Clinical Utility of Fetal Short-Lag Spatial Coherence Imaging

Abstract

In this study, we evaluate the clinical utility of fetal short-lag spatial coherence (SLSC) imaging. Previous work has documented significant improvements in image quality with fetal SLSC imaging as quantified by measurements of contrast and contrast-to-noise ratio (CNR). The objective of this study was to examine whether this improved technical efficacy is indicative of the clinical utility of SLSC imaging. Eighteen healthy volunteers in their first and second trimesters of pregnancy were scanned using a modified Siemens SC2000 clinical scanner. Raw channel data were acquired for routinely examined fetal organs and used to generate fully matched raw and post-processed harmonic B-mode and SLSC image sequences, which were subsequently optimized for dynamic range and other imaging parameters by a blinded sonographer. Optimized videos were reviewed in matched B-mode and SLSC pairs by three blinded clinicians who scored each video based on overall quality, target conspicuity and border definition. SLSC imaging was highly favored over conventional imaging with SLSC scoring equal to (28.2 ± 10.5%) or higher than (63.9 ± 12.9%) B-mode for video pairs across all examined structures and processing conditions. Multivariate modeling revealed that SLSC imaging is a significant predictor of improved image quality with p ≤ 0.002. Expert-user scores for image quality support the application of SLSC in fetal ultrasound imaging.

Keywords: Beamforming; Clutter reduction; Fetal sonography; Harmonic imaging; Image quality; Reader study; Spatial coherence.

Figure 1

Example matched (a) raw B-mode, (b) raw SLSC, (c) post-processed B-mode, and (d) post-processed SLSC images of the fetal bladder shown with sonographer-optimized parameters for dynamic range and short-lag. Arrows indicate the location of the bladder. The anechoic organ is significantly degraded by clutter in B-mode, but readily visualized with high contrast in both raw and post-processed SLSC images.

Figure 2

Example matched (a) raw B-mode, (b) raw SLSC, (c) post-processed B-mode, and (d) post-processed SLSC images of the fetal stomach shown with sonographer-optimized parameters for dynamic range and short-lag. Arrows indicate the lateral boundary of the stomach, which is significantly degraded by reverberation clutter in B-mode. SLSC imaging appears to reduce the appearance of this clutter, resulting in improved conspicuity and definition of the stomach and its boundaries.

Figure 3

Example matched (a) raw B-mode, (b) raw SLSC, (c) post-processed B-mode, and (d) post-processed SLSC images of the fetal cerebral ventricles shown with sonographer-optimized parameters for dynamic range and short-lag. In both raw and post-processed B-mode images, reverberation from the uterine wall and off-axis clutter result in poor visibility of the choroid plexus (CP) and ventricular walls (VW). These structures appear better visualized in SLSC as a result of clutter suppression.

Figure 4

Outcome measure score distributions for raw video pairs of the fetal bladder, stomach, and cerebral ventricles. Histograms are organized in columns for different outcome measures (TC, BD, OQ) and in rows for different imaged structures. Individual histograms depict the number of matched video pairs in different score categories with SLSC score plotted as a function of B-mode score. The dashed white lines denote categories in which SLSC and B-mode scores are the same. Video pairs above this diagonal indicate increase in outcome measure score from B-mode to SLSC. For each histogram, the percentage of video pairs with SLSC preference and B-mode preference are indicated in the top-left and bottom-right corners, respectively.

Figure 5

Outcome measure score distributions for post-processed video pairs of the fetal bladder, stomach, and cerebral ventricles. Histograms are organized in columns for different outcome measures (TC, BD, OQ) and in rows for different imaged structures. Individual histograms depict the number of matched video pairs in different score categories with SLSC score plotted as a function of B-mode score. The dashed white lines denote categories in which SLSC and B-mode scores are the same. Video pairs above this diagonal indicate increase in outcome measure score from B-mode to SLSC. For each histogram, the percentage of video pairs with SLSC preference and B-mode preference are indicated in the top-left and bottom-right corners, respectively.

Figure 6

Outcome measure score distributions for Readers 1, 2, and 3. Histograms are organized in columns for different outcome measures (TC, BD, OQ) and in rows for different readers. Individual histograms depict the number of matched video pairs in different score categories with SLSC score plotted as a function of B-mode score. The dashed white lines denote categories in which SLSC and B-mode scores are the same. Video pairs above this diagonal indicate increase in outcome measure score from B-mode to SLSC. For each histogram, the percentage of video pairs with SLSC preference and B-mode preference are indicated in the top-left and bottom-right corners, respectively.

Figure 7

Quantiles of estimated errors from the multivariate model fit plotted against the quantiles of the standard normal distribution for all three outcome measures. Linearity of the points in each plot indicates strong adherence of model fit residuals to the Gaussian distribution.

Video Figure 1

Example video showing matched B-mode and SLSC image sequences of the cerebral ventricles generated from raw channel data acquired using the modified clinical system. Image sequences are able to successfully capture fetal and probe motion at 14 fps over the 3-second acquisition.