Title: Are time‐intensity curves helpful in differentiating between benign vertebral compression fracture and vertebral metastasis?
Abstract: We read with interest the article by Chen et al (1) in the March 2002 issue of the Journal of Magnetic Resonance Imaging. The authors describe the use of blood perfusion of vertebral lesions with gadolinium-enhanced dynamic MRI in patients with acute benign compression fracture, chronic benign compression fracture, and metastatic disease with or without compression fracture. The introduction provides a comprehensive explanation of the blood perfusion technique with gadolinium-enhanced dynamic MRI and its application in several conditions, especially neoplasms. Nonetheless, a close reading of the article brings up two concerns. The first concern is whether or not one should use intravenous power injection as opposed to manual injection of contrast agent. In the “Materials and Methods—MRI” section, the authors indicate that contrast media was administered manually in each patient at the same injection rate. How can one ensure that the rate of bolus is constant and reproducible when it is injected manually? We are concerned about the rate of contrast injection, since the curves may vary as the rate changes. In a prospective study, Kopka et al (2) aimed to evaluate the optimization of injection rates with an automatic power injector versus manual injection for contrast-enhanced breath-hold three-dimensional MR angiography of the abdominal aorta and its branches. They demonstrated that the substantially larger SDs of the signal-to-noise ratios and contrast-to-noise ratios after manual injection can be explained by the difficulty in obtaining a reproducible and uniform rate of contrast flow, despite the efforts of an experienced contrast material administrator. They add that achieving a precise measurement of the test bolus is also more difficult, which might lead to improper timing of the diagnostic examination. Because a slower or faster injection rate leads to decreased qualitative and quantitative image quality, they concluded that the use of an automatic MR power injector is superior to manual injection of contrast material. In another study, Earls et al (3) aimed to determine the usefulness of the timing examination and MR power injector with breath-hold single-dose gadolinium-enhanced three-dimensional MR aortography. In 15 patients, an MR power injector was used and a timing examination was performed. In 15 other patients, manual injection was used and a timing examination was not performed. They also concluded that the combined use of power injector and a timing examination improve signal-to-noise ratios and contrast-to-noise ratios. The second, lesser concern is in regard to the statistical results. In the “Results—Patterns of Time Intensity Curves” section, the authors mention that all 12 type D curves (100%) were found in malignant groups (groups III and IV). However, Table 3 shows 11 patients from group III and two from group IV with type D curves. Which account is correct? Also in Table 3, there are four patients with type A curves found to have chronic benign compression fracture. Based on a specificity and positive predictive value of 100%, we may conclude that the type A curve—as the authors concluded for type D and E curves—is valuable in the diagnosis of chronic benign compression fracture. Finally, there is one substantial limitation to the study in general: the numbers for each type of curve are quite small. The two positive predictive values for the metastatic group and benign compression fracture group are only calculated on 13 and seven patients, respectively. Ali Guermazi MD*, Bachir Taouli MD*, Lynne S. Steinbach MD*, Harry K. Genant MD*, * Department of Radiology, University of California, San Francisco, California.