To the Editor:
We appreciate the opportunity to respond to the comments of Guermazi et al regarding our recent article (1) in the Journal of Magnetic Resonance Imaging.
The main results of the studies of Kopka et al ( 2) and Earls et al (3) were that the signal-to-noise and contrast-to-noise ratios were higher by using a power injector. We do accept that the peak enhancement percentage and slope in a contrast-enhanced dynamic MR study could be slightly different by using different injection methods. However, in our study, the enhancement percentage and slope showed no significant difference between the compression fracture and metastatic groups. It is the enhancement pattern (type AϳE) and especially the second part of the curve after the rapidly rising first part that is helpful in differentiating between benign and malignant lesions. In our results, the type D pattern (the early washout phenomenon) had a 100% specificity for malignant lesions. There is no evidence that a power injector will change the tissue enhancement pattern in comparison with a manual bolus injection.
There are several MR perfusion studies using the manual bolus injection method (4 -7). In those studies, Gd-DTPA was injected by hand within 2-4 seconds. Tsukamoto et al evaluated the marrow perfusion of the femoral head in a dog model by using manual injection of the contrast medium, which showed good correlation with a microsphere blood flow study (r ϭ 0.86) (4). In Verstraete's study (5), the correlation coefficient between enhancement slope and vascularization was 0.93; therefore, manual bolus injection could also be an acceptable method for evaluating tissue blood perfusion in those institutions that do not have a power injector.
We apologize for not picking up the mismatch type D case number in the final proofreading. There should be 13 type D cases, all belonging to the malignant group (groups III and IV) (the 18th line at the right aspect of page 311 was mistyped). The small number of cases limits our statistical significance; however, in combin-ing our experience with other studies (6,7,8), we believe that an early washout phenomenon is a specific perfusion pattern for malignant lesions, which is a useful sign in equivocal cases.