• Which Products are you interested in ?

    CST offers a wide range of EM simulation software to address design challenges across the electromagnetic spectrum, from static and low frequency to microwave and RF, for a range of applications, including EDA & electronics, EMC & EMI and charged particle dynamics.

  • Antenna Magus
  • IdEM
  • FEST3D
  • Optenni Lab
  • Looking for a Training, Workshop or eSeminar ?

    CST STUDIO SUITE® is being demonstrated at trade shows and workshops all over the world. Take a look at the list of conferences and exhibitions CST will be attending and get further information regarding CST workshops, eSeminars and training days.

  • TrainingsRegular training courses are held in CST's offices in Asia, Europe, and North America. Please check our trainings section for detail of trainings in all over the globe. Advance registration is normally required.

  • WorkshopsCST hosts workshops in multiple languages and in countries around the world. Workshops provide an opportunity to learn about specific applications and refresh your skills with experienced CST support staff. Make sure you visit our workshop section.

  • eSeminarsThroughout the year, CST simulation experts present eSeminars on the applications, features and usage of our software. You can also view past eSeminars by searching our archive and filtering for the markets or industries that interest you most.

  • Check our latest Events
  • Why create a MyCST Account ?

    A MyCST account may facilitate your access to many of the offerings on the CST website, for example the registration for eSeminars and the watching of eSeminars recordings, setting email preferences, and there is more functionality to come. It is required to participate in workshops and trainings.

  • Personal PreferencesAllows you to update your email preferences and areas of interest. It helps us to personalize your experience.

  • EventsSearch for events by location, industry and application. Once you are registered, you will be able to manage your registrations and check important details about your events. This section also provides you with a repository for Workshop & Training material.

  • LibraryYou can collect articles you find on the CST website to reference or read later by clicking on the “Add this article” button at the bottom of the article page.

  • Create Your Own Account
  • Need technical Support ?

    Customers can customize their accounts once they have completed the account creation process. This platform acts as vivid interface between CST and our customers.

    We therefore offer access to the latest Service Packs (including an automatic notification that a new Service Pack is available), a steadily growing database of Frequently Asked Questions (FAQs), Application Notes and Training Videos, as well as an individual FTP section for easy exchange of large files with our support team.

  • Do I need an Account?To access the Support Site a valid maintenance contract and a one-time registration is required.

    Please note that your Support login does not work for the MyCST account.

  • Get Support
  • How to request a Trial License ?

    Get your license in only three steps:

    1. Fill in the required fields in the contact form on the right and click "Send Us Your Request".

    2. Lean back and wait until one of our CST Experts contacts you.

    3. Enjoy a our trial license.

  • Student Edition

    Student Edition The CST STUDIO SUITE® Student Edition has been developed with the aim of introducing you to the world of electromagnetic simulation, making Maxwell’s equations easier to understand than ever. With this edition you have, bar some restrictions, access to our powerful visualization engine and some of the most advanced solvers of CST STUDIO SUITE.

    Student Edition

CST – Computer Simulation Technology

EM field distribution and SAR in a Human Head with MRI Coil

In Ultra-High Field MRI systems, e.g. for B0 beyond 7 T, the performance of the RF coils is essential to provide a great image quality with a reasonable B1-field homogeneity in the imaging area, low SARs in the biological tissues and a good signal to noise ratio (SNR). Despite the many advantages in increasing the B0-field strength (higher resolution and SNR, reduced scan time), operating at higher frequencies adds significant technical complexity to NMR experiments and consequently to the RF coils design. As frequencies increase, the wavelength shortens (60 cm in the vacuum and 8.5 cm inside the head at 500 MHz), and becomes comparable to the electrical dimensions of the head/body and the RF coil. RF fields interact more strongly with human tissues and wave behavior of the B1-field should strongly affect its homogeneity inside the highly permittive and lossy tissues. While B1 inhomogeneities cause non-uniform intensity distribution in MR images, the RF electric field counterpart, potentially inhomogeneous too, should expose biological tissues to an excessive RF power deposition with induced local heating. Coupled to detailed anatomical human models, computational methods offer an indispensable tool for the investigation of the distribution of the magnetic field or the maximum local SAR values inside the tissues and for the design and evaluation of the RF coils' performance....

This article provides a summary of the work carried out by CEA Saclay, France using CST MICROWAVE STUDIO® (CST MWS) and the HUGO Dataset with the permission and courtesy of Xavier Hanus and his colleagues[1].

Figure 1: CST MWS Setup with HUGO Head model and the definition of Lines for Field Evaluation

CST MWS was used in conjunction with the 3D anatomical data set HUGO to simulate the time varying fields of an RF coil loaded by a human head section of the HUGO model with a mass of 7.81kg. A Dell 650 station was used with CPU P4 Xeon 2.8 GHz, 2 Go of RAM and SCSI HD. The model setup is shown in Figure 1 with the lines defined for the fields' extraction.

Figure 2: Details of the meshing of the anatomical 3D human model inserted in the coil in axial (a,b) and sagital (c,d) planes

For the example presented here, the total number of mesh cells over the entire volume of calculation is 1,982,178 as shown in Figure 2, with about 1,100,000 cells for the tissues corresponding to a 3 by 3 by 5 mm average resolution (roughly 18 voxels per 1 cm3 of tissue).

Figure 3: Locations of the 4-ports (a) and detail of the meshing in the area of port 1 (b,c)

All the outer surfaces of the calculation volume are set to open boundaries with PML layers. As shown in Figure 3, four discrete ports have been defined at the bottom of the coil at 90° in the axial plane, with adjustable impedance and lumped capacitance in parallel for better matching when loading with the head.

Figure 4: S-Parameters for the head loaded Coil

For the high meshing intensive calculations, the excitations are performed over 0-800 MHz through the ports 1 and 3 in quadrature. As a result of its polarization, this mode, called B1, is not transmitted between the ports in quadrature as indicated by the transmission S 3,1 for the loaded coil at 480 MHz as shown in Figure 4.

Figure 5: Post-combination of the 1-port linear excitations Lin1P1 and Lin1P3 into the 1 watt circular H-field

The fields and power loss density are obtained at a specific frequency for each port excitation. As shown Figure 5, the B1-mode presents a magnetic vector oriented linearly along -Oy when excited (Lin1P1) by the port 1 along x (cf. Figure 3.a and 5.a). The results are then combined as a post-processing step with specific amplitudes compensating for reflections (|S11| and |S33|), and phase-shifting (90°) in order to create the circularly polarized excitation. When animated with wt, the magnetic vector field appears rigorously circular in the axial plane for the empty coil (Fig. 5.a3) but quite disturbed in the head (Fig. 5.b3). In MRI, only the strictly circular component of the rotating magnetic field is effective on the spins excitation and participates to the formation of the images.

Figure 6: Magnitude and phase of H+1 along x and y for empty and loaded coils

Figure 6 shows the spatial variation of the magnitude (left) and phase (right) of the H+1 vector along the transverse axes for both empty and loaded coil. |H+1| is enhanced with a sharp focusing effect at the center of the brain : up to 1.2 A/m for the loaded coil compared to the 0.95 A/m uniform profile of the unloaded coil (Fig. 6.a). When loading with the head, phases are not symmetrically distributed over -45° and a strong phase-shifting is acting at the high/low permittivity interfaces of the tissues white and grey matter/bones and fat (positions 150/250 mm curve blue for the x-direction Fig. 6.b).

Figure 7: 1g local SAR plots on xy and yz planes

Numerical investigations of SAR and B1 profiles provide crucial information about head loaded coils designed for UHF-MRI. |B1| and SAR values normalized to an effective power injected of 1 Watt CW give the necessary amplification for given tip angles and allow the calculations of expected SARs for MRI typical pulse sequences in accordance to guidelines. More studies have to be carried out in order to improve the performances of the coil. Such studies include the increasing of the Q (Qloaded=40), the influence of the ports disposition, the investigation of multi-excitation scheme, composing a better uniform and circular rotating B1+ becoming a major challenge in UHF-MRI with the inherent reduction of the wavelength.


[1] X. Hanus, M. Luong, F. Lethimonnier, "Electromagnetics Fields and SAR Computations in a Human Head with a Multi-port Driven RF Coil at 11.7 Tesla", Proc. Intl. Soc. Mag. Reson. Med. 13 (2005).

Rate this Article

0 of 5 Stars
5 Stars
4 Stars
3 Stars
2 Stars
1 Stars
contact support

Your session has expired. Redirecting you to the login page...

We use cookie to operate this website, improve its usability, personalize your experience, and track visits. By continuing to use this site, you are consenting to use of cookies. You have the possibility to manage the parameters and choose whether to accept certain cookies while on the site. For more information, please read our updated privacy policy

Cookie Management

When you browse our website, cookies are enabled by default and data may be read or stored locally on your device. You can set your preferences below:

Functional cookies

These cookies enable additional functionality like saving preferences, allowing social interactions and analyzing usage for site optimization.

Advertising cookies

These cookies enable us and third parties to serve ads that are relevant to your interests.