title: Underestimation of myocardial blood flow by dynamic perfusion CT: Explanations by two-compartment model analysis and limited temporal sampling of dynamic CT.
abstract: OBJECTIVE
  Previous studies using dynamic perfusion CT and volume perfusion CT (VPCT) software consistently underestimated the stress myocardial blood flow (MBF) in normal myocardium to be 1.1-1.4 ml/min/g, whilst the O 15-water PET studies demonstrated the normal stress MBF of 3-5 ml/min/g. We hypothesized that the MBF determined by VPCT (MBF-VPCT) is actually presenting the blood-to-myocardium transfer constant, K1. In this study, we determined K1 using Patlak plot (K1-Patlak) and compared the results with MBF-VPCT.
  
  
  METHODS
  17 patients (66 ± 9 years, 7 males) with suspected coronary artery disease (CAD) underwent stress dynamic perfusion CT, followed by rest coronary CT angiography (CTA). Arterial input and myocardial output curves were analyzed with Patlak plot to quantify myocardial K1. Significant CAD was defined as >50% stenosis on CTA. A simulation study was also performed to investigate the influence of limited temporal sampling in dynamic CT acquisition on K1 using the undersampling data generated from MRI.
  
  
  RESULTS
  There were 3 patients with normal CTA, 7 patients with non-significant CAD, and 7 patients with significant CAD. K1-patlak was 0.98 ± 0.35 (range 0.22-1.67) ml/min/g, whereas MBF-VPCT was 0.83 ± 0.23 (range 0.34-1.40) ml/min/g. There was a linear relationship between them: (MBF-VPCT) = 0.58 x (K1-patlak) + 0.27 (r(2) = 0.65, p < 0.001). The simulation study done on MRI data demonstrated that Patlak plot substantially underestimated true K1 by 41% when true K1 was 2.0 ml/min/g with the temporal sampling of 2RR for arterial input and 4RR for myocardial output functions.
  
  
  CONCLUSIONS
  The results of our study are generating hypothesis that MBF-VPCT is likely to be calculating K1-patlak equivalent, not MBF. In addition, these values may be substantially underestimated because of limited temporal sampling rate.
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan.
authors: Masaki
authors: M
authors: Ishida
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan.
authors: Kakuya
authors: K
authors: Kitagawa
authors: Faculty of Radiological Technology, Fujita Health University School of Health Science, Toyoake, Aichi, Japan.
authors: Takashi
authors: T
authors: Ichihara
authors: Faculty of Radiological Technology, Fujita Health University School of Health Science, Toyoake, Aichi, Japan.
authors: Takahiro
authors: T
authors: Natsume
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan.
authors: Ryohei
authors: R
authors: Nakayama
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan.
authors: Naoki
authors: N
authors: Nagasawa
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan.
authors: Makiko
authors: M
authors: Kubooka
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan.
authors: Tatsuro
authors: T
authors: Ito
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan.
authors: Mio
authors: M
authors: Uno
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan.
authors: Yoshitaka
authors: Y
authors: Goto
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan.
authors: Motonori
authors: M
authors: Nagata
authors: Department of Radiology, Mie University Hospital, Tsu, Mie, Japan. Electronic address: sakuma@clin.medic.mie-u.ac.jp.
authors: Hajime
authors: H
authors: Sakuma
mesh_terms: D000368:Aged; D001783:Blood Flow Velocity; D000072226:Computed Tomography Angiography / Q000379:methods*; D003198:Computer Simulation; D017023:Coronary Angiography / Q000379:methods*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging* / Q000503:physiopathology; D003326:Coronary Circulation; D023921:Coronary Stenosis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D003331:Coronary Vessels / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D055414:Myocardial Perfusion Imaging / Q000379:methods*; D011237:Predictive Value of Tests; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D012984:Software; D013997:Time Factors; D014665:Vasodilator Agents / Q000008:administration & dosage
chemical_list: D014665:Vasodilator Agents
keywords: Absolute myocardial blood flow; Myocardial perfusion CT; Patlak plot method; Quantitative analysis; Transfer constant