IMG-23

CT pitch

p = I / (N T). Table feed per rotation over total collimation.

Reading speed

CTIEC pitch

Governing equation

p=I/(N T)

$I \in \left[2, 80\right]$

where

I: Table feed / rotation (mm)
N: Rows (—)
T: Detector width (mm)
p: Pitch (—)

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

p=I/(N T)

$I \in \left[2, 80\right]$

$I = 2$ $p = 0.05$

Along the curve

②

Domain of the variable — blue

I_{\min} = 2,\quad I_{\max} = 80

$I \in \left[2, 80\right]$

$I = 2$ $I = 2$

Along the curve

③

Response curve — green

p=I/(N T)

$I \in \left[2, 80\right]$

$I = 2$ $p = 0.05$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}p}{\mathrm{d}I}

$I \in \left[2, 80\right]$

$I = 2.491$ $p^{\prime} = 0.025$

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-23 — CT pitch) is the form associated with IEC pitch. Working symbols: $I$ , $N$ , $T$ $\rightarrow$ $p$ . p < 1 overlaps; p > 1 interpolates. Pitch enters CTDIvol as 1/p.

Purpose

Purpose: compute

p

from

I

N

T

in Medical imaging via

p=I/(N T)

p = I / (N T). Table feed per rotation over total collimation. 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

I = 24.000\,\mathrm{mm}

N = 64.000\,\mathrm{—}

T = 0.625\,\mathrm{mm}

, the governing relation

p=I/(N T)

yields

p = 0.600\,\mathrm{—}

. A helix of pitch p around the patient. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Table feed / rotation I24 mmRows N64 —Detector width T0.625 mm

Outputs

Pitch p0.600 —

Reading speed

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Narration of this film

A helix of pitch p around the patient.

p < 1 overlaps; p > 1 interpolates. Pitch enters CTDIvol as 1/p.

Reading speed

Watch on YouTube