To the Editor.
—The MIDAS study by Dr Borhani et al1 uses high-resolution ultrasound to determine the thickness of carotid artery intima as a marker for progression of atherosclerosis. However, the type of ultrasound probe used and its frequency were not defined in the protocol. The measurements were reported to the nearest 0.01 mm, but the statistical analysis and results reported data to the third decimal place. Moreover, I have trouble believing their report on the basis of the physics of ultrasound probes now commercially available. Axial resolution of ultrasound probes is related to the frequency of the probe; the maximum resolution for 7.5-to 10-MHz probes is reported to range ±0.2 mm and for 5-MHz probes ±mm.2 For a 2-cycle system, the resolution is 1.54 divided by the frequency in megahertz. Therefore, the data analysis and results of this study may well overstate the ability of current
Kaufman JL. The Multicenter Isradipine Diuretic Atherosclerosis Study (MIDAS). JAMA. 1997;277(4):297. doi:10.1001/jama.1997.03540280035023