Thyroid nodules are extremely common with prevalence over 50% in autopsy specimens,
while only a small proportion are malignant (5-15%) [1].
Conventional ultrasound (US) is used widely as a first line imaging technique for thyroid evaluation [2,
3].
US is sensitive for detecting thyroid nodules and has utility for characterization as several conventional sonographic features are predictive of malignancy or benignity.
However,
its overall accuracy for malignancy is suboptimal as no single criterion is highly accurate,
while combining criteria increases the specificity at the cost of lowered sensitivity,
and vice versa [4].
In clinical practice,
nodules that are suspicious or indeterminate for malignancy on conventional US usually undergo fine-needle aspiration for cytology (FNAC),
which is minimally invasive and has a high specificity (>90%).
However,
FNAC is subject to interpretation errors,
is suboptimal for discriminating follicular lesions,
and up to 20% of FNACs are technically inadequate [5].
Even if FNAC were to be perfectly accurate,
judicious selection of suspicious nodules based on sonographic criteria is still required as it not cost-effective or ethical to biopsy every nodule detected in routine clinical practice.
Consequently,
there is still a need for an accurate and non-invasive diagnostic tool to detect thyroid malignancy.
Elastography refers to imaging techniques that evaluate tissue elasticity,
and can be performed using different imaging modalities including US.
A relatively recent refinement of US elastography called shear wave elastography (SWE) can estimate tissue stiffness in real-time and produces quantitative stiffness output in units of shear wave velocity (m/s) or estimated tissue stiffness (kPa).
Unlike an older and more extensively studied elastographic technique termed strain elastography,
SWE uses acoustic radiation impulses to mechanically stimulate tissues,
and does not require the operator to perform compression-decompression cycles for elastogram generation.
As a consequence,
SWE is reportedly relatively operator-independent,
i.e.
resistant to minor variations in operator practical technique.
Previous studies of SWE for thyroid nodules have documented generally optimistic accuracy results for detecting malignancy,
however,
the range of kPa values of benign and malignant nodules and optimum discriminatory cut-offs have varied considerably [6-9].
Unsurprisingly,
some investigators have questioned the reproducibility of elasticity measurement using SWE in the thyroid [10-11].
In this regard,
the amount of resting pressure,
i.e.
(pre)compression applied during SWE by the operator can influence SWE stiffness values,
and this phenomenon has been systematically evaluated in the liver and breast [12-13]. Furthermore,
there are sparse published biomechanical data from experiments on ex-vivo thyroidectomy specimens,
which suggests that different types of thyroid nodule vary in their rate of change in stiffness according to the resting pressure applied [14].
However,
to our best knowledge,
the effect of compression on SWE on thyroid tissue has not been evaluated in vivo in a systematic study.
The aim of this preliminary study was to evaluate the influence of variations in resting pressure applied by a transducer on SWE stiffness measurements of benign and malignant thyroid nodules and normal thyroid parenchyma.