07 MRI
FOV from readout gradient
FOV = BW / (γ G_read). Higher gradient or lower bandwidth shrinks FOV.
Listen
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Simulation
FOV from readout gradient — Change the numbers; the scene follows.
Where it works
MRI scanner
Gradient coils
In the gradient coils — slice thickness, FOV, diffusion encoding, voxel size.
Open this machineFormula
Variables
Results
FOV
Field of view
117.4343mm
FOV
Field of view
11.7434cm
Explanation
What it means
Readout FOV = receiver bandwidth / (γ G_read). A stronger readout gradient or a lower bandwidth shrinks FOV (and may alias if anatomy is larger). Pixel bandwidth is BW/N_x. This is a working relation in MRI physics.
Where it is used
Clinically it sits on the MRI scanner — Gradient coils. In the gradient coils — slice thickness, FOV, diffusion encoding, voxel size. MRI physics lives in the magnet, the gradient, and the voxel: Larmor, Ernst, diffusion, and SAR. These relations decide whether a sequence is possible, safe, and worth the time.
MRI scanner · Open this machineHow to use it
50 kHz on 10 mT/m → FOV ≈ 117 mm. To keep FOV while raising resolution, raise N_x and BW together (or accept more chemical-shift pixels). Change one input and watch the curve and the simulation follow.
Symbols
- BWReceiver bandwidth50 kHz
- G_readReadout gradient10 mT/m
- γ/2πGyromagnetic ratio42.577 MHz/T
Worked example
A typical case from the default values: BW = 50 kHz (Receiver bandwidth); G_read = 10 mT/m (Readout gradient); γ/2π = 42.577 MHz/T (Gyromagnetic ratio). Substituting into the relation gives FOV = 117.4343 mm; FOV = 11.7434 cm. These are teaching numbers — align them with your machine.
Typical values give
- FOV = 117.4343mm
- FOV = 11.7434cm
Where it comes from
The displayed formula is the working relation. FOV = BW / (γ G_read). Higher gradient or lower bandwidth shrinks FOV. Usual reference: McRobbie. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: McRobbie
Assumptions & limits
Linear gradient, no concomitant fields, no gradient nonlinearity (which warps FOV at the edges of large FOV scanners).
Pitfalls
γ for ¹H is not γ for ¹³C. Ernst angle needs the true T1 at that field, not a 1.5 T table used at 3 T. SAR scales with B₀² and flip² — a 3 T copy of a 1.5 T protocol is not automatically legal. Linear gradient, no concomitant fields, no gradient nonlinearity (which warps FOV at the edges of large FOV scanners).
Keep this
Name the nucleus and the field before you quote a Larmor frequency. Linear gradient, no concomitant fields, no gradient nonlinearity (which warps FOV at the edges of large FOV scanners).
In this specialty