MR Image Quality Cognizance

SIEMENS Healthineers MR Image Quality & Artifacts Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Page 1 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Understand Image Quality SIEMENS Healthineers ⋅Image quality is a key parameter in MR imaging. ⋅Always there is a trade-off between IQ and Scan time. ⋅ The goal is to optimize image quality in relation to the scan time Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 2 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Pulse sequence to Image SIEMENS Healthineers 90° 180° 90° ⋅This ends just one of the RF MA-number of Fourier lines that are required for the - - GS 22 image. The next line begins GR at the repetition time TR. ?? Both TE and TR are - - - - GP sequence parameters that - - influence the image MR contrast. FID Spin echo FID - - TE TR Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 3 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 k-space SIEMENS Healthineers 90° kz 180° ⋅The echo is saved in a RF temporary storage called the raw data memory. For every GS phase encoding step a spin GR ky echo is created and stored in the raw data matrix. The GP phase encoding gradient amplitude determines the k- MR number and thus its position raw data in the k-space FID spin echo in k-space Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 4 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 From Raw Data to Image Data SIEMENS Healthineers kz z ky 2D FT y raw data in the k-space Image data ⋅The measured data (raw data) are Fourier transformed into the image data. ⋅Every raw data value in the acquired k-space contributes to every pixel in the image! ⋅I.e., every pixel in the image is influenced from every raw data point in the k-space! Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 5 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 What are we trying to optimize ? SIEMENS Healthineers ⋅ Contrast ⋅ Signal ⋅ Noise Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 6 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Contrast SIEMENS Healthineers SA Difference in signal ------- Relative difference in the signal strength between two adjacent tissue type. SB In Other words, Contrast is equal to the difference in signal: Contrast Contrast = Difference in signal = SA - SB Contrast Resolution is the ability to distinguish differences in grayscale colors of adjacent structures Image comparison: Low T1-contrast (left), high T1-contrast (right) Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 7 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Signal SIEMENS Healthineers Noise MR signal in MRI is produced by the process of resonance, which is the result of radiofrequency coils. Signal Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 8 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Noise SIEMENS Healthineers Noise A signal from un wanted area Noise is undesired signal resulting from the MR system, the environment and the patient. Signal It Occurs at all frequencies and randomly in time. Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 9 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 SNR SIEMENS Healthineers It is ratio between signal and noise in an MR Image. Signal SNR = Noise A higher SNR means a less grainy image. Image comparison: The two images on the left were acquired in the same way and subsequently subtracted from one another (= pixel-by-pixel difference in gray values). What remains is background noise (on the right). Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 10 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Signal to Noise SIEMENS Healthineers S/N is determined by: mr10613 Harmony Anonymous MR 2002B STUDY 1 6/1 9/06 ⋅voxel volume 5:29:20 PM 2 IMA 2/1 ⋅used receiver coils An improper selection of matrix vs field of view ⋅TR, TE, TI, flip angle, bandwidth per pixel ⋅number of measurements (phase- 0cm encoding steps, averages) MF 1.00 TI 120.0 TR 2500.0 TE 73.0 E ⋅field strength TA 01:37*2 BW 130.0 SP R9.2 SL 4.0 MIND FoV 300*300 A1/R/SAT1 256*512s SP3,4,5 Sag tir2d1 11 /180 W 642 251 Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 11 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Signal to Noise – Coil Size SIEMENS Healthineers ⋅ Most noise is thermal noise originating Body Coil Large Flex Coil Shoulder Shoulder Avanto 111 MR B13 in the patient and picked up by the STUDY 3 STUDY 3 HFS 15/09/2006 15/09/2006 +LPH 09:02:32 09:07:13 2 IMA 12 /20 3 IMA 12/ 20 receive coils. The larger the coil the greater the noise! ⋅For this reason, the receive coils are S/N RA RA optimized for both anatomy and MF 1.00 MF 1.00 coverage. TR 595.0 TR 595.0 TE 16.0 TE 16.0 TA 04:31 SP P61.2 TA 04:31 BW 100.0 SL 3.0 BW 100.0 MIND NORM FoV 160*160 MIND NORM SL 3.0 FoV 160*160 AUSATT 486*5121 A1/SAT1 486*5121 CBC Cor>Sag(34.4) Cor>Sag(34.4) *se2d1 / 90 W 1830 C:FL W 706 929 *se2d1 /90 298 Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 12 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 FOV (Field of View) SIEMENS Healthineers What is the field of view? Less spatial Res.. Is the square or rectangular image area to be measured (in mm). In Short the FOV determines what you can see in the MR image. Image comparison: FOV = 230 mm (left), FOV = 330 mm (right) is unnecessarily large Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 13 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Matrix SIEMENS Healthineers ⋅ Determines resolution and measurement time. Measurement time = FOV 256 mm FOV 350 mm Matrix 256x256 Matrix 256x256 Right image is magnified to show the same size of the head. Pixels Phase resolution x TR (repetition time) x Number are larger, resolution is lower. of acquisitions Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 14 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Resolution SIEMENS Healthineers ⋅Spatial Resolution is a important property of an MR Image. ⋅In MR we need to consider in-plane and through – plane resolution ⋅In –plane resolution is larger dimension and a critical parameter in Image Quality F Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 15 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Key parameter to Control matrix size SIEMENS Healthineers TA: 1:20 PM: REF Voxel size: 1.2x1.2x5.0 mm] Rel. SNR: 1.00 : se Common iPAT Filter FoV read 300 nm We will be looking at the effects of FoV phase 100.0 % these parameters on the Resolution tab card on Image Slice thickness 5.0 mm Resolution. For all following slides only FoV Base resolution 256 read and slice thickness will remain the same. The effect of the Phase resolution 100 other parameters on the Image Matrix will be discussed. These parameters will have an Phase partial Fourier Off effect on the scan time TA, the Voxel size and/or the signal-to- noise ratio SNR. These will be displayed at the bottom left of each slide. Keep your eye on these. Program Routine Contrast Resolution Geometry System Physio Inline Sequence Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 16 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Matrixes – The 256 x 256 Matrix SIEMENS Healthineers This results in the same The base matrix is 256. resolution in both read-out A square matrix. and phase-encoding directions. Read Out 2D FT Phase Encoding Base resolution 256 Scan Time: 1:20 Voxel size: 1.2 x 1.2 x 5.0 [mm] Rel SNR: 1.00 Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 17 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Matrixes – The 512 x 512 Matrix SIEMENS Healthineers Increasing the base matrix to Doubling the spatial 512 results is a higher spatial resolution decreases the pixel resolution, but a lower S/N. size by 75%: less signal. Read Out ding o 2D FT Enc e s Pha Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 18 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Matrixes – Phase Oversampling SIEMENS Healthineers Read Out The Phase-encoding .................... samples are increased, but the Over sampling in most outer parts are the Phase direction 2D FT discarded (dotted voxels). Resolution is kept, S/N increases Phase Encoding slightly, but the scan time also!! Phase oversampling 100 Scan Time: 2:40 Voxel size: 1.2 x 1.2 x 5.0 [mm] Rel SNR: 1.41 Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 20 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Matrixes – 50% Phase Resolution SIEMENS Healthineers The rectangular matrix 128 But it degrades resolution in x 256. phase-encoding direction. Read Out 2D FT ding o Enc e s Pha Phase resolution 50 Scan Time: 0:42 Voxel size: 2.3 x 1.2 x 5.0 [mm] Rel SNR: 1.41 Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 21 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Matrixes – Partial Fourier 4/8 SIEMENS Healthineers With Half-Fourier about 60% of the square matrix ...resulting in isotropic resolution, are measured... but reduced signal-to-noise. Read Out 2D FT ding o Enc e s Pha Phase partial Fourier 4/8 Scan Time: 0:44 Voxel size: 1.2 x 1.2 x 5.0 [mm] Rel SNR: 0.73 Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 22 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Matrixes – Reducing the Matrix SIEMENS Healthineers Reducing the base Results in a reduction in resolution (matrix)… image resolution. Read Out 2D FT ding o Enc e s Pha Base resolution 128 E Scan Time: 0:42 Voxel size: 2.3 x 2.3 x 5.0 [mm] Rel SNR: 2.83 Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 24 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 SIEMENS Healthineers Image Quality Is proportional to Scan time Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 25 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Clinical Benefits of shorter scan times: SIEMENS Healthineers ⋅ Higher image quality (less motion artifacts, shorter breath-holds ...) ⋅ Higher temporal resolution in dynamic (contrast-enhanced) scans ⋅ Better diagnosis Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Page 26 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Parallel Imaging SIEMENS Healthineers PAT iPAT mSENSE GRAPPA Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Page 27 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Scan Time (conventional 2D imaging) SIEMENS Healthineers TA < TR √ MAPhase Acq √ TA Time of Acquisition scan time = MAPhase Matrix size in phase-encoding direction number of echoes per acquisition = Acq Number of Acquisitions (averages) for better signal-to-noise ratio (SNR) Unrestricted © Siemens Healthcare GmbH, 2016 Textmasterformat, Disclaimer Page 28 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 So we need array coils … SIEMENS Healthineers 1 channel is not sufficient We need multiple channels Aeschna dragonfly 28,000 facets Unrestricted © Siemens Healthcare GmbH, 2016 Textmasterformat, Disclaimer Page 29 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Parallel Imaging SIEMENS Healthineers Parallel acquisition techniques combine the signals of several coil elements in a phased array to reconstruct the image. ⋅ To improve the signal-to-noise ratio ⋅Accelerate acquisition and reduces scan time Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 30 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 PAT & Array Coils SIEMENS Healthineers Array coils are required for PAT, otherwise the PAT reconstruction will fail (At least some) array coil elements need to be aligned along the phase-encoding direction A pe pe P H F Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Page 31 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 i-PAT - Parallel Acquisition Techniques SIEMENS Healthineers Two Families of PAT: Image-based PAT k-space-based PAT mSENSE GRAPPA SENSE - method reconstruct than correct GRAPPA – method correct than reconstruct Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 32 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 SENSE (Sensitive Encoding) SIEMENS Healthineers knowledge of the coil sensitivity profiles FFT oil 1 c SENSE Recon FFT oil 2 c array under- FFT RecFoV equation full FoV coil sampled with system without elements k-space aliasing aliasing Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 33 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 SENSE SIEMENS Healthineers knowledge of the coil sensitivity profiles FFT .............. oil 1 c SENSE Recon ............. FFT ............. oil 2 ............ c coil array under- FFT RecFoV equation full FoV calibration coil sampled with system without elements k-space aliasing aliasing Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 34 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 GRAPPA – Generalisied Autocalibirating Partial SIEMENS Healthineers Parellel Acquistion knowledge of the coil sensitivity profiles GRAPPA Recon FFT oil 1 c GRAPPA Recon FFT oil 2 c array under- calculation complete FFT full FoV coil sampled of 'artificial' k-space & array without elements k-space echoes comb. aliasing Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 35 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 GRAPPA SIEMENS Healthineers knowledge knowledge of the coil of the coil sensitivity sensitivity profiles profiles GRAPPA Recon FFT oil 1 c GRAPPA Recon FFT oil 2 c coil array under- calculation complete FFT full FoV calibration coil sampled of 'artificial' k-space & array without elements k-space echoes comb. aliasing Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 36 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 'Pre-Aliasing', Phase FOV 75% SIEMENS Healthineers mSENSE 2 GRAPPA 2 FoV 75% FoV 75% Auto-Calibration Auto-Calibration 24 reference lines 24 reference lines Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 37 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 'Pre-Aliasing', Phase FOV 66.7% SIEMENS Healthineers mSENSE 2 GRAPPA 2 FoV 66.7% FoV 66.7% Auto-Calibration Auto-Calibration 24 reference lines 24 reference lines Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 38 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 'Pre-Aliasing', Phase FOV 50% SIEMENS Healthineers mSENSE 2 GRAPPA 2 FoV 50% FoV 50% Auto-Calibration Auto-Calibration 24 reference lines 24 reference lines Unrestricted © Siemens Healthcare GmbH, 2016 Textmasterformat, Disclaimer Magnetom Cognizance Page 39 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 MR - Artifacts SIEMENS Healthineers Any irregularity noted in an MR image which is related to the imaging process rather than to an anatomical or physiological abnormality. Unrestricted © Siemens Healthcare GmbH, 2017 Textmasterformat, Disclaimer Magnetom Cognizance Page 40 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Types of artifacts SIEMENS Healthineers ⋅Patient motion ⋅Inhomogeneity ⋅Metal artifact ⋅Aliasing artifact ⋅Chemical shift artifact ⋅Gibbs artifact ⋅Zipper artifact ⋅Shading artifact ⋅Moire artifact ⋅Magic angle Textmasterformat, Disclaimer Magnetom Cognizance Page 41 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 ARTIFACTS CAUSED BY PATIENT MOTION SIEMENS Healthineers GHOSTING AND SMEARING NORMAL IMAGE CAUSE: when there is a magnitude and/or phase deviation from optimal k-space encoding Textmasterformat, Disclaimer Magnetom Cognizance Page 42 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 SIEMENS Remedies for patient motion artifacts Healthineers REMEDY: Fast Spin Echo acquisition time 2 minutes 22 seconds Images of the brain at the level of the pons shows higher spatial resolution AX T2-spin-echo in acquisition OTHER REMEDIES: single DISADVANTAGE: time 12 minutes 48 seconds shot section imaging HASTE and The higher signal intensity of periorbital fat -effect of J coupling Parellel imaging and other factors. Textmasterformat, Disclaimer Page 43 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 REMEDIES FOR INVOLUNTARY MOTION SIEMENS Healthineers CAUSE: CARDIAC MOTION CAUSE: RESPIRATORY R MOTION E CARDIAC GATING- k-space is linked with a specific 1. CARDIAC GATING M time point in the cardiac cycle with help of a ECG E REMEDY: 1. Breath holding D 2. PROSPECTIVE TRIGGERING PROSPECTIVE TRIGGERING: image acquired at the Y Breath holding end of diastole- static imaging – mainly for anatomy 2. Examination divided Examination divided into breif aquisations aquisations -20 -40 3. Gating using bellows Gating using bellows -80 placed at lower -80 abdomen level •Image with respiratory artifact. •(rectangular box) selected for respiratory monitoring with a navigator pulse. DISADVANTAGE: Long acquisition time •The one-dimensional temporal data is collected show the relative position of the diaphragm (y- axis) over time (x-axis). cine SSFP images obtained with prospective cardiac gating (triggering) Textmasterformat, Disclaimer Page 44 •respiratory gating allowed reduction of the respiratory motion–related artifact Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 ARTIFACTS DUE TO PULSATILE MOTION SIEMENS Healthineers After remedy CAUSE: Artifact due to the pulsation of the vascular Remedy: structures (CSF, BLOOD) ghosting will occur at a constant Parallel Saturation interval in phase encoding direction Apply flow compensation Textmasterformat, Disclaimer Page 45 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 INVOLUNTARY MOTION SIEMENS Healthineers REMEDY: SATURATION PULSE REMEDY: GRADIENT NULLING applied ant to the spine. Performed by applying additional They are additional RF pulses that gradient pulses to eliminate the are applied before the imaging phase shifts produced by moving sequence- thereby reducing the protons,while signal from their signal intensity of pulsating stationary counter parts is rephased stuctures CAUSE: CSF PULSATION–related artifact in the CAUSE: ESOPHAGEAL MOTION - low signal intensity (arrows) that represent ghosting artifacts phase encoding direction DISADVANTAGE: SAR increses Textmasterformat, Disclaimer Page 46 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 MAGNETIC SUSCEPTIBILITY SIEMENS Healthineers REMEDY REMEDY: CAUSE: MAGNETIC SUSCEPTIBILITY substantial high-signal-intensity at the junction PARALLEL IMAGING factor of 2 of the midbrain and sphenoid sinus and at the shows the reduction of these interface of the temporal horns and mastoid air artifacts cells Textmasterformat, Disclaimer Page 47 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 METTALLIC OBJECTS ARTIFACT SIEMENS Healthineers OTHER REMEDIES: REMEDY: 1. Smaller pixel sizes Aneurysm clip 1. 2. Using a short TE or short inter- ADDING OF A 180 ADDING OF A 180° RF PULSE RF PULSE- time of TE/2 echo interval – 3. inverts the polarity of phase change among protons. Increasing the sampling bandwidth so, at TE, the protons that were exposed to CAUSE: METALLIC OBJECT ARTIFACT 4. field inhomogeneities are once again in phase WARP Aneurysm clip seen without affecting with those that were not exposed to those 5. inhomogeneities. image quality SEEMAC Due to its presence (eg: surgical hardware), it distorts T2 spin echo nearby structures and also may result in signal dropout, depending on the sequence used Textmasterformat, Disclaimer Page 48 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 GRADIENT NON GRADIENT NON-LINEARITY AND RF FIELD INHOMOGENIETY LINEARITY AND RF FIELD INHOMOGENIETY SIEMENS Healthineers REMEDY: Use Dixon for the off center fat suppresion CAUSE: GRADIENT NON LINEARITY resulting in GRADIENT NON-LINEARITY REMEDY: An automatic correction technique geometric distortions, with vertebral bodies appearing was used to correct the artifactual distortion. CAUSE: RF FIELD INHOMOGENEITY causing progressively smaller toward the inferior edge of the These are in built. prominent inhomogeneity of fat suppression. FOV (arrow) Textmasterformat, Disclaimer Page 49 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 ALIASING OR WRAP AROUND ARTIFACT SIEMENS Healthineers Image taken with increased FOV WHEN ZOOMED Note: spacial resolution has incresed But ALIASING ARTIFACT Is seen in incresed FOV REMEDY: 1. Increase oversampling 2. Use of surface coil in ROI 3. Switching phase and encoding direction 4. Saturation pulses may be applied to structure non-imaged Textmasterformat, Disclaimer Page 50 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 CHEMICAL SHIFT ARTIFACT SIEMENS Healthineers REMEDY REMEDY: CAUSE: CHEMICAL SHIFT ARTIFACT due to differences in larmor frequency of fat and water 1. Higher bandwidth sampling rate leads spatial misregistration of the MR signal 2. Fat suppression will eliminate it totally Seen more in fat-water interface 3. Proper selection TE Textmasterformat, Disclaimer Page 51 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 TRUNCATION ARTIFACT SIEMENS Healthineers CAUSE: data is omitted(truncated) in k-space,causing signal intensity of a given pixel on the final image to vary REMEDY: Decrease the pixel size or use from its ideal intensity additional filters Manifest as ripple Textmasterformat, Disclaimer Page 52 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 ZIPPER ARTIFACT SIEMENS Healthineers A dense line on the image at specific point RF CAUSE: extraneous RF entering the room at a certain frequency. Leak in the RF shielding of the room FREQUENCY REMEDY: Call the engineer to locate the leak and repair it. CHESS Textmasterformat, Disclaimer Page 53 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 SHADING ARTIFACT SIEMENS Healthineers Difference in signal intensity across the imaging volume CAUSE: 1. Non uniform RF excitation because of non Non uniform RF excitation because of non uniform anatomy. 2.Abnormal loading of the coil REMEDY: B 1.Correct excitation 2.Load the coil 2.Load the coil correctly correctly Textmasterformat, Disclaimer Page 54 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 MOIRE ARTIFACT SIEMENS Healthineers A black and white banding artifact , always seen in gradient echo imaging typically when large FOV is used. CAUSE: Due to Magnet field in Due to Magnet field in - homogeneity homogeneity Banding Appearance REMEDY: Use small FOV Textmasterformat, Disclaimer Page 55 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 MAGIC ANGLE SIEMENS Healthineers Appears as high signal intensity on some tendons and mimic pathology CAUSE: structures that contain tightly bound fibres lie at an angle of 55 fibres lie at an angle of 55 deg to the main field to the main field ,altering its signal intensity REMEDY: 1.alter the position of anatomy 2. Change TE Textmasterformat, Disclaimer Page 56 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 Conclusion SIEMENS Healthineers ⋅Use proper positioning aids…. ⋅Use fast sequences like – Haste ⋅Use motion artifact reduction sequence like Blade / Propeller Magnetic Susceptibility - Use High bandwidth / SEMAC ⋅Magnetic Susceptibility Use High bandwidth / SEMAC etc..... Textmasterformat, Disclaimer Magnetom Cognizance Page 57 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018 SIEMENS Healthineers Now’s our time Thank you for your attention to inspire the future of healthcare together Engineering success. Pioneering healthcare. Textmasterformat, Disclaimer Page 58 Author / Department HC XX HOOD05162002737284 Effective date: 01/24/2018