Fundmentls of Spine MRI nd Essentil Protocols A. C. Dougls-Akinwnde, MD Octoer 13, 2009 Fundmentls of Spine MRI Lerning Ojectives: 1. List the essentil sequences for Spine MRI exmintion 2. Discuss the importnce of ech sequence in mking dignoses 3. Understnd the indictions for contrst 4. Discuss how different MR imging prmeters ffect metl relted rtifcts 5. Discuss how different MR imging sequences nd techniques cn e implemented to reduce metl relted rtifcts. Outline A. Typicl sequences on Spine MRI 1. Sgittl nd Axil T1 2. Sgittl nd Axil T2 3. Sgittl STIR 4. Ax 3D vol GRE 5. Ft suppressed 6. 3-D Spce B. Medicl reson for ech sequence 1. Degenertive disese Ax T2 vs 3-D Vol GRE 3-d spce clinicl exmple t SPINE 2. Infection/Cncer contrst ft st Clinicl exmples C. Indictions for CONTRAST 1. Infections 2. Inflmmtory/ Autoimmune 3. Neoplsm 4. Prior surgery D. Trum 1. GRE 2. Ax Ft st T1 E. Specil circumstnces Metl hrdwre Typicl sequences Spine MRI Bck Pin Protocol Lumr Spine AX T1, T2 through disc spces Thorcic Ax T2 survey Cervicl Ax 3D vol GRE Ax T2 Typicl sequences on Spine MRI Axil T2 Must Answer Questions for ech cse: Is the Bone Mrrow signl norml? Is the lignment ntomic? Are the ony elements intct? Are the discs norml? Wht is the signl in the spinl cord? Is there cord compression? At ech level is there spinl cnl stenosis? neurl forminl stenosis? nerve root impingement? Wht is the cuse? Are the surrounding tissues norml? SAG T1 SAG T2 SAG STIR Axil T1 1
Essentil Elements: Sgittl T1 Bone mrrow signl nemi cncer Size of neurl formen Alignment Fcet Degenertive disese Sucute lood Essentil Elements: T2/ STIR Disc nnulr ter hydrtion Cortex of one frcture one ruise Size of spinl cnl STIR cord signl/ MS muscle normlity Ax disc hernition Nerve root impingement SAG T2 SAG STIR Norml Disc Degenertive Spine disese At ech level is there spinl cnl stenosis? neurl forminl stenosis? nerve root impingement? Wht is the cuse? Type 1: one mrrow edem Acute or su-cute inflmmtory chnges Is it degenertive disese or Infection discitis/ osteomyelitis?. Extrusion Sequestrtion Disc Hernitions: Disc Hernitions: Morphology Protrusion Focl Bse is <25% periphery of disc Brod-sed 2
Spine MRI Cncer / Infection Protocol Lumr Spine AX T1, T2 through disc spces Thorcic Ax T2 survey Cervicl Ax 3D vol GRE Ax T2 Gdolinium Ft suppressed SgT1 Ax T1 Cor T1 Mets with pthologic frcture nd cord compression Is the Mrrow signl norml? Pthologic frcture Cord compression Intrspinl Extrspinl enhncement On the T2 the normlity is centered in the one rther thn the disc thus discitis is less likely. DDX discitis osteomyelitis epidurl scess ut note no disc enhncement norml endplte nd drk signl of disc on T2. Spine MRI Cncer / Infection Evlution Leptomeningel metstsis Clumping of nerve roots Anorml enhncement Leptomeningel metstsis Axil T2 Pre contrst T1 Post contrst ft st T1 Axil T1 Prspinnl muscle normlity Intrmedullry neoplsm Are the surrounding tissues norml? Sg T2 T1 Post Gd T1 signl in the spinl cord? cord compression? DDX Neoplsm primry Mets Infectious myelitis Multiple sclerosis Trnsverse myelitis Infrction 3
Spine MRI: Trum Protocol Spine MRI: Trum Protocol Sgittl T1 Sgittl T2 Sgittl STIR Sgittl GRE Axil T1 Axil T2 No Contrst SAG T1 SAG T2 SAG GRE Acute epidurl hemtom C6-T1 cute epidurl hemtom gre GRE T2 Persistent pin or new symptoms my develop fter surgery requiring imging. However, evluting the spine of ptients with metllic hrdwre hs een limited y the lck of dignostic informtion in the vicinity of the hrdwre. On MRI, susceptiility rtifcts from the hrdwre oscure the djcent tissues However, MRI prmeters my e modified to reduce hrdwre relted rtifcts. Metl Artifct Fctors tht Influence Metllic Artifct Genertion Hrdwre Relted Fctors 1. Composition of the hrdwre 2. Position of the hrdwre in the min mgnetic field 3. Geometry of the hrdwre Figure 1: Axil TSE T2 weighted (TR/TE 3850/116) imge t L5-S1 shws severe susceptiility rtifct which mkes ssessment of the spinl cnl nd neurl formin impossile. Mgnetic Resonnce Imging 1. Locl Eddy currents in the hrdwre 2. Strength of the mgnetic field ( B0) 3. Slice thickness/ Sptil resolution 4. Receiver Bndwidth ( rbw) 5. Frequency encoding direction 6. Echo Time (TE) / Echo spcing 7. Sequence selection Prcticl Tips for minimizing Metl Artifcts: Hrdwre composed of titnium, prllel to B o, cylindricl, nd smll dimeter produces less rtifct. The frequency encoded direction should e chnged such tht it is NOT prllel to the ntomy of interest. Avoid GRE, or frequency selective ft suppression techniques, s they produce mssive signl voids. Avoid imging on 3T or greter scnners. Prcticl Tips for minimizing Metl Artifcts: Optimiztion of TSE sequences my e chieved y incresing the rbw, ETL, cquisiton mtrix nd y reducing the FOV, nd slice thickness. pulse sequences with optimized prmeters produce less rtifct thn TSE, or SE sequences. The dt set cn e re-processed fter cquisition to meliorte the extent of rtifct for etter evlution of criticl ntomy. 4
3-Dimensionl Turo Spin Echo (3-D TSE) 3-D TSE sequences employ long trin of multiple spin echoes which re generted y 180 O refocusing RF pulse. This refocusing RF pulse coupled with short echo spcing reduce the mount of spin dephsing tht occurs; consequently the mgnetic field inhomogeneity is reduced nd the susceptiility rtifct is minimized. In ddition, 3D sequences lso llow smller voxel size which reduces the intr-voxel dephsing. 3-D sequences re intrinsiclly more efficient thn 2-D cquisitions of multiple slices. Therefore the loss of SNR cn e compenste for y using smller voxel size nd higher ndwidth. (Smpling Perfection with Appliction optimized Contrst using different flip ngle Evolutions) is volumetric sequence in which the flip ngle of the refocusing RF pulse is modified to optimize the imge contrst nd minimize the RF power deposition (specific sorption rte (SAR)). This sequence genertes single primry isotropic dt set tht llows for the reconstruction of highresolution reformtted imges in ny desired plne. In ddition, the optimized vrile refocusing flip ngles reduce lurring which further minimize the rtifcts compred to conventionl TSE sequences with constnt flip ngles. Effect of Sequence on Susceptiility Artifct Figure 8: Sgittl () nd coronl () T2-weighted (Tr/Te 1500/146) sections from cquisition with rbw of,voxel dimensions of 3.2 3.2 0.9 mm 3. The rtifct ( ) from the titnium plte is miniml nd does not interfere with the evlution of the spinl cnl or djcent one. Note the excellent delinetion of the spinl cord, CSF, nd the disk/csf interfce. A centrl disk hernition ( )is noted t C4-5. SPACE results in mrkedly improved visuliztion of disk hernitions in the xil plne s well, together with the possiility for ssessment of the neurl formin in true cross section. Effect of Sequence on Susceptiility Artifct Figure 9 : Demonstrtes the difference in the ppernce of susceptiility rtifct using T2- weighted 2-D TSE T2 nd 3-D SPACE sequences. The imges were otined from 54 yer old femle with titnium intrpediculr screw t L4.. Sgittl TSE T2 weighted (Tr/Te 3000/105) imges otined with mtrix of 320 x 380 x 0.3 shows 2D TSE T2 : Re-processed with smller section thickness Sgittl T2 weighted imges otined from 54 yer old femle with titnium intr-pediculr screw t L4 shows the difference in susceptiility rtifct when the section thickness is 0.9mm () from the primry volumetric dt compred to the reprocessed imge with 0.3 mm (). With the higher sptil resolution, the rtifct is more defined nd Frequency encoded direction A P H-F 5