myocardial blood flow with ¹³NH₃ PET in patients with hypertrophic cardiomyopathy.
abstract: OBJECTIVE
  Transmural abnormalities in myocardial blood flow (MBF) are important causes of ischaemia in patients with left ventricular (LV) hypertrophy. The study aimed to test whether pixel-wise parametric mapping of (13)NH3 MBF can reveal transmural abnormalities in patients with hypertrophic cardiomyopathy (HCM).
  
  
  METHODS
  We submitted 11 HCM patients and 9 age-matched controls with physiological LV hypertrophy to rest and stress (dipyridamole) (13)NH3 PET. We measured MBF using a compartmental model, and obtained rest and stress parametric maps. Pixel MBF values were reorganized to obtain subendocardial and subepicardial MBF of LV segments.
  
  
  RESULTS
  MBF at rest was higher in the subendocardial than in the subepicardial layer: 0.78 ± 0.19 vs. 0.60 ± 0.18 mL/min/g in HCM patients; 0.92 ± 0.24 vs. 0.75 ± 0.24 mL/min/g in controls (both p < 0.0001). Transmural perfusion gradient (TPG = subendocardial MBF/subepicardial MBF) at rest was similar: 1.35 ± 0.31 in HCM patients; 1.28 ± 0.27 in controls (NS). During stress, controls maintained higher subendocardial MBF: 2.44 ± 0.54 vs. 1.96 ± 0.67 mL/min/g tissue (p < 0.0001), with a TPG of 1.33 ± 0.35 (NS vs. rest). In HCM patients, the difference between subendocardial and subepicardial MBF was reduced (1.46 ± 0.48 vs. 1.36 ± 0.48 mL/min/g tissue, p < 0.01) and TPG decreased to 1.11 ± 0.34 (p < 0.0001 vs. rest and vs. controls). In HCM patients 8 of 176 segments had subendocardial MBF less than -2 × SD of the mean, versus none of 144 segments in controls (p < 0.01).
  
  
  CONCLUSIONS
  Pixel-wise parametric mapping of (13)NH3 MBF enables the identification of transmural abnormalities in patients with HCM.
authors.affiliation: Nuclear Medicine Unit, Department of Experimental and Clinical Biomedical Sciences, University of Florence, Largo Brambilla 3, 50134, Florence, Italy, r.sciagra@dfc.unifi.it.
authors.forename: Roberto
authors.initials: R
authors.lastname: Sciagrà
authors.forename: Alessandro
authors.initials: A
authors.lastname: Passeri
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Cipollini
authors.forename: Helga
authors.initials: H
authors.lastname: Castagnoli
authors.forename: Iacopo
authors.initials: I
authors.lastname: Olivotto
authors.forename: Cyrill
authors.initials: C
authors.lastname: Burger
authors.forename: Franco
authors.initials: F
authors.lastname: Cecchi
authors.forename: Alberto
authors.initials: A
authors.lastname: Pupi
mesh_terms: D000328:Adult; D000641:Ammonia / Q000493:pharmacokinetics*; D001783:Blood Flow Velocity; D002312:Cardiomyopathy, Hypertrophic / Q000000981:diagnostic imaging / Q000503:physiopathology*; D003326:Coronary Circulation; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D055414:Myocardial Perfusion Imaging / Q000379:methods*; D009590:Nitrogen Radioisotopes / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D009590:Nitrogen Radioisotopes; D019275:Radiopharmaceuticals; D000641:Ammonia