CMR [
30,
31], computed tomography (CT) [
32,
33], ultrasound [
34‐
36], and nuclear techniques [
37,
38] all offer alternative approaches to assess coronary artery disease noninvasively. By using sub-mm spatial resolution and analyzing the lumen cross-sectional area, CMR has been shown to have adequate resolution to detect coronary vasodilation to NTG in two prior studies [
12,
13]. CMR can also directly image the coronary wall, with increased wall thickness demonstrated in patients with Type I DM [
39] and non-obstructive CAD [
39,
40]. CT can provide high-resolution structural imaging of the coronary lumen and wall [
32], but the radiation and contrast involved make it suboptimal for serial imaging of coronary vasomotor changes. One recent study did look retrospectively at patients who had more than one coronary CT scan, where NTG was used in one and not in another, and did show significantly larger coronary diameter with NTG [
41]. The feasibility of transthoracic echocardiography for measuring epicardial coronary vasodilation has recently been shown in healthy men [
42]. The other main approach to assess coronary function noninvasively has been to measure coronary flow or perfusion reserve to a vasodilator stimulus (e.g., adenosine). This is primarily a measure of coronary
microvascular function in the absence of epicardial stenoses. This can be performed by CMR [
30,
31,
43], positron emission tomography (PET) [
37,
38], and transthoracic Doppler techniques [
34‐
36] and has been shown to be impaired in patients with coronary risk factors [
31,
38], including DM[
35,
38]. More data comparing the prognostic significance of epicardial vs. microvascular vasomotor function are needed.