Goetz Hannes Welsch MD, Presenter: Nothing to Disclose

Tallal Charles Mamisch MD, Abstract Co-Author: Consultant, Siemens AG

Vladimir Juras, Abstract Co-Author: Nothing to Disclose

Peter Baer, Abstract Co-Author: Employee, Siemens AG

Hiroyuki Fujita, Abstract Co-Author: President, Quality Electrodynamics LLC

Siegfried Trattnig MD, Abstract Co-Author: Nothing to Disclose

To compare signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of different anatomical structures within the knee joint at high (3T) and ultra-high fields (7T).

MRI of the knee joint was performed in 10 healthy volunteers at a 3T and a 7T whole-body system (Siemens) with an 8-channel knee coil (InVivo) at 3T and a new 28-channel knee coil (QED) at 7T. Sequence protocols consisted of a 2D proton-density turbo-spin-echo (PD-TSE), an isotropic 3D T1-weighted fast low-angle shot (FLASH) and an isotropic 3D steady-state free-precession (True-FISP) sequence. The sequences were adapted by two application specialists and a physicist to a 3T-protocol (18:29min.), a 7T-protocol with the same resolution and reduced acquisition time (“fast”) (7:20min.) and a 7T-protocol with higher resolution (~x2) and the same acquisition time (“high resolution”). SNR of cartilage, menisci, bone, fluid and muscle and CNR for cartilage/fluid, cartilage/bone, cartilage/meniscus, and meniscus/fluid was assessed. Due to known limitations of SNR measurements based on multi-channel coils and parallel-imaging, conventional SNR as well as non-uniformity (NU) assessment was performed. Analysis-of-variance was performed.

The trend of both SNR evaluations (conventional versus NU) was comparable, although parts of the results revealed differences. The mean SNR values, for all sequences and anatomical structures together, showed a significant increase of 57% (p<0.05) for the “high-resolution” protocol and an increase of 26% (p<0.05) for the “fast” protocol, compared to the 3T protocol. In between both 7T protocols, the “high-resolution” protocol revealed 28% higher results (p<0.05). The CNR evaluation showed clearly higher results for the “high-resolution” (115%; p<0.05) and the “fast” (80%; p<0.05) 7T protocol compared to the 3T protocol. The SNR improvement in between 3T and 7T was most pronounced for the PD-TSE sequence, the CNR improvement was highest for the FLASH sequence.

Through higher field strength and an optimal coil, resolution can be increased (x2) or acquisition time can be reduced (1/2), with still superior SNR and CNR values at 7T compared to 3T.

With newly available dedicated multi-channel coils for 7T MRI, “high-resolution” or “fast” imaging protocols of the knee joint are feasible and might base the first step in its clinical applicability.

Welsch, G, Mamisch, T, Juras, V, Baer, P, Fujita, H, Trattnig, S, MR Imaging of the Knee Joint: Comparison between 3 and 7 Tesla‚Initial Experience.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9012033.html