The reproducibility of time-of-flight PET and conventional PET for the quantification of myocardial blood flow and coronary flow reserve with (13)N-ammonia

Preliminary protocol for measuring the reproducibility and accuracy of flow values on digital PET/CT systems in [15O]H2O myocardial perfusion imaging using a flow phantom

BACKGROUND

Several factors may decrease the accuracy of quantitative PET myocardial perfusion imaging (MPI). It is therefore essential to ensure that myocardial blood flow (MBF) values are reproducible and accurate, and to design systematic protocols to achieve this. Until now, no systematic phantom protocols have been available to assess the technical factors affecting measurement accuracy and reproducibility in MPI.

MATERIALS AND METHODS

We implemented a standard measurement protocol, which applies a flow phantom in order to compare image-derived flow values with respect to a ground truth flow value with [15O]H2O MPI performed on both a Discovery MI (DMI-20, GE Healthcare) and a Biograph Vision 600 (Vision-600, Siemens Healthineers) system. Both systems have automatic [15O]H2O radio water generators (Hidex Oy) individually installed, allowing us to also study the differences occurring due to two different bolus delivery systems. To investigate the technical factors contributing to the modelled flow values, we extracted the [15O]H2O bolus profiles, the flow values from the kinetic modeling (Qin and Qout), and finally calculated their differences between test-retest measurements on both systems.

RESULTS

The measurements performed on the DMI-20 system produced Qin and Qout values corresponging to each other as well as to the reference flow value across all test-retest measurements. The repeatability differences on DMI-20 were 2.1% ± 2.6% and 3.3% ± 4.1% for Qin and Qout, respectively. On Vision-600 they were 10% ± 8.4% and 11% ± 10% for Qin and Qout, respectively. The measurements performed on the Vision-600 system showed more variation between Qin and Qout values across test-retest measurements and exceeded 15% difference in 7/24 of the measurements.

CONCLUSIONS

A preliminary protocol for measuring the accuracy and reproducibility of flow values in [15O]H2O MPI between digital PET/CT systems was assessed. The test-retest reproducibility falls below 15% in majority of the measurements conducted between two individual injector systems and two digital PET/CT systems. This study highlights the importance of implementing a standardized bolus injection and delivery protocol and importance of assessing technical factors affecting flow value reproducibility, which should be carefully investigated in a multi-center setting.

Influence of different time framings, reconstruction algorithms and post-processing methods on the quantification of myocardial blood flow from 13 N-NH3 PET images

BACKGROUND

The aim was to investigate to what extent the quantification of myocardial blood flow (MBF) from dynamic 13 N-NH3 positron emission tomography (PET) images is affected by time frame schemes, time-of-flight (ToF), reconstruction algorithms, blood pool volume of interest (VOI) locations and compartment models in patients with suspected chronic coronary syndrome.

METHODS

A standard MBF value was determined from 25 patients' rest/stress 13 N-NH3 PET/CT images reconstructed with ordered subset expectation maximization (OSEM), 5 s time frame for the first frames without ToF, subsequently analyzed using a basal VOI and the deGrado compartment model. MBFs calculated using 2 or 10 s for the first frames, ToF, block-sequential regularized expectation maximization (BSREM), apical or large VOI, Hutchins or Krivokapich compartment models were compared to MBFstandard in Bland-Altman plots (bias ± SD).

RESULTS

Good agreement in global rest/stress MBF (mL/min/g) was found when changing the time frame scheme or reconstruction algorithm (MBFstandard vs. MBF2s : -0.02 ± 0.06; MBF10s : 0.01 ± 0.07; MBFBSREM : 0.01 ± 0.07), while a lower level of agreement was found when altering the other factors (MBFstandard vs. MBFToF : -0.07 ± 0.10; MBFapical VOI : -0.27 ± 0.25; MBFlarge VOI : -0.11 ± 0.10; MBFHutchins : -0.08 ± 0.10; MBFKrivokapich : -0.47 ± 0.50).

CONCLUSIONS

Quantification of MBF from 13 N-NH3 PET images is more affected by choice of compartment models, ToF and blood pool VOIs than by different time frame schemes and reconstruction algorithms.

EANM procedural guidelines for PET/CT quantitative myocardial perfusion imaging

The use of cardiac PET, and in particular of quantitative myocardial perfusion PET, has been growing during the last years, because scanners are becoming widely available and because several studies have convincingly demonstrated the advantages of this imaging approach. Therefore, there is a need of determining the procedural modalities for performing high-quality studies and obtaining from this demanding technique the most in terms of both measurement reliability and clinical data. Although the field is rapidly evolving, with progresses in hardware and software, and the near perspective of new tracers, the EANM Cardiovascular Committee found it reasonable and useful to expose in an updated text the state of the art of quantitative myocardial perfusion PET, in order to establish an effective use of this modality and to help implementing it on a wider basis. Together with the many steps necessary for the correct execution of quantitative measurements, the importance of a multiparametric approach and of a comprehensive and clinically useful report have been stressed.

Radiopharmaceutical tracers for cardiac imaging

Cardiovascular disease (CVD) is the leading cause of death and disease burden worldwide. Nuclear myocardial perfusion imaging with either single-photon emission computed tomography or positron emission tomography has been used extensively to perform diagnosis, monitor therapies, and predict cardiovascular events. Several radiopharmaceutical tracers have recently been developed to evaluate CVD by targeting myocardial perfusion, metabolism, innervation, and inflammation. This article reviews old and newer used in nuclear cardiac imaging.

The impact of prompt gamma compensation on myocardial blood flow measurements with rubidium-82 dynamic PET

BACKGROUND

Rubidium-82 myocardial perfusion imaging is a well-established technique for assessing myocardial ischemia. With continuing interest on myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurements, there is a requirement to fully appreciate the impact of technical aspects of the process. One such factor for rubidium-82 is prompt gamma compensation (PGC). This study aims to assess the impact of PGC on MBF and MFR calculated from dynamic Rb-82 data.

METHODS

Dynamic rest and stress images were acquired on a Siemens Biograph mCT and reconstructed with and without PGC in 50 patients (29 male). MBF and MFR were measured in the three main coronary territories as well as globally.

RESULTS

With PGC, statistically significant reductions in MBF were observed in LAD (-6.9%), LCx (-4.8%), and globally (-6.5%) but only in obese patients. Significant increases in MBF were observed in RCA (+6.4%) in only nonobese patients. In very obese patients, differences of up to 40% in MBF were observed between PGC and non-PGC images. In nearly all cases, similar PGC differences were observed at stress and rest so there were no significant differences in MFR; however, in a small number of very obese patients, differences in excess of 20% were observed.

CONCLUSION

PGC results in statistically significant changes in MBF, with the greatest reductions observed in the LAD and LCx territories of obese patients. In most cases, the impact on stress and rest data is of similar relative magnitudes and changes to MFR are small.

Review of Cardiovascular Imaging in the Journal of Nuclear Cardiology in 2016. Part 1 of 2: Positron Emission Tomography, Computed Tomography and Magnetic Resonance

Several original articles and editorials have been published in the Journal of Nuclear Cardiology last year. It has become a tradition at the beginning of each year to summarize some of these key articles (AlJaroudi and Hage in J Nucl Cardiol 22:507-512, 2015, 23:122-130, 2016; Hage and AlJaroudi in J Nucl Cardiol 22:714-719, 2015; 23:493-498, 2016). In this part one, we will discuss some of the progress made in patients with infiltrative disease, cardiomyopathies (non-ischemic, ischemic, and diabetic), hybrid and molecular imaging, using advancement in positron emission tomography, computed tomography, and magnetic resonance imaging.

Updates on Stress Imaging Testing and Myocardial Viability With Advanced Imaging Modalities

OPINION STATEMENT

Non-invasive stress testing plays a key role in diagnosis and risk stratification in patients with coronary artery disease. Technical advances in CT, MRI, and PET have lead to increased utility of these modalities in myocardial perfusion imaging. The aim of the review is to provide a succinct update on CT, PET, and MRI for myocardial stress perfusion imaging.