Why Talk About Technique? MRI of the Knee: Part 1 - Imaging Techniques Mark Anderson, M.D. University of Virginia Health Sciences Center Charlottesville, Virginia Always had an interest teach our fellows practical bad image? why? can we improve it? UVA experience declining image quality We can t afford not to 1.5T Why Talk About Technique? Are we adding value? Prompt service Accurate diagnosis Quality imaging Anatomy / pathology Speak their language Why Talk About Technique? Image quality how to obtain how to maintain how to improve Protocol design better efficiency more consistency best possible images Technologists job? integral role only partial understanding Describe which MR pulse sequences are most useful for imaging the knee and why each is used Educational Objectives At the end of the presentation, each participant should be able to: Discuss the role of imaging hardware in obtaining high resolution MR images of the knee List some of the newer software options that may provide added benefit when scanning the knee. Pulse sequences Imaging planes Hardware field strength surface coils extremity scanners? Other options Protocol design Lecture Outline 1
Technique: Pulse Sequences Technique: Pulse Sequences T1 overall anatomy marrow specificity sensitivity T1 overall anatomy marrow (specificity) subacute hemorrhage fat (muscle atrophy) Include at least one non-fat saturated sequence Technique: Pulse Sequences FSE PD: blurring artifact Proton Density overall anatomy better SNR vs T1 menisci cartilage CSE TR: 2400 TE: 17 FSE TR: 4000 TE eff : 17 ETL: 16 Caution: blurring artifact Technique: Pulse Sequences Technique: Fat Saturation T2 fat saturation FS-T2 / STIR fluid / edema soft tissue injury Why? Increases dynamic range soft tissue marrow marrow pathology cartilage 2
Fat Saturation Fat saturation for marrow pathology Fat-Sat chemical FS freq selective FS Inversion recovery STIR SPIR SPAIR Fat Saturation Technique: Pulse Sequences FS-T2 Fat-Sat used with T1, PD, T2 better SNR vs STIR used with Gd (T1) heterogeneity Gradient Echo (T2*) STIR PVNS - good - hemosiderin - loose bodies Inversion Recovery Menisci Articular cartilage (3D) susceptibility effects GRE - bad marrow pathology STIR poorer SNR more homogeneous Technique: Articular Cartilage GRE T2* FSE T2 with fat sat Contrast MRI findings 3 cartilage joint fluid subchondral bone FS-T2, STIR, PD, GRE diffuse focal geographic, flap, fissure delamination?
Technique: Articular Cartilage Contrast cartilage joint fluid subchondral bone FS-T2, STIR, PD, GRE 2 weeks earlier MRI findings diffuse focal geographic, flap, fissure delamination? Kendall, AJR 2005 Technique: Articular Cartilage Technique: gadolinium Contrast cartilage joint fluid T2 Mapping Intravenous cystic vs. solid mass FS-T2 FS-T1 STIR subchondral bone FS-T2, STIR, PD, GRE infection inflammation MRI findings diffuse focal geographic, flap, fissure delamination? Newer Intraarticular off-label use meniscal healing osteochondral pathology DGEMRIC, T2 Mapping Tissues / Pulse Sequences Technique: Imaging Planes Menisci Tendons Ligaments Muscle Fluid Bone marrow Cartilage Short TE sequence (<20 msec) Proton density / gradient echo / (T1) Caution with FSE PD (blurring) FSE T2 with fat saturation Inversion recovery (STIR) FSE T2 with fat saturation Inversion recovery (STIR) T1 for specificity Don t use gradient echo Good contrast between fluid, cartilage and subchondral bone Advanced imaging techniques Sagittal menisci 50% tears seen on sag only cruciate ligaments cartilage trochlear groove tendons extensors 4
Technique: Imaging Planes Technique: Imaging Planes Coronal collateral ligaments menisci (bodies) 3% tears on cor only cartilage medial /lateral Axial patellofemoral cartilage retinaculae popliteal fossa ligaments menisci supplemental Technique: Imaging Planes Technique: Imaging Planes Oblique planes? 3D Imaging previously: thin slices non-isotropic voxels limited sequences Recently 3D acquisition isotropic voxels instant reconstructions any plane GRE,T1, PD, T2 SPACE, CUBE Hardware: field strength 0.2 0.5 1.0 1.5 3.0 + Hardware: field strength 0.2 0.5 0.6 1.0 1.5 3.0 + ultra-low low mid high ultra-high ultra-low low mid high ultra-high High field strength does not guarantee high quality images 3T 0.6T 0.7T Field strength? 1.5T 0.7T It is what it is Is it diagnostic? 5
SNR Resolution SNR Resolution MRI MRI SNR SNR Resolution Slice thickness Field of view Matrix NEX - Field strength Surface coil Hardware: surface coils Critical for image quality Phased array multichannel smaller coil elements improved SNR higher resolution faster scanning COIL EFFECT 1.5T STD 1.5T 8 CH 6
Hardware: extremity scanners? Extremity scanners Advantages cost siting requirements claustrophobia patient comfort Disadvantages extremities only - no shoulders / hips limited bore - larger patients Image Quality? Courtesy of William Morrison, M.D. Option: motion reduction Option: metal artifact suppression Patient comfort T2 FS w/ BLADE T2 FS Alphabet soup STIR WARP Software options MAVRIC BLADE / PROPELLER JET, RADAR uncooperative pts uncontrolled movements penalties increases acq time may limit matrix size MAVRIC SL SEMAC VAT Warp STIR PD Option: metal artifact suppression Option: metal artifact suppression - MARS Not GRE FSE sequences STIR (not fat sat T2) Increase BW Decrease voxel size (increase matrix) Align hardware B 0 Swap phase / freq - MARS Not GRE FSE sequences STIR (not fat sat T2) Increase BW Decrease voxel size (increase matrix) Align hardware B 0 Swap phase / freq GRE Toms, Clin Radiol 2010 Toms, Clin Radiol 2010 7
Option: metal artifact suppression Metal Artifact Suppression - MARS FSE GREPD - MARS T2 FSE STIR FSPD Not GRE Not GRE FSE sequences FSE sequences STIR (not fat sat T2) STIR (not fat sat T2) Increase BW Increase BW Decrease voxel size (increase matrix) Decrease voxel size (increase matrix) Align hardware B 0 Swap phase / freq Align hardware B 0 Swap phase / freq Toms, Clin Radiol 2010 Toms, Clin Radiol 2010 Knee MRI: protocol design Pulse Sequences meniscus short TE (PD, GRE) ligs / tendons T2-FS / STIR bone T2FS / STIR + T1 cartilage multiple options Other options motion? BLADE, etc metal artifact reduction Imaging Planes sagittal coronal axial 3D imaging Hardware surface coil phased array multichannel 8