Duplex scan‐derived thyroid blood flow in euthyroid and hyperthyroid patients

Using a high‐resolution real‐time scanner to locate the superior thyroid artery (STA), the absolute blood flow has been measured with a pulsed Doppler flow meter. The diameter of the vessel and the angle of inclination of the ultrasound beam to the axis of the vessel were measured from the real‐time image and the blood flow then computed in the on‐board computer. Vessel diameter measurements were performed by the computer to 1/10 mm and all examinations were performed under identical conditions. In 24 randomly selected, clinically and biochemically euthyroid, preoperative, general surgical patients on no drugs (12 males, 12 females; age range, 18–65) the STA was located and blood flow measured in 46 arteries (96%). Mean blood flow was 18.3 ml/min ± 6.0 SD (range, 5.8–29.2). Bilateral measurements were made in 20 of 22 (5 males, 17 females; range 27–80 years) hyperthyroid patients. Mean blood volume flow was 73.0 ml/min±34.3 SD (range, 30–140), significantly higher (p < 0.01) than in the euthyroid group. No sex differences were seen. For euthyroid and thyrotoxic patients together, thyroid blood flow correlated with FT4 (r = 0.77,p <0.001), and, in the thyrotoxics, blood flow was significantly correlated with FT3 (r = 0.51,p <0.05), 4‐hr123I uptake (r =0.60,p <0.01), and 48‐hr123I uptake (r =0.63,p < 0.01), but not with FT4 (r = 0.40). The within artery coefficient of variation for volume flow was 17.4% for euthyroid subjects and 24.4% for hyperthyroid subjects. However, the mean comparable coefficient of variations for time‐averaged velocity were 9.2% and 13.8%, respectively. It is concluded that this noninvasive Duplex scanning method for measuring thyroid blood flow is accurate, reproducible, suitable for examining this parameter in relation to thyroid disease and drug effects, and may have a role to play in the management of patients with hyperthyroidism.