**5.1 Imaging**

Most clinicians would request thyroid ultrasound (US) and often isotope scanning is seldom available in India. Imaging tests are investigator dependant and hence experience and qualification of a person doing the test does matter, also matter is instruments used, hence a high-frequency linear probe should be used. GD is often, but not invariably, characterised by diffuse thyroid enlargement and by hypoechogenicity, both of which are assessed by ultra-sonogram and conventional grey scale analysis [20].

A colour-flow or power Doppler examination is characterised by vascular patterns and can quantify vascularity of thyroid [21]. Thyroid vascularity is significantly increased in severe Grave's disease and it typically shows a pulsatile pattern in thyroid gland which is called as "thyroid inferno" that is multiple small areas of increased intrathyroidal flow seen throughout the gland [22]. To measure accurately thyroid artery flow velocity and peak systolic velocity (PSV), it requires adjustments of pulse repetition frequency of wall filters and control of the insonation angle between 0 and 60°. The PSV is capable of differentiation between GD related thyrotoxicosis or amiodarone-induced thyrotoxicosis type 2, where the blood flow is reduced [23]. A typical US finding along with TRAB results can make diagnosis almost certain but thyroid scintigraphy is needed prior to Radioactive iodine ablation so that multinodular goitre can be differentiated [20].
