Scanners
The MRI scanner that is used during acquisition puts various constraints on the MR sequences that can be used. These constraints include safety considerations, such as tissue heating, and hardware constraints, such as maximum gradient strength and slew rate. Currently, MRIBuilder only considers the latter.
To define a sequence appropriate for a specific scanner, a user would define a new Scanner with the appropriate B0, maximum variables.gradient_strength, and maximum variables.slew_rate. This scanner would then be passed on to the sequence optimisation.
For ease of use, the gradient_strength and slew_rate of many scanners have already been pre-defined. These are listed below.
Scanners API
MRIBuilder.Scanners — Module
Define general Scanner type and methods as well as some concrete scanners.
MRIBuilder.Scanners.Default_Scanner — Constant
A default 1.5T scanner.
Matches the one used in pulseq (https://github.com/pulseq/pulseq/blob/master/matlab/%2Bmr/opts.m).
MRIBuilder.Scanners.Siemens_Connectom — Constant
Siemens 3T Connectom MRI scanner (fan22_MappingHumanConnectome).
MRIBuilder.Scanners.Siemens_Connectom_v2 — Constant
Siemens 3T Connectom 2.0 MRI scanner (huang21_ConnectomeDevelopingnextgeneration)
MRIBuilder.Scanners.Siemens_Prisma — Constant
Siemens MAGNETOM 3T Prisma MRI scanner (https://www.siemens-healthineers.com/en-uk/magnetic-resonance-imaging/3t-mri-scanner/magnetom-prisma).
MRIBuilder.Scanners.Siemens_Terra — Constant
Siemens MAGNETOM 7T Terra MRI scanner (https://www.siemens-healthineers.com/en-uk/magnetic-resonance-imaging/7t-mri-scanner/magnetom-terra)
MRIBuilder.Scanners.Scanner — Type
Scanner(;B0=3., gradient=Inf, slew_rate=Inf, units=:kHz)Properties of an MRI scanner relevant for the MR signal simulations.
B0: magnetic field strength (in Tesla)gradient_strength: maximum gradient strength long each axis.slew_rate: maximum rate of change in the gradient strength
By default gradient and slew_rate are expected to be provided in units of, respectively, kHz/um and kHz/um/ms. However, if the keyword units=:Tesla is set, the gradient and slew_rate should be provided in units of, respectively, mT/m and T/m/s.
MRIBuilder.Scanners.B0 — Method
B0(scanner)
B0(sequence)Returns the magnetic field strength of the scanner in Tesla.
MRIBuilder.Scanners.gradient_strength — Function
gradient_strength(scanner[, units])Returns the maximum magnetic field gradient of the scanner in kHz/um. By setting units to :Tesla, the gradient strength can be returned in mT/m instead.
MRIBuilder.Scanners.slew_rate — Function
slew_rate(scanner[, units])Returns the maximum magnetic field slew rate of the scanner in kHz/um/ms. By setting units to :Tesla, the slew rate can be returned in T/m/s instead.