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Abdomen: Diffusion-weighted MR Imaging with Pulse-triggered Single-Shot Sequences¹

¹ From the Department of Radiology, University of Bonn, Sigmund-Freud-Strasse 25, D-53105 Bonn, Germany (P.M., S.F., F.T., H.H.S.); and Philips Medical Systems, Best, the Netherlands (J.S.B., J.G.). Received June 27, 2001; revision requested August 16; revision received October 24; accepted December 10. P.M. supported by a BONFOR grant from the Medical Department of the University of Bonn. Address correspondence to P.M. (e-mail: muertz@uni-bonn.de).

View larger version (149K): [in a new window]   Figure 1. Scout image shows the section positions (1-4) that were used for the ADC measurements.

View larger version (19K): [in a new window]   Figure 2. Graph plots signal attenuation in the kidney versus trigger delay for diffusion-weighted MR images obtained with a b value of 400 sec/mm2. Mean values () and SDs (error bars) are depicted for eight repeated measurements for the same volunteer, with diffusion gradients in the S' direction. The relative signal intensity—SIk/SIw, where SIk is the signal intensity of the kidney and SIw is the signal intensity of water—is scaled to the value with a trigger delay of 600 msec.

View larger version (19K): [in a new window]   Figure 3. Graphs plot signal attenuation—ln(SIb/SI0), where SIb is the signal intensity on the diffusion-weighted MR image and SI0 is the signal intensity on the 0-b factor image—versus b factor for a region of interest placed in the kidney on diffusion-weighted MR images obtained without triggering (WOT) and with triggering (WT) with a trigger delay (Td) of 570 msec. Mean values () and SDs (error bars) are depicted for the pixels within the region of interest obtained in a single measurement, with diffusion gradients in the S' direction. ADCs are measured by means of linear regression to the relation ln(SIb/SI0) = -ADC x b. The trigger delay is the delay time for starting the sequence after the slope of the pulse wave is increased. Better linearity is demonstrated with triggering, which results in improved accuracy of ADC measurements.

View larger version (122K): [in a new window]   Figure 4. Diffusion-weighted MR images of the abdomen were obtained with single-shot spin-echo echo-planar sequences (left) without triggering and (right) with triggering with a trigger delay of 675 msec. Images were obtained in one volunteer, with diffusion gradients in the S' direction, and they depict section 3 (see Fig 1). The following b values were used in the acquisitions: first row, 50 sec/mm2 (sample regions of interest are outlined); second row, 700 sec/mm2; and third row, 1,300 sec/mm2. In the fourth row, ADC maps are shown. Improved quality of diffusion-weighted MR images and resulting ADC maps is seen with triggering. On all diffusion-weighted MR images and particularly on the ADC maps, liver, spleen, and kidney appear much more homogeneous and complete.

View larger version (24K): [in a new window]   Figure 5. Bar charts show (left) mean ADCs and (right) SDs of three repeated measurements for all 12 volunteers on MR images obtained without triggering (WOT) and with triggering (WT) at the optimum trigger delay. Data were obtained in the region of interest placed in the spleen in section 4 (see Fig 1), with diffusion gradients in the S' direction. The range of the mean ADCs and SDs is much smaller with triggering than without it. Mean ADCs with triggering, 52-76 x 10-5 mm2/sec, and without triggering, 51-162 x 10-5 mm2/sec. SDs with triggering, 1-14 x 10-5 mm2/sec, and without triggering, 2-86 x 10-5 mm2/sec.