Myocardial Blood Flow (MBF) Definition
MBF refers to the absolute quantification of blood flow to the heart muscle, measured in milliliters per minute per gram of tissue (mL/min/g), which provides direct assessment of coronary perfusion beyond traditional relative imaging methods. 1
Clinical Significance
MBF quantification represents a fundamental advancement over conventional relative perfusion imaging because it:
- Detects global flow reductions that relative imaging misses, particularly in balanced multivessel coronary artery disease where all territories are equally affected 2
- Overcomes the normalization problem inherent in SPECT imaging, where regional tracer uptake is compared only to the "best" segment, potentially missing diffuse disease 2
- Provides prognostic information independent of visual perfusion defects, with reduced MBF predicting increased cardiovascular events 3, 4
Measurement Methodology
MBF is most accurately measured using PET imaging with specialized tracers including:
- Rubidium-82 (generator-produced)
- N-13 ammonia (cyclotron-produced)
- O-15 water
- F-18 flurpiridaz (newer agent) 1
These tracers enable dynamic imaging with kinetic modeling to calculate absolute flow values during both rest and pharmacologic stress 1.
Key Parameters Derived from MBF
Myocardial Flow Reserve (MFR) is calculated as the ratio of stress MBF to rest MBF, representing the heart's capacity to increase blood flow during demand 3, 4. This parameter:
- Identifies subclinical coronary artery disease before anatomic stenoses become severe 4
- Assesses microvascular dysfunction in patients with chest pain but no obstructive disease 3, 5
- Monitors response to risk factor modification and preventive therapies 4
Clinical Applications
MBF quantification is particularly valuable for:
- Multivessel disease characterization where relative imaging underestimates disease extent 4
- Microvascular dysfunction assessment in diabetes, hypertension, and inflammatory conditions 6
- Cardiac transplant surveillance for allograft vasculopathy 6
- Risk stratification as impaired flow reserve predicts adverse outcomes even without visible perfusion defects 6
Important Caveats
Body mass index is the single most important factor affecting MBF values, with higher BMI associated with lower stress and rest MBF measurements 7. Sex and hypertension also independently influence resting MBF 7.
MFR remains the most robust parameter across different patient characteristics, showing stable lower reference limits despite BMI variation 7. This makes MFR potentially more reliable than absolute MBF values for clinical decision-making.
The technique requires appropriate clinical context interpretation - hyperemic MBF reductions are non-specific and must be evaluated alongside wall motion analysis, microvascular function assessment, and coronary anatomy 3.