title: Assessment of absolute Tc-99m tetrofosmin retention in the myocardium as an index of myocardial blood flow and coronary flow reserve by gated-SPECT/CT: a feasibility study.
abstract: OBJECTIVE
  Estimation of myocardial blood flow (MBF) and coronary flow reserve (CFR) by SPECT myocardial perfusion imaging (MPI) remains challenging. Our aim was to approximate MBF and CFR by quantifying the absolute Tc-99m tetrofosmin retention in the myocardium via gated-SPECT/CT MPI.
  
  
  METHODS
  Tracer retention was calculated on the basis of the microsphere kinetic model and served as an index of MBF at stress and rest (sMBFi, rMBFi). CFR was given by the sMBFi/rMBFi ratio. A planar first-pass acquisition during dipyridamole stress and at rest provided the data for tracer input determination. The input was represented by the integral of a gamma variate fitted on the time-activity curve of the left ventricle. Gated-SPECT/CT was performed 1 h post tracer injection and myocardial activity was measured in attenuation-corrected transaxial slices by a threshold VOI. The input was also compensated for tissue attenuation by measuring the distance from the centre of the left ventricle to the body surface on fused SPECT/CT slices. Input and uptake results were adjusted for planar-SPECT counting geometry differences by the aid of a phantom experiment. Thirty-nine subjects with low probability of coronary artery disease (CAD), age lower than 75 years and normal MPI (control group) were compared with 57 patients with documented CAD (CAD group).
  
  
  RESULTS
  CFR and sMBFi values of CAD patients (1.39 ± 0.37 and 1.42 ± 0.35 ml/min/g) were considerably lower (p < 0.0001) than controls (1.68 ± 0.25 and 1.72 ± 0.37 ml/min/g). Significant difference in CFR (p = 0.03) was also noted between CAD patients with normal MPI (1.48 ± 0.38) and controls. However, sMBFi managed to discriminate certain CAD subgroups (normal MPI/ischemia/scar/scar and ischemia) more efficiently than CFR. Maximum heart rate-blood pressure product (RPP) during stress was an independent predictor of sMBFi and CFR. The other independent CFR correlates were resting RPP and diabetes mellitus, while sMBFi was associated with age, sex, smoking, and stress perfusion defects.
  
  
  CONCLUSIONS
  Despite the low myocardial extraction fraction of Tc-99m tetrofosmin, an approximation of MBF and CFR is feasible with gated-SPECT/CT MPI. These flow indices together were able to discriminate CAD patients from controls and stratify different patient subgroups.
authors.affiliation: Department of Nuclear Medicine, University Hospital of Patras, University of Patras, Medical School, 26504, Rion Patras, Greece, dimap@med.upatras.gr.
authors.forename: Dimitris J
authors.initials: DJ
authors.lastname: Apostolopoulos
authors.forename: Agaristi
authors.initials: A
authors.lastname: Kaspiri
authors.forename: Trifon
authors.initials: T
authors.lastname: Spyridonidis
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Patsouras
authors.forename: Christos A
authors.initials: CA
authors.lastname: Savvopoulos
authors.forename: Pericles
authors.initials: P
authors.lastname: Davlouros
authors.forename: Pavlos J
authors.initials: PJ
authors.lastname: Vassilakos
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Alexopoulos
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D055426:Cardiac-Gated Single-Photon Emission Computer-Assisted Tomography; D016022:Case-Control Studies; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging / Q000378:metabolism / Q000503:physiopathology; D005240:Feasibility Studies; D005260:Female; D053805:Fractional Flow Reserve, Myocardial; D006321:Heart / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D009206:Myocardium / Q000378:metabolism*; D009943:Organophosphorus Compounds / Q000378:metabolism*; D015609:Organotechnetium Compounds / Q000378:metabolism*; D019047:Phantoms, Imaging; D012146:Rest; D013312:Stress, Physiological; D013997:Time Factors; D014057:Tomography, X-Ray Computed
chemical_list: D009943:Organophosphorus Compounds; D015609:Organotechnetium Compounds; C078700:technetium tc-99m tetrofosmin