We appreciate the comments of Elstein et al and recognize their considerable experience in the evaluation, monitoring, and treatment of individuals with Gaucher disease. With respect to estimation of liver and spleen volume, they have demonstrated that organ volumes can be accurately estimated from linear ultrasound measurements. Despite their success with this modality, we believe there are important advantages to the use of MRI and CT for this purpose. Both MRI and CT provide more detailed information about parenchymal changes (eg, infarcts, fibrosis, scarring) in the liver and spleen, which are frequently observed in patients with Gaucher disease. Recognition of parenchymal lesions can be important for understanding subsequent changes in organ volume, the general progress of the disease, and the presence of other concurrent disorders. Magnetic resonance imaging and CT also enable accurate measurement of organ volumes when the organ contours are highly irregular and their shapes do not conform to the models used for converting linear measurements to volumes. Finally, while estimation of organ volume from ultrasound is reliable in their center, it is not clear how accurate or reproducible such estimations would be when performed in a variety of different centers by different technicians. As the authors note, ultrasound examination avoids repeated exposure to ionizing radiation, and for this same reason, and the superior resolution, we prefer MRI to CT, when it is available.