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Re: CAT Scan dosage
Several pieces of information are required to give the correct answer to
this question.
What was the slice width? -- 10, 5, 3, 1 mm? What was the technique
used? -- mAs (kVp is generally fixed at 120). Were the slices
overlapping. 40 - 45 slices seems to be a very large number of slices for
a lung. I'll bet that the scan was both a chest and abdomen.
If you assume that the slices are non-overlapping then the contribution to
the total dose from one slice to the next is that amount of radiation
contained in the "tail" of the slice. The slice profile will look like a
three phase x-ray generator's waveform. (e.g. steep rise with a slight
ripple along the top).
Annually a qualified medical physicist will take CTDI measurements on the
machine for both head and body. The output on a head phantom is between 1
and 2 R/100 mAs. Thus the dose can be between 2.5 and 5.0 R per slice.
Please note that since the slices are contiguous rather than overlapping
the total dose to the volume of tissue is that of the "nominal slice dose"
plus the contribution of the slice tails. The dose to individual slices is
not summed.
On the second question wrt "red" material injected during a CT scan. In
CT we use contrast media, non of which is colored. If the syringe is "back
flushed" ... e.g. the plunger is pulled back ... while the needle is in the
vein, the contrast media will be redish from the blood that was pulled back
into the syringe.
The contrast media that is injected into a vein is clear. It is an Iodine
based solution that can be either ionic or nonionic.
Hope this helps.
JERRY THOMAS
At 12:22 09/05/97 -0500, you wrote:
> Your original CT certification and acceptance of performance of X-Ray
> tube output should give you or should be able to calculate the mR/mAs,
> depending on the technique factors (mA and kVp) for lung scan..mike
> coogen sends
>
>
>______________________________ Reply Separator
_________________________________
>Subject: CAT Scan dosage
>Author: radsafe@romulus.ehs.uiuc.edu at Internet
>Date: 9/5/97 10:28 AM
>
>
>Good Morning -
>
>Does anyone have any information on what sort of dosage you can receive
>when you undergo a CAT scan? As a guess, probubly 40-45 slices.
>
>This is to determine the size of a spot on the lung.
>
>
>
>---------------------------------------------------------------------------
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>Eric A. Staib Nuclear Science Dept.
>Schlumberger-Doll Research Tel: (203) 431-5362
>Ridgefield, Ct.06877-4108 Fax:(203) 438-3819
>staib@ridgefield.sdr.slb.com
>---------------------------------------------------------------------------
---
>
>
>
>
>
CAPT Jerry A. Thomas, MSC, USN
Chief Radiological Physics
Department of Radiology/Nuclear Medicine
Uniformed Services University of the Health Sciences
4301 Jones Bridge Road
Bethesda, MD 20814-4799
mailto:thomas@bob.usuf2.usuhs.mil
Phone: (301) 295-3246
Fax: (301) 295-3893
Homepage: http://radlinux1.usuf1.usuhs.mil/rad/