Re: CT scanners

[David Scherer <scherer@uiuc.edu>]

At 06:55 AM 7/11/96 -0500, you wrote:
>I have a friend who just had a series of CT scans, and she is wondering if
>anyone knows the comparative radiation doses and image resolutions for the
>various brands of scanners.  Which ones are the true top of the line.  This
>may be a difficult question, but she just would like to know.
>
>Thanks in advance.
>
>John Lobdell
>lobdell@HiWAAY.net 
>
The differences in brands are not as important as the differences in the
ways the scanners are used.  For modern systems (3d generation and beyond),
the spatial resolution is limited mainly by the matrix size employed.  The
reconstruction algorithm has some influence, but all the manufacturers have
a whole suite of algorithms to choose from.  The contrast resolution and
dose are both dominated by the kVp and mAs used for the study, and this is
selected by the operator/clinic.  Every radiologist has his/her favorite,
but I am not aware of any clearly superior model.

The most important improvement in years is the introduction of helical (or
spiral) CT for body CT.  The patient table is fed through the gantry while
the tube and detector array make multiple revolutions, allowing the exam to
be completed in one breath hold.  Under the conventional method, called
dynamic CT, the patient is asked to hold their breath for each slice.  If
the patient inhales a different volume during succesive slices, sometimes a
lesion moves around such that it does not show up in any of the slices.

Remember that CT is only one of the diagnostic tools available.  Plane
films, MRI, ultrasound, nuclear medicine imaging , lab tests, and clinical
exam all may com into play.  The diagnosis is often made on the basis of a
number of studies, especially when one or results are equivocal.

Any other insight from the physicians who monitor the list?

Regards,

Dave Scherer
scherer@uiuc.edu