Adam Braithwaite MD, Presenter: Nothing to Disclose

Brian M. Dale MD, Abstract Co-Author: Employee, Siemens AG

Elmar Max Merkle MD, Abstract Co-Author: Speakers Bureau, Siemens AG Speakers Bureau, General Electric Company Consultant, Schering AG (Berlex Inc) Consultant, Bracco Group Research support, Schering AG (Berlex Inc) Research support, Bracco Group Research support, GlaxoSmithKline plc Research support, Pfizer Inc Stockholder, Siemens AG Stockholder, General Electric Company

Daniel Tobias Boll MD, Abstract Co-Author: Nothing to Disclose

To determine the effect of field strength and b-value on ADC measurements in various abdominal tissues with DWI.

20 volunteers were imaged at 1.5 T and 3 T (MAGNETOM Avanto and Tim Trio, Siemens) using body array coils for signal reception. A standardized protocol was used at both field strengths. The volunteers were examined in random order on the same day with a time between scanners of less than 30 minutes. DW images of the abdomen were acquired axially using a free breathing technique with a trace b-value of 0/400. In addition, a series was performed at b-value 0/400 in 3 orthogonal directions and with trace b-values of 0/50 and 0/50/400/800. ADC maps were generated automatically for each DWI series. ADC values were measured using 3 separate regions of interest (ROI) in the posterior right hepatic lobe, pancreatic head, body, and tail, and spleen. These measurements were performed in an identical fashion on all DWI datasets per field strength for each location. The data were analyzed with GLM statistics (General Linear Model) in a multi-factor repeated-measures design. Wilks’ Lambda was used to test the null hypothesis that the various b-values and field strengths have no influence on the ADC values.

One subject had no pancreatic tail and was excluded from the analysis. The ADC values were significantly higher (p<0.001) at 3 T than at 1.5 T. The b-400 trace was not significantly different (p=0.192) from the b-400 in 3-orthogonal directions, but both were significantly different from the b-50 and b-800 (p<0.001) with the lower b-values yielding higher mean ADC values. The pancreatic head was not significantly different (p=0.325) from the pancreatic tail, but all other tissues were significantly different from each other (p<0.001).

DWI measurements are not pure measurements of ADC as values are significantly influenced by variations in field strength and b-values. This is particularly evident at 3 T leading to significantly higher ADC values for 3 T than 1.5 T for abdominal tissues.

This is of importance for quantitative analysis of DWI during follow up studies e.g. the quantitative analysis of liver fibrosis or chronic pancreatitis.

Braithwaite, A, Dale, B, Merkle, E, Boll, D, Effect of Field Strength and b-Value on Apparent Diffusion Coefficient Measurements in Diffusion-weighted Imaging of the Abdomen at 1.5 and 3 Tesla.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5013887.html