MR Essentials - Fat Suppression Online Training

Welcome to the MR Essentials - Fat Suppression Online Training course. This course will discuss 5 main approaches for suppressing fat signal relative to water signal.     Upon successful completion of this course, you will be able to: Explain why fat and water have different signal Describe different methods for fat suppression Summarize the benefits of using fat suppression techniques with MRI Congratulations! You have completed the MR Essentials - Fat Suppression Online Training course. Listed below are key points about the fat saturation techniques that have been presented. Take time to review the material before proceeding to the final assessment.  Technique Method Time Penalty SAR Sensitivity to B0 Sensitivity to B1 FatSat Chemical Shift Small Medium High High Dixon Chemical Shift Large Low Low Low Water Excitation Chemical Shift Small Low High Low STIR T1 Large Med Low Low SPAIR Hybrid Large High High Low . Fat and water have different molecular environments. Water always consists of two hydrogen atoms bonded to an oxygen atom Fat is a mixture of molecules with varying structures Large parts of fat molecules have a series of carbon and hydrogen atoms   There are several methods for fat suppression, including: STIR SPAIR Fat Saturation Dixon Water Excitation   Fat Suppression Techniques Learn about properties of different fat suppression techniques.     Technique Method Time Penalty SAR Sensitivity to B0 Sensitivity to B1 FatSat Chemical Shift Small Medium High High Dixon Chemical Shift Large Low Low Low Water Excitation Chemical Shift Small Low High Low STIR T1 Large Med Low Low SPAIR Hybrid Large High High Low STIR or Short TI Inversion Recovery uses relaxation time differences to suppress signal. Three considerations: Possible to change the display of a STIR image STIR requires long TR to allow significant T1 relaxation to occur between excitation pulses Causes tissues to lose their signal as their T1 relaxation time approaches that of fat when a T1 contrast agent is used   Inversion Recovery Learn more about Inversion Recovery. Element HTMLInversion Recovery Uses a 180o RF pulse to invert the net magnetization for the slice After a short time known as the Inversion Time TI, the image is acquired Net magnetization starts negative, crosses through zero, and then becomes positive The point when this occurs is known as the null point The TI which results in this null point depends on the particular tissue and its T1 time 2 1 0 -1 -2TInullNet MagnetizationTime Sound File Audio ScriptWith Inversion Recovery, a 180 degree RF pulse is used to invert the net magnetization for the slice. After a short time known as the Inversion Time TI (pronounced "T-eye"), an image is acquired. The signal amplitude for a given tissue is based on the T1 (pronounced "T-one") relaxation time relative to the inversion time. One characteristic of Inversion Recovery is that the net magnetization starts negative and then crosses through zero before becoming positive as indicated in the diagram. The point when this occurs is known as the null point. The TI (pronounced "T-eye") which results in this null point depends on the particular tissue and its T1 (pronounced "T-one") time. This characteristic allows for signal suppression.   Additive T1 and T2 Contrast Learn about the STIR technique. Element HTML180o90oa b cContrastc bMxyMzTI Sound File Audio ScriptTo reiterate spin-echo imaging, tissue with a longer T1 appears darker in the image and tissue with a longer T2 appears brighter when using a long TR and a long TE. When a short inversion time TI is used, the inversion-recovery technique obtains a rather interesting contrast: additive T1 and T2 weighting (this sequence is known as STIR or Short TI Inversion Recovery. In this case, tissue with a long T1 (seen with b and c) shows a negative longitudinal magnetization. After the 90-degree excitation pulse, the tissue generates stronger signals (the T1 portion). With longer echo times, the contrast is further enhanced (the T2 portion). T1 and T2 effects work in the same direction.   SPAIR or Spectral Adiabatic Inversion Recovery, is an Inversion Recovery for only the fat protons. Inversion pulse is a narrow bandwidth pulse centered specifically at the fat resonant frequency Pulse inverts only the fat hydrogen, not the water hydrogen     FatSat uses a narrow frequency RF pulse applied at the fat resonance frequency. Applied more frequently than the normal RF pulses for slice excitation Fat will be saturated and suppressed in signal compared to the water FatSat cannot be done on low field systems due to the reduced frequency difference.     Disclaimer: 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 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. Please contact your local Siemens sales representative for the most current information. Functionalities described in the material or parts of this functionality may not yet be released for customers and not yet be commercially available in every country. Due to regulatory requirements, the future availability of said functionalities or parts thereof in any specific country is not guaranteed. The Operator Manual shall be used as your main reference, in particular for relevant safety information like warnings and cautions. 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 rights, including rights created by patent grant or registration of a utility model or design, are reserved. Copyright © Siemens Healthcare GmbH, 2018 These fat suppression techniques take advantage of the chemical shift difference between fat hydrogen and water hydrogen atoms. This requires a uniform magnetic field throughout the imaging volume.  Shimming is used to minimize the magnetic field differences Three fat suppression techniques are based on chemical shift differences: Fat Saturation Dixon Water Excitation   Chemical shift difference the resulting difference in the resonance frequencies of the fat hydrogen and water hydrogen. Fat hydrogen has a lower resonant frequency than a water hydrogen Able to manipulate the signal of fat separately from the water signal H2O -CH2- +5 -5 0 Water Excitation uses a pair of RF pulses to selectively excite water hydrogen. For 90o excitation, the two pulses are 45o each First pulse excites both fat and water hydrogen Fat hydrogen rotates 180o out of phase to the water hydrogen Second 45o pulse is applied Result: water hydrogen will be excited 90o while the fat hydrogen will be forced back along the magnetic field. Shift of Fat & Water Artifact Eliminated by Fat Suppression Dixon takes advantage of different resonant frequencies between fat and water. Normal image with fat and water hydrogen atoms precessing in phase Second image acquired when the fat hydrogen is out of phase with the water hydrogen Addition of these images creates a water-only image. Subtraction creates a fat-only image. Water Fat In-phase Out-of-phase