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MR Management of Field Uniformity - Numaris X

This Job Aid provides information on the management of field uniformity.

SIEMENS Healthineers MR Management of Field Uniformity Version 2020.09 USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Template Effective Date: 27 MAY 2019 | HOOD05162003010284 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Management of Field Uniformity – SIEMENS Healthineers Table of Contents Shim 3 Differentiation of Water-Fat-Silicone peaks 7 SIEMENS. Healthineers Techniques of fat saturation 9 O O MAGNETOM Sola ABloMatik System IHM USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Shim – SIEMENS Healthineers Principle • Shimming is the process of increasing the homogeneity of the static B0 field for a certain measurement. In general, the B0 field is optimized for a high homogeneity in the center of the magnet. However off-center measurements and patient-induced disturbances of the B0 field often require an additional shim step to optimize homogeneity for a specific FOV and scan. • During shimming the scanner analyzes the B0 field in a defined region - the adjustment volume - and optimizes the B0 field within this volume. In most cases the adjustment volume is equal to the acquisition volume, however, in rare cases it might be appropriate to choose an adjustment volume which differs from the acquisition volume (e.g. scan with saturation bands). • The judicious positioning of the adjustment volume (loosely described as shim) makes it possible to limit the impact of the non-uniformity of the magnetic field. • This phenomenon is illustrated in the diagram, in which the orange box represents the acquisition volume, while the green box represents the magnetic field adjustment volume. USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Shim – SIEMENS Healthineers Adjustment Strategy • Certain Sequences (TSE and EPI SE) permit a SliceAdjust adjustment strategy, which performs a slice-by-slice adjustment rather than the adjustment of a given volume. @ 2:49 min Auto @ None @ 0.4x0.4x3.0 mm3 1.00 Routine Contrast Resolution Geometry System Physio Inline Sequence Coils Miscellaneous Adjustments Adjust Volume Tx/Rx Adjustment Strategy Standard Adjustment Tolerance Auto (Maxi ... BO Shim Standard SliceAdjust Adjust with Body Coil FastView Confirm Frequency Never Assume Silicone Manual Adjustments USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Shim – SIEMENS Healthineers B0 Shim Modes • Shim Mode selection is found on the System – Adjustment tab. • Tune-up: No adjustment is made at the start of the sequence: the system uses the values determined during system installation. This shim mode is to be prioritized in sequences that do not require the correction of patient-induced non-uniformity (SE/GE without FatSat). • Standard: The adjustment volume is superimposed onto the acquisition volume. • Standard Neck: Meets specific requirements related to the use of fat saturation in the neck, in the sagittal direction only. This adjustment is made with the neck coil only. • Advanced (**): Uses additional iterations (longer adjustment time) for the diffusion and spectroscopy sequences. • Cardiac: Allows the adaptation of measurements due to specific requirements related to heartbeats. Foot/Ankle: Optimization of foot and ankle examinations. • Brain/Breast/Prostate (**): Optimization of measurements for the use of spectroscopy in different anatomical • locations. • Abdomen: Optimization of abdominal examinations in a transverse view. • Whole body (**): for whole body diffusion • Note: (**) Shim mode available in certain sequences only USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Shim – SIEMENS Healthineers Use of Manual Shim Scan Assistant ? • If a sequence has been saved with manual shim adjustment Your last change (green box representing the adjustment volume has manually ? Adjustment Strategy Standard -+ SliceAdjust been positioned), the following message will appear when it is will adapt the following parameters: RA BO Shim Standard -+ Whole Body reopened. TP F36 SP L46.0 OK Undo FoV 308*340 Sag>Cor(-42)>Tra(-6) Ch 881 Scan Assistant ? × Not for diagnostic use 394 RR 1014 +/- 33; 7 heartbeats RR /1014 +/- 33; 7 heartbeats Dot 1:42 min Auto @ 2 2.0x2.0x5.0 mm3 1.00 ? The adjust volume is normally calculated automatically. Routine Contrast Resolution Geometry System Physio Diff Sequence In this protocol it was changed explicitly. Coils Miscellaneous Adjustments Adjust Volume PTX Tx/Rx It is strongly recommended to readjust the adjust volume manually or to fall back to the automatic mode. Adjustment Strategy SliceAdjust ... Adjustment Tolerance Auto (Maxi ... BO Shim Whole Body Adjust with Body Coil [] Automatic Manual B1 Shim TrueForm Confirm Frequency Never Assume Silicone • Automatic button resets size of shim volume in relation to the mode defined in the menu System – Adjustments (Standard, Manual Adjustments Fine tuning, etc.). • Manual button applies the shim volume as set manually when recording the sequence. • Positioning of this volume (green box) must then be checked and/or adjusted. USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Differentiation of Water-Fat-Silicone Peaks – SIEMENS Healthineers Physical Principle • Different molecular compositions of water, fat, and silicone are responsible for a shift in resonance frequency between the water, fat, and silicone protons. Silicone • These known shifts allow for the selective removal Fat of one or other of these components. Water Hz USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Differentiation of Water-Fat-Silicone Peaks – SIEMENS Healthineers Physical Principle • Proper operation of this selective removal depends on the precise adjustment of the system to the water peak. This adjustment is carried out automatically. • Certain situations (e.g., certain products used for marking in the digestive tract) or anatomical areas (areas where dominant fat may be greater than dominant water: such as breast region, for example) can give rise to error. • Check adjustment: in Sequence > System > Adjustments Parameter Card, click on Confirm Frequency. • Note: adjustment must always be carried out on water peak (peak on right to be selected), except for sequence where the objective is to remove the signal of the silicone protons, in which case the silicone peak must be selected. SIEMENS »> breast » Breast Dot Engine » Medium channel coils » stir ws_tra silicone bilateral ? > Confirm Frequency Adjustment General 3:20 min Auto @ 2 @ 0.9x0.9x4.0 mm3 @ 1.00 Protocol Parameters Routine Contrast Resolution Geometry System Physio Inline Sequence Voice Commands Miscellaneous Adjustments Adjust Volume |Tx/Rx Execution Image Management Adjustment Strategy Standard Adjustment Tolerance Auto |Max| 6,643 Auto Load BO Shim Standard Adjust with Body Coil Copy References Preview B1 Shim TrueForm Confirm Frequency Always Never Mag Assume Silicone Always When Changed 123.253.111 123.258.219 CoilShim Off Coil Combined ADC - Frequency (sys) [Hz] 123255651 Frequency (temp) [Hz] 123255651 Apply USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Addin Configuration ... OK Cancel Continue Cancel Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers STIR – Short Tau Inversion Recovery • STIR Sequence is a fat saturation technique by means of Inversion Recovery, based on the difference in Mz relaxation time between water and fat protons. fat • Inversion Recovery Sequences use an RF inversion pulse that reverses the magnetization of the spins. TI • For a STIR sequence, a good knowledge of the fat water time protons’ inversion time (TI) makes it possible to trigger the excitation pulse of the sequence at the moment when the magnetization of the fat is zero. • In this way, it does not appear in the image signal. • @ 1.5T: TI between 150 ms and 170 ms 180º excitation • @ 3T: TI between 210 ms and 230 ms fat+water USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers STIR – Short Tau Inversion Recovery • Advantages • Less sensitive to inhomogeneity in B0 magnetic field • Compatible with spectral saturation (e.g.: silicone implants) • Disadvantages • Longer acquisition time • May unintentionally obscure tissue: Don’t use after injection of contrast medium HAL RA USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers FATSAT – Spectral Saturation • Spectral Fat Saturation Technique is based on the difference in resonance frequency between water and fat protons (3.4 ppm or 220 Hz @ 1.5T). RF • A selective RF pulse for fat protons followed by water + Spoiling a spoiler (a very powerful gradient pulse) excitation suppresses the signal from this tissue. fat • A Faible (Low) saturation mode exists in order to preserve part of the anatomical information on fatty tissue. • By clicking on “ …,” a Articulation (Joint) saturation mode exists in order to improve the "3.4 ppm frequency efficiency of saturation for the examination of small bones (knee, wrist, etc.) USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers FATSAT – Spectral Saturation HAL • Advantages • Faster than STIR • Does not affect the contrast of other tissues: usable ARF after the injection of contrast medium • Disadvantages • Sensitive to B0 and B1 inhomogeneities (B1: electromagnetic field generated via RF pulses) • Longer sequence adjustment due to Shim RAF USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers SPAIR – Spectral Adiabatic Inversion Recovery • SPAIR Saturation Technique is a combination of the Inversion Recovery Technique and the Spectral Saturation Technique of fat protons. • A selective spectral pulse is applied to invert the fat protons only. water • By clicking on “ … ,” 3 saturation modes, fat Abdomen & Pelvis, Breast*, Thorax (Abdomen & Pelvis, Breast*, Chest) appear, in order to time adapt the saturation efficiency for these 3 types of examination. excitation • (*) This mode exists with 3T only. fat adiabatic inversion pulse (B, insensitive) USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers SPAIR – Spectral Adiabatic Inversion Recovery • Advantages • Not sensitive to B1 inhomogeneities • Does not affect the contrast of other tissues • Usable after injection of contrast medium • Disadvantages • Longer than conventional spectral saturation due to the embedded TI • Better saturation of fat protons results in a bigger decrease in SNR (signal-to-noise ratio) compared to a Fatsat* • Increase in SAR* USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 *Please note: These disadvantages apply also to STIR © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers Water Excitation – Selective Water Excitation • Technique is based on the difference in resonance 1 2 1 frequency between water and fat protons. It is based 45º on the use of a composite RF pulse (several RF pulses, 22.5º 22.5º dephasing dephasing the sum of which corresponds to a 90° flip angle). in-phase opp-phase in-phase opp-phase • In contrast to previously presented fat saturation water fat techniques, water excitation does not suppress fat signal but only excites water spins. Hence no fat signal is created, and only water signal appears in the images. Maximum excitation on the frequency of water Minimal excitation on the Please note: The Fast excitation mode is 2 pulses 45°– frequency of fat • 45° (1-1), while the Normal excitation mode is 3 pulses 22.5°– 45°– 22.5° (1-2-1). 1-1 1-2-1 2 1-3-3-1 RF exitation 1-4-6-4-1 fat frequency USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers Water Excitation – Selective Water Excitation • Advantages • Fast compared to STIR • Does not affect the contrast of other tissues: usable after the injection of contrast medium RHA • Disadvantages • Accessible on certain sequences only USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers DIXON • DIXON Technique is based on the difference in resonance frequency of water and fat protons. • Contrasts between Water and Fat images are generated from two acquisitions at specific times (in-phase and opposed-phase). SignalinPhase = Water + Fat SignaloppPhase = Water + Fat Water Signal = 0.5x (SignalinPhase + SignaloppPhase) Fat Signal = 0.5x (SignalinPhase – SignaloppPhase) USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers DIXON • DIXON TSE 1 Echo in RF/ADC Exc. Refoc. Readout gradient 2 Echo opp RF/ADC Exc. Refoc. Readout gradient .......... Atopp-in USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers DIXON • Advantages • Robust to inhomogeneities of B0 and B1 magnetic fields • Acquisition of several contrasts • Does not affect the contrast of other tissues: usable after the injection of contrast medium • Possibility to retrieve in-phase (i.e. non-fat saturated) and fat only images from same acquisition • Disadvantages • Longer acquisition time • More sensitive to movement • Degradation of spatial resolution in Monopolar mode due to asymmetry of echoes USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of Fat Saturation – SIEMENS Healthineers DIXON • DIXON TSE Wrist Head Knee HLA ALF HAR RHA RAH RPH USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 SIEMENS Healthineers Please note that the learning material is for training purposes only! For the proper use of the software or hardware, please always use the Operator Manual or Instructions for Use (hereinafter collectively “Operator Manual”) issued by Siemens Healthineers. This material is to be used as training material only and shall by no means substitute the Operator Manual. Any material used in this training will not be updated on a regular basis and does not necessarily reflect the latest version of the software and hardware available at the time of the training. The Operator's Manual shall be used as your main reference, in particular for relevant safety information like warnings and cautions. Note: Some functions shown in this material are optional and might not be part of your system. Certain products, product related claims or functionalities (hereinafter collectively “Functionality”) may not (yet) be commercially available in your country. Due to regulatory requirements, the future availability of said Functionalities in any specific country is not guaranteed. Please contact your local Siemens Healthineers sales representative for the most current information. The reproduction, transmission or distribution of this training or its contents is not permitted without express written authority. Offenders will be liable for damages. All names and data of patients, parameters and configuration dependent designations are fictional and examples only. All rights, including rights created by patent grant or registration of a utility model or design, are reserved. Copyright © Siemens Healthcare GmbH 2020 Siemens Healthineers Headquarters Siemens Healthcare GmbH Henkestr. 127 91052 Erlangen, Germany Telephone: +49 9131 84-0 siemens.com/healthineers USA HRT Effective Date: 1.12.2021 | HOOD05162003145777 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020