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<head><title>Phantom Diameter</title></head>
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<H3>Phantom Diameter</H3>
The phantom diameter is automatically calculated by <TT>CTSim</TT> from
the phantom definition. The maximum of the phantom length and
height is used to define the square that completely surrounds the
phantom. Let <EM>Pl</EM> be the width
and height of this square. The diameter of this boundary box,
<EM>Pd</EM>, is given by the
Pythagorean theorem and is
<BR>
<CENTER><EM>Pl x sqrt(2)</EM></CENTER><BR>
CT scanners collect projections around a
circle rather than a square. The diameter of this circle is
the diameter of the boundary square
<EM>Pd</EM>.
<CENTER><img src="scangeometry.gif"></CENTER>
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