To the Editor.
—The article by Ladenson et al in the May Archives (1983; 143:1015-1017) concerning a sequestered substernal goiter notes that the substernal component failed to concentrate iodine 123 or Tc 99m. Neither of these radionuclides are appropriate imaging agents for substernal thyroid tissue. The relatively low-energy γ-radiations of these isotopes (technetium Tc 99m, 140 keV;123I, 159 keV) are not able to penetrate the bone of the manubrium and sternum to any substantial degree. Substernal goiters should be imaged with iodine 131 whose 364-keV γ-radiations are much more likely to successfully image substernal functional thyroid tissue.