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Thyroid / Parathyroids, Ultrasound, Elastography, Diagnostic procedure
A. Chandramohan, A. Deepak thomas , M. T. Manipadam, T. V. Paul; Vellore/IN
Methods and materials
This is an IRB approved prospective study.
Consecutive patients with primary hyperparathyroidism planned for parathyroid surgery and patients with solid thyroid nodules planned for thyroidectomy were recruited into the study after informed consent.
After B-mode ultrasound and colour Doppler,
ARFI elastography was performed on the solid or mixed solid and cystic parathyroid lesions and predominantly solid thyroid nodules.
Thyroid and parathyroid nodules with extensive calcification and predominantly cystic lesions were excluded.
Shear wave elastography using ARFI technology was performed using 9 MHz linear probe of Seimens S2000 ultrasound equipment. Shear wave velocity (SWV) was measured in meters/ second using virtual touch quantification (VTQ) soft ware.
A 6 x 5 mm sized region of interest (ROI) is placed in the parathyroid or thyroid lesion and five successful readings were recorded.
Figure 1 shows the ROI in the parathyroid lesion.
Definitive SWV was documented as the mean of these five readings.
Reading were obtained in quiet breathing unless patient was anxious and breathing related movement interfered with the test.
Interference from carotid pulsations was minimized by tilting the probe in a direction away from the carotids.
Values were obtained only from the solid portion of the lesion carefully avoiding cystic or calcified components of the nodules,
capsule of the lesion and the surrounding tissues.
In small parathyroid lesions the probe was tilted to obtain oblique images of the lesion which would fit the ROI within the lesion.
Values XXX m/s were considered incorrect: probably due to movement artifact,
too low or too high values in very soft or hard portions of the nodule beyond the range detectable by the soft ware.
Range of detectable SWV values consisted of 0.3 – 8.4 m/s.
Elasticity index (EI) was obtained using Asteria four point scale using virtual touch imaging (VTI) software.
(12) Stiffness of the lesion is displayed as shades of grey with light shade denoting a soft lesion and dark shade denoting a hard lesion.
EI of one was given to a lesion that is entirely soft; EI of two was given to nodules which were partly soft and same in size as the b-mode ultrasound image; EI of three was given to lesions which were partly hard and same in size as B-mode ultrasound; EI of four was given to lesions which were entirely hard and larger in size compared to its B-mode ultrasound image.
Apart from the EI the appearance of parathyroid and thyroid lesions on VTI was also noted.
Only patients with surgical histopathology were included for final analysis.
Appearance of the lesion on VTI,
SWV and EI of parathyroid and thyroid nodules were compared.
IBM SPSS Analytics 16.0 software (Chicago,
USA) was used for statistical analysis.
Continuous variables like age and mean SWV (m/s) of thyroid and parathyroid lesions were compared using Wisconsin rank sum test and categorical variables like elasticity index,
VTI appearance were compared using Chi square test.
ROC curve analysis was performed to assess the diagnostic performance of ARFI elastography in differentiating parathyroid and thyroid lesions and the best cut off value of SWV (m/s) which differentiates parathyroid and thyroid lesions was obtained.
positive predictive value,
negative predictive value and accuracy of VTI appearance,
EI and SWV in were calculated.