Review Article
Improvement in PET myocardial perfusion image quality and quantification with flurpiridaz F 18

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Abstract

Rubidium-82 (82Rb), the currently commercially available radiotracer for positron emission tomography (PET) myocardial perfusion imaging (MPI), has led to wide availability of PET-MPI for stress-rest imaging. Compared to SPECT MPI, myocardial perfusion PET images have higher spatial and contrast resolution, are less affected by radiotracer scatter, benefit from more precise attenuation correction, and allow dynamic first pass imaging. In addition, PET imaging allows assessment of myocardial function at peak stress and measurement of absolute myocardial blood flow, thus providing critical data not available with SPECT imaging. Further enhancements of the high quality of PET perfusion images may be realized by technologies under development such as respiratory gating, combined respiratory, and ECG gating to generate “motion-frozen” cardiac images, automated patient motion correction software, and high-definition PET, which reduces distortions introduced by the circular geometry of the scanner. Early studies indicate that the experimental PET radiopharmaceutical flurpiridaz F 18 provides high-quality, high-resolution myocardial perfusion images that may enable improved clinical MPI, and has properties well suited to optimized performance by application of these quantitative analytic technologies.

Introduction

Positron emission tomography (PET) offers several advantages over single-photon emission computed tomography (SPECT) for myocardial perfusion imaging (MPI). Importantly, PET has improved spatial and contrast resolution and more accurate attenuation and scatter correction. In addition, PET-MPI allows assessment of myocardial function at peak stress, and measurement of absolute blood flow at rest and at peak stress. These characteristics have combined to yield higher sensitivity and specificity of PET-MPI for detection of coronary artery disease (CAD) as compared to SPECT.1,2 Recent technical developments and a new radiopharmaceutical currently undergoing clinical trials offer the promise to further improve the quality and the accuracy of PET-MPI. This manuscript addresses these new developments, as well as how they might be used to improve the image quality and quantitation of myocardial imaging with flurpiridaz F 18.

Section snippets

Improved Image Quality and Detection of Myocardial Perfusion Defects with SPECT Versus PET

Positron emission tomographic MPI has been shown to result in improved image quality compared to SPECT-MPI, due in large part to the improved count statistics, robust attenuation correction, and scatter correction. This improvement in the quality of PET versus SPECT images results in increased certainty of interpretation. In one study that compared gated images acquired with rubidium-82 (82Rb) and technetium-99m (99mTc) sestamibi, a higher proportion of PET than SPECT MPI scans were interpreted

Further Improvements in Image Quality and Detection of Myocardial Perfusion Defects with SPECT Versus PET using Flurpiridaz F 18

In the authors’ experience during early clinical trials, flurpiridaz F 18 produces higher resolution myocardial perfusion images than either 99mTc SPECT tracers or 82Rb PET. In animal studies, myocardial extraction of flurpiridaz F 18 exhibits a more linear relationship with blood flow over a wide flow range compared to SPECT agents, and, therefore, is promising for the measurement of absolute myocardial blood flow and calculation of coronary flow reserve.4,5 Nitrogen-13-labeled ammonia

Case Examples

We have gained experience with this new tracer in the recently completed flurpiridaz F 18 Phase 2 clinical trial. Figure 1A and B show stress and rest SPECT and PET images acquired from an asymptomatic 61-year-old female with elevated cholesterol, non-specific ST abnormalities, and a family history of early CAD. The SPECT image quality (Figure 1A) is not ideal, but is typical for a SPECT study. Characteristic of SPECT-MPI, the borders of the myocardium are not clearly defined, and there is mild

Quantitative Analysis of PET-MPI

Quantitative analyses of SPECT and PET myocardial perfusion images provide accurate and reproducible assessments of regional myocardial perfusion.8,9 These techniques, developed with available SPECT and PET perfusion tracers, can be applied to a new agent to potentially enhance diagnostic performance. Doing so requires development of tracer-specific normal data files.

Conclusion

In the authors’ experience, these early clinical results suggest that image quality is enhanced, and detection of the extent and severity of perfusion defects may be improved with flurpiridaz F 18 PET perfusion imaging compared to SPECT. These preliminary approaches to relative quantitation of myocardial perfusion with this new PET tracer have shown that there is less variation in regional counts than has been observed with SPECT tracers in similar healthy patients. The investigations with

Disclosure

Dr Berman reported receiving grant support from Lantheus Medical Imaging, Astellas Healthcare, and GE Healthcare. He reported receiving royalties from Cedar-Sinai Medical Center. He reported stock ownership in Spectrum Dynamics. He reported being a consultant for Astellas Healthcare, Bracco Diagnostics, Gilead Sciences, Lantheus Medical Imaging, and GE Healthcare. Dr Germano reported receiving royalties from Cedar-Sinai Medical Center. Dr Slomka reported receiving royalties from Cedar-Sinai

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