Arturo Cardenas-Blanco PhD, Presenter: Nothing to Disclose

Leonard Avruch MD, Abstract Co-Author: Nothing to Disclose

Mark E. Schweitzer MD, Abstract Co-Author: Nothing to Disclose

Richard Van der Jagt, Abstract Co-Author: Nothing to Disclose

Wael M. Shabana MD, Abstract Co-Author: Nothing to Disclose

Diffusion MRI assessment of lymphoma response to treatment has demonstrated a very strong correlation with PET. Lymphoma shows a significantly restricted signal on ADC maps. The precision of ADC measurement depends on the noise level and the selection of the b-values. The Cramer-Rao Lower Bound theory (CRLB) states that the variance of ADC values, can be estimated using the Fisher matrix. Thus our aim was to optimize the measurement of ADC, by minimizing its variance, using the Cramer-Rao Lower Bound theory to find the optimum b-values. 

A cohort of 16 patients with B cell lymphomas was evaluated. Diffusion weighted acquisition were acquired at 1.5T using following parameters: DW-EPI, TR/TE=870/78 ms, matrix=192x144, thickness= 10mm, b-vals= {0, 50, 100, 200, 400, 600, 800 s/mm^2}. The mean ADC values ranged from 0.5 e-3 to 2 e -3 mm^2/s. The CRLB algorithm was implemented to obtain the optimum 4, 6 and 8 b-value sampling to perform diffusion measurements within the given range.

The optimum 4, 6 and 8 b-values obtained using the CRLB algorithm were the following ones: b-vals(4)={0, 720, 720, 720}, b-vals(6)={0, 0, 430, 630, 630, 1370}, b-vals(8)={0, 0, 0, 515, 630, 630, 630, 1025}. The implementation of these b-values is followed by a reduction in the COV (ADC) of: 22% and 10% for the cases of 8 and 6 b-values respectively. In case of 4 optimum b-values there is a slight increase of 6% on the covariance (see attached graph). 

Optimized ADC measurement using 4 b-values could be achieved with an slight increase of the COV (6%) and reducing the acquisition time in 50% compared to 8 b values. A more conservative approach can be applied, by using 6 optimized CRLB b-values and decreasing the COV in 10% while reducing in 25% the total acquisition time.

Providing accurate ADC measurement in a clinically feasible acquisition time is a helpful strategy to standardize Diffusion MRI as a follow up tool for assessing treatment response.

Cardenas-Blanco, A, Avruch, L, Schweitzer, M, Van der Jagt, R, Shabana, W, Optimization of Diffusion Measurement in B Cell Lymphomas Using Cramer-Rao Lower Bound Theory.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12030221.html