Abstract
Background99mTc-PYP scintigraphy provides differential diagnosis of ATTR cardiomyopathy (ATTR-CM) from light chain cardiac amyloidosis and other myocardial disorders without biopsy. This study was aimed to assess the diagnostic feasibility and the operator reproducibility of 99mTc-PYP quantitative SPECT.MethodThirty-seven consecutive patients who underwent a 99mTc-PYP thorax planar scan followed by SPECT and CT scans to diagnose suspected ATTR-CM were enrolled. For the quantitative SPECT, phantom studies were initially performed to determine the image conversion factor (ICF) and partial volume correction (PVC) factor to recover 99mTc-PYP activity concentration in the myocardium for calculating the standardized uptake value (SUV) (unit: g/ml). SUVmax was compared among groups of ATTR-CM, AL cardiac amyloidosis, and other pathogens (others) and among categories of Perugini visual scores (grades 0–3). The intra- and inter-operator reproducibility of quantitative SPECT was verified, and the corresponded repeatability coefficient (RPC) was calculated.ResultsThe ICF was 79,327 Bq/ml to convert count rate in pixel to 99mTc activity concentration. PVC factor as a function of the measured activity concentration ratio in the myocardium and blood-pool was [y = 1.424 × (1 − exp(− 0.759 × x)) + 0.104]. SUVmax of ATTR-CM (7.50 ± 2.68) was significantly higher than those of AL (1.96 ± 0.35) and others (2.00 ± 0.74) (all p < 0.05). SUVmax of grade 3 (8.95 ± 1.89) and grade 2 (4.71 ± 0.23) were also significantly higher than those of grade 1 (1.92 ± 0.31) and grade 0 (1.59 ± 0.39) (all p < 0.05). Correlation coefficient (R2) of SUVmax reached 0.966 to 0.978 with only small systematic difference (intra = − 0.14; inter = − 0.23) between two repeated measurements. Intra- and inter-operator RPCs were 0.688 and 0.877.Conclusions99mTc-PYP quantitative SPECT integrated with adjustable PVC factors is feasible to quantitatively and objectively assess the burden of cardiac amyloidosis for diagnosis of ATTR-CM.
Highlights
Cardiac amyloidosis is related to the pathogen that the primary interstitial protein deposition occurs in the extracellular space of the myocardium, leading to impairment of myocardial wall contractility, systolic/diastolic dysfunction, arrhythmia, and eventually heart failure to cause high morbidity and mortality [1]
The aim of our study is set to report the feasibility and the reproducibility of 99mTcPYP quantitative single-photon emission computed tomography (SPECT) in differential diagnosis of cardiac amyloidosis when SPECT images were reconstructed with full physical corrections, and the correction for partial volume effect to recover true activity concentration in the myocardium was integrated into the quantitation process
The partial volume correction (PVC) factor described by fitting parameters (a, b, c) in the exponential recovery function can only be transferable to the same camera system with the matched set of imaging parameters
Summary
Cardiac amyloidosis is related to the pathogen that the primary interstitial protein deposition occurs in the extracellular space of the myocardium, leading to impairment of myocardial wall contractility, systolic/diastolic dysfunction, arrhythmia, and eventually heart failure to cause high morbidity and mortality [1]. Positron emission tomography (PET) with β-amyloid-specific imaging tracers such as 18F-florbetapir, 18F-flutemetamol, and 11C-PIB enables the quantitative scheme to evaluate cardiac amyloidosis [14,15,16]. This quantitative imaging tool is not yet ready for routine clinical utilization. Systematic evaluation of the scintigraphy with 99mTc-labeled phosphate tracers (e.g., technetium-99m 3, 3-diphospho-1, 2-propanodicarboxylic acid (99mTcDPD), technetium-99m pyrophosphate (99mTc-PYP), or 99mTc-hydroxymethylene diphosphonate (99mTc-HMDP)) has been reported as an outstanding non-invasive imaging tool to distinguish ATTR-CM from AL cardiac amyloidosis with excellent performance in differential diagnosis (sensitivity 84–97%, specificity 94–100%) [17,18,19]. The aim of our study is set to report the feasibility and the reproducibility of 99mTcPYP quantitative SPECT in differential diagnosis of cardiac amyloidosis when SPECT images were reconstructed with full physical corrections, and the correction for partial volume effect to recover true activity concentration in the myocardium was integrated into the quantitation process
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