Job Aid MR Scanning Parameters

Parameter Scanning MRI Wahyu Widhianto Magnetic Resonance MR Triangle MAGNETOM Sola 2 Restricted © Siemens Healthineers, 2020 MR Triangle SIEMENS Healthineers In MRI, each parameter that we modify Relative Signal-to-Noise will affecting • Signal to Noise • Time Acquisition • Voxel size Our goal is to adjust it according to clinical situation or balance this three Time Acquisition Scan time Voxel size Resolution 3 Restricted © Siemens Healthineers, 2020 Relative Signal to Noise Ratio (relSNR) SIEMENS Healthineers A B Relative SNR comparing SNR from one image to other, or ratio. Some vendor describe the value in percentage some other in decimal. Let’s say image A has SNR 40 and image B has SNR 70, SNR ratio image A to B is 40Τ70 = 0.57 SNR ratio image B to A is 70Τ40 = 1.75 A B Saved protocol always has SNR 1 SA Difference in signal SA Difference in signal SB A B A B 4 Restricted © Siemens Healthineers, 2020 Relative Signal to Noise Ratio (relSNR) SIEMENS Healthineers 0.8 0.9 1 0.4 0.6 0.7 5 Restricted © Siemens Healthineers, 2020 Relative Signal to Noise Ratio (relSNR) SIEMENS Healthineers 0.8 1 0.9 1.1 1.2 1 0.4 0.6 0.6 0.8 0.9 0.7 6 Restricted © Siemens Healthineers, 2020 Spatial resolution MAGNETOM Sola 7 Restricted © Siemens Healthineers, 2020 Spatial resolution SIEMENS Healthineers A B Spatial resolution in radiology refers to the ability of the imaging modality to differentiate two objects. Low spatial resolution techniques will be unable to differentiate between two objects that are relatively close together. Spatial resolution determines how "sharp" the image looks. In MRI, spatial resolution is defined by the size of the imaging voxels Image B has smaller voxel size than B, hence image B looks sharper. 0.9x0.9x3mm 0.4x0.4x3mm 8 Restricted © Siemens Healthineers, 2020 Spatial resolution SIEMENS Healthineers Voxel size determined by pixel size and slice thickness. Pixel size itself determined by the size of imaging Field of View (FOV) divided by the number of imaging matrix - Pixel Pixel size = FOV - -- - Voxel Matrix size - 9 Restricted © Siemens Healthineers, 2020 Scan time MAGNETOM Sola 10 Restricted © Siemens Healthineers, 2020 Scan time SIEMENS Healthineers 180º 90º Image acquisition started with 90˚ RF excitation pulse and repeated with specific Time Repetition (TR). FID Before an image is reconstructed each signal need to be “stored” in k-space until all phase echo resolution line filled. This process may be repeated in to more than TE= 2T one number of acquisitions if needed to increase TR the signal to noise ratio. Ky 1 2 kx Measurement time = phase resolution x x TR (repetition time) x number of acquisitions 11 Restricted © Siemens Healthineers, 2020 Scanning parameters MAGNETOM Sola 12 Restricted © Siemens Healthineers, 2020 Scanning parameter SIEMENS Healthineers 1. “MR triangle” indicator TA: 2:50 PM: REF Voxel size: 0.7x0.7x5.0mm Rel. SNR: 1.00 se 1 • TA : Time Acquisition Routine Contrast Resolution Geometry System Physio Inline Sequence 2 • Voxel size (mm) Slice group FoV read 230 mm • Slices 24 FoV phase Rel. SNR 100.0 % Dist. factor 30 % Slice thickness 5.0 - mm 2. Scanning parameter Position Isocenter TR 500.0 group card ms Orientation Sagittal TE 3 8,9 ms 3. Scanning parameter Phase enc. dir. A >> P Averages AutoAlign Head > Basis Concatenations Phase oversampling 30 Filter Normalize, Elliptica Coil elements BC 13 Restricted © Siemens Healthineers, 2020 Scanning parameter SIEMENS Healthineers Routine Contrast Resolution Geometry System Physio Inline Sequence Routine card Slice group 1 FoV read 230 mm 1. FoV read 7 Slices 24 2 FoV phase 100.0 % 2. FoV phase 8 Dist. factor 30 % 3 Slice thickness 5.0 : mm 3. Slice thickness Position Isocenter 4 TR 500.0 ms 4. TR Orientation Sagittal 5 TE 8.9 ms 5. TE Phase enc, dir. A>> P 6 Averages 6. Averages AutoAlign Head > Basis Concatenations 7. Slices 9 Phase oversampling 30 % Filter Normalize, Elliptica ... 8. Distance factor Coil elements BC 9. Phase oversampling 14 Restricted © Siemens Healthineers, 2020 Scanning parameter SIEMENS Healthineers Routine Contrast Resolution Geometry System Physio Inline Sequence Resolution card Common Filter Image Filter Rawdata 10. Base resolution FoV read 230 mm 11. Phase resolution FoV phase 100.0 % Slice thickness 5.0 mm 10 Base resolution 320 11 Phase resolution 80 % Phase partial Fourier Off Interpolation 15 Restricted © Siemens Healthineers, 2020 Scanning parameter SIEMENS Healthineers Routine Contrast Resolution Geometry System Physio Inline Sequence Sequence card – part 1 Part 1 Part 2 Assistant 12. Bandwidth (Hz/px) Introduction Contrasts 12 Bandwidth 150 : Hz/Px Multi-slice mode Interleaved Asymmetric echo Allowed 16 Restricted © Siemens Healthineers, 2020 Scanning parameter SIEMENS Healthineers Routine Contrast Resolution Geometry System Physio Inline Sequence Sequence card – part 2 Part 1 Part 2 Assistant 13. Turbo factor Define Turbo factor RF pulse type Normal 13 Turbo factor 17 Gradient mode Normal Echo trains per slice 21 WARP Phase correction Automatic Acoustic noise reduction None Red. EC sensitivity 17 Restricted © Siemens Healthineers, 2020 Scanning parameter SIEMENS Healthineers No Parameters Action SNR Voxel Time size Lets fill this table, with acq. 1 FoV read arrow : 2 FoV phase Increase 3 Slice thickness 4 Time Repetition (TR) 5 Time Echo (TE) Decrease 6 Averages Constant 7 Slices 8 Distance factor 9 Phase oversampling 10 Base resolution 11 Phase resolution 12 Bandwidth 13 Turbo factor 18 Restricted © Siemens Healthineers, 2020 Modifying parameter SIEMENS Healthineers TA: 3:02 PM: REF PAT: 2 Voxel size: 0.5x0.5x5.0mm Rel. SNR: 1.18 : tseR When modifying parameter Routine Contrast Resolution Geometry System Physio inline Comience a. Can type a number or Slice group 1 Fol a 250 press up/down button. Slices 20 FoV phase b. Color bar shown Dist. factor 30 % Slice thickness 5.0 mm informed minimum and Position Isocenter TR 4000.0 ME maximum possible value Orientation Transversal TE 194 ms and current value. Green Phase enc. dir. R>> L Averages bar indicate changing AutoAlign Concatenations value in this range would Phase oversampling 0 % Filter Prescan Normalize ... not effect other Coil elements HL;HU parameter, but red will. b 250 92 450 210 19 Restricted © Siemens Healthineers, 2020 FoV read (mm) SIEMENS Healthineers TA: 3:02 PM: REF PAT: 2 Voxel size: 0.5x0.5x5.0mm Rel SNR: 1.18 TA: 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel SNR: 1.00 FoV read 230 FoV read 250 Increase FoV read • TA : Constant • Voxel size : increase • Rel. SNR : increase 20 Restricted © Siemens Healthineers, 2020 FoV read (mm) Increasing the FoV read while maintain all parameters unchanged, make the anatomy covered is larger but the voxel size getting bigger. More signal but less “sharp” Original FoV Increasing FoV 21 Restricted © Siemens Healthineers, 2020 FoV read (mm) Increasing the FoV read while maintain all parameters unchanged, make the anatomy covered is larger but the voxel size getting bigger. More signal but less “sharp” Original FoV Increasing FoV 22 Restricted © Siemens Healthineers, 2020 Scanning parameter SIEMENS Healthineers No Parameters Action SNR Voxel Time size Lets fill this table, with acq. 1 FoV read 1 arrows : 2 FoV phase Increase 3 Slice thickness 4 Time Repetition (TR) 5 Time Echo (TE) Decrease 6 Averages Constant 7 Slices 8 Distance factor 9 Phase oversampling 10 Base resolution 11 Phase resolution 12 Bandwidth 13 Turbo factor 23 Restricted © Siemens Healthineers, 2020 FoV phase (%) SIEMENS Healthineers TA: 2:30 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 0.87 TA 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Decrease FoV phase • TA : decrease • FoV phase 90,6 FoV phase Voxel size : constant • Rel. SNR : decrease 24 Restricted © Siemens Healthineers, 2020 FoV phase (%) Decrease FoV phase will resulted rectangular FoV instead of square. Ky The scan time is decrease because less k-space line 256 filled. And decrease SNR. Since the FoV may be smaller than the anatomy aliasing 256 Kx artifact may be occur 3 1 128 Phase Decrease FoV phase Less k-space line 25 Restricted © Siemens Healthineers, 2020 FoV phase (%) Decrease FoV phase will resulted rectangular FoV instead of square. The scan time is decrease because less k-space line filled. And decrease SNR. Since the FoV may be smaller than the anatomy aliasing artifact may be occur Square FoV Rectangular FoV 100% FoV phase Decreasing FoV phase 26 Restricted © Siemens Healthineers, 2020 Slice thickness (mm) SIEMENS Healthineers TA: 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x3.0mm ReL SNR: 0.60 TA 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Decrease slice thickness • TA : constant • Voxel size : decrease • Rel. SNR : decrease Slice thickness 5.0 Slice thickness 27 Restricted © Siemens Healthineers, 2020 Time repetition (ms) SIEMENS Healthineers TA: 2:56 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 TA 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Decrease Time repetition • TA : decrease • Voxel size : constant • Rel. SNR : constant TR 4000.0 TR 3870.0 28 Restricted © Siemens Healthineers, 2020 Time Repetition Time Repetition effect on “MR Triangle” happen indirectly Mz and would not shown in the User Interface. TR and TE will effecting image contrast. Δ Signal From the graph, if we change the TR from 3000 to 500 the signal intensity of the tissue is not fully relaxed yet and has lower intensity. 500 3000 TR [ms] 29 Restricted © Siemens Healthineers, 2020 Time echo (ms) SIEMENS Healthineers TA: 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel SNR: 1.00 TA 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Decrease Time echo • TA : constant • Voxel size : constant • Rel. SNR : constant TE 94 TE 115 30 Restricted © Siemens Healthineers, 2020 Discussion – Time Repetition Time Echo effect on “MR Mxy Triangle” happen indirectly and would not shown in the User Interface. TR and TE will effecting image contrast. From the graph, if we change the TE from 15 to 120 the signal intensity of the tissue is decaying, and has lower intensity. Δ Signal 15 60 90 120 TE [ms] 31 Restricted © Siemens Healthineers, 2020 Averages SIEMENS Healthineers TA: 1:34 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 0.71 TA 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Decrease Averages • TA : decrease • Voxel size : constant • Rel. SNR : decrease Averages Averages 32 Restricted © Siemens Healthineers, 2020 Discussion – Averages Ky Averages (AVG/NEX), defined k-space Image space how many times the data will be acquired, it will increase the time acquisition but since Kx more signal is collected hence SNR will increase. 256 Fourier transform 256 + Fourier transform 33 Restricted © Siemens Healthineers, 2020 Discussion – Averages A B Image A : 1 averages Image B : 2 averages Image B looks better because less grainy. But the san time is doubled 34 Restricted © Siemens Healthineers, 2020 Averages More averages also mean more data in the center of k-space and less motion artifact. 2 Averages 4 Averages 35 Restricted © Siemens Healthineers, 2020 Slices SIEMENS Healthineers TA: 3:39 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel SNR: 1.00 TA 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Increase Slices • TA : increase (if TR Slices 20 Slices 25 changes) • Scan Assistant Voxel size : constant x • Rel. SNR : constant Your last change Slices 20 25 will adapt the following parameters: TR 4000 4840 ms 36 Restricted © Siemens Healthineers, 2020 Distance factor (%) SIEMENS Healthineers TA: 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel SNR: 1.00 TA 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Decrease Distance factor • TA : constant • Voxel size : constant • Rel. SNR : constant Dist. factor Dist. factor 10 37 Restricted © Siemens Healthineers, 2020 Distance factor (%) SIEMENS Healthineers Ideal slice profiles Actual slice profiles cross-talk http://www.mri-q.com/cross-talk.html 38 Restricted © Siemens Healthineers, 2020 Phase oversampling (%) SIEMENS Healthineers TA: 4:38 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR. 1.22 TA 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel SNR: 1.00 Increase Phase oversampling • TA : increase • Voxel size : constant • Rel. SNR : increase Phase overs ampling Phase oversampling 50 39 Restricted © Siemens Healthineers, 2020 Aliasing Phase encoding aliasing can only be eliminated by increasing the effective FOVPE for the scan. This may be accomplished either by increasing the FOVPE or by increasing the phase encoding oversampling. Source : M Dale et.al, MRI Basic Principles and Applications 256 256 512 Sumber: Brown and Semelka, 2003 hal 118 40 Restricted © Siemens Healthineers, 2020 Base resolution SIEMENS Healthineers TA: 2:46 PM: REF PAT: 2 Voxel size: 0.5x0.5x5.0mm Rel. SNR: 1.22 TA: 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Decrease Base resolution • TA : decrease • Voxel size : increase • Rel. SNR : increase Base resolution 512 Base resolution 448 41 Restricted © Siemens Healthineers, 2020 Discussion – Base resolution Y Y On the sample, with higher base resolution the matrix size is bigger, when the FoV is keep unchanged the voxel became smaller make the images sharper, but mind the SNR which is decrease. 256 X 512 X 42 Restricted © Siemens Healthineers, 2020 Artifacts: Edge oscillations Phase resolution (%) SIEMENS Healthineers Recon.: 0.45x0.45x5.00 mm TA: 2:30 PM: REF PAT: 2 Acq.: 0.75x0.45x5.00 mm Rel. SNR: 1.12 TA 3:02 PM: REF PAT: 2 Recon.: 0.45x0.45x5.00 mm Rel. SNR: 1.00 Acq.: 0.60x0.45x5.00 mm Decrease Phase resolution • TA : decrease • Voxel size : increase • Rel. SNR : increase Phase resolution 75 Phase resolution 44 Restricted © Siemens Healthineers, 2020 Phase resolution (%) SIEMENS Healthineers Y Ky 128 128 Kx x 256 256 45 Restricted © Siemens Healthineers, 2020 Bandwidth (Hz/px) SIEMENS Healthineers TA: 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 0.87 TA: 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Increase Bandwidth • TA : constant • Bandwidth Voxel size : constant Bandwidth 191 250 • Rel. SNR : decrease 46 Restricted © Siemens Healthineers, 2020 Bandwidth se_15b130 Sequence Timing Diagram 1808 Signal is being sampled at 90ª RF 2.56 ms 2.58 ms 7.68 ms defined Time Echo with SL sampling time (Ts), in the RE picture Ts shown 7.68 ms TE = 15 ms PH - 7.68 ms ECHO TE/2 SAMPLING (ADC-on interval) D 30 us Ts Ts 47 Restricted © Siemens Healthineers, 2020 Bandwidth Bandwidth Higher the bandwidth shorter the Time sampling. High The effect in image quality is : • SNR decrease due lo less signal acquired Medium • Less susceptibility artifact • Less metal artifact Low 48 Restricted © Siemens Healthineers, 2020 Chemical Shift SIEMENS Healthineers TSE, T2-Contrast. The fat-image is shifted with respect to the water-image in readout-direction running left - right 49 Restricted © Siemens Healthineers, 2020 Distortions – Image Examples 2- single shot EPI RF GF Gp T* FID TEeff 50 Restricted © Siemens Healthineers, 2020 Single Shot Technique - EPI SIEMENS Healthineers Read out Gradient (GF) is switched GRE KY ky in bipolar fashion. Within the FID EPI Conventional Meandering entire k-space lines are filled. 1 Because the FID relatively short 2 2 (100 ms), the matrix for EPI is 3 limited from 64 to 256 kx kx 128 51 Restricted © Siemens Healthineers, 2020 Turbo factor SIEMENS Healthineers TA: 4:06 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 TA: 3:02 PM: REF PAT: 2 Voxel size: 0.4x0.4x5.0mm Rel. SNR: 1.00 Decrease Turbo factor • TA : increase • Turbo factor 17 Turbo factor 13 Voxel size : constant • Rel. SNR : constant 52 Restricted © Siemens Healthineers, 2020 Turbo factor SIEMENS Healthineers S S 20 TF 11 TF 53 Restricted © Siemens Healthineers, 2020 Scanning parameter SIEMENS Healthineers No Parameters Action SNR Voxel Time size Lets fill this table, with acq. 1 FoV read arrow : 2 FoV phase Increase 3 Slice thickness 4 Time Repetition (TR) 5 Time Echo (TE) Decrease 6 Averages Constant 7 Slices 8 Distance factor 9 Phase oversampling 10 Base resolution 11 Phase resolution 12 Bandwidth 13 Turbo factor 54 Restricted © Siemens Healthineers, 2020 SIEMENS Healthineers Thank You