Learn · Part 2. The tests · 5 min read

PET myocardial perfusion imaging and blood flow

What PET adds to perfusion imaging: image quality, absolute myocardial blood flow and flow reserve, lower radiation, and the limits of availability and exercise.

60-second take

PET gives perfusion images with routine attenuation correction, plus absolute myocardial blood flow (mL/g/min) and flow reserve at no extra scan time.
Flow quantification helps with balanced ischemia in multivessel disease and with microvascular dysfunction; the best cutoffs for flow reserve are not yet settled.
Guidelines call PET reasonable in preference to SPECT, if available, and the 2026 ASNC position statement recommends it as the preferred perfusion modality. These compare PET with SPECT, not with echo, CT or MRI.
Rubidium-82 and ammonia studies are under 3 mSv; fluorine-18 flurpiridaz falls in a 3 to 20 mSv range. Most studies use vasodilator stress; treadmill exercise PET is possible with flurpiridaz but loses flow quantification.
Availability and tracer supply are the main practical limits.

What it is and how it works

Positron emission tomography (PET) myocardial perfusion imaging is a nuclear test like SPECT, but it uses tracers that give off positrons and a scanner that detects them in coincidence. The result is higher spatial and contrast resolution, and images that are corrected for attenuation as a routine part of the study . Most scanners are PET/CT, and the CT can add a coronary calcium score or a visual estimate of calcium .

PET can also measure myocardial blood flow (MBF) in absolute terms, in milliliters per gram per minute, at rest and at peak stress. Hyperemic flow divided by resting flow is the myocardial flow reserve (MFR) . The 2021 guideline calls the same ratio myocardial blood flow reserve, and says it adds diagnostic and prognostic information to the perfusion images .

The tracers

Rubidium-82 has a half-life of 75 seconds and comes from a generator. Nitrogen-13 ammonia has a 10-minute half-life and depends on an on-site cyclotron .
Fluorine-18 flurpiridaz is approved by the FDA, has a 110-minute half-life, and can be delivered as a unit dose from a regional cyclotron, so a lab does not need its own generator or cyclotron .

What you get

You receive four kinds of information from one study:

Perfusion images at stress and rest, with the same reading of reversible and fixed defects used in SPECT.
Left ventricular function, including wall motion and ejection fraction .
Quantitative MBF and MFR, globally and by territory, which usually adds no scanning time or radiation .
Coronary calcium, when CT is available.

What flow adds. Relative perfusion images show the worst-perfused area and can miss milder lesions in multivessel disease. Adding regional hyperemic flow and flow reserve helps untangle the effect of the remaining lesions. Marked reductions in all three territories together with transient ischemic dilation identify diffuse or balanced ischemia that relative perfusion alone is likely to miss . Flow quantification also confirms that the vasodilator worked and can reveal coronary microvascular dysfunction, a cause of angina without obstructive disease .

What flow does not yet settle. The PET criteria note that the best threshold for an abnormal hyperemic flow or flow reserve is not yet defined, and that more evidence is needed on diagnostic accuracy for microvascular dysfunction . The same document describes flow quantification as adding incremental prognostic value, so read the numbers with the clinical picture.

Accuracy. The PET criteria report mean sensitivity of about 92% and specificity of about 90% for hemodynamically obstructive disease . Those figures come from different studies from those behind numbers for other tests, so avoid placing them side by side.

Strengths and limitations

Strengths

High image quality, even in challenging patients, and relatively quick acquisitions that reduce motion artifact .
Low radiation exposure with the short-lived tracers (see below), which matters for patients who will need repeat imaging .
Utility described as unaffected by sex, body habitus or very high calcium score, and feasible despite arrhythmias, implanted devices or contrast allergy .
In LBBB or paced rhythm, artifactual septal defects are seen less often than with SPECT .

Limitations

Availability. PET needs a PET scanner and a tracer supply, and the 2021 and 2023 guidelines word their advice as “if available” .
Exercise is difficult. Table A of the 2023 criteria states that PET is not widely available with exercise , so most studies use a vasodilator.
Still uses ionizing radiation, and the dose depends on the tracer (see below).
Less is known about how PET findings change management and outcomes than about their diagnostic and predictive value .

What “preferred” means in this chapter

The 2021 chest pain guideline and the 2023 chronic coronary disease guideline say PET is reasonable in preference to SPECT, if available, when a nuclear test is chosen. This is a class 2a recommendation in the US guidelines, and class 1 in the 2024 European guidelines . The 2026 ASNC position statement goes further and recommends PET as the preferred modality for all patients who meet criteria for myocardial perfusion imaging . These statements concern the choice between PET and SPECT within perfusion imaging. The appropriate use criteria rate each test by scenario and do not rank tests against each other, and this site never names a single best test.

Practical points

Radiation	About 3 mSv for rest-stress rubidium-82 . The ASNC guideline puts rubidium-82, nitrogen-13 ammonia and oxygen-15 water below 3 mSv, and groups fluorine-18 flurpiridaz with technetium SPECT in a 3 to 20 mSv range .
Tracer, contrast	IV tracer; no iodinated contrast for the perfusion study. Proton-pump inhibitors can add gastric uptake with rubidium-82, and stopping them for 3 to 5 days may help .
Stressor	Vasodilator (regadenoson, adenosine, dipyridamole) or dobutamine. Exercise PET is possible only in some labs (below).
Suits	Patients with LBBB or paced rhythm; patients with advanced obesity or dense breast tissue, where attenuation limits SPECT; patients who need repeat imaging; and those in whom flow quantification is wanted, for example suspected microvascular angina .
Struggles	Places without PET; questions about exercise capacity, where exercise testing is the better source ; pregnancy and some breastfeeding situations.

What the sources say about exercise PET

Exercise PET has been tried with rubidium-82, ammonia and oxygen-15 water, but the short half-lives and logistics limited its use. Ammonia needs the treadmill in the same room as the scanner, and exercising on a supine bicycle inside the scanner allows MBF measurement but is hard to do and can blur the images .

Flurpiridaz changes this. In the second phase 3 trial, treadmill exercise PET with flurpiridaz had better image quality and diagnostic accuracy than SPECT . The catch is that a treadmill outside the scanner cannot capture the bolus at peak exercise, so MBF quantification is lost .

Breastfeeding. The ASNC guideline recommends no interruption after rubidium-82 or oxygen-15 water, 1 hour after ammonia, and at least 12 hours after flurpiridaz. As with SPECT, a pregnancy test is mandatory before injection if pregnancy is possible .

The ASNC position statement is a society opinion document, not a guideline with graded recommendations. The PET criteria themselves warn that the wider availability and high sensitivity of PET, combined with fear of missed diagnoses, can lead to inappropriate use, and they aim to limit unnecessary cost and radiation . Both messages are useful: PET has real technical advantages, and it still has to be the right test for the clinical question.

A reduced MFR is not specific to epicardial stenosis. It can reflect obstructive disease, early atherosclerosis or microvascular dysfunction . A normal stress perfusion pattern on PET widely signifies the absence of obstructive epicardial disease, while flow reserve can still assess the microvasculature . The chronic coronary disease guideline gives a 2a recommendation for adding MBFR to stress PET or stress CMR in patients with chronic coronary disease to improve diagnostic accuracy and risk stratification . Because thresholds are not settled, ask the lab which tracer and method produced the numbers.

Example from the tool

Inconclusive stress imaging (SPECT)

A SPECT study that cannot be interpreted leaves the clinical question open. See how the criteria rate the options that follow, including a PET study.

Exercise ECGRarely Appropriate
Exercise SPECTRarely Appropriate
Pharmacologic SPECTRarely Appropriate
Pharmacologic PETMay Be Appropriate
Exercise echoMay Be Appropriate
Dobutamine echoMay Be Appropriate
Stress CMRMay Be Appropriate
CAC scoreMay Be Appropriate
CCTAAppropriate
Invasive angiographyMay Be Appropriate
No testRarely Appropriate

See the reasons for each rating in the tool →

Open this scenario in the builder → for the reasons behind each rating. The criteria also cover inconclusive stress imaging for the other tests, and the builder → lets you describe your own patient.

Try it in the tool

Sources cited on this page

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