title: Evaluation of variability of phase indices of the left ventricle in the course of time.
abstract: OBJECTIVE
  Since the effect of time on phase indices is still unclear, the aim of the study was to evaluate the variability of phase indices of the left ventricle which were derived from stress and rest single-photon emission computed tomography (SPECT) imaging acquired at early and late times.
  
  
  METHODS
  One hundred twenty-one patients (72 men, 49 women) were included into the study. All stress and rest gated myocardial perfusion imaging (gMPI) acquisitions were acquired at two different time points as early in 15 ± 5 min and late in 45 ± 5 min. The peak of the phase histogram (PP), the standard deviation of the phase distribution (SDPH), the width of the band (BPH), and the symmetry (histogram skewness, HS) and peakedness of the phase histogram (histogram kurtosis, HK) which are the parameters for assessing left ventricular systolic dyssynchrony were calculated in all stress and rest SPECT images acquired twice.
  
  
  RESULTS
  The phase indices derived from the late rest scans were smaller than those of the early rest scans but, the differences were not significant. When considering the comparisons of phase indices derived from two different time points after stress, PP showed a tendency to decrease (from 160.8 ± 18.3 to 152.5 ± 17.3; p < 0.001) over time but SDPH (from 20.2 ± 10.6 to 22.4 ± 12.2; p = 0.018) and BPH (from 61.5 ± 36.0 to 66.3 ± 37.3; p = 0.045) tended to increase over time. When the post-stress and the resting dyssynchrony parameters derived at two different time points were compared to each other; PP decreased at early and late times approximately 12 and 9 %, respectively, SDPH increased at early and late times approximately 28.5 and 14 %, respectively, and BPH increased at early and late times approximately 23 and 12 %, respectively.
  
  
  CONCLUSIONS
  In resting conditions, phase indices of the left ventricle, and therefore, the phase histogram tend to remain constant over time but, in conditions after exercise, the phase histogram tend to be long and narrow due to changes in phase indices and it shows tendency to return to resting conditions in time. Therefore, it appears that postexercise acquisition times should be standardized if we want to compare the phase indices results of the studies in the literature.
authors.affiliation: Department of Nuclear Medicine, Gülhane Military Medical Academy and School of Medicine, Etlik, Ankara, 06018, Turkey.
authors.forename: Ozdes
authors.initials: O
authors.lastname: Emer
authors.forename: Alper O
authors.initials: AO
authors.lastname: Karacalioglu
authors.forename: Erol
authors.initials: E
authors.lastname: Gursoy
authors.forename: Semra
authors.initials: S
authors.lastname: Ince
mesh_terms: D000328:Adult; D055424:Cardiac-Gated Imaging Techniques / Q000379:methods*; D005260:Female; D006352:Heart Ventricles / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D055414:Myocardial Perfusion Imaging / Q000379:methods*; D010507:Periodicity; D012146:Rest; D012189:Retrospective Studies; D013312:Stress, Physiological; D013995:Time; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*