Examining the sensitivity of 18F-NaF PET for the imaging of cardiac amyloidosis.

BACKGROUND: Conventional nuclear imaging with bone-seeking radiopharmaceuticals has been shown to be a sensitive test for the detection of transthyretin cardiac amyloidosis (ATTR); however, to date, few data exist on the utility of 18F-sodium fluoride (NaF) positron emission tomography (PET) in subjects with cardiac amyloidosis (CA). METHODS: Myocardial perfusion imaging and cardiac 18F-NaF PET/CT of 7 subjects with ATTR, four with light-chain CA (AL), and four controls were retrospectively reviewed. Qualitative interpretation and quantitative analyses with average left ventricular standardized uptake values (SUVmean) and target-to-background ratios (TBRmean) were performed. RESULTS: Average TBRmean was significantly increased in subjects with ATTR (0.98 ± 0.09) compared to AL (0.85 ± 0.08, P = .026) and CTL (0.82 ± 0.07, P = .020), while SUVmean was not (P = .14). Receiver-operator characteristic (ROC) analysis yielded an area under the curve (AUC) of 0.91, with a sensitivity/specificity of 75%/100% for TBRmean using a cutoff value of 0.89 for the diagnosis of ATTR. Qualitative interpretation resulted in a sensitivity/specificity of 57%/100% for ATTR. CONCLUSIONS: While 18F-NaF PET/CT demonstrates good diagnostic accuracy for ATTR, particularly when using quantitative analysis, the low TBRmean values observed in ATTR indicate poor myocardial signal. 18F-NaF PET/CT is not yet ready for clinical use in CA until further comparison studies are performed with 99mTc-DPD/PYP.

Comparison of two dipyridamole infusion protocols for myocardial perfusion imaging in subjects with low likelihood of significant obstructive coronary artery disease.

BACKGROUND: Myocardial perfusion imaging (MPI) with positron emission tomography allows accurate measurements of myocardial blood flow (MBF). Stress MBF thresholds have been proposed to provide diagnostic and prognostic information in different pathology. Most studies relying on dipyridamole use a 5-minute infusion protocol, while current guidelines recommend a 4-minute infusion. The purpose of this study is to compare the effects of different dipyridamole infusion times on stress MBF. METHODS: The charts of 2,207 patients who underwent rubidium-82 MPI were retrospectively reviewed and 147 subjects with low likelihood of significant coronary artery disease (CAD) defined as calcium score = 0, body mass index < 45 kg·m-2, and summed stress score ≤ 3 were included. Of those, 65 were imaged with a 4-minute dipyridamole infusion (0.56 mg·kg-1) protocol and 82 with a 5-minute protocol (0.70 mg·kg-1). RESULTS: Stress MBF (3.23±0.76 vs 3.02±0.71 mL·min-1·g-1, P = 0.09), myocardial flow reserve (2.70±0.67 vs 2.85±0.74, P = 0.20), and coronary vascular resistance index (30±10 vs 31±9 mmHg × g × min·mL-1, P = 0.38) were not significantly different between the two protocols. The 5-minute protocol was associated with higher prevalence of symptoms (92.7% vs 81.5%, P = 0.04) and greater decrease in systolic blood pressure (- 9 vs - 6 mmHg, P = 0.03). CONCLUSIONS: The 4-minute and 5-minute dipyridamole infusion protocols produce comparable myocardial flow response, hemodynamic changes, and symptoms, in subjects with low likelihood of significant obstructive CAD.

Assessment of left ventricular ejection fraction with cardiofocal collimators: Comparison between IQ-SPECT, planar equilibrium radionuclide angiography, and cardiac magnetic resonance.

BACKGROUND: IQ-SPECT has been shown to significantly reduce acquisition time and administered dose while preserving image quality in myocardial perfusion imaging. Whether IQ-SPECT provides accurate left ventricular ejection fractions (LVEF) with gated blood pool SPECT (GBPS) remains unknown. METHODS: Sixty patients underwent IQ-SPECT GBPS and planar imaging. Among those patients, 11 underwent both cMRI and GBPS. GBPS LVEF, LVEDV, and LVESV were calculated using 2 validated software; QBS (Cedars-Sinai Medical Center, Los Angeles, USA) and MHI (Montreal Heart Institute, Montreal, Canada). LVEF, LVEDV, and LVESV obtained with the different modalities were compared. RESULTS: Average planar LVEF was 48 ± 11% (mean ± SD), average LVEDV was 177 ± 59 mL (range 63 to 342 mL), and average LVESV was 96 ± 46 mL (range 16 to 234 mL). GBPS LVEF and their correlation coefficient with planar LVEF were 40 ± 12% (r = 0.70) and 44 ± 12% (r = 0.83) with QBS and MHI, respectively. Correlation coefficient between cMRI and planar LVEF was 0.65 and were 0.69 and 0.52 between cMRI and GBPS using QBS and MHI, respectively. CONCLUSIONS: LVEF calculated with GBPS using IQ-SPECT correlates with planar measurements. Correlation is best using the MHI method and variation is independent of LVEDV.

Utility of FDG-PET/CT for the Detection and Characterization of Sternal Wound Infection Following Sternotomy.

PURPOSE: FDG-PET/CT has the potential to play an important role in the diagnosis of sternal wound infections (SWI). The purpose of this study was to analyze the diagnostic accuracy of FDG-PET/CT for SWI in patients following sternotomy. METHODS: We performed a single-center, retrospective analysis of patients who had undergone median sternotomy and FDG-PET/CT imaging. The gold standard consisted of positive bacterial culture and/or the presence of purulent material at surgery. Qualitative patterns of sternal FDG uptake, SUVmax, and associated CT findings were determined, and an imaging scoring system was developed. The diagnostic performances were studied in both the recent (≤ 6 months between sternotomy and imaging) and remote surgery phase (> 6 months). RESULTS: A total of 40 subjects were identified with 11 confirmed SWI cases. Consensus interpretation was associated with a sensitivity of 91% and specificity of 97%. Combination of uptake patterns yielded an AUC of 0.96 while use of SUVmax yielded an AUC of 0.82. CONCLUSIONS: Results suggest that FDG-PET/CT may be useful for the diagnosis of SWI with optimal diagnostic accuracy achieved by identifying specific patterns of uptake. SUVmax can be helpful in assessing subjects with remote surgery, but its use is limited in the context of recent surgery. Further studies are required to confirm these results.

Characterization and reproducibility of forearm arterial flow during reactive hyperemia.

Peripheral arterial flow has been assessed for a variety of indications including characterization of endothelial function during reactive hyperemia. However, quantification of this blood flow as a surrogate remains an imperfect reflection of endothelial function. We sought to better characterize hyperemic reaction to (1) elucidate the influence of the endothelial function and (2) assess the reproducibility of our modeling over time. Sixteen normal subjects underwent simultaneous forearm reactive hyperemia testing with a near-infrared system at baseline, baseline +24 h and baseline +27 h. Baseline flow was measured to 3.6 +/- 0.2 ml dl(-1) min(-1), and was highly reproducible 24 and 27 h later. With reactive hyperemia, the blood flow increased to 20.5 +/- 4.6 ml dl(-1) min(-1). Arterial blood flow curves during reactive hyperemia displayed a bimodal pattern, with the second peak occurring 59.1 +/- 10.6 s after the onset of hyperemia. We believe that this latest peak represents the contribution of endothelial factors to the hyperemic reaction. Modeling of hyperemic curves led to the introduction of a reproducible new parameter (etafactor) that reflects the normalized contribution of this second peak. In conclusion, forearm arterial flow during reactive hyperemia revealed a bimodal distribution where functional interpretation allowed distinction of the two components. Basal flow measurements and results of this modeling were reproducible 24 and 27 h later.