MRI may show a section of aortic narrowing seen above the level of the aortic valve, and it can be used in evaluation for stenosis of aortic arch vessels. Phase contrast imaging may be used to evaluate the gradient across the stenosis. MRI offers the best evaluation of LV function and degree of LV hypertrophy by evaluating myocardial mass. MRA findings are otherwise similar to those of CT. Long sedation times for cardiac MRI are a disadvantage but are often outweighed by many other imaging advantages.

An M mode echocardiogram may show supravalvular aortic narrowing.

Two-dimensional (2D) echocardiography using parasternal long-axis and short-axis views may show echoes at the superior margin of the sinuses of Valsalva with luminal narrowing. The aortic root diameter is greater than the ascending aorta diameter. Both hourglass and hypoplastic types may be seen. The internal diameter of the ascending aorta is less than 80 % of the internal diameter of the aortic ring.

Pulsed wave Doppler sequential evaluations of the left ventricular outflow tract and proximal aorta can show the origin of turbulent flow, indicating the location of the hemodynamically significant stenosis. Gradients greater than 75 mmHg on Doppler requires surgery. Note that the Doppler peak gradient tends to overestimate and has a poor relation to catheter-measured gradients.

Angiography will show a well-defined focus of intraluminal contrast narrowing above the level of the aortic valve in SVAS (hourglass shape). Angiography offers the gold standard for evaluating gradients across the stenosis. Stenosis of the peripheral pulmonary arteries and coronary arteries are also evaluated (Figs. 5.2 and 5.3), as can engorgement of the coronary arteries, which is produced by systolic pressure increases secondary to proximal aortic stenosis.

Because of increased risk of morbidity and mortality, predominantly in patients with coronary artery stenosis , cardiac catheterization should be done only when indicated. Patients with SVAS and gradients greater than 30–50 mmHg at catheterization require surgery. Pulmonary artery stenosis can include stenoses at the arterial branch points, peripherally. An end-hole catheter is used to detect the site of stenosis by utilizing the pressure gradient on pullback traces.

CT scans are the first-line imaging tool for William syndrome. CT information is often used to guide cardiac catheterization .

The differential diagnosis for Williams syndrome includes these disorders:

The general features of Williams syndrome include systemic arteriopathy secondary to a microdeletion of the ELN gene producing elastin haploinsufficiency. This is seen in addition to characteristic elfin facies , idiopathic hypercalcemia , cardiovascular disease, and cognitive impairment . Supravalvular aortic stenosis is the most common cardiovascular abnormality and is most commonly associated with the syndrome.