Background
Evaluation of myocardial deformation by two-dimensional speckle-tracking is useful for clinical and research purposes. However, differences may exist among different ultrasound machines, software packages, frame rates, and observers.
Methods
Thirty patients underwent echocardiography on both GE (Vivid 9; GE Vingmed Ultrasound AS, Horten, Norway) and Philips (iE33; Philips Ultrasound, Bothell, WA) ultrasound systems. From each study, two sets of images were stored in Digital Imaging and Communications in Medicine format, optimized for strain evaluation: one set of images at the acquisition frame rate (55–90 frames/sec) and one set of images at a compressed frame rate of 30 frames/sec. Vendor-independent software (VIS; TomTec 2D Cardiac Performance Analysis, Munich, Germany) was used to measure strain in multiple directions and was compared with vendor-specific software (GE EchoPAC; GE Vingmed Ultrasound AS).
Results
Intraobserver and interobserver coefficients of variation ranged from 5.5% to 8.7% for longitudinal strain, from 10.7% to 20.8% for circumferential, and from 15.3% to 33.4% for radial and transverse strain. Strain values obtained using VIS were comparable with those obtained using vendor-specific software for longitudinal strain, regardless of ultrasound machine or frame rate. For circumferential strain, a consistent large bias was observed between VIS and vendor-specific software, with higher values using VIS. Slightly higher strain values were observed by analysis at the acquisition frame rate compared with the low frame rate, but no consistent bias was observed between images from different vendors.
Conclusions
Global longitudinal strain consistently showed good reproducibility, while reproducibility was moderate for circumferential strain and poor in the radial direction. Retrospective analysis of legacy Digital Imaging and Communications in Medicine data at 30 frames/sec can be reliably performed for longitudinal strain.
Left ventricular strain analysis by two-dimensional (2D) echocardiographic speckle-tracking is rapidly growing in use for the evaluation of global and regional left ventricular function. Strain measurements are retrospectively being applied to large population studies and previously existing legacy images. However, there are practical questions concerning reproducibility among different ultrasound machines, software packages, and observers. Differences may exist between speckle-tracking strain determined using vendor-specific software (VSS; generally before scan conversion and output to Digital Imaging and Communications in Medicine [DICOM] format) and strain determined using vendor-independent software (VIS) derived from legacy DICOM images (after scan conversion). A recent study evaluated strain values determined using VSS and VIS in children and found differences in measurements among ultrasound machines, software packages, and observers, and more studies are warranted in this area, including in the adult population.
The present study was performed with the following objectives: (1) to investigate the reproducibility of various 2D global strain analyses using VIS in adults, (2) to investigate the agreement of strain measurements obtained using VIS on recordings from different machines and at different frame rates, (3) to compare global strain measurements obtained using VIS with measurements using VSS, and (4) to specifically assess whether strain analysis can be reliably measured from stored DICOM legacy images at a compressed frame rate of 30 frames/sec.
Methods
Study Population
This study was performed in 30 adult outpatients using both Philips iE33 (Philips Ultrasound, Bothell, WA) and GE Vivid 9 (GE Vingmed Ultrasound AS, Horten, Norway) ultrasound systems, with images optimized for speckle-tracking analysis. The studies were acquired as part of routine quality assessment. Exclusion criteria were the presence of congenital heart disease, arrhythmias (such as atrial fibrillation), or poor image quality that would not allow strain analysis in any view. In addition to the 30 patients included in the study, another two patients were excluded because of poor image quality. Patients were included on the basis of the availability of imaging equipment, experienced personnel, and adequate time to perform both acquisition studies. Images were collected in tandem, and the order of imaging systems used was entirely random. The protocol was approved by the institutional ethics review committee.
Echocardiographic Image Acquisition
All echocardiographic studies were performed by sonographers experienced in obtaining and analyzing regional and global speckle-tracking strain. Participants were initially scanned for clinical purposes using either a GE Vivid E9 or a Philips iE33 ultrasound machine with a 3.5-MHz ultrasound probe. Grayscale images, including a short-axis view at the papillary muscle level and the three apical views (four-chamber, two-chamber, and apical long-axis views), were then acquired on both systems for offline speckle-tracking analysis. In all views, three consecutive heart cycles were stored. All images were acquired at frame rates of 55–90 frames/sec.
A flow diagram is shown in Figure 1 . An imaging study was acquired by each ultrasound system and then stored in two different sets of images in DICOM format in Philips Xcelera (Philips Medical Systems, Eindhoven, The Netherlands) with one set compressed to 30 frames/sec and another set stored at the acquisition frame rate for analysis using the VIS package 2D Cardiac Performance Analysis version 4.5 (TomTec Imaging Systems, Munich, Germany). In addition, the study acquired on the GE system was stored as raw-data images in the VSS package EchoPAC version BT 09 (GE Vingmed Ultrasound AS) for comparative analysis.
