Impact of residual subtraction on myocardial blood flow and reserve estimates from rapid dynamic PET protocols

The role of cardiac PET in diagnosis and prognosis of patients with ischemia with no obstructive coronary arteries (INOCA)

Chest pain, a common symptom in cardiovascular care, often leads to the investigation of obstructive coronary artery disease (CAD). However, many patients experience chest pain without obstructive CAD, termed INOCA (Ischemia with Non-Obstructive Coronary Arteries) or CMD (Coronary Microvascular Dysfunction). INOCA can be attributed to endothelial dysfunction, vascular smooth muscle dysfunction, or both, affecting about 20-30 % of patients with nonobstructive CAD. The diagnostic approach for INOCA includes both invasive and non-invasive methods, with cardiac PET (Positron Emission Tomography) playing a significant role in risk stratification and management. PET evaluates various parameters like myocardial blood flow under stress and rest, myocardial flow reserve, and myocardial ischemia. Such comprehensive assessment is essential in accurately diagnosing and managing INOCA, considering the complexity of this condition.

Integrated myocardial flow reserve (iMFR) assessment: optimized PET blood flow quantification for diagnosis of coronary artery disease

PURPOSE

Distinguishing obstructive epicardial coronary artery disease (CAD) from microvascular dysfunction and diffuse atherosclerosis would be of immense benefit clinically. However, quantitative measures of absolute myocardial blood flow (MBF) integrate the effects of focal epicardial stenosis, diffuse atherosclerosis, and microvascular dysfunction. In this study, MFR and relative perfusion quantification were combined to create integrated MFR (iMFR) which was evaluated using data from a large clinical registry and an international multi-center trial and validated against invasive coronary angiography (ICA).

METHODS

This study included 1,044 clinical patients referred for 82Rb rest/stress positron emission tomography myocardial perfusion imaging and ICA, along with 231 patients from the Flurpiridaz 301 trial (clinicaltrials.gov NCT01347710). MFR and relative perfusion quantification were combined to create an iMFR map. The incremental value of iMFR was evaluated for diagnosis of obstructive stenosis, adjusted for patient demographics and pre-test probability of CAD. Models for high-risk anatomy (left main or three-vessel disease) were also constructed.

RESULTS

iMFR parameters of focally impaired perfusion resulted in best fitting diagnostic models. Receiver-operating characteristic analysis showed a slight improvement compared to standard quantitative perfusion approaches (AUC 0.824 vs. 0.809). Focally impaired perfusion was also associated with high-risk CAD anatomy (OR 1.40 for extent, and OR 2.40 for decreasing mean MFR). Diffusely impaired perfusion was associated with lower likelihood of obstructive CAD, and, in the absence of transient ischemic dilation (TID), with lower likelihood of high-risk CAD anatomy.

CONCLUSIONS

Focally impaired perfusion extent derived from iMFR assessment is a powerful incremental predictor of obstructive CAD while diffusely impaired perfusion extent can help rule out obstructive and high-risk CAD in the absence of TID.

Measuring myocardial blood flow using dynamic myocardial perfusion SPECT: artifacts and pitfalls

Dynamic acquisition allows absolute quantification of myocardial perfusion and flow reserve, offering an alternative to overcome the potential limits of relative quantification, especially in patients with balanced multivessel coronary artery disease. SPECT myocardial perfusion is widely available, at lower cost than PET. Dynamic cardiac SPECT is now feasible and has the potential to be the next step of comprehensive perfusion imaging. In order to help nuclear cardiologists potentially interested in using dynamic perfusion SPECT, we sought to review the different steps of acquisition, processing, and reporting of dynamic SPECT studies in order to enlighten the potentially critical pitfalls and artifacts. Both patient-related and technical artifacts are discussed. Key parameters of the acquisition include pharmacological stress, radiopharmaceuticals, and injection device. When it comes to image processing, attention must be paid to image-derived input function, patient motion, and extra-cardiac activity. This review also mentions compartment models, cameras, and attenuation correction. Finally, published data enlighten some facets of dynamic cardiac SPECT while several issues remain. Harmonizing acquisition and quality control procedures will likely improve its performance and clinical strength.

Influence of image reconstruction on quantitative cardiac 15O-water positron emission tomography

BACKGROUND

The impact on quantitative 15O-water PET/CT of a wide range of different reconstruction settings, including regularized reconstruction by block-sequential regularized expectation maximization (BSREM), was investigated.

METHODS

Twenty clinical stress scans from patients referred for assessment of myocardial ischemia were included. Patients underwent a 4-min dynamic stress PET scan with 15O-water on a digital PET/CT scanner. Twenty-two reconstructions were generated from each scan and a clinical reconstruction was used as reference. Varied parameters were number of iterations, filter, exclusion of time-of-flight and point-spread function, and regularization parameter with BSREM. Analyses were performed in aQuant utilizing two different methods and resulting regional myocardial blood flow (MBF), perfusable tissue fraction (PTF), and transmural MBF (MBFt) values were evaluated.

RESULTS

Across the two analyses, correlations toward the reference reconstruction were strong for all parameters (ρ ≥ 0.83). Using automated analysis and the diagnostic threshold of hyperemic MBF at 2.3 mL⋅g-1⋅min-1, diagnosis was unchanged irrespective of reconstruction method in all patients except for one, where only four of the most extreme reconstruction methods resulted in a change of diagnosis.

CONCLUSION

The low sensitivity of MBF values to reconstruction method and, as previously shown, scanner type and PET/CT misalignment, confirms that diagnostic hyperemic MBF cutoff values can be consistently used for 15O-water.