Left Ventricular Strain from Myocardial Perfusion PET Imaging: Method Development and Comparison to 2-Dimensional Echocardiography

Is cardiopulmonary transit time (CPTT) measured by using dynamic rubidium cardiac PET/CT a predictor for cardiac function?

Cardiopulmonary transit time (CPTT) represents the time needed for the circulation of blood from the right to the left ventricle. This parameter can be measured during dynamic acquisition of rubidium ([82Rb]) cardiac PET/CT. To further characterize this marker, we wanted to assess the association between CPTT and parameters of cardiac function derived from echocardiography. Retrospective single center analysis of patients referred to [82Rb]RbCl-PET/CT with rest/stress protocol on an integrated hybrid PET/CT system (Biograph mCT, Siemens Healthineers, Erlangen, Germany) and echocardiography within 100 days. After intravenous injection of 7.5 MBq/kg [82Rb]RbCl dynamic scans with initially 12 × 10 s frames were started. For data analysis a volume of interest (VOI) was drawn in the left and right ventricle using dedicated software. The difference between the peak time for the two time activity curves (TAC) was extracted as CPTT and normalized for heart rate (NCPTT). Associations between NCPTT and echo parameters such as left ventricular ejection fraction (EFEcho) were analyzed using linear regression models. 44 patients (sex: 28 male, 16 female) were enrolled with a time difference between PET and echocardiography of 19.65 ± 23.3 days. 9 patients had a rest CPTT of 0 s, 32 patients 10 s and 3 patients 20 s. The association between EFEcho and NCPTT revealed a significant negative correlation (beta = -0.77; CI: -1.32, -0.22; p = 0.007). Given this association, univariate predictive models for EFEcho were applied. Root mean square error was 6.83% for the EFPET, and 6.0% for NCPTT, which indicates a slightly higher predictive performance for the NCPTT model with a lower error. Pulmonary transit time can be estimated with [82Rb]RbCl-PET/CT, with a high positive association to rest EFEcho. However, smaller time frames than 10 s are needed, for more accurate estimation of cardiac function.

Gated SPECT-Derived Myocardial Strain Estimated From Deep-Learning Image Translation Validated From N-13 Ammonia PET

RATIONALE AND OBJECTIVES

This study investigated the use of deep learning-generated virtual positron emission tomography (PET)-like gated single-photon emission tomography (SPECTVP) for assessing myocardial strain, overcoming limitations of conventional SPECT.

MATERIALS AND METHODS

SPECT-to-PET translation models for short-axis, horizontal, and vertical long-axis planes were trained using image pairs from the same patients in stress (720 image pairs from 18 patients) and resting states (920 image pairs from 23 patients). Patients without ejection-fraction changes during SPECT and PET were selected for training. We independently analyzed circumferential strains from short-axis-gated SPECT, PET, and model-generated SPECTVP images using a feature-tracking algorithm. Longitudinal strains were similarly measured from horizontal and vertical long-axis images. Intraclass correlation coefficients (ICCs) were calculated with two-way random single-measure SPECT and SPECTVP (PET). ICCs (95% confidence intervals) were defined as excellent (≥0.75), good (0.60-0.74), moderate (0.40-0.59), or poor (≤0.39).

RESULTS

Moderate ICCs were observed for SPECT-derived stressed circumferential strains (0.56 [0.41-0.69]). Excellent ICCs were observed for SPECTVP-derived stressed circumferential strains (0.78 [0.68-0.85]). Excellent ICCs of stressed longitudinal strains from horizontal and vertical long axes, derived from SPECT and SPECTVP, were observed (0.83 [0.73-0.90], 0.91 [0.85-0.94]).

CONCLUSION

Deep-learning SPECT-to-PET transformation improves circumferential strain measurement accuracy using standard-gated SPECT. Furthermore, the possibility of applying longitudinal strain measurements via both PET and SPECTVP was demonstrated. This study provides preliminary evidence that SPECTVP obtained from standard-gated SPECT with postprocessing potentially adds clinical value through PET-equivalent myocardial strain analysis without increasing the patient burden.

Myocardial perfusion imaging-derived left ventricular strain: Regional abnormalities associated with transthyretin cardiac amyloidosis

Background

Transthyretin (ATTR) cardiac amyloidosis is associated with an apical-sparing strain pattern on TTE. We hypothesize that strain indices derived from myocardial perfusion imaging (MPI) can identify this abnormality.

Methods

A group with ATTR amyloidosis was compared to age-matched controls with LVH but without amyloidosis who underwent PET or SPECT MPI. Strain values were used to calculate the apical strain index (ASI), apex-to-base ratio (ABR), and ejection fraction to global strain ratio in multiple planes.

Results

A direct comparison using Welch's t-tests reveals 6 statistically significant metrics. After regression analysis, the circumferential ASI and ABR at rest remain significantly greater in the ATTR group compared to controls.

Conclusion

MPI-derived strain from the circumferential plane at rest may distinguish cardiac amyloidosis from other forms of LVH. If these findings are confirmed with validation studies, routine MPI-derived strain analysis could identify patients with subclinical amyloidosis who may benefit from further testing.