Cardiopulmonary transit time
Cardiopulmonary transit time (CPTT), or central circulation transit time, is a simple measure of cardiopulmonary performance, representing the time or number of heart beats needed for blood to travel through the cardiopulmonary system. CPTT reflects the balance between stroke volume and total blood volume in the central circulation. Prolonged CPTT is associated with many pathologies of the heart, including dilated left ventricle, valvular disease, diastolic dysfunction, and pulmonary hypertension.
Invasive assessment of CPTT between large vessels has been replaced by non-invasive imaging techniques, such as CT and MRI (Müller et al., 2000; Shors et al., 2003), which even allow measurement of regional circulation transit time between individual central cardiovascular structures (Cao et al., 2018). Dynamic PET imaging studies of the heart can be used to assess the CPTT between the right and left ventricles, providing that the bolus administration of radiopharmaceutical is sharp and very fine framing rate is achievable (Peters & Myers, 1998; Wu et al., 2005). CPTT has been assessed in mice with [18F]FDG PET (Peters & Myers, 1998; Wu et al., 2005), and in humans with [15O]H2O (Harms et al., 2015) and [13N]ammonia PET (Harms et al., 2022). Any cardiac PET study with a bolus injection performed with the intention of quantifying perfusion contains the information required for calculation of CPTT as an additional parameter (Harms et al., 2022).
PET data analysis
From dynamic PET image data, the time-activity curves (TACs) from LV and RV cavities are extracted, avoiding the ventricular walls. Regions of interest in LV and RV cavities can be drawn manually or with semi-automatic clustering method (Wu et al., 2005). Then the first-pass peaks of the curves are isolated from the recirculation phase using exponential downslope fitting (Peters & Myers, 1998; Wu et al., 2005) or fitting gamma variate function to the portion of TAC prior to the time when the first recirculation arrived at the ROI of the ventricle (Chen et al., 1996). After this, the mean arrival time (TA) of each peak is calculated as the centroid (centre-of-mass). Mean arrival time equals mean residence time (MRT), a term used in pharmacokinetic literature, and it can be calculated from the recirculation corrected LV and RV blood TACs as:
, where AUMC is the area under the moment curve, and AUC is the area under the concentration-time curve. CPTT (min) is then calculated as the time difference between the LV and RV arrival times (Peters & Myers, 1998; Wu et al., 2005; Harms et al., 2022).
CPTT (min) can further be normalized for heart rate by multiplication with the heart rate during the PET scan, resulting in CPTT (beats) expressed in heartbeats (Harms et al., 2022).
- Cardiac output and stroke volume
- Cardiac PET imaging
- Circulatory system
- Pulmonary circulation
- MRT and MTT in PK
- Cerebral perfusion pressure and MTT
Harms HJ, Bravo PE, Bajaj NS, Zhou W, Gupta A, Tran T, Taqueti VR, Hainer J, Bibbo C, Dorbala S, Blankstein R, Mehra M, Sörensen J, Givertz MM, Di Carli MF. Cardiopulmonary transit time: A novel PET imaging biomarker of in vivo physiology for risk stratification of heart transplant recipients. J Nucl Cardiol. 2022; 29(3): 1234-1244. doi: 10.1007/s12350-020-02465-x.
Harms HJ, Tolbod LP, Hansson NH, Kero T, Orndahl LH, Kim WY, Bjerner T, Bouchelouche K, Wiggers H, Frøkiær J, Sörensen J. Automatic extraction of forward stroke volume using dynamic PET/CT: a dual-tracer and dual-scanner validation in patients with heart valve disease. EJNMMI Phys. 2015; 2(1): 25. doi: 10.1186/s40658-015-0133-0.
Harms HJ, Tolbod LP, Kero T, Bouchelouche K, Frokiaer J, Sorensen J. Quantification of cardiopulmonary blood volume turnover using dynamic PET. Eur Hear J Cardiovasc Imaging 2015; 16: i33. doi: 10.1093/ehjci/jev049.
Peters M, Myers MJ: Physiological Measurements With Radionuclides in Clinical Practice, 3rd ed., Oxford University Press, 1998. ISBN: 978-0192619945.
Wu H-M, Kreissl MC, Schelbert HR, Ladno W, Prins M, Shoghi-Jadid K, Chatziioannou A, Phelps ME, Huang S-C. First-pass angiography in mice using FDG-PET: a simple method of deriving the cardiovascular transit time without need of region-of-interest drawing. IEEE Trans Nucl Sci. 2005; 52(5): 1311-1315. doi: 10.1109/TNS.2005.858239.
Updated at: 2023-05-05
Created at: 2023-01-13
Written by: Vesa Oikonen