Satvika Bharadwaj,1,2 Komal N. Shah,1 Yifan Zhao,3 Aparna Harindranath,1 Arun George,4 Kajoli B. Krishnan,1 Manish Arora1
1Indian Institute of Science (India) 2National Institute of Advanced Studies (India) 3Cranfield Univ. (United Kingdom) 4St. John's Medical College Hospital (India)
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We have built upon an existing freehand 3D ultrasound imaging technique to enable display-less scanning at a local site by novice users and remote reading by integrating an electromagnetic tracker with a 2D probe. Seventy-two volumes are generated using a reconstruction algorithm from data collected by three users in a single longitudinal sweep across a 23- week fetus phantom in four different configurations for six scan durations ranging from 5-s to 30-s. The acquisition is semi-blinded: the user knows the fetal orientation but scans without image display and guidance of a conventional scan. Three non-expert readers and one expert Radiologist extract the clinically relevant planes and measure four key biometric features from the 3D images. In this paper, we propose (1) a risk metric R to rate the quality of the scan as a function of probe motion and contact and (2) a measurability index M for the availability of the 2D planes within the volume and visibility of the biometric features. Our analysis shows that R is the lowest and M the highest for 15-s acquisitions corresponding to an average transducer sweep speed of 2.4-cm/s. The finding is consistent with a reported speed range of 3-4 cm/s recommended for a low cost teleradiology solution for 2D ultrasound. The errors in average biometric measurements compared to the 50th percentile values in the fetal biometry tables for corresponding gestational week are within -3.8 to 5.7%. R, M, accuracy and precision of measurements are useful indicators of performance of the 3D ultrasound system.
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