[Intl_DxMedPhys] [EXTERNAL] Thyroid Uptake Tests: discordance between 2 different probes

[Jerry Thomas]

Erin,

     I don't know the Captus unit; but, my first "guess" is that the
collimators are different.   Thyroid measurements should be taken with a
flat field collimator vice a "tube shaped" collimator.  If you look at a
flat field collimator it tapers from the collimator opening to the
crystal.  The taper is about 15 degrees.  This colliator gives a
flat/uniform response across the end of the collimator and thus higher
counts.  If the collimator on the Captus is straight with no taper the
field is no longer uniform at the edges of the collimator.  There will be a
fall-off of counts on the edges of the FOV due to attenuation of the edges
of the collimator at its opening.

Jerry


Jerry Thomas, MS, FAAPM, DABR, CHP, DABSNM
Diagnostic Medical Physicist / Radiation Safety Officer
Ascension Via Christi Hospitals Wichita
Wichita, KS  67214

Phone:  316-268-5958  (office)
            240-447-1014  (cell)


On Tue, Jan 28, 2025 at 10:31 AM Erin Niven via Intl_dxmedphys_wd_osu_list <
intl_dxmedphys_wd_osu_list at lists.osu.edu> wrote:

> Good afternoon, We are in the process of switching from an Atomlab 960 to
> a Captus 4000e and noticed a significant difference between uptake
> measurements. The protocols are the same - just comparing the counts of the
> pill placed in the thyroid
> Good afternoon,
>
> We are in the process of switching from an Atomlab 960 to a Captus 4000e
> and noticed a significant difference between uptake measurements.  The
> protocols are the same - just comparing the counts of the pill placed in
> the thyroid phantom to the counts from the patient's thyroid 24 hours
> apart.  The Atomlab is yielding much higher uptake measurements compared to
> the Captus (pills and patients were counted on both probes, one after the
> other).
>
> I have a suspicion as to why this might be, but can't get around to doing
> some measurements today or tomorrow.  So I thought I would see if anyone
> else has run into this problem before, or if you have suggestions for me to
> test.
>
> Sincerely,
> Erin Niven, PhD, CHP, RRPT, MCCPM
>
>
>
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