Judy Shinyoung Choe MD, Presenter: Nothing to Disclose

Bonnie N. Joe MD,PhD, Abstract Co-Author: Nothing to Disclose

Benjamin M. Yeh MD, Abstract Co-Author: Nothing to Disclose

Mei-Hsiu Chen PhD, Abstract Co-Author: Nothing to Disclose

Aliya Qayyum MD, Abstract Co-Author: Spouse, Employee, Koninklijke Philips Electronics NV (Stentor)

Fergus Vincent Coakley MD, Abstract Co-Author: Nothing to Disclose

To investigate the role of a test bolus to determine the time to peak aortic enhancement and to optimize timing of the corticomedullary phase for renal MR imaging.

We retrospectively identified 74 patients (47 men, 27 women, mean age 58 yrs) who underwent dynamic enhanced renal MR imaging after a test bolus (2cc intravenous gadolinium-DTPA followed by 10cc saline injected at 2cc/s and monitored every second with a spoiled gradient echo T1 axial slice through the upper abdominal aorta). Time to peak aortic enhancement was determined for each patient from aortic signal intensity-time curves. Time to peak plus half injection duration was used as the scan delay for corticomedullary phase of MR enhancement. In the subset of patients (n = 19) with prior dynamic enhanced renal MR imaging performed using a fixed scan delay of 30 seconds, regions of interest were drawn over the renal cortex and medulla for both current and prior studies. A paired t-test was used to compare the corticomedullary signal intensity ratios between exams timed with a test bolus versus a fixed scan delay.

The average time to peak aortic enhancement was 25.7 seconds, but with wide variation between patients (standard deviation of 10.7 seconds, range of 11.5-62.4). Univariate and multivariate linear regression models were fitted for the time to peak aortic enhancement using age, weight, and gender as predictors, and showed the time to peak was positively correlated with patient age (p<0.05), but not with patient gender or weight. The ratio of cortical to medullary enhancement was significantly higher for images obtained with scan delays determined by a test bolus than for those obtained with a fixed scan delay (3.8 versus 1.7, p < 0.01).

The time to peak aortic enhancement at dynamic enhanced renal MR imaging is unpredictable, and arterial phase timing is best calculated by using a test bolus, as confirmed by improved corticomedullary differentiation with this approach as compared to a fixed scan delay technique.

We show that the role of test bolus timing should be expanded beyond MR Angiography to use in determining patient-specific MR scan delays for visceral organs.

Choe, J, Joe, B, Yeh, B, Chen, M, Qayyum, A, Coakley, F, Optimization of Corticomedullary Phase Enhancement at Renal MR Imaging: Test Bolus versus Fixed Scan Delay.  Radiological Society of North America 2006 Scientific Assembly and Annual Meeting, November 26 - December 1, 2006 ,Chicago IL. http://archive.rsna.org/2006/4439129.html