Matrix 3D ultrasound-assisted thyroid nodule volume estimation and radiofrequency ablation: a phantom study

Abstract

Background: Two-dimensional (2D) ultrasound is well established for thyroid nodule assessment and treatment guidance. However, it is hampered by a limited field of view and observer variability that may lead to inaccurate nodule classification and treatment. To cope with these limitations, we investigated the use of real-time three-dimensional (3D) ultrasound to improve the accuracy of volume estimation and needle placement during radiofrequency ablation. We assess a new 3D matrix transducer for nodule volume estimation and image-guided radiofrequency ablation.

Methods: Thirty thyroid nodule phantoms with thermochromic dye underwent volume estimation and ablation guided by a 2D linear and 3D mechanically-swept array and a 3D matrix transducer.

Results: The 3D matrix nodule volume estimations had a lower median difference with the ground truth (0.4 mL) compared to the standard 2D approach (2.2 mL, p < 0.001) and mechanically swept 3D transducer (2.0 mL, p = 0.016). The 3D matrix-guided ablation resulted in a similar nodule ablation coverage when compared to 2D-guidance (76.7% versus 80.8%, p = 0.542). The 3D mechanically swept transducer performed worse (60.1%, p = 0.015). However, 3D matrix and 2D guidance ablations lead to a larger ablated volume outside the nodule than 3D mechanically swept (5.1 mL, 4.2 mL (p = 0.274), 0.5 mL (p < 0.001), respectively). The 3D matrix and mechanically swept approaches were faster with 80 and 72.5 s/mL ablated than 2D with 105.5 s/mL ablated.

Conclusions: The 3D matrix transducer estimates volumes more accurately and can facilitate accurate needle placement while reducing procedure time.

Keywords: Imaging (three-dimensional); Phantoms (imaging); Radiofrequency ablation; Thyroid nodule; Ultrasonography.

Conflict of interest statement

The authors declare that they have no competing interests.

© 2021. The Author(s).

Figures

Fig. 1

Method depictions. a Three-dimensional (3D) view of the phantom with nodule volume in milliliter (mL) being estimated. b Side view of the ablation set-up with a grounding pad, radiofrequency ablation needle, and transducer and the red triangle indicating the danger triangle. Beneath that the 3D matrix (real-time 3D transducer) view of a nodule ablation. c Slicing, photographing, and pixel-based analysis of the body and nodule after ablation. 2D: Two-dimensional (conventional 2D transducer); 3D: Three-dimensional; 3D matrix Real-time 3D transducer; 3Dms: 3D mechanically swept transducer;

Fig. 2

Boxplot of the differences in mL of the volume estimation measurements as compared to the reference value per transducer and measurement approach with corresponding p values

Fig. 3

Transversal (left) and sagittal (right) view of the nodule phantom during ablation with the three-dimensional (3D) matrix (real-time) transducer

Fig. 4

Ablation results using conventional two-dimensional (2D) and three-dimensional mechanically swept (3Dms) transducer guidance. The blue triangle indicates the danger triangle, free from ablation in the nodule and outside the nodule. The magenta colour in the body indicates an overablation outside the nodule

Fig. 5

Ablation results using 3D matrix guidance. The dashed line indicates the ablation needle orientation. The green circle indicates an area ablated closely to the edge with minimal ablation outside the target. The blue triangle indicates the danger triangle with zero ablation outside the target. The yellow circle indicates an edge of the nodule fully ablated as well as the area outside of the nodule showing ablation

Fig. 6

Boxplot of the nodule ablation coverages per transducer with corresponding p values

Fig. 7

Boxplot of the volume ablated outside the nodule per transducer with corresponding p values