Original Article
One-tissue compartment model for myocardial perfusion quantification with N-13 ammonia PET provides matching results: A cross-comparison between Carimas, FlowQuant, and PMOD

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Abstract

Purpose

To cross-compare three software packages (SPs)—Carimas, FlowQuant, and PMOD—to quantify myocardial perfusion at global, regional, and segmental levels.

Materials and Methods

Stress N-13 ammonia PET scans of 48 patients with HCM were analyzed in three centers using Carimas, FlowQuant, and PMOD. Values agreed if they had an ICC > 0.75 and a difference < 20% of the median across all observers.

Results

When using 1TCM on the global level, the agreement was good, and the maximum difference between 1TCM MBF values was 17.2% (ICC = 0.83). On the regional level, the agreement was acceptable except in the LCx region (25.5% difference, ICC = 0.74) between FlowQuant and PMOD. Carimas-1TCM agreed well with PMOD-1TCM and FlowQuant-1TCM. Values obtained with FlowQuant-1TCM had a somewhat lesser agreement with PMOD-1TCM, especially at the segmental level.

Conclusions

The global and regional MBF values (with one exception) agree well between the different software packages. There is significant variability in segmental values, mainly located in the LCx region and segments. Out of the studied tools, Carimas can be used interchangeably with both PMOD and FlowQuant for 1TCM implementation on all levels—global, regional, and segmental.

Introduction

Absolute quantification of myocardial blood flow (MBF) in mL·min−1·g−1 of myocardial tissue with dynamic PET imaging constitutes an essential tool for clinicians. It can provide relevant information complementary to relative myocardial perfusion imaging.1,2 Currently, optimized acquisition protocols, incremental computational power, and fast image reconstruction enable list-mode-acquired PET imaging and myocardial perfusion quantification (MPQ) to be applied in clinical routine.3

There has been a continuous effort to harmonize imaging workflow. One factor that remains unconstrained is the software package (SP) variability.1,4,5 In 2014, we published a comparative study4 that considered ten SPs for Rb-82 PET. Results showed that MBF and MFR values obtained with different SPs could differ by a factor of two or more. However, the agreement was satisfactory when only one specific model—a one-tissue compartment model (1TCM,6)—was applied.

Nitrogen-13 ammonia represents another widely used perfusion PET tracer. It has a short half-life and therefore requires an on-site cyclotron for its clinical implementation. It has also demonstrated more favorable extraction and retention kinetics and quantification precision than Rb-82.7 Previous data on SPs comparison for N-13 ammonia MPQ were reported8 in patients with known or suspected coronary artery disease (CAD).

Furthermore, MPQ has been performed in pathological conditions beyond CAD, such as cardiomyopathies. Studies in hypertrophic cardiomyopathy (HCM) demonstrated hampering of the vasodilator reserve and microvascular dysfunction, impacting the prognosis for the patients.9,10 Despite these efforts at characterizing perfusion abnormalities in HCM, there is a lack of reports addressing the MPQ agreement considering this particular pathology.

Hence, the present study aimed to cross-compare stress MPQ with N-13 ammonia between three SPs—Carimas, FlowQuant, and PMOD—which provide different implementations of the same one-tissue compartment model (1TCM). The MPQ agreement evaluation was performed in the patients with HCM at the three levels of segmentation—global, regional, and segmental (based on the 17-segment AHA model.11)

Section snippets

Materials and Methods

The study group consisted of 48 patients with known HCM referred to PET MPQ (patient characteristics are in Table 1).

Absolute Values of Stress MBF

All MBF estimates, as well as calculated median values, are in Table 2. In general, FlowQuant had the lowest and PMOD—the highest MBF values obtained with the 1TCM.

Agreement Between the Global and Regional Values Using 1TCMs

Figure 1 presents comparisons between MBF values obtained with the same 1TCMs in the studied SPs at the global and regional levels. The maximum difference between MBF values at the global level was in the acceptable range—17.2% (ICC = 0.83) between FlowQuant and PMOD. Regionally, the values obtained with different SPs agreed well

Discussion

The present study compared three SPs for myocardial perfusion quantification with N-13 ammonia—Carimas, FlowQuant, and PMOD—in a population of 48 patients with HCM. The comparison was made on 48 pharmacological stress images, and the obtained MBF estimates were compared on three sequential levels—global, regional, and segmental. All three tools were analyzed for their implementation of the 1TCM described in.12

Of the MBF values obtained, PMOD generally—global, all regional, and 14 of 17

New Knowledge Gained

The global and regional MBF values (N-13 ammonia PET MPQ) agree well between the different software packages implementing 1TCM; segmental values show significant variability. Carimas can be used interchangeably with both PMOD and FlowQuant on all levels.

Conclusions

  • 1

    The global and regional MBF values (with one exception) agree well between the different software packages,

  • 2

    However, there is significant variability in segmental values, mainly located in the LCx region and segments.

  • 3

    Out of the studied tools, Carimas can be used interchangeably with both PMOD and FlowQuant for 1TCM implementation on all levels—global, regional, and segmental.

Funding

Open access funding provided by University of Turku (UTU) including Turku University Central Hospital.

Disclosures

Juhani M. Knuuti declares AstraZeneca and GE Healthcare paid to him for study protocol commenting (consultancy); Merck, GE healthcare, Boehringer-Ingelheim, and Lundbeck paid money to him for lectures including service on speakers bureaus. Robert A. deKemp declares Jubilant DraxImage paid grants, consulting fees, and royalties for Rubidium PET Technologies to his institution and INVIA Medical Imaging Solutions paid royalties for myocardial blood flow technologies to his institution. Sergey V.

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