MBF using [15O]H2O and dynamic PET
PET enables noninvasive quantification of myocardial blood flow (MBF). PET tracers that are used for estimation of blood flow include diffusible tracer [15O]H2O and partially extracted tracers 82Rb and [13N]ammonia, and in case of myocardium also [11C]acetate.
Measurement of myocardial perfusion with [15O]H2O is based on the general model for radiowater. Blood curve from the LV cavity is used as input function. The methods that are specifically developed for myocardium differ in the correction methods for spillover and partial volume effects, and determine the tissue perfusion from the washout rate (k2) of the tracer (Iida et al., 1988, 1991, and 1992). ROI drawn on RV cavity can be used to correct septum for the additional spillover from RV cavity (Hermansen et al., 1998a; Harms et al., 2011). An alternative but less used method is to use factor analysis to correct for spillover effects (Hermansen et al., 1998b; Ahn et al., 2001; Lee et al., 2005). Myocardial perfusion estimation based on k2 could even be applied to PET image that is not attenuation corrected (Lubberink et al., 2010; Tuffier et al., 2016).
[15O]H2O model provides not only the perfusion, but also the water perfusable tissue fraction (PTF). PTF can be used as an alternative to FDG PET to assess myocardial viability (Iida et al., 2012). PTF is, however, more sensitive to scatter, movement, and misalignment between PET and attenuation map than MBF (Koshino et al., 2012; Hirano et al., 2012).
[15O]CO study is often combined to myocardial radiowater PET to get a blood volume image. Anatomic tissue fraction (ATF) represents the mass (density) of extravascular tissue in a region of interest, and it can be calculated by subtraction of blood volume image from transmission image (Iida et al., 1991). Perfusable tissue index (PTI) can be calculated as the ratio of PTF and ATF (Iida et al., 1991). PTI represents the fraction of extravascular tissue being perfused by water, and is a marker of viable myocardium (Knaapen et al., 2003). Parametric PTI image can be calculated from a single [15O]H2O study (Harms et al., 2011).
2013 ESC guidelines state that detection of ischemia is important in the management of patients with suspected coronary artery disease (CAD). Radiowater PET has higher diagnostic accuracy for this purpose than SPET or coronary CT angiography (Danad et al., 2017).
The short halflife of 15O enables repeating the MBF study without problems of background radioactivity from the previous study. Coronary flow reserve (CFR), or myocardial flow reserve (MFR), can therefore be easily measured in a rest-stress study setting:
However, absolute stress perfusion alone has been shown to be superior to perfusion reserve in detection of coronary artery disease (Joutsiniemi et al, 2014; Cho et al., 2018). Both sex and age should be taken into account in diagnostic use (Danad et al., 2014). Hyperaemic MBF alone also has better diagnostic value than longitudinal flow gradient, the abnormal decrease in hyperaemic MBF from the base to the apex of the left ventricle (Bom et al., 2018).
PET CFR imaging can act a noninvasive gatekeeper for fractional flow reserve (FFR) measurement using invasive coronary angiography; PET imaging cannot allocate mendable culprit lesions like FFR and it does not distinguish focal epicardial from diffuse and small-vessel disease, and therefore the additional FFR measurements are required to drive revascularization strategy (Driessen et al., 2018).
LV volumes and ejection fraction
Motion corrections methods could also greatly improve the accuracy of MBF measurements (Armstrong & Memmott, 2018).
Recommended analysis method
Our currently recommended analysis method (MET5817) is to use Iida’s MBF model (Iida et al., 1988, 1991, and 1992), as implemented in Carimas™ (Nesterov et al., 2009; Harms et al., 2014). Measurements of MFR are highly reproducible within and between two observers with different experience. Full hybrid model combining MFR PET and CTA further improves discrimination between significant and non-significant CAD at vessel level (Thomassen et al., 2018).
If you have previously used older versions of fitmbf (2.0 or less), please note that in the current version:
- Only one study can be analyzed with one command. If α needs to be constrained
to a basal study, it can be done with option
- Existing result file with the same name is overwritten
- Result files can be processed further, e.g. mean and s.d. from different subjects or differences between studies can be calculated before importing results to spreadsheet programs
- fitmbf can optionally provide confidence limits and/or s.d. for the MBF, α and Va
Partition coefficient of water, p, is needed in the calculation, and by default it is set to value p=0.9464 mL/mL, which is based on the p value 0.91 mL/g used by (Iida et al (1988), multiplied by myocardial tissue density 1.04 g/mL. Bergmann et al (1989) used value p=0.92 mL/g, equalling p=0.96 mL/mL, which was also used by Lammertsma et al (1992).
Older fitmbf version (2.0)
To use this, enter the command with version number:
The results between this version and versions 2.1.* or later are similar inside three digits.
The differences are in the usage:
- Two or three studies may be calculated at one run, constraining α to the α estimate from the first (basal) study.
- Result file format is different. If more than one study is analyzed at one run, all results are written in the same file.
- If result file exists previously, it is not overwritten, but new results are appended to the end.
Even older software version(s)
Even older versions exist, but only on Solaris/SUN. Usage of those is not recommended.
- Partial volume and spillover effects in cardiac PET
- Model for [15O]H2O
- MBF using [18F]Flurpiridaz
- MBF using [13N]NH4+
- MBF using 82Rb
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Updated at: 2019-01-03
Created at: 2007-05-09
Written by: Vesa Oikonen, Chunlei Han