José Raya MSc, Presenter: Nothing to Disclose

Olaf Dietrich, Abstract Co-Author: Nothing to Disclose

Michael Paul Recht MD, Abstract Co-Author: Nothing to Disclose

Christian Glaser MD, Abstract Co-Author: Nothing to Disclose

To demonstrate the feasibility of in vivo diffusion tensor imaging (DTI) of knee articular cartilage with a line-scan diffusion tensor imaging (LSDTI) sequence in a 7T-scanner using a dedicated knee coil. Line-scan diffusion tensor imaging (LSDTI) is a spin-echo based sequence, where only one line is excited and acquired per repetition time avoiding phase encoding (i.e. motion artefacts) and reducing acquisition time. LSDTI suffers from intrinsically low SNR, so that the combination of 7T with dedicated multi-element coils may make LSDTI suitable for in vivo cartilage imaging.

Eight knees (healthy volunteers) were imaged twice on a whole-body 7T scanner using a birdcage transmit, 28-Ch receive knee coil (QED, Cleveland OH) and a FS LSDTI sequence (TE/TR/TReff=45/220/3080 ms, matrix=256×112, FOV=154×67 mm², rotation angle=20°, b-values=10,450 mm²/s, 6 directions, 2 averages, thickness=2 mm, bandwidth=450 Hz, 3 dummy scans, acquisition time=3:03 min per axial slice over the patellar cartilage . ADC and FA maps and their mean values for cartilage, synovial fluid and muscle were calculated. SNR was calculated in the b0 image (difference method). Intraindividual variability was assessed by RMSQ of the coefficient of variation (COV). b0 image quality was rated from 1 to5.

b0 image rating was 3.8 indicating good overall LSDTI image quality. SNR was 25 in cartilage, 38 in muscle and 64 in synovium. ADC/FA values were respectively (1.3±0.4) 10-³ mm²/s / (0.2±0.2) for cartilage, (1.3±0.2) 10-³ mm²/s / (0.3±0.1) for muscle and (2.9±0.3) 10-³ mm²/s / (0.1±0.2) for synovium. ADC decreased from the articular surface (1.6±0.3) 10-³ mm²/s to the bone-cartilage interface (0.8±0.4) 10-³ mm²/s. FA increased form the surface (0.1±0.1) to the deep radial zone of the cartilage (0.6±0.3). Mean COV of ADC / FA were 20.6%/10.3% (cartilage), 12.5% 23% (muscle) and 9%/12% (synovium).

For a first time in vivo acquisition of cartilage DTI data providing high image quality become feasible using a line scan approach and combining 7T with a multi-array coil. In vivo ADC and FA are consistent with published ex vivo results.  

This pilot project may prepare the way for DTI as a new imaging biomarker to assess cartilage degradation in vivo.

Raya, J, Dietrich, O, Recht, M, Glaser, C, In Vivo DTI of the Knee at 7 T Using a Dedicated Birdcage Transmit, 28-channel Receive Knee Coil: First Results.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9015207.html