IMG-14

Slice thickness

Δz = BW_rf / (γ Gss). RF bandwidth over the slice-select gradient.

Reading speed

MRISlice select

Governing equation

\Delta z=BW_{\mathrm{rf}}/(\gamma G_{ss})

$G_{ss} \in \left[1, 40\right]$

where

BW_{rf}: RF bandwidth (Hz)
G_{ss}: Slice gradient (mT/m)
\Delta z: Slice thickness (mm)

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

\Delta z=BW_{\mathrm{rf}}/(\gamma G_{ss})

$G_{ss} \in \left[1, 40\right]$

$G_{ss} = 1$ $\Delta z = 18.79$

Along the curve

②

Domain of the variable — blue

G_{ss}_{\min} = 1,\quad G_{ss}_{\max} = 40

$G_{ss} \in \left[1, 40\right]$

$G_{ss} = 1$ $G_{ss} = 1$

Along the curve

③

Response curve — green

\Delta z=BW_{\mathrm{rf}}/(\gamma G_{ss})

$G_{ss} \in \left[1, 40\right]$

$G_{ss} = 1$ $\Delta z = 18.79$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}\Delta z}{\mathrm{d}G_{ss}}

$G_{ss} \in \left[1, 40\right]$

$G_{ss} = 1.245$ $\Delta z^{\prime} = -12.6$

Along the curve

Lecture brief

Historical brief

Larmor precession, CT Beer projections, SNR and Nyquist sampling are why MRI and CT images exist as numbers. The lab computes frequency, dose and resolution limits. This sheet (IMG-14 — Slice thickness) is the form associated with Slice select. Working symbols: $BW_{rf}$ , $G_{ss}$ $\rightarrow$ $\Delta z$ . Thinner slices need more G or less BW. Crosstalk appears if gaps are too small.

Purpose

Purpose: compute

\Delta z

from

BW_{rf}

G_{ss}

in Medical imaging via

\Delta z=BW_{\mathrm{rf}}/(\gamma G_{ss})

Δz = BW_rf / (γ Gss). RF bandwidth over the slice-select gradient. Use it when a real medical imaging question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

BW_{rf} = 800.000\,\mathrm{Hz}

G_{ss} = 10.000\,\mathrm{mT/m}

, the governing relation

\Delta z=BW_{\mathrm{rf}}/(\gamma G_{ss})

yields

\Delta z = 1.88\,\mathrm{mm}

. A slab of spins lit by a frequency window. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

RF bandwidth BW_{rf}800 HzSlice gradient G_{ss}10 mT/m

Outputs

Slice thickness \Delta z1.88 mm

Reading speed

Watch on YouTube

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Narration of this film

A slab of spins lit by a frequency window.

Thinner slices need more G or less BW. Crosstalk appears if gaps are too small.

Reading speed

Watch on YouTube