Management of field uniformity

SIEMENS Healthineers Management of field uniformity Version 2020.09 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 SIEMENS Healthineers Differentiation of Water-Fat-Silicone peaks 7 Techniques of fat saturation 9 O O MAGNETOM Solo 2 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. 3 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Shim – SIEMENS Healthineers Adjustment strategy Certain sequences, TSE and EPI SE, permit a SliceAdjust 0 2:49 min | Auto @ None 0.4x0.4x3.0 mm3 1.00 adjustment strategy, which performs a slice-by-slice Routine Contrast Resolution Geometry System Physio Inline Sequence Coils Miscellaneous Adjustments Adjust Volume Tx/Rx adjustment rather than the adjustment of a given volume. Adjustment Strategy Standard Adjustment Tolerance Auto (Maxi ... BO Shim Standard SliceAdjust Adjust with Body Coil FastView Confirm Frequency Never Assume Silicone Manual Adjustments 4 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. • Cardio: 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 (**) Shim mode available in certain sequences only 5 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Shim – Scan Assistant ? x SIEMENS Healthineers Use of manual shim ? The adjust volume is normally calculated automatically. In this protocol it was changed explicitly. It is strongly recommended to readjust the adjust volume manually or to fall back to the automatic mode. If a sequence has been saved with manual shim adjustment Automatic Manual (green box representing the adjustment volume has manually been positioned), the following message will appear when it is Scan Assistant ? × reopened. ? Your last change Adjustment Strategy Standard -+ SliceAdjust will adapt the following parameters: 0cm RA BO Shim Standard - Whole Body TP F36 SP L46.0 Undo FoV 308*340 OK S2D Sag>Cor(-42)>Tra(-6) Ch 881 Not for diagnostic use 394 nEN RR 1014 +/- 33; 7 heartbeats RR 1014 +/- 33; 7 heartbeats The Automatic button resets the size of the shim volume in . . . . . . . . . . ......... Dot 1:42 min Auto @ 2 2.0x2.0x5.0 mm3 ~ 1.00 relation to the mode defined in the menu System – Adjustments Routine Contrast Resolution Geometry System Physio Diff Sequence (Standard, Fine tuning, etc.). Coils Miscellaneous Adjustments Adjust Volume PTx Tx/R> The Manual button applies the shim volume as set manually Adjustment Strategy SliceAdjust Adjustment Tolerance Auto (Maxi ... BO Shim Whole Body Adjust with Body Coil when recording the sequence. B1 Shim TrueForm Confirm Frequency Never The positioning of this volume (green box) must then be checked Assume Silicone and/or adjusted. Manual Adjustments Author | Department 6 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Differentiation of Water-Fat-Silicone peaks – SIEMENS Healthineers Physical principle The different molecular compositions of water, fat, and silicone are responsible for a shift in resonance frequency Silicone between the water, fat, and silicone protons. Fat These known shifts allow for the selective removal of one or other of these components. Water < Hz 7 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Differentiation of Water-Fat-Silicone peaks – SIEMENS Healthineers Physical principle The proper operation of this selective removal depends on the precise adjustment of the system to the water peak. This adjustment is carried out automatically. However, certain situations (for example certain products used for marking in the digestive tract) or anatomical areas (areas where the dominant fat may be greater than the dominant water: such as the breast region, for example) can give rise to error, hence the need to check this adjustment: in the sequence’s System tab, then in Adjustment, click on Confirm Frequency. Please note: the adjustment must always be carried out on the water peak (peak on the right to be selected), except for the sequence where the objective is to remove the signal of the silicone protons, in which case the silicone peak must be selected. Confirm Frequency Adjustment SIEMENS >> breast > Breast Dot Engine >> Medium channel coils > stir_ws_tra_silicone bilateral ? x General 3:20 min 4 Auto @ 2 0.9x0.9x4.0 mm3 1.00 Protocol Parameters Routine Contrast Resolution Geometry System Physio Inline Sequence Voice Commands Miscellaneous Execution Adjustments Adjust Volume Tx/ Rx |Max| 6,643 Image Management Adjustment Strategy Standard Adjustment Tolerance Auto Auto Load BO Shim Standard Adjust with Body Coil Copy References Preview B1 Shim TrueForm Confirm Frequency Always Mag Assume Silicone Never Always f [Hz] When Changed 123.253.111 123.258.219 CoilShim Off Coil Combined ADC Frequency (sys) [Hz] 123255651 Frequency (temp) [Hz] 123255651 Apply 8 AddIn Configuration ... OK Cancel Effective Date: 10 SEP 2020 | HOOD05162003112100 Continue Cancel © Siemens Healthineers, 2020 Techniques of fat saturation – SIEMENS Healthineers STIR – Short time inversion recovery The STIR sequence is a fat saturation technique by means M2 of inversion recovery, based on the difference in relaxation time between water and fat protons. fat time An inversion recovery sequence uses an RF inversion pulse water that reverses the magnetization of the spins. For a STIR sequence, a good knowledge of the fat protons’ inversion time (TI) makes it possible to trigger the 180º excitation excitation pulse of the sequence at the moment when the fat+water 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 @ 3T: TI between 210 ms and 230 ms 9 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of fat saturation – SIEMENS Healthineers STIR – Short time inversion recovery Advantages • Less sensitive to inhomogeneity in the B0 magnetic field • Compatible with spectral saturation (e.g.: silicone implants) Disadvantages • Longer acquisition time HAL • May unintentionally obscure tissue: not to be used after the injection of contrast medium 10 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of fat saturation – SIEMENS Healthineers FATSAT – Spectral saturation The spectral fat saturation technique is based on the RF water Spoiling difference in resonance frequency between water and fat excitation fat protons (3.4 ppm or 220 Hz @ 1.5T). A selective RF pulse for fat protons followed by a spoiler (a very powerful gradient pulse) suppresses the signal from this tissue. 3.4 ppm frequency 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 efficiency of saturation for the examination of small bones (knee, wrist, etc.) 11 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of fat saturation – SIEMENS Healthineers FATSAT – Spectral saturation Advantages HAL • Faster than STIR • Does not affect the contrast of other tissues: usable after the injection of contrast medium ARF Disadvantages • Sensitive to B0 and B1 inhomogeneities (B1: electromagnetic field generated via RF pulses) • Longer sequence adjustment due to Shim RAF 12 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of fat saturation – SIEMENS Healthineers SPAIR – Spectral adiabatic inversion recovery The SPAIR saturation technique is a combination of the inversion recovery technique and the spectral saturation M- water technique of fat protons. A selective spectral pulse is applied to invert the fat fat protons only. time By clicking on “ … , ” 3 saturation modes, Abdomen & Pelvis, Breast*, Thorax (Abdomen & Pelvis, Breast*, Chest) excitation appear, in order to adapt the saturation efficiency for these 3 types of examination. Hat adiabatic inversion pulse (B, insensitive] (*) This mode exists with 3T only. 13 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 the injection of contrast medium Disadvantages • Longer than conventional spectral saturation due to the embedded TI • The better saturation of fat protons results in a bigger decrease in SNR (signal-to-noise ratio) compared to a Fatsat* • Increase in SAR* R 14 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 This technique is based on the difference in resonance 1 2 1 frequency between water and fat protons. It is based on 45º the use of a composite RF pulse (several RF pulses, the 22.5 22.5º dephasing dephasing sum of which corresponds to a 90° flip angle). wh in-phase -- +- opp-phase in-phase ---- opp-phase In contrast to previously presented fat saturation water L 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°– 45° frequency of fat (1-1), while the Normal excitation mode is 3 pulses 22.5°– 45°– 22.5° (1-2-1). 1-1 1-2-1 . 1-3-3-1 RF exitation 1-4-6-4-1 fat water frequency 15 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 HR 16 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020 Techniques of fat saturation – SIEMENS Healthineers DIXON The 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) ) 17 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 18 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 19 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 20 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 21 Effective Date: 10 SEP 2020 | HOOD05162003112100 © Siemens Healthineers, 2020